CIRCUIT

Transistor Circuits

noreply@blogger.com (KAI) — Mon, 19 May 2014 08:29:00 +0000

This page explains the operation of transistors in circuits. Practical matters such as testing, precautions when soldering and identifying leads are covered by the Transistors page.

Transistor circuit symbols

Types of transistor

There are two types of standard transistors, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. This page is mostly about NPN transistors and if you are new to electronics it is best to start by learning how to use these first.

The leads are labelled base (B), collector (C) and emitter(E).
These terms refer to the internal operation of a transistor but they are not much help in understanding how a transistor is used, so just treat them as labels!

A Darlington pair is two transistors connected together to give a very high current gain.

In addition to standard (bipolar junction) transistors, there are field-effect transistors which are usually referred to as FETs. They have different circuit symbols and properties and they are not (yet) covered by this page.

Transistor currents

The diagram shows the two current paths through a transistor. You can build this circuit with two standard 5mm red LEDs and any general purpose low power NPN transistor (BC108, BC182 or BC548 for example).

The small base current controls the larger collector current.

When the switch is closed a small current flows into the base (B) of the transistor. It is just enough to make LED B glow dimly. The transistor amplifies this small current to allow a larger current to flow through from its collector (C) to its emitter (E). This collector current is large enough to make LED C light brightly.

When the switch is open no base current flows, so the transistor switches off the collector current. Both LEDs are off.

A transistor amplifies current and can be used as a switch.

This arrangement where the emitter (E) is in the controlling circuit (base current) and in the controlled circuit (collector current) is called common emitter mode. It is the most widely used arrangement for transistors so it is the one to learn first.

Functional model of an NPN transistor

The operation of a transistor is difficult to explain and understand in terms of its internal structure. It is more helpful to use this functional model:

The base-emitter junction behaves like a diode.
A base current I_B flows only when the voltage V_BE across the base-emitter junction is 0.7V or more.
The small base current I_B controls the large collector current Ic.
Ic = h_FE × I_B (unless the transistor is full on and saturated)
h_FE is the current gain (strictly the DC current gain), a typical value for h_FE is 100 (it has no units because it is a ratio)
The collector-emitter resistance R_CE is controlled by the base current I_B:
- I_B = 0 R_CE = infinity transistor off
- I_B small R_CE reduced transistor partly on
- I_B increased R_CE = 0 transistor full on ('saturated')

Additional notes:

A resistor is often needed in series with the base connection to limit the base current I_B and prevent the transistor being damaged.
Transistors have a maximum collector current Ic rating.
The current gain h_FE can vary widely, even for transistors of the same type!
A transistor that is full on (with R_CE = 0) is said to be 'saturated'.
When a transistor is saturated the collector-emitter voltage V_CE is reduced to almost 0V.
When a transistor is saturated the collector current Ic is determined by the supply voltage and the external resistance in the collector circuit, not by the transistor's current gain. As a result the ratio Ic/I_Bfor a saturated transistor is less than the current gain h_FE.
The emitter current I_E = Ic + I_B, but Ic is much larger than I_B, so roughly I_E = Ic.

There is a table showing technical data for some popular transistors on the transistors page.

Touch switch circuit

Darlington pair

This is two transistors connected together so that the current amplified by the first is amplified further by the second transistor. The overall current gain is equal to the two individual gains multiplied together:

Darlington pair current gain, h_FE = h_FE1 × h_FE2
(h_FE1 and h_FE2 are the gains of the individual transistors)

This gives the Darlington pair a very high current gain, such as 10000, so that only a tiny base current is required to make the pair switch on.

A Darlington pair behaves like a single transistor with a very high current gain. It has three leads (B, C and E) which are equivalent to the leads of a standard individual transistor. To turn on there must be 0.7V across both the base-emitter junctions which are connected in series inside the Darlington pair, therefore it requires 1.4V to turn on.

Darlington pairs are available as complete packages but you can make up your own from two transistors; TR1 can be a low power type, but normally TR2 will need to be high power. The maximum collector current Ic(max) for the pair is the same as Ic(max) for TR2.

A Darlington pair is sufficiently sensitive to respond to the small current passed by your skin and it can be used to make a touch-switch as shown in the diagram. For this circuit which just lights an LED the two transistors can be any general purpose low power transistors. The 100kresistor protects the transistors if the contacts are linked with a piece of wire.

Using a transistor as a switch

When a transistor is used as a switch it must be either OFF or fully ON. In the fully ON state the voltage V_CE across the transistor is almost zero and the transistor is said to be saturated because it cannot pass any more collector current Ic. The output device switched by the transistor is usually called the 'load'.

The power developed in a switching transistor is very small:

In the OFF state: power = Ic × V_CE, but Ic = 0, so the power is zero.
In the full ON state: power = Ic × V_CE, but V_CE = 0 (almost), so the power is very small.

This means that the transistor should not become hot in use and you do not need to consider its maximum power rating. The important ratings in switching circuits are the maximum collector current Ic(max) and the minimum current gain h_FE(min). The transistor's voltage ratings may be ignored unless you are using a supply voltage of more than about 15V. There is a table showing technical data for some popular transistors on the transistors page.

For information about the operation of a transistor please see the functional model above.

Protection diode

If the load is a motor, relay or solenoid (or any other device with a coil) a diode must be connected across the load to protect the transistor from the brief high voltage produced when the load is switched off. The diagram shows how a protection diode is connected 'backwards' across the load, in this case a relay coil.

Current flowing through a coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the coil which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.

When to use a relay

Relays

Photographs © Rapid Electronics

Transistors cannot switch AC or high voltages (such as mains electricity) and they are not usually a good choice for switching large currents (> 5A). In these cases a relay will be needed, but note that a low power transistor may still be needed to switch the current for the relay's coil!

Advantages of relays:

Relays can switch AC and DC, transistors can only switch DC.

Relays can switch high voltages, transistors cannot.

Relays are a better choice for switching large currents (> 5A).

Relays can switch many contacts at once.

Disadvantages of relays:

Relays are bulkier than transistors for switching small currents.
Relays cannot switch rapidly, transistors can switch many times per second.
Relays use more power due to the current flowing through their coil.
Relays require more current than many ICs can provide, so a low power transistor may be needed to switch the current for the relay's coil.

Connecting a transistor to the output from an IC

Most ICs cannot supply large output currents so it may be necessary to use a transistor to switch the larger current required for output devices such as lamps, motors and relays. The 555 timer IC is unusual because it can supply a relatively large current of up to 200mA which is sufficient for some output devices such as low current lamps, buzzers and many relay coils without needing to use a transistor.

A transistor can also be used to enable an IC connected to a low voltage supply (such as 5V) to switch the current for an output device with a separate higher voltage supply (such as 12V). The two power supplies must be linked, normally this is done by linking their 0V connections. In this case you should use an NPN transistor.

A resistor R_B is required to limit the current flowing into the base of the transistor and prevent it being damaged. However, R_B must be sufficiently low to ensure that the transistor is thoroughly saturated to prevent it overheating, this is particularly important if the transistor is switching a large current (> 100mA). A safe rule is to make the base current I_B about five times larger than the value which should just saturate the transistor.

Choosing a suitable NPN transistor

The circuit diagram shows how to connect an NPN transistor, this will switch on the load when the IC output is high. If you need the opposite action, with the load switched on when the IC output is low (0V) please see the circuit for a PNP transistor below.

The procedure below explains how to choose a suitable switching transistor.

NPN transistor switch
(load is on when IC output is high)

Using units in calculations
Remember to use V, A and or
V, mA and k. For more details
please see the Ohm's Law page.

The transistor's maximum collector current Ic(max) must be greater than the load current Ic.
load current Ic =
supply voltage Vs
load resistance R_L
The transistor's minimum current gain h_FE(min) must be at least five times the load current Ic divided by the maximum output current from the IC.
h_FE(min) > 5 ×
load current Ic
max. IC current
Choose a transistor which meets these requirements and make a note of its properties: Ic(max) and h_FE(min).
There is a table showing technical data for some popular transistors on the transistors page.
Calculate an approximate value for the base resistor:
R_B =
Vc × h_FE
where Vc = IC supply voltage
(in a simple circuit with one supply this is Vs)
5 × Ic
For a simple circuit where the IC and the load share the same power supply (Vc = Vs) you may prefer to use: R_B = 0.2 × R_L × h_FE
Then choose the nearest standard value for the base resistor.
Finally, remember that if the load is a motor or relay coil a protection diode is required.

Example
The output from a 4000 series CMOS IC is required to operate a relay with a 100 coil.
The supply voltage is 6V for both the IC and load. The IC can supply a maximum current of 5mA.

Load current = Vs/R_L = 6/100 = 0.06A = 60mA, so transistor must have Ic(max) > 60mA.

The maximum current from the IC is 5mA, so transistor must have h_FE(min) > 60 (5 × 60mA/5mA).

Choose general purpose low power transistor BC182 with Ic(max) = 100mA and h_FE(min) = 100.

R_B = 0.2 × R_L × h_FE = 0.2 × 100 × 100 = 2000. so choose R_B = 1k8 or 2k2.

The relay coil requires a protection diode.

PNP transistor switch
(load is on when IC output is low)

Choosing a suitable PNP transistor

The circuit diagram shows how to connect a PNP transistor, this will switch on the load when the IC output is low (0V). If you need the opposite action, with the load switched on when the IC output is high please see the circuit for an NPN transistor above.

The procedure for choosing a suitable PNP transistor is exactly the same as that for an NPN transistor described above.

Using a transistor switch with sensors

LED lights when the LDR is dark

LED lights when the LDR is bright

The top circuit diagram shows an LDR (light sensor) connected so that the LED lights when the LDR is in darkness. The variable resistor adjusts the brightness at which the transistor switches on and off. Any general purpose low power transistor can be used in this circuit.

The 10k fixed resistor protects the transistor from excessive base current (which will destroy it) when the variable resistor is reduced to zero. To make this circuit switch at a suitable brightness you may need to experiment with different values for the fixed resistor, but it must not be less than 1k.

If the transistor is switching a load with a coil, such as a motor or relay, remember to add a protection diode across the load.

The switching action can be inverted, so the LED lights when the LDR is brightly lit, by swapping the LDR and variable resistor. In this case the fixed resistor can be omitted because the LDR resistance cannot be reduced to zero.

Note that the switching action of this circuit is not particularly good because there will be an intermediate brightness when the transistor will be partly on (not saturated). In this state the transistor is in danger of overheating unless it is switching a small current. There is no problem with the small LED current, but the larger current for a lamp, motor or relay is likely to cause overheating.

Other sensors, such as a thermistor, can be used with this circuit, but they may require a different variable resistor. You can calculate an approximate value for the variable resistor (Rv) by using a multimeter to find the minimum and maximum values of the sensor's resistance (Rmin and Rmax):

Variable resistor, Rv = square root of (Rmin × Rmax)

For example an LDR: Rmin = 100, Rmax = 1M, so Rv = square root of (100 × 1M) = 10k.

You can make a much better switching circuit with sensors connected to a suitable IC (chip). The switching action will be much sharper with no partly on state.

A transistor inverter (NOT gate)

Inverters (NOT gates) are available on logic ICs but if you only require one inverter it is usually better to use this circuit. The output signal (voltage) is the inverse of the input signal:

When the input is high (+Vs) the output is low (0V).
When the input is low (0V) the output is high (+Vs).

Any general purpose low power NPN transistor can be used. For general use R_B = 10k and R_C = 1k, then the inverter output can be connected to a device with an input impedance (resistance) of at least 10k such as a logic IC or a 555 timer (trigger and reset inputs).

If you are connecting the inverter to a CMOS logic IC input (very high impedance) you can increase R_B to 100k and R_C to 10k, this will reduce the current used by the inverter.

http://electronicsclub.info/transistorcircuits.htm

Printed Circuit Boards (PCBs)

noreply@blogger.com (KAI) — Sat, 17 May 2014 08:13:00 +0000

Bittele Electronics provides high quality mixed technology PCB assembly services. Our circuit assembly capability includes Surface-Mount parts (SMD), Through-Hole parts (THD), or any mix of them. We also offer Prototype printed circuit boardservices, for rigid or flexible, RoHS compliant, High Tg boards.

Toronto-based contract electronics manufacturer Asian Circuits Inc. has expertise in providing affordable one-stopPCB manufacturing and assembly services for both Thru-Hole and Surface Mount Technology (SMT).

Printed circuit boards have copper tracks connecting the holes where the components are placed. They are designed specially for each circuit and make construction very easy.

Designing, Creating and Soldering your own PCBs

The website build-electronic-circuits.com provides clear instructions on designing, creating and soldering your own PCBs.

Preparing a PCB ready for Soldering

Clean off the protective coating from the PCB using a PCB rubber or steel wool so that all the copper tracks are bright and shiny. The PCB rubber has grit in it to make it very abrasive.
In fact the coating can be left on and it should melt away around the joints as you solder but you may get better results by removing the coating.
Drill the holes with a 1mm diameter bit. This is easiest with a proper electric PCB drill in a stand, but a hand-held miniature electric drill can be used if you take care to avoid twisting and snapping the small drill bit. Wear safety spectacles.
A hand-drill is not suitable for such small bits unless you are very skilled.
A few may holes may need to be larger, for example preset resistors usually need a 1.5mm diameter hole. It is simplest to re-drill these special holes afterwards.
Check carefully to make sure you find all the holes.
Even with experience it is easy to miss one or two!

WARNING! The small drill bits are fragile. Drill gently but firmly. If you are using a hand-held drill you must take great care to avoid twisting the drill sideways because this will snap the drill bit.

http://electronicsclub.info/pcb.htm

Oscilloscopes (CROs)

noreply@blogger.com (KAI) — Fri, 16 May 2014 02:00:00 +0000

An oscilloscope is a test instrument which allows you to look at the 'shape' of electrical signals by displaying a graph of voltage against time on its screen. It is like a voltmeter with the valuable extra function of showing how the voltage varies with time. A graticule with a 1cm grid enables you to take measurements of voltage and time from the screen.

The graph, usually called the trace, is drawn by a beam of electrons striking the phosphor coating of the screen making it emit light, usually green or blue. This is similar to the way a television picture is produced.

Oscilloscopes contain a vacuum tube with a cathode(negative electrode) at one end to emit electrons and ananode (positive electrode) to accelerate them so they move rapidly down the tube to the screen. This arrangement is called an electron gun. The tube also contains electrodes to deflect the electron beam up/down and left/right.

The electrons are called cathode rays because they are emitted by the cathode and this gives the oscilloscope its full name of cathode ray oscilloscope or CRO.

A dual trace oscilloscope can display two traces on the screen, allowing you to easily compare the input and output of an amplifier for example. It is well worth paying the modest extra cost to have this facility.

Precautions

An oscilloscope should be handled gently to protect its fragile (and expensive) vacuum tube.
Oscilloscopes use high voltages to create the electron beam and these remain for some time after switching off - for your own safety do not attempt to examine the inside of an oscilloscope!

Setting up an oscilloscope

Oscilloscopes are complex instruments with many controls and they require some care to set up and use successfully. It is quite easy to 'lose' the trace off the screen if controls are set wrongly!

There is some variation in the arrangement and labelling of the many controls so the following instuctions may need to be adapted for your instrument.

This is what you should see
after setting up, when there
is no input signal connected

Switch on the oscilloscope to warm up (it takes a minute or two).
Do not connect the input lead at this stage.
Set the AC/GND/DC switch (by the Y INPUT) to DC.
Set the SWP/X-Y switch to SWP (sweep).
Set Trigger Level to AUTO.
Set Trigger Source to INT (internal, the y input).
Set the Y AMPLIFIER to 5V/cm (a moderate value).
Set the TIMEBASE to 10ms/cm (a moderate speed).
Turn the timebase VARIABLE control to 1 or CAL.
Adjust Y SHIFT (up/down) and X SHIFT (left/right) to give a trace across the middle of the screen, like the picture.
Adjust INTENSITY (brightness) and FOCUS to give a bright, sharp trace.
The oscilloscope is now ready to use!
Connecting the input lead is described in the next section.

Further information on the controls: Timebase | Y amplifier | AC/GND/DC switch

Connecting an oscilloscope

Construction of a co-axial lead

Oscilloscope lead and probes kit
Photograph © Rapid Electronics

The Y INPUT lead to an oscilloscope should be a co-axial lead and the diagram shows its construction. The central wire carries the signal and the screen is connected to earth (0V) to shield the signal from electrical interference (usually called noise).

Most oscilloscopes have a BNC socket for the y input and the lead is connected with a push and twist action, to disconnect you need to twist and pull. Oscilloscopes used in schools may have red and black 4mm sockets so that ordinary, unscreened, 4mm plug leads can be used if necessary.

Professionals use a specially designed lead and probes kit for best results with high frequency signals and when testing high resistance circuits, but this is not essential for simpler work at audio frequencies (up to 20kHz).

An oscilloscope is connected like a voltmeter but you must be aware that the screen (black) connection of the input lead is connected to mains earth at the oscilloscope! This means it must be connected to earth or 0V on the circuit being tested.

The trace of an AC signal
with the oscilloscope
controls correctly set

Obtaining a clear and stable trace

Once you have connected the oscilloscope to the circuit you wish to test you will need to adjust the controls to obtain a clear and stable trace on the screen:

The Y AMPLIFIER (VOLTS/CM) control determines the height of the trace. Choose a setting so the trace occupies at least half the screen height, but does not disappear off the screen.
The TIMEBASE (TIME/CM) control determines the rate at which the dot sweeps across the screen. Choose a setting so the trace shows at least one cycle of the signal across the screen.
Note that a steady DC input signal gives a horizontal line trace for which the timebase setting is not critical.
The TRIGGER control is usually best left set to AUTO.

If you are using an oscilloscope for the first time it is best to start with an easy signal such as the output from an AC power pack set to about 4V.

http://electronicsclub.info/cro.htm

Voltage Dividers

noreply@blogger.com (KAI) — Fri, 16 May 2014 01:53:00 +0000

A voltage divider consists of two resistances R1 and R2 connected in series across a supply voltage Vs. The supply voltage is divided up between the two resistances to give an output voltage Vo which is the voltage across R2. This depends on the size of R2 relative to R1:

If R2 is much smaller than R1, Vo is small (low, almost 0V)
(because most of the voltage is across R1)
If R2 is about the same as R1, Vo is about half Vs
(because the voltage is shared about equally between R1 and R2)
If R2 is much larger than R1, Vo is large (high, almost Vs)
(because most of the voltage is across R2)

If you need a precise value for the output voltage Vo you can use Ohm's law and a little algebra to work out the formula for Vo shown on the right. The formula and the approximate rules given above assume that negligible current flows from the output. This is true if Vo is connected to a device with a high resistance such as voltmeter or an IC input. For further information please see the page on impedance. If the output is connected to a transistor Vo cannot become much greater than 0.7V because the transistor's base-emitter junction behaves like a diode.

Voltage dividers are also called potential dividers, a name which comes from potential difference (the proper name for voltage).

One of the main uses of voltage dividers is to connect input transducers into circuits...

Using an input transducer (sensor) in a voltage divider

Most input transducers (sensors) vary their resistance and usually a voltage divider is used to convert this to a varyingvoltage which is more useful. The voltage signal can be fed to other parts of the circuit, such as the input to an IC or a transistor switch.

The sensor is one of the resistances in the voltage divider. It can be at the top (R1) or at the bottom (R2), the choice is determined by when you want a large value for the output voltage Vo:

Put the sensor at the top (R1) if you want a large Vowhen the sensor has a small resistance.
Put the sensor at the bottom (R2) if you want a large Vo when the sensor has a large resistance.

Then you need to choose a value for the resistor...

Choosing a resistor value

The value of the resistor R will determine the range of the output voltage Vo. For best results you need a large 'swing' (range) for Vo and this is achieved if the resistor is much larger than the sensor's minimum resistance Rmin, but much smaller than the sensor's maximum resistance Rmax.

You can use a multimeter to help you find the minimum and maximum values of the sensor's resistance (Rmin and Rmax). There is no need to be precise, approximate values will do.

Then choose resistor value: R = square root of (Rmin × Rmax)
Choose a standard value which is close to this calculated value.

For example:
An LDR: Rmin = 100, Rmax = 1M, so R = square root of (100 × 1M) = 10k.

swapping over the resistor and sensor

The resistor and sensor can be swapped over to invert the action of the voltage divider. For example an LDR has a high resistance when dark and a low resistance when brightly lit, so:

If the LDR is at the top (near +Vs),
Vo will be low in the dark and high in bright light.
If the LDR is at the bottom (near 0V),
Vo will be high in the dark and low in bright light.

Using a variable resistor

The sensor and variable
resistor can be swapped
over if necessary

A variable resistor may be used in place of the fixed resistor R. It will enable you to adjust the output voltage Vo for a given resistance of the sensor. For example you can use a variable resistor to set the exact brightness level which makes an IC change state.

The variable resistor value should be larger than the fixed resistor value. For finer control you can use a fixed resistor in series with the variable resistor. For example if a 10k fixed resistor is suitable you could replace it with a fixed 4.7k resistor in series with a 10k variable resistor, allowing you to adjust the resistance from 4.7k to 14.7k.

If you are planning to use a variable resistor connected between the +Vs supply and the base of a transistor you must include a resistor in series with the variable resistor. This is to prevent excessive base current destroying the transistor when the variable resistor is reduced to zero. For further information please see the page on Transistor Circuits.

http://electronicsclub.info/vdivider.htm

Voltage and Current

noreply@blogger.com (KAI) — Fri, 16 May 2014 01:44:00 +0000

Voltage attempts to make a current flow, and current will flow if the circuit is complete. Voltage is sometimes described as the 'push' or 'force' of the electricity, it isn't really a force but this may help you to imagine what is happening. It is possible to have voltage without current, but current cannot flow without voltage.

Voltage and Current
The switch is closed making a complete circuit so current can flow.
Voltage but No Current
The switch is open so the circuit is broken and current cannot flow.
No Voltage and No Current
Without the cell there is no source of voltage so current cannot flow.

Voltage, V

Connecting a voltmeter in parallel

Voltage is a measure of the energy carried by the charge.
Strictly: voltage is the "energy per unit charge".
The proper name for voltage is potential difference or p.d. for short, but this term is rarely used in electronics.
Voltage is supplied by the battery (or power supply).
Voltage is used up in components, but not in wires.
We say voltage across a component.
Voltage is measured in volts, V.
Voltage is measured with a voltmeter, connected in parallel.
The symbol V is used for voltage in equations.

Voltage at a point and 0V (zero volts)

Voltage is a difference between two points, but in electronics we often refer to voltage at a point meaning the voltage difference between that point and a reference point of 0V (zero volts).

Zero volts could be any point in the circuit, but to be consistent it is normally the negative terminal of the battery or power supply. You will often see circuit diagrams labelled with 0V as a reminder.

You may find it helpful to think of voltage like height in geography. The reference point of zero height is the mean (average) sea level and all heights are measured from that point. The zero volts in an electronic circuit is like the mean sea level in geography.

Zero volts for circuits with a dual supply

Some circuits require a dual supply with three supply connections as shown in the diagram. For these circuits the zero volts reference point is the middle terminal between the two parts of the supply.

On complex circuit diagrams using a dual supply the earth symbol is often used to indicate a connection to 0V, this helps to reduce the number of wires drawn on the diagram.

The diagram shows a ±9V dual supply, the positive terminal is +9V, the negative terminal is -9V and the middle terminal is 0V.

Connecting an ammeter in series

Current, I

Current is the rate of flow of charge.
Current is not used up, what flows into a component must flow out.
We say current through a component.
Current is measured in amps (amperes), A.
Current is measured with an ammeter, connected in series.
To connect in series you must break the circuit and put the ammeter acoss the gap, as shown in the diagram.
The symbol I is used for current in equations.
Why is the letter I used for current? ... please see FAQ.

1A (1 amp) is quite a large current for electronics, so mA (milliamps) are often used. m (milli) means "thousandth":

1mA = 0.001A, or 1000mA = 1A

The need to break the circuit to connect in series means that ammeters are difficult to use on soldered circuits. Most testing in electronics is done with voltmeters which can be easily connected without disturbing circuits.

Voltage and Current for components in Series

Voltages add up for components connected in series.
Currents are the same through all components connected in series.

In this circuit the 4V across the resistor and the 2V across the LED add up to the battery voltage: 2V + 4V = 6V.

The current through all parts (battery, resistor and LED) is 20mA.

Voltage and Current for components in Parallel

Voltages are the same across all components connected in parallel.
Currents add up for components connected in parallel.

In this circuit the battery, resistor and lamp all have 6V across them.

The 30mA current through the resistor and the 60mA current through the lamp add up to the 90mA current through the battery.

http://electronicsclub.info/voltage.htm

Analogue and Digital Systems

noreply@blogger.com (KAI) — Thu, 15 May 2014 17:42:00 +0000

Analogue signal

Analogue meter display

Analogue systems

Analogue systems process analogue signals which can take any value within a range, for example the output from an LDR (light sensor) or a microphone.

An audio amplifier is an example of an analogue system. The amplifier produces an output voltage which can be any value within the range of its power supply.

An analogue meter can display any value within the range available on its scale. However, the precision of readings is limited by our ability to read them. For example the meter on the right shows 1.25V because the pointer is estimated to be half way between 1.2 and 1.3. The analogue meter can show any value between 1.2 and 1.3 but we are unable to read the scale more precisely than about half a division.

All electronic circuits suffer from 'noise' which is unwanted signal mixed in with the desired signal, for example an audio amplifier may pick up some mains 'hum' (the 50Hz frequency of the UK mains electricity supply). Noise can be difficult to eliminate from analogue signals because it may be hard to distinguish from the desired signal.

Digital (logic) signal

Digital meter display

Digital systems

Digital systems process digital signals which can take only a limited number of values (discrete steps), usually just two values are used: the positive supply voltage (+Vs) and zero volts (0V).

Digital systems contain devices such as logic gates, flip-flops, shift registers and counters. A computer is an example of a digital system.

A digital meter can display many values, but not every value within its range. For example the display on the right can show 6.25 and 6.26 but not a value between them. This is not a problem because digital meters normally have sufficient digits to show values more precisely than it is possible to read an analogue display.

Logic signals

Logic states

True
False

1
0

High
Low

+Vs
0V

On
Off

Most digital systems use the simplest possible type of signal which has just two values. This type of signal is called a logic signal because the two values (or states) can be called true and false. Normally the positive supply voltage +Vs represents true and 0V represents false. Other labels for the true and false states are shown in the table on the right.

Noise is relatively easy to eliminate from digital signals because it is easy to distinguish from the desired signal which can only have particular values. For example: if the signal is meant to be +5V (true) or 0V (false), noise of up to 2.5V can be eliminated by treating all voltages greater than 2.5V as true and all voltages less than 2.5V as false.

http://electronicsclub.info/analogue.htm

Connectors and Cables

noreply@blogger.com (KAI) — Wed, 07 Sep 2011 09:29:00 +0000

Photographs © Rapid Electronics

Battery clips and holders

The standard battery clip fits a 9V PP3 battery and many battery holders such as the 6 × AA cell holder shown. Battery holders are also available with wires attached, with pins for PCB mounting, or as a complete box with lid, switch and wires.

Many small electronic projects use a 9V PP3 battery but if you wish to use the project for long periods a better choice is a battery holder with 6 AA cells. This has the same voltage but a much longer battery life and it will work out cheaper in the long run.

Larger battery clips fit 9V PP9 batteries but these are rarely used now.

PCB
terminal
block
Terminal block

Photographs © Rapid Electronics

Terminal blocks and PCB terminals

Terminal blocks are usually supplied in 12-way lengths but they can be cut into smaller blocks with a sharp knife, large wire cutters or a junior hacksaw. They are sometimes called 'chocolate blocks' because of the way they can be easily cut to size.

PCB mounting terminal blocks provide an easy way of making semi-permanent connections to PCBs. Many are designed to interlock to provide more connections.

Crocodile clips

Crocodile clips
Photographs © Rapid Electronics

The 'standard' crocodile clip has no cover and a screw contact. However, miniature insulated crocodile clips are more suitable for many purposes including test leads. They have a solder contact and lugs which fold down to grip the cable's insulation, increasing the strength of the joint. Remember to feed the cable through the plastic cover before soldering! Add and remove the cover by fully opening the clip, a piece of wood can be used to hold the jaws open.

4mm terminal
and solder tag

Photographs © Rapid Electronics

4mm plugs, sockets and terminals

These are the standard single pole connectors used on meters and other electronic equipment. They are capable of passing high currents (typically 10A) and most designs are very robust. Shrouded plugs and sockets are available for use with high voltages where there is a risk of electric shock. A wide variety of colours is available from most suppliers.

Plugs
Plugs may have a screw or solder terminal to hold the cable. Check if you need to thread the cable through the cover before connecting it. Some plugs, such as those illustrated, are 'stackable' which means that they include a socket to accept another plug, allowing several plugs to be connected to the same point - a very useful feature for test leads.

Sockets
These are usually described as 'panel mounting' because they are designed to be fitted to a case. Most sockets have a solder contact but the picture shows other options. Fit the socket in the case before attaching the wire otherwise you will be unable to add the mounting nut.

Terminals
In addition to a socket these have provision for attaching a wire by threading it through a hole (or wrapping it around the post) and tightening the top nut by hand. They usually have a threaded stud to fit a solder tag inside the case.

Photograph © Rapid Electronics

2mm plugs and sockets

These are smaller versions of the 4mm plugs and sockets described above, but terminals are not readily available. The plugs illustrated are stackable. Despite their small size these connectors can pass large currents and some are rated at 10A.

DC power plugs and sockets

Photographs © Rapid Electronics

These 2-pole plugs and sockets ensure that the polarity of a DC supply cannot be accidentally reversed. The standard sizes are 2.1 and 2.5mm plug diameter. Standard plugs have a 10mm shaft, 'long' plugs have a 14mm shaft. Sockets are available for PCB or chassis mounting and most include a switch on the outer contact which is normally used to disconnect an internal battery when a plug is inserted.

Miniature versions with a 1.3mm diameter plug are used where small size is essential, such as for personal cassette players.

¼" (6.3mm) jack plug and socket

3.5mm jack plug and socket

3.5mm jack line socket
(for fitting to a cable)

Photographs © Rapid Electronics

Jack plugs and sockets

These are intended for audio signals so mono and stereo versions are available. The sizes are determined by the plug diameter: ¼" (6.3mm), 3.5mm and 2.5mm. The 2.5mm size is only available for mono.

Screened plugs have metal bodies connected to the COM contact. Most connections are soldered, remember to thread cables through plug covers beforesoldering! Sockets are designed for PCB or chassis mounting.

¼" plug connections are similar to those for 3.5mm plugs shown below. ¼" socket connections are COM, R and L in that order from the mounting nut, ignore R for mono use. Most ¼" sockets have switches on all contacts which open as the plug is inserted so they can be used to isolate internal speakers for example.

The connections for 3.5mm plugs and sockets are shown below. Plugs have a lug which should be folded down to grip the cable's insulation and increase the strength of the joint. 3.5mm mono sockets have a switch contact which can be used to switch off an internal speaker as the plug is inserted. Ignore this contact if you do not require the switching action.

3.5mm jack plug and socket connections
(the R connection is not present on mono plugs)

L = left channel signal
R = right channel signal
COM = common (0V, screen)

Do not use jack plugs for power supply connections because the contacts may be briefly shorted as the plug is inserted. UseDC power connectors for this.

Photographs © Rapid Electronics

Phono plugs and sockets

These are used for screened cables carrying audio and video signals. Stereo connections are made using a pair of phono plugs and sockets. The centre contact is for the signal and the outer contact for the screen (0V, common). Screened plugs have metal bodies connected to the outer contact to give the signal additional protection from electrical noise. Sockets are available for PCB or chassis mounting, singly for mono, or in pairs for stereo. Line sockets are available for making extension leads.

Construction of a screened cable

Photographs © Rapid Electronics

Coax plugs and sockets

These are similar to the phono plugs and sockets described above but they are designed for use with screened cables carrying much higher frequency signals, such as TV aerial leads. They provide better screening because at high frequencies this is essential to reduce electrical noise.

BNC plug, photograph © Rapid Electronics

BNC plugs and sockets

These are designed for screened cables carrying high frequency signals where an undistorted and noise free signal is essential, for example oscilloscope leads. BNC plugs are connected with apush and twist action, to disconnect you need to twist and pull.

Plugs and sockets are rated by their impedance (50 or 75) which must be the same as the cable's impedance. If the connector and cable impedances are not matched the signal will be distorted because it will be partly reflected at the connection, this is the electrical equivalent of the weak reflection which occurs when light passes through a glass window.

DIN plug

5 way 180° DIN socket
(chassis mounting)

Photographs © Rapid Electronics

DIN plugs and sockets

These are intended for audio signals but they can be used for other low-current purposes where a multi-way connector is required. They are available from 3 way to 8 way. 5 way is used for stereo audio connections. The contacts are numbered on the connector, but they are not in numerical order! For audio use the 'common' (0V) wire is connected to contact 2. 5 way plugs and sockets are available in two versions: 180° and 270° (the angle refers to the arc formed by the contacts).

Plastic covers of DIN plugs (and line sockets) are removed by depressing the retaining lug with a small screwdriver. You may also need small pliers to extract the body from the cover but do not pull on the pins themselves to avoid damage. Remember to thread the cable through the cover before starting to solder the connections!

Soldering DIN plugs is easier if you clamp the insert with the pins. Wires should be pushed into the hollow pins - first 'tin' the wires (coat them with a thin layer of solder) then melt a little solder into the hollow pin and insert the wire while keeping the solder molten. Take care to avoid melting the plastic base, stop and allow the pin to cool if necessary.

Mini-DIN connectors are used for computer equipment such as keyboards and mice but they are not a good choice for general use unless small size is essential.

Photographs © Rapid Electronics

D connectors

These are multi-pole connectors with provision for screw fittings to make semi-permanent connections, for example on computer equipment. The D shape prevents incorrect connection. Standard D-connectors have 2 rows of contacts (top picture); 9, 15 and 25-way versions are the most popular. High Density D-connectors have 3 rows of contacts (bottom picture); a 15-way version is used to connect computer monitors for example.

Note that covers (middle picture) are usually sold separately because both plugs and sockets can be fitted to cables by fitting a cover to a chassis mounted connector. PCB mounting versions of plugs and sockets are also available. The contacts are usually numbered on the body of the connector, although you may need a magnifying glass to see the very small markings. Soldering D-connectors requires a steady hand due to the closeness of the contacts, it is easy to accidently unsolder a contact you have just completed while attempting to solder the next one!

Photographs © Rapid Electronics

IDC communication connectors

These multi-pole insulation displacement connectors are used for computer and telecommunications equipment. They automatically cut through the insulation on wires when installed and special tools are required to fit them. They are available as 4, 6 and 8-way versions.

The 8-way RJ45 is the standard connector for modern computer networks. If you regularly use these you may be interested in thelead tester project.

Standard UK telephone connectors are similar in style but a slightly different shape. They are called BT (British Telecom) connectors.

Cables

Cable... flex... lead... wire...
What do all these terms mean?

A cable is an assembly of one or more conductors (wires) with some flexibility.
A flex is the proper name for the flexible cable fitted to mains electrical appliances.
A lead is a complete assembly of cable and connectors.
A wire is a single conductor which may have an outer layer of insulation (usually plastic).

Single core equipment wire

This is one solid wire with a plastic coating available in a wide variety of colours. It can be bent to shape but will break if repeatedly flexed. Use it for connections which will not be disturbed, for example links between points of a circuit board.

Typical specification: 1/0.6mm (1 strand of 0.6mm diameter), maximum current 1.8A.

Stranded wire

This consists of many fine strands of wire covered by an outer plastic coating. It is flexible and can withstand repeated bending without breaking. Use it for connections which may be disturbed, for example wires outside cases to sensors and switches. A very flexible version ('extra-flex') is used for test leads.

Typical specifications:
10/0.1mm (10 strands of 0.1mm diameter), maximum current 0.5A.
7/0.2mm (7 strands of 0.2mm diameter), maximum current 1.4A.
16/0.2mm (16 strands of 0.2mm diameter), maximum current 3A.
24/0.2mm (24 strands of 0.2mm diameter), maximum current 4.5A.
55/0.1mm (55 strands of 0.1mm diameter), maximum current 6A, used for test leads.

'Figure 8' (speaker) cable

Photograph © Rapid Electronics

'Figure 8' cable consists of two stranded wires arranged in a figure of 8 shape. One wire is usually marked with a line. It is suitable for low voltage, low current (maximum 1A) signals where screening from electrical interference is not required. It is a popular choice for connecting loudspeakers and is often called 'speaker cable'.

Photograph © Rapid Electronics

Signal cable

Signal cable consists of several colour-coded cores of stranded wire housed within an outer plastic sheath. With a typical maximum current of 1A per core it is suitable for low voltage, low current signals where screening from electrical interference is not required.

The picture shows 6-core cable, but 4-core and 8-core are also readily available.

Screened cable (mono)

Screened cable (stereo)

Photographs © Rapid Electronics

Screened cable

The diagram shows the construction of screened cable. The central wire carries the signal and the screen is connected to 0V (common) to shield the signal from electrical interference. Screened cable is used for audio signals and dual versions are available for stereo.

Construction of a screened cable

Photograph © Rapid Electronics

Co-axial cable

This type of screened cable (see above) is designed to carry high frequency signals such as those found in TV aerials and oscilloscope leads.

Mains flex

Photograph © Rapid Electronics

Flex is the proper name for the flexible cable used to connect appliances to the mains supply. It contains 2 cores (for live and neutral) or 3 cores (for live, neutral and earth). Mains flex has thick insulation for the high voltage (230V in UK) and it is available with various current ratings: 3A, 6A and 13A are popular sizes in the UK.

Mains flex is sometimes used for low voltage circuits which pass a high current, but please think carefully before using it in this way. The distinctive colours of mains flex should act as a warning of the mains high voltage which can be lethal; using mains flex for low voltage circuits can undermine this warning.

http://electronicsclub.info/connectors.htm

Capacitors

noreply@blogger.com (KAI) — Wed, 07 Sep 2011 09:24:00 +0000

Function

Polarised (> 1µF) | Unpolarised (< 1µF) | Real Values | Variable & trimmers

Also see: Capacitance and Uses of Capacitors

Function

Capacitors store electric charge. They are used with resistors in timing circuits because it takes time for a capacitor to fill with charge. They are used to smoothvarying DC supplies by acting as a reservoir of charge. They are also used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals.

Capacitance

This is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to show the smaller values.

Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):

µ means 10^-6 (millionth), so 1000000µF = 1F
n means 10^-9 (thousand-millionth), so 1000nF = 1µF
p means 10^-12 (million-millionth), so 1000pF = 1nF

Capacitor values can be very difficult to find because there are many types of capacitor with different labelling systems!

There are many types of capacitor but they can be split into two groups, polarised andunpolarised. Each group has its own circuit symbol.

Polarised capacitors (large values, 1µF +)

Examples: Circuit symbol:

Electrolytic Capacitors

Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering.

There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.

It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum for most battery circuits.

Tantalum Bead Capacitors

Tantalum bead capacitors are polarised and have low voltage ratings like electrolytic capacitors. They are expensive but very small, so they are used where a large capacitance is needed in a small size.

Modern tantalum bead capacitors are printed with their capacitance, voltage and polarity in full. However older ones use a colour-code system which has two stripes (for the two digits) and a spot of colour for the number of zeros to give the value in µF. The standard colour code is used, but for the spot, grey is used to mean × 0.01 and white means × 0.1 so that values of less than 10µF can be shown. A third colour stripe near the leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink 35V). The positive (+) lead is to the right when the spot is facing you: 'when the spot is in sight, the positive is to the right'.

For example:   blue, grey, black spot   means 68µF
For example:   blue, grey, white spot   means 6.8µF
For example:   blue, grey, grey spot   means 0.68µF

Unpolarised capacitors (small values, up to 1µF)

Examples: Circuit symbol:

Small value capacitors are unpolarised and may be connected either way round. They are not damaged by heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at least 50V, usually 250V or so. It can be difficult to find the values of these small capacitors because there are many types of them and several different labelling systems!

Many small value capacitors have their value printed but without a multiplier, so you need to use experience to work out what the multiplier should be!

For example 0.1 means 0.1µF = 100nF.

Sometimes the multiplier is used in place of the decimal point:
For example: 4n7 means 4.7nF.

Capacitor Number Code

A number code is often used on small capacitors where printing is difficult:

the 1st number is the 1st digit,
the 2nd number is the 2nd digit,
the 3rd number is the number of zeros to give the capacitance in pF.
Ignore any letters - they just indicate tolerance and voltage rating.

For example: 102 means 1000pF = 1nF (not 102pF!)

For example: 472J means 4700pF = 4.7nF (J means 5% tolerance).

A colour code was used on polyester capacitors for many years. It is now obsolete, but of course there are many still around. The colours should be read like the resistor code, the top three colour bands giving the value in pF. Ignore the 4th band (tolerance) and 5th band (voltage rating).

For example:

brown, black, orange means 10000pF = 10nF = 0.01µF.

Note that there are no gaps between the colour bands, so 2 identical bands actually appear as a wide band.

For example:

wide red, yellow means 220nF = 0.22µF.

Polystyrene Capacitors

This type is rarely used now. Their value (in pF) is normally printed without units. Polystyrene capacitors can be damaged by heat when soldering (it melts the polystyrene!) so you should use a heat sink (such as a crocodile clip). Clip the heat sink to the lead between the capacitor and the joint.

Real capacitor values (the E3 and E6 series)

You may have noticed that capacitors are not available with every possible value, for example 22µF and 47µF are readily available, but 25µF and 50µF are not!

Why is this? Imagine that you decided to make capacitors every 10µF giving 10, 20, 30, 40, 50 and so on. That seems fine, but what happens when you reach 1000? It would be pointless to make 1000, 1010, 1020, 1030 and so on because for these values 10 is a very small difference, too small to be noticeable in most circuits and capacitors cannot be made with that accuracy.

To produce a sensible range of capacitor values you need to increase the size of the 'step' as the value increases. The standard capacitor values are based on this idea and they form a series which follows the same pattern for every multiple of ten.

The E3 series (3 values for each multiple of ten)
10, 22, 47, ... then it continues 100, 220, 470, 1000, 2200, 4700, 10000 etc.
Notice how the step size increases as the value increases (values roughly double each time).

The E6 series (6 values for each multiple of ten)
10, 15, 22, 33, 47, 68, ... then it continues 100, 150, 220, 330, 470, 680, 1000 etc.
Notice how this is the E3 series with an extra value in the gaps.

The E3 series is the one most frequently used for capacitors because many types cannot be made with very accurate values.

Variable capacitors

Variable Capacitor Symbol

Variable Capacitor
Photograph © Rapid Electronics

Variable capacitors are mostly used in radio tuning circuits and they are sometimes called 'tuning capacitors'. They have very small capacitance values, typically between 100pF and 500pF (100pF = 0.0001µF). The type illustrated usually has trimmers built in (for making small adjustments - see below) as well as the main variable capacitor.

Many variable capacitors have very short spindles which are not suitable for the standard knobs used for variable resistors and rotary switches. It would be wise to check that a suitable knob is available before ordering a variable capacitor.

Variable capacitors are not normally used in timing circuits because their capacitance is too small to be practical and the range of values available is very limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is necessary to vary the time period.

Trimmer capacitors

Trimmer Capacitor Symbol

Trimmer Capacitor
Photograph © Rapid Electronics

Trimmer capacitors (trimmers) are miniature variable capacitors. They are designed to be mounted directly onto the circuit board and adjusted only when the circuit is built.

A small screwdriver or similar tool is required to adjust trimmers. The process of adjusting them requires patience because the presence of your hand and the tool will slightly change the capacitance of the circuit in the region of the trimmer!

Trimmer capacitors are only available with very small capacitances, normally less than 100pF. It is impossible to reduce their capacitance to zero, so they are usually specified by their minimum and maximum values, for example 2-10pF.

Trimmers are the capacitor equivalent of presets which are miniature variable resistors.

Credit by:http://www.kpsec.freeuk.com/components/capac.htm

Electricity and the Electron

noreply@blogger.com (KAI) — Mon, 05 Sep 2011 03:33:00 +0000

What is electricity?

Electricity is the flow of charge around a circuit carrying energy from the battery (or power supply) to components such as lamps and motors.

Electricity can flow only if there is a complete circuit from the battery through wires to components and back to the battery again.

The diagram shows a simple circuit of a battery, wires, a switch and a lamp. The switch works by breaking the circuit.

With the switch open the circuit is broken - so electricity cannot flow and the lamp is off.

With the switch closed the circuit is complete - allowing electricity to flow and the lamp is on. The electricity is carrying energy from the battery to the lamp.

We can see, hear or feel the effects of electricity flowing such as a lamp lighting, a bell ringing, or a motor turning - but we cannot see the electricity itself, so which way is it flowing?

Imaginary positive particles
moving in the direction of
the conventional current

Which way does electricity flow?

We say that electricity flows from the positive (+) terminal of a battery to the negative (-) terminal of the battery. We can imagine particles with positive electric charge flowing in this direction around the circuit, like the red dots in the diagram.

This flow of electric charge is called conventional current.

This direction of flow is used throughout electronics and it is the one you should remember and use to understand the operation of circuits.

However this is not the whole answer because the particles that move in fact have negative charge! And they flow in the opposite direction! Please read on...

The electron

When electricity was discovered scientists tried many experiments to find out which way the electricity was flowing around circuits, but in those early days they found it was impossible to find the direction of flow.

They knew there were two types of electric charge, positive (+) and negative (-), and they decided to say that electricity was a flow of positive charge from + to -. They knew this was a guess, but a decision had to be made! Everything known at that time could also be explained if electricity was negative charge flowing the other way, from - to +.

The electron was discovered in 1897 and it was found to have a negative charge. The guess made in the early days of electricity was wrong! Electricity in almost all conductors is really the flow of electrons (negative charge) from - to +.

By the time the electron was discovered the idea of electricity flowing from + to - (conventional current) was firmly established. Luckily it is not a problem to think of electricity in this way because positive charge flowing forwards is equivalent to negative charge flowing backwards.

To prevent confusion you should always use conventional current when trying to understand how circuits work, imagine positively charged particles flowing from + to -.

Circuit Symbols

noreply@blogger.com (KAI) — Mon, 05 Sep 2011 03:25:00 +0000

Circuit symbols are used in circuit diagrams which show how a circuit is connected together. The actual layout of the components is usually quite different from the circuit diagram.

To build a circuit you need a different diagram showing the layout of the parts on stripboard or printed circuit board.

Temporary and trial circuits are often built on breadboardwhich does not require soldering.

Wires and connections

Component
Circuit Symbol
Function of Component

Wire

To pass current very easily from one part of a circuit to another.

Wires joined

A 'blob' should be drawn where wires are connected (joined), but it is sometimes omitted. Wires connected at 'crossroads' should be staggered slightly to form two T-junctions, as shown on the right.

Wires not joined

In complex diagrams it is often necessary to draw wires crossing even though they are not connected. The simple crossing on the left is correct but may be misread as a join where the 'blob' has been forgotten. The bridge symbol on the right leaves no doubt!

Power Supplies

Component
Circuit Symbol
Function of Component

Cell

Supplies electrical energy.
The larger terminal (on the left) is positive (+).
A single cell is often called a battery, but strictly a battery is two or more cells joined together.

Battery

Supplies electrical energy. A battery is more than one cell.
The larger terminal (on the left) is positive (+).

Solar Cell

Converts light to electrical energy.
The larger terminal (on the left) is positive (+).

DC supply

Supplies electrical energy.
DC = Direct Current, always flowing in one direction.

AC supply

Supplies electrical energy.
AC = Alternating Current, continually changing direction.

Fuse

A safety device which will 'blow' (melt) if the current flowing through it exceeds a specified value.

Transformer

Two coils of wire linked by an iron core. Transformers are used to step up (increase) and step down (decrease) AC voltages. Energy is transferred between the coils by the magnetic field in the core. There is no electrical connection between the coils.

Earth
(Ground)

A connection to earth. For many electronic circuits this is the 0V (zero volts) of the power supply, but for mains electricity and some radio circuits it really means the earth. It is also known as ground.

Output Devices: Lamps, Heater, Motor, etc.

Component
Circuit Symbol
Function of Component

Lamp (lighting)

A transducer which converts electrical energy to light. This symbol is used for a lamp providing illumination, for example a car headlamp or torch bulb.

Lamp (indicator)

A transducer which converts electrical energy to light. This symbol is used for a lamp which is an indicator, for example a warning light on a car dashboard.

Heater

A transducer which converts electrical energy to heat.

Motor

A transducer which converts electrical energy to kinetic energy (motion).

Bell

A transducer which converts electrical energy to sound.

Buzzer

A transducer which converts electrical energy to sound.

Inductor
(Coil, Solenoid)

A coil of wire which creates a magnetic field when current passes through it. It may have an iron core inside the coil. It can be used as a transducer converting electrical energy to mechanical energy by pulling on something.

Switches

Component
Circuit Symbol
Function of Component

Push Switch
(push-to-make)

A push switch allows current to flow only when the button is pressed. This is the switch used to operate a doorbell.

Push-to-Break Switch

This type of push switch is normally closed (on), it is open (off) only when the button is pressed.

On-Off Switch
(SPST)

SPST = Single Pole, Single Throw.
An on-off switch allows current to flow only when it is in the closed (on) position.

2-way Switch
(SPDT)

SPDT = Single Pole, Double Throw.
A 2-way changeover switch directs the flow of current to one of two routes according to its position. Some SPDT switches have a central off position and are described as 'on-off-on'.

Dual On-Off Switch
(DPST)

DPST = Double Pole, Single Throw.
A dual on-off switch which is often used to switch mains electricity because it can isolate both the live and neutral connections.

Reversing Switch
(DPDT)

DPDT = Double Pole, Double Throw.
This switch can be wired up as a reversing switch for a motor. Some DPDT switches have a central off position.

Relay

An electrically operated switch, for example a 9V battery circuit connected to the coil can switch a 230V AC mains circuit.
NO = Normally Open, COM = Common, NC = Normally Closed.

Resistors

Component
Circuit Symbol
Function of Component

Resistor

A resistor restricts the flow of current, for example to limit the current passing through an LED. A resistor is used with a capacitor in a timing circuit.
Some publications use the old resistor symbol:

Variable Resistor
(Rheostat)

This type of variable resistor with 2 contacts (a rheostat) is usually used to control current. Examples include: adjusting lamp brightness, adjusting motor speed, and adjusting the rate of flow of charge into a capacitor in a timing circuit.

Variable Resistor
(Potentiometer)

This type of variable resistor with 3 contacts (a potentiometer) is usually used to control voltage. It can be used like this as a transducer converting position (angle of the control spindle) to an electrical signal.

Variable Resistor
(Preset)

This type of variable resistor (a preset) is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than normal variable resistors so they are often used in projects to reduce the cost.

Capacitors

Component
Circuit Symbol
Function of Component

Capacitor

A capacitor stores electric charge. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.

Capacitor, polarised

A capacitor stores electric charge. This type must be connected the correct way round. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.

Variable Capacitor

A variable capacitor is used in a radio tuner.

Trimmer Capacitor

This type of variable capacitor (a trimmer) is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment.

Diodes

Component
Circuit Symbol
Function of Component

Diode

A device which only allows current to flow in one direction.

LED
Light Emitting Diode

A transducer which converts electrical energy to light.

Zener Diode

A special diode which is used to maintain a fixed voltage across its terminals.

Photodiode

A light-sensitive diode.

Transistors

Component
Circuit Symbol
Function of Component

Transistor NPN

A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit.

Transistor PNP

A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit.

Phototransistor

A light-sensitive transistor.

Audio and Radio Devices

Component
Circuit Symbol
Function of Component

Microphone

A transducer which converts sound to electrical energy.

Earphone

A transducer which converts electrical energy to sound.

Loudspeaker

A transducer which converts electrical energy to sound.

Piezo Transducer

A transducer which converts electrical energy to sound.

Amplifier
(general symbol)

An amplifier circuit with one input. Really it is a block diagram symbol because it represents a circuit rather than just one component.

Aerial
(Antenna)

A device which is designed to receive or transmit radio signals. It is also known as an antenna.

Meters and Oscilloscope

Component
Circuit Symbol
Function of Component

Voltmeter

A voltmeter is used to measure voltage.
The proper name for voltage is 'potential difference', but most people prefer to say voltage!

Ammeter

An ammeter is used to measure current.

Galvanometer

A galvanometer is a very sensitive meter which is used to measure tiny currents, usually 1mA or less.

Ohmmeter

An ohmmeter is used to measure resistance. Most multimeters have an ohmmeter setting.

Oscilloscope

An oscilloscope is used to display the shape of electrical signals and it can be used to measure their voltage and time period.

Sensors (input devices)

Component
Circuit Symbol
Function of Component

LDR

A transducer which converts brightness (light) to resistance (an electrical property).
LDR = Light Dependent Resistor

Thermistor

A transducer which converts temperature (heat) to resistance (an electrical property).

Logic Gates

Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low, 0V, off).
For more information please see the Logic Gates page.
There are two sets of symbols: traditional and IEC (International Electrotechnical Commission).

Gate Type
Traditional Symbol
IEC Symbol
Function of Gate

NOT

A NOT gate can only have one input. The 'o' on the output means 'not'. The output of a NOT gate is the inverse (opposite) of its input, so the output is true when the input is false. A NOT gate is also called an inverter.

AND

An AND gate can have two or more inputs. The output of an AND gate is true when all its inputs are true.

NAND

A NAND gate can have two or more inputs. The 'o' on the output means 'not' showing that it is a Not ANDgate. The output of a NAND gate is true unless all its inputs are true.

OR

An OR gate can have two or more inputs. The output of an OR gate is true when at least one of its inputs is true.

NOR

A NOR gate can have two or more inputs. The 'o' on the output means 'not' showing that it is a Not OR gate. The output of a NOR gate is true when none of its inputs are true.

EX-OR

An EX-OR gate can only have two inputs. The output of an EX-OR gate is true when its inputs are different (one true, one false).

EX-NOR

An EX-NOR gate can only have two inputs. The 'o' on the output means 'not' showing that it is a Not EX-ORgate. The output of an EX-NOR gate is true when its inputs are the same (both true or both false).

Sets of circuit symbols to download

You can download complete sets of all the circuit symbols shown above. The sets are 'zipped' for convenience and they are provided in three formats:

WMF circuit symbols (32K) - Windows Metafiles.
These vector drawings are the best format for printed documents on most computer systems, including Windows where they can be used in Word documents for example. They can be enlarged without loss of quality. If you are not sure which format is best for you I suggest you try this one first.
GIF circuit symbols (43K) - Graphics Interchange Format.
These bitmap images are the best format for web pages but they print poorly and their bitmap nature will become obvious if they are enlarged. You can download individual symbols by saving the images used above on this page.
Drawfile circuit symbols (29K) - for RISC OS (Acorn) computers.
These high quality vector drawings are suitable for almost all documents on a RISC OS computer. All the symbols were originally drawn in this format. They print perfectly and can be enlarged without loss of quality. Sorry, this format is NOT suitable for Windows computers.

Simple AC circuit calculations

noreply@blogger.com (KAI) — Tue, 26 Jul 2011 05:53:00 +0000

Over the course of the next few chapters, you will learn that AC circuit measurements and calculations can get very complicated due to the complex nature of alternating current in circuits with inductance and capacitance. However, with simple circuits (figure below) involving nothing more than an AC power source and resistance, the same laws and rules of DC apply simply and directly.

AC circuit calculations for resistive circuits are the same as for DC.

Series resistances still add, parallel resistances still diminish, and the Laws of Kirchhoff and Ohm still hold true. Actually, as we will discover later on, these rules and laws always hold true, its just that we have to express the quantities of voltage, current, and opposition to current in more advanced mathematical forms. With purely resistive circuits, however, these complexities of AC are of no practical consequence, and so we can treat the numbers as though we were dealing with simple DC quantities.

Because all these mathematical relationships still hold true, we can make use of our familiar “table” method of organizing circuit values just as with DC:

One major caveat needs to be given here: all measurements of AC voltage and current must be expressed in the same terms (peak, peak-to-peak, average, or RMS). If the source voltage is given in peak AC volts, then all currents and voltages subsequently calculated are cast in terms of peak units. If the source voltage is given in AC RMS volts, then all calculated currents and voltages are cast in AC RMS units as well. This holds true for any calculation based on Ohm's Laws, Kirchhoff's Laws, etc. Unless otherwise stated, all values of voltage and current in AC circuits are generally assumed to be RMS rather than peak, average, or peak-to-peak. In some areas of electronics, peak measurements are assumed, but in most applications (especially industrial electronics) the assumption is RMS.

REVIEW:
All the old rules and laws of DC (Kirchhoff's Voltage and Current Laws, Ohm's Law) still hold true for AC. However, with more complex circuits, we may need to represent the AC quantities in more complex form. More on this later, I promise!
The “table” method of organizing circuit values is still a valid analysis tool for AC circuits.

ref:http://www.allaboutcircuits.com/vol_2/chpt_1/4.html

Short-Circuit Calculation Methods

noreply@blogger.com (KAI) — Tue, 26 Jul 2011 05:48:00 +0000

All electrical systems are susceptible to short circuits and the abnormal current levels they create. These currents can produce considerable thermal and mechanical stresses in electrical distribution equipment. Therefore, it's important to protect personnel and equipment by calculating short-circuit currents during system upgrade and design. Because these calculations are life-safety related, they're mandated by 110.9 of the NEC, which states:

“Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted.”

When you apply these requirements to a circuit breaker, you must calculate the maximum 3-phase fault current the breaker will be required to interrupt. This current can be defined as the short-circuit current available at the terminals of the protective device.

You can assume that 3-phase short circuits are “bolted,” or have no impedance. In addition, a 3-phase short circuit can be considered a balanced load, which means you can use a single-phase circuit to analyze one of the phases and the neutral.

Distribution equipment, such as circuit breakers, fuses, switchgear, and MCCs, have interrupting or withstand ratings defined as the maximum rms values of symmetrical current. A circuit breaker can't interrupt a circuit at the instant of inception of a short. Instead, due to the relay time delay and breaker contact parting time, it will interrupt the current after a period of five to eight cycles, by which time the DC component will have decayed to nearly zero and the fault will be virtually symmetrical.

Closing a breaker against an existing fault makes it possible to intercept the peak of the asymmetrical short-circuit current, which is greater than the rms value of the symmetrical current. For this reason, equipment is also tested at a particular test X/R ratio value typical to a particular electrical apparatus, such as switchgear, switchboards, or circuit breakers, and is designed and rated to withstand and/or close and latch the peak asymmetrical current described above.

Fault analysis is required to calculate and compare symmetrical and asymmetrical current values in order to select a protective device to adequately protect a piece of electrical distribution equipment.

Methods of calculation. Rather than using a theoretical approach to determine short-circuit currents, published standards offer methods to compute a symmetrical steady state solution to which you can apply a multiplier in order to obtain the peak value of an asymmetrical current. The result is precise enough to fall within an acceptable tolerance to meet NEC requirements.

The classical approach and the method defined by ANSI/IEEE are two such industry-accepted methods for calculating short circuits. Both methods assume that the fault impedance is zero (bolted short circuit) and the pre-fault voltage is constant during the evolution of the fault. In actuality, the fault has its own impedance, and the voltage drop, due to the short-circuit current, lowers the driving voltage.

This over-simplified one-line diagram of a power distribution system included values necessary for working through the two methods of short-circuit calculation referred to in the text.

The classical approach is used to calculate the Thevenin equivalent impedance as “seen” by the system at the point of the fault. Thevenin impedance is defined as the impedance seen at any point in a circuit once all the voltage generators have been short circuited and all the current generators have been opened. Transformer and utility impedances and rotating machine subtransient reactances describe all possible contributions to a short circuit. Once we have calculated the symmetrical and peak duties, we can determine the required rating of the protective device by direct comparison to manufacturer equipment ratings.

The ANSI/IEEE short-circuit calculation method follows a step-by-step process.

The ANSI/IEEE method, which is described in IEEE Std. C37.010-1979 and its revision in 1999, is used for high-voltage (above 100V) equipment. It calls for determining the momentary network fault impedance, which makes it possible to calculate the close and latch rating of the breaker. It also calls for identifying the interrupting network fault impedance, which makes it possible to calculate the interrupting duty of the breaker. The interrupting network fault impedance value differs from the momentary network fault impedance value in that the impedance increases from the subtransient to transient level.

The IEEE standard permits the exclusion of all 3-phase induction motors below 50 hp and all single-phase motors. Hence, no reactance adjustment is needed for these motors. The Chart at right clarifies the ANSI/IEEE procedure.

Classical calculation. Begin by converting all impedances to “per unit” values. Per unit base values and formulae used are as follows:

S_base =100MVA

V_base =26.4 kV

Let's run through an example calculation to make this discussion a little more tangible. Refer to the one-line diagram in the Figure above with the following input data:

Utility: 26.4kV, 1,200MVA, X/R=41
Transformer (T₁): 2MVA, 26.4/4.16kV, DY-G, Z=7%, X/R515
Motor 1 (M₁): Induction, 4.16kV, 1,000 hp, PF=0.8, efficiency50.8, X"_d= 0.16 pu, X/R=28
Motor 2 (M₂): Induction, 4.16kV, 49 hp, PF=0.8, efficiency=0.8, X"_d=0.17 pu, X/R=10

Now it's possible to calculate the equivalent Thevenin impedance for a fault at Bus 2 by combining the per unit X and R values to obtain the relative impedances.

Z_Fault=(Z_utility+Z_T1)||Z_Motor1||Z_Motor2=(0.0021+j0.083+0.005+j0.07)||(0.49+j13.8)||(29.8+j298)=0.166+j2.817 pu=2.823ej^86.6

We may now calculate the short-circuit current rms at Bus 2:

The peak duty the breaker is required to close and latch may be evaluated using the following formula, which constitutes a multiplier to the rms current, which was calculated above:

Use Table 1, page 1 in ANSI C37.06-1997 Preferred Ratings and Related Required Capabilities to rate new switchgear. It's useful in comparing calculated duty (4,916A and 12,692A) and standard ratings. The Table includes sample values extracted from the ANSI table.

Compare calculated duty and standard ratings using Table 1 in ANSI C37.06-1997.

These are the short-circuit current ratings required for our switchgear duty corresponding to a continuous current, for example, 1,200A. No further steps have to be taken, as the table itself, by comparison, provides the required specifications for the equipment to be installed.

ANSI/IEEE calculation. The ANSI/IEEE calculation method is based on the same per unit quantities as calculated before. However, it differs from the classical method because it makes it possible to study two separate circuits derived from the original one: one resistive only and one reactive only. This will be carried out for both momentary and interrupting network fault impedances.

For each network, Thevenin equivalent resistance and Thevenin equivalent reactance will then be combined in order to obtain the equivalent Thevenin impedance. This is the significant difference between the ANSI/IEEE procedure and the classical calculation method.

As mentioned before, the momentary network fault impedance is based on the subtransient reactances of the rotating machines, which allows for the calculation of the first-cycle peak fault duty. The total fault resistance and reactance values will be calculated separately, following the same formula as the Z_Fault equation in the classical calculation section, except the Zs must be replaced with the Rs and Xs.

Then they'll be combined as total fault impedance Z_Fault, which will yield I_SC3-phaseand I_Peak according to the formulas.

The interrupting network fault impedance is based on individual equipment transient reactances. In the previous example, only the reactance of Motor 1 needs to be adjusted. It's acceptable to neglect Motor 2 at medium voltage levels. The resistances of the network, in fact, don't vary with respect to time. ANSI C37.010-1999 identifies the adjustment factor as 1.5.

In this case, the total fault resistance and fault reactance (with adjustments) will be calculated separately as already seen.

I_SC3-phase, symmetrical duty is calculated as it was in the classical method. However, it's typically characterized by a smaller magnitude because the Z_fault “interrupting” current is larger than the one in the momentary network calculation.

I_SC3-phase is essential because a multiplier factor is applied to this quantity for comparison to the breaker interrupting rating.

This multiplier will account for:

The additive contribution of the DC current component, which might still be “alive” after the time of contact parting.
The eventual subtractive contribution of the AC current decay, due to the evolution of the reactances toward larger values. This effect is possible when the generation of power is local.

Multipliers necessary for one short-circuit calculation method are shown in ANSI C37.010-1999.

The multipliers, in function of time of contact parting and of the ratio X/R at the point of fault, are described in curves starting from figure A-8, page 60, C37.010-1999 (Figure).

Once I_SC3-phase has been multiplied by this factor (between 1 and 1.25), you have the minimum rating of your equipment. As in the classical method, you can also use Table 1, page 1 in ANSI C37.06-1997 to determine a standard rating.

Which method is better? Both methods basically provide the same results. There are no theoretical reasons to prefer one to the other, only practical reasons. The ANSI/IEEE approach is the evolution of a method conceived in the '70s in the United States, when no computer-assisted calculations were available. ANSI/IEEE C37.010-1999 can only be used at medium or high voltages and only at 60 Hz. Calculation programs have been developed to determine fault currents that apply the multiplier factors called for in this standard. In fact, some clients may ask for the application of this calculation methodology by contract. Manufacturers may also recall the ANSI/IEEE standard in their catalogues. The classical method is used mainly in low-voltage studies and can also be applied at 50 Hz. It's a well-known procedure because it's a common topic in every “power system” college course.

Mitolo is an associate electrical engineer at Chu & Gassman Consulting Engineers in Middlesex, N.J.

High-Voltage Regulator With Short Circuit Protection

noreply@blogger.com (KAI) — Sun, 27 Mar 2011 05:02:00 +0000

There are many circuits for low voltage regulators. For higher voltages, such as supplies for valve circuits, the situation is different. That’s why we decided to design this simple regulator that can cope with these voltages. This circuit is obviously well suited for use in combination with the quad power supply for the hybrid amp, published elsewhere in this issue. The actual regulator consists of just three transistors. A fourth has been added for the current limiting function.

The circuit is a positive series regulator, using a pnp transistor (T2) to keep the voltage drop as low as possible. The operation of the circuit is very straightforward. When the output voltage drops, T4 pulls the emitter of T3 lower. This drives T2 harder, which causes the output voltage to rise again. R4 restricts the base current of T2. C1 and C2 have been added to improve the stability of the circuit.

These are connected in series so that the voltage across each capacitor at switch-on or during a short circuit doesn’t become too large. You should use capacitors rated for at least 100 V for C1-C3. D1 protects T2 against negative voltages that may occur when the input is short-circuited or when large capacitors are connected to the output. We use two zener diodes of 39 V connected in series for the reference voltage, giving 78 V to the base of T3.

Because R6 is equal to R7 the output voltage will be twice as large, which is about 155 V. T4 acts as a buffer for potential divider R6/R7, which means we can use higher values for these resistors and that the voltage is not affected by the base current of T2 (this current is about the same as the emitter current of T3). This is obviously not a temperature compensated circuit, but for this purpose it is good enough.
[...]
Source:
Author: Ton Giesberts – Copyright: Elektor Electronics

http://www.extremecircuits.net/2010/06/high-voltage-regulator-with-short.html

Missing pulse detector circuit using NE555

noreply@blogger.com (KAI) — Sun, 27 Mar 2011 04:56:00 +0000

An NE555 timer IC connected as shown here can detect a missing pulse or abnormally long period between two consecutive pulses in a train of pulses,Such circuits can be used to detect the intermittent firing of the spark plug of an automobile or to monitor the heart beat of a sick patient.

The signal from the pick up transducer is shaped to form a negative going pulse and is applied to pin 2 of the IC which is connected as a mono stable.As long as the spacing between the pulse is less than the timing interval,the timing cycle is continuously reset by the input pulses and the capacitor is discharged via T1.A decrease in pulse frequency or a missing pulse permits completion of time interval which causes a change in the output level.

Source: http://www.circuitstoday.com/category/automotive-circuits/page/3

Radio Frequency (RF) Watt Meter

noreply@blogger.com (KAI) — Mon, 21 Mar 2011 12:38:00 +0000

For RF (radio frequency) transmitter experiment, watt meter is useful for optimizing the transmitter circuit. A simple RF watt meter circuit is shown in the schematic diagram below. Because circuit is not frequency sensitive, calibration is accurate on all HF bands. The sensitivity is affected by meter movement, number of turns in primary coil, and resistive voltage driver.
Pots can be adjusted for full-scale values from 1-14 W with values shown on the diagram. C1 and C2 are 3-20 pF. Diodes are 1N34A, 1N60, or equivalent. L1 is 46 turns No. 28 on Amidon T-50-2 toroid, with 2 turns No. 22 between ends of L1 for L2. Connect resistive dummy load to one coax receptacle and RF power source to other to adjust, with R2 at maximum resistance. We can provide highest meter reading and make that the FWD position with place the switch on the upper position. Switch to other position, which becomes REF, and for null reading, adjust C1. Reverse RF source and load, leaving switch at FWD, and adjust C2 for null. Now, we can calibrated the Wattmeter. [Circuit's schematic diagram source: seekic.com]

Ref:http://freecircuitdiagram.com/2010/12/08/radio-frequency-rf-watt-meter/

1 KW Power (Watt) Meter

noreply@blogger.com (KAI) — Fri, 18 Mar 2011 02:07:00 +0000

This watt-meter circuit has measurement range up to 1-KW. This circuit can give the complete (X)(Y) function although uses only one transistor. Actually, this circuit is used for 117 Vac±50 Vac operation. For lower or lower voltage, this circuit can be modified easily. This circuit only measure power on negative cycles. The advantages of this circuit is this circuit does not need external power supply. This circuit measures true power that is delivered to the load. Here is the schematic diagram of the circuit:

At idle section, this circuit draw only 0.5W. This circuit has load current-sensing voltage of 10mV and load voltage loss of 0.01%. For linear loads, Rejection of reactive load currents is better than 100:1. When using a 50-μA meter movement, the nonlinearity of this circuit is about 1% full scale. Copper shunt can be used to give correct gain due to temperature. [Circuit's schematic diagram source: seekic.com]

Ref:http://freecircuitdiagram.com/2011/03/03/1-kw-power-watt-meter/

LM10 Battery Voltage Threshold Indicator

noreply@blogger.com (KAI) — Fri, 18 Mar 2011 02:03:00 +0000

A battery threshold indicator circuit shown in the schematic diagram below has current regulation mechanism in driving the LED. A sufficient current should be satisfied at the minimum voltage but no excessive current when the voltage is at the highest level. Balance pin (5) is used as the reference voltage for regulating the current. This pin generate 23 mV, which is internally temperature compensated.

When the voltage on the reference-feedback terminal (8) drops below 200 mV, the reference output (1) rises to supply the feedback voltage to the op amp through D2, so the LED current drops to zero. The minimum threshold voltage for these circuits is basically imited by the bias voltage for the LEDs. Typically, this is 1.7V for red, 2V for green and 2.5V for yellow. These two circuits can be made to operate satisfactorily for threshold voltages as low as 2V if a red diode is used. [National Semiconductor Application Note]

This battery voltage threshold indicator circuit overcomes the difficulties caused by voltage change across the diode biasing resistor. [Circuit's schematic diagram source: National Semiconductor Application Note]

Ref:http://freecircuitdiagram.com/2011/03/11/lm10-battery-voltage-threshold-indicator/

DC/DC Converter From +1.5V To +34V

noreply@blogger.com (KAI) — Tue, 21 Dec 2010 00:18:00 +0000

An interesting DC/DC converter IC is available from Linear Technology. The LT1615 step-up switching voltage regulator can generate an output voltage of up to +34V from a +1.2 to +15V supply, using only a few external components. The tiny 5-pin SOT23 package makes for very compact construction. This IC can for example be used to generate the high voltage needed for an LCD screen, the tuning voltage for a varicap diode and so on. The internal circuit diagram of the LT1615 is shown in Figure 1. It contains a monostable with a pulse time of 400 ns, which determines the off time of the transistor switch.If the voltage sampled at the feedback input drops below the reference threshold level of 1.23 V, the transistor switches on and the current in the coil starts to increase. This builds up energy in the magnetic ﬁeld of the coil. When the current through the coil reaches 350 mA, the monostable is triggered and switches the transistor off for the following 400 ns. Since the energy stored in the coil must go somewhere, current continues to ﬂow through the coil, but it decreases linearly. This current charges the output capacitor via the Schottky diode (SS24, 40V/2A). As long as the voltage at FB remains higher than 1.23V, nothing else happens.
As soon as it drops below this level, however, the whole cycle is repeated. The hysteresis at the FB input is 8mV. The output voltage can be calculated using the formula Vout = 1.23V (R1+R2) / R2 The value of R1 can be selected in the megohm range, since the current into the FB input is only a few tens of nano-amperes. When the supply voltage is switched on, or if the output is short-circuited, the IC enters the power-up mode. As long as the voltage at FB is less than 0.6V, the LT1615 output current is limited to 250mA instead of 350mA, and the monostable time is increased to 1.5µs.These measures reduce the power dissipation in the coil and diode while the output voltage is rising. In order to minimize the noise voltages produced when the coil is switched, the IC must be properly decoupled by capacitors at the input and output. The series resistance of these capacitors should be as low as possible, so that they can short noise voltages to earth. They should be located as close to the IC as possible, and connected directly to the earth plane. The area of the track at the switch output (SW) should be as small as possible. Connecting a 4.7-µF capacitor across the upper feedback capacitor helps to reduce the level of the output ripple voltage.

Switching Voltage Regulator

noreply@blogger.com (KAI) — Tue, 21 Dec 2010 00:17:00 +0000

The Analog Devices ACP3610 is a voltage doubler that works with a switched-capacitor converter, using the push-pull principle. The switching frequency at the output is approximately 550 kHz. The term ‘push-pull’ refers to the two charge pumps, which work in parallel but in opposite directions in order to deliver the output voltage and current. Whenever one capacitor is supplying current to the output, the other one is being charged. This technique minimizes voltages losses and output ripple. The converter works with input voltages between 3 and 3.6 V. It provides an output voltage of around 6V at a maximum current of 320mA, if 2.2µF switched capacitors with low ESR (equivalent series resistance) are used.

A shut-down input is provided to allow the voltage doubler to be enabled or disabled by a logic-level signal. The IC is enclosed in a special package, which can dissipate up to 980mW at room temperature. The schematic diagram shows a typical application for the ADP3610. Here it works as a non-regulated voltage doubler. In theory, a voltage doubler can provide exactly twice the input voltage at its output, but in practice the combination of internal losses in the electronic switches and the internal resistances of the capacitors always causes the output voltage to be somewhat lower. The output voltage drops from a no-load value of 6 V to 5.4 V with a 320mA load, with a nearly linear characteristic.

A small capacitor is connected across the two supply pins at the input of the IC. It suppresses noise, brief voltage ﬂuctuations, and current peaks when the ADP3610 switches. This capacitor (CIN) must have a low internal resistance (ESR). A larger capacitance value is necessary if long supply leads to the ADP3610 are present. The 1µF output capacitor (CO) is alternately charged by the two capacitors of the charge pump, CP1 and CP2. The internal resistance is an important factor here as well. It largely determines the amount that the voltage drops under load, and the amount of ripple in the output voltage. Ceramic or tantalum capacitors are recommended. The ESR can also be reduced by connecting several smaller-value capacitors in parallel. With small loads, the value of CO may be reduced.

http://www.extremecircuits.net/2010/08/switching-voltage-regulator.html

Variable Voltage Regulator using the L200

noreply@blogger.com (KAI) — Tue, 21 Dec 2010 00:17:00 +0000

This is a circuit diagram of the circuit variable regulator, which uses IC L200, as regulator of voltage and current, IC For this comes from the company SGS-Thomson, which gives this series. This diagram circuit output voltage can be set, we can set the output voltage, with RV1. You can use this power supply circuit in various applications

Component :
R1=0.7 / Io max
R2=10 ohms
R3=1Kohm
R4=820 ohms
RV1=4.7Kohm pot.
C1=4700uF 63V
C2-3=100nF 100V
C4=47uF 63V
Q1=BDW51
Q2=BC108
IC1=L200

Voltage Regulator Using LM338

noreply@blogger.com (KAI) — Tue, 21 Dec 2010 00:17:00 +0000

This circuit is a circuit diagram power supply. Circuit diagram works on voltage +13.8 V 5A with electric currents. This circuit controlled by the LM338 IC. Many times we need a supply of relatively strong in the framework we provide a variety of equipment with + 13.8V, as transceivers CB, cargo lead-acid batteries, and others known to use the circuit capable of providing complete in his exit, when This continuously operating 5A and 12A peak current. Not only need a few external components. Setting the voltage at + 13.8V to the trimmer TR1, (multiturn). The IC1 LM338 must in each case is placed on one suitable heatsink, which both supported by one fan. All the connections by the circuit become with big cross-section cable, because the current through from within their already high enough. The following is a schematic drawing:

Component :
R1=270R 1/4W 2%
TR1=4k7 (Multiturn)
C1=10000uF 40V
C2-3=100 nF 100V Polyester
C4-5=10uF 25V
D1-2=1N4002 (1A/100V)
B1=25A Bridge Rectifier
IC1=LM338
T1=220Vac/15VAC – 8A Mains Transformer
S1=2 Pole Single Throw Mains Switch
F1=250mA Fuse

http://freecircuitdiagram.net/voltage-regulator-using-lm338.html

2-25V 5A Power Supply Using LM338

noreply@blogger.com (KAI) — Wed, 08 Dec 2010 23:56:00 +0000

This circuit is a circuit diagram power supply circuit uses a LM338 adjustable 3 terminal regulator to supply a current of up to 5A over a variable output voltage of 2V to 25V DC. It will come in handy to power up many electronic circuits when you are assembling or building any electronic devices. The schematic and parts list are designed for a power supply input of 240VAC. Change the ratings of the components if 110V AC power supply input is required. The mains input is applied to the circuit through fuse F1. The fuse will blow if a current greater than 8A is applied to the system. Varistor V1 is used to clamp down any surge of voltage from the mains to protect the components from breakdown. Transformer T1 is used to step down the incoming voltage to 24V AC where it is rectified by the four diodes D1, D2, D3 and D4. Electrolytic capacitor E1 is used to smoothen the ripple of the rectified DC voltage.

Diodes D5 and D6 are used as a protection devices to prevent capacitors E2 and E3 from discharging through low current points into the regulator. Capacitor C1 is used to bypass high frequency component from the circuit. Ensure that a large heat sink is mounted to LM338 to transfer the heat generated to the atmosphere.

http://freecircuitdiagram.net/2-25v-5a-power-supply-using-lm338.html

Regulated 12 Volt Supply

noreply@blogger.com (KAI) — Wed, 08 Dec 2010 23:56:00 +0000

This circuit above uses a 13 volt zener diode, D2 which provides the voltage regulation. Aprroximately 0.7 Volts are dropped across the transistors b-e junction, leaving a higher current 12.3 Volt output supply. This circuit can supply loads of up to 500 mA.This circuit is also known as an amplified zener circuit.

Transformerless Power Supply

noreply@blogger.com (KAI) — Wed, 08 Dec 2010 23:55:00 +0000

If you are not experienced in dealing with it, then leave this project alone.Although Mains equipment can itself consume a lot of current, the circuits we build to control it, usually only require a few milliamps. Yet the low voltage power supply is frequently the largest part of the construction and a sizeable portion of the cost.

This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn't generate very much heat.The circuit draws about 30ma AC. Always use a fuse and/or a fusible resistor to be on the safe side. The values given are only a guide. There should be more than enough power available for timers, light operated switches, temperature controllers etc, provided that you use an optical isolator as your circuit's output device. (E.g. MOC 3010/3020) If a relay is unavoidable, use one with a mains voltage coil and switch the coil using the optical isolator.C1 should be of the 'suppressor type'; made to be connected directly across the incoming Mains Supply. They are generally covered with the logos of several different Safety Standards Authorities. If you need more current, use a larger value capacitor; or put two in parallel; but be careful of what you are doing to the Watts. The low voltage 'AC' is supplied by ZD1 and ZD2.

The bridge rectifier can be any of the small 'Round', 'In-line', or 'DIL' types; or you could use four separate diodes. If you want to, you can replace R2 and ZD3 with a 78 Series regulator. The full sized ones will work; but if space is tight, there are some small 100ma versions available in TO 92 type cases. They look like a BC 547. It is also worth noting that many small circuits will work with an unregulated supply. You can, of course, alter any or all of the Zenner diodes in order to produce a different output voltage. As for the mains voltage, the suggestion regarding the 110v version is just that, a suggestion. I haven't built it, so be prepared to experiment a little.

I get a lot of emails asking if this power supply can be modified to provide currents of anything up to 50 amps. It cannot. The circuit was designed to provide a cheap compact power supply for Cmos logic circuits that require only a few milliamps. The logic circuits were then used to control mains equipment (fans, lights, heaters etc.) through an optically isolated triac. If more than 20mA is required it is possible to increase C1 to 0.68uF or 1uF and thus obtain a current of up to about 40mA. But 'suppressor type' capacitors are relatively big and more expensive than regular capacitors; and increasing the current means that higher wattage resistors and zener diodes are required. If you try to produce more than about 40mA the circuit will no longer be cheap and compact, and it simply makes more sense to use a transformer.

Dual Regulated Power Supply

noreply@blogger.com (KAI) — Wed, 08 Dec 2010 23:55:00 +0000

In this circuit, the 7815 regulatates the positive supply, and the 7915 regulates the negative supply. The transformer should have a primary rating of 240/220 volts for europe, or 120 volts for North America. The centre tapped secondary coil should be rated about 18 volts at 1 amp or higher,allowing for losses in the regulator. An application for this type of circuit would be for a small regulated bench power supply.