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Saturday, February 5, 2011
ic datasheet
Friday, January 21, 2011
Inductor (coil)
An inductor is a coil of wire which may have a core of air, iron or ferrite (a brittle material made
Inductor (miniature) 
Ferrite rod
Photographs © Rapid Electronics
circuit symbol
from iron). Its electrical property is called inductance and the unit for this is the henry, symbol H. 1H is very large so mH and ยตH are used, 1000ยตH = 1mH and 1000mH = 1H. Iron and ferrite cores increase the inductance. Inductors are mainly used in tuned circuits and to block high frequency AC signals (they are sometimes called chokes). They pass DC easily, but block AC signals, this is the opposite of capacitors.
Inductors are rarely found in simple projects, but one exception is the tuning coil of a radio receiver. This is an inductor which you may have to make yourself by neatly winding enamelled copper wire around a ferrite rod. Enamelled copper wire has very thin insulation, allowing the turns of the coil to be close together, but this makes it impossible to strip in the usual way - the best method is to gently pull the ends of the wire through folded emery paper.Photographs © Rapid Electronics
Warning: a ferrite rod is brittle so treat it like glass, not iron!
An inductor may be connected either way round and no special precautions are required when soldering.
Buzzer and Bleeper
These devices are output transducers converting electrical energy to sound. They contain an |  |
| Buzzer (about 400Hz) | Bleeper (about 3kHz) |
| circuit symbol |  |
Buzzers have a voltage rating but it is only approximate, for example 6V and 12V buzzers can be used with a 9V supply. Their typical current is about 25mA.
Bleepers have wide voltage ranges, such as 3-30V, and they pass a low current of about 10mA.
Buzzers and bleepers must be connected the right way round, their red lead is positive (+).
Loudspeaker
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| Photograph © Rapid Electronics |
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| capacitor in series to block DC |
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| circuit symbol |
and 64. If a project specifies a 64 speaker you must use this higher resistance to prevent damage to the driving circuit.Most circuits used to drive loudspeakers produce an audio (AC) signal which is combined with a constant DC signal. The DC will make a large current flow through the speaker due to its low resistance, possibly damaging both the speaker and the driving circuit. To prevent this happening a large value electrolytic capacitor is connected in series with the speaker, this blocks DC but passes audio (AC) signals. See capacitor coupling.
Loudspeakers may be connected either way round except in stereo circuits when the + and - markings on their terminals must be observed to ensure the two speakers are in phase.
Correct polarity must always be observed for large speakers in cabinets because the cabinet may contain a small circuit (a 'crossover network') which diverts the high frequency signals to a small speaker (a 'tweeter') because the large main speaker is poor at reproducing them.
Miniature loudspeakers can also be used as a microphone and they work surprisingly well, certainly good enough for speech in an intercom system for example.
Piezo transducer
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| circuit symbol |
Piezo transducers can also be used as input transducers for detecting sudden loud noises or impacts, effectively behaving as a crude microphone.
Transistors
This page covers practical matters such as precautions when soldering and identifying leads. The operation and use of transistors is covered by the Transistor Circuits page.
Types | Connecting | Soldering | Heat sinks | Testing | Codes | Choosing | Darlington pairAlso see: Heat sinks | Transistor Circuits
Function
Transistors amplify current, for example they can be used to amplify the small output current from a logic IC so that it can operate a lamp, relay or other high current device. In many circuits a resistor is used to convert the changing current to a changing voltage, so the transistor is being used to amplify voltage.A transistor may be used as a switch (either fully on with maximum current, or fully off with no current) and as an amplifier (always partly on).The amount of current amplification is called the current gain, symbol hFE.
For further information please see the Transistor Circuits page.
Types of transistor
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| Transistor circuit symbols | |
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.
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| Transistor leads for some common case styles. |
Connecting
Transistors have three leads which must be connected the correct way round. Please take care with this because a wrongly connected transistor may be damaged instantly when you switch on.If you are lucky the orientation of the transistor will be clear from the PCB or stripboard layout diagram, otherwise you will need to refer to a supplier's catalogue to identify the leads.The drawings on the right show the leads for some of the most common case styles.
Please note that transistor lead diagrams show the view from below with the leads towards you. This is the opposite of IC (chip) pin diagrams which show the view from above.
Please see below for a table showing the case styles of some common transistors.
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| Crocodile clip |
Soldering
Transistors can be damaged by heat when soldering so if you are not an expert it is wise to use a heat sink clipped to the lead between the joint and the transistor body. A standard crocodile clip can be used as a heat sink.Do not confuse this temporary heat sink with the permanent heat sink (described below) which may be required for a power transistor to prevent it overheating during operation. |
| Heat sink |
Heat sinks
Waste heat is produced in transistors due to the current flowing through them. Heat sinks are needed for power transistors because they pass large currents. If you find that a transistor is becoming too hot to touch it certainly needs a heat sink! The heat sink helps to dissipate (remove) the heat by transferring it to the surrounding air.For further information please see the Heat sinks page.Testing a transistor
Transistors can be damaged by heat when soldering or by misuse in a circuit. If you suspect that a transistor may be damaged there are two easy ways to test it: |
| Testing an NPN transistor |
1. Testing with a multimeter
Use a multimeter or a simple tester (battery, resistor and LED) to check each pair of leads for conduction. Set a digital multimeter to diode test and an analogue multimeter to a low resistance range.Test each pair of leads both ways (six tests in total):- The base-emitter (BE) junction should behave like a diode and conduct one way only.
- The base-collector (BC) junction should behave like a diode and conduct one way only.
- The collector-emitter (CE) should not conduct either way.
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| A simple switching circuit to test an NPN transistor |
2. Testing in a simple switching circuit
Connect the transistor into the circuit shown on the right which uses the transistor as a switch. The supply voltage is not critical, anything between 5 and 12V is suitable. This circuit can be quickly built on breadboard for example. Take care to include the 10k resistor in the base connection or you will destroy the transistor as you test it!If the transistor is OK the LED should light when the switch is pressed and not light when the switch is released.To test a PNP transistor use the same circuit but reverse the LED and the supply voltage.
Some multimeters have a 'transistor test' function which provides a known base current and measures the collector current so as to display the transistor's DC current gain hFE.
Transistor codes
There are three main series of transistor codes used in the UK:- Codes beginning with B (or A), for example BC108, BC478
The first letter B is for silicon, A is for germanium (rarely used now). The second letter indicates the type; for example C means low power audio frequency; D means high power audio frequency; F means low power high frequency. The rest of the code identifies the particular transistor. There is no obvious logic to the numbering system. Sometimes a letter is added to the end (eg BC108C) to identify a special version of the main type, for example a higher current gain or a different case style. If a project specifies a higher gain version (BC108C) it must be used, but if the general code is given (BC108) any transistor with that code is suitable. - Codes beginning with TIP, for example TIP31A
TIP refers to the manufacturer: Texas Instruments Power transistor. The letter at the end identifies versions with different voltage ratings. - Codes beginning with 2N, for example 2N3053
The initial '2N' identifies the part as a transistor and the rest of the code identifies the particular transistor. There is no obvious logic to the numbering system.
Choosing a transistor
Most projects will specify a particular transistor, but if necessary you can usually substitute an equivalent transistor from the wide range available. The most important properties to look for are the maximum collector current IC and the current gain hFE. To make selection easier most suppliers group their transistors in categories determined either by their typical use or maximum power rating.To make a final choice you will need to consult the tables of technical data which are normally provided in catalogues. They contain a great deal of useful information but they can be difficult to understand if you are not familiar with the abbreviations used. The table below shows the most important technical data for some popular transistors, tables in catalogues and reference books will usually show additional information but this is unlikely to be useful unless you are experienced. The quantities shown in the table are explained below.| NPN transistors | ||||||||
| Code | Structure | Case style | IC max. | VCE max. | hFE min. | Ptot max. | Category (typical use) | Possible substitutes |
| BC107 | NPN | TO18 | 100mA | 45V | 110 | 300mW | Audio, low power | BC182 BC547 |
| BC108 | NPN | TO18 | 100mA | 20V | 110 | 300mW | General purpose, low power | BC108C BC183 BC548 |
| BC108C | NPN | TO18 | 100mA | 20V | 420 | 600mW | General purpose, low power | |
| BC109 | NPN | TO18 | 200mA | 20V | 200 | 300mW | Audio (low noise), low power | BC184 BC549 |
| BC182 | NPN | TO92C | 100mA | 50V | 100 | 350mW | General purpose, low power | BC107 BC182L |
| BC182L | NPN | TO92A | 100mA | 50V | 100 | 350mW | General purpose, low power | BC107 BC182 |
| BC547B | NPN | TO92C | 100mA | 45V | 200 | 500mW | Audio, low power | BC107B |
| BC548B | NPN | TO92C | 100mA | 30V | 220 | 500mW | General purpose, low power | BC108B |
| BC549B | NPN | TO92C | 100mA | 30V | 240 | 625mW | Audio (low noise), low power | BC109 |
| 2N3053 | NPN | TO39 | 700mA | 40V | 50 | 500mW | General purpose, low power | BFY51 |
| BFY51 | NPN | TO39 | 1A | 30V | 40 | 800mW | General purpose, medium power | BC639 |
| BC639 | NPN | TO92A | 1A | 80V | 40 | 800mW | General purpose, medium power | BFY51 |
| TIP29A | NPN | TO220 | 1A | 60V | 40 | 30W | General purpose, high power | |
| TIP31A | NPN | TO220 | 3A | 60V | 10 | 40W | General purpose, high power | TIP31C TIP41A |
| TIP31C | NPN | TO220 | 3A | 100V | 10 | 40W | General purpose, high power | TIP31A TIP41A |
| TIP41A | NPN | TO220 | 6A | 60V | 15 | 65W | General purpose, high power | |
| 2N3055 | NPN | TO3 | 15A | 60V | 20 | 117W | General purpose, high power | |
| Please note: the data in this table was compiled from several sources which are not entirely consistent! Most of the discrepancies are minor, but please consult information from your supplier if you require precise data. | ||||||||
| PNP transistors | ||||||||
| Code | Structure | Case style | IC max. | VCE max. | hFE min. | Ptot max. | Category (typical use) | Possible substitutes |
| BC177 | PNP | TO18 | 100mA | 45V | 125 | 300mW | Audio, low power | BC477 |
| BC178 | PNP | TO18 | 200mA | 25V | 120 | 600mW | General purpose, low power | BC478 |
| BC179 | PNP | TO18 | 200mA | 20V | 180 | 600mW | Audio (low noise), low power | |
| BC477 | PNP | TO18 | 150mA | 80V | 125 | 360mW | Audio, low power | BC177 |
| BC478 | PNP | TO18 | 150mA | 40V | 125 | 360mW | General purpose, low power | BC178 |
| TIP32A | PNP | TO220 | 3A | 60V | 25 | 40W | General purpose, high power | TIP32C |
| TIP32C | PNP | TO220 | 3A | 100V | 10 | 40W | General purpose, high power | TIP32A |
| Please note: the data in this table was compiled from several sources which are not entirely consistent! Most of the discrepancies are minor, but please consult information from your supplier if you require precise data. | ||||||||
| Structure | This shows the type of transistor, NPN or PNP. The polarities of the two types are different, so if you are looking for a substitute it must be the same type. |
| Case style | There is a diagram showing the leads for some of the most common case styles in the Connecting section above. This information is also available in suppliers' catalogues. |
| IC max. | Maximum collector current. |
| VCE max. | Maximum voltage across the collector-emitter junction. You can ignore this rating in low voltage circuits. |
| hFE | This is the current gain (strictly the DC current gain). The guaranteed minimum value is given because the actual value varies from transistor to transistor - even for those of the same type! Note that current gain is just a number so it has no units. The gain is often quoted at a particular collector current IC which is usually in the middle of the transistor's range, for example '100@20mA' means the gain is at least 100 at 20mA. Sometimes minimum and maximum values are given. Since the gain is roughly constant for various currents but it varies from transistor to transistor this detail is only really of interest to experts. Why hFE? It is one of a whole series of parameters for transistors, each with their own symbol. There are too many to explain here. |
| Ptot max. | Maximum total power which can be developed in the transistor, note that a heat sink will be required to achieve the maximum rating. This rating is important for transistors operating as amplifiers, the power is roughly IC × VCE. For transistors operating as switches the maximum collector current (IC max.) is more important. |
| Category | This shows the typical use for the transistor, it is a good starting point when looking for a substitute. Catalogues may have separate tables for different categories. |
| Possible substitutes | These are transistors with similar electrical properties which will be suitable substitutes in most circuits. However, they may have a different case style so you will need to take care when placing them on the circuit board. |
Darlington pair
This is two transistors connected together so that the amplified current from the first is amplified further by the second transistor. This gives the Darlington pair a very high current gain such as 10000. Darlington pairs are sold as complete packages containing the two transistors. They have three leads (B, C and E) which are equivalent to the leads of a standard individual transistor.You can make up your own Darlington pair from two transistors.For example:
- For TR1 use BC548B with hFE1 = 220.
- For TR2 use BC639 with hFE2 = 40.
The pair's maximum collector current IC(max) is the same as TR2.
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