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I have learnt loads about biasing a transistor, but I never managed to understand them. They talk about DC load line, Class A, B, C and various types of biasing. What are they all about and where can I get Information about them?

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closed as too broad by Olin Lathrop, Leon Heller, Matt Young, Nick Alexeev♦, placeholder Jul 28 '13 at 18:40

There are either too many possible answers, or good answers would be too long for this format. Please add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs. If this question can be reworded to fit the rules in the help center, please edit the question.
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You can't really expect us to write a whole book on transistor biasing here. This question is way too broad as it stands now. Try asking some specific questions about specific circuits where you don't understand biasing. –  Olin Lathrop Jul 28 '13 at 15:45
    
I don't expect people to write a book for me. They could rather post some links which contain information about my question. –  Dharmaputhiran Jul 28 '13 at 16:22
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The focus of this site is questions and answers, not questions and links to answers. Read the relevant pages before you pose a question, for instance electronics.stackexchange.com/about : Don't ask - "Questions with too many possible answers or that would require an extremely long answer" –  Wouter van Ooijen Jul 28 '13 at 16:44
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Not to be picky, but can you really say you learnt loads about biasing a transistor if you never managed to understand them ? You can think of biasing a transistor as 'setting up' the transistor. Different 'settings' do different things. –  efox29 Jul 28 '13 at 17:40

1 Answer 1

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A simple run through of bias A - D.

Class A bias means the device is conducting current throughout the whole output cycle. This means that with no signal it still has to dissipate half the output power. The collector voltage is set at about half the supply to give the maximum swing (down to zero, up to supply). This bias produces low distortion but dissipates large amounts of heat.

Class B bias means the device is conducting for only half of the output cycle. This means that for no signal input it dissipate no power. There are two transistors (a PNP and an NPN - complimentary pair) used in a 'push-pull' circuit. Each transistor conducts for half the cycle. This can produce a 'cross-over' distortion as each transistor needs 0.6V before they turn on. To prevent this both transistors receive a small turn on bias signal - this is Class AB.

Class C bias means the output device is turned on for LESS THAN half a cycle. This is power efficient and is used with inductive or tuned circuits that only require a pulse of current rather than the whole waveform.

Class D bias means the output is just being switched ON or OFF and is very efficient in the use of power. These output stages can be used with pulse width modulated signals.

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