Class B amplifier

[shoba]

Hi guys,
do you know any good reference website or materials to class B amplifier?

 

[samcheetah]

usually websites dont explain these things as books do. so you should consult some book about amplifiers. like the book by Douglas Self.

what do u want to know about class B amplifier. are u building an amplifier. or do u want to write a paper about it?

 

[shoba]

I just want to know the basic operation of it

 

[samcheetah]

well as i said that u should consult a book like "Audio Power Amplifier Handbook" by Douglas Self for all the classes of amplifiers.

well in class b the output current flows for half of the cycle of the input voltage. that is, class B produces an output current for half the time class A does. this is done by biasing the transistor at cutoff. only a positive cycle of the ac input voltage will drive an NPN transistor into conduction. for a PNP transistor a negative cycle will drive the transistor into conduction. in class A the trasistor remains in conduction for the full cycle. thats why alot of energy is lost as heat. and hence class A has the least efficiency of all the classes. but in class B the transistor remains in conduction for half the time. so less energy is dissipated as heat. therefore it has a greater efficiency. and as u progress along the alphabets the time for which the transistor remains in conduction decreases and the efficiency increases.

on the other hand there is a trade off to this increase in efficiency. the output waveform is a highly distorted version of the input waveform. but there is a way out of this. class B amplifiers are usually connected in a push pull arrangement. one transistor connected as class B conducts for half of the cycle and the other for the second half. this way the job is distributed among two transistors. and the efficiency increases.

class B amplifiers connected in a push pull arrangement are usually found at the last stage of the amplifier system. they have the capability to drive heavy loads like speakers.

i hope that helped.

 

[VISHOK]

class b amp

i dont know whether it helped "shoba" but that was a good explaination of class B amp. and a freshup for me.

 

[lavenatti]

Yes, excellent explanation.

 

[shoba]

yes that helped a lot,
thx..