Class AB Amplifier

299

05:43:33

run in ac analysis to get the frequency response

replace led with 2 diode to compensate darlington pair drop

published 5 years ago

hurz

5 years ago

I think you will have a lot of trouble to bring this common emitter design to work in real life. DC gain of BJTs depends on temperatur, this thing will be very very unstable.

prinzrainer

5 years ago

load now on emitter side, and preamp added some emitter resistance

hurz

5 years ago

Yeah, thats a different design. Resistors against termal runaway are missing but for spave reason some people left them out. Without overall feedback, one can see how distorted the sine wave is. Still a lot todo for a good amplifier.

prinzrainer

5 years ago

I'd like to know more on those feedback techniques they use.

hurz

5 years ago

Yes, feedback is essentiell for a good amplifier design.

prinzrainer

5 years ago

can you give me example of that feedback design

hurz

5 years ago

Yes sure, based on your darlington design i have modified a simple example. Play with the input resistor and feedback poti. Quiescent current i have set to about 75mA to make it more a pure class B amplifier. The class A componente is quite low. Have fun http://everycircuit.com/circuit/5547503051866112

hurz

5 years ago

what you can also do is to put your amplifier almost unchanged into the loop. Check this http://everycircuit.com/circuit/6077163183538176

prinzrainer

5 years ago

the output driver seems to be already correct I've tried directly driving it with coupled voltage source but the first stage needs to be feedback, it's like instead of using rail voltage for the biasing on the first stage we use the output voltage?

hurz

5 years ago

yes, we compare whats going out with what comes in and reduce with subtraction (negative feedback) the error we make with all nonlinearity our ampilfier puts to the signal. This lowers the distortion significat if you use as first stage an OpAmp and not just a simple one transistor amplifier. An OpAmp get see any little difference we make to the output and tune the output perfect to almost zero error to the wanted input signal form. OpAmps have a high openloop gain of more the 100000 or even 1Mio. Hope this helps

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.