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push pull amplifier

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roronoa

New Member
Hi everyone,can someone please explain to me the purpose of placing the 2 1k resistor and 170 ohm resistor in the circuit ??

Are they use to to decrease the crossover distortion??how they function to decrease the distortion if im correct?

thanks for replying.
 

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Hero999

Banned
The 1k resistors are required to bias the transistors on.

The 170R resistor is there to minimise crossover distortion.

I wouldn't recommend using this circuit because it's very sensitive to supply voltage fluctuations.
 

RCinFLA

Well-Known Member
Yes, that is what the center resistor is for, to get some forward bias on the two transistors. It is not a very good design. The base-emitter junctions are temp dependent and as they get hotter the current will get higher. Thermal runaway is possible.

Usually two mirroring diodes are used in place of the center resistor, sometimes with a small resistor in series to adjust output device idle bias.
 
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Hero999

Banned
I would use diodes as suggested above and add a 1R emitter resistor to each transistor.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hopefully the OP is aware that the circuit he's posted isn't a practical design, just a theoretical model to show the principle - it's a long way short of a working design.

Mostly the 170 ohm resistor is replaced by a Vbe multiplier, which allows you to adjust the current - using diodes requires special diodes, and is fraught with more problems.
 
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