BJT Amplifier

252

07:34:12

This circuit is mentioned in “Op Amps For Everyone” pp. 2-10

Specs are AC voltage gain of 4, and p-p signal swing of 4V.
The source signal voltage/frequency are not mentioned.

The circuit isn’t really doing what it’s supposed to atm, and I’m not sure why because I’m still wrapping my head around what it actually does (I get the voltage divider and decoupling cap, but why the 1000uF capacitor?)

published 7 years ago

PrathikP

7 years ago

I think the 1000uf cap is there to prevent unwanted oscillations. Im not too sure about that.

PrathikP

7 years ago

http://everycircuit.com/circuit/5309248476282880

PrathikP

7 years ago

Try this, but it's not really good.

hurz

7 years ago

1000uF is to big. Its not against unwanted oscillation. Its there to short the 300 Ohm for AC. Suppose this is an Audioamp the lowest frequency is around 20Hz. 1/((300¦¦500) Ohm × 2pi × 20Hz)= 42uF. So to be on the safe side 100uF is ok. But 1000uF is tooo much

hurz

7 years ago

And gain 4 is only if the 300 Ohm is short circuit for AC, while gain = Rc/Re = 400 Ohm / 100 Ohm = 4 !

hurz

7 years ago

Check this with and without the emitter capacitor http://everycircuit.com/circuit/5935368271822848

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