# (PNP) Collector Feedback Bias Amplifier Circuit

Discussion in 'Homework Help' started by huntlk, Feb 22, 2010.

1. ### huntlk Thread Starter New Member

Feb 19, 2010
12
0
To bias a (pnp) collector feedback amplifier circuit with a Q point set to approximately 5mA of collector current. Choose a base resistor that will provide a reasonably stiff bias.

VEE = +18V
RC = 1.2k
βDC = 200

All of the circuits that I have dealt with have used VCC. I am not sure how to calculate the RB value. Please help!

Last edited: Feb 22, 2010
2. ### hobbyist Distinguished Member

Aug 10, 2008
789
73
This is just a quick guess at your question.

Wait for a while until the real good posts come in, then you can evaluate the correct answer.

I'm only a hobbiest, so take this for what it is...

VCC is noted as collector supply voltage, where negative term. is grounded.

VEE is emitter supply voltagte where neg. term is grounded.

Collector feedback consists of a resistor between collector terminal and base.

Start with quiescent voltage at the collector. for a properly biased amp.

Vcq=?

then with no emitter resistor, solve for base voltage.

Vb= (Vee - Vbe) Vbe is voltage drop between base and emitter.

Vb=?

The base resistor for collector feedback, conects directly between base and collector terminals.

So voltage across base resistor = VRb

VRb = (Vb - Vcq)=?

Now determine amount of base current using Beta and collector current. = Ibq.

First collector current Icq.

Icq= (Vcq / RC)

Ibq= (Icq / Beta)

Ibq=?

Base rersistor= Rb.

Rb= (VRB / Ibq)

Rb=?