Question

a) For the following circuit (See attachment) determine VE,VC and IC when Vin=0
b) Determine VE,VC and IC when Vin=2V

I'm not sure how to calculate this, mostly because I don't know how I can find a voltage in just a certain point in the circuit.
Would it be the same as calculating VBE and VCE?
Should I use Kirchoff's rule?

All help well appreciated!

Answer 1

Assume VBE .7 V and IE = IC
IC R1 + Vee = VE, Vcc - IC R2 = VC
VCE = Vcc - IC R2 - IC R1 - Vee
VCE = Vcc - Vee - IC (R1 + R2)
IC = (VBE - Vee)/R1
solve
For Vin = 2
IC = (Vin + VBE - Vee)/R1
solve

Answer 2

@KenLJW thank you for the quick response! but hmm why do you define IC = (VBE-Vee)/R1 rather than IC = (Vee-VBE)/R1? and why is it positive in the equation for VE and negative in the equation for VC?

Answer 3

I use IC as positive going into the collector. so I go from + to - for positive value.

Answer 4

@KenLJW I see, but if I was to find the voltage amplification Ac and Ae? how would I go about doing that?

Answer 5

Will in the case where Vin is sinusoidal you would need the signal model for the BJT, a approximation would be Ae =1 and Ac = R2/R1

Answer 6

@KenLJW hmm I got Ae=1 but my Ac is negative (I got less potential voltage in b) than in a))

Answer 7

Yes it is negative, I was giving absolute value.
Yes with b) you'll have less VCE than with a) therefore limiting Vin sinusoidal for linear range.

Answer 8

@KenLJW okay thank you so much for your help!