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2 transistor circuit input output question.

dorke

Jun 20, 2015
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Thanks for the link.
Much more so for the site...A window to history;)
 

Herschel Peeler

Feb 21, 2016
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Feb 21, 2016
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If you do a Tevenin equivalent of the 5k and 20K bias resistors, you will get a voltage Vbb =8V and a series resistor of 4k.



i10K=VE/10k=(VB-0.7)/10K
ib=(8-VB)/4k
i10k=2*iE=2*(beta+1)*ib=2*(beta+1)*(8-VB)/4k

thus
2*(beta+1)*(8-VB)/4k=(VB-0.7)/10K
solve for VB and make an assumption on beta(if not given)

for beta=30 we get VB=7.95v
for beta=100 we get VB=7.98v

Unnecessarily complicated.
The 5K and 20K make a voltage divider that puts the base at9mV. For outputs A and B to be the same the other base must also be at 8 V. If the bases are at 8 V the emitter must be 0.7 V below that.
 
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