I really can't find a solution for this

Okay so I have a project due tomorrow and I can't get it right, I need to find how many Ohms can the resistor Rb be, so the transistor can be in a state of saturation, the link is a screenshot to the task, I'll try to build a circuit on the platform as well. UBX is Uin.


I can't quite get it, since nobody explained anything, during the COVID situation, so we're all left with a bunch of PDF files, having to teach ourselves.

by adtrajkov
June 30, 2020
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1 Answer

Answer by Foxx

If you look at the data sheet for this transistor the collector to emitter saturation voltage is 0.2v and the base to emitter voltage is about 0.9v. So the drop across R2 must be 14-.2=13.8v and this requires a collector current of 13.8/1000=.0138 amp or 13.8ma.. You've given a beta of 55 so base current should be .0138/55=251 microamp. Assuming the base to emitter voltage is 0.9v there is 8-.9=7.1 volt left to push 251 microamp through to R1 so R1 must be 7.1/(251e-6) or 28.29 k. It's been 60 years since I worked on this so I hope it's right.

+1 vote
by Foxx
July 02, 2020
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