# colector voltage in Dc analisis

Discussion in 'Homework Help' started by mosfat, Dec 8, 2013.

1. ### mosfat Thread Starter New Member

Dec 8, 2013
4
0
i need to find the Vout voltage.
i know drain current of M1 is 5mA

i need to find the collector voltage in Q1
how to do that?

thanks

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2. ### WBahn Moderator

Mar 31, 2012
20,237
5,758
You need to show YOUR best effort to work YOUR homework problem. That gives us a starting point for discussion as it allows us to see what you are grasping and what you are overlooking.

3. ### mosfat Thread Starter New Member

Dec 8, 2013
4
0
its like a chane
my goal is to find Vout

my work:
it comes dows to finding the voltage on the collector of Q1
the voltage on the base of Q1 is 4
the voltage on the emiter is zero because its DC analises and the small signal is zero.
the problem is ,if emitter voltage and its in the active state
VB-VE=0.7
VE=4 (the voltage sorse bellow)
so VE cant be zero althogh its active state

4. ### WBahn Moderator

Mar 31, 2012
20,237
5,758
Well, you seem to be struggling with the right things -- or at least realizing that you are struggling with the things where you are not going about it right.

Yes, the base of Q1 is Vb=4V.

But if the emitter is 0V, then you have a transistor with a 4V base-emitter voltage. At the very least this would have to be in hard saturation, if not well into the smoke-emitting region of operation.

Yes, if Q1 is in the active state, the Vb-Ve=0.7V (or close enough for our needs), but then on what basis do you say that Ve=4V. Think about this.

If Vb=4V and Ve=4V, then wouldn't Vb-Ve be 0V?

So try again. You are on the right track. One you have the correct Ve, then it should be a simple matter to find Ie for Q1. With Ie, you should be able to find Ic and, from there, Vc very quickly.