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Subject: Amplifier design question

Date: 12/18/00 at 5:46 AM
Posted by: Tom
E-mail: Ethan04@aol.com
Message Posted:

I need some help with a school Lab/Homework assingment to design a 2-stage,voltage divider, CE amp with capacitive coupling and capacitors to ground between the two RE resistors.
The given design will have a input of 500mv peak and a final out put across the load resistor of 5v peak.
The given components are:
Vcc 15vdc, No beta is given but we are using a 2n3904

Stage 1 R1=?, R2=10k, RC=4k, RE=total of 1.8k (RE1 + RE2 with the cap between them)and VCE to = 8v
A=2

Stage 2 R1=?, R2=10k, RC=2k, RE=total of 1k (with the same cap as the first)
Load resistor off the collector=10k and IC=2ma.
A=5
The teacher gave us these parameters but when I told him I had trouble with the values working out and not clipping he said we could change what we needed to change.
I think I have the first stage correct it is the 2nd stage that gives me a problem.

On the first stage I have a R1 of 42k, a RE1of 1225ohms and a RE2 of 575ohms.
On paper and on Electronic Workbench this has the correct results. It has the
correct gain and voltages and the wave does not clip.

But on the second stage, I Put a R1=45k, RC=3.5k, RE1=420, and RE2=580.
On Electronics Workbench it works fine with the proper voltages and currents
and a Gain of 5 but when I do it on paper I get a gain of 6.
What could be wrong?

Any help of hints would be appreciated.
Thanks, Tom
Email: ethan04@aol.com

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