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Basic Electronics » CE EMITTER_BIAS CONFIGURATION

March 31, 2012
by dfitzgerald
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Hello,

Can anyone explain to me the equation for input impedance for an unbypassed common emitter transistor?

I understand Zb = Bre + (B + 1)Re.

I don't understand Zb = Bre + ((B+1)+ Rc/ro) / 1 + (Rc + Re)/ro) * Re

Thanks for you help!

Dan

April 01, 2012
by Akeshish
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Do you know how to do the AC modeling of a transistor (called the hybrid Pie model) ?

If yes, i can explain it one way?

If no, i have to explain it a whole different way?

April 01, 2012
by dfitzgerald
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Akeshish,

No, I don't know the hybrid Pie model. Right now I'm covering the re model but, further into the chapter they get into the hybrid pie and hybrid equivalent model. I'm just curious of how that equation was put together.

Thanks,

Dan

April 01, 2012
by Akeshish
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Can you send me your email, i did the derivation on paper and need to take a picture of it and send.

I didnt get quite the equations you have there but im sure i can just manipulate them to get the same equation.

BTW, im assuming your are building this on a bread board with resistors and capacitors. If you want to build them only with IC's let me know i have to change the equations. (capacitors to block the DC portion from the AC portion)

Im also assuming you have DC biased the transistors correctly and pick a Q point that lies in middle of your load line. (IC vs VCE)

April 02, 2012
by dfitzgerald
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dfitz90@hotmail.com

At the moment I'm just trying to get through a book I'm reading called "Electronic Devices And Circuit Theory" by Robert L. Boylestad, and this equation is in the book without an explanation of how it was derived at. It's stated in the book that the equations using ro in them are to be used only when r0 is less then 10 times some of the circuit parameters. If you could send me what you have written down that would be great.

April 02, 2012
by Akeshish
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Sent, check your email. Let me know if you have any questions.

I also included how to DC bias a transistor in order to place your Q point in the middle of your load line. This will insure maximum output swing.

I tried to make it as step by step as possible.

April 03, 2012
by dfitzgerald
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For some reason I did not receive your e-mail. Can you resend?

April 03, 2012
by Akeshish
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sent again.

April 06, 2012
by dfitzgerald
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For some reason your e-mail is not getting through. If you still have that write up you can try sending it to:

dfitzgerald@dornier.com

April 06, 2012
by Ralphxyz
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Actually, I'd like to see it posted or maybe a link, it is far over my head but I'd probable get a little more understanding.

Ralph

April 09, 2012
by Akeshish
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sent again, Ralph please send me your email

April 10, 2012
by Ralphxyz
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rhulslander gmail

I was actually hoping to see discussion because this is way over my head. I couldn't even come up with a question but I "think" I understand the principle dfitzgerald is looking at.

But thank you, I'd appreciate the email.

Ralph

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