In the voltage-current negative feedback,what is the value of the negative feedback voltage of the output voltage? It says that "Vref=3DVo*Re1/(Re1+Rf)" in the text book,why is that? Should I consider the output resistance of the emission pole of the first transistor?I think the Re1 should be taken place by Re1//(rbe/(=DF+1)),and there also should be an equivalent negative voltage that equals to be vi*rbe/(Re1*(=DF+1)). I think there may be something wrong with my consideration, who can help me? Is there any way to upload the schematic?=20 Thanks in advance!
Who can help me think about the negative feedback in analog circuit?
Mar 31, 2006
1 Replies
In a bipolar transistor, using an emitter resistor acts as a form of negative feedback.
The input to the transistor can be thought of as the Vbe minus a portion of the Ie*Re product. Hence the emitter resistance provides negative feedback. In order to understand this, you need to thoroughly undertand the transistor models. It has been a long time since I have studies this, but some searches into the "Ebers-Moll" model and the "Early Effect" may help shed some light on this subject.
It is my opinion that most text books do a poor job of teaching transistors with respect to real world applications because they concentrate too heavilly on properties such as Beta and other process dependant features. I would sugges the book, The Art of Electronics for a more realistic discussion of transistor circuits.
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