Author Topic: Feedback on transistors  (Read 1082 times)

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Offline chagliTopic starter

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Feedback on transistors
« on: November 23, 2019, 12:54:19 pm »
Hi,
I am building a low-power FM transmitter based on a pre-existing design.
The first stage is a simple discrete audio amplifier consisting of one NPN transistor (see attached picture).
I would like to understand and adapt it.
I think I have the minimum education concerning bipolar transistors (Ebers and Hybrid-Pi models).
But I am not very familiar with feedback on transistor level. I often see some qualitative statements concerning the effects but no rigorous development.
Could you recommend me a book which addresses feedback at transistor level ?
Thank you.
 

Offline ferdieCX

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Re: Feedback on transistors
« Reply #1 on: November 23, 2019, 01:35:05 pm »
This circuit has only DC feedback.
You will find the basic circuit discussed in chapter 10 of "Electronic Devices and Circuits" by Millman and Halkias

https://archive.org/details/ElectronicDevicesCircuits/page/n142

Feedback is discussed in chapter 17
 
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Offline chagliTopic starter

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Re: Feedback on transistors
« Reply #2 on: November 23, 2019, 01:45:42 pm »
Hi,
Thanks for your answer I will look at the reference.
I think the capacitor C2 is a way to apply pre-emphasis to the audio signal by lowering the feedback at higher frequencies (thus increasing the gain).
 

Offline ferdieCX

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Re: Feedback on transistors
« Reply #3 on: November 23, 2019, 02:24:42 pm »
You are probably right. The feedback is high at 20 Hz and very low at 15 KHz
 

Offline newbrain

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Re: Feedback on transistors
« Reply #4 on: November 23, 2019, 02:36:08 pm »
Note that the symbol for the transistor is wrong!

It should have the arrow pointing out (NPN) not in (PNP).

The 2N3565 is, in fact, an NPN transistor.
Nandemo wa shiranai wa yo, shitteru koto dake.
 

Offline chagliTopic starter

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Re: Feedback on transistors
« Reply #5 on: November 23, 2019, 03:51:40 pm »
That's right !
 

Offline chagliTopic starter

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Re: Feedback on transistors
« Reply #6 on: December 19, 2019, 07:33:26 pm »
I finally found a book which is quite exhaustive about feedback and has examples on transistor level :
'Feedback Circuits and Op. Amps' from D. H. Horrocks.
 


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