"gm/id" method for 2N3903 bjt

Thread Starter

yef smith

Joined Aug 2, 2020
235
Hello Bordodynov i got a plot of Ic/Ib as shown bellow.
I just want to know what biasing to do i order to a small signal analysis.



1611504891949.png
 

Audioguru again

Joined Oct 21, 2019
3,172
The datasheet for any transistor shows a wide range of base-emitter voltage an beta. Also, when the temperature changes then the base-emitter voltage changes that affects the transistor circuit.

To make a product work with all transistors having the same part number then you must add some AC and DC negative feedback.
For a 2N3904 its datasheet shows in a graph that is "typical" base-emitter voltage at a collector current of 0.5mA is 0.65V. It might vary 0.4V with different transistors even if they have the same part number. A graph shows how much temperature change affects the base-emitter voltage.

Usually a transistor has an emitter resistor so that base-emitter voltage differences are reduced. The emitter resistor reduces distortion and voltage gain.

Usually the base-emitter-resistor is biased from a two-resistors voltage divider. Here is a typical circuit:
 

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