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Created November 11, 2012
Last modified April 15, 2013
Tags constant-current-sink   constant-current-source  


Q2 collector current is held roughly constant over a wide range of V1.

Use PNPs for a current source.

F5 to simulate.


The collector current of Q2 is approximately given by:

Ic_Q2 = Vbe_Q1/R1


Vbe_Q1 is between 0.55V and 0.7V, nominally 0.6V


R1 is the value of R1

So for R1 = 100R, Ic_Q2 ~ 6mA.

For background, see Fig 2.25 of:


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