2 transistor constant current sink 01

Created by	signality
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.

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The collector current of Q2 is approximately given by:

Ic_Q2 = Vbe_Q1/R1

where:

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

and,

R1 is the value of R1

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

For background, see Fig 2.25 of:

2 transistor constant current sink 01 PUBLIC