modified 8 years ago

Compensating the Vbe drop in a current source

01:25:39

Art of Electronics 3rd ed. Figure 2.33

A PNP transistor is used to cancel the 0.6V Vbe offset of the NPN transistor which is used as a current sink.

The signal generator gives Vgen=0-10V input for the base of the PNP which gives +0.6V higher to the base of the NPN, which then creates the same Ve voltage on the NPN current sink. The current it sinks is Ic≈Vgen/Re. Re is 1K, so for every volt input, the NPN  sinks 1mA of current (programmable current sink).

published 8 years ago

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