Created by
Created February 24, 2013
Last modified February 24, 2013
Tags constant-current-sink   current-sink   opamp-current-sink   precision-current-sink  


A precision current sink using an opamp.

Simulate > Time Domain > Run Time-Domain Simulation


A precision current sink.

I(D1) = V(ref)/Rscale1

If we assume base current of Q1 is negligible then we can say:

I(D1) = I(Rscale1)


I(Rscale1) = V(ref)/Rscale1

For higher precision, the error due to the base current in Q1 can be removed by replacing Q1 with an N-channel MOSFET.

By forcing the emitter current of Q1 to be independent of the collector load of Q1, OA1 and Q1 form a precision current source. Therefore, the collector of Q1 appears as a very high impedance.

F5 to simulate.


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