|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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