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variable current source

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Thread Starter

nikomas

Joined Mar 31, 2010
11
BillB3857 said:
What part of the circuit do you not understand? Left op amp section or right op amp section? Is this homework?
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It is not homework. I just find that on internet. I don't understand circuit in global. I think that I understand how left section work (like current source). But how is that related with right part?
 
ErnieM

ErnieM

Joined Apr 24, 2011
8,377
Both amps are connected to run in a constant current mode.

Left amp will turn left fet on and keep the voltage across R1 = Vin. This makes the current thru the fet Vin/R1, which flows thru R2.

Right amp keeps the voltage across R3 same as the voltage across R2 with both referenced to Vcc.

The current thru R3 that develops will drive Io, thus this is a current SOURCE.

If you eliminate everything above & to the right of the VN2222 that point is a current SINK.
 
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