Constant current output

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vijayaummadi

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Hi,

I need to design a circuit which provides constant current output of 2mA for the Variable resistance load(which varies from 350Ω to 45KΩ) in my Project. When the load varies, the output current should be constant and Voltage can be varied in order to maintain current as constant. Please let me know your suggestions how to proceed.

Thanks in Advance!!
 

You did not say if the circuit must source 2mA or sink 2mA.
You also did not say how accurate the circuit must be.

In Google Images there are hundreds of constant current circuits. Simple ones are simply one transistor, a zener diode and two resistors.
 

You'll need 90 V to push 2mA through 45k ohm.

Assuming you have that high a supply V, there is also the classic 2-transistor current source. It uses an NPN and a PNP.
 


The circuit must source 2mA and the design has to be accurate so that the output source current has to be with in 5% tolerance i.e 1.9mA to 2.1mA
 

A very simple circuit can easily produce a constant current with only 5% accuracy. I found these constant current sink circuits in Google but PNP transistors can produce a constant current source circuit:
 

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According to the schematic below, you will get constant 2mA output current at 350-45k ohm load. At the beginning, connect an ammeter at load end and adjust the pot P1 for 2mA output current.
 

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