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constant current source


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hello everyone...
i am new to this forum.. 8)
i have one query here...

anybody here has a circuit for constant current source using LM324..
i want to use it with the RTD PT100OPAMP... ;D

if anybody have this circuit please let me know...

thanks in advance... :)

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Here is a current source using an OPAMP.
It will work nicelly with LM324.
Alternative you can check at the datasheet (page 10) for another current source circuit.

LM324 Datasheet
http://www.national.com/ds/LM/LM124.pdf

Hope that gives you a start point.

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You know that when they post a circuit with a constant current source they don't mean the inclusion of an opamp. I tend to think that the opamp configuration for a constant current source is there as an example of how one could do it if the current you need is high enough. A circuit diagram with a constant current source is probably just a transistor with a constant base voltage set up to source.

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Kevin,
A transistor as a current source has a small variation in its base-emitter voltage with changing current through it. This causes its "constant" current to also vary, making its peformance lousy.
An opamp with its enormous gain cancels this variation.
The opamp circuit works well at high current (carried by the transistor, not the opamp) and at extremely low current.

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