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Using a comparator as an opamp in an error amplifier

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guhapriya.sivasubramaniam

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Hello.

My design has a few comparators and a few opamps on board. Due to reasons like reduction of cost and board space, I am trying to use a comparator as an opamp in the error amplifier circuit. I believe STMicroelectronics has some related option, but when I search in the i.net it is mostly about using an opamp as a comparator. Could any of you give me pointers on USING A COMPARATOR AS AN OPAMP(in an error amplifier circuit) ?

Thanks,
Guha
 

A comparator will not be stable in a closed loop as required by typical op amp error amplifier circuits and it's rather difficult to make them stable. That's why you can't find much info on doing that. It's just not very practical.

You can use an op amp as a comparator but they tend to have slow response due their internal compensation for stability that dedicated comparator circuits don't have. What is the response speed you require from your comparator circuits?
 

I've seen the LM339 used as an OPAMP for slowly varying signals, compensated with a feedback capacitor as usual.
You should be careful about selecting an output pull-up resistor low enough, with respect to the load AND the feedback network.
 

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