Electronic – use an op-amp in voltage follower configuration as variable voltage power supply

operational-amplifierpotentiometervoltage dividervoltage-regulator

I see that this works in theory, but I my gut feeling says there is a drawback or caveat of which I'm not aware. Basically what I want to achieve is described best by the circuit diagram below.

schematic

simulate this circuit – Schematic created using CircuitLab

I have a power supply (2A @ 12VDC) that I want to use to make a variable voltage power supply. In the voltage follower configuration, whatever is on the non-inverting terminal on the op-amp is present on the output terminal. The extra current at the output terminal needed to keep the voltage up is provided by the op-amp's supply. Since I'm using a linear pot as a voltage divider to set the input voltage to the op-amp, will this work as an effective variable power supply from 0V to almost 12V? If not, why can this configuration not be used this way?

Best Answer

It can be used but for most op-amps the maximum current you would be able to drive from the output will be limited to less than 50mA. Op-amps are not miracle workers! On the other hand you can attach an NPN and PNP transistor in a push-pull configuration and get more current: -

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(source: northwestern.edu)

Or, you could use an OPA541 - it is an op-amp and can supply up to 10 amps: -

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I guess this one is a bit of a miracle worker!

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