In desktop computers, it's common to have headers that control fans with a 0-12V analog output, capable of up to 1A. This works fine for one or two fans, but with more than three fans, you can exceed the 1A rated current.
The obvious solution to me is to make a voltage buffer with power fed from the power supply's 12V rail, and I'm amazed this isn't available already. I know how to do this with an op-amp, but that would not supply enough power and it seems that a buck regulator would be better suited to this, but I can't figure out how to do it. Are there any buck regulator ICs that would be able to implement a 0-12V 5A voltage buffer, fed by a 12V input? Is there a better way to do this? I don't care about high frequency response, and a ~10Hz lowpass filter would be ideal.