Opamps and comparators, input max voltage?

Check the common mode range of the input.

That depends on the specific op-amp design.

You would want an op amp or comparator which supports "rail to rail" inputs... or, at least, inputs which come up to the positive rail.

Quite a few op amps (and comparators I suspect) won't work properly for inputs this close to the rail... many need at least one diode-drop of headroom, and some require more.

Who the hell could possibly know wtf you're talking about? Dunno the problem but the thinking is so impaired am not surprised to hear you have one.

FET amps commonly include the positive rail. LM358, LM393, LM2903, etc. include negative rail. 741, LM833, etc. include neither. TLV2372 includes both (and also has a rail-to-rail output).

The spec you're looking for is common mode input range.

Tim

-- Seven Transistor Labs Electrical Engineering Consultation Website:

Hi all

I found, that using an ordinary opamp, and a PNP darlington makes more sense, so I can keep the measuring and reference at app 1V. A P-channel mosfet is actually more expensive than a PNP Darlington. So basically I am back to what the K8071 is :)

I also found chips like NCP3065 which implements all I need which makes my idea kind of obsolote.

Also MAX16832, HV9910 and HV9925 will do very well.