Kyrre Aalerud wrote...

>Problem is:
>
>FET off = 16 Volts.
>FET on = 0-70 mV.
>
>I need to compare the voltage when FET is on to a set reference of 70 mV.
>If Voltage across FET is abowe 70mV I have a over-current condition and
>should turn FET off.

70 mV is pretty small for the PIC's comparator to deal with, and
16V is way too large for its inputs to tolerate.  The attached
circuit will fix both problems: diode D1 clamps the voltage from
the FET to protect the opamp while R1 limits the current drawn
from the FET to less than a milliamp, and the opamp amplifies the
FET's VDS(ON) by a factor of 48, giving you about 3.5 volts at
the PIC's input.

Dave D.

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