Michael wrote

> btw: some PowerFETs need gatevoltages near ot higher then a standard Opamp
> can have as an max. outputvoltage with a Vcc of 5V, so I would suggest a
> VCC for the Opamp higher then 5V, 8V should be ok, 12V are ok.
>
There are logic level power FETs that overcome the gate
voltage problem.

BTW
The FET could be driven efficiently with direct PWM and
the PIC monitors the current with a peak current detector
as the feed back to the PIC A/D, in turn altering the
PWM to maintain constant current.
I throw this side issue in as this is what I am building at
this very moment with a motor control scheme. The
advantage of the PIC in the loop is the ability of move
from constant current, to other control curves freely under
software control.
I am just using the peak detector from Microchip AN531

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Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

www.psych.auckland.ac.nz

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