> I added in inline 0.1-ohm resistor right at this solenoid to be able to s=
ee the
> ripple during the hold phase, but the drive circuit does not use this for
> feedback this time.  I am considering adding a current-sense amp at that
> same point, and using that for feedback, so I can dynamically control the
> current.  All because I expect that in a practical circuit, variations in=
 the +12V
> supply will vary the peak and hold currents.

Why do you need to measure the current while the FET is off?=20

Surely you only need to measure it (using a low value source R) when it tur=
ns on, because the conservation of energy says the solenoid will maintain t=
he same current through the clamp diode while the FET is off, for the LR ti=
me constant of the injector, so you only need to know how long to wait to t=
urn the FET on again.



--=20
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