> Usually you don't need vast average gate drive mA - you need
> around an amp while the FET is switching but most of the time
> the gate does not require current to hold it on or off

AIUI the current is needed mostly to charge the gate cap quickly to
keep the switching time low (ie keep out of the linear region as much
as possible). And once turned on, the FET is voltage, rather than
current, driven

I PWM a 1/2HP 12V motor with 3 paralleled FETs using a BC337/
BC327 push-pull pair and that works fine, even though the BCs are
rated at only 500-800mA. Stall / start current is many times the run
current so I do tend to try and remember to soft start

Neil, useable speed / torque might not kick in until the PWM is quite
high. I think mine is around 30%. Below that the energy simply heats
the windings without the motor turning usefully. This may or may not
be a problem. For example if there's fan cooling on the shaft

My scrollsaw has a *proper* variable-frequency speed control
for the induction motor and can be run slowly enough (with good
torque, so it's tempting to use it too long) to cause damage if forced
cooling isn't used to assist the internal fan

Joe


-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2015.0.5577 / Virus Database: 4253/8751 - Release Date: 12/17/14

--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.