Jinx wrote:
>
> This is for motor driving - PWM and reversibility, and protection
> against spikes and stalling is critical. A few $$ extra at assembly
> time is no big deal if it means no time on the service bench

> The lowest Schottky in my list is the IR 42CTQ030, 30V 40A 0.38V
> which I think should complement the IRL3402. The bridge will run at
> either 12V or 18V (the IRL3402 is a 20V 85A 180W 10mohm device)

Hi Jinx, so you're building a 40 amp PWM'ed
h-bridge for the first time? I hope you are going
to do testing on resistive load at reduced current
to start with, then add your inductive load in
series with your resistive load for further testing
and I suggest a real heavy duty load snubber to start
with, gradually reducing the snubber size as you
are confident that you are handling all recirculating
current paths etc and allowing for load accel and decel.
:o)

Re the schottky's, WES in Aust have;
S16C60A, TO220, $1.95 AUD, dual diode 2x 16A, 60v
S30D60C, TOP3, $2.55 AUD, dual diode 2x 30A, 60v

I have used these for some time, they are cheap and
quite rugged, Vf is good depending on what currents
you have. The dual diodes are available in both configs
which may help reduce package count.


> As for stalling protection / detection. I know some people measure
> voltage drop across a resistor in the supply line, but wonder if a
> current sensor, eg Hall Effect, is a viable alternative. Not knowing
> the absolute current through the motor isn't as important as knowing
> when it's passed a safe limit so the drive can be shut down

Since you don't need instant (ie PWM) current
sensing you can use a coil of heavy wire wrapped
around a reed switch. :o)
-Roman

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