> In a product, we are controlling the speed of a PMDC motor (12V, 80W,
> 8.3A) by PWM (@ ~2 kHz).

> However, we would like to replace the MBR3045 with something like an
> MUR860 (ON Semi, Ultrafast, 8A average, 16A peak repetitive @ 20kHz)
> diode, since the MBR3045 seems to be an overkill.

> What are the parameters that decide the selection of a freewheeling
> diode? If the motor is rated 8.3A @ 12V, should the FW diode be rated
> more than this?

Apart from transients at switching time, the free wheeling diode will "pick 
up" the motor current at FET switch off. So a nminally 8A diode should be 
fine. As the diode is not carrying this current all the time an even lower 
spec one should suffice - but I'd not do that if possible. The diode should 
be cooled as requied by specifications to meet the thermal load. Peak 
Wattage is around 10 Watts so far less on average, hopefully.


    R
. 

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