MOSFET full bridge driving small motor question

[Joel Kolstad]

For a MOSFET full bridge circuit driving a small AC motor (~25 watts at
~12V -- this is at a 50kHz switching frequency, BTW), is it OK to count on
the body diodes of the MOSFET to carry the circulating current during the
dead time that all the switches are off? Or should I really add discrete
diodes in parallel with all the switches?

Thanks,
---Joel Kolstad

 

[CBarn24050]

Hi, only if you insist on running at that frequency, 15KHz should be more than
fast enough.

 

[Jamie]

i am trying to picture a sync motor running at 50k hz ?
when you say dead time are you referring to regenerative
current from the motor? if this is your worry i its not
a problem how ever, many drives use Regen braking or some
times called dynamic braking. it first causes a shutting of
regen current to be drained to attempt in keeping the motor
from load swinging or over acceleration. in some cases if the
regen braking does not work in a defined time period a mechanical
brake is applied.
is it possible that your actually driving a stepping motor?