Sean Breheny wrote:
>=20
> If the motor inductance is high enough and the PWM frequency high
> enough, this actually works fine - I have used this many times before.
> You end up with a zero average current (at 50% duty) but a small ripple
> current. One advantage of this ON forward-ON reverse mode over the more
> "traditional" ON forward-OFF mode is that there is no significant
> portion of the PWM cycle where the FET body diodes (or inductive clamp
> diodes if using BJTs) conduct, so the losses can be lower in the
> switching devices. Since the ripple current causes some additional
> losses in the motor, this isn't usually an overall efficiency benefit
> but it can reduce the heatsinking requirements of the switches.
>=20
> In the above analysis, I am assuming that the PWM frequency, in any PWM
> mode, is high enough that the current does not decay to zero during any
> part of each PWM cycle if the average current is high. This is much
> more efficient than using a very low PWM frequency and relying on
> mechanical "averaging" of the motor torque.
>=20
Thanks Sean, that's really good to know.


Cheers,
David



--=20
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