In message , Craig Carmichael
craig@saers.com> writes
>Max-min current control sounds good. But would require a second
>voltage comparator that can handle the spikes and noise. I just
>copied the 'fixed off period' mode from another chip. (Allegro
>A3938/A3932 IIRC. But that was intended for <1HP and couldn't take
>the power/switching spikes from a larger motor.)
>
>As it is, I managed to make the IR2133 into a single chip BLDC motor
>controller except for the quad XOR gate to reverse direction.
>
>I believe you but I'm not sure why external diodes would be better...
>to share the heat loading?
>
INSERT.
Actually now I think of it...
You shouldn't need to worry about the current flow transition from the
channel to the diode in the MOSFETs in a BLDC motor controller 'cause
there is always a high-impedance intermediate state when both the upper
and lower MOSFETs are turned off, between the high and low driving
states.
It's different in a class-D amp, because the totem-pole output
(half-bridge) goes straight from being pulled high to low and back again
at around 300kHz. There is usually about a 50 nanosecond deadtime to
stop shoot through of course. During this deadtime, the diodes can be
forced into conduction as there is still current flowing in the L of the
output filter.
/INSERT
>...or if they were Schottky diodes with a lower forward voltage drop.
>Say, I rather like that idea. It might improve regenerative braking a
>little?
>
>(I'd more expect this sort of subject would have come up on a motor
>controller list like osmc@yahoogroups.com or ?? You just never know
>where a conversation will lead!)
>
>Craig
>
As I said in a reply elsewhere: I'l have a look at that motor controller
list to avoid overloading this one with highly technical matters of
little concern to people who simply want to get in their boat, switch on
the motor, and set off somewhere!
Regards,
Chris.
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