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Topic: fast direction changes instead of PWM (Read 750 times) previous topic - next topic


If you are driving a bridge that already generates dead-time (shoot-through prevention),
then you don't have to do anything special, just drive it in anti phase using inverter(s).

If not then you must switch off both high and low driver before switching to the other
set, leaving enough deadtime for the switches to switch (for MOSFETs this is usually a
few 100 ns.

Some bridges are wired diagonally so that you can only drive in antiphase, in other
words inverters are built in to the bridge.

For 3-phase motors you have 6 inputs to the bridge and inverters cannot be used, you
have to sequence those 6 signals correctly.  The antiphase scheme in superimposed on
the commutation pattern.  I know this because I've done it using a whacky scheme
where one timer is setup to produce PWM on an unconnected pin, and a pin-change
interrupt registered on that pin so an ISR does the actual bridge sequencing!  I should
document it sometime in a separate thread I think as its quite a handy way to get multiple
PWM pins from one timer.
[ I won't respond to messages, use the forum please ]

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