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Originally Posted by Kevin Sevcik
Actually, you're both wrong. Sort of. The control scheme for the motor only pulses the high side FET for a direction, and leaves the low side FET on.
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Just to be clear: I didn't say that the Jag turns the low side FET off for pulsing. I just showed what the current path would look like
if it were switching the low side... and I asked if anyone knew, definitively, what the switching method is:
See attached images. For simplicity, I showed path through only one FET of each pair, and only for + currents. Green path is during ON portion. Blue path is during OFF portion (for high-side switching). Red path is during OFF portion (for low-side switching).
I don't know if the Jags use high-side, or low-side, or some other switching method. Does anyone know, definitively, what switching method the Jags use? I've heard many different claims.
How do you know that the Jag switches only the high side? Did you discover this during your analysis of the firmware, that you posted earlier? Or did you find it in some document somewhere?
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So one low side FET pair remains conducting during the entire PWM cycle, and you only have the forward drop from the opposing low side FET pair's zener diodes when the current cycles back through in that direction.
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I added the bold stuff for clarity. You also have the opposing back emf if the motor is spinning. See attached PDF.
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And since we're talking about the motor inductance driving the current in the off phase, the voltage is going to increase to compensate for that 1V drop anyways.
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Exactly. See attached PDF.