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Old Oct 20, 2003, 04:45 AM
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South Africa
Joined Aug 2003
587 Posts
Continuing on with Brushless designs, I am close to finalizing mine and have progressed to my second PCB version that now incorporates the sensor circuitry. I have managed to get a HD motor running without a problem, but when I attempted my Mega motor, I promptly burned out the high side FETs. There seems to be limited information relating to the method of drive and I do not have a commercial one at my disposal that would answer all my questions.

Now this may sound like a very stupid question to those that know, but what I need to know is … when starting the motor, a PWM signal is applied. But once up and running, then what? Is the PWM discarded and short pulses triggered at the start of each new phase? In other words, fire the “controlled” pulse, which accelerates the motor, and then wait for “crossing” feedback whilst motor decelerates. The controlled pulse width then determines the final speed. Is this the way it is done, or is the PWM signal being used all the time? I am finding that an extended duration PWM signal is the cause of my FETs going bang. They are being driven via a FET driver IC.

My controller at present is an overkill as far as the digital stuff goes. Wanted to play with a logic device, so added it in order to make controller more flexible and allow very high speeds. Will post pic as soon as I get a motor running.
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