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Old Jan 29, 2004, 02:58 AM
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South Africa
Joined Aug 2003
587 Posts
I see some talk still going on about the feedback sensing. Whats wrong with Takao Shimizu scheme?

The addition of caps filter out all the noise.

My sensing circuitry used – bummer cant add images like we used too. Too bad.

I have used it and it works really well. Once a phase is driven and the corresponding feedback signal THEN monitored, I find no jitter or PWM interference coming through at all. The other feedback lines can generate false information during this time with pleasure, as I am not interested in them. I suspect that other people like to monitor all three feeback signals together and drive the output phases according to the all 3 feedback signals. Hence, bad feedback information at any time will probably cause problems. From what I can understand, this is why there is so called ‘off times’ to measure/sense. Please correct me if I am wrong here.

In my case, the three op-amp outputs are digitally combined to provide a serial stream that is synchronized with the driven phases. Easy as pie. That way, all jitter, false triggers, ect are eliminated. The micro code becomes a lot simpler as it only has to look at one input pin as well. Under start conditions, the steam coming back will look like a mess until such time the load starts to turn properly. You then get short duration pulses that correspond to how much you are overdriving the motor. At that stage, you switch from ‘manual’ commutation to automatic so to speak.

Stumax ...Mr DIY (BTW, what's your name? ), it's Brian.
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