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Brushless motor control

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matt1eg

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Hi

I have to design a controller for a brushless dc motor (Maxon EC 45 flat) with variable speed control. This motor has hall sensors to detect rotor position and I know that I can use this to create a look up table to get pattern for driving the motor.
I have done some electronics before but have never covered motor controls or related areas and have been reading alot about it all. I have used PICs before so understand how they work.

I am using the L6234 from ST as the driver(power stage) and plan to use a PIC to control everything. I have read the datasheet and application note for the L6234 and there is a schematic that offers closed loop speed and torque control(Fig 23 P12) but I am not sure as to how it works or if I can use that when I need variable speed control? There aren't many details on how it works and like I said a lot of this is new to me.

I am hoping somone can help shed some light on this circuit. Could I use a pot. to vary the reference voltage to change the speed? Or have I got it totally wrong?

Also the output from the loop seems to be a PWM signal. Can this be used to change the duty cycle of the PIC pwm output. I'm thinking that a capture module could possibly detect the frequency of the signal, but not sure exactly what that signal represents?

Sorry for the long post just trying to be thorough and show that I have had a think about it and not just looking for an easy way out.

Thanks for any help
 
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