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Will I be able to see the PWM waveforms on my BLDC driver output when no motor is connected

Question asked by Gareth Bale on Dec 17, 2018
Latest reply on Jan 9, 2019 by Gareth B

I have a FRDM-MC-LVBLDC driver and I'm using it with FRDM KV-11z. I wanted to observe my pwm waveforms on Phase A,B and C output ports before I provide it as the input to my motor. The reason behind it is because I tried measuring them with the motor being connected and my BLDC driver MOSFET was damaged due to some issue. I didn't wanted to take risk this time so I using an oscilloscope first to check what type of waveform I'm getting first.

 

When I observe the waveform on the oscilloscope, the PWM frequency is accurate but the duty cycle is showing as 95% ON time. I'm using the basic SDK example "mc_bldc" , which has a duty cycle of 50% and no matter now many changes I do by changing the value of "FTM0->CONTROLS[0].CnV"  , "FTM0->CONTROLS[1].CnV" and so on , it just doesn't change the duty cycle of the waveform.

 

So I wanted to know if it's possible to observe the waveforms or it's mandatory to connect it with a Motor to observe my waveforms.  Any kind of guidance will be helpful

 

Thank you

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