I'm hoping someone can help me understand why the o-scope trace looks the way it does from my speed controller. This is for a 3-phase BLDC motor. See the attached images of the voltage trace of one of the phases and my circuit.
The middle part of the trace is where the PWM power is on for that phase. Each PWM duty cycle peaks at 12V (the supply voltage), but then immediately begins to slope down. The next duty cycle peaks at 12 again and then slopes down again. It's like resistance is being added to the line. I don't see why the voltage doesn't hold steady at 12V for the entire duty cycle.
I'm using complimentary PWM, so I don't think it's the booster cap running out of juice. The FETs are BUK7535-55A with IR2011 drivers. The PWM is at 7.8kHz.
Any thoughts or ideas?
Thanks!
The middle part of the trace is where the PWM power is on for that phase. Each PWM duty cycle peaks at 12V (the supply voltage), but then immediately begins to slope down. The next duty cycle peaks at 12 again and then slopes down again. It's like resistance is being added to the line. I don't see why the voltage doesn't hold steady at 12V for the entire duty cycle.
I'm using complimentary PWM, so I don't think it's the booster cap running out of juice. The FETs are BUK7535-55A with IR2011 drivers. The PWM is at 7.8kHz.
Any thoughts or ideas?
Thanks!
Attachments
Last edited: