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LucasHall
Level 2
Level 2
10 replies posted 5 questions asked 10 sign-ins

I am using the EVAL-M1-IM828-A and EVAL-M1-101T to prototype a single shunt brushless DC motor controller. This DC link voltage is 720VDC.

Referring to application note AN2020-14 "Bootstrap circuit design for the CIPOS IPM series", V_BS is recommended to be between 12.5V and 18.5V, and the ripple on V_BS is recommended to be not more than 1.0V peak to peak. Also, the waveform is shown as a characteristic capacitive charging and discharging with a period equal to the motor phase current.

In the attached Image1.png, I used an oscilloscope to monitor the voltage across the bootstrap capacitor (channel 3, blue) and the motor phase current on the same phase (channel 4, red). The bootstrap capacitor voltage ranges from 8V to 19V, and has a 12V peak to peak ripple. Furthermore, the shape of the bootstrap voltage waveform does not match the shape described in the application note. Please advise if these waveforms are expected / acceptable, and how I might modify the bootstrap circuit to achieve a waveform as described in the application note.

For reference, the attached image2.png shows the three bootstrap voltages together with one phase current.

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Vicky_S
Moderator
Moderator
Moderator
50 solutions authored 10 likes received 5 likes given

Hello @LucasHall ,
It looks like bootstrap capacitor value is not enough. 
What is the value of bootstrap capacitor?

Best regards,
Vicky S

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Vicky_S
Moderator
Moderator
Moderator
50 solutions authored 10 likes received 5 likes given

Hello @LucasHall ,
It looks like bootstrap capacitor value is not enough. 
What is the value of bootstrap capacitor?

Best regards,
Vicky S

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