Timeline for H-Bridge Problem: Vgs dropping with increased motor speed
Current License: CC BY-SA 4.0
9 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jan 12, 2022 at 22:40 | vote | accept | Chris | ||
| Nov 1, 2021 at 19:01 | comment | added | Bruce Abbott | 5.5V was just a guess based on 50% PWM and motor running at ~90% of Kv x rpm (would be 6V if there was no voltage drop in windings). | |
| Nov 1, 2021 at 17:31 | comment | added | Chris | @bruceabbott Thank you for the insight. If you don't mind me asking, how did you arrive at 5.5V for the motor generator voltage in your simulations, or did you just try many different voltages and the one that matched my traces the best? | |
| Oct 30, 2021 at 18:46 | comment | added | Bruce Abbott | @MarkoBuršič I simulated it in LTspice. The waveforms matched. The 'MOSFET keeps conducting' is actually Q1 and Q4 body diodes conducting. With a +12V supply body diode current peaked at ~4A when the FETs turned off, and internal motor coil inductor voltage peaked at -23V (with lumped coil resistance of 1 ohm and 5.5V representing generator voltage at 50% rpm). | |
| Oct 30, 2021 at 17:57 | comment | added | Marko Buršič | Not so sure that your explanation is correct. What you red circled is that MOSFET keeps conducting when it shouldn't, there is no negative voltage caused by inductive dump. | |
| Oct 29, 2021 at 19:15 | comment | added | Bruce Abbott | The HIP4081 has independent control of each FET, and has delays to prevent shoot-through, so it should be able to do it. Q3 and Q4 would be turned on alternately of course,not at the same time. | |
| Oct 29, 2021 at 15:46 | comment | added | Chris | Thank you for your response. This makes sense now that you have explained it. I'm a little uncertain about your proposed remedy, as driving both Q3 & Q4 would lead to shoot through, shorting the motor supply, no? The HIP4081 won't allow both Q3 & Q4 to be driven at the same time, either, but perhaps I'm misunderstanding. If I were to drive both sides (high signal on both CCW_PWM & CW_PWM), what the HIP4081 would do is turn on Q2 & Q4, but perhaps this is actually what you intend, as this would short the motor terminals and bring both to ground, allowing the caps to charge? | |
| Oct 29, 2021 at 2:19 | history | edited | Bruce Abbott | CC BY-SA 4.0 |
added 211 characters in body
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| Oct 29, 2021 at 2:00 | history | answered | Bruce Abbott | CC BY-SA 4.0 |