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H-bridge motor control circut burns MCU after some time
rasul:
Hi everyone!
I got a problem recently. I have already spent for about a week trying to figuring out what is causing the problem. I'm not very experienced in the field of motor control electronics.
Circut's schematics is attached.
Basically it's a simple H bridge with five 1 Ohm resistors connected in parallel and used as overcurrnt detectors. It's controlled by MCU.
This circut works fine while motor current is below 3 amp. But when I use motors with about 7A current consumption after some time system stops working. At first I thought that this was caused by voltage spikes during start of the motor on current sensor resistors. And I was right. On all malfunctioning boards they was damaged and had higher resistance. I fixed this problem by lowering they resistance and by using resistors with higher power rating. After that fix I don't observe any dangerous voltage spikes on those resistors and boards are working for a few hours longer ;D .
After some time I start to observe 12V on MCU pins and this condition reset MCU which also reset it's outputs and 12V dissapears. Looks like this voltage somehow come from outputs controlling this H bridge. And sometimes it just destroy MCU - it starts overheating and stops working.
I have also tried to reduse resistance of R4, R11, R12 and R13 so parasitic capacitors on MOSFET charge faster but it didn't helped.
This circuit was designed to be cheap for motors consuming 7A under nominal load. I replaced those cheap chinese MOSFETs with irfz44n and irf4905 but it didn't helped either.
Any ideas why it's happening? I'm totaly confused.
0xdeadbeef:
Fully discrete H-bridges are somewhat dangerous. Some small bug and you have a short e.g. over the left highside and lowside, burning the FETs.
Are you sure you're at least using blanking times when switching directions? For inductive loads, active freewheeling might be necessary to stop recirculation.
I'd recommend to just use a monolithic H-Bridge or at least some dedicated IC to control the FETs.
wraper:
This circuit is non functional. With 47k R1 and 2.2k R2 (times 4), this won't ever react to any control signals.
Benta:
--- Quote from: wraper on March 26, 2019, 07:46:24 pm ---This circuit is non functional. With 47k R1 and 2.2k R2 (times 4), this won't ever react to any control signals.
--- End quote ---
Not only non functional, it's also dysfunctional. With 47k and 2.2k, the lower MOSFETs are on all the time.
rasul:
Thank you guys!
--- Quote from: wraper on March 26, 2019, 07:46:24 pm ---This circuit is non functional. With 47k R1 and 2.2k R2 (times 4), this won't ever react to any control signals.
--- End quote ---
Yes. You right. I changed those values later. But I forgot to change schematics and now even don't remember what exact values I used there after. I'm sorry for misleading.
--- Quote from: 0xdeadbeef on March 26, 2019, 07:39:49 pm ---Fully discrete H-bridges are somewhat dangerous. Some small bug and you have a short e.g. over the left highside and lowside, burning the FETs.
Are you sure you're at least using blanking times when switching directions? For inductive loads, active freewheeling might be necessary to stop recirculation.
I'd recommend to just use a monolithic H-Bridge or at least some dedicated IC to control the FETs.
--- End quote ---
Thanks! I will consider this. Delays are long but there is a part in this device's behavior which can result in immediate direction switch (i just thought about this condition).
But I don't understand how this can lead to 12V going to MCU pins. Anyway I should change this behavior, maybe it' a part of a problem at least.
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