Hi,
I've designed (and subsequently blown up) a H bridge PCB with a HIP4081a, controlled by a 31khz output from an Arduino. It worked fine for a while, but then one of the FETs stuck on and everything blew up. Quite spectacular, one of the FETs was glowing red... I have since decided that's because of bad PCB layout and grounding, so I'm in the process of designing another board. The last board was fairly electrically noisy, so I'm trying to improve that in this revision. At the mo, I have a common mode choke attached between the FETs and motor. I've checked out the waveform between the choke and motor, and it's some kinda weird sine wave. Doesn't seem quite right to me as between the FETs and choke is a proper PWM signal. I'm attempting to use the choke to filter noise from the motors, but I've been struggling to find much info on the 'net about chokes and high currents (and especially with PWM). Have I got the position/requirement of the choke completely wrong?
Common mode choke shouldn't have any effect on the differential signal, but would attenuate the common-mode signal (which will act as RFI radiating from the motor and its wiring)
There are many pitfalls and causes of MOSFET failure at high voltages and currents - protection components are increasingly important as the power levels increase. Overvoltage, overcurrent, gate-source over-voltage can all destroy a FET. Stray inductance in high-current wiring can lead to big voltage spikes that a naive analysis of the circuit wouldn't be aware of. In particular the high-current route from the source terminal must not be shared with the path from source to the gate-driver's ground line, and any gate-source protection zener clamp needs to be right close to the MOSFET to be effective. MOSFET Vds ratings should be more than twice the supply voltage as a rule of thumb - drain-source breakdown will lead to massive power dissipation and likely vaporization of the MOSFET die. TVS diodes are suggested across the drain-source of each leg of the bridge, and also for the power rail itself - reduces the chance of inductive spikes exceeding the devices' ratings.
Thanks for your reply. I did think (correctly it seems!) that the common mode choke shouldn't affect the PWM signal itself, maybe the motor's causing the sine wave-like appearance at the motor terminals.
I do have 50v transient voltage suppressors across the drain and source (i.e. to drain to ground) on the lower half of the bridge, but not on the upper half (i.e. Vsupply to source). Neither do I have them between supply and ground. I was generally following the OSMC schematic which doesn't have upper TVSs.
I think perhaps as the ground was noisy and falling below 0v, Vgs may have exceeded the 20v maximum, and caused the FETs to blow. I don't have gate voltage clamping zeners at the mo, I shall add them as close to the FETs as I can. I think what you explained about the inductance in the wiring causing high voltage spikes was occurring at one point, as I observed 50v being generated on the FET side, even though the input is just 24v. I guess the 50v TVSs were doing their job! I thought the choke had something to do with it, but perhaps not.
The FETs I'm using are rated for 60v and 57a so should be sufficient. They only ever blow when the motor is having to do a fair amount of work (about 10 amps stall current, so not massive), when they're lightly loaded at about 1 amp the bridge seems fine.
I'm not 100% sure what you mean when you say "In particular the high-current route from the source terminal must not be shared with the path from source to the gate-driver's ground line". Do you mean the path from FET source to ground should be separate to the path from the driver's Vss pin to ground? I had it shared at first, but then split it later on when I was getting issues.
Thanks so much for your help though, I really enjoy experimenting with electronics, just eventually I run out of patients/ideas and have to ask for a few hints!