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I am designing a BLDC motor controller and facing some issues with using an IRS2007 along with IRFB3607.

enter image description here

For one phase, the high side and low side give clean wave forms as long as V_Pow is disconnected. Rise time - 300ns; Fall time-100 ns; On time - 312us; Period- 416us;

Once V_pow is connected, the input signal to the low side of the mosfet driver leaks to the high side and drives the gate of the high side mosfet. The gate of the low side mosfet is off.

This creates a high to high short over 2 phases of the motor and the motor immediately stops. This happened first time after running for about 1 min. Ever since, the motor does not run when powered by 3 phases.

The motor is a 48V 900W motor driven at 12V, no load (1A).

If driven by the two other phases, the motor runs.

------------------------End of current issue-----------------------------

Background:--------------------------

I have tried this configuration multiple times, at first I used a complimentary BJT (PNP_NPN) duo to increase the current pumped to the gate of the MOSFET

enter image description here

In this case the driver would work properly when V_POW was not connected but fail after V_POW was connected to 12 Volts.

Each time, with 3 phases and V_pow disconnected, the gate pulses would be in order. Once V_pow was connected, one phase would randomly fail before 1 cycle was completed.

After that the remaining 2 phases would happily power the motor till the failed Mosfet driver was replaced and then again within 1 cycle 1 phase would randomly fail.

In the above config, on mosfet driver failure, both HO and LO pins would be shorted with pins of V_Boost & V_in respectively. I presumed it was an internal MOSFET failure due to over current.

As of now I have destroyed 17 drivers trying to figure out what happened. Don't know what I am doing wrong, The power mosfets mosfets don't seem to fail. Max current through the power circuit is hardly 1 -2 amps.

enter image description here enter image description here

The oscilloscope images are made into a powerpoint presentation which can be downloaded from https://drive.google.com/open?id=1nlpuCNPgn9C2LMH-RJehQwbQ5_Q2hv2O

Original circuit enter image description here

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    \$\begingroup\$ Do you know what decoupling capacitors are? Or deadtime? Or flyback diodes? \$\endgroup\$ – DKNguyen Jan 27 at 4:19
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    \$\begingroup\$ Flyback diodes are built into the mosfets (I checked). Deadtime of 500ns is built into the mosfet driver. The 1nF capacitors are meant to short HF pulses to ground. I think thats what you mean by decoupling capacitors. \$\endgroup\$ – Sujoy Bhattacharya Jan 27 at 4:26
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    \$\begingroup\$ No, C7/C8 is not what I am talking about Look up decoupling capacitors. Are you aware the LO side needs to turn on periodically to refresh to bootstrap cap so cannot run at 100% duty cycle? Or too low frequency at too high a duty cycle? \$\endgroup\$ – DKNguyen Jan 27 at 4:29
  • \$\begingroup\$ I would also scope your between VS-LO and between VB-HO and see if you are getting any ringing or spikes. I suspect C7/C8 are not doing you any good. They are significant relative to your gate-source capacitance. Scope it on your first circuit too. It was not clear in your post which one you were using. \$\endgroup\$ – DKNguyen Jan 27 at 4:46
  • \$\begingroup\$ I edited the question a bit to make it more understandable. I think this will help. Also I had missed a few more caps in the schematic somehow... Added them now. I'll upload the waveforms in a few hours once I reach office. In the off condition, all waves are clean but when powered on, it doesn't stay on for long enough to test anything. \$\endgroup\$ – Sujoy Bhattacharya Jan 27 at 5:05
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You're most likely overloading the gate driver with the gate current at turn-off. Try removing the diodes D_RX_GATES and try again. If that helps, do a redesign with a turn-off resistor in series with the diode.

When turning on the transistor, the gate current is limited by V/R_G, when turning off, the gate current is limited by V/R_diode, where R_diode is the equivalent resistance of the diode (very low, that's why you need an additional resistor). That's pretty well covered in any basic application note regarding gate driver design, for instance: AN2015-06 from Infineon, take a look at fig. 8.

AN2015-06 from Infineon

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  • \$\begingroup\$ The issue is that it works properly when V_pow is not connected. So there is something in the transients that is messing up the mosfet driver. \$\endgroup\$ – Sujoy Bhattacharya Jan 28 at 8:49
  • \$\begingroup\$ When V_pow is not connected you don't have a discharge through the Miller capacitance and the D_RX_GATE diode \$\endgroup\$ – Ken Grimes Jan 28 at 12:50
  • \$\begingroup\$ WOW! Finally a new point of view. Thanks and let me look into it..... Regarding the Gate Diode, the On current of the Driver is 260mA and Off current is 600mA. I remember reading that having a resistor with a diode in parallel ensures that the turn off is faster than the turn on. Can you please explain a bit more on why the diode may be a problem?.................Also can you take a look at the waveforms? \$\endgroup\$ – Sujoy Bhattacharya Jan 28 at 13:04
  • \$\begingroup\$ I edited my answer to answer that \$\endgroup\$ – Ken Grimes Jan 28 at 16:59
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Problem's solved. I needed to add a capacitance between V_pow and Ground on each of the 3 phases.

Since I was mostly working on low currents, I hadn't added an input capacitor or considered the length of the wire from the battery to the boards. Supposedly due to the wire inductance, when the high side mosfet turned off, there was a short, sharp voltage spike on the V_pow line.

That is why the motor would run with 2 phases as there were only 2 current carrying switching actions per cycle. When 3 phases were activated, I speculate that one mosfet would turn on during the V_pow peak and maybe damage the gate driver due to dV/dt or something.

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  • \$\begingroup\$ This is what I was about to answer ;) For your 20A motor you need enough ceramic caps and a good amount of low ESR electrolytic caps to take that ripple current and ensure V_pow has low inductance to prevent voltage spikes. Note that if the motor is spinning and you lower the PWM value, motor will act as a brake and a generator, which will feed power back into the power supply. This is fine on batteries, but can be a problem on mains-powered supply. \$\endgroup\$ – bobflux Feb 1 at 13:54
  • \$\begingroup\$ Ceramic Caps and Low ESR Electrolytic caps where? Do I need to add any more? I am aware of regeneration...but does a motor regenerate if Duty cycle is reduced from 80% to 10% ? I think it will just slow down due to load. \$\endgroup\$ – Sujoy Bhattacharya Feb 1 at 17:00
  • \$\begingroup\$ If the PWM slows down faster than motor rotation then the motor will act as a generator... The role of decoupling caps on your power supply voltage rail is not to absorb energy generated by the motor during braking (caps won't be enough for that) but to provide a local low inductance power supply whose voltage won't spike up or down when FETs turn on/off causing large di/dt current. If "L" is the inductance of your power supply and di/dt is your current switching speed, remember e=L*di/dt will be the height of the voltage spike... \$\endgroup\$ – bobflux Feb 1 at 20:09

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