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UCC27712: Spikes on Gate-Emitter during driving of high current in a half bridge with series resonance load

Tony Philip45
Intellectual 755 points
Part Number: UCC27712

Hi , 

We have a Half bridge. The output of the Half bridge is fed into a Series resonance LC (where the  L is the Coil of 110uh, and the C is .6uF MKP Capacitor). We have placed around 1.2uS deadtime, which is enough for the IGBT being used.

I m seeing these spikes on the bottom IGBT gate when we are running at a considerable amount of current draw by the half bridge. I have tried lowering the gate drive resistance and increasing the capacitance to reduce these spikes (which I believe are due to dv/dt of the Collector-gate capacitance) .

Here Channel 1 = Low Side IGBT VGC , Channel 2 = High Side IGBT VGC

If this is due to coupling via the Cgc, will a miller clamped isolated IGBT driver help?

Regards,

Tony

  • 0
    TI__Mastermind 23015 points

    Hello Tony,

    The changes you describe, lowering the gate resistance and increasing the capacitance (which I assume is gate to emitter capacitance), are the changes I would recommend to reduce the Vge spike during the Vce falling time. These voltage spikes are typically caused by the Ccg capacitance and the dV/dt on the switch node as you mention. Another important consideration is the PWB trace layout from the gate driver output to the IGBT gate, and the IGBT emitter to gate driver ground trace layout. The traces should be short in length to minimize the parasitic inductance of the board traces. If there is a capacitor from gate to emitter, make sure the capacitor is very close to the IGBT pins.

    A gate driver with the miller clamp function will help clamp the Vge during the power switch off time and still allows you to program the gate drive turn off resistance to control the Vge falling dV/dt. There is usually some delay from the gate drive turn off edge and activating the miller clamp, to allow for a lower miller clamp resistance (or no resistance).

    Let us know if this addresses your question, or you can post additional questions to this thread.

    Regards,

    Richard Herring