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UCC27211: Noise and short-circuit in the High side gate of a Full Bridge

Part Number: UCC27211

Hello Everyone.

First of all please put the thread in the correct place, I didn't found a better forum to ask it.

I'm designing a high frequency inverter to drive high voltage a piezo emitter.

The power is driven by on two UCC27211. The voltage of the bridge is 24Vdc and the load right now is a transformer (primary - 65uH - 1.27Ohm), in the secundary I have a piezo emitter.

The mosfets used on the bridge are 4 IRFP4410z with 4820 pF of Input Capacitance.

The signal in the output is 20kHz to 60kHz and to recreate the sinusoidal I use a 10x PWM signal, so the maximum frequency in the driver and mosfets is 600kHz.

The schematic is attached, during my tests I made different changes, removed and added different components what I have now is more or less the attached schematic. The colored circles are the colors of the signals of the screenshots from the oscilloscope.

The most strange for me is the signal generated in the gate of the high-side mosfet, because according to the scope it's the same signal than the source of the mosfet (middle point of the bridge). The output signal of the low side mosfet is good enough, but the rest of the signals are not the best. I also can not figure out why I have 115V in the high side gate if the voltage from the supply is only 24, according to the datasheet should be around 36V (24V + 12Vgs).

Can someone helps me?

Thanks a LOT.

  • Hi  Daniel,

    Thank you for using the UCC27211. Yes, this is the appropriate forum.

    First of all, can you confirm where each probe is referenced to?

    Regards,
    Mateo

  • Hello Mateo.

    Thanks for your interest. All the probes are referenced to ground.
    I have to say that the connection between the UCC27211 ground pin to the general ground is made using a Ferrite Bead of 65 Ohm at 1Mhz from Würth Electronic.

    Right now I removed it and seems to be better.
  • Hi Daniel,

    For future reference, the high-side gate voltage should be referenced to the source, not ground, using differential probes.

    The ringing seen at the gate and switch node can be attributed to parasitic series capacitance and inductances. Do you have a dc-link capacitor between the dc bus and source of the FETs?

    Is the dc-link voltage 24Vdc? We are confused as to why this is not DC.

    Regards,
    Mateo

  • Hello Mateo.

    I measured using single probes because I haven't differential probes, but later I measured only the gate-source with one channel using the ground of the scope in the source pin of the mosfet and the signal was more or less normal, square signal with about 12V.

    I have 3 1000uF capacitors in the 24Vdc line dedicated to the mosfet bridges (I have 2 in the same PCB, but the second one is not solded right now), one important thing is that the capacitors are far from the bridges, about 10-15 cm. The power supply is a 24V 6.3A connected directly to the capacitors, I use a DC-DC converter connected to the main 24V power supply 12V to the UCC drivers.

    The mosfets have no 24Vdc directly connected to the supply (Vbridge1 in the schematics) because I have a ressetable fuse and a diode in series between the dc-link and the bridges.

    I have changed the 12V Zener diode in parallel with the bootstrap capacitor by a bidirectional tranzorb and also the 12V zener in the supply line of the Mosfet drivers. Also I removed the ferrite beads.

    Attached are the signals of all the gate pins referenced to GND. Seems to be better, but I still have ringing in the high side (maybe due to the voltage in the soirce pin of the high side generated by the primary of the transformer).

  • Hi Daniel,

    I am still looking into this and will update you soon!