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  1. #1
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    Gate and Collector of IGBT is showing short

    Hello all,
    Good day!
    I am new to this forum thus please pardon me if I make any mistake while asking my question.

    I have been trying to make a small VFD (variable frequency drive).
    I have used STGP19NC60KD IGBTs for the purpose and using IRS2109S for driving the gate.
    I am driving the IGBT with a PWM frequency of 8KHz.
    It works well when no load is connected and I can see the required output.
    When I connected a motor, the motor ran for 5 seconds, and then the first set of IGBT(high & low side) which is used for driving phase R got burnt, and its driver IC is also damaged.
    When I checked at IGBT terminals, I see that its gate and collector is short-circuited.
    I replaced the IGBT and again tried, but it still burnt the same IGBT.

    In first attempt, it burnt both high and low side IGBTs and all the resistors and zener diode.
    In the second attempt, it burnt High side IGBT only and driver IC.
    Also all the resistor on both high/low sides and zener diode were also damaged.

    I have tried searching a lot but couldn't find anyone with the same problem.
    I see that Collector-Emitter or Drain-Source short circuit is a common problem, but in my case, gate-Collector is short circuit and I can't find any explanation for it.
    I have also attached the schematic of one of the IGBT path.

    I really appreciate any help to show me the direction of the problem.
    Thanking You all.
    Click image for larger version. 

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  2. #2
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    Re: Gate and Collector of IGBT is showing short

    the symbol in your schematic is a PNP transistor, not an IGBT
    are the IGBTs in correctly?

    Phase R goes to the motor
    please show the motor and the the remaining circuit

    the motor runs, but is it controlled?

    what is the bus+ voltage?



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  3. #3
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    Re: Gate and Collector of IGBT is showing short

    Hello,
    I have gathered few more inputs.
    Please find them in the attachment.

    I used PNP that is only for getting proper footprint. They are soldered correctly in the circuit.
    The circuit is powered directly from 230VAC and is rectified to DC. The Bus voltage is around 340V DC.

    I observed that only R phase IGBTs are burning and other are working perfectly.
    This R phase IGBTs are at the farthest distance from the output terminal, can it be a problem?



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  4. #4
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    Re: Gate and Collector of IGBT is showing short

    your IGBT's are upside down in the schematic ... and do not show the internal diodes of the STGP19NC60KD

    you need a high quality film / foil cap across the HVDC bus right at the igbt's else the turn off current spikes may kill the devices ( ESR / ESL in electro ) - then the open layout will radiate RFI as the HVDC bus goes up and eventually upset your control and possibly even your gate drive chips causing shoot thru failure

    try 12VDC on the HVDC bus first with a dummy load R & L, then 24V then 36, 48, 75, 110 and so on until it fails again ...

    - - - Updated - - -

    also your insulation system is not up to 600VDC ( heatsink ) check to see if there is a short thru the heatsink ....



  5. #5
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    Re: Gate and Collector of IGBT is showing short

    Hi,
    Thanks for the reply.

    Sorry for the schematic error. Actually I used that symbol during design only to get the required pads on PCB, but otherwise I have made connections correctly and according to the datasheet. I had seen the output of IGBTs on DSO, by applying 12V to HVDC and I could see the correct pulses at the output.
    Also, my motor runs good for some time.
    We had a 5Amp fuse, Circuit breaker as a protection and then never trip. We had connected a multimeter in neutral line for measuring the return current and it never crossed 2.5Amp.
    Also, I checked for the shorts on heatsink before connecting voltage to the system and there is no short through it.

    I will try by reducing the switching frequency.
    Also, I would like to give it a try by adding some capacitors directly on IGBT.
    Is it Ok if I add 100nF/1KV at the collector and grond for the High side IGBT.
    Should I also add 100nF/1KV at the collector and grond for low side IGBT?
    There is a bootstrap circuit for high side IGBT, can these capacitors have any effect on it?

    Please suggest. Thanks.



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  6. #6
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    Re: Gate and Collector of IGBT is showing short

    DO NOT PUT CAPS DIRECTLY ACROSS THE IGBT'S

    across the HVDC supply yes - but 100nF is way too small

    have you tested your insulation system at 400V ..? I doubt it ...

    if the bootstrap does not have UVLO ( under voltage lock out - i.e.stop ) then you may have problems ...

    - - - Updated - - -

    you need a high quality film / foil cap across the HVDC bus right at the igbt's else the turn off current spikes may kill the devices ( ESR / ESL in electro ) - then the open layout will radiate RFI as the HVDC bus goes up and eventually upset your control and possibly even your gate drive chips causing shoot thru failure
    please re-read the above ...



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