IGBT ON but reversed biased

Discussion in 'General Electronics Chat' started by praondevou, Aug 23, 2011.

  1. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011
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    There was another thread where someone wanted to do exactly this. Turning an IGBT on applying a positive gate /emitter voltage and then applying a reverse voltage to collector/emitter, positive to emitter, negative to collector.

    The voltage would be halfwave of 230VAC, i.e. 325Vpeak (if it does not conduct, of course)

    It's the STGP6NC60HD.
    http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00058424.pdf

    I was wondering what would happen. Would it conduct through the internal body diode or is the body diode function depended on the state of the IGBT, on or off?

    I don't have an IGBT to try this out..:D
     
  2. JDT

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    Feb 12, 2009
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    It will conduct through the internal body diode if it has one. Not all IGBT's do.

    If no diode, it will block the reverse voltage. This is within the specifications and will not damage the IGBT provided the voltage is not greater than the maximum allowed.

    When reversed biased, the device will not be affected by the value of the emitter-gate voltage.

    MOSFETs however, can conduct in the reverse direction.
     
  3. praondevou

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    It has a body diode . (see datasheet I had attached)

    And there is no such parameter like maximum allowable Emitter/collector voltage because this is not a valid condition for the IGBT.
     
  4. t_n_k

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    It does specify VCES=600V.
     
  5. praondevou

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    I'm talking about a positive voltage on emitter and negative on the collector.;)

    VCES is thought to be the breakdown voltage of a non-conducting IGBT, i.e. the body diode's reverse voltage.

    It's a question for someone who has insight into the physical structure and relationship of IGBT/body diode.

    Thanks
     
  6. JDT

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    See figure 16 in the datasheet.

    Around 2.5V at 15A reverse currunt.
     
  7. praondevou

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    The question actually was : Does the internal body diode function depend on the IGBT being turned ON or OFF or would the internal IGBT structure not allow this?

    I finally found a IRG4PF50WD (TO247) and made a test.

    The body diode DOES conduct when forward biased, independently of the voltage from gate to emitter, i.e. IGBT on/off.

    Thanks
     
  8. t_n_k

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    It would be surprising if the diode didn't conduct when forward biased irrespective of the gate condition. Presumably the manufacturer would make it abundantly clear if that wasn't the case.

    How did you know the current was actually flowing in the body diode since the diode connections are inaccessible?;)
     
  9. praondevou

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    good question. deduction. the reverse current and voltage drop is exactly the same in both gate conditions (-15V and +15V).to be really sure I would have to do the same test with an IGBT that doesn't have a body diode.

    I don't think the manufacturer would mention this condition, since the IGBT is not supposed to be connected like this.

    I know that the body diode is physically detached from the IGBT in bigger IGBT modules, I wasn't sure how it's done in the small packages. in these too, they are obviously totally independent
     
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