IGBT question?

Discussion in 'General Electronics Chat' started by wkyong, Apr 30, 2008.

  1. wkyong

    Thread Starter Active Member

    Apr 29, 2008
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    What is the meaning for anti-parallel hyperfast diodes for an IGBT?Does it means they cannot be parallel up ?
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    I have never heard about them but i guess from the name that they are very fast parallel diodes with the ones anode connected with the others cathode and the others anode connected with the others cathode.
     
  3. Dave

    Retired Moderator

    Nov 17, 2003
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    Yes, that exactly what it means. It's s bit of a misleading name, as it is not the parallel arrangement that is "anti" but the polarities - and even then "anti" should be inferred as "reversed".

    Dave
     
  4. jpanhalt

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    Jan 18, 2008
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    I always thought the term used by the OP meant the single diode that is placed "anti-parallel" between the source and drain of IGBT's and Mosfets to protect from inductive kick. The diode's cathode is attached to the high-side potential. Thus, it conducts opposite to the IGBT/Mosfet device.

    It is not a pair of diodes connected as described. That connection described by Mik3 conducts in both directions and would not be a good idea across the drain and source of a IGBT/mosfet. John
     
  5. Dave

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    mik3's explanation of anti-parallel is correct, namely that devices (lets keep it abstract for the moment) are connected in parallel but with the polarities reversed. The notion of "anti-parallel hyperfast diodes" takes some reading into, and without seeing it stated in context I cannot offer more of an explanation from an application point of view.

    Your explanation seems plausible John, so you are suggesting that the diode is (anti-)connected across the collector/emitter of the IGBT? Strictly speaking, this isn't a set of anti-parallel diodes as per the OP. Therefore this does raise the question that there is some confusion about the terminology of "anti-parallel"?

    Dave
     
  6. jpanhalt

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    Dave, I agree with your comment. My comment was based on the context used by the OP in reference to the diode and IGBT/mosfet devices. The transistor device counts as one of the "diodes" in the anti-parallel pair, except the active device is switched.

    I did not want the OP to leave thinking that the device would have a pair of anti-parallel diodes across it. John
     
  7. Dave

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    Actually think about this, I think this may refer to an arrangement of anti-parallel IGBT-diode pairs. Connect the IGBT-diode pairs in the common-emitter configuration and you have uni-direction current control switch operational through each device.

    Dave
     
  8. jpanhalt

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    Hi Dave, I am not sure of the circuit you propose, particularly the phrase, "switch operational through each device."(emphasis added) Can you post a schematic?

    To clarify my comment, I have added a schematic. Unfortunately, I couldn't find an IGBT device in Eagle, so I used a Mosfet. Just assume for now it is an IGBT. Circuit A is what I am referring to. The diode is often referred to as the anti-parallel diode in the way that the OP referred to it. Circuit B is simply two anti-parallel diodes (Mik3's description). Circuit D is a Triac and C is a Diac.

    The circuit you describe sounds to me a lot like a triac with control of the gate...much like an scr with gate turn-off control. Obviously, I am confused, so a picture would help.

    In any event, I think the OP was referring to the configuration in Circuit A.

    John
     
  9. Dave

    Retired Moderator

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    See the attachment (you don't get any fancy layouts with me John, drawn by hand on a tablet!!).

    Essentially it is a common-emitter back-to-back switch. I understand my initial explanation was a touch confusing, would it be better if I said that this switch arrangement is such that you can control the current direction through each switch independently of one another.

    It is also anti-parallel diodes (of a sort) in an IGBT application.

    Dave
     
  10. jpanhalt

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    Now, it's clear what you meant. Thanks. John
     
  11. JoeJester

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    Apr 26, 2005
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    here's a datasheet
     
  12. Dave

    Retired Moderator

    Nov 17, 2003
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    So it is as John described. Interesting little device.

    Dave
     
  13. mrmeval

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    Jun 30, 2006
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