Simple IGBT failure

Discussion in 'General Electronics Chat' started by Fowlet, Aug 20, 2011.

  1. Fowlet

    Thread Starter New Member

    Aug 20, 2011
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    Hello All,

    I am an English student currently in Fort Portal, Uganda, attempting to build an induction generator controller with very limited resources. As part of the design, I intend to to PWM the ~240V RMS produced by the generator. Right now, I am attempting to simply switch mains on/off at low frequency to test some IGBTs. I have a 12V transformer, that after RMS peak and a regulation of around 1.4 gives around 20V pk-pk AC out. I rectify this, then divide it using two 1kOhm resistors to give 0V, ~10V and ~20V connections.

    The IGBTs have integrated antiparallel diodes, so I place them in antiseries, with common emitters. I connect the emitters to the ~10V connection. I then run a wire from the two IGBT gates, and manually touch it to the 0V and 20V connections, in an attempt to give gate-emitter voltages of -10V and 10V. The IGBTs do not respond, seemingly blocking in one direction regardless of connection. I have attached a diagram of the circuit I intend to use this method in; ignore everything in grey, and ignore the transistor; as I said, I am manually connecting the wire to avoid any complications.

    I would greatly appreciate any insight into the IGBT's lack of response.

    [​IMG]
     
  2. Fowlet

    Thread Starter New Member

    Aug 20, 2011
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    I should add that the IGBTs are ST's STGP6NC60HD, details Here
     
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Please post the whole circuit you are using right now to test the IGBTs. E.g. what are the collectors connected to? If I ignore everything in grey, then the collectors are open.
     
  4. Fowlet

    Thread Starter New Member

    Aug 20, 2011
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    Apologies, here is a hastily thrown together representation of the current test circuit:

    [​IMG]
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    I drew your schematic again and attached it.

    First of all I think it's dangerous to experiment with a circuit at this high voltage if you are not exactly sure if/how it works. Why not use a smaller voltage to switch?

    Then, when turning ON both IGBTs you are applying to one of them a reverse voltage (+ on emitter and - on collector) depending on the 230VAC polarity.
    This is not a valid condition for a conducting IGBT.
    Are u sure they are still ok?

    If you want to use 1 conducting IGBT and the body diode of the other (blocking) IGBT, you have to alternate the gate signals for each IGBT (1 OFF , the other ON)

    It would be be helpful to explain what your final goal is in terms of voltage / current etc. and the components you want to use.
     
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