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Flyback question

  1. Apr 20, 2012 #1
    If I have a circuit driving a motor - say 7A @ 220V through an IGBT that has the anti-parallel C-E diode internal to the part, is there need in putting a flyback diode across the motor still?
     
  2. jcsd
  3. Apr 20, 2012 #2
    I do just to be safe. I would guess that IGBT internal body diodes are tough considering the applications of IGBTs, but that's only a guess. The concern you should have is if the body diode is fast enough such that when its reversed biased it doesn't conduct and waste energy. I use fast recovery diodes for flybacks because its simple to do.
     
  4. Apr 20, 2012 #3
    The body diode is marked as 'ultrafast' with a Trr of 31nS. That's why I'm not sure what the best course of action is (cost vs. benefit). Yay consumer products...

    If I understand correctly, the flyback across the motor would force the load to dissipate its own energy to protect the IGBT while the C-E body diode allows the inductive current to flow past the IGBT without the destroying it. Correct?
     
  5. Apr 20, 2012 #4
    its to protect against a high voltage condition. The inductive spike happens when the switch turns on/off and the large di/dt creates a voltage spike that can blow transistors. The body diode or flyback will let the current keep flowing, hence a lower di/dt and reduces the voltage spike.
     
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