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Calculating resistor for IGBT and choosing flyback diode

  1. Feb 7, 2017 #1
    On the circuit I've drawn up, how do I calculate a current limiting resistor for the gate of the IGBT?

    The IGBT being used is a stgp6nc60hd.

    Also, how would I go about choosing a flyback diode for the motor?

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  2. jcsd
  3. Feb 7, 2017 #2


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    Staff: Mentor

    I don't use IGBTs, but since it's a FET input, why does it need a current-limiting resistor? I've seen resistors to ground to turn them off faster, but I'm not sure I've seen current limiting resistors into their gates. Of course, I could be wrong.

    For the flyback diode, you need to figure out the max reverse voltage and the max forward current. The max forward current can be calculated from the parasitic capacitance (or an explicit capacitance that you add) and the winding inductance.
  4. Feb 7, 2017 #3


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    Staff: Mentor

    There are some application notes that show how to choose a series gate resistor to limit current and improve switching. From what I can tell it has to do with the IGBT gate looking like a small capacitive load and taking advantage of the driving resistance to "tune" the response as well as curtail current spikes. Took me all of ten seconds to spot them with a google search ("IGBT gate resistor").

    But the OP should show some effort here and do the search and some reading.
  5. Feb 7, 2017 #4


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    Staff: Mentor

    Thanks, I love learning new things here. :smile:
  6. Feb 9, 2017 #5

    rude man

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    The IGBT will be saturated and the inductive nature of the motor load will limit transient current surges so I don't see the point of a series gate resistor to limit load surges. Maybe to protect the TLP251 driver though as the gate capacitance can be substantial.
    As for the flyback diode, just make sure it can handle the transient load current when the IGBT shuts off, and of course the 18V reverse voltage.

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