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MOSFET switching loss from datasheet parameters

  1. Apr 23, 2014 #1
    Greetings. I am not sure how to approximate a MOSFET's switching energy from datasheet parameters. I have stumbled upon a few ways, but in all cases I've found it is pretty rare to find a datasheet with all the correct parameters.

    Here are some ways I've found:

    1) Eon and Eoff are listed directly in the datasheet. Very rare find.

    2) The turn-on/turn-off voltage and current waveforms are provided on a single time plot, so I can multiply them together and integrate (usually with geometric approximations). Also very rare.

    3) The method outlined in this document:
    http://www.btipnow.com/library/whit...lculation Using the Data-Sheet Parameters.pdf. Seems to be based off of a particular test-circuit (some test circuits have Rg going from the gate to ground instead of gate to pulse generator and don't include the upper mosfet/inductor). Also, the "gate plateau voltage" is a rare find in the datasheets for me....unless it is listed with a different name. I actually haven't found any datasheets with this parameter listed.

    So I'd like to know if there is a way to approximate switching energy that could be derived from the most common mosfet datasheet parameters.

    Thanks in advance
     
  2. jcsd
  3. Apr 25, 2014 #2

    Baluncore

    User Avatar
    Science Advisor

    The switching loss will be determined by the gate drive and the load circuit topology.
    You must use the mosfet parameters to evaluate turn on and turn off transition times.
    It is usually enough to know the gate charge, drain capacitance and drain to gate capacitance.

    A simple estimate of switching loss is = frequency * 0.5 * (total transition time) * (off voltage) * (on current).

    So if you are switching 24 volt, 10 amp at 10 kHz and it takes 1 usec to turn on and 2 usec to turn off, the switching loss will be... = 10 k * 0.5 * (1u + 2u) * 24 * 10 = 3.6 watt.
     
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