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MOSFET going to continuous conduction

ravi kondeti

Hello Guys,

Following is a circuit i am working on. input is from a isolated DC-DC converter (flyback configuration) set at 12v. using bk precision electronic load i am testing at 500mA. i wanted to observe the dynamic behaviour of flyback converter while switching the load at higher rate so i kept a mosfet rated for 60V,2A. while switching observed that current is peaking and FET is gone. later changed FET to a higher rating one (TK4R1A10PL). even then MOSFET after sometime goes into continuous conduction even when i am removing gate pulses (using a function generator to give pulses), this is happening when i am increasing the frequency of the gate pulses (5-10kHz). using function generator a wrong approach? or any corrections i need make. please suggest

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    A FET in this configuration would likely only die from heat. If the device didn't get hot to the touch it means it would have been a very fast internal heating due to high inrush current.

    If it did get hot, then maybe the drive signal isn't turning the FET on completely. What gate voltage is being used?

    Is it possible to measure the transient current during turn on of the load?

    One other possibility is if the load is inductive there could be a high voltage spike on turn off. This could be mitigated using a snubber diode across the load. 

  • 0 in reply to dougw

    hello dougw,

    i was observing a peaking current while turn on nearly 8 times the set point(500mA). i observed that initially heating was occuring so chose a fet with higher power rating. i am using a function generator with 10V amplitude.

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