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Forum MOSFET going to continuous conduction
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Forum Thread Details
  • State Verified Answer
  • Replies 17 replies
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Related

MOSFET going to continuous conduction

ravi kondeti
ravi kondeti over 3 years ago

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

image

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  • navadeepganeshu
    navadeepganeshu over 3 years ago +7
    Hi Ravi, The 60V, 2A MOSFET seems ok for this application. But just ensure that the MOSFET is able to drive that much current for the gate voltage you apply(the Vgs/Id characteristics in the datasheet…
  • shabaz
    shabaz over 3 years ago +6
    Hi, Continuous conduction means the MOSFET is damaged, one or more parameters was exceeded. To troubleshoot, you'd need a 'scope probe to see the gate voltage and the drain with respect to the source…
  • dougw
    dougw over 3 years ago +6
    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…
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  • dougw
    0 dougw over 3 years ago

    One other possibility is that the FET is working properly, but the drive signal just never goes to the right voltage to turn it off.

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  • ravi kondeti
    0 ravi kondeti over 3 years ago in reply to dougw

    mosfet seems shorted as i checked with turning off the load, power supply too and again turning them on

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  • dougw
    +1 dougw over 3 years ago in reply to ravi kondeti

    One final thing to try - put a resistor from the gate to ground to ensure no residual voltage is left at the gate.

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  • ravi kondeti
    0 ravi kondeti over 3 years ago in reply to dougw

    I will try this 

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  • ravi kondeti
    +1 ravi kondeti over 3 years ago in reply to dougw

    hello dougw,

    i have added a 1k gate to source resistance along with cap. also a reverse diode across the electronic load. this seems to resolve the issue. thank you.

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  • navadeepganeshu
    0 navadeepganeshu over 3 years ago in reply to ravi kondeti

    Nice! A higher one would be good. Like a 100K pulldown resistor to hold the state of GATE in GND when driving signal OFF. There is that seemingly fictitious capacitor inside which takes some time to (dis)charge.

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  • navadeepganeshu
    0 navadeepganeshu over 3 years ago in reply to ravi kondeti

    Nice! A higher one would be good. Like a 100K pulldown resistor to hold the state of GATE in GND when driving signal OFF. There is that seemingly fictitious capacitor inside which takes some time to (dis)charge.

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