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Heating effect on the primary side of the newly designed inverter

Amal
Expert 1140 points

hai.

we have been designing an inverter.Its a simple pushpull based one.We are using a push pull topology on the primary side of the design.The design has mosfets on the upper half and the lower half of the transformer.While the center tapped portion is connected to the a voltage range of 24 to 48.The transformer designed by us would output a +350v and -350v in the secondary on the corresponding cycles of the design.The major issue we are facing now is that the mosfets placed on the upper halfs and the lower halfs gets heated.What would be the possible reason for the heating of the mosfets on the half cycles of the design? Is it due to the spikes in the voltage in the drain, that results in heating of the mosfets? Will placing snubbers in the push pull design across the mosfets help? If so how will a design a snubber for a particular voltage range 24 to 48v Or is it due to the leakage inductance of transformer?

  • 0
    TI__Mastermind 25570 points

    Hello Amal

    There are a number of reasons why the MOSFETs will heat up:

    The RMS current that flows in them.

    If the gate voltage is not sufficient to keep the devices in the ON condition

    If the drain/source avalanches due to voltage spiking - look for abrupt clamping action on the spike (flat topping)

    Insufficient heatsinking

    Snubbers will reduce the dissipation in the MOSFETs but won't reduce the overall dissipation - the energy gets dissipated in the snubber rather than in the MOSFET. Leakage inductance in the transformer will increase the energy available to cause spikes on the primary and careful transformer design can reduce it. There may also be inductance associated with long PCB tracks - especially tracks where the current it turned on and off by the switching action - tracks in series with the drain or source connections for example.

    Snubber design is covered in the articles at https://www.ti.com/seclit/an/slup100/slup100.pdf    https://e2e.ti.com/blogs_/b/powerhouse/archive/2016/05/05/calculate-an-r-c-snubber-in-seven-steps  

    Regards

    Colin