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LM5116: LM5116

Daliya Rajan
Prodigy 10 points
Part Number: LM5116

Our power supply consists of 3 outputs. 41V,5A is one among them. Circuit posses primary and secondary section. Universal AC (90V-265V ) is the input to primary side while at secondary section provides 55V dc rail.

This 55V dc is the input to LM5116 to get output of 41V.  At 90Vac input,the power supply was unable to deliver 41V when the lower MOSFET gate was 10ohm . On contrary,with 4.7 ohm or 0 ohm,LM5116 could deliver output. What could be the possible reason and solution for the same??

NB:We need 10 ohm gate resistor for lower MOSFET to reduce EMI emissions.

  • 0
    TI__Mastermind 40040 points
    Hello Daliya,

    The series resistance in the low side FET (LSF) Gate will drop a voltage across it as the Lo pin sinks current in to the pin (Lo Low). If the voltage drop across the low side Gate resistor exceeds the Vth of the Los Side FET, then the Low Side FET will turn on when its not supposed to, as the high side FET is on, creating a current limit event. This is what I think is happening with a 10ohm resistor.

    Because the LSF is zero voltage switching (due to body diode conducting during the dead times) , a gate resistor is not needed for the LSF gate, suggest installing zero ohms.

    Hope this helps?

    David.