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LM5034: LM5034: Conduction of body diode during off time of the synchronous rectifier MOSFET in diode mode

Sivadharshan Kamaraj
Prodigy 60 points
Part Number: LM5034

Tool/software:

Hi,

             I have used LM5034 for a 250W (28 Vin to 50 Vout) converter module.

Currently I'm operating the synchronous rectification MOSFETs in diode mode.  I have attached the waveforms of Primary N-CH MOSFET VDS and Secondary bottom MOSFET VDS which was taken at full load condition.

Vout - 50V, Iout - 5A.

Below is the same waveforms at minimum load condition (160mA).  The VDS drop wasn't observed this time.

Why does the VDS drops on its off time?  Is it body diode conduction?

  • 0
    TI__Guru 73005 points

    Hi,

    50V 5A voltage drop should be due to the transformer - either primary side drop or secondary side winding drop. So you need to check which drop. If primary side drop, it looks you need add more input capacitance to sustain the energy delivery or reduce the input source to transformer impedance. If the secondary side winding drop you need to redesign your transformer to use bigger wire or to avoid transformer saturation.