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LM5026: LM5026 Self synchrounous rectification at secondary side question

James Su5
Expert 1340 points
Part Number: LM5026

For LM5026 Self synchrounous rectification at secondary side design, effectiveness and SR MOSFET VDS Ripple is good,

but in Light load MOSFET VDS Ripple is to big (reference below pic), please heve comment how to modify can reduce VDS ripple, thanks !

Light load

Full load

sch

  • 0
    TI__Mastermind 31580 points
    Hi James,

    If the Vds spikes are not exceeding the Vds rating of the SR devices, I suggest you try an optimise the values of the RC circuits that are in parallel with the SR's in the schematic, R79/C69 and R126/C105. It should be possible to tune this circuits to reduce the ringing waveform to a single spike which is critically damped.

    If the Vds rating is exceeding the Vds rating of the SR's I suggest adding a TVS diode in parallel to clamp the voltage waveform. Alternative a clamping snubber circuit can be used to limit the Vds voltage.

    Please use this link for a very good paper on snubber design.

    www.ti.com/.../slup100.pdf

    Regards

    Peter
  • 0 in reply to Peter Meaney
    TI__Intellectual 1410 points

    Hi Peter,

    Based on the SCH, could you kindly suggest R79/C69 and R126/C105 value for our reference?

    In addition, SCH already have TVS diode circuit, may i have your help to check any thing need to improve?

    Thank you for your kindly help.

    Best regards,

    Edward Chen