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UCC28950EVM-442

Harrison 2011
Expert 2085 points

Hello,

Can anybody explain the function of R6, C1,R8 and R9 in the schematic on Page 4 of sluu421a.pdf?

Thank you,

  • 0
    TI__Guru 65965 points

    These components along with diodes D4 and D6 form what is known as a snubber/RCD clamp.  Generally  there is a lot of ringing at the switch nodes caused by leakage inductance and parasitic capacitance.  Without this circuitry this ringing could produce large voltages that could damage the synchronous rectifiers.

  • 0 in reply to Mike O'
    Expert 2085 points

    Hi Mike,

     

    Thank you very much for the reply.

     

    Could you please let me know the formulas/equations you used to calculate the snubber values such as the capacitance and resistance?I used some formulas from SMPS books , but I cann't get the same number as those in the schematic.

     

    Thank you,

     

  • 0 in reply to Harrison 2011
    TI__Guru 65965 points

    Hello Harrision,

    The theoretical calculations are a starting point based on theoreticals, that does not take into account trace inductance and all parasitic capacitances.  In most cases you will have to adjust the snubber in the actual circuit.  This is why the values used do not match your exact calculations. 

    Regards,

    Mike

  • 0 in reply to Mike O'
    Expert 2085 points

    Hi Mike,

    Appreciate it a lot for your reply.

    is that possible to let me know what are the equations you used as a start point? I need to reconfigure the circuit and my result is too far from the values in the schematic as a start point.

     

    thank you,