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UCC28063A: ZCD More Accurate Time Delay Circuit Design

PYTsai
Genius 10255 points
Part Number: UCC28063A

Hi

We are using UCC28063A and would like to use More Accurate Time Delay Circuit (Figure 26 from the datashet)

Any document or tool explaining how calculate below circuit?

Thanks!

  • 0
    TI__Mastermind 34465 points

    Hi,

    The initial component values are derived empirically by measuring the resonant period of the drain voltage.
    You then set the RC time constant of the above circuit at 25% of the resonant drain period.
    For valley switching you need the ZCD signal to reach its minimum value when the drain voltage is at a minimum.

    Because of parasitics in the drain voltage capacitance, pcb layout and noise pickup on ZCD there is no accurate formula for calculating the component values.
    They are derived experimentally.

    By the way I just noticed an error in the above figure 26 from the data sheet.
    The winding is not a CT (current transformer). It actually represents the ZCD winding on the boost inductor.

    Regards

    John