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PMP4478: Valley switching

Baskaran M
Prodigy 75 points
Part Number: PMP4478
Other Parts Discussed in Thread: UCC28740

How to control the valley switching  330pf 1A--00000.pdf

  • 0
    TI__Prodigy 660 points

    Hi,

      You can refer to data sheet "7.3.2 Valley-Switching and Valley-Skipping" of UCC28740 to know how it work. Basically, in fly back converter, it store the energy in On-Period. deliver the energy to output in Off-Period. When you work in CV. It should be maintain the output voltage by store energy again before Off-Period output voltage drop to out of specification. Before that, "valley switching" will be choice from Pin_VS(Pin2).

    So, the valley switching is decided by the main regulated output voltage/current. You can refer to your waveform, I guess the voltage/current of main regulated should be changed. So the frequency is change too.

  • 0
    TI__Expert 4750 points

    Hi Baskaran,

    You can either modify the current sensing resistor value, or transformer inductance to adjust the valley switching point. Please note that UCC28740 controller is designed to operate at discontinuous-conduction mode (DCM). Thus, you will have to make sure at minimum input voltage and maximum load, the converter is still operated under DCM.

    Regards,

    Sheng-Yang Yu