This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PMP4259: UCC28070 Dynamic load behavior

Part Number: PMP4259


I'm curious about output voltage regulation for dynamic load change between 0%-100% of the UCC28070? Does it have sth similar to burst mode which can not be considered as voltage regulation! EMI and efficiency performance can be reduced at light-(no)loads, but my priority is voltage regulation at dynamic loads. Thank you for your time.

  • Dear Sir,

    UCC28070 is a PFC device; the loop bandwidth of a PFC needs to be lower than
    2x AC frequency, so typically Fco is around 80Hz. Means, dynamic performance is poor.
    But a PFC is typically part of a two stage solution, followed by the isolating DC/DC.
    So the intermediate bulk capacitor provides the needed energy by dropping from
    400V down to 350V in case of load transient.

    If you need dynamic performance in general out of a boost topology be aware that
    energy is transferred to output as switch is OPEN. So in CCM loop bw will be limited
    by RHPZ, a function of magnetizing inductance, duty and load resistance. To improve
    dynamics you could reduce inductance, best is turning into DCM - but peak current
    increases and you have to check AC stress at winding and core losses.
    If DCM is possible just performance of error amplifier (GBw & AOL) and Nyquist
    Criteria (Fsw) will be your limitation.

    Best regards, Bernd

  • Dear Bernd,

    Thank you for your quick response.

    Actually 80HZ Fco seems to be sufficient for our application. What I'm interested in is the behavior of the UCC28070 or PMP4259 design at no-load condition, will it still regulate the output voltage (400V) when there is no current passing through the load? Thank you.

  • Hi Suheyl,

    Yes the power supply will maintain the 400V output with no load.