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Original question:

UCC28063: How to change soft start time of UCC28063?

UCC28063: Question about UCC28063's brownout and audible noise.

Gabriel Wang1
Genius 3825 points
Part Number: UCC28063

Dear Expert

1.We set brownout voltage is 150V ,and we test input AC voltage below 150V ,the drive waveform will shut down but then still exist about 200ms ,after that 

the drive wavefrom will shutdown. We don't know why the drive waveform coluld not shutdown all the time.

~Below waveform bule is BUS voltage ,green is Vgs.

2.When we use input AC is higher than 260V ,the C117 behind the rectifier bridge is making noise ,what could be reason?

and we test the Bus voltage and drive waveform.

  • +1
    TI__Genius 9140 points

    Hi Gabriel.

    do you mean at 150VAC when the controller triggers brown out threshold, the controller stops switching and then restart again?

    can you offer me schematic that can be seen clearly?

    for the second question, usually it is caused by not enough votlage between input peak votlage and the output votlage of PFC, can you please increase a little bit of output voltage, for example from 380Vdc to 390Vdc? 

  • 0 in reply to David Huang33
    Genius 3825 points

    1.do you mean at 150VAC when the controller triggers brown out threshold, the controller stops switching and then restart again?

    Yes u are right.

    Full Schemetic。

    Part of the schemetic.

    2. The large capacitance voltage is raised to 410, noise is still generated.

  • 0 in reply to Gabriel Wang1
    TI__Genius 9140 points

    hello Gabriel,

    if you use a film cap behind the bridge and the cap flow through too much high frequency current, it also may cause some noise. In order to decrease the noise, I suggest you add  pi filter after bridge not just a film cap to see whether any difference.

    You can also change the PFC inductor value to change the working frequency in case the noise is from oscillation between the film cap frequency and PFC working frequency.

    for brown our chatter issue, since the vinac sampling point is behind the bridge, it the voltage behind the bridge has a  big oscillation, then it is possible that the controller trigger the brown out threshold and then after 200ms it triggers brown in threshold again.

    please double confirm the Vinac sampling and you can also try increasing C178 to see whether it improves.