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UCC28061: Zero-crossing distortion correction

tateo yamashiro
Guru 10890 points
Part Number: UCC28061

Hi,

We got a question from customer about UCC28061.
Could you help us?

[Question]
- They would like to make sure more detail of zero-crossing distortion correction. Is there any application note, paper reports or something?

- Does this function affect the operation at light load? They are concerned about side effect of this function.

Best Regards,
tateo

  • 0
    TI__Mastermind 34465 points

    Hello Tateo,

    As far as I am aware TI does not have an application note that details this technique.

    However I can describe to you the reasoning behind it and how it works.
    The VINAC pin on the UCC28061 senses a scaled down version of the rectified AC line.
    Around the zero crossings (and especially at light load) the capacitor on the DC side of the bridge rectifier tends to hold up the voltage.
    This means that the AC input will be lower than the rectified DC and therefore the AC line cannot conduct around the zero crossings.
    This so-called crossover distortion will decrease power factor and increase THD.

    TI's solution to this issue was to slightly increase the on time of the MOSFET which helps to discharge the capacitor .
    This will have the effect of decreasing these "dead zone" times. It is a well known and effective method of increasing performance.

    Regards

    John Griffin

  • 0 in reply to John Griffin1
    Guru 10890 points

    Hi, It's been a long time. We got additional question. Could you help us?

    - Does this function be related to COMP voltage? Will the ON time change as COMP voltage changes?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Mastermind 34465 points

    Hi Tateo

    No this function only relates to the VINAC voltage.
    But of course the average ON time decreases as the input voltage increases and it does this in order to maintain the correct output voltage.

    Regards

    John