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UCC28070A: UCC28070A

user4537791
Prodigy 20 points
Part Number: UCC28070A
Other Parts Discussed in Thread: PMP40261

We are developing a 1200W power supply by using your UCC28070A. the power supply adopts bridgeless PFC construction. There are some unstable AC input current at certain AC input condition (85.8Vac, 104.3Vac, 118.2Vac, etc) when apply full load, the worst condition is at around 85.8Vac and full load, but 83Vac and 87Vac condition become normal. When adjust AC input to 104.3Vac and 118.2Vac condition, there is also sudden unstable (<0.5s) but becomes normal immediately. When apply half load, there is no obvious unstable current any more. We see there is around 500us phase difference between AC input voltage and VINAC pin 5 of UCC28070A, not sure this is a problem. Also we set around 200us dead time (disable PFC gate driver) at AC zero-crossing duration, not sure this is the cause to the problem. Attached file show the schematic diagram and related waveforms, please help to study. Thanks in advance!AC21302LF PFC UCC28070 schematic and waveform comparison.xls

  • 0
    TI__Genius 9790 points

    Hi, E2E user

    The issue you post is under analysis, please expect a response by next Monday.

    YS

  • 0 in reply to Yunsheng Qu
    TI__Genius 9140 points

    Hi E2E user,

    please make sure vinac resistor divider is the same with Vsense resistor divider first.

    and secondly check whether the controller triggers the Power limit function at low line full load condition.

  • 0 in reply to David Huang33
    Prodigy 20 points

    Hi David,

             We have already kept the same divider ratio between VinAC and Vsense. Also there is no power limit issue as 83Vac is ok and even 75Vac is still ok to load.

             As the issue occurs at certain AC input voltage point, whether  there is some step gain setting inside control IC? And it becomes unstable due to gain hysteresis at those certain marginal AC input voltage conditions? We tried to change the divider resistor on Vinac to a little different value, then the unstable AC input voltage also shift a little.

             Thanks advance.

  • 0 in reply to user4537791
    TI__Genius 9140 points

    Hi user4537791,

    if you look at Vinac and AC voltage, there is a very high spike during the current distortion, please double confirm why there is a spike here.

    unfortunately I can see clearly the schematic after zoom in.

    in the datasheet page 21  at paragraph 7.3.10, there is table 1 for feedforwd function. you can refer to it to see whether it can match the distortion you have .

    also you can increase the VINAC pin filter cap to see whether it works.

    I also suggest you can follow PMP40261 as a reference.

    www.ti.com/.../PMP40261