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UCC38503: UCC38503 : AC input current settle time too long when start up

Ginger Lin
Prodigy 100 points
Part Number: UCC38503

Hi TI :

I use UCC38503 for 200W/12V power model with forward & PFC structure. I use 220Vac input & E-load(2A CC mode) to test the power model. But the waveform showed that the PFC spend 600ms from 12V established to Iac become stable. This current was too high and some noise occurred form inductance or transformer. How could I speed up the start up process. 

thank you

  • 0
    TI__Mastermind 31580 points

    Hi Ginger

    We need to zoom into the first couple of cycles on the AC line line current as the PFC choke may be saturating during the start-up of the 12V output.

    Please also measure the voltage on the PKLIMIT pin as well.

    Thanks

    Peter

  • 0 in reply to Peter Meaney
    Prodigy 100 points

    Hi Ti

    Today, when I take  the power model  out the metal case (iron case) to measure the signal. It became work normally. And the abnormal AC input current waveform showed again when I put the power model into case. I guess some disturbance affected the PWM IC when start up. I will do some experiment on Y capacitor. 

    Thank you 

    out of case

    in the case