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Original question:

UCC28951-Q1: RCS calculation

UCC28951-Q1: Magnetization support

Hisao Uchikoshi
Genius 15100 points
Part Number: UCC28951-Q1
Other Parts Discussed in Thread: UCC28951,

Hi Experts,

We add 66uF capacitor on the primary side of transformer to prevent the magnetization. The magnetic flux density is 150mT but it looks the transformer is saturated.

Does UCC28951 compensate the magnetization?

Regards,

Uchikoshi

  • 0
    TI__Mastermind 25570 points

    Hello Uchiloshi-san

    If the UCC28951-Q1 is operated in Peak Current Mode (PCM) control (Resistor at RSUM pin connected to GND) then it will protect against transformer saturation and a capacitor in series with the primary of the transformer is not necessary.

    If the UCC28951-Q1 is operated in Voltage Mode Control (Resistor at RSUM pin connected to VREF) then a DC blocking capacitor is needed to prevent transformer saturation. In your case you are using a 66uF part which sounds a bit too large (I have not done any calculations on this). The paper at  https://www.ti.com/seclit/ml/slup102/slup102.pdf  uses a 1.2uF, 450V part on a 500W 200kHz design.

    It could be that your capacitor is too large - but I don't have an analysis showing what the 'correct' capacitance should be. Most PSFB designs using the UCC28951-Q1 controller use PCM and this is what I would reccommend.

    Regards
    Colin

  • 0 in reply to Colin Gillmor
    TI__Mastermind 25570 points

    Hello Uchiloshi-san

    It's been a while since this thread was active so I'll assume that the issue has been resolved. You can open a linked / related thread if you need any further help.

    Regards

    Colin