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UCC28810: UCC28810 Start Up Circuit

Part Number: UCC28810

Hi expert,

I'm designing a high PFC single stage flyback using UCC28810 as the controller. I found that some reference designs use voltage regulation circuit in the start-up & aux winding circuit. 

Due to the limited size of my PCB board, I would like to connect the start-up RC directly to VDD adding a 18V TVS, shown as below. Is it ok for UCC28810? Please help review and give some comments.

  • Hi Joyce,

    Thank you for your interest in the UCC28810.

    You can power VCC directly as shown. However, the drawbacks from the startup circuit in our reference designs is that your initial power up will be ~10x slower (RC time constant =200kΩ x 47uF = 9.4 seconds vs. 20kΩ x 47uF = 0.94 sec) and also that you will be always be burning ~10x more power through R1 = R4 = 100kΩ than if they were 1MΩ. Just be aware of these trade-offs.

    Thank you,
    Ray