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Original question:

UCC3817: Hold up time

UCC3817: design of 1.5kw Boost pfc

Bharat Upadhye
Prodigy 80 points
Part Number: UCC3817

hello, 

can you please provide detail (How to design) of vcc supply design (Red circled portion) in below mentioned attachment of Application of UCC3817 (datasheet)

http://www.ti.com/lit/ds/symlink/ucc3817.pdf

thank you

Regards,

Bharat

  • 0
    TI__Genius 13660 points
    Hi Bharat,

    Here I just wanna analyze the work process of this self-powered circuit. Then you can design by yourself and try to simulate in the simulation software to deepen understanding.
    First, input ac (Vline) is connected, the voltage after the rectifier (D3) charges the C10 and C11 passing R15 and R18. Once the charged voltage connected to VCC achieves the startup voltage IC works, VCC will have little voltage drop. Then the voltage of C10 connected to VCC is supplied by transformer L1. The ripple of the C10 voltage is filtered by C10 and C11. So the value of C10 and C11 are designed with consideration of startup supply ability and filter ability.

    Regards,
    Teng