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UCC28730-Q1: DC INPUT

rick Yu
Prodigy 120 points
Part Number: UCC28730-Q1
Other Parts Discussed in Thread: UCC28730,

Hi Madam/Sir,

We want to design a isolated power regulator from a high DC input up to 300V.

I download a SLUC579_UCC28730 Design Calculator excel file from TI website , it is designed for AC input,

When I set the line frequency to 0, many cell will show invalid, can you please share a new design calculator for DC input?

  • 0
    TI__Intellectual 2430 points

    Hi Rick,

    You can refer the Webench or datasheet equation for DC input application.

  • 0 in reply to Adam E2E
    Prodigy 120 points

    Yes, I am trying to understand the operation fundamental, I don't understand below two parameter and equations:

    1. DMAGCC is defined as the secondary diode conduction duty cycle during constant current, CC, operation. In the
    UCC28730-Q1, it is fixed internally at 0.432.  I don't under stand it seems a parameter related with transformer secondary side, but why it is fixed value internally by controller ?  what is the difference between it and primary MOSFET duty cycle? Is there any detail explanation about it ?

    2. I don't understand Vccr and its defination "Constant-current regulation factor", what is it?

    3. In page12, Rcs=(VccrX Nps) square(η)/2xIocc, I don't understand how this formula , can you explain more detail?

    BTW, I want to attach the design for review, but I don't know how to attach file

  • 0 in reply to rick Yu
    TI__Guru 72635 points

    Hello,

    1. DMAGCC is the transformer demagnetizing time over the switching period when the device is operating in critical conduction.  When selecting the transformer turns ratio this should be 0.423.  Equation 10 in the data sheet will show how this relates to Dmax.

    2. VCCR = 0.319V, Constant-current regulation factor. Nps = primary to secondary turns ratio.  Iocc = output current in constant current mode.  Rcs is the current sense resistor.   The square root of the transformer efficiency term.  I am not sure how this equations was derived.  However in general practice the efficiency of the transformer is around 0.96 to 0.97.

    Reards,