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UCC28180: Calculator Excel Required Minimum Output Voltage Value

Mert Kantarcioglu
Intellectual 390 points
Part Number: UCC28180

Hi,

In SLUC506 UCC28180 Design Calculator Tool, there is a "Required Minimum Ouput Voltage:" value in the section of ouput capacitor. How can I specify this value?

In my design there is a PSFB circuit after PFC and it is designed for 370VDC - 400VDC, according to this specs I tried to enter 370VDC at his area but then output capacitors value is very much. How can I fine tune here?

Regards,

  • 0
    TI__Mastermind 26790 points

    Hello Mert,

    Thank you for your interest in the UCC180 PFC controller.

    The "Required Minimum Output Voltage" refers to the lowest allowable voltage the PFC output must maintain in the event of the loss of AC input for a certain number of line cycles.  This is often referred to as AC Dip or dropout.  The minimum voltage is the minimum value at which the down-stream DC/DC converter can still regulate. The number of line-cycles for the dropout is specified in the next user-entry "Nhold_up".  (This can be fractional-cycles, too, not just whole numbers.)

    In your case the PSFB has a minimum input rating of 370Vdc, however 370V to 400Vdc sounds like a nominal range and it is possible that the true minimum value is lower than this.  Please check to determine what the true minimum input voltage really is to maintain regulation at full power.  The lower this value is, the smaller the PFC-Cout can be.

    Very likely, your nominal PFC output voltage is specified at 380V~390V.  The extraordinarily-high capacitance recommendation for the PFC results from the requirement to keep PFC-Vout > 370V for some number of missing AC line cycles. Minimum capacitance will be at Nhold_up = 0.      
    If you do require some hold-up time, higher capacitance is necessary, however make sure you are using the true minimum input voltage for the PSFB.

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Intellectual 390 points

    Hello Ulrich,

    Thanks for the detailed information. Regards.