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Original question:

UCC2818A-Q1: VFF pin voltage

UCC2818A-Q1: VFF pin voltage range

Gene Qiu
Intellectual 1720 points
Part Number: UCC2818A-Q1

Hi Team,

As I notice on datasheet figure 5, Typical Application Circuit, the Vline is 85-270Vac. From customer requirements, if Vline ranges from 70-280Vac, can the Vff go beyond 4.7V? Or in this case how could customer adjust to use? Customer set 70Vin to VFF=1.4V, while Vin=280V, VFF=5.6V, is there any influence for VFF beyond 4.7V?

Best Regards,

Gene

  • 0
    TI__Mastermind 34465 points

    Hello Gene,

    Most pfc applications are designed for an input voltage range of 85Vac to 270Vac . This corresponds to about  3.2 to 1 range.
    If you operate from an input voltage range of 70Vac to 280Vac the scale corresponds to a 4 to 1 range.

    As you correctly point out the multiplier of the UCC2818A-Q1 must operate within its linear range of 1.4V to 5.6V so that means a system with a 4 to 1 input range will be slightly less accurate than a system with a  3.2 to 1 input range..
    This means that the line transient response and perhaps the harmonics and power factor will be better with the 85-270Vac input than with the 70-280Vac input.
    This is true for any optimized pfc controller that uses an input voltage multiplier.

    I recommend that you use the calculator tool in the design of the pfc circuit 

    Regards

    John