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UCC28070A: Power versus mains

user3863678
Prodigy 10 points
Part Number: UCC28070A

Hello

I am designing a 1500W PFC based on UCC28070A. Requirements are 1500Watt from 120VAC to 264VAC, below 120VAC i use peak limit to limit power. The problem is that from 230VAC to 264VAC the output power goes from 1500watt to approx 2000watt at 264VAC.

The VinAC resistor divider places 120VAC at 1.3V corresponding to level 3 (Table 1 in datasheet) and 230VAC at 2.5V corresponding to level 7. This gives a power limit at aprox 1550 W which is fine, but when increasing the mains voltage, it does not seem transit to level 8 which should happen at 240VAC, so power limit just increases with the square of the voltage (264/230)^2=32% >2000watts which is way to much.

What can be the issue?

Claus

  • 0
    TI__Mastermind 40530 points

    Hello User3863678,

    Thank you for your interest in the UCC28070A PFC controller.

    Per Table 1 of the UCC28070A datasheet (page 21), in order to reach Level 8, the peak of the VINAC signal must exceed 2.6V.
    Please check the amplitude of the signal at the VINAC pin at 230Vac and 264Vac.  It is possible that the signal peak may be clamped or rounded off before it can reach 2.6V.  Also check your divider to verify that the ratio is providing the correct VINAC amplitude that you expect from a given line peak.  

    Regards,

    Ulrich