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UCC28070 Output power limit

Pero Ceklic
Prodigy 10 points
Other Parts Discussed in Thread: UCC28070

We are making the PFC with the UCC28070 controller and we are facing a problem with the power limiting on the 115 Vac power supply. We made the PFC with the power limitation on 4800 W on 230 Vac power supply, but we are not able to limit the power on 115 Vac. Is one R sense resistor enough for both power supply, or it is necessary to have two different R sense resistors for 230 Vac and 115 Vac power supply? Should the same resistor limit the power on 4800 W for 230 Vac power supply and limit the power on 2400 W for 115 Vac power supply? We are not able to limit the PFC on 2400 W on 115 Vac. Instead, it goes over 3000 W and it is not working properly. Is there anything else which affects power limiting?

Best Regards,

Pero

  • 0
    TI__Mastermind 34465 points

    Hi Pero,

    The resistor that you select on the IMO pin (RIMO) sets the power limit capability of your circuit.
    Only one resistor sets the power and this power is the same at 155Vac and 230Vac if your circuit is otherwise functioning properly.
    Page 21 of the data sheet describes how this is accomplished. The line current directly tracks the signal on RIMO and this signal is directly proportional to VINAC and inversely proportional to KVFF. (Equation 13)
    KVFF is directly proportional to  the square of VRMS and so IMO is inversely proportion to VRMS.
    This is what you need to achieve a constant power limit with a variable line input.

    I suggest that you use the calculator tool for the UCC28070 and check that the calculated values are in agreement with the values in your circuit.

    John Griffin

  • 0
    TI__Mastermind 40580 points
    Hello Pero,

    I have notified the group associated with this part to address your questions.

    Regards,
    Ulrich