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UCC28C42-Q1: Output voltage for the inputs lower than the designed range

Ajmal T
Intellectual 420 points
Part Number: UCC28C42-Q1
Other Parts Discussed in Thread: UCC28C42, PMP10833

Hi,

For a flyback converter with UCC28C42 IC designed for the input range of 30-212VAC and output of 14VDC/6A, What will be the output voltage for the following inputs?

1. Vin = 25VAC, load=2A, Vout=?

2. Vin = 20VAC, load= 1A, Vout=?

3. Vin= 15VAC, load= 1A, Vout=?

4. Vin=10VAC, load=1A, Vout=?

Please some one help me. You can refer the design with you have for the other operating limits and can check the output for lower input level than the designed range.

Thanks and Regards,

Ajmal T

  • 0
    TI__Expert 7080 points

    Hi Ajmal,

    UCC28C42 is a fixed frequency controller can support CCM operation. the maximum duty cycle is 96%  and VDD_ON is 14.5V , VDD_OFF is 9V.

    Since you didn't specified a transformer design ,  I assuming transformer turn ratio Nps is 9 , so reflected voltage Vreflected is around 126 . the duty cycle at 30Vac_in is 0.75 , even at 10Vac input , The duty cycle is 0.9 , still less than 0.96 . so generally speaking you can still get a regulated output voltage ,, once the voltage drop to let duty cycle larger than 0.96. output voltage will drop . but please note that the VDD_ON voltage is 14.5V , if you turn on the converter at 10Vac_in , the VDD can not be charged to 14.5V. the converter can't start up.

    Due to the turn on delay of FET , the effective maximum duty cycle maybe smaller than 0.96 a little.

    Thanks.

  • 0 in reply to Jaden Ning
    Intellectual 420 points

    Hi Jaden  Ning,

    Thank you very much for the clear explanation.

    As per the Webench tool, the Np/Ns=16/6=2.67. So VR is 39V. So the Dmax at 10VACin will be ~0.8. So I can get regulated output. Am I right?

    I have noted the VDD_ON and VDD_OFF voltages. As per the requirement my design should work from 15VAC onwards.

    Regards,

    Ajmal T

  • 0 in reply to Ajmal T
    TI__Expert 7080 points

    Hi Ajmal T,

    Yes, you can get a regulated output if the maximum duty is ~0.8. and the small turn ratio is avoid the controller running at a so high duty cycle.

    please note that the small turn ratio requires a high voltage rectifier diode or SR FET on secondary side  when input voltage is 212Vac.

    Thanks .

  • 0 in reply to Jaden Ning
    Intellectual 420 points

    Hi Jaden,

    Thanks for the clarification. This clarifies my doubts.

    Can you please suggest a non-isolated converter design for my requirement. I don't want to use a transformer in the design. There is no isolation requirement.

    Regards,

    Ajmal 

  • 0 in reply to Ajmal T
    TI__Genius 13660 points

    Hi Ajmal,

    Sorry for the delay response.

    In my view, I wouldn't like to recommend you to use a non-isolated topology for this spec.

    If you prefer non-isolated topology, a buck solution with UCC28C42 for your reference.

    https://www.ti.com/lit/df/tidrg53/tidrg53.pdf

    Regards,

    Teng

  • 0 in reply to Teng Feng
    Intellectual 420 points

    Hi Teng,

    Thanks for the suggestion.

    I am working on the redesign of the PMP10833 Design using UCC28C42 for my requirements.

    Regrds,

    Ajmal