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Original question:

UCC28070: UCC28070

UCC28070: UCC28070

Jayant Kulkarni
Prodigy 60 points
Part Number: UCC28070

UCC28070 is used in interleaved PFC boost converter in continuous conduction mode. If there is a power interruption for few seconds will the switching MOSFET be short?

  • 0
    TI__Mastermind 40020 points

    Hello Jayant, 

    A power interruption of a few seconds will definitely allow the load on the PFC to pull Vout down out of regulation.  If the UCC28070 still receives VCC during the power interruption time, the low Vout will result in saturation of VAO up to 5V (maximum error voltage).  The UCC28070 will continue to drive PWM output in an attempt to restore regulation.

    When AC power returns, there might be an inrush surge current into Cout if the line peak is higher than Vout.  A bypass diode should be present to shunt this current around the boost inductors to avoid saturating them.  If there is no bypass diode, or one is present but not effective in shunting the current, the inrush surge may exceed the rating of the MOSFETs while the MOSFETs are switching and they can fail.  

    If the line peak voltage is lower than Vout when power returns, then the inductor current should be under control either by max duty cycle or by PKLMT and the peak currents should be within the MOSFET's rating.  

    If AC power will be lost for more than a few half-cycles of the line, then I suggest to cut VCC power or disable the PFC by pulling VSENSE to GND until AC returns. 
    Then re-enable and the PFC will restart with a soft-start.  

    Regards,
    Ulrich