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UCC28180: soft start required to control the Inductor inrush current

k.prabhu PRABHU
Prodigy 30 points
Part Number: UCC28180

Tool/software:

Hi TI,

have a nice day.

How to use the soft start limit by IComp pin. to limit the inductor inrush current ?  because Vth(current sense volt ) =0.7v., while turn on the PFC, obiviously takes Vth=1.2v (current sense volt ) .  depans upoon the inductor material and inductance its going huge inrush current. Kindly guide me how to implement the soft start to get inrush current  control?

  • +1
    TI__Mastermind 40550 points

    Hello Prabhu, 

    Thank you for your interest in the UCC28180 CCM-PFC controller. 

    As in all boost-PFC converters, it is not possible for the controller (any controller) to limit the inductor inrush current at initial AC power up. 
    This is because there is a direct DC path from the input bridge rectifier through the inductor and output side to the output capacitor (Cout), and it will charge Cout to the peak of the input line voltage. 

    The UCC28180 controller ( and any boost-PFC controller) is not able to control the current through the inductor until Vout is >/= Vin_peak. 
    Normally, a standard-recovery low-Vf diode is used to bypass the inductor and output boost-diode to charge Cout from the bridge, and an NTC resistor is used to limit the peak inrush current.  In some designs, a relay is used to bypass the inrush-limiting resistor to reduce power loss after the inrush charging is completed. 

    The Typical Application schematic diagram on page 22 of the UCC28180 datasheet ( https://www.ti.com/lit/gpn/ucc28180 ) shows the usual implementation of bypass diode D2 and NTC resistor RT1.  (A relay is not used in this design example.) 

    Regards,
    Ulrich