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Original question:

UCC28060: Regarding Transition mode PFC IC UCC28060 PFC Inductor

UCC28060: Regarding Transition mode PFC IC UCC28060 Minimum Frequency

Sachin Khante
Prodigy 50 points
Part Number: UCC28060

Dear TI Team,

What will be the limitation to select Fmin.

In the datasheet application note 300W , Fmin selected as  45KHz. and Calculated Inductor Value =340uH.

1. Is it possible to increase Fmin to 100Khz and Calculate the Inductor , because designing the Inductor with Low switching frequency , size will be increase.

2. If I increased the Frequency to 100Khz for my application then the calculated Inductor = 94uH and the RT resistor value is coming 29.53Kohm from the equation and as per the recommended value                                TSET resistor =( 66.5 to 270Kohm), since resistor value 29.53k ohm < 66.5kohm , as per my understanding I can not go with 100KHz frequency (please confirm)

3.It means the Fmin value is limited by the recommended by TSET resistor (66.5kohm to 270Kohm). (please confirm)

4.During the Inductor Design shall we go for  1/2 Inductor value of calculated inductor . (please confirm)

Thank you.

Regards,

Sachin Khante

  • +1
    TI__Mastermind 40120 points

    Hello Sanchin,

    Thank you for your interest in the UCC28060 PFC controller.

    TI does not recommend using a value lower than 66.5kR for the TSET resistor.  This resistor sets the maximum on-time for the controller and that limits the maximum output power at the lowest input voltage. R-values a little lower than 66.5kR will run into some non-linear effects on the timing and values significantly lower can cause abnormal switching behavior.  Please do not set Rtset < 66.5kR.

    As a consequence, Fmin will probably be lower than you wish for.

    The design equations for the inductor value directly result in the actual inductance for each boost inductor.  Do not cut the calculated value in half.      

    Regards,

    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    Hello  Ulrich,

    Thank you for your quick response.

    There is one doubt regarding Inductor design.

    As per the TI calculator Excel sheet , calculated Inductor = 206uH.

    As we selected the Kool Mu Core.

    Its No load inductance value = 268.45uH.

    And load Inductance = 206.54uH AT 7Apk.

    Could you please share your view for the go ahead of this Kool Mu Inductor for this two phase transition mode  application.

    Thank you.

    Kind Regards,

    Sachin Khante 

     

  • +1 in reply to Sachin Khante
    TI__Genius 9140 points

    Hi Sachin,

    for Kool Mu core, because it has the inductance reduce when increasing the the DC current on the indcutor, so if the calculated inductor is 206uH, we should design the inductor value at its max current condition(usually it is at low line full load and peak line period) to make sure the power supply can output the full power.

    So your design is correct.

  • 0 in reply to David Huang33
    Prodigy 50 points

    Thank you David. ThumbsupThumbsup