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UC2879: Power Loss Calculation

Ernest Yong
Expert 4315 points
Part Number: UC2879

Hi Team,

I am interested in calculating the junction temperature for this device, and to calculate the junction temperature I need to find the power loss.

I understand that to find the actual power loss, we need to include many things like the conduction loss of the fet, switching loss, current consumption loss and etc...

Here is my question:

1) Do you have any power dissipation calculation guides for PWM controller? I can only find those guides for drivers not PWM

2) By any chance is there any formula(don't have to be very accurate) for us to quickly estimate the total power dissipation? 

3) How do people normally measure/calculate/estimate their power dissipation for PWM controller?

Thank you very much.

Best Regards,

Ernest

  • +1
    TI__Genius 13660 points

    Hi Ernest,

    An estimation of the chip-junction temperature, TJ, can be obtained from the following equation:
    TJ = TA + ( RθJA × PD )...
    where: TA = ambient temperature for the package ( °C )
    RθJA = junction to ambient thermal resistance ( °C / W )
    PD = power dissipation in package (W)

    In which, PD = VDD * I_total,

    The tatal VDD current is the sum of quiescent VDD and the average OUT current.

    the average current can be calculated by 

    Iout = Qg x fsw.

    Qg is MOSFET gate charge fsw is switching frequency.

    Regards,