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UC2843: tempature rise in flyback topology

Jeff Xie
Intellectual 1780 points
Part Number: UC2843

Hi all,

Customer use UC2843 in the control of flyback power supply.

Spec is: DC 48V input (37VDC~60VDC), output 12V/7A. Working environment: - 40 ~55 C. Because of the sealed environment, the temperature in the chamber may reach more than 70 degrees.

What is the power disspipation and tempature rise in this application?

  • 0
    TI__Genius 13660 points

    Hi Jeff,

    The efficiency of power depends on many factors including transformer design, device selection and PCB layout.

    Considering mentioned power spec and operating condition, it is better to use a heat sink. 

    Regards,

    Teng

  • 0 in reply to Teng Feng
    TI__Intellectual 1780 points

    Hi Teng,

    I want to know the power dissipation of UC2843.

    According to datasheet, it will be VCC*supply sucrrent, is 25mA(IVCC) in datasheet should be used in this case? Thanks.

  • 0 in reply to Jeff Xie
    TI__Genius 13660 points

    Hi Jeff,

    Total VCC current is the sum of quiescent VCC current and the average OUTPUT current. Quiescent VCC current is 0.5 mA. Knowing the operating frequency and the MOSFET gate charge (Qg), average OUTPUT current can be calculated as IOUTPUT = Qg × fSW.   Thus the power dissipation of device is PD = VCC * ( 0.5 + Qg × fSW).
    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)

    Regards,

    Teng