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UC3825A: Heating of the IC UC3825

Skanda rama
Prodigy 170 points
Part Number: UC3825A
Other Parts Discussed in Thread: LM5045, UCC28950

Hi,

   I am using UC3825DW IC for PWM generation at 350kHz for resonant full bridge inverter . This is operated at 17volts ac. Rc=1.39kOhms and Ct=1.22nF. This IC getting heating up very much. Results in frequency tarts at 362kHz-365kHz and reduces to 352 kHz over a period of operation in 5 to 10 minutes. This frequency variation is becoming a problem since overall unit operating time gets reduces due to input dc voltage variation. How t o reduce this tolerance. I am unable to control the gain of the inverter.I have attached the my IC circuit diagram for your reference.

  • 0
    TI__Mastermind 34465 points
    Hello Skanda Rama,
    Sorry about the delay in answering your question.
    Here are a few items to look at:
    (1) 17V is the max value of the UVLO for this ic
    You should investigate starting the ic from a higher voltage and then reduce VCC to 12V or so for normal operation
    (2) Use a gate driver ic to interface to the full bridge

    The oscilator is specified with a frequency range of 6% over temperature.
    You are getting 3.5% which is reasonable.
    You will get a more stable frequency is you can control the temperature of the device

    So you can investigate items 1 and 2 above, heatsink the ic or use a phase shift resonant controller such as the LM5045 or the UCC28950.
    Regards
    John
  • 0 in reply to John Griffin1
    Prodigy 170 points

    Hi John,

       I am using SG3626 and gate driver transformer for driving the mosfets. Please suggest any other solution.

    Regards,

    Skanda

  • 0 in reply to John Griffin1
    Prodigy 170 points
    Hi John,

    I am using SG3626 and gate driver transformer for driving the mosfets. Please suggest any other solution.Also I changed supply from 17 to 12 volts.
    Is there variation in temperature rise from IC to IC?

    Regards,

    Skanda