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PWM controller Power Dissipiation

Other Parts Discussed in Thread: UC1844, UCC27524

Hi,

I am using UC1844 in my SMPS design. I am observing the chip is getting hot around 30 deg C rise above ambient, I have 22 ohm series resistor which is common for Turn on and off, if I increase it the power dissipation is reducing however the Mosfet starts becoming Hot. the chip is rated for 1A drive, what is optimum peak current we should consider?

Is it normal for the PWM converters to Run HOT like 30 deg C rise? any method by which we can reduce its temperature.

Regards,

Chaitanya

 

 

  • Hi Chaitanya,
    What is the MOSFET you are using?
    the working frequency? VCC level?
    Based on these information, you could calculate the power dissipation of the driving block.
    If you are using relatively big MOSFET(Higher current, big input capacitance), you may need a separate MOSFET Driver such as UCC27524 to get high efficiency and make the power dissipation on driver and MOSFET lower.

    And how do you produce VCC?

    Br
  • Hi Kening,

    I am using SCT2450KE mosfet, it has fairly low input capacitance 463 pF. 100 KHz switching frequency, 20V Auxiliary supply.
    Can you send me your mail ID so that I can forward you my schematic?

    I have seen TI appnote, www.ti.com/.../PMP10415;tisearch=tidesigns-power#descriptionArea

    The appnote is using the same FET with lower power gate drive chip (25mA as compared to 1A what I have), the temperature rise is similar close to 25 deg C.

    As per my simple calculation it is 7 deg C is expected, what rise have you observed in your designs? I tried changing the Gate Resistor it is not helping that much, same for frequency reduction.


    Regards,

    Chaitanya
  • Hi Chaitanya,My email is Kening-gao@ti.comBr