Bn44-00623B pfc mosfet very hot

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  • alltvrepairs
    Badcaps Veteran
    • Jan 2014
    • 211
    • Malta
    #1

    Bn44-00623B pfc mosfet very hot

    Hi,
    Found pfc mosfet Qp802c shorted. Replaced together with Pfc ic and blu ceramic caps.
    Now pfc is working at 388v. However the heatsink is too hot to the touch. Have compared most values with a scrap o
    Pcb and consulted circuit.

    Any tips on this common board?
    I have the 46 model.
    The 42 is Bn4400622b with same pfc circuit.

    Thanks.
    Tags: None
    • R_J
      Badcaps Legend
      • Jun 2012
      • 9515
      • Canada
      #2
      Re: Bn44-00623B pfc mosfet very hot

      How was QP802C shorted? was it shorted D~G ? if it was you may have damaged the gate drive components, likely a shorted diode. Also check if there is a zener diode off the IS pin of the drive ic that may be shorted
      On the BN44-00622b schematic, check dp806,rp804,rp805 and zdp801, Check that dp803 or dp805 are not shorted.
      Did you replace the mosfet with the same part number?
      Last edited by R_J; 06-25-2022, 12:25 PM.

        Comment

        • alltvrepairs
          Badcaps Veteran
          • Jan 2014
          • 211
          • Malta
          #3
          Re: Bn44-00623B pfc mosfet very hot

          I have swapped twice mosfet with an identical from another board. Mosfet was shorted drain to source. Have already checked those components but will try sgain desoldering diodes just in case.
          Tks

            Comment

            • alltvrepairs
              Badcaps Veteran
              • Jan 2014
              • 211
              • Malta
              #4
              Re: Bn44-00623B pfc mosfet very hot

              Attached Files

                Comment

                • dskall
                  Badcaps Legend
                  • Oct 2016
                  • 2905
                  • usa
                  #5
                  Re: Bn44-00623B pfc mosfet very hot

                  Do you have an oscilloscope to check gate drive is turning gate off?
                  I assume no responsibility for any stupid suggestions I might post.

                    Comment

                    • alltvrepairs
                      Badcaps Veteran
                      • Jan 2014
                      • 211
                      • Malta
                      #6
                      Re: Bn44-00623B pfc mosfet very hot

                      Yes i have oscilloscope. Tbh its been a while since i last used it.

                        Comment

                        • dskall
                          Badcaps Legend
                          • Oct 2016
                          • 2905
                          • usa
                          #7
                          Re: Bn44-00623B pfc mosfet very hot

                          I would have to think one of the components on gate drive or CS is out of spec. Not allowing fet to completely turn off and on. You do have to isolate your ground to check gate drive with oscilloscope.
                          Last edited by dskall; 06-26-2022, 10:11 AM.
                          I assume no responsibility for any stupid suggestions I might post.

                            Comment

                            • alltvrepairs
                              Badcaps Veteran
                              • Jan 2014
                              • 211
                              • Malta
                              #8
                              Re: Bn44-00623B pfc mosfet very hot

                              HI,

                              I have replaced most of the Gate driver compoinents and others as highlighted in pdf attached.
                              I have scoped both the bad board and a good one I have as spare. There is a slight frequency difference as both settings where the same.

                              Offset 0V

                              Bad board Gate pin

                              Good board Gate pin

                              Highlighted schematic


                              Still no progress.
                              I am trying the board on its own now on the bench. Still heats up, a bit less due to less load but still more than the good one.
                              Any clues?
                              Attached Files

                                Comment

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