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Protecting against over volts when fitting a buck regulator controller. Good Idea?

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    Protecting against over volts when fitting a buck regulator controller. Good Idea?

    Hi guys
    Here is a general question and I would like to hear your thoughts on it

    I've just replaced a very small 11 contact MP2329 QFN on a motherboard

    This supplies 1.8V STBY to the PCH - but the faulty one was only giving 0.7V

    Anyway I fitted it, but it is very close to the DIMM sockets and I can not clearly see down one side of it to make sure it has soldered properly ,even shining a torch down there. The other sides look OK under the microscope and also in a jewellers loop. This is the side that has two resistors that set the output voltage

    Datasheets on this thread
    https://www.badcaps.net/forum/showthread.php?t=95281


    So I was wondering if it is possible to have a fault (or bad soldering) on a buck regulator where the output voltage goes too high. Mine has 3.3V input which it drops to 1.8V. As I obviously don't want to trash the PCH I wondered should temporarily connect a 2V zener on the output capacitor side of the inductor, such that if the voltage goes above 2V it shorts it out.

    So what are your thoughts on that, a good idea or am I just being paranoid?

    Rich
    Attached Files
    Last edited by dicky96; 04-30-2021, 07:39 AM.
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    #2
    Re: Protecting against over volts when fitting a buck regulator controller. Good Idea

    if you where using a buck/boost in your own circuit then a big zener may be wise,
    but this circuit has been designed and then sold in numbers - so it's obviously reliable.

    Comment


      #3
      Re: Protecting against over volts when fitting a buck regulator controller. Good Idea

      Originally posted by dicky96 View Post
      Hi guys
      Here is a general question and I would like to hear your thoughts on it

      I've just replaced a very small 11 contact MP2329 QFN on a motherboard

      This supplies 1.8V STBY to the PCH - but the faulty one was only giving 0.7V

      Anyway I fitted it, but it is very close to the DIMM sockets and I can not clearly see down one side of it to make sure it has soldered properly ,even shining a torch down there. The other sides look OK under the microscope and also in a jewellers loop. This is the side that has two resistors that set the output voltage

      Datasheets on this thread
      https://www.badcaps.net/forum/showthread.php?t=95281


      So I was wondering if it is possible to have a fault (or bad soldering) on a buck regulator where the output voltage goes too high. Mine has 3.3V input which it drops to 1.8V. As I obviously don't want to trash the PCH I wondered should temporarily connect a 2V zener on the output capacitor side of the inductor, such that if the voltage goes above 2V it shorts it out.

      So what are your thoughts on that, a good idea or am I just being paranoid?

      Rich

      Using Zener for clamping the output of the power supply is pretty common, you see that is used in lots of AC-DC 5V power supply, they will have 6.2V zener. Typical Buck converter has switching MOSFET in series with inductor which is connected to the output, if MOSFET shorted out then the input Voltage will be dump to the output and it can really ruin lot of part due to over Voltage.
      Last edited by budm; 04-30-2021, 02:20 PM.
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      Comment


        #4
        Re: Protecting against over volts when fitting a buck regulator controller. Good Idea

        Yeah I do know it is fairly common to see this in devices. Also crowbar circuits using a zener plus thyristor or similar

        @stj
        I know this circuit is designed to work correctly/reliably. I was more concerned that a fault in my soldering of the replacement QFN could cause a dangerous condition for the load (in this case the Northbridge/PCH)

        This is why I wondered if it would be good practice to use a zener as a safeguard (and hope it goes short in a fault condition rather than open)

        Or even build a little reusable circuit with a zener plus a transistor or FET or something that could be strapped across any voltage rail and set to protect it in this sort of situation of basically faulty workmanship in case it occurs. Even an Arduino circuit or whatever, though it would have to react fast.

        Or maybe as I said in the OP, I am just being paranoid
        Last edited by dicky96; 04-30-2021, 03:49 PM.
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        Comment


          #5
          Re: Protecting against over volts when fitting a buck regulator controller. Good Idea

          well... if u had a known good working board, u'd be able to probe and measure the mosfet's gate, drain and source legs to see the normal proper resistances of each and then compare those readings to the board u just worked on. that way u'd know if u soldered it on right or not.

          Comment


            #6
            Re: Protecting against over volts when fitting a buck regulator controller. Good Idea

            @chaoslegionnaire
            Yes that is true, but I don't have. I have another motherboard with same chipset but it does not use the same voltage regulators

            It seems to me two options

            1. Plug it in and turn it on
            2. Take some sort of precautions

            Rich
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              #7
              Re: Protecting against over volts when fitting a buck regulator controller. Good Idea

              Have confidence in your work. Plug it in and turn it on.

              Comment


                #8
                Re: Protecting against over volts when fitting a buck regulator controller. Good Idea

                Tried it and I now have 0.2V output and no Vcc

                I'll try again, I ordered a pack of five spares as the parts were much cheaper than the postage was LOL
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