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SI4812BDY-T1-E3CT-ND more robust version

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    #1

    SI4812BDY-T1-E3CT-ND more robust version

    So I have had several Acer 7736z laptops with a shorted U60 mosfet lately. Some of the new mosfets have shorted immediately after I've replaced them, some of them are still running. I would like to find a more robust version of the same part. The part I have been using is a SI4812BDY-T1-E3CT-ND. Anybody know a better replacement?
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    #2
    Re: SI4812BDY-T1-E3CT-ND more robust version

    shorted immediately after I've replaced them
    Are you taking proper ESD precautions?

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      #3
      Re: SI4812BDY-T1-E3CT-ND more robust version

      With the first two that died, yes. Plus, they lasted for a few days each. The last one that died I did not. It was on a board I picked up off of ebay. Lasted all of about a second.

      Whatever this defect is I'm guessing it may be caused by a bad SMD chip somewhere up the line, but I can't find it and most of the time the laptops seem to work fine after a MOSFET replacement. I'd like to find a new fet with the same specs but less sensitive.

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        #4
        Re: SI4812BDY-T1-E3CT-ND more robust version

        The effects of ESD damage don't always show up right away.

        How they end up shorted can give a good clue as to whether it's ESD or not --- if the gate is shorted to source/drain that is a very good sign of ESD puncturing the gate oxide.

        Looking here you can see all the Vgs don't go over 25V so you're unlikely to be able to get a "more robust version".

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          #5
          Re: SI4812BDY-T1-E3CT-ND more robust version

          Source was shorted to drain on every one. Gate was closed. This happens on every MOBO in this laptop I've had to repair so far. I was unsure if maybe I should get a replacement without the schlottky diode? Maybe one with a higher amp diode?

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            #6
            Re: SI4812BDY-T1-E3CT-ND more robust version

            Source was shorted to drain on every one. Gate was closed.
            In other words, there's infinite resistance between the gate and source/drain, but 0 resistance between source and drain (both ways; remember a normal one has a body diode)? That suggests a drain-source overvoltage. You could try one with a higher Vdsmax than 30V, but the diode is mandatory and intrinsically part of all MOSFETs.

            This document has some interesting pictures and discussion:

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              #7
              Re: SI4812BDY-T1-E3CT-ND more robust version

              Precisely. Yes, it goes both ways. This suggests to me that the diodes are being severely overpowered. I was thinking that one higher than 7A (I think that's what my replacement used) would be better at preventing this from happening in the future. What do you think?

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                #8
                Re: SI4812BDY-T1-E3CT-ND more robust version

                I'm thinking about using this one instead. Thoughts?

                http://www.mouser.com/ProductDetail/...KZgFl3gEhVI%3d

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                  #9
                  Re: SI4812BDY-T1-E3CT-ND more robust version

                  That has a higher current rating and lower Rdson, but if the previous ones died of drain-source overvoltage (inductive spikes? this is a laptop so the PSU is already around 20V, 30V isn't much higher) then it won't be any different - this one is rated for 30V too.

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