low G-S resistance of mosfet

Discussion in 'General Electronics Chat' started by senderj, Sep 11, 2014.

  1. senderj

    Thread Starter New Member

    Aug 25, 2014
    3
    0
    I have a PC motherboard that refused to boot. It has 8 VRMs for Vcore, 2 for Vram, 2 for Vtt and 2 for Vdisplay (CPU's display function). Each VRM use 2 n-mosfet for switching. After it fail and power off, I measure the resistance of G-S of one of the Vcore VRMs and it read 3 ohm. I though it must have been demaged. But when I measure the others, they all has very low resistance in G-S, 3 to 24 ohm. Also, they are slowly rising. Some took just 8-10 mins to become open but some took >10 hours. I don't know if this is normal for mosfet, or all of them are demaged??
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    they are slowly rising because of the high g-s capacitance. out of the circuit they should read as open after a charge up time.
     
  3. senderj

    Thread Starter New Member

    Aug 25, 2014
    3
    0
    I tried to speed up the rising by shorting G & S to varies places but they still go by their pace. Is there any method to shorten the charge up time while they are in circuit?
     
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