Choosing a MOSFET for 1A Bypass Switch

Discussion in 'The Projects Forum' started by stryker23, Nov 21, 2011.

  1. stryker23

    Thread Starter Member

    Apr 15, 2009
    13
    0
    I am designing a circuit to be used in an electric vehicle battery management system. I'm basically trying to choose a MOSFET that will bypass 1A of current with a low gate threshold voltage. The total battery voltage will be 3.96 volts (3 NiMH cells). This will provide 1.98 volts to the gate of the MOSFET. An image of the sample circuit is attached. The far right MOSFET is a switch on the IC I am using. It will trigger the external MOSFET.

    The following MOSFET has very low on-resistance and decent power dissipation. My only question is that Id at 1.8 volts is much higher than 1A. As far as I understand this shouldn't be a problem as long as I limit the current across the MOSFET with a resistor above the drain. Do I have this correct?

    First Option:
    http://www.fairchildsemi.com/ds/FD/FDS6574A.pdf


    This is one other option I found. I am afraid it may be to limited by max temperature and power dissipation.
    A second option:
    http://www.fairchildsemi.com/ds/FD/FDG1024NZ.pdf

    Any suggestions would be appreciated.
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    Your first option should work fine. The second option is marginal.

    You want a low on-resistance to minimize transistor power dissipation when the MOSFET is "on". Yes, the MOSFET needs a resistor load in the drain to limit its "on" current.
     
  3. stryker23

    Thread Starter Member

    Apr 15, 2009
    13
    0
    Great. Thanks for confirming that for me.
     
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