Bi-directional Switching using MOSFET

Discussion in 'The Projects Forum' started by DirtyBits, Mar 2, 2013.

  1. DirtyBits

    Thread Starter New Member

    Jul 30, 2011
    Hi there,
    I am working on project which has only one line for Input and Output. Which also requires switching at load current of 500mA to 1A. Basically there are two loads 1. runs on Vin while
    2. runs on battery
    but both use the same wire.
    I do not have much experience with MOSFET and my initial attempt is as follow ;)


    Que: What would be the Output voltage Vout = Vbat - Vds?? = 5V - (Ids*Rds) or 5V - 0.7V ??
    Also is there any readily available chip that can be used for this kind of application?
    Please point out any flaw in the circuit and really appreciate your suggestion/advice on this matter.

  2. crutschow


    Mar 14, 2008
    First off you don't want R3 and R5. The just reduce the gate drive and which causes a higher ON resistance for the FETs.

    Your math is off by an order of magnitude. The ON resistance of the MOSFET is 70mΩ so the source-drain voltage drop at 1A is 70mV not 700mV.

    You circuit just requires two MOSFETs and two resistors. You can't get much simpler than that.