PMOS Switch (high side switch)

Discussion in 'Analog & Mixed-Signal Design' started by Qual, Oct 18, 2017.

  1. Qual

    Thread Starter Member

    Aug 5, 2016
    Hi All,

    I want to switch on / off a 1A load, so using P-Channel Mosfet and gate is connected to 3.3V MCU .

    When MCU sends Gate = 1 Mosfet is OFF.
    MCU sends Gate = 0 Mosfet ois ON.

    Here source is connected to +5V so when GATE = 0 the load is suppose to be on and should get +5V and current flow of 1A to it.
    i have doubt on switching on mosfet using MCU, ( Gate = 0) is there any thing i should take care.

    VGS is suppose to be -ve , i am using only 5V, 3.3V

    How i am suppose to select p chaneel mosfet with these requirement
    Last edited: Oct 18, 2017
  2. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    The VGS will be -1.7V when the MOSFET should be off. That means that the minimum gate threshold voltage should be greater than or equal to 1.7V.

    The VGS will be -5V when the MOSFET should be on. That means that the MOSFET should be able to pass 1A with very low VDS. Check the VGS at which RDSon is specified. If it is 5V or less it will do fine. If not that MOSFET still might be OK. You will need to check the performance graphs in the datasheet carefully.
    Qual likes this.
  3. crutschow


    Mar 14, 2008
    It would be better if you added an NPN driver transistor to control the gate voltage.
    That way the gate can go from 0V (fully ON) to 5V (fully OFF).
    You still need a logic-level P-MOSFET that turns fully on at a Vgs of -5V.
  4. Qual

    Thread Starter Member

    Aug 5, 2016
    Well i thought same but doubtful on choosing MOSFET:confused: as need to on/off load ( 5V , 1A) so prefer for high side.
  5. dl324

    AAC Fanatic!

    Mar 30, 2015
    It's still a high side switch:
    Qual and GopherT like this.