Two high-side switches, selecting between 12 or 5v

Discussion in 'The Projects Forum' started by BrunoAA, Jul 30, 2012.

  1. BrunoAA

    Thread Starter New Member

    Jul 30, 2012
    Hello everyone,

    I have to switch the power supply of a sensor between 12 or 5v regarding:
    - One of the regulators (12v or 5v) can be switched off.
    - The voltage drop across the switch must be minimal.
    - Maximum of 100mA of load.
    - 3.3v logic control.
    - Must consume very little power.
    - Cheap.

    I think the best/cheap solution for doing this is using high-side p-channel fet's, but the body diodes of the fet's will cause reverse conduction when the 12V is selected to power the sensor and the 5v regulator is on.

    I've made this circuit to prevent this, it will work as well?

  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Lots of parts there... what should the output of this be? 12V or 5V, or do you further regulate it to that 3.3V?

    One neat trick I use is to pick a LDO regulator as the switch element. Many of these come with an enable input which needs very little voltage to switch on, meaning the 3.3V logic signal is just fine as a direct enable control.
  3. BrunoAA

    Thread Starter New Member

    Jul 30, 2012
    Hello ErnieM,

    The output, that is on pin 1 of "SENSOR 1", must be 12v or 5v or open.

    There will be 6 circuits like this one in my board, so I cannot use two regulators for each one, it will be expensive.