Power via low-dropout transistor?

Discussion in 'The Projects Forum' started by nigelmercier, Feb 7, 2012.

  1. nigelmercier

    Thread Starter New Member

    Oct 9, 2010
    10
    0
    I'm constructing a device with a PIC and an opto sensor [OPB760]. This has an operating voltage range of 4.75V to 5.25V, and in total draws less than 50mA.

    My original design had the sensor powered directly from the 5V rail, but it occurred to me that I could power it down when the PIC is in sleep mode. This is where I hit the problem, to keep the voltage above 4.75V I need a transistor to supply the power to the sensor with a voltage drop Vce of less than 0.25V.

    Any suggestions?
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Take a look at logic level power MOSFETS. They have R(on) resistance in the milliohm range.
    Also, please post a schematic of your circuit and a link to your sensor. It might help.

    Ken
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,432
    3,360
    For low drop-out power switch use a pnp pass transistor. High signal on the base shuts off the power. Low signal on the base gives Vce less than 100mV.
     
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