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?

 

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

 

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.