Dave-

The emitter will see the same 5v supply that's going to Vdd on the PIC. I want to use a single transistor to turn on and off some downstream components.

After reading more about BOR and using MCLR, I'm not going to use the same transistor to switch the supply to the PIC itself anymore.

So it's basically just a PNP on the supply side of several downstream components. As those components are spread out a bit and my board space is super limited, I wanted to switch them all with 1 transistor (well within it's power rating), rather than putting NPN's on the ground side of all the components or having to route ground traces everywhere.


Right now I've got the schematic like this......


{5v Supply} ----------------------- {PIC}
|
|
-------------{NPN}------ collector to downstream loads --->
|
|----- base via a 2k resistor direct to PIC pin set as Output


I've seen this setup in several other schematics and never saw a diode in there - maybe that's only required if driving the pic's supply itself as I stated in my OP?

When the Pic boots up, it'll bring that pin low to turn on the downstream stuff, then before "shutting down" it'll bring it high then sleep which will bring it's MCLR low as well as pulling Vdd below the BOR - so it should be shut all the way down.

What I don't understand is why that pin (to the PNP base) doesn't drop back to ground when the PIC goes into reset. I've tried it with an LED being sunk, and the LED does go out as soon as the PIC shuts down, so it would seem that reset does not cause all the output pins to click back to ground.

Can someone give me a warm fuzzy that this is correct? I don't want a PIC in reset to allow a pin to float back down to ground (after being in reset for say - a week or two), and all of a sudden that PNP comes open again and powers up all the downstream stuff without the PIC being alive. Nothing really bad would happen except it would quickly kill the limited onboard battery supply.

Thoughts?

Thanks!!