Correct use of pnp transistors

My understanding is that I need to use a PNP transistor for high side switching. So far i have tried three different ones (PN2907A, BC327, and 2N4403) with the same result which tells me I have missed something important. I am using a 12 volt power supply to power a .15 amp dc motor. I connect the collector to +12v, the emitter to load to GND, and a 10k resistor from base to GND to make it switch on. After a second or 2, the resistor starts to smoke followed by the transistor popping.
datasheets- PN2907A :http://www.taydaelectronics.com/datasheets/A-108.pdf,
BC327: http://www.taydaelectronics.com/datasheets/A-228.pdf
2N4403: http://www.taydaelectronics.com/datasheets/A-119.pdf
I can understand that i have the transistor hooked up incorrectly ( which i did try reversing it to no avail) but why does the resistor get so hot so fast : V^2 / R = .014 watts << 1/2 watt power rating? and what else am I missing?

No, no, a PNP is the precise opposite, voltage-wise, to an NPN. Take a known circuit for NPN and redraw it flipped upside down - easy.

So the correct wiring: emitter to +12V, collector to load, base via resistor to ground to switch on (but note that this resistor will pull up to 12V when the transistor is off, cannot be controlled from 5V circuit).

Whatever you've done its not what you describe - a 10k resistor is never going to smoke at 12V.

a 10k resistor is never going to smoke at 12V.

  • my thoughts exactly and yet it did on a 12v supply.

(but note that this resistor will pull up to 12V when the transistor is off, cannot be controlled from 5V circuit).

I failed to consider this... I wanted to make an H-bridge out of a couple of extra parts I had so i could control the direction of my DC motor. Looks like it is more trouble to make than it is worth just to buy one.

Transistors are fairly simple: they need more than 0.7v (higher for darlingtons) between their b-e junctions to conduct. The issue with pnp-based high-side switches is usually that the you cannot bring thebase to within 0.7v of the emitter to shut it off.

In those cases, use level shifter, or a zener.

  • my thoughts exactly and yet it did on a 12v supply.

No it did not. It is impossible, you must have misunderstood something. A resistor might have smoked, if so it was either not 12V or not 10K. Work out the maximum power that 12V and 10K gives you. What wattage was your resistor? It is simply not physically possible.

oops wrong resistor- 100 ohm. accidentally slipped one in with the 10k's baggie.

That makes sense now, 1.44W would get a normal 1/4 W resistor to burn up... P = V^2/R

So for a level shifter, I have a 2N2222 switching the base of a PNP which is pulled up to +12v with 360K resistor. It seems to work OK on the breadboard. any unforeseen problems I might have before I connect it to the microcontroller?

You need a resistor in the base of the PNP to limit the current when you pull it low.

http://incredulist.blogspot.com/2012/10/high-side-switching.html

Yep just like that circuit.