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> In case you are wondering what I am up to, I'm just looking for general
> purpose ways of doing this.  I like to play with banks of LEDs, motors,
> relays, VFD displays, ect and always seem to run into the problem of
> neefing to multiplex a lot of source currents
The last time I needed to do high side swtiching of a voltage higher 
than the pics supply (though neither the voltage or the current was all 
that high current arround 150ma voltage arround 10-15V) I used a circuit 
with two bipolar transistors one NPN one PNP (the transistors I used 
were a 2N3904 and a 2N3906 but the circuit should work with pretty much 
any bipolar transistors). A small schematic is attatched.

Suitable resistor values need to be calculated from the currents and 
voltage conditions the circuit needs to operate under and the current 
gains of the transistors.

Calculation method

(note: when doing this calculation you should use the minimum values for 
Hfe under the conditions you are operating as the values in the 
equations and you should round risistor values down to get real values. V+

IR2 = ILOAD / HFET2
VR2= Vsupply-1 (the 1 needs to be increased a bit if either transistor 
is a darlington)
R2=VR2/IR2
IR1 = IR2/HFE2
VR1 = VLOGIC-1
R1 = VR1/IR1

This circuit as it stands is not very power efficiant especially if the 
load is variable but it should be pretty easy to design a mosfet based 
variant that is (should just  be a matter of doing away with the 
existing resistors and adding a pullup).

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