I'm trying to drive logic-level PNPs through a shift register from the arduino. The PNPs are switching from an 11v source, but i don't think i can drive them unless i've got the signal coming from the shift register at the same voltage and i've been told that I can use an NPN transistor to both level shift and amplify the signal to a higher voltage so that the PNP can be driven. Can someone explain this to me?
The arduino output is 0/5V. With the PNP emitter at +12V and its base connected to the arduino output, the base will always be more negative (less positive) than the emitter and therefore forward-biased (C_E in conduction) either way. The solution is to get the PNP base a lot closer to its emitter to get it to turn off.
This schematic uses 24V, but just change that to 12V in your head, same difference.