pnptransistors
I've been delving into analog a bit more and am a little confused by a configuration I saw of two PNP BJTs.
I saw two emitters tied together and then their collectors tied together through a resistor. Their bases had different drives. What does this configuration accomplish.
simulate this circuit – Schematic created using CircuitLab
EDIT: I'm not 100%, but I believe in the circuit that I have found the inputs. Apologies if it looks vague. I'm attempting to keep the question simple.
You need NPN transistors like this (1 channel)
PNP transistors will switch up to a positive supply and you have already stated that the controller inputs need to be grounded. 1k2 resistors are fine and virtually any NPN transistor will be fine.
A low output from the arduino does not trigger the NPN therefore it remains open circuit. A high from the arduino turns on the NPN transistor.
Your control pulls the base of Q1 down, so you need to connect a pull-up resistor to it in order to bring it back up as quickly as possible. You will need to pick a value high enough that you don't bleed too much current through M1 when on (since every milliamp through the pull-up, R1, and M1 is wasted), but low enough so that the MPSA92 actually saturates with the voltage created by the divider created by the pull-up and R1 and M1.
Best Answer
If there are no other power supply connections, then they might be some sort of protection circuit, using the back-to-back BE junctions as crude zener diodes.