I want to confirm if i calculated a base resistor for a PNP transistor correctly. Attached is the schematic
I have an 8550S transistor.
I found a Data Sheet here:
http://www.digchip.com/datasheets/parts/datasheet/670/8550S-D-T92-B-pdf.phpI don't know if it's the right manufacturer or not.
I'm assuming there are 20mA going through the diodes. For the base current calculation, I assumed a beta of 100. So that give me 0.2mA (20ma/100) at the base. I am going to have an Arduino control the transistor. To turn on a PNP I bring the base to zero. I'm assuming a 1 volt drop across the transistor - I got this V
BE in the data sheet, but I'm not positive I picked the right number. That means my resistor has to drop 4 volts at 0.2mA which equals 20k ohms.
As you can see in the schematic, my diodes don't go to ground but to -9 volts. I'm hoping that's not an issue with the circuit working properly.
This is a circuit that already exists and I'm trying to get an Arduino pro-mini (3.3v version) to interface with it. I guess that bring up another question, is 3.3 volts enough to turn the transistor off?
If this isn't going to work, I can desolder the transistor and put in something else in it's place, but I can't change any "wiring" around since it's on a PCB.