I'm struggling with a NPN transistor switching problem, and in the process I've burned out a board elsewhere in my machine. Electronics is not my strong suit. I want to use a 5V signal to switch 12V. Problem is that the grounds between the 5V and 12V are not close in potential. They are about 7V apart, so I cannot connect them. I have the circuit configured like this:
Which, based off of my research on this site - should work right? And it did work for a period of time! A board that I'm drawing my variable voltage from got fried somehow down the line though.
Are there any dangers to setting the circuit up as such? I feel like some excess current/voltage got drained into the variable return - messing something up down the line. Or maybe it was that I'm only using the high line from the power into the circuit (return line not attached to anything?).
When I get my board back from repair, I want to retest this configuration but with some sort of safeguard installed to protect the other components in the machine. What suggestions are there for this?
I'm very concerned about the potential difference (about 7V) between the negative line on the power, and the negative line on the variable. On most examples I've seen recommended (necessary maybe?) that the grounds be connected somewhere in the circuit.
Could be that this is indeed correct! And that I burned my board while going through the experimentation process that led me to this haha.
NOTE: diagram is wrong. I'm using R1 = 500 Ohm, R2 = 1k Ohm