I'm looking to build a circuit where current only flows when there is a potential difference across the entire circuit of more than 12 volts (+- 0.1 V). I also need there to be only a small amount of resistance across the part of the circuit that controls whether current will flow, in order to prevent overheating. I'm not sure what I should use to control this; I was thinking of using a zener diode, but cannot find any with a forward voltage above 7V. I'm thinking that there might be some other type of semiconductor I could use, but I'm not sure what it would be. Perhaps I could use a zener diode but put it in reverse orientation rather than forward? I'm not sure how much resistance that would add however. What would you guys recommend using?
you could do this perhaps, I've drawn it rotated 180 degrees from your diagram.