Okay. I'm completely at a loss here. I was trying to design a switching circuit for a 3A load (Solenoid) using a photo-interrupter. I got to about here:
But I have no idea what to look for in my parts. I plan to use these as the current limiters, and I have to use this as the photo-interrupter. I was thinking I could set one of the current limiters to the specifications of the photo-interrupter, but I don't know if it would work. (I really hope it would.)
As for the transistor, I was thinking of finding an pnp switching transistor that can carry 3A without overheating, but I've never been transistor shopping before, so I don't know what to look for in the specs. Also, I don't know what to set the current for the… Transistor collector? I was thinking of looking for something that switches at the same input current for the phototransistor, so when current stops flowing through the phototransistor, it goes through the collector.
I plan to have a coil of wire as the load, with a total resistance of about 1.213Ω.
Can anyone tell me if my plan will work? Also, if so, where to look for parts? I tried Ebay and Amazon, but neither have any interactive spec chart for Transistors.
Best Answer
It's not a great circuit. The PNP transistor would not switch on fully so I'd use an NPN with the emitter grounded - this way, current into the base turns the transistor on to about 0.1 volt across collector and emitter and wastes less power.
Having said all that I'd use an N channel MOSFET that maybe switches on to a few millivolts.