Activate BJT with Digital HIGH

Question

Hi all. It's been a while since I studied transistors and I'm having a bit of trouble adapting my needs to the theory of transistors. Specifications for transistors detail the voltage across combinations of the collector, base, and emitter of the transistor. However, my need and thought process is based on the indepentent voltage on each pin of the BJT. My need is to switch a +12V supply completely on or off (trickle current is not a problem, though; we're not being idealistic) using a digital HIGH on the base (I'm planning on using an Arduino Uno, so if someone knows the characteristic voltage of a HIGH on the Uno's digital I/O pins, assume approximately that). Is a BJT appropriate for my needs? Can you think of or suggest a BJT that approximately meets these specifications?

Catwell · Answer

You might want to use a relay that completely cuts off the input power instead. Even if you use a BJT, some power will leak through. Usually it is not enough to cause any issues, but I personally like to cut the power completely off. (Safety issues) Is this 12V a DC source? Cabe

e14 Contributor · Answer

You can use opto couplers. PS7206-1A-E3-A PS7206-1A-E3-A can handle 28volts, 600 ma for my application. The switching speed would be better than the relay. A BC547 NPN should work with your 12 volt source, but it can dissipate a lot less power. Alternately you can use ULN2803

e14 Contributor · Answer

You can use this particular part as well : TN2-L2-4.5V TN2-L2-4.5V . You do require a driver for it though. We use PCB mounted relays with contact rating of 1amp from OMRON and O/E/N. You can try those manufacturers as well.