So I was playing around with slapping two transistors together to make a darlington and I have come across a really weird issue. For all transistors that I use, the darlington only behaves as it should when one or both transistors are put in "upside down".
For instance, if I am using two NPN transistors: When both their collectors are facing "upwards" and connected to the load/resitor that is between them and the power rail - they don't conduct. Nothing gets through. However, when I flip one of them round so the emitter is "upwards" it works. It doesn't matter which one. Actually it can be both! Why is this?
I thought I had labeled my transistors wrong, but I hadn't. I am running into this with all of my BJT transistors. I have double and triple checked datasheets to make sure I don't have the pinout mixed up. When I use a transistor individually though, it behaves like expected.
I should note that I came across this making a bazz fuss, so I am wondering if it has something to do with the collector-base diode in that design?