So it appears I know how a lot of things work but I can never actually MAKE them work when I build them. Here's about the most simple NPN switching circuit you could imagine. I was just fooling around with this Breadboard Companion(tm) thing which has a 555 IC on it (which I might use for a PWM circuit) which controls an output pin, called Clk, which has a duty cycled controlled by a trim pot on the board. Here's my circuit: Code: 470 LED |----/\/\/\/------>|--------||| Clk | 5v 5k C / o-----------/\/\/\/-----------B| E \ | | | o 12v See anything wrong with it? No? Yeah, neither do I. The LED switches on and off just fine, with the exact same duty cycle as the LED on the companion PCB. But here's what I don't get - The voltage drop across the NPN transistor is around 8 or 9 volts...leaving the collector output to be only 3 to 4 volts. What's with the huge voltage drop? The base voltage input voltage is around 3-5v and the emitter input is always 12v. How the hell does the collector output manage to be less than the base input? I thought these things were supposed to amplify. I've been using 2N3904s, 2N333s and a dozen other NPN transistors that have been festering in my basement for some 20 or 30 years. Most of them work, but they all act the same way. Now maybe I'm missing some very important concept about NPN transistors here, but I'm quite confused as to why this isn't working how I think it should be working. I even flipped the transistor, reversing C and E, which of course made it act funny and get quite warm quite quickly. So...what am I doing wrong here? I've ruled out that it's the transistor itself and I've tried many input voltages (used a trim pot) so the only thing I have left to blame it on is my incompetance. This isn't a practical circuit for anything but I'd like to know what I'm doing wrong before I go trying to design something useful...thanks.