Early voltage in 2n3906 transistor1/16/2024 First we get that current, then we guess at the required base current based on some estimate of h FE then we figure out how much collector current the NPN (base current of PNP plus 10k resistor current) will have and with another estimate of h FE for the NPN, we get a required base current. I don't recall a load being given for the PNP transistor. The thing about transistor circuits is that you must start with the output current and work backwards. I ran an LTSpice simulation with no base resistor and the base current is just 10 uA but I only had a 1k load on the output. I pretty much use 330 Ohm in series with all inputs and outputs just to protect the uC or FPGA. I would still put a 330 Ohm resistor in series with the NPN base. The only reason the circuit works is that 4.3k resistor that raises the emitter voltage which raises the base voltage to a point where the current flow doesn't harm the uC. That the schematic doesn't even show a base resistor causes me an issue. One of the risks in this project is applying 12V to a uC output pin, with or without a series base resistor. So that leads me to the question on how to determine if a basic 2222a transistor is turned on or off? I guess I have to find a way to measure current, and forget all about measuring voltage (potential)? I'm absolutely NOT seeing 0v anywhere but that probably is how it should be. I added a few comments on the picture indicating where I did the measurements, but you probably have to zoom in to see them. I then connected the boosters + to the collector through a load resistor of about 1MOhm. I added back my booster to so I could get the 12v. So what's the right way to measure? I took a picture of my setup on a bread board. I just didn't see 0 volt - again getting the current confused with voltage (potential). That said, when the transistor is "on", I get a full potential of 5v as there's now a straight line to ground. So I'm back to a question I've posted about before, on how to actually measure what voltage is being "turned on". However, if I place the meter on the emitter I get the voltage potential of +5v because the emitter is connected straight to ground. If I put the meter gnd on gnd, and place the plus on the collector pin, there's a voltage potential between that point and ground through the resistor and LED/Diode. I think I'm confusing potential with actual voltage. I still didn't see 0 volt (more about that in a moment) but I did see the LED go on/off on the collector side when the base got +5v (using 2n222a). Thanks for the advice - I went even further back to basic, recreated stuff I've done before and that worked. I'm focused on voltage, not current here. And there in lies one of my issues I think. What's a good source to get what's going on here? ALL I really wanted to learn was creating a switch using a transistor that turned on/off a higher voltage. Not sure why - in particular I'm not sure why I see a voltage on the 2N3906 when I have nothing connected to the base, just the emitter (and the collector is going through a 2Kohm resistor to ground to simulate a small load). Even with 5 volts on the collector on an NPN I don't seem to be able to fully turn off the power. Granted, it's much easier for me to understand the NPN than PNP, but still I thought I had the basics down. I've read and followed quite a few talks (youtube etc) and well, I thought I understood transistors. If I measure the base I get about 6v on it? When I build the circuit referred here with a 22 all I get is a constant voltage regardless of applying a voltage to the base of the 2N2222a. Base isn't even pulled to ground (if I do it short circuits so there's definitely something I don't get). So I've simplified things things, and I have a single 2N3906 PNP transistor (I know, not the one mentioned in the drawing - it's all I have). In particular, as I tried this option in particular this circuit: Simple right? Well, every time I attempt anything with the few transistors I have (getting a better collection by the weekend) I don't see anything remotely as I thought I would. I have a 12v line that I want a "high" from an arduino to turn on. I'm running in circles, having tried several different approaches.
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