![]() ![]() For example, consider the simple case of a load and and a voltage source. PNP devices are used to switch from the positive side. Thus the most common use for NPN devices is for switching the ground side of a circuit. Someone sees it at PackExpo last week and now they're wondering what's so hot about NPN outputs. A current flowing into the base of the NPN turns on the transistor whereas a current flowing out of the base turns on the PNP. It's a differentiator from his brother-in-law's cousin's machine, so he has to make up some BS as to why NPN outputs are great. They lower the list price to below the PNP version and some penny-pincher in Jersey puts them in his niche machine for no reason. You finally make a RevB and put PNP stuff in there and stop buying NPN cards and now your PLC maker is sitting on a big stock of stuff people aren't buying. You end up selling a lot of them, so the PLC maker has to do another production run of NPN output cards that they hadn't made any of for 2 years and they don't want to do it again, so they make a boat load of them. Then when that machine goes into production, you forget to change the part numbers and wiring back to PNP and now you have a production machine with NPN outputs. You need to track down NPN output cards for your PLC and modify the electrical drawings because the lead time on the PNP stack light is 6 weeks for some reason and NPN outputs are in stock at your distributor and the machine ships in 2 days. Then when your intern orders that NPN stack light for your new machine design by accident, even though the PNP part number is clearly the one in the BOM. So it makes sense that you can buy an NPN stack light because you'd need one if you were driving it with a $0.25 IC with NPN outputs. Today, with modern push/pull circuitry, it isn't really a factor outside of research level speeds, but once someone uses one NPN output card in 1982, it gets stuck in the spec forever. u/bltmn pointed out something I never thought of, and that is that sinking signals are indeed faster, so in the early days, it may have been a speed consideration where NPN output cards had lower latency. ![]() That explains why you can buy NPN inputs, but why NPN output cards? So cheap sensors or whatever might force you to use NPN inputs to get signals back from them. I have only encountered one technical reason that NPN had to be used: When outputs are being driven by a tiny IC on a 3rd party device, they have to use NPN outputs and PNP inputs because the IC in question couldn't supply current to be a sourcing device for anything. PNP is sourcing outputs and sinking inputs that isn't a subjective naming convention that depends on your perspective, so if someone is like, "well you could say it is sourcing common" or some other crap, they are just wrong. You should only use PNP unless you cannot use it PNP is more intuitive (voltage comes out of outputs and goes into inputs), and others have already mentioned that faults to ground create phantom signals in NPN systems. ![]() Please click "report" on spam Related sub-reddits: (*) At mods' discretion, certain self-promotion submissions from people who contribute to this sub in other ways may be allowed and tagged with the "Self-promo" flair No shit posts (memes - pictures with superimposed text - are OK).No spam no self-promotion (*) Employment ads (offer or wanted) go to the weekly thread.If asking a question, ask the actual question, fully yet concisely, right in the title.Be civil: do not insult no all-caps, no excessive "!" and "?", please.Job announcements (oustide the monthly job thread).Single Board computers: r/Raspberry_pi, r/Arduino, r/linux_devices, r/linuxboards.Hardware design that does not include a PLC for electronic circuits: /r/AskElectronics.PLC internship, employment and education questions. ![]() Homework help but make it clear it's homework.Refer BJT vs FET for difference between BJT and FET transistor types.ĭifference between FDM and OFDM Difference between SC-FDMA and OFDM Difference between SISO and MIMO Difference between TDD and FDD Difference between 802.11 standards viz.This sub is dedicated to discussion and questions about Programmable Logic Controllers (PLCs): "an industrial digital computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis." On topic subjects Table-1: Resistance values between transistor terminals The full form of NPN is Negative-Positive-Negative. The full form of PNP is Positive-Negative-Positive. Movement of free electrons from emitter to collector is responsible for Movement of holes from emitter to collector is responsibleįor conduction of current in PNP transistor. It consists of two N regions and a thin P-region between them. It consists of two P regions and a thin N-region between them. ![]()
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