But is "that" positive source always the emitter in a PNP transistor? Im pretty sure that it works the opposite of an NPN, where the current flows(conventionally) from a "positive source" through the base to ground. In a PNP, is the collector always hooked up to ground and the emitter to positive voltage? Current flows (conventionally) from the positive Base through the emitter to ground, when enough current flows it opens up the channel from the Collector to the emitter to allow a larger current to flow. In an Npn circuit, the collector is hooked up to the positive voltage and the emitter is hooked to ground. NPN emitters emit -ve electrons, PNP emitters The charge carriers have opposite sign, so you just have to flip the sign of every current and voltageīetween PNP and NPN, think of them as mirror opposite. Hello, i am trying to learn more about transistors, I have used NPN transistors in numerous projects but there are some things i don't understand about PNP. And, even then, a "ground" doesn't have to be assigned. That doesn't happen until the battery is applied to a circuit. Because, "Ground" hasn't been established yet. Are the terminals on a battery labeled "Positive" and "Ground"? No. It's a reference point, and thus is always the 0 voltage point - i.e., the point from which all other voltages are measured, or referred to. It's easy to get confused and think of Ground as a polarity. A circuit can be assigned a Negative ground, and all the voltages are measured as Positive, or the same circuit can be assigned a Positive ground, and all the voltages are measured as negative. And that's the thing - it's all arbitrary. And, all the polarities are based on where ground is arbitrarily assigned. In all cases, Ground is measured as 0 Volts. In a three-rail system, like is common with Op-Amp circuits, ground is somewhere in the middle. Also, some early cars had a Positive Ground - which merely meant, the positive side of the battery was connected to the chassis. īut, Ground can, also, be on the Positive side-in which case, all the other voltages are Negative! Emitter Coupled Logic is an example of this case. Ground is merely a convention, chosen to refer to a common reference. The concept of "Ground" was just about the most confusing when I was learning electronics. Notice my language: I never said "ground". The Drain-Source path is called the "Channel". In both cases, it's a current flowing in the Base-Emitter junction, that controls a current flowing in the Collector-Emitter junction.
With a PNP, this is reversed: Emitter towards the Positive, Collector towards the Negative, and a Conventional current flowing from the Emitter to the Base, controls current from the Emitter to the Collector. A Conventional current, flowing from Base to Emitter, controls current flowing from Collector to Emitter. An NPN Emitter is, in most cases, connected on the more negative side, the Collector, towards the positive.
And, for this reason, the polarities are reversed, as well. The same functionality, just with opposite current directions. The simple difference between an NPN and a PNP is this: The currents flow in opposite directions. I guess that doesnt really matter right, as long as you hook the emitter to positive voltage and the collector to negative? I noticed that the physical pin can be located in different places in different PNP transistors.įor instance on the ss8550 pnp (with the flat part of the transistor facing you) the emitter is the left pin.īut with the bc327 pnp ( with the flat part of the transistor facing you) the emitter is the right pin.
I always thought that the word "collector" meant that it had to be hooked up to possitive, but i guess it varies between NPN and PNP. It does not work backwards to an NPN, however, if it makes sense to you so be it.īoth are current controlled switches you are describing.įor the NPN, current goes from +5V to Arduino output pin to base to emitter to GND.įor the PNP, current goes +5V to emitter to base to Arduino output pin to GND.īoth transistors turn off when the base current path is disrupted. Yes for a negative GND system like we use in an Arduino project. “In a PNP, is the collector always hooked up to ground and the emitter to positive voltage?”
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