This was a setup where you have a Distribution switch and below are all the Access switches. I was able to make it work with the following. Thank you for the Good information and the links to the good data. Our models idealize the behavior of a transistor as a switch if we decide to study electrical engineering, we will learn many transistor models that describe them more accurately, but for our purposes, our toy model suffices. In our model, we can think of the base as a remote control of the switch between points A and B. Remember that the job of a model is to describe how something works, not how something really is. In both cases, though, we place the transistor in saturation when we create a current that flows through both the emitter and the base of the transistor.Īlthough physically the base of a transistor is connected to the emitter and collector, our toy model shows the base always disconnected from the emitter and the collector. The NPN and NPN transistors operate in opposite ways: the NPN transistor is in saturation when the base receives a logical 1, while the PNP is in saturation when the base receives a logical 0. Ideal behavior of NPN and PNP BJTs in the saturation region This is the TO-92 package pin configuration of the two transistors: The spec sheets of these transistors areīoth the 2N2222A and the 2N2907 come in the same TO-92 package so they look the same if our circuit is not working correctly, one of the first things to do it to make sure we are using the correct transistor. We are going to use the 2N2907 PNP transistor, which is a complementary PNP transistor for the NPN 2N2222. NPN and PNP transistors that have similar specs and operate in the same voltage range are called complementary. However, we are not designing an integrated circuit but instead working with discrete elements on a breadboard, so for that effect they are equivalent. NPN transistors have certain advantages at the time of designing integrated circuits, e.g., they are faster than PNP ones and use less silicon area. In our lab circuits, we used 2N2222 transistors, which are NPN. The sandwiched region is called the ‘base’, while the regions on the sides are called the emitter and the collector. An NPN transistor has two n-type semiconductor material sandwiching a p-type one the PNP transistor is the reverse. There are two types of BJTs: NPN (n-type/p-type/n-type) and PNP (p-type/n-type/p-type). BJTs operate faster than most other types of transistors, but for our purposes, their particular advantage is that they are fairly resistant to static electricity, so we are less likely to damage them with the static electricity of our bodies, and we can handle them with our hands without having to be grounded be aware that most other types of transistors are not so forgiving and touching them without being grounded are likely to damage them. There are several types of transistors one of such types is called BJT (Bipolar Junction transistors). In practice, even simple designs are likely to use standard transistor models that take into account voltage drops at the junctions, leaked currents, βs, and so on, but for us that have no background in electronics, our simple functional models are enough. In this page, I describe a bare-bones model for the transistors, which has no use other than to make clear how an ideal transistor would replace a physical switch. I’ll try to write something unusual each time I write one of these supplements. This material supplements section 1 – circuits.
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