The construction can simply be explained with a two diode analogy for transistor as shown in the above image, if you want to learn more about diodes, you can consider reading his article. The two outer layers are where the collector and emitter terminals are fixed and the base terminal is fixed at the center layer. The BJT is formed by three layers of semiconductor materials, if it is a PNP transistor, it will have two P-type regions and one N-type region, likewise, if it is an NPN transistor, it will have two N-type regions and one P-type region. The Direction of the arrow represents the direction of current flow in the transistor, in PNP the current will be flowing from emitter to base, similarly in the NPN transistor current will be flowing from the base to emitter.Īnother important difference is that an NPN transistor remains open until it receives a signal on the base pin while a PNP transistor remains closed until a control signal is provided to the base pin as shown in the above GIF file.Ĭonstruction of Bipolar Junction Transistor The difference between the PNP and NPN transistors is that the arrow mark at the emitter end if you have noticed, the arrow in the PNP transistor is mentioned as moving from the emitter to the base whereas in the NPN transistor the arrow will be moving from the base to the emitter. As I said, you will be able to see the three terminals Emitter, Collector, and Base for both the type of Transistor. The one on the left is the symbol of the PNP transistor and the one on the right is the symbol of the NPN transistor. The below diagram shows the symbols of the two types of transistors. Let's start with the symbol of transistors so that you can identify them in a circuit. But how exactly does it work? And how to use a transistor to build interesting circuits? That's exactly what we are going to answer in this Tutorial. Again you can think of emitter and collector as the two ends of your switch and instead of pressing the switch, we have the base pin which can receive the control signal. Technically speaking, BJT is a three-terminal device with an Emitter, collector, and a base pin, the current flow through the emitter and collector are controlled by the amount of current applied to the base. But, the most basic (oldest) of the transistor is the BJT Transistor, hence in this article, we get into details of that, you can use the links to learn more about other power switches.īJT is the short form of Bipolar Junction Transistor, it is a solid-state current-controlled device which can be used to electronically switch a circuit, you can think of it as your normal Fan or Light switch, but instead of you turning it on manually it can be controlled electronically. Do remember that many switching devices like BJT, MOSFET, IGBT, SCR, TRIAC, DIAC, etc. In fact, your microcontrollers and microprocessors are nothing but a collection of a large number of transistors synthesized to perform a collective operation. These humble components can almost be found everywhere from simple relay driver circuits to complex motherboard circuits, transistors prove their presence. Transistors are one of the very important components used in electronic circuit constructions.
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