The circuit and symbol of NPN is shown below:

The above connection is also known as the forward-active operating mode. Working of NPN transistorĬonnection Setup: The battery's negative terminal (VEE) is connected to the emitter n++ slab and the battery's positive terminal (VCC) to the collector n+ slab.

Here, the emitter junction 'n++' is heavily doped, and the collector junction 'n+' is lightly doped. A p slab is inserted between the two n slabs forming an NPN semiconductor. The '++' sign indicates the heavy impurity doping concentrations, while the '+' indicates the moderate impurity doping concentration. The equivalent circuit of an NPN transistor as a combination of the two p-n junctions is shown below: The structure of the NPN transistor is shown below: The NPN transistor consists of one P-doped region between the two N-doped regions. There are two types of Bipolar Junction Transistor, NPN transistor and PNP transistor. In the case of BJT, the base-emitter region is connected in the forward bias, and the base-collector region is connected in the reverse bias. It pulls the charge from the junction making the depletion region or base wider, which does not allow the charge to flow easily. It is because the contact of the junction has two charges of opposite nature, which attracts them. The flow of charge in case of reverse bias is zero. We can say that the connection is opposite as compared to the forward bias. The battery's positive terminal is connected with the region containing negative charge carriers (n region) and the negative terminal containing positive charge carriers (p region). The forward bias is the connection of the transistor, where the (+) terminal of the battery is connected with the region containing positive charge carriers (p region) and (-) terminal with the region containing negative charge carriers (n region). There are two types of voltage bias, i.e., forward bias and reverse bias. The collector region has the maximum width among the three region of the BJT. In amplifiers, it is considered as the output region. It receives charge carriers from the base. It is often connected in reverse biased with the base, which does allow any charge flow. The collector region is the lightest doped region.

It has the opposite polarity from the emitter and the collector region. It will stop the electrons and holes from recombining and will pass more electrons towards the base region. It is small to avoid carrier recombination. The base region is the smallest region of the transistor. It means that the charge flows from the emitter to the collector. It is the region where the charge starts flowing. The emitter region is the highly doped region as compared to the other two regions of the transistor. The three terminals of BJT are as follows: 1. Let's first discuss the three configuration of the BJT before proceeding with its working. Here, we will discuss the following topics: The three terminals of the Bipolar Junction Transistor are shown below:Ī single p-n junction transistor is shown below: It is because the input current determines its output. The emitter junction in BJT is highly doped.īJT is also known as the current controlled device. The charge moves from the high concentration (emitter) region towards the low concentration (collector). The p region has majority charge carriers holes (possesses positive charge), and the n region has majority charge carriers electrons (possesses negative charge). The p-n junction is made of two doped regions 'p' and 'n.' Thus, BJT is a device that has three terminals (emitter, base, and collector), two p-n junctions, with the three separately doped regions. The transistor is a three terminal semiconductor device that regulates the flow of current. The junction refers to the p-n junction that allows the flow of charge carriers and the current in a particular direction. The bipolar junction transistor is derived from three words, bi, junction, and transistor.

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Bipolar transistor charging