![]() ![]() ![]() ![]() Virtually all modern bipolar transistors are made from silicon semiconductor materials. Such devices had many practical disadvantages: they were fragile, excessively temperature-sensitive, electronically noisy, and had very poor power-handling capacities. In the early years of bipolar transistor usage, most transistors were made from germanium semiconductor materials. A pnp transistor needs a negative supply - its main terminal current flows from emitter to collector, and is controlled by an emitter-to-base input current that flows to a negative bias voltage. Polarity connections to (a) npn and (b) pnp transistors.Īn npn device needs a supply that makes the collector positive to the emitter - its output or main-terminal signal current (I c) flows from collector to emitter, and its amplitude is controlled by an input “control” current (I b) that flows from base to emitter via an external current-limiting resistor (R b) and a positive bias voltage. In use, npn and pnp transistors each need a power supply of the appropriate polarity, as shown in Figure 3.įIGURE 3. Basic construction (a) and symbol (b) of pnp transistor. If it uses a p-n-p structure, as in Figure 2(a), it is known as a pnp transistor and uses the symbol in Figure 2(b).įIGURE 2. Basic construction (a) and symbol (b) of npn transistor. If it uses an n-p-n construction sandwich, as in Figure 1(a), it is known as an npn transistor and uses the standard symbol in Figure 1(b).įIGURE 1. The term “bipolar” means that the device is made from semiconductor materials in which conduction relies on both positive and negative (majority and minority) charge carriers.Ī normal transistor is made from a three-layer sandwich of n-type and p-type semiconductor material, with the base or “control” terminal connected to the central layer, and the collector and emitter terminals connected to the outer layers. BIPOLAR TRANSISTOR BASICSĪ bipolar transistor (first invented in 1948) is a three-terminal (base, emitter, and collector), current-amplifying device in which a small input current can control the magnitude of a much larger output current. The remaining seven parts of the series will present a wide range of practical bipolar transistor application circuits. This opening episode concentrates on basic transistor theory, characteristics, and circuit configurations. In its discrete form, it can function as either a digital switch or as a linear amplifier, and is available in many low, medium, and high power forms. A single integrated circuit can be developed using the transistor.The bipolar transistor is the most important “active” circuit element used in modern electronics, and it forms the basis of most linear and digital ICs and op-amps, etc.The life expectancy is high and no power is needed to operate.The first advantage is it is small in size and also very cost-efficient.The following are the advantages of transistors: Read Also: Types of Field-Effect Transistors and Their Working Output Characteristics: This graph shows a plot of changing output current with respect to a change in output voltage when the input current is constant.Input characteristics: This shows the change in input current with varying output current when the output voltage is constant.The size of the collector is larger than the emitter. It is present on the right side of a transistor and is moderately doped. Collector: The collector is the positive terminal of the transistor.Emitter is of moderate size and heavily doped. Emitter: It is the negative terminal of the transistor.It is present in the center of the transistor. Read Also: Characteristics of TransistorsĪ transistor is a fusion of three terminals which are made up of semiconducting materials that allow the current to flow. This is the reason why it is called the current controlling device. Transistors can change the intensity of current via one channel and control the flow of current through the other channel.Transistors perform the function of a vacuum triode and it uses semiconductor junctions in place of heating electrodes.They can work on low-voltage supply and provide greater safety. ![]() Transistors also work as a switch and an amplifier.NPN (negative-positive-negative) transistors are the majority used transistors.It has the ability to control the current flowing through the circuit. There are two types of transistors: NPN (negative-positive-negative) and PNP (positive-negative-positive). ![]()
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