• Poornima Mani

How does a transistor work?

Updated: Sep 4, 2020

In this article, we are going to discuss working a transistor. But first, what is a #transistor? It is a simple yet complex #electronic component that is used as an amplifier or a switch.

Before jumping onto the working, we first need to know what the transistor is made of. Let us consider the component as an electronic sandwich. And there are two types of these sandwiches, n-p-n (with the p-type in between the two slabs of n-type) and p-np (with a slice of n-type silicon as the filling between two slices of p-type).

Structure of Transistor

A basic transistor structure involves three distinct areas, namely:-

  1. BASE.



1. Base: The base is the region that is responsible for activating the transistor. It is lightly doped and triggers a heavy flow of current from emitter to collector.

2. Emitter: The emitter is the section that provides a large amount of majority charge carriers and hence called so. It should be made on the point that the emitter is always forward biased with respect to the base.

3. Collector: This is the region where the majority of current carriers are injected and the current flows from the emitter to the collector.


Now that you know the basic elements of the transistor, let us check out an overview of its working.

We can recognize transistor as two p-n junctions connected back to back, where the emitter-base junction is forward biased and the collector-base junction is reverse biased. For more clarity on the topic, let us consider an NPN transistor, considering the advantage that they have majority electron carriers.

As the current passes through the base-emitter junction, electronics escape the emitter to reach base. But since the base is lightly doped, the number of holes available for recombination is less in number. Hence most of the electrons successfully pass right through the layer to reach the collector. Compared to the collector the combining of electrons is few in the base, hence proving that collector current is much higher.

Why don't we look more into the flow of current through the circuit with the help of visual representation?

By now, you would be thorough with the concept that a transistor is made up of semiconductor material. So, the flow of current from base to emitter opens the pathway for current to flow from collector to emitter.

NPN transistor is most often used due to greater advantage in factors such as carrier mobility, production costs, and negative grounding. A standard NPN transistor requires a potential of 0.7V between the base and emitter for the transistor turning ON thus enabling current flow from collector to emitter.

Explanation with a circuit

In the given circuit, a 9V battery is connected to an LED and a resistor that connects through the transistor hence allowing no current to pass through the circuit until the transistor is ON.

For the transistor to be turned ON, a potential of 0.7v has to be applied from base to emitter. When this happens, our #circuit is switched ON and there you have the #LED shining bright as a star.

A transistor can be configured in multiple ways to produce different outputs with respect to input impedance, output impedance, and power gain. the most common configurations are given below.

The working of a transistor is a beautiful concept that every #electronic #engineer must understand thoroughly. Check out other articles to know more about the configurations of transistors.

See also:

  1. Interfacing LDR Sensor with Arduino

  2. Interfacing Relay with Arduino

  3. Interfacing 4*4 Keypad with a Raspberry Pi

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