[otw_is sidebar=otw-sidebar-1]What is Phototransistor
I hope you all are fine; this is the fourth article in the series on introduction to basic electronic components. In the previous article I have briefly discussed the diode in this article I will discuss the Phototransistor.







Introduction to Phototransistor:


After reading this article the reader will be able to learn about the working of the phototransistor, construction and applications of the phototransistor. Moreover the reader will find this article useful if they want to design the circuit based on the phototransistor. So sit back, keep reading and enjoy learning.

What is Phototransistor

The word phototransistor is composed of two terms “photo” which means light and “transistor” which is a terminal active electronic component. In case of simple bipolar junction transistor the device has three terminals called “collector”, “emitter” and “base”. Any stimulus that is the input signal is connected to the base transistor in the response of which the transistor gets on and performs the task for which the circuit is designed.

In case of the phototransistor as the name implies the stimulus to this transistor is applied to the base as well but the stimulus in this case is not the voltage signal or the current signal but the stimulus is the light. When the proper biasing circuit of the phototransistor has been designed and the light shines on its base the current will begin to flow through it. The schematic symbol of the phototransistor is as shown in the following image:

Basic Construction of Phototransistor:

The basic construction of the phototransistor is not different from the ordinary transistor; the phototransistor consists of the base of say P-Region that is sandwiched between the collector and emitter of N-Region. This type of phototransistor is bipolar that is the conduction through the phototransistor is due to the flow of both types of charge carriers holes and electrons. The basic construction of the phototransistor is as shown in the following figure:

Construction of Phototransistor,npn Phototransistor

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The PN junction is sensitive to light, so it is actually the PN junction on which the light is projected and the current begins to flow. The base of the transistor is covered with the transparent object so that the light can easily pass through it. The phototransistor works on the principle of photoelectric effect.

Working of Phototransistor:

As stated earlier the Phototransistor works on the principle of photoelectric effect. When light shines on the PN junction an electron-hole pair is generated if the photon has sufficient energy. In case when no potential is applied across the phototransistor no current will and electron-hole gets combined but in case of applied voltage the electrons and holes move in their respective course to establish the current. The amount of current that flows through the Phototransistor depends on the intensity of light. The circuit of the phototransistor is as shown in the following figure:

Working of Phototransistor,basic of PhototransistorApplications of the Phototransistor:

Although a phototransistor is not a commonly used electronic component but it finds applications in optoelectronics. The applications of the phototransistor are listed as shown in the following.

  • Phototransistor is used in opto-coupler.
  • Phototransistor can be used in line following robot.
  • Phototransistor can be used in the light monitoring system such as greenhouse.

I hope this article would be helpful for you, I have discussed the basics of the Phototransistor that is all for now, in the next article I will discuss other basic electronic components. Till then stay connected, keep reading and enjoy learning.