{"id":79505,"date":"2024-05-08T14:00:26","date_gmt":"2024-05-08T12:00:26","guid":{"rendered":"https:\/\/botland.com.pl\/blog\/phototransistor-what-is-it-and-what-is-it-used-for\/"},"modified":"2026-04-08T10:58:00","modified_gmt":"2026-04-08T08:58:00","slug":"phototransistor-what-is-it-and-what-is-it-used-for","status":"publish","type":"post","link":"https:\/\/botland.store\/blog\/phototransistor-what-is-it-and-what-is-it-used-for\/","title":{"rendered":"Phototransistor – what is it and what is it used for?"},"content":{"rendered":"Reading time:<\/span> 4<\/span> min.<\/span><\/span>\t\t
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A phototransistor is an electronic component that combines the functions of a transistor and a photodiode. What is its mechanism of action and what can it be used for?<\/p>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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What is a phototransistor?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Phototransistor<\/strong> <\/a>is one of the variants of the transistor<\/strong><\/a>, which is an electronic component consisting of three layers of semiconductor with varying types of conductivity: emitter, base and collector. Standard trans<\/strong> istors are current-controlled, while in the case of phototransistors<\/strong> the change in value on the collector is dependent on the intensity of light. Therefore, it can be said that components of this type combine the properties of a photodiode and a transistor, and the basis. The basis of their application is the dependence of the value of the larger current between the base-collector junction on changes in the value of the smaller current flowing in the base-emitter junction.<\/p>

A distinctive feature of phototransistors<\/strong> is that they are much more sensitive to light than standard components of this type, which can be achieved by exposing the base terminal. As a result, it is possible to precisely change the current flowing between the emitter and collector in response to changes in illumination. This makes phototransistors applicable, among others. In various types of optical sensors.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t

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L-53P3C 5mm 940nm phototransistor.<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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How does a phototransistor work?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Work phototransistor <\/strong><\/a>is based on the use of the basic concept of operation of a bipolar transistor<\/strong><\/a>. These types of components can be created by exposing the semiconductor of an ordinary transistor to light – mostly they are of almost identical design, differing only in the absence of a housing at the base terminal. As a result, electrons released by light incident on the semiconductor can cause the base current to flow, which is proportionally transferred to the collector.<\/p>

In phototransistors, the value of the current at the base-collector junction is controlled by the intensity of light incident on the semiconductor. Photons polarize the junction in the direction of conduction, so that a current begins to flow at the output with a value that depends on the value of the illumination. When the transistor is not illuminated, it does not conduct current.<\/p>

What are the differences between a phototransistor and a standard transistor?<\/h3>

The construction of a phototransistor is very similar to an ordinary transistor. However, the differences may be in the semiconductors used, as well as in the housing of the component. With standard variants, primarily germanium and silicon are used – although they can also be used in phototransistors, a more common sight these days, among others. Gallium, which features a much stronger light response. The housing, in turn, is constructed to allow light to fall on the base area: transparent plastic, for example, can be used for this purpose. What’s more, phototransistors usually do not use an outward leading of the base.<\/p>

Photodiode vs. phototransistor<\/h3>

Both the photodiode and phototransistor convert light energy into electrical energy. However, these are components with slightly different applications, due to differences in their properties. In particular, the following points should be noted:<\/p>