optotransistor

An optotransistor, also known as a phototransistor, is a semiconductor device that is sensitive to light. It is essentially a bipolar transistor where the base-collector junction is exposed to light. When light strikes this junction, it generates electron-hole pairs, which are then amplified by the transistor action. This results in a change in the collector current that is proportional to the incident light intensity.

Optotransistors are commonly used as light sensors in a variety of applications. They can be found in automatic lighting systems, where they detect ambient light levels to control the switching of lights. In optocouplers, an optotransistor is paired with an LED. The LED emits light that is detected by the optotransistor, allowing for electrical isolation between two circuits. This is useful for protecting sensitive electronic components from voltage surges or noise.

The output of an optotransistor is an electrical current, making it easy to interface with other electronic circuits. They are available in various packages, including through-hole and surface-mount components, and can be designed for specific wavelengths of light. Compared to photodiodes, phototransistors generally offer higher sensitivity due to their internal amplification, but they may have a slower response time. The sensitivity and spectral response of an optotransistor can be tailored by the semiconductor materials used and the manufacturing process.