fototransistorers

A phototransistor is a semiconductor device that utilizes a transistor's amplifying capability to enhance the sensitivity of a photodiode. It is essentially a bipolar transistor where the base terminal is exposed to light. When light strikes the base-region, it generates electron-hole pairs. This light-induced current acts as a base current for the transistor, which is then amplified by the transistor's current gain (beta). Consequently, a much larger collector current flows, proportional to the intensity of the incident light.

Phototransistors are typically two-terminal devices, with the collector and emitter terminals serving as the output. Some phototransistors have a third, base terminal that can be used for biasing or control, allowing for more precise operation and gain adjustment. The sensitivity of a phototransistor is generally higher than that of a photodiode, making them suitable for applications where detecting low levels of light is necessary.

The primary function of a phototransistor is to convert light energy into an electrical signal. The electrical output is directly related to the amount of light falling on the device. They are often used in light-sensing applications, such as automatic lighting controls, optical switches, object detection, and remote controls. Their relatively simple construction and operation, coupled with their amplified response to light, make them a common choice in many optoelectronic circuits. Different types of phototransistors exist, including those sensitive to visible light and others optimized for infrared radiation.