A phototransistor is an electronic component that amplifies and switches current based on exposure to light. It has exposed base sections that activate the component when exposed to light. The operating range can be controlled by the intensity of light applied. It is commonly used in devices such as optical remote controls, light pulse counters, and light meters. Modern components use different junction materials for higher efficiency. The operating range can be controlled by varying the intensity of light. It is ideal for light measuring instruments and optical remote controls. It is also used in different types of day/night switches and security motion detectors.
A phototransistor is a current-amplifying and switching electronic component that relies on exposure to light to function. A phototransistor has exposed base sections which, when exposed to light, activate the component rather than the electric current used in conventional examples. As with most normal transistors, the operating range of the phototransistor is also dependent on the base input. This means that the operating range of the transistors can be controlled by the intensity of the light applied. The component is commonly used in devices such as optical remote controls, light pulse counters and light meters.
Bipolar transistors are one of the most commonly used forms of semiconductor electronic components. Typically made up of a collector, emitter, and base sections, a normal transistor will remain inactive until it receives an appropriate electrical pulse at its base input. This input turns on the transistor and allows current to flow through the collector/emitter section of the component. The extent to which the transistor conducts or transmits this current depends on the size or magnitude of the base current. A phototransistor works in exactly the same way, except that it relies on light falling on its base to activate it.
All transistors, and indeed most semiconductor components, are sensitive to light. The phototransistor has been optimized to take advantage of this feature. These components feature clear base sections that allow for unobstructed light gathering and, in most cases, have no base wire at all. Those that have a basic wire use it to polarize or control how current flows rather than for triggering. Aside from these differences, it is identical in construction and application to its conventional brethren.
Early phototransistors used single semiconductor materials such as germanium and silicone in their construction. Modern components use different junction materials including gallium and arsenide which give the components much higher levels of efficiency. The physical structure of the transistor is also optimized to allow for maximum exposure to light. This usually involves placing the component contacts in a staggered configuration to avoid obstructing light falling onto the base.
The operating range of the phototransistor is also dependent on the base input, i.e. the extent to which the component conducts can be controlled by varying the intensity of the light to which it is exposed. This makes a phototransistor ideal for light measuring instruments such as light photometers. Many optical remote controls also use this feature to allow the system to transmit a series of instructions. Meters that use light pulses also use phototransistors in their circuitry as well as different types of day/night switches. The infrared phototransistor is also often used in light-dependent proximity switches such as door close sensors and security motion detectors.
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