Photo Diodes

Photo diodes are a semiconductor device, made of a material like silicon, which converts light into current. The current is generated when the photons are absorbed into it. Similar to semiconductor diodes, they may be either exposed (to detect UV or X-rays) or packaged with window or optical fibre connections to allow light to reach the sensitive part of the device. Their circuitry can be changed for digital, control switching or digital signal processing. Photo diodes are judged by their responses, dark current, response time and noise-equivalent power. There are several types of photo diodes. They can be combined with LED to detect the presence of a mechanical obstruction to a beam or to couple two circuits. The PN junction version is less used today and the PIN type is the most common because it generates more current. The avalanche photo diode has a reverse bias and increased responsivity. Generally, they can be operated in two modes: the photovoltaic or photoconductive mode. Photo diodes have a number of applications. They are used to make accurate measurements of light intensity in science and industry. The components in cameras to measure light are also photo diodes. They are installed in smoke detectors, CD players and the receivers for infrared remote control.

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