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    What is the working principle of photodiode?


    A photodiode is a semiconductor device that converts an optical signal into an electrical signal.Its core part is also a PN junction. Compared with ordinary diodes, the structure is different. In order to facilitate the acceptance of incident illumination, the PN junction area is made as large as possible, the electrode area is as small as possible, and the junction depth of the PN junction is very large.Shallow, generally less than 1 micron.When there is light, the photon carrying the energy enters the PN junction, and transfers the energy to the bound electrons on the covalent bond, causing some of the electrons to break free from the covalent bond, thereby generating electron-hole pairs, called photo-generated carriers..

    If a load is connected to an external circuit, an electrical signal is obtained on the load, and this electrical signal changes correspondingly as the light changes.Photodiodes and phototransistors are photosensitive devices widely used in electronic circuits.In addition to the photoelectric conversion function, the phototransistor also has an amplification function, and the character symbol is generally VT in the circuit diagram.Since the phototransistor is an optical signal, there are usually only two pin lines of the collector and the emitter.The positive and negative resistance values are large and small for photodiodes.Photodiode detection: First, the pole is judged according to the mark on the outer casing. The pin with the color point on the outer casing or the pin near the pipe key is the positive pole, and the other pin is the load.Then remove the blackout cloth, the photodiode receiving window is facing the light source. At this time, the multimeter’s hand should be deflected to the right. The deflection angle indicates the sensitivity. The larger the deflection angle, the higher the sensitivity.


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