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A diode is defined as a two-terminal electronic component that only conducts current in one direction (operated within a specified voltage level). An ideal diode will have zero resistance in one direction and infinite resistance in the reverse direction. A diode allows current flow in one direction and very high resistance in the reverse direction preventing current flow acting like a valve for an electrical circuit.
7.4.1 PHOTODIODES
7.4.1 PHOTODIODES
It is a form of light sensor that converts light energy into electrical energy.
Photodiode is a type of semi-conducting device with PN junction. Between the positive and negative layers, an intrinsic layer is present. The photo diode accepts light energy as input to generate electric current
A reverse biased semiconductor diode passes only a very small leakage current (a fraction of 1uA) if the junction is not exposed to light.
The current rises almost in directly proportional to the light intensity.
When the device operates with a reverse voltage, it functions as a photoconductive device.
When operating without the reverse voltage, it functions as a photovoltaic device.
The photodiode has an advantage over the photoconductive cell.
Its response time is much faster, so that it can be used in applications in which the light fluctuations occur at quite high frequencies.
7.4.2 PHOTOTRANSISTOR
7.4.2 PHOTOTRANSISTOR
Phototransistor is a photodiode with an added junction which makes it an n-p-n device.
Phototransistor provides a much larger output current than the photodiode for a given area of light illumination.
This means that phototransistor is more sensitive than photodiode.
Phototransistor has a lower switching time than photodiode
The Usage of Phototransistor in a Circuit
Photodiode VS Phototransistor VS Photoresistor
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