To photo diode é uma junção PN ou estrutura PIN que quando uma luz relativamente forte atinge a junção, it excites an electron thereby creating a free electron positively charged. This mechanism is also known as ” photoelectric effect “, also common in transistors and integrated circuits, since they are made of semiconductors, and pn junctions contain.
Almost all active components are potentially photo-sensors. The PN junction needs to be exposed to light, so that for using a semiconductor, como um foto-sensor sua placa de silício deverá ser exposta, in a transparent glass ampoule or pour silicone.
These diodes with these characteristics can be used to measure the light intensity, above circuit.
The photo Transistor é essencialmente, a bipolar transistor, que funciona como um fotodiodo, but with a much higher sensitivity to light, since the electrons that are generated by photons in the base-collector junction is applied within the base, its current is then amplified by the transistor operation. However, the photodiode has faster response time than the phototransistor.