A, the pole is different
1, photodiode, also known as photodiode (English: photodiode) is a light can be used according to the way, converted into a current or voltage signal light detector.
Tube core often use a PN junction with light-sensitive features, very sensitive to changes in light, with unidirectional conductivity, and light intensity of different times will change the electrical characteristics, so you can use the intensity of light to change the current in the circuit.
2, light-emitting diode referred to as LED. made of compounds containing gallium (Ga), arsenic (As), phosphorus (P), nitrogen (N) and so on.
When the electron and hole complex can radiate visible light, and therefore can be used to make light-emitting diodes. In circuits and instruments as indicators, or composed of text or digital display.
Gallium arsenide diodes emit red light, gallium phosphide diodes emit green light, silicon carbide diodes emit yellow light, gallium nitride diodes emit blue light. Because of the chemical nature of organic light-emitting diodes OLED and inorganic light-emitting diodes LED.
Second, the principle of different
1, photodiode
Photodiode is a semiconductor device that turns the light signal into an electrical signal. Its core part is also a PN junction, and ordinary diodes, compared to the structural difference is that, in order to facilitate the acceptance of incident light, the PN junction area as large as possible, the electrode area as small as possible, and the PN junction junction depth is very shallow, generally less than 1 micron.
Photodiodes operate under a reverse voltage. When there is no light, the reverse current is very small (generally less than 0.1 microamps), called the dark current. When there is light, photons carrying energy enter the PN junction and transfer the energy to the bound electrons on the *** valence bond, causing some of the electrons to break free from the *** valence bond, thus producing electron-hole pairs called photogenerated carriers.
2, light-emitting diode
It is a semiconductor diode, can convert electrical energy into light energy. Light-emitting diode and ordinary diode is composed of a PN junction, also has a unidirectional conductivity.
When the light-emitting diode plus forward voltage, from the P region injected into the N region of the hole and from the N region injected into the P region of the electron, in the vicinity of the PN junction within a few microns of the N region of the electron and the P region of the hole, respectively, composite, resulting in the spontaneous radiation of fluorescence. Different semiconductor materials have different energy states in which the electrons and holes are located.
Three, different applications
1, photodiode
In scientific research and industry, photodiodes are often used to accurately measure light intensity because it has better linearity than other photoconductive materials.
Photodiodes also have a wide range of applications in medical applications such as X-ray computed tomography and pulse detectors.
PIN junction photodiodes are generally not used to measure very low light intensities. Avalanche photodiodes, photocouplers or photomultiplier tubes can be useful if a high sensitivity detector is required for low light situations, such as astronomy, spectroscopy, night vision equipment, laser range finders and other applications.
2, light-emitting diodes
1) AC Power Indicator
The circuit is connected to the 220V/50Hz AC power supply line as long as the LED will be lit, indicating that the power supply is on. Current-limiting resistor R resistance value of 220V/IF.
2) AC switch indicator
With LED as incandescent switch indicator circuit, when the switch is off the bulb goes out, the current through R, LED and bulb EL to form a circuit, LED is bright, convenient for people to find the switch in the dark. At this time the current curved in the circuit is very small, the bulb is not bright. When the switch is turned on, the bulb is lit, and the LED is off.
3) AC outlet indicator
The AC outlet indicator circuit with a two-color (*** cathode) LED. The power supply to the socket is controlled by switch S. When the red LED is on, the socket is not powered; when the green LED is on, the socket is powered.
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