Circuit Symbol and Construction | Operating Principle of Photodiode
Circuit Symbol and Construction.
Photodiode is another opto-electronic device whose reverse current changes with illumination. The construction and symbol of photodiode The arrows in the symbol represent the incoming light.
The package of the photodiode is transparent so that the light can reach P-N junction. A lens is used in the package to focus maximum light on the junction. The active diameter of device is about 2.5 mm. One side of P-N junction is lightly doped, so that depletion region widens and large area is available for illumination.
To have large reverse current, sometimes an insulator layer is sandwitched between P and N regions. The diode is called P-I-N photodetector.
Operating Principle of Photodiode
Operating Principle of Photodiode.
The photodiode is operated in reverse bias, As previously discussed, in reverse bias, the diode current is mainly due to thermally generated minority carriers. If reverse biased P-N junction is illuminated, the photons are absorbed. They dislodge valence electrons. The number of the minority carriers depends on the intensity of light incident on the junction. The stronger the light, the greater is the number of minority carriers and larger is the reverse current. A photodiode has been optimized for its sensitivity to light.
Because of fast response the photodiodes are often used in switching circuits as optical detector. In optical systems like remote controls, character recognition system, burglar alarms, etc. it is used as optocoupler along with the LED.8.3 Characteristics of Photodiode
The characteristic of the photodiode The photodiode acts as a normal diode when illumination is zero. The effect of light on forward characteristic of diode is negligible.
