Photodiode: Basic Working and Practical Applications of Photodiode

The photodiode is an optical diode which operates in reverse bias condition. Today you’ll learn the basic working and practical applications of the photodiode.

How Photodiode works

A photodiode is an optical diode whose resistance varies with the intensity of light. Under the ordinary condition, the resistance of photodiode is very high and the current flowing through the diode is negligible. With an increase in the intensity of light the reverse biased current flowing through the diode increases.

How it looks and its symbol

The photo below displays a commonly available photodiode which is usually available at $2-3. A photodiode has a small transparent surface which allows the light to fall over the PN junction.
Its symbol is exactly similar to the normal diode with additional arrows over it which indicate the falling light.

What you should know

The actual current flow of the photodiode (in other words resistance) is determined by irradiance. Irradiance is the intensity of light falling on the diode. The actual relationship between irradiance and resistance is determined from the graph of the diode and it can vary based on different models. Generally, a resistance of 8 MΩ is expected at 0.5 mW/cm2 and a resistance of 100-200 kΩ is expected around at 20 mW/cm2.

Practical Applications

  1. Is used for counting in industries.
  2. Used in optocouplers.
Learn about other types of diodes. The video below explains an application of photodiode in the industrial manufacturing process.

Leave a Reply

Your email address will not be published. Required fields are marked *

%d bloggers like this: