10. Structure and function of photodiodes and phototransistors
Photodiodes and phototransistors are so called optoelectric devices or components.
They make use of a semiconductors characteristic that the material resistance is reduced if the semiconductor material is illuminated/lit up. During the illumination of the material electrons free themselves from their connections through the influence of the energy of light.
In connection with other electronic components this characteristic of photodiodes and phototransistors can be used for various control and regulation tasks (e.g. gas flame control, light-dependent switches, sensors, etc....)..
Diagram 67: Characteristic curve and circuit symbol of a rectifier diode
Diagram 68: Two photoresistors (on the left side without case and on the right side with case, ready for installation)