Phototransistor

All transistors are light sensitive. Phototransistors are similar to ordinary transistors but doesn't have a base terminal. The Light input on the phototransistor, forward and reverse biases the transistor and hence switches ON or OFF the phototransistor. They are developed to react to specific wavelength of light. They consist of a opening at the top covered with glass through which the input light is received.

 

Figure 1: Phototransistor Symbol

 

Figure 2: Phototransistor