Photo transistor is a type of transistor whose base bias is infrared light. The amount of current flowing between the collector and the emitter is proportional to the intensity of light received by the photo transistor. Photo transistors are often used as an infrared light control switch, which utilizes saturation (saturation) and off (cut off) conditions from the photo transistor. The photo transistor works as a switch when the base receives infrared light so the photo transistor will be in saturation state and when it does not receive infrared light the photo transistor is off. The phototransistor structure is similar to bipolar transistor (bipolar junctoin transistor).
In the base region can be entered from the outside by a transparent gap from outside the taransistor. This gap is usually protected by a small lens that focuses light on the emitter base connector edge.
Characteristics of phototransistor
Working Principles of Photo Transistor Sensors The connection between the base and the collector, operated in a back supply and functions as a photodiode that responds to the incoming rays from outside. When no incoming light, the current through the back-feed connection is equal to zero. If the light from the photon energy is sufficient and regarding the connection of the back connections, the addition of hole and electron pairs will occur in the depletion region, causing the connection to carry.
The number of holes and electrons generated in the connection will be proportional to the intensity of the light on it. The connections between the emitter bases can be advanced, allowing them to function as conventional bipolar transistors. The collector current of the phototransistor is given by: The base terminal of the photo transistor does not require a connection (no connect) to work. If the base is not connected and VCE is positive, the collector base connection will behave as a remanufactured photodiode. The collector current may flow in response from one of the inputs, with the base current or the input of the light intensity L1. Example of Photo Transistor Sensor Basic Sample