What Is a Phototransistor?

Optoelectronic functional crystals are mainly functional crystals that use photoelectric conversion. There are many types, such as optical crystals, laser crystals, nonlinear optical crystals, electro-optic crystals, piezoelectric crystals, scintillation crystals, and magneto-optical crystals. Its role is to accept optical signals and convert them into electrical signals.

Phototransistor

Photoelectric crystals are generally used in the open state of the base (there are two cases of external wires), and a voltage is applied to the two terminals of the emitter and the collector to apply reverse bias to the collector junction. In this state,

Can be divided into closed tank type and resin sealed type, and each type can be divided into

Phototransistor object detection

Send a beam of light to the object to be measured, and use the phototransistor to receive the reflected light to determine the object's black and white and grayscale. By using light emitters (often light emitting diodes) with different emission wavelengths and phototransistors that are sensitive to different wavelengths, the color of objects can also be detected. After converting the optical signal into an electrical signal in this way, a series of processing is performed. A common "auto-tracking car" uses phototransistors to detect black lines on the ground.

Phototransistor optical coupling (optical coupling)

Schematic diagram of the internal structure of the optocoupler

An opto-coupler is an electronic switch made using a combination of light-emitting diodes and phototransistors. As shown in the figure, the 1, 2 pins are connected to the light emitting diode, and the 3, 4 pins are output. When turned off, the LEDs between 1 and 2 do not emit light, and the 3 and 4 pins are almost disconnected. When a voltage is applied to 1, 2, the diode emits light, so that the resistance between 3 and 4 is greatly reduced. Its function is similar to a relay (hence also called photorelay), and the input and output are isolated like a relay, and the signal is transmitted in one direction.

Phototransistor optical communication

Short-distance communication, such as on-site construction or contact during mountain climbing, can be performed by converting and modulating the signal at the transmitting end into an optical signal, and receiving it at the other end via a phototransistor, and reducing it to an electrical signal. Therefore, there is no need to worry about eavesdropping, nor to apply for a license such as a radio transceiver.