Photosensitive resistor

Photosensitive resistor

Photoresistor is a device made of semiconductor photoelectric effect principle.When the semiconductor is exposed to light,a large number of holes and electrons are generated, and the holes and electrons arrive at the other electrode by an electrode prior to the recombination,so that the resistivity of the photoconductor changes.The photoresistor shows a high resistance state when there is no light;when there is light,its resistance decreases rapidly.Now widely used in the building corridor of the acousto-optic two control energy-saving lamps,on the use of a photoresistor.

The detection method of the photoresistor is very simple.The pointer type multimeter is used to detect the resistance of the photoresistor,and the light receiving condition of the photoresistor is changed at the same time,you can see that the pointer of the multimeter swings with the change of the illumination,and if the swing is small or basically does not move,it can be judged that the photoresistor is invalid. 

Third, the photodiode is also called photodiode,is the device that converts light energy into electrical energy,and its structure is similar to ordinary diode,the difference is that there is a personal shooting window on the shell,which can focus the received light on the semiconductor chip.In the absence of light,the photodiode has the same unidirectional conductivity as the ordinary diode,and if the forward voltage is applied, the current is exponentially related to the terminal voltage,if the reverse voltage is applied,a larger resistance will appear;when there is light,if the reverse voltage is still added on the photodiode,the current proportional to the light will be generated, which is called photocurrent.The photodiode can be measured by the " RX1k " block of the multimeter,and the forward resistance of the photodiode is about 10 kohms,the reverse resistance is infinite,indicating that the tube is good;when there is light exposure,the reverse resistance decreases as the intensity of light increases,and the resistance can be reduced to less than a few thousand ohms or 1000 ohms,and the tube is good;if the reverse resistance is the sign of the diode or 0,the pipe is broken.

Four, photosensitive transistor

A photosensitive transistor is a transistor equivalent to a photodiode on base and collector.In order to respond well to light,the area of the base area is much larger than that of the emission area,so as to enlarge the illumination area.There are three pins in the photosensitive transistor,and two in the two pipes.The transparent window is the base.Its equivalent circuit and symbol are shown as shown in Figure.

In order to further expand the sensitivity of photosensitive transistors,Darlington type photosensitive transistors have been manufactured.When the Darlington type photosensitive transistor is illuminated,the equivalent photosensitive diode converts the light signal into an electrical signal,which is magnified by the two transistor. Therefore,the total magnification is equivalent to the product of two transistor magnification,so the sensitivity is much higher than that of the ordinary photosensitive transistor,usually up to dozens of milli photocurrent.Above.

The detection of photosensitive transistors can be carried out in the following steps.

The multimeter is placed in the "RX1k" block to measure the resistance between the two poles of the photosensitive transistor.At this time,the transparent window of the photosensitive transistor is covered with an object,and the reading of the multimeter should be infinitely large.

Remove the shade,make the transparent window of the photosensitive transistor toward the light source,then the meter's needle should turn right to about 1kn.The more the needle deflection is,the higher the sensitivity of the tube,the pipe is good.