Photoresistors

    l  The characteristics of photoresistors

Photoresistor is a special resistor made of semiconductor photoconductive effect. In a light and dark environment, its resistance changes, and it is a component that can convert the optical signal to the electric signal.

A device made of a photoresistor is also called a " light pipe ", which is a photosensitive conversion element that is subject to light exposure and the conductivity increases. According to the materials used to make the photosensitive layer, the photoresistor can be divided into a polycrystalline photoresistor and a single crystal photoresistor. According to the spectral characteristics of the photoresistor, it can be divided into ultraviolet photoresistor, visible light photoresistor and infrared photoresistor. Visible light photoresistors are selenium, cadmium sulfide, cadmium selenide, cadmium telluride, gallium arsenide, silicon, germanium, zinc sulfide photoresistor, etc. The ultraviolet photosensitive resistor is very sensitive to ultraviolet ray, and can be used for detecting ultraviolet ray, and the more common photosensitive resistor of cadmium sulfide and cadmium selenide. The infrared photosensitive resistor includes lead sulfide, lead telluride, lead selenide, indium antimonide, lead telluride, germanium doped mercury, germanium doped gold and other photosensitive resistors. The ultraviolet photosensitive resistor and the infrared photoresistor are mainly used in industrial electric appliances and medical instruments. The visible light photoresistor can be applied to various household electronic devices in preparation.

l  The main parameters of the photoresistors

( 1 ) The relationship between the voltage applied across the photoresistor and the current flowing across the photoresistor is called the volt-ampere characteristic, and the higher the voltage is, the larger the photocurrent, the less saturation. At a given voltage, the number of photocurrent will increase with the increase of illumination.

(2) Photocurrent.

The resistance of photosensitive resistor is called "dark resistance" or dark resistance when it is not exposed to light. The current flowing through it is called "dark current". The resistance in light is called "bright resistance" or "light resistance", and the current is called "light current". The difference between a bright current and a dark current is called a photocurrent. The larger the dark resistance, the smaller the photoresist, the greater the photocurrent, the higher the sensitivity of the photosensitive resistor. In fact, the dark resistance of photoresist is generally Mega ohmic, and the resistance is less than a few thousand ohms. The ratio of dark resistance to photoresist is about 1: 100.

(3) Light characteristics. A photosensitive resistor is very sensitive to light. When no light is applied, the photosensitive resistor is in a high resistance state, and the resistance decreases rapidly when exposed.

l  The detection of a photosensitive resistor

The resistance of photosensitive resistor varies with the intensity and intensity of the light emitted by human, and there is no positive or negative polarity. The dark resistance of photosensitive resistor is larger when no light is irradiated, and the brightness resistance measured by light irradiation is smaller.

(1) the detection of the light resistance and the dark resistance of the photosensitive. First , the photosensitive resistor is placed in the dark, the light sensitive resistor is shielded with a black paper, and the two form of the two form is arbitrarily connected to the two pin of the photosensitive resistor. At this time, the pointer of the multimeter is basically kept and the resistance is close to the infinity. This value is the dark resistance value, the greater the sensitivity of the resistor.

 If the value is small or close to zero, the photosensitive resistor has been damaged. The photosensitive resistor is placed on the bright spot and the light sensitive resistor is illuminated with a light source. The pointer of the multimeter should be greatly swung and the resistance value decreases obviously. This value is a bright resistance value. The better the resistance is, the better the performance of the photosensitive resistor. If this value is large or even infinite, it indicates the open circuit damage of the photosensitive resistor.

 ( 2 ) Detection sensitivity changes the photoresistor in the dark place in the dark, and the pointer of the multimeter should swing around with the light and dark changes. If the multimeter pointer does not swing, the photosensitive material of the photoresistor has been broken.