Photosensitive resistance consists of structure

A voltage is applied between the metal electrodes at both ends of the photosensitive resistance, in which a current passes through. When the light at the appropriate wavelength is irradiated, the current will increase with the increase of light intensity, thus achieving photoelectric conversion.Photosensitive resistor has no polarity, it is purely a resistance device. When using, it can add either dc voltage or ac voltage.

Photosensitive resistance is made of semiconductor material and works by internal photoelectric effect.Under the action of light its resistance value tends to become smaller, this phenomenon is called the photoconductive effect, therefore, photosensitive resistance is also known as the photoconductive tube.

Structure principle

Photosensitive resistance is a special resistor made of semiconductor materials such as sulfur barrier or selenide barrier.The principle of photosensitive resistance is based on the internal photoelectric effect, that is, the semiconductor photosensitive material on both ends of the electrode lead, it is encapsulated in a tube shell with transparent window to form a photosensitive resistance.To increase sensitivity, the two electrodes are often shaped like combs.

The conductivity of a semiconductor depends on the number of carriers in the conductor band.When the photosensitive resistor is illuminated, the electrons in the valence band absorb the photon energy and then jump to the conduction band, becoming free electrons. At the same time, holes are generated.The stronger the light, the more photoelectron-hole pairs, and the lower the resistance.When a voltage is applied to both ends of the resistor, the current flowing through the resistor increases with the increase of light.The incident light disappears, the electron-hole pair gradually recombines, the resistance gradually returns to the original value, and the current gradually decreases.

Photosensitive resistance is sensitive to light, its in the absence of light, a high impedance state, dark resistance can reach 1.5 M Ω commonly.When a light, inspire free electrons and holes in the materials, the resistance value decreases, and with the increase of light intensity, reduced resistance rapidly, light resistance value can be as small as 1 k Ω below.

The light properties of photoresistors are nonlinear in most cases and linear only in a small range.

The sensitivity of a photoresistor is the relative change in the value of its resistance when it is not exposed to light (dark resistance) and when it is exposed to light (light resistance).The ratio of the dark resistance value to the light resistance value is about 1500:1, the larger the dark resistance value, the better, when using to apply dc or ac bias, MG type photosensitive resistor is suitable for visible light.It is mainly used in various occasions such as automatic control circuit, photoelectric counting, photoelectric tracking, light-controlled lamp, automatic exposure of camera and automatic brightness control circuit of color TV set.

It works like this:

The main materials used in the manufacture of photosensitive resistors are metal semiconductors such as sulphide selenide and telluride.Generally, thin photosensitive resistor and comb ohm electrode are made by coating, spraying, sintering and other methods on the insulation substrate, and then the lead wire is connected and encapsulated in the sealed shell with transparent mirror, so as to avoid the influence of moisture on its sensitivity.The principle and structure of photosensitive resistor are shown in the figure.

In dark environment, its resistance value is very high, when when exposed to light, as long as the photon energy is greater than the semiconductor materials forbidden band width, the valence band of electron absorbs a photon energy after the transition to the conduction band, and produced a positively charged in the valence band hole, the electrons produced by light - hole to increase the number of carriers in semiconductor material, make its resistivity decreases, thus causing the deterioration of photosensitive resistance tolerance.The stronger the light, the lower the resistance.When the incident light disappears, the electron-hole pair generated by the photon excitation will gradually compound, and the resistance value of the photosensitive resistance will gradually recover to the original value.

A voltage is applied between the metal electrodes at both ends of the photosensitive resistance, in which a current passes through. When the light at the appropriate wavelength is irradiated, the current will increase with the increase of light intensity, thus achieving photoelectric conversion.Photosensitive resistor has no polarity, it is purely a resistance device. When using, it can add either dc voltage or ac voltage.

Photoresistor is a device which USES semiconductor photoconductance to detect optical signal.It can be monocrystalline thin film, polycrystalline thin film, burned polycrystalline film, vacuum evaporation film, chemical deposition film or sputtering film.

Photosensitive resistance, also known as optical conductivity, is almost always made of semiconductor materials.The structure and wiring diagram of the photosensitive resistor are shown in the figure.

When the photosensitive resistance is exposed to light, its conductivity is enhanced by the internal photoelectric effect, and the resistance value decreases. Therefore, the current flowing through the load resistance RL and its voltage at both ends also change.The stronger the light, the greater the current, and the lower the resistance.When the light stops, the photoelectric effect disappears and the resistance returns to its original value.If the photosensitive resistor is connected into a closed circuit, the current in the circuit can be changed by changing the intensity of light, and the optical signal can be converted into electrical signal.

Photosensitive semiconductor materials include silicon, germanium, cadmium sulfide, lead sulfide, indium antimonide, cadmium selenide and so on.For pure semiconductors without luminescence characteristics, an appropriate amount of impurities can be added to produce photoelectric effect characteristics.The substances used to produce this effect are composed of metal sulfides, selenides, tellurides, etc., such as cadmium sulfide, lead sulfide, thallium sulfide, bismuth sulfide, cadmium selenide, lead selenide, lead telluride, etc.The application of photoresistor depends on a series of characteristics, such as dark current, photocurrent, volt-ampere characteristic of photoresistor, light characteristic, spectral characteristic, frequency characteristic, temperature characteristic, sensitivity, time constant and optimal working voltage of photoresistor.