Photoresist symbol recognition and application circuit

Photocoupler

Photosensitive resistors, also known as light pipes, are characterized by a rapid decrease in resistance under the illumination of specific light and can be used to detect visible light. The photoresistor is a resistor made by utilizing the photoelectric effect of the semiconductor to change with the intensity of the incident light; the incident light intensity, the resistance is reduced, the incident light is weak, and the resistance is increased. Photoresistors are commonly used for light measurement, light control, and photoelectric conversion (converting changes in light into electrical changes).

Classified by material:
Polycrystalline and single crystal photoresistors can also be classified into cadmium sulfide (CdS), cadmium selenide (CdSe), lead sulfide (PbS), lead selenide (PbSe), indium antimonide (InSb) photoresistors, etc. Classification of spectral characteristics:
UV Photosensitive Resistors: Sensitive to UV light for UV detection.
Infrared Photosensitive Resistors: widely used in missile guidance, astronomical detection, non-contact measurement, human lesion detection, infrared spectroscopy, infrared communication and other visible light photoresistors: mainly used in various photoelectric control systems, such as photoelectric automatic switch portal, navigation light Automatic lighting of street lamps and other lighting systems, automatic water supply and automatic water stop devices, mechanical automatic protection devices and "position detectors", thickness detectors for extremely thin parts, camera automatic exposure devices, photoelectric counters, smoke alarms , photoelectric tracking system and other aspects.
Photoresist parameters:
(1) Photocurrent, bright resistance. When a photoresistor is exposed to light at a certain applied voltage, the current flowing through it is called photocurrent. The ratio of applied voltage to photocurrent is called bright resistance. It is commonly used as “100LX” to indicate (2) dark current and dark resistance. . When a photoresistor is exposed to a certain applied voltage, the current flowing through it is called a dark current. The ratio of applied voltage to dark current is called dark resistance and is usually expressed as "0LX".
(3) Sensitivity. The sensitivity refers to a relative change value of the resistance value (dark resistance) when the photoresistor is not irradiated with light and the resistance value (bright resistance) when irradiated with light.
(4) Spectral response. Spectral response, also known as spectral sensitivity, refers to the sensitivity of a photoresistor to monochromatic light at different wavelengths. If the sensitivity at different wavelengths is plotted as a curve, a curve of the spectral response can be obtained.
(5) Lighting characteristics. The illumination characteristic refers to the characteristic that the electrical signal output by the photoresistor changes with illuminance. It can be seen from the light characteristic curve of the photoresistor that as the light intensity increases, the resistance of the photoresistor begins to decrease rapidly. If the light intensity is further increased, the resistance value decreases and then gradually becomes gentle. In most cases, this property is non-linear.
(6) Voltammetric characteristic curve. The volt-ampere characteristic curve is used to describe the relationship between the applied voltage of the photoresistor and the photocurrent. For a photosensitive device, the photocurrent increases as the applied voltage increases.
(7) Temperature coefficient. The photoelectric effect of the photoresistor is greatly affected by temperature, and some of the photoresistors have higher photoelectric sensitivity at low temperatures and lower sensitivity at high temperatures.
(8) Rated power. Rated power refers to the power that a photoresistor is allowed to consume in a certain line. When the temperature rises, the power consumed by it decreases.
Photosensitive resistor application circuit:
a, the control LED is on, when the photoresistor RL has illumination, the resistance becomes smaller, and the voltage at point A decreases. When the voltage at point A is lower than the voltage at point B, the comparator LM393 outputs a low level, that is, the voltage at point C is 0V. The LED light is on. The adjustable resistor RP is used to adjust the sensitivity. (LXD-4MM or LXD-5MM series high precision photoresistors are recommended)


b. When there is light, VT1 is turned off, and the relay is driven when there is no light.

c. When there is no light, the voltage of the comparator 2 input terminal is increased. When the voltage is higher than the voltage of the positive input terminal 3, the 6-pin output low-level driving relay acts, the relay normally open contact is closed, and the control is outside. Circuit.