China Photoresistor Supplier

What is a Photoresistor?
Light-dependent resistors (light-dependent resistors, the latter abbreviated as ldr) or photoconductors are commonly made of cadmium sulfide, and there are also materials such as selenium, aluminum sulfide, lead sulfide, and bismuth sulfide. These fabrication materials have the characteristic that their resistance value decreases rapidly under the irradiation of light of specific wavelength. This is because the carriers generated by light are all involved in conduction, drifting under the action of an external electric field, the electrons rush to the positive pole of the power supply, and the holes rush to the negative pole of the power supply, so that the resistance of the photoresistor drops rapidly.

Introduction to photoresistors
Photoresistors are special resistors made of semiconductor materials such as cadmium sulfide or cadmium selenide, and their working principle is based on the internal photoelectric effect. The stronger the light, the lower the resistance. As the light intensity increases, the resistance value decreases rapidly, and the bright resistance value can be as small as below 1KΩ. Photoresistors are very sensitive to light. When there is no light, they are in a high-resistance state, and the dark resistance can generally reach 1.5MΩ. The special properties of photoresistors will be widely used with the development of science and technology.
A photoresistor is a resistor made of the photoconductive effect of a semiconductor whose resistance value changes with the intensity of the incident light, also known as a photoconductive detector;
When the incident light is strong, the resistance decreases, and when the incident light is weak, the resistance increases. There is another kind of weak incident light, the resistance decreases, and the incident light is strong, the resistance increases.
Photoresistors are generally used for light measurement, light control, and photoelectric conversion (conversion of light changes into electrical changes). Commonly used photoresistors are cadmium sulfide photoresistors, which are made of semiconductor materials. The sensitivity of the photoresistor to light (that is, the spectral characteristics) is very close to the response of the human eye to visible light (0.4~0.76) μm. As long as the light that the human eye can perceive will cause its resistance to change. When designing the light control circuit, the light of incandescent bulb (small electric bead) or natural light is used as the control light source, which greatly simplifies the design.

CDS Photoresistor - PGM Series Photoresistors are typically constructed using an active semiconductor material layer attached to an insulating substrate. Semiconductors are generally added with a small amount of additives to enable it to have the necessary level of conductivity. Contact surfaces are usually placed on both sides of the skin. Photoresistors, CDS or LDR are often used in low-cost light-sensing components. Such as photographic light meters, smoke, flame and burglar detectors, card readers, lighting controls, and street lights that have been used for many years. YAXUN electronic PGM series provides design engineers with an economical, high-quality, high-performance CdS and LDR commercial-grade photosensitive components with high sensitivity and small size. Available in standard sizes of 5mm, 12mm, and 20mm, the PGM is epoxy-coated or hermetically sealed to provide high-quality performance for applications requiring fast response and good spectral characteristics. YAXUN Electronics has decades of experience in the production, design, and manufacture of high-performance photoelectric components, providing a wide range of photoelectric products, and our experience is as mature as customer-defined photoresistors. Email or call us for the latest information on this product. characteristic:      High sensitivity and small size.      Ambient temperature -30°C ~ +70°C.      Epoxy or metal hermetic package.      Good spectral characteristics and good reliability. application:      Light control switch.      Light control relay.      Automatic flash camera.      Electronic toys, industrial control.

Environmentally Friendly Photosensor PT-IC-GC Series Environmentally friendly photosensitive sensor PT-IC-GC series adopts advanced infrared filter coating process, which can filter infrared rays, high temperature resistance, and high consistency. Photosensitive triode, also known as photoelectric triode, is a photoelectric conversion device. Its basic principle is that when light shines on the P-N junction, it absorbs light energy and converts it into electrical energy. When the photosensitive triode is applied with a reverse voltage, the reverse current in the tube changes with the light intensity. The greater the light intensity, the greater the reverse current, and most of them work in this state. The phototransistor is similar to the ordinary triode, and it also has a current (Current) amplification effect, but its collector current is not only controlled by the base circuit and current, but also by light radiation. Usually the base is not drawn out, but the base of some photosensitive triodes is drawn out for temperature compensation and additional control. PT-IC-GC is packaged with imported chips, and the surface of the chip is super-coated with infrared filter film technology, which can completely filter infrared interference, no need to add sleeves and filters, and effectively filter the impact of infrared emission light reflection in security products. Through the selection of the precision of the chip in the early stage and the strict management of the subsequent production process, the batch consistency of the finished product is excellent! Compared with similar photosensitive devices, the consistency is 3~5 times higher. The minimum accuracy can be controlled to plus or minus 10%. It can fully meet the customer's demanding requirements on the starting LUX value. The internal temperature compensation process of the chip works at high temperature, and its temperature resistance is twice as high as that of similar products. Features : Similar to the human eye's light sensitivity, the peak light sensitivity wavelength is 520nm, the chip uses a super 82-layer coating process, and 100% filters infrared interference. The batch consistency is good, and the phenomenon of premature start of the infrared lamp or poor consistency is completely solved. Fast response and stable performance, the starting point does not drift after aging for 1000H at +85°C high temperature/65% high humidity conditions. nice appearance. Function : It replaces traditional CDS photoresistors, does not contain harmful substances such as cadmium and lead, and complies with EU ROHS standards. It is specially used for infrared monitoring products, and controls the operation of infrared lamps under low illumination, without adding casings and filters. Tailored : Different dimensions can be provided upon request, which is convenient for installation in any position of the product. The most suitable bright currentdark current (bright resistancedark resistance) can be provided according to the demand, which makes the product more consistent and more competitive in the market.

Specifications and models of photoresistors
Usually, photoresistors are made into thin sheets to absorb more light energy. When it is irradiated by light, electron-hole pairs are excited in the semiconductor sheet (photosensitive layer) to participate in conduction, so that the current in the circuit is enhanced. In order to obtain high sensitivity, the electrode of the photoresistor often adopts a comb pattern, which is formed by evaporating metal such as gold or indium on the photoconductive film under a certain mask. The structure of a general photoresistor is shown on the right.
A photoresistor usually consists of a photosensitive layer, a glass substrate (or resin moisture-proof film) and electrodes. The photoresistor is represented by the letter "R" or "RL" or "RG" in the circuit.
Photoresistors are commonly made of cadmium sulfide (CdS). It is divided into two types, epoxy resin package and metal package, both of which belong to the wire type (DIP type). Epoxy resin encapsulated photoresistors are divided into Ø3mm, Ø4mm, Ø5mm, Ø7mm, Ø11mm, Ø12mm, Ø20mm, Ø25mm according to the diameter of the ceramic substrate.

Parameter characteristics of photoresistors
According to the spectral characteristics of the photoresistor, it can be divided into three types of photoresistors: ultraviolet photoresistors, infrared photoresistors, and visible light photoresistors.
The main parameters of the photoresistor
The main parameters of the photoresistor are:
(1) Photocurrent, bright resistance: Under a certain applied voltage, when there is light, the current flowing through the photoresistor is called photocurrent, and the ratio of the applied voltage to photocurrent is called bright resistance, which is often expressed by "100LX".
(2) Dark current, dark resistance: Under a certain applied voltage, when there is no light, the current flowing through the photoresistor is called dark current. The ratio of the applied voltage to the dark current is called the dark resistance, which is often expressed as "0LX" (the intensity of light is measured with an illuminance meter, and its unit is Lax lx).
(3) Sensitivity: Sensitivity refers to the relative change value of the resistance value (dark resistance) when the photoresistor is not irradiated by light and the resistance value (bright resistance) when it is irradiated by light. The ratio between the dark resistance and the light resistance of the photoresistor is about 1500:1, and the larger the resistance value of the dark resistance, the better the characteristics. The larger the dark resistance, the smaller the bright resistance, and the greater their relative change value, that is, the larger the bright current, the smaller the dark current, and the higher the sensitivity of the photoresistor.
(4) Spectral response: Spectral response, also known as spectral sensitivity, refers to the sensitivity of the photoresistor under the irradiation of monochromatic light of different wavelengths. If the sensitivity at different wavelengths is plotted as a curve, a curve of spectral response can be obtained.
(5) Illumination characteristics: Illumination characteristics refer to the characteristics that the electrical signal output by the photoresistor changes with the illuminance. It can be seen from the light characteristic curve of the photoresistor that as the light intensity increases, the resistance value of the photoresistor begins to drop rapidly. If the light intensity is further increased, the change of the resistance value decreases, and then gradually tends to be gentle. In most cases, this characteristic is non-linear.
(6) Volt-ampere characteristic curve: Under a certain illuminance, the relationship between the voltage and current applied to both ends of the photoresistor is called the volt-ampere characteristic. Under a given bias voltage, the greater the illuminance, the greater the photocurrent. Under a certain illuminance, the greater the applied voltage, the greater the photocurrent, and there is no saturation phenomenon. But the voltage cannot increase infinitely, because any photoresistor is limited by the rated power, maximum working voltage and rated current. Exceeding the maximum working voltage and maximum rated current may cause permanent damage to the photoresistor.
(7) Temperature coefficient: The photoelectric effect of photoresistor is greatly affected by temperature. Some photoresistors have higher photoelectric sensitivity at low temperature, but lower sensitivity at high temperature.
(8) Rated power: The rated power refers to the power that the photoresistor is allowed to consume in a certain circuit. When the temperature rises, the power consumed will decrease.
(9) Refers to the photoresistor from the light jump to the stable bright current.

Frequency characteristics of photoresistors
When the photoresistor is irradiated by pulsed light, the photocurrent will reach a stable value after a period of time, and the photocurrent will not be zero immediately after the light is stopped, which is the time delay characteristic of the photoresistor. Due to the photosensitive and resistive delay characteristics of different materials, their frequency characteristics are also different. The frequency of use of lead sulfide is much higher than that of cadmium sulfide, but the time delay of most photoresistors is relatively large, so it cannot be used in applications requiring fast response.

Application of Photoresistor
Photoresistors are semiconductor photosensitive devices. In addition to the characteristics of high sensitivity, fast response, good consistency of spectral characteristics and r value, it can also maintain a high degree of stability and reliability in harsh environments with high temperature and humidity. Can be widely used in cameras, solar garden lights, lawn lights, banknote detectors, quartz clocks, music cups, gift boxes, mini night lights, light and sound control switches, street light automatic switches and various light control toys, light control lighting, lamps, etc. Automatic switch control field. Several typical application circuits are given below.

Dimming circuit of photoresistor
Figure (1) is a typical light control dimming circuit, its working principle is: When the ambient light becomes weaker, the resistance of the photoresistor increases, which increases the partial pressure on the capacitor C, and then increases the conduction angle of the thyristor, so as to increase the voltage at both ends of the lighting lamp. Conversely, if the surrounding light becomes brighter, the resistance of RG decreases, resulting in a smaller conduction angle of the silicon controlled rectifier, and the voltage at both ends of the lighting lamp also decreases at the same time, dimming the light, thereby realizing the control of the light illuminance.
The rectifier bridge in the above circuit must provide a DC pulsating voltage, which cannot be converted into a smooth DC voltage by capacitor filtering. It can also make the charging of the capacitor C start from zero every half cycle, and accurately complete the synchronous phase-shift triggering of the thyristor.

light switch
There are many forms of light-controlled switch circuits with relay control output using photoresistors as the core components, such as self-locking bright excitation, dark excitation and precision bright excitation, dark excitation, etc. Several typical circuits are given below.
Figure (2) is a simple dark excitation relay switch circuit. Its working principle is: When the illuminance drops to the set value, VT1 is turned on due to the rise of the resistance value of the photoresistor. The excitation current of VT2 makes the relay work, the normally open contact is closed, and the normally closed contact is disconnected to realize the control of the external circuit.
Figure (3) is a sophisticated dark excitation delay relay switching circuit. Its working principle is: When the illuminance drops to the set value, due to the rise of the resistance value of the photoresistor, the potential of the inverting terminal of the operational amplifier IC rises, and its output excites VT to turn on. The excitation current of VT makes the relay work, the normally open contact is closed, and the normally closed contact is disconnected to realize the control of the external circuit.

Advantages and disadvantages of photoresistors
The internal photoelectric effect has nothing to do with the electrodes (the photodiode is only relevant), that is, a DC power supply can be used.
The sensitivity is related to the semiconductor material and the wavelength of the incident light; the photoconductive gain is greater than 1. Depending on the photoconductive material, the spectral response can be extended from ultraviolet light, visible light, near-infrared to far-infrared.
Coated with epoxy, Good reliability, Small volume, High sensitivity, Quick response, Good spectrum characteristic.
The measured light intensity range is wide, which can measure both strong light and weak light.