Photoresistor or photoresistor (LDR) Light-dependent resistor is known in English as one of the electronic components made with a special substance that can change its resistance when light hits it. To learn more about this component, let's find out more information in the content below.
What is Photoresistor (LDR)?
Photoresistor also known as photoresistor, photoresistor, photocell is one of the components made with a special substance that can change its resistance when light hits it. Basically, you can understand it as a photovoltaic cell that works on the principle of photoconductivity. Or it can be understood as a resistor that can change its value according to the intensity of light.
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Photoresistor is widely used in light sensor circuits, street lights, light alarms, outdoor clocks, etc.
Structure and working principle of photoresistor
1. Structure of photoresistor
The structure of the photoresistor consists of two parts: the upper part and the lower part are metal films connected to each other through the terminals. The device is designed in such a way as to provide the maximum contact area with the 2 metal films and is housed in a plastic case that can be exposed to light and can sense changes in intensity. the light.
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The main component to create the photoresistor is Cadmium Sulphide (CdS) used as a photoconductor, usually containing no or very few electrons when not illuminated by light.
2. Working principle
The photoresistor is made of a very high impedance semiconductor without a junction. In the dark, photoresistors often have a resistance of several MΩ. When there is light on, the resistance value can be reduced from one to several hundred Ω.
The principle of operation of photoresistor is based on the principle of photoelectric effect in a mass of matter. When photons with enough energy hit, they will cause electrons to bounce off molecules and become free electrons in the mass and from semiconductors to conduct electricity. The degree of electrical conductivity of the photoresistor depends on the majority of the absorbed photons.
When light enters the photoresistor, electrons will be released and conductivity will be increased. Depending on the semiconductor, the photoresistors will react differently to different types of photon waves.
Advantages and disadvantages and some simple photoresistor application circuits
- Advantages: Optical resistors have a number of advantages such as low cost, variety of sizes that can be applied to many different boards, common sizes with a face diameter of 10mm. Along with that is energy consumption and small operating voltage.
- Cons: Slow response time so accuracy will not be high. Photoresistor response times range from tens to hundreds of milliseconds.
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Some simple photoresistor application circuits
1. Alarm circuit using photoresistor
When the photoresistor is illuminated, the resistance will be very small at this time, the gate voltage of the SCR will not drop enough current to trigger the SCR to operate. When there is no light source, the R value of the photoresistor will increase rapidly, causing the SCR gate voltage to increase, making the SCR conductive, the current will now pass through the load to make the alarm circuit work.
2. Circuit to open electric lights automatically at night
During the day with light shining on the photoresistor, the resistor value will be very small at this time, so the voltage at point A1 will not be enough to open the Diac, so no electricity will go through the control pin of the Triac, so the Triac will not work. , resulting in no light.
At night, when there is no light on the photoresistor, the value at this time will increase, causing the voltage at point A1 to increase, opening the Diac and activating the Triac to conduct electricity and light the bulb.
Reference: Encyclopedia of Clinical Neuropsychology
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