The area of zigzag separates the metal-placed areas into two regions. Where the Ohmic contacts are made either on the sides of the area. The resistances of the contacts must be as less as possible to make sure that the resistance, mainly varies due to the light effect only. The working principle of an LDR is photoconductivity, which is nothing but an optical phenomenon.
When the light is absorbed by the material then the conductivity of the material enhances. When the light falls on the LDR, then the electrons in the valence band of the material are eager to the conduction band. But, the photons in the incident light must have energy superior to the bandgap of the material to make the electrons jump from one band to another band valance to conduction. Hence, when light having ample energy, more electrons are excited to the conduction band which grades in a large number of charge carriers.
When the effect of this process and the flow of the current starts flowing more, the resistance of the device decreases. A voltage supply is given to the load.
This circuit changes the AC supply into a DC. The bridge rectifier circuit uses a step-down transformer to step-down the voltage from v into 12v. The diodes are connected in the form of a bridge used to alter the AC voltage into DC. The voltage regulator is used to change the 12v DC-6v DC, and then, this DC voltage is supplied to the entire circuit. A v AC supply for both the bridge rectifier and the load is to be kept continuously for continuous operation of the light sensor circuit. This is due to the resistance offered by the light-dependent resistor in the daytime or when the light falls on the LDR, then it is less compared to the resistance of the remaining part of the sensor circuit.
We are alert of the principle of current, that the flow of current always flows in the path of low resistance. Therefore, the relay coil does not get sufficient supplies to get strengthened. Hence, the light is switched off in the daylight. Thus, due to the high resistance of the resistor , the flow of current is low or almost zero.
Now, the flow of current through the low-resistance lane such that it increases the base voltage of the Darlington pair to reach more than 1. As the Darlington pair transistor is triggered, the relay coil acquires enough supply to get energized, and hence, the light switches in the nighttime. Devices that are made with different materials will respond in a different way to the wavelengths of light, which means that the various components can be employed for a variety of applications. But once working with IR, we should take care to evade heat build-up caused due to the heating effect of the radiation.
Latency is the main aspect associated with an LDR which means the time taken to respond to the components for any changes. So, this feature is particularly significant for designing a circuit. It is often used as light sensor, light meter, Automatic street lights and in area where we need to have light sensitivity.
Now a transparent coating is applied on the top so that the zig-zag shaped photosensitive material gets protected and as the coating is transparent the LDR will be able to get light from the environment for its working. It works on the principle of photoconductivity whenever the light on its photoconductive material falls it absorbs its energy and the electrons of that photoconductive material that is in the valence band get excited and go to the conduction band and thus increases the conductivity as per the increase in light intensity.
Also, the energy in incident light should be greater than the bandgap gap energy so that the electrons from the valence band got excited and go to conduction band. The LDR has the highest resistance in dark around Ohm and this resistance decreases with the increase in Light. Photodiodes give quick response and are used where needed to detect quick response on and off like in optical communication, optoisolators.
The photodiodes are semiconductor devices and work on PN junctions. The photodiode works on the principle of converting the light energy into electric energy while the LDR is a resistance and its resistance decreases with the increase in light intensity. This type of photoresistor is made with pure semiconductors without any doping.
This kind of photoresistor uses pure semiconductors like silicon and germanium. This type of photoresistor uses the doped semiconductor; this means some impurities are mixed with the semiconductor to make this photoresistor.
Save my name, email, and website in this browser for the next time I comment. Sign in Join. Sign in. These devices are doped with impurities and these impurities creates a new energy bands above the valence band. These bands are filled with electrons. Hence this decrease the band gap and small amount of energy is required in moving them.
These resistors are mainly used for long wavelengths. The circuit diagram of a LDR is shown below. When the light intensity is low, then the resistance of the LDR is high. This stops the current flow to the base terminal of the transistor. So, the LED does not light. So current flows onto the base of the first transistor and then the second transistor.
Consequently the LED lights. Here, a preset resistor is used to turn up or down to increase or decrease the resistance. Light dependent resistors have a low cost and simple structure. These resistors are frequently used as light sensors. These resistors are mainly used when there is a need to sense the absence and presence of the light such as burglar alarm circuits, alarm clock, light intensity meters, etc. LDR resistors mainly involves in various electrical and electronic projects.
For better understanding of this concept, here we are explaining some real time projects where the LDR resistors are used. This security system controlled by an electronic eye project is based on photo sensing arrangement. The proposed system uses a stage ripple carry binary counter to sense the intensity of light using LDR. This project is very useful to deter burglars from shopping malls, banks and jewelry shops, etc. This project uses a light dependent resistor.
When light falls on the LDR sensor, then the resistance of the sensor decreases, which lead to activate an alarm to give an alert to the user.
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