Typical application circuit diagram of photoresistor type light control switch

Photoresistors are generally widely used in various light control circuits, monitoring light panels, toy controls, etc., such as light control and adjustment, and can also be used for light control switches. Here are several typical application circuits.

1. Photoresistor dimming circuit

The picture shows a typical light-controlled dimming circuit. Its working principle is: when the surrounding light becomes weak, the resistance of the photoresistor RG increases, causing the partial voltage on the capacitor C to increase, thereby increasing the thyristor's resistance. The conduction angle increases to achieve the purpose of increasing the voltage across the lighting lamp. On the contrary, if the surrounding light becomes brighter, the resistance of RG decreases, causing the conduction angle of the thyristor to become smaller, and the voltage at both ends of the lighting lamp also decreases, making the light darker, thereby achieving control of the light illumination.

2. Photoresistor type light control switch

There are many forms of light-controlled switch circuits with relay control output using photoresistors as core components, such as self-locking bright excitation, dark excitation, precision bright excitation, dark excitation, etc. Several typical circuits are given below. The picture shows a simple dark-excited relay switching circuit. Its working principle is: when the illumination drops to the set value, the rise in the resistance of the photoresistor triggers VT1 to turn on, and the excitation current of VT2 causes the relay to work. The normally open contact is closed and the normally closed contact is opened to realize control of the external circuit.

3. Simple dark-activated light-controlled switch

The picture shows a sophisticated dark excitation time-delay relay switching circuit. Its working principle is: when the illumination drops to the set value, the potential of the inverting end of the op amp IC increases due to the increase in the resistance of the photoresistor. Its output stimulates VT to conduct, and the excitation current of VT causes the relay to work and the normally open contact closes. , the normally closed contact is disconnected to realize control of the external circuit.