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Working Principle and Application Knowledge of Photoresistor

Working Principle and Application Knowledge of Photoresistor

Photoresistor applications are widely used. In addition to a variety of light control circuits, such as lighting control, adjustment and other occasions, can also be used for light control switches.

There are several photoresistor applications listed here.


1. Photoresistor dimming circuit

Fig. 1 is a typical light controlled dimming circuit. Its working principle is: when the surrounding light weakens, the resistance value of photoresistor RG increases, the partial voltage added to capacitor C increases, and then the conduction angle of thyristor increases, so as to increase the voltage at both ends of the lamp. On the contrary, if the surrounding light becomes bright, the resistance value of RG will decrease, which will reduce the conduction angle of thyristor, and the voltage at both ends of the lamp will decrease at the same time, so that the light will be dimmed, so as to realize the control of light illuminance.

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Fig. 1 light controlled dimming circuit


2. Photoresist light control switch

There are many kinds of light controlled switch circuits with relay control output, which take photoresist as the core element, such as self-locking light excitation, dark excitation, precise light excitation, dark excitation and so on.


Fig. 2 is a simple dark excitation relay switch circuit. Its working principle is: when the illuminance drops to the set value, due to the rise of photosensitive resistance value, VT1 is activated on, the excitation current of vt2 makes the relay work, the normally open contact is closed, and the normally closed contact is open, so as to realize the control of the external circuit.

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Figure 2 simple dark excitation light control switch


Fig. 3 is a precise switch circuit of dark excitation delay relay. Its working principle is: when the illuminance drops to the setting value, the reverse terminal potential of the op amp IC will rise due to the rise of the resistance value of the photoresist, the output will activate the VT conduction, the excitation current of the VT will make the relay work, the normally open contact will be closed, and the normally closed contact will be open, so as to realize the control of the external circuit.

 

Fig. 3 precise dark excitation light control switch


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