Photosensitive automatic dimming desk lamp circuit and principle

The automatic dimming desk lamp introduced in this article can automatically adjust the amount of light emitted by the desk lamp according to the intensity of the surrounding environment. When the ambient illumination is weak, its luminous brightness increases; when the ambient illumination is strong, its luminous brightness decreases.

Dimmable desk lamp circuit and working principle

The lamp circuit is shown in Figure 1. When the switch S is moved to position 2, it is an ordinary dimming desk lamp. RP, C and neon bubble N form a relaxation oscillator, which is used to generate pulses to trigger the thyristor VS. Generally, the glow turn-on voltage of neon bulbs is 60-80V. When C is charged to the glow voltage, N glow turns on and VS is triggered to turn on. Adjusting RP can change the C charging rate, thereby changing the VS conduction angle to achieve the purpose of dimming. R2 and R3 form a voltage divider that also charges C through VD5. Changing the voltage divider of R2 and R3 can also change the VS conduction angle, causing the brightness of the lamp to change.

When S is turned to position 1, the photoresistor RG replaces R3. When the surrounding light is weak, RG shows high resistance, the potential at the right end of VD5 increases, the charging rate of capacitor C accelerates, the oscillation frequency becomes higher, and the VS conduction angle increases. The voltage across the lamp increases and the height increases. When the ambient light increases, the RG resistance becomes smaller. Contrary to the above, the voltage across the lamp becomes lower and the height decreases.

Component selection, production and debugging

When debugging, adjust RP to the zero resistance position, place S in position 2, use a multimeter to measure the AC current at both ends of the lamp and it should be above 200V. If it is lower than 200V, you can slightly reduce the resistance of R1 or increase the resistance of R3 to make it reach Require. The photoresistor RG should be installed on the side of the desk lamp base where the desk lamp light cannot be directly illuminated to sense the ambient illumination. The light bulb of the dimming desk lamp should be a 40W incandescent lamp. The adjusted circuit can be put into use; Dial S to 2 for an ordinary dimming desk lamp, adjust RP to select the appropriate high density; Dial S to 1 for an automatic desk lamp, first adjust RP to select the appropriate brightness, such as when the ambient illumination dims , the brightness of the desk lamp will gradually become brighter, increasing the illumination.