Stable brightness dimming desk lamp circuit

Dimmable desk lamp with stable brightness. Not only is the brightness of this dimmable desk lamp adjustable, but the adjusted brightness will not change due to fluctuations in the grid voltage. working principle 　　　　　　　　　　　　　　　　　　　　

The circuit is shown in Figure 1. The resistor-capacitor phase shift circuit composed of R2, RP1 and C1 determines the conduction angle of the thyristor. When the voltage at both ends of C1 rises to the conduction voltage of the bidirectional trigger tube through R2 and RP1, the triac VS is triggered to conduct. When the alternating current crosses zero, the triac makes its own judgment. Adjusting RP1 can change the voltage of C1. Charging time, thereby changing the conduction angle of the triac during the positive and negative half cycles of the alternating current, in order to obtain the required brightness. In the figure, R3, RP2 and photoresistor R4 are connected in series and then in parallel with C1. When R3 and RP2 are fixed, the size of the shunt is determined by the resistance of the photoresistor R4. When the power grid voltage rises, the brightness of the light increases, the illumination received by the photoresistor R4 increases, the resistance decreases, and the shunt increases. The voltage across C1 rises slowly, the conduction angle of the thyristor increases, the output voltage increases, and the brightness of the light also increases accordingly. This automatically stabilizes the output voltage at the required value, ensuring the stability of the light brightness. The component selection and production component list is shown in the table below. No. Name Model Quantity R1 Resistor 5.1K 1 R2 Resistor 6.8K 1 R3 Resistor 47K 1 R4 Photoresistor 1 RP1 Adjustable resistor 47K (with switch) 1 RP2 Trimming resistor 200K 1 C1 Polyester capacitor 0.01－0.047u 1 KS Bidirectional trigger tube DB -3 1 VS Triac 3A/400V 1 Triac VS optional 3A/400V. RP1 is a 47K potentiometer with switch. The two-way trigger tube can be replaced by a fluorescent lamp starter neon bulb. The photoresistor R4 can be installed on the decoration of the desk lamp, and it is required to be illuminated by the desk lamp. When debugging, first adjust RP2 to the minimum value, and use paper to block the light so that the photoresistor is not exposed to light, turn on the power, and adjust RP1 to make the light at its brightest. Then take the paper away. If the light changes slightly, it means that RP2 does not need to be adjusted at this time. If the brightness does not change after R4 is illuminated, you should adjust RP2 to make the light drop slightly. If the brightness of R4 changes greatly after being illuminated, the resistance of R3 should be increased; RP2 does not need to be adjusted again after being adjusted once.