Four-speed touch dimming circuit designed with MC14017

The circuit is shown in the figure below. After the power passes through the light bulb, it is rectified by the BR1 bridge, and then limited by the resistor R1, filtered by the capacitor C1, and stabilized by the voltage regulator D1 to provide a 6V DC power supply to the integrated circuit MC14017.

R2, C2 and push button switch SW1 form a clock pulse trigger circuit. Each time SW1 is pressed, a pulse is input to U1's (14) pin, and U1's (3), (2), (4) and (7) pins output high levels. Due to the different values ​​of R3~R6, the Vb voltage of transistor Q1 varies between 0.28V, 0.52V, 0.62V and 0.63V, and the conduction degree of the thyristor SCR is also different. Therefore, the light bulb changes cyclically between full brightness → brighter → dark → darkest → full brightness, achieving the purpose of four-speed dimming.