Working principle diagram of KD-211 digital segment switch

The electrical schematic diagram is drawn based on the actual object as shown in the attached figure.

　　The core component of this circuit is a decade counter (timing decoder) IC

　　HEF4017BP (pin 10 is the power supply terminal, pin 8 is the ground terminal, pin 10 is the pulse signal input terminal, and pin 10 is the reset terminal), two 12v relays and two NPN transistors C945, etc., constitute a two-unit combined electronic switch. The circuit power supply passes through two voltage regulator diodes VD1jll]VD2 (1N4741A) that serve as both voltage regulator and rectifier. A full-wave rectifier circuit is cleverly formed.

　　1. Working principle analysis

　　1. Rectification and filtering part

　　When the main switch zK is closed, the positive half-cycle voltage of the AC power is reduced and limited by capacitor C1, and the voltage regulator VD| is rectified by the rectifier tube, and VD2 plays a voltage stabilizing role. D2 and VD2 are connected in series in the same direction, which increases the voltage stabilization value of VD2 by about 0.7V. D2 provides the positive half-cycle circuit of the AC power.

　　It also isolates the negative half cycle of the mains. When the negative half cycle of the mains comes, the voltage regulator tube VD2 acts as a rectifier tube, and VD1 acts as a voltage regulator. D1 is connected in series with VD1, which increases the voltage regulation value of VD1 by about 0.7V. Similarly, D1 also provides a negative half cycle loop for the mains, and isolates the positive half cycle. In this way, VDI and VD2 form a full-wave rectification. A DC voltage of about 12V is obtained at the negative end of VD1 and VD2. After filtering by C2 and C4, one path supplies power to the two relays of the electronic switch, and the other path provides a zero-crossing pulse signal for the ⑩ pin of IC through the current limiting resistor R5. At the same time, this voltage is rectified twice by D8 and filtered by C3 to provide working voltage for the power supply terminal ⑩ pin of lCHEF401'IBP.

　　2. Working principle of electronic switch part

　　When the main switch ZK is closed for the first time, the pulse signal provided by the resistor R5 is input from the pulse signal input terminal ⑩ of IC, and after being recognized and processed by the IC timing decoder, a high level is output from the ③ pin, so that the electronic switch composed of transistors Q1 and Q2 and two 12V relays DJ1 and DJ2 and other components are all activated, and the normally open contacts JK1 and JK2 of the two relays are closed, and the white and yellow lamps are fully lit. The light is soft and the color and color temperature are comfortable.

　　When the main switch ZK is closed for the second and third time, Ic (②, ④ feet output high level respectively, so that DJ1 and DJ2 are respectively actuated. The corresponding relay normally open contacts JK1 and JK2 are respectively closed. The white light and the yellow light are respectively lit. Users can choose as needed.

　　In the attached figure, D3 to D6 are isolation diodes, which respectively isolate the high levels of Ic②, ③, and ④ pins, so that they will not interfere with the operation of the electronic switch.