Chandelier control circuit

(1) Circuit composition The chandelier control circuit consists of a power supply circuit and a trigger control circuit, as shown in the figure.
    In the circuit, the power circuit is composed of power switch S, rectifier diodes VD1 ~ VD4, current limiting resistor R4, discharge resistor R, filter capacitor
c! and Zener diode vS} The trigger control circuit is composed of four NAND gate integrated circuits It is composed of IC (D1-D4), diodes VD1~VD4, resistor
island~wind, capacitors G, G, transistor VT and thyristor VTH.
    (2) Switch on state After the switch S is turned on, one channel of AC 220V voltage is applied to the third group of lighting lamps EL3 through S, and EL3 is lit;
the other channel is rectified by VD1~VD4, island current limiting step-down, and Cl filtered And after vs voltage stabilization, +12V voltage is generated. In addition to being the working power supply of the IC, the +12V voltage
also charges G through Rz and VD5. When the +12V voltage is first generated, since the voltage at both ends of G cannot change suddenly,
the input terminal of the NAND gate Dl (pins ① and ② of IC) is low level , and its output terminal (pin ◎ of lC) is at a high level. VD7 charges G, causing
the output terminals of NAND gates D and D3 (pins ④ and ⑩ of 1C) to be low level, VT and VTH are not conductive, and the lighting lamp EL1 of the first group and the lighting lamp EL2 of the second group
are not connected. Bright.
    (3) When the switch is turned off and on again, when S is turned off and then turned on immediately, during the short period of power outage. The charge stored on cl
is quickly discharged, but the charge stored on G remains unchanged. After powering on again, the +12V voltage is charged by R2 and VD5 to resist c3, causing
the charging polarity of c3 to change (from the left (negative right positive changes to left positive and right negative), the input terminals of NAND gates D and D3 (IC pins ⑤, ⑥ and ⑧, ⑨
) change from high level to low level, and the output terminal changes to high level. , causing VT1 to conduct. The high level triggers the VT and turns
it on. EL1-EL3 all light up.