Design and analysis of touch delay switch circuit composed of CD4011 and CD4001

Touch delay switch circuit composed of CD4011 and CD4001

The figure shows the touch delay switch experimental circuit. It consists of a full-wave bridge rectifier circuit composed of rectifier diodes VD1~VD4, which serves as the working power supply of the integrated circuit. The four 2-input NAND gates 4011 and the unidirectional thyristor VS1 form the touch switch circuit. The full-wave bridge rectifier circuit outputs up to 200V pulsating DC, which is divided by resistors R1 and R2 and filtered by capacitor C1 to output about 13V DC as the working power supply of the IC. When the lighting lamp EL is on, the total steady-state working current of 4011 (click to view: CD4011 Chinese data (function, truth table, pin diagram and electrical parameters)) is less than 20μA. When the light is off, the current of 401l (using a 50μA range) is almost impossible to measure, which shows the low power consumption of CMOS integrated circuits. In addition, when the lighting lamp EL is on, the R2 voltage drops to 2V, and 4011 can still work. This is why CMOS digital integrated circuits are selected.

Figure Touch delay switch circuit

When the metal sheet A end is touched by hand, the induced AC signal added to the input end of IC-1 through the voltage-dropping resistors R3 and R4. In the positive half cycle of AC, the pins 1 and 2 of IC-1 are high, and its output end drops to a low level. The output pin 4 of the connected IC-2 rises to a high level, and charges the timing capacitor C2 through the switching diode VD5, so that the input end of IC-3 rises to a high level, and its output pin 10 is low. The output pin 11 of IC-4 is high, and is added to the unidirectional thyristor control electrode G through the resistor R7, triggering VS1 to turn on, and the load lighting lamp EL lights up. When the charge of C2 is gradually discharged through the timing resistor R6, causing the voltage to drop below the CMOS gate opening voltage, the output end of IC-3 rises to a high level, the output end of IC-4 is low, the unidirectional thyristor is blocked, and EL is extinguished. When R6 is 1MΩ and C2 is 10μF, the touch switch control delay is about 17s. When C2 is changed to 22μF, the delay is doubled. When C2 is 47μF, the delay is more than enough.

In the touch switch circuit, R5 is a pull-down resistor. Although its resistance value is 1MΩ, the input of the NAND gate IC-1 is at a low level, indicating that the input impedance of the CMOS digital integrated circuit is very high. The remaining inputs of the four-input NAND gate 4011 cannot be left floating. They are connected in parallel and used as a NOT gate. The IC can also use the four-input NAND gate 4001