Use NE555 to make push-button delay energy-saving lamps (1)

The circuit of using NE555 to make a push-button delay energy- saving lamp is shown in Figure 3-5. The circuit
consists of a time base integrated circuit, a power supply circuit and a relay control circuit.
    Normally, the normally open contact kl between the key switch SB and the relay is partially open, so the lamp H does not light up and the entire circuit does not consume
power. When you need to turn on the light, just press the switch SB, and the light H will be powered on and glow immediately. At the same time, the 220V AC power is stepped down by capacitor
C1, rectified by diodes VDl~VD4, stabilized by voltage regulator tube VD5 and filtered by capacitor C2, and outputs about 12V DC voltage.
At this time, the capacitor C3 is charged through the resistor R2. Since the voltage at both ends of the capacitor cannot change suddenly, the value terminal 6 of the time base circuit A
is at a high level, the time base circuit is reset, and its output terminal 3 outputs a low level, and the relay K gets the electric suction table, and the contact kl is closed
to make the circuit self-locking, so even though the switch SB is tripped at this time, the lamp H can still keep lighting. As the charging of capacitor C3
continues, the level of pin 2 of the trigger terminal of time base circuit A continues to decrease. When it drops to 1/3 of the power supply voltage, the circuit flips and sets
, pin 3 of the output terminal outputs high level, and relay K loses When the electricity is released, the contact kl jumps to release the self-locking, the circuit returns to the original
starting state, and the light H goes out. At this time, the charge stored in C3 can be discharged through the internal resistance of the time base circuit and the diode VD6
, which can prepare for the delay of turning on the light next time. The delay time of the circuit, that is, the lighting time of lamp H, only depends on
the charging time constants of R2 and C3, and has nothing to do with other factors such as the power supply voltage. Using the graphic data, each time SB is pressed, the light will light up for about two
to three minutes. If you need to extend the time, you can increase the value of R2 (or C3); otherwise, decrease the value of R2 (or C3).