NE555 makes electrical intermittent operation controller

This circuit is mainly composed of a 555 time-base integrated circuit. It has the characteristics of simple circuit, stable and reliable operation, easy installation and use, and the opening and closing time of the controlled electrical appliance can be adjusted separately.

1. Working Principle

The circuit schematic is shown in the attached figure. In the figure, IC555 and RP1, R1, RP2, R2, VD1, VD2 and C1 form an astable circuit, and C5 and R4 (discharge resistor of C5), VD4, VD5, VD6, R3, C3 and C4 form a DC regulated power supply. The working process of the circuit is as follows:

When the switch SA is closed, the 220V AC voltage is stepped down by C5 and R4 (discharge resistor of C5), rectified by VD4 and VD5, and stabilized and filtered by VD6, R3, C3, and C4 to provide a relatively stable DC voltage to IC555. When SA is just closed, because the voltage across the capacitor C1 is zero and cannot change suddenly, the ② and ⑥ pins of IC are low level, the ③ pin outputs high level, and the relay K is closed. The electrical appliances are powered and the controlled appliances start to work.

At the same time, because the pin 3 of Ic is high, its pin 7 is also high, the diode VD1 is turned on, VD2 is turned off, and the power supply charges C1 through RP1 and R1, and the charging speed is adjusted by RP1. When the voltage on C1 is charged to 2/3 of the power supply voltage, the pins 2 and 6 of Ic become high, and the pin 3 becomes low accordingly. Relay K1 is released, the electrical appliance loses power, and the controlled appliance stops working. Since the pin 3 of Ic becomes low, the pin 7 will also become low, the diode VD1 is turned off, and VD2 is turned on. The capacitor C1 discharges through R2 and RP2, and the discharge speed is adjusted by RP2. When the voltage on C1 is reduced to 1/3 of the power supply voltage, the pins 2 and 6 of IC become low again, and the entire circuit will repeat the above working process.

2. Component selection

In this circuit, the integrated circuit IC uses the NE555 time base circuit. The relay K1 can use a small or medium power relay with a rated working voltage between 9V and 12V, and the size of its contact power should be selected according to the power size of the controlled appliance. The voltage regulator diode VD6 can be selected with a voltage regulator value of about 12V, such as 2DW21. The capacitor C5 should be a non-polar capacitor with a withstand voltage of more than 400V. There are no special requirements for other components. Just select according to the parameters marked in the figure.

3. Installation and debugging

In the circuit shown in the attached figure, except for the potentiometers RP1 and RP2, all other components can be installed on a printed circuit board. The entire circuit can be powered on for debugging only after it has been installed and checked to be correct.

After the circuit is powered on, RP1 and RP2 should be adjusted to the minimum resistance (zero resistance) first. At this time, relay K should be constantly energized and released. Its energizing and releasing time is determined by the resistance of R1 and R2 respectively. According to the values ​​given in the figure, its energizing and releasing time is about 5 seconds. If the relay does not energize or does not release after energizing after energizing, it indicates that there is a fault in the circuit. At this time, the relay and VD3 can be temporarily disconnected from pin 3 of Ic, and then the voltage of pin 3 can be measured with the voltage block of the multimeter to see if it changes continuously between high level (about 10V) and low level (0V). If it changes, it means that the astable circuit part is normal, and the fault lies in relay K and protection diode VD3. If the voltage of pin 3 of Ic does not change (always high or low), it means that there is a fault in the astable circuit part.

After the circuit works normally, you can calibrate the time at the knobs of RP1 and RP2. Adjust RP1 and RP2 appropriately according to the working time of the electrical appliances to control the working and stopping time of the electrical appliances. According to the values ​​of RP1, RP2 and C1 marked in the figure, the maximum working and stopping time of the electrical appliances can be controlled to be about 60 minutes. If a longer time is required, the values ​​of RP1, RP2 and C1 can be appropriately increased.