Fully automatic multi-purpose intelligent lighting circuit design

When night comes, you are working and studying under the lamp, and suddenly there is a power outage and the surroundings are dark, you will definitely be at a loss. We had to fumble around in the dark looking for candles and flashlights, which was very inconvenient. There are also some special places such as hotels, restaurants or basements where people flow intensively. Due to the limitations of the building structure, artificial lighting is also required during the day. If there is a sudden power outage, especially a power outage caused by unexpected reasons such as earthquakes and fires. , which will cause great difficulties in evacuation.

The emergency light introduced in this article is usually connected to the mains power and is in a fully charged standby state. Only when the mains power suddenly fails and the ambient light suddenly changes from strong to weak, it can intelligently determine that this is darkness caused by the power outage and light it up in time. Emergency lights. It will automatically turn off after 10 minutes. At this time, people have generally evacuated to a safe place and there is no need to provide lighting. Turning off the emergency lights can also prevent excessive discharge from damaging the lead-acid battery.

Working principle: The fully automatic emergency light circuit is composed of a battery constant voltage current limiting float charging circuit and a light control delay circuit. The AC voltage is stepped down through a transformer and rectified and filtered to obtain a DC voltage of 18V. The constant voltage, current-limiting floating charge uninterruptible power supply is composed of D2, R4, 12V/1.2Ah lead-acid batteries and LM317, which can ensure that the battery is fully charged at all times. status, the floating charge voltage of the 12V lead-acid battery is 14.4V. LM317 is connected as a constant voltage source, and W is a precision multi-turn adjustable potentiometer. By adjusting W, the output point A can output a stable 15.1V DC voltage. Resistor R4 can limit the charging current, and D2 can prevent the battery from reverse discharge after a power outage. R1, R2, C1, D1, and F1 form an AC voltage detection circuit. When the AC voltage is normal, the voltage at point B is about 8 volts after voltage division. After being inverted by F1, it outputs a low level. When the AC voltage fails, because of the isolation of D1, the voltage at point B quickly drops to 0 volts, and then outputs a high level after being inverted by F1. CD4011BP is a COMS type four NAND gate integrated circuit. The logical relationship of NAND gate operation is: the output terminal outputs low level only when both input terminals input high level; as long as one of the input terminals inputs low level, it outputs high level. level. If two input terminals are connected in parallel to form one input terminal, then this NAND gate is equivalent to a NOT gate. The input characteristics of the gate circuit are: when the input voltage is less than 40% of the power supply voltage, it is an input low level; when the input voltage is greater than 60% of the power supply voltage, it is an input high level. When the output is high, the output voltage is close to the positive supply voltage; when the output is low, the output voltage is close to 0 volts. In the figure, two NAND gates F3, F4, C5, and R6 form a monostable delay circuit. The delay time is determined by the values ​​of C5 and R6. According to the values ​​in the figure, the delay time is about 10 minutes. When the delay circuit When entering the delayed monostable state, F4 outputs a low level, causing the transistor T to conduct and the light bulb to light up. The working condition of the monostable delay circuit is that F2 outputs a low level. To make F2 output a low level, both input terminals of F2 must input a high level. One of the input terminals is used to monitor the AC voltage, and only when there is a power outage. It will output a high level, and the other input terminal is the light control detection terminal. R3, GR, C4 and R5 form a light control detection circuit to detect changes in ambient light. When the ambient light gradually changes from strong to weak (from day to night) or from weak to strong (from night to day), The resistance of the photoresistor GR changes slowly, causing the voltage at both ends to change slowly. Due to the isolation of the differential capacitor C4, the voltage at both ends of R5 is 0V. The delay circuit is not triggered to output a high level, and the driving transistor T does not When the ambient light suddenly changes from weak to strong (turn on the lights at night), the resistance of GR changes from large to small, and a negative jump voltage is generated at both ends of GR, which is driven by C4 and R5. The voltage at both ends of R5 is still 0V, and the emergency lights also do not light up; only when the surrounding light suddenly changes from strong to weak (a power outage causes the light to go out), the resistance of GR suddenly changes from small to large, forming a positive jump at both ends of GR. The voltage is changed, and a positive pulse is generated at both ends of R5 through the differential circuit C4 and R5. If the AC voltage disappears at this time, the other input terminal of F2 is also high level, then F2 outputs low level, triggering the monostable delay circuit Work, when the delay circuit enters the delay, F4 outputs low level T and turns on, and the light bulb lights up. After about 10 minutes, the monostable delay circuit exits the monostable state, outputs a high level, T ends, and the light bulb goes out. K is a function switch with three positions: the middle position is forced disconnection, the left position is automatic, and the right position is manual connection. The position of K can be flexibly switched according to needs. During normal use, the fully automatic emergency light can be connected to the AC power supply and K placed in the automatic position. Purpose: This emergency light can be installed in places where there is no natural light all year round, or in places where there is sufficient light during the day and emergency lighting is needed at night.