When the night comes, when you are working under the lamp, you suddenly lose power, and the surrounding area is dark, you will be overwhelmed. It is very inconvenient to find a candle and a flashlight in the dark. There are also some special places such as: hotels, restaurants or basement personnel are densely populated, subject to the structure of the building, and artificial lighting is required during the day. If there is a sudden power outage, especially due to sudden accidents, such as: earthquake, fire It will cause great difficulties for evacuation of personnel.
The emergency light introduced in this article is usually connected to the mains, and is in a fully charged state. Only when the mains suddenly loses power and the surrounding ambient light suddenly becomes weaker, it can be intelligently judged that this is due to the darkness caused by the power failure, and it lights up in time. Emergency light. After 10 minutes, it will automatically shut down. At this time, the personnel have generally been evacuated to a safe place, no need to provide lighting. Turning off the emergency light can also prevent over-discharge from damaging the lead-acid battery.
Working principle: The automatic emergency light circuit consists of two parts: the battery constant voltage current limiting floating charging circuit and the light control delay circuit. The AC voltage is stepped down by the transformer, and the DC voltage is 18V after rectification and filtering. The D2, R4, 12V/1.2Ah lead-acid battery and LM317 form a constant voltage and current-limited floating charging uninterruptible power supply, which can ensure that the battery is fully charged at any time. State, 12V lead-acid battery float voltage is 14.4V. LM317 is connected to a constant voltage source, W is a precision multi-turn adjustable potentiometer, by adjusting W, the output terminal A can output a stable 15.1V DC voltage. Resistor R4 can limit the amount of charging current, and D2 can prevent reverse discharge of battery after mains power failure. R1, R2, C1, D1, and F1 form an AC voltage detection circuit. When the AC voltage is normal, the voltage at point B is divided into 8 volts. After F1 is inverted, the output is low. When the AC voltage is cut off, because of the D1 isolation, the voltage at point B drops rapidly to 0 volts, and the high level is output after F1 is inverted. CD4011BP is a COMS type NAND gate integrated circuit. The logic relationship between NAND and NAND gate operation is: the output terminal outputs low level only when two input terminals are input high level; if one of the input terminals inputs low level, the output is high. Level. If the two inputs are connected in parallel to form an input, then the NAND gate is equivalent to a NOT gate. The input characteristics of the gate circuit are: input low level when the input voltage is less than 40% of the power supply voltage; input high level when the input voltage is greater than 60% of the power supply voltage. 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 and C5, R6 form a monostable delay circuit. The delay time is determined by the values ​​of C5 and R6. According to the numerical delay time in the figure is about 10 minutes, when the delay circuit When entering the delay monostable state, F4 outputs a low level, so that the transistor T is turned on and the bulb is lit. The operating condition of the monostable delay circuit is that the F2 output is low. To make the F2 output low, the two inputs of F2 must all input a high level. One of the inputs is used to monitor the AC voltage, only when the power is off. It will output a high level and the other input will be the light control detection terminal. R3, GR, C4 and R5 form a light control detection circuit for detecting changes in ambient light, when the ambient light gradually becomes weaker (from day to night) or weaker (from night to day). The resistance of the photoresistor GR changes slowly, so that the voltage across it changes slowly. Because the isolation of the differential capacitor C4 makes the voltage across R5 0V, the delay circuit is not triggered to output a high level, driving the transistor T is not Work, the emergency light does not light; when the surrounding light suddenly becomes weaker and stronger (lighting at night), the resistance of GR changes from large to small, generating a negative transition voltage across the GR, which is made by C4 and R5. The voltage at both ends of R5 is still 0V, and the emergency light is also not bright; only when the ambient light suddenly becomes weaker (the light is extinguished due to power failure), the resistance of GR changes from small to large, forming a positive jump at both ends of GR. Variable voltage, through the differentiating circuits C4, R5, a positive pulse is generated across R5. If the AC voltage disappears at this time, the other input of F2 is also high level, then F2 outputs a low level, triggering a one-shot delay circuit Work, delay circuit enters delay time F 4 output low level T is turned on, the bulb is lit. After about 10 minutes, the one-shot delay circuit exits the monostable state, the output is high, T is off, and the bulb is off. K is a function switch, which has three positions: it is forced to open in the middle position, automatic in the left position, and manually turned on the right side, and the position of K can be flexibly switched as needed. In normal use, the fully automatic emergency light can be connected to the AC power supply and K placed in the automatic position. Uses: The emergency light can be installed in places where there is no natural light for many years, or it can be installed in places with sufficient light during the day and emergency lighting at night.
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