Simple and practical emergency light

This emergency light can automatically switch power supply when power is off. When power is normally supplied, it automatically charges the backup battery and has charging protection function. The circuit is shown in the figure below. The working principle is introduced below.

When the power supply is normal, J2 is energized and closed, and its moving contact is connected to "N/O (normally open point)", and the positive terminal of the backup battery is connected to the inverting terminal of IC1. IC1 (LM308) and D5 and D6 form a voltage comparator, and the reference voltage is determined by D5 and D6. Here, a silicon diode (D5) and a 6.2V voltage regulator diode (D6) are used to form a 6.9V reference voltage to monitor the charging voltage. When the input voltage of IC1's 2nd pin (i.e., the battery voltage) is lower than 6.9V, IC1's 6th pin outputs a high level, T1 is turned on, J1 is energized, and its moving contact is connected to "N/O (normally open point)", and the power supply voltage charges the battery through R2, and LED2 lights up as a charging indication. The charging current can be adjusted by changing the resistance value of R2. As the charging time increases, the voltage at pin 2 of IC1 gradually increases. When the voltage is greater than the reference voltage of 6.9V, pin 6 of IC1 outputs a low level, T1 is cut off, J1 loses power, and the charging circuit is disconnected, realizing the automatic charging protection function.

When power outage occurs, J2 loses power, its moving contact is connected to "N/C (normally closed point)", and the battery supplies power to the emergency light circuit through S1, realizing the automatic switching function during power outage. S1 is used here to manually cut off the emergency light circuit.   

The emergency light circuit is composed of IC2 (NE555), T2, T3, T4, X2, etc. IC2 is a 50Hz signal generator. The 50Hz signal is output from the 3rd pin of IC2. After being inverted and amplified by T2, it drives the push-pull circuit composed of T3, T4, and X2 respectively. 220V AC is induced on the high-voltage side of X2 to light up the fluorescent tube. Here, X2 can directly use a finished power transformer with a secondary of 4.5V and a primary of 220V. The power is determined by the power of the fluorescent tube. When using, pay attention to the heat sink of T3 and T4.   

When making it, X1 uses a power transformer with a secondary of 6V/200mA. J1 and J2 use relays with a coil voltage of 6V. For other device selections, refer to the diagram, and there are no special requirements. Circuit debugging is very simple. When the main power is turned on, J2 should act, and LED1 is the power indicator. Then measure whether the voltage of pin 3 of IC1 is about 6.9V, and then an external power supply can be connected to the IC2 pin to adjust the charging protection circuit. When the input voltage is greater than 6.9V, J1 should act and disconnect. Short open S1, connect the emergency light circuit with an external power supply, measure whether the output of IC2 is 50Hz, and then measure whether the voltage of the output part of X2 is about 220V. LED3 is the power outage/emergency light working indicator.