An energy-saving 2.5W LED emergency lighting

Here is a practical LED automatic emergency lighting circuit, which uses 24 light-emitting diodes connected in series and parallel to standby. It can automatically light up 24 LED lights when the city power is off or the AC circuit in the home fails or the fuse is blown. The circuit has few components, low price, and power consumption of 2.5W. It has the advantages of low power consumption, stable light emission and long service life. It is suitable for fire escape passages and home backup.

Working principle of the circuit: As shown in the attached figure, when the power switch S1 is closed, the voltage of 220V is generated when the mains is normally powered. After the voltage is stepped down by capacitors C1 and C2, it is rectified by VD1-VD4, stabilized and filtered by voltage regulator tube VD5 and capacitor C3, and a stable 11.5V DC voltage and 75mA current are generated to charge 9 1.2V rechargeable batteries. At the same time, the relay coil K is powered on, and its normally closed contact K1 is disconnected, and the LED light does not light up without power; on the other hand, the normally open contact K2 is closed, and the switch S1 is turned on to form a pulse current to the rechargeable battery to float charge the 11.5V battery E. R3 is a current limiting resistor, the battery will not heat up, the battery is usually in a voltage holding state, the charging current is small, which is what people call floating charging, and the battery life is about 1-2 years. LED1~LED24 are white light-emitting tubes, and every 3 are connected in series into a group, so that 24 can form 8 groups, and the 8 groups are connected in parallel and connected to the circuit according to the diagram. Since the working voltage of each light-emitting tube is 3.5V. Three LEDs connected in series with a voltage of 10.5V basically meet the requirements. And the working current of each LED is between 25-30mA, so that each LED can work normally.

Once the mains power grid circuit fails or the household fuse blows, the relay coil K loses power. The K2 contact opens, and the K1 normally closed contact closes, connecting the power of the rechargeable battery and lighting up the 24 LED tubes to provide emergency lighting for people.

Selection of components: C1 and C2 in the figure are 1μF/400V high-quality polyester capacitors. K is a sensitive relay with a working voltage of 10-12V and a current of about 45mA, such as JPX-12F, etc. LED1-LED24 are white light-emitting tubes with φ5mm. E is made of 9 No. 7 1.2V rechargeable batteries connected in series, or a 12V maintenance-free livestock battery. Others are selected according to the markings in the figure, and there are no special requirements.

The whole circuit is placed in a well-insulated PVC fireproof plastic box, the lead wires are connected to the mains, and LED1-LED24 are placed in different places as needed.