Automatic LED emergency light circuit
The automatic power failure emergency light charges the battery when the power is ON and automatically lights ON the LED when the power goes out.
The circuit consists of a battery charging section, with a regulated and limited current DC supply of 6V and relay controlled LED lights.
The relay energised when the supply has a live line. So the common pole of the relay contacts to the normally open terminal. Thus, the battery connects to the input DC supply and charges.
When power fails, the relay changes to Normally closed position and the battery switches to the LED light. Here we are using a five parallel set of two 3V LEDs in series. So, without any resistors, a 6V battery can connect directly to LEDs.
The switch S1 can be used to select whether the light to be always ON automatically or to ON/OFF manually. For a permanent automatic operation, the switch can be closed always or shorted instead.
Emergency light – Components required
LM317 – Voltage Regulator
Resistor – R1, R4 – 1k, R2 – 3.9k, R3- 2ohms
Capacitor – C1 – 2200uf
Diode – D1-D5 -1N4007, D6-D15 – White LED 3V
Transistor – Q1- BC547
Transformer – T1- 230V/6V,1A
Relay – SPDT relay 6V
Switch – S1 – SPST