3 Simple LED Emergency Light Circuit

This LED emergency light project is simple, cheap and easy to build. The circuit do the charging of the battery and when the main source is not available such as in brownouts, the white LEDs automatically turn on. Click schematic below to enlarge.

emergency light schematic diagram

Initially, the voltage output from 220V to 12V converter is fed to the input of LM317 regulator. Then this voltage is regulated down to 7.37V using 240 ohms and 1.2K resistor combination (see LM317 Calculator). At this instant, the battery is in charging mode and the transistor Q1 is off. Indicator LED serves two purposes, one primarily is to give us idea that the battery is charging and another is to ensure that the Q1 is off. During brownouts, the transistor Q1 is on and delivers current to 16 white LED of about 20mA each, thus a fully charged battery (6V/4.5Ah) can last up to 14 hours.
The charger has no built in over-current control but still it protects the battery from overcharging since the charging voltage is set only to 7.4V.

Part List: 6V VERSION
D1 - 1N4001 diode (3pcs)
C1 - 1000uF/25V electrolytic capacitor
R1 - 200 ohms 1/4W
R2 - 1 kilo ohms 1/4W
R3 - 1.5 kilo ohms 1/2W
R4 - 120 ohms 1/4W (16pcs)
LM317 - varaible voltage regulator
indicator LED - red or any low power LED (3mm or 5mm)
LED - white LED 3V@30mA (16pcs)
Q1 - TIP42C or similar PNP transistor
Transformer - 220V to 12V-0-12V , center tap 12VA
Battery - 6V 4.5ah lead -acid battery

Part List: 12V VERSION

D1 - 1N4001 diode (3pcs)
C1 - 1000uF/25V electrolytic capacitor
R1 - 220 ohms 1/4W
R2 - 2.2 kilo ohms 1/4W
R3 - 1.5 kilo ohms 1/2W
R4 - 390 ohms 1/4W (16pcs)
LM317 - varaible voltage regulator
indicator LED - red or any low power LED (3mm or 5mm)
LED - white LED 3V@30mA (16pcs)
Q1 - TIP42C or similar PNP transistor
Transformer - 220V to 12V-0-12V , center tap 12VA
Battery - 12V lead-acid battery

Part list diagrams: click to enlarge

TIP42C pins

LED pins

LM317 pinout

But if you want a much handy and smaller led emergency light, try building a cellphone charger-based led emergency lighting.