Load shedding is the common problem in developing country where student is more effected. By keeping this problem in mind the group of dreamlover technology post very simple, useful and inexpensive project using ultra-bright white LEDs which provide sufficient light for reading purpose which consume very low power i.e. 3 watts of power. It works like emergency light i.e. when AC mains failure, the battery backup circuit instantly light up the LEDs but when the power resumes, the battery supply is automatically disconnected and this circuit again works on AC mains.

Circuit Description of LED-based reading lamp

For power section the circuit of LED-based reading lamp use bridge rectifier connected to secondary coil of 0-7.5V, 500mA step-down transformer X₁. Pulsating DC from output of rectifier is given to input of voltage regulator IC₁ for pure DC output. All LEDs (LED₁ to LED₁₀) is connected in parallel across the output of voltage regulator. Here resistors R₁ to R₁₀ are connected in series with the LEDs respectively to limit the current. In this circuit 5 more LEDs can be used for lamp to increase intensity in the same manner used. When AC mains available relay RL₁ energized and disconnect to battery and vice-versa on absent of AC mains. For charging battery, a lead from rectifier is directly connected to positive and negative terminals of battery. Here diode D₅ andD₆ is used as reverse-current protection diode that don’t allow the battery current to flow towards the supply section and diode D₇ is for reverse polarity protection.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁- R₁₀ = 56 Ω

Capacitors

C₁ = 1000 µF/16V

C₂ = 0.1 µF

Semiconductors

IC₁ = 7805 Voltage regulator

D₁ – D₈ = 1N4007

LED₁ – LED₁₀ = White LED

Miscellaneous

RL₁ = 6V, 100 Ω 1C/O Relay

X₁ = 230V AC primary to 0-7.5V, 500mA secondary transformer

SW₁, SW₂ = On/off switch

6V, 4Ah Battery

6V, 4Ah Battery terminal

Heat sink for voltage regulator IC