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Emergency Light. Home Utility Circuit 10

emergency-lightMake your own Emergency light using only a few components. It is powered by a 4 V 2 Ah Mini Lead Acid battery and uses Six 0.5 Watts White LED. Its output will be 3 Watts. Let us start to make it.

You need the following components
1. 6-0-6, 500 mA Transformer
2. IN 4007 Diodes – 3 Nos
3. 470 uf 25V Electrolytic capacitor – 1 No
4. 68 Ohms ½ watt resistor – 1No
5. 4.7K ½ watt resistor – 1No
6. 2.7K ¼ watt resistor – 1No
7. 4.7Ohms ½ resistors – 6 Nos
8. BD 140 PNP Transistor – 1No
9. 0.5W White LED – 6 Nos
10. 4V 2 Ah rechargeable Lead Acid battery – 1 No.

Working of the circuit is simple. When the mains power is available, D3 forward biases and battery charges through R1. At the same time, the base of NPN transistor T1 remains high through R2. So it will be off. When the mains power fails, D3 reverse biases and the current through R2 ceases. This makes the base of T1 low and it conducts. Current from the battery flows through T1 to light the White LEDs.

Resistors R4 to R9 restricts the LED current . 0.5 Watt White LED handles more than 100 mA current so you can change the value of R4-R9 according the brightness required. Lower value increases brightness and higher value decreases the brightness.