The circuit above is for use of lighting a certain area in a house or workshop when a power failure occurs. The circuit uses leds(red, green and white(for lighting) ), a n-channel mosfet, lm317, diodes, various resistors, and pnp transistor. The circuit is for either modifying a old power failure light to be more reliable and efficient or just building the circuit from scratch and to be used in needed places. This circuit is better and efficient because it uses leds instead of the incandescent lights and uses nickel-metal hydride (Ni-Mh) batteries. This light will run longer than standard incandescent, won't overcharge its batteries because of the constant voltage from the lm317 and no need for replacing batteries every 5-6 months like the 6v lead acid batteries in the old standard lights. With 6 Ni-Mh batteries, it gives about 7.8v with a capacity of 2200Mah, you can get a run time of 7-8hours if the leds are 3watts on each side(total of 6 watt light output from Leds 400-500 lumens).
This light works by when the pnp transistor base senses the 9v supply from the 120v-9v transformer, the transistor switches off and when there is no 120v power, the transistor turns on, conducting and turns on the n-channel mosfet which turns on the light.
I do not recommend using this light in businesses, buy standard emergency lights than would be approved by an inspector!
Do this at your own will!
