This is an LDR based Emergency Lamp that turns on a High watt White LED when there is darkness in the room. It can be used as a simple emergency lamp in the child’s room to avoid the panic situation in the event a sudden power failure.It gives ample light in the room.
The circuit is too simple so that it can be enclosed in a small box. A 12 volt miniature battery is used to power the circuit. Two transistors T1 and T2
are used as electronic switches to turn on / off the white LED. When there is sufficient light in the room, LDR conducts so that the base of the PNP transistor T1becomes high and it remains off. T2 also remains off since its base is grounded. In this state, White LED remains off. When the light falling on the LDR decreases, it cease to conduct and T1 forward bias providing base current to T2. It then turns on and White LED switches on.White LED used in the circuit is 1 watt High bright Luxeon LED . Since 1 watt White LED consumes around 300 milli ampere current, it is better to switch off the lamp after few minutes to conserve battery power
are used as electronic switches to turn on / off the white LED. When there is sufficient light in the room, LDR conducts so that the base of the PNP transistor T1becomes high and it remains off. T2 also remains off since its base is grounded. In this state, White LED remains off. When the light falling on the LDR decreases, it cease to conduct and T1 forward bias providing base current to T2. It then turns on and White LED switches on.White LED used in the circuit is 1 watt High bright Luxeon LED . Since 1 watt White LED consumes around 300 milli ampere current, it is better to switch off the lamp after few minutes to conserve battery power
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14 comments :
wat is d use of resistors n capactor here?
sorry nt capctr
so could we use a phototransistor or some much more light sensitive device by slightly varying the working.
i need abstract of emergency light
dis circuit is faulty one..nt workin..
i do this project,i didn't got the output.near the second transister u can add the one resister.easily got the output.
can u give more information about this........
it is fault one not working
i have done this project, but when i am switch on the supply, the led has been glowing during the day time also,what modification i will do for this project and say some more information about this project
If the pot is turned fully clockwise, the BD140 will take more current and this will flow through the base-emitter junction of the BD139. This current will be more than required by the BD139 and it will be damaged.
The current taken by the 1watt LED will be 12v - 4v = 8v / 33 = 240mA. The wattage of the 33R will be 8 x .24 = 2 watts.
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i need the full correct detail.
where can i gt d pcb layout nd see demo of dis project??
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