Friday, April 12, 2013

LM317 Automatic Low Cost Emergency Light

Here is an emergency lighting based on white LEDs offer the following advantages:

1. It is very bright thanks to the use of white LEDs.

2. The light turns on automatically when the mains fails and shuts down when power resumes.

3. It has its own office. When the battery is fully charged, the charging stops.

The circuit consists of two parts: the charger from the socket and the power LED part driver.The Charger is built around the 3-terminal adjustable regulator (IC1) LM317, while the LED driver is built on part of the transistor BD140 (T2). In the power charger power transformer in the AC input is a step down to give a 9V 500mA bridge rectifier consisting of diodes (IN4007x4). Filter capacitor (25v/1000uf) to eliminate the ripples. Unregulated DC power is fed to IC1 pin 3 and provides a charging current through the diode IN4007 (D5) and limiting resistance (16ohm) R16. By providing pre-k 2.2 (VR1), the output voltage can be adjusted to provide the required charging current. When the battery may require a 6.8V, and the barrier makes the charging current regulator (IC1) to find a path through the transistor BC547 (T1) to ground and stops charging. LED driver section is used a total of twelve 10 mm white LEDs.

Circuit diagram :

LOW-COST-AUTOMATIC-EMERGENCY-LIGHT-e1297471252686Automatic Low Cost Emergency Light LM317  Circuit diagram

All LEDs are connected in parallel with the resistance of 100 ohms in series with each other. junction common anode for all twelve LED is connected to the collector of PNP transistor T2 and the emission level of the transistor T2 is directly related to the positive terminal of 6V battery. Unregulated DC voltage produced by the cathode junction of Bridge (diodes), is fed to create a transistor T2 through a resistor of 1k. When the voltage is available, the fund is still high transistor T2 and T2 does not happen. The lights are off. On the other hand, if the power does not, the transistor T2 will be a small fund and it does. This causes all the LEDs (LED1 through LED12) is lit. Network, as it is available, download and keep the lights off the battery as an indicator of transistor T2 is cut-off. During the blackout, the workload is steady and makes the battery will light up.

Assemble the circuit on a general purpose PCB and enclose in a cabinet with enough space for the battery and switches. Mount the LED in the housing to illuminate the room. A hole in the box must be drilled to connect the 230V AC input to the transformer primary. I tested the circuit with twelve white 10 mm LEDs.You can use several diodes, provided that the total energy consumption does not exceed 1.5. Driver transistor T2 can provide up to 1.5 In accordance with a proper heat sink.

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