automatic low power emergancy light


Posted on Feb 5, 2014

A white-LED-based emergency light that offers the following advantages. 1-It is highly bright due to the use of white LEDs. 2-The light turns on automatically when mains supply fails, and turns off when mains power resumes. 3-It has its own battery charger. When the battery is fully charged, charging stops automatically. The charger power


automatic low power emergancy light
Click here to download the full size of the above Circuit.

supply section is built around 3-terminal adjustable regulator IC LM317 (IC1), while the LED driver section is built around transistor BD140 (Q2). In the charger power supply section, an input AC main is stepped down by T1 to deliver 9V, 500mA to the bridge rectifier, which comprises diodes D1 through D4. Filter capacitor C1 eliminates ripples. Unregulated DC voltage is fed to input pin 3 of IC1 and provides charging current through D5 and limiting resistor R15. By adjusting preset P1, the output voltage can be adjusted to deliver the required charging current. When the battery gets charged to 6. 8V, D6 conducts and charging current from IC1 finds a path throughQT1 to ground and it stops charging of the battery. When mains power is available, the base of Q2 remains high and Q2 does not conduct. Thus LEDs are off. On the other hand, when mains fails, the base of Q2 becomes low and it conducts. This makes all the LEDs glow. The mains power supply, when available, charges the battery and keeps the LEDs off as Q2 remains cut-off. During mains failure, the charging section stops working and the B1 supply makes the LEDs glow. Assemble the circuit on a general-purpose PCB and enclose in a cabinet with enough space for battery and switches. We have tested the circuit with twelve 10mm white LEDs. You can use more LEDs provided the total current consumption does not exceed 1. 5A. Driver transistor Q2 can deliver up to 1. 5A with...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    PC Printer Port Controls I-V Curve Tracer
    Digital Temperature Controller
    Audio noise generator
    Switching regulator operating at 200Khz
    Remote ring extender switch
    Buffer Circuit Schematic Diagram
    Transistor current mirror circuit
    measurement Measuring large differential voltage
    relay circuit diagram
    control circuit for nokia tv tuner 5827
    guitar amplifier circuit diagram 100w
    8-Way MIDI Drum Pads
    Stepper Motor Driver
    With self-locking function of the forward start circuit



    Top