Emergency Light Circuit Using a Flashlight Bulb

Though it's the world LEDs today, an ordinary flashlight bulb can also be considered a useful light emitting candidate especially because it's much to configure than an LED.

The shown circuit diagram is quite simple to understand, a PNP transistor is used as the primary switching device.

A straight forward power supply provides the power to the circuit when mains is available.

As long as power is present, the transistor T1 remains positively biased and therefore remains switched OFF.
This inhibits battery power from entering the bulb and keeps it switched OFF.

The mains power is also utilized for charging the involved battery via the diode D2 and the current limiting resistor R1.

However, the moment AC mains fails, T1 is instantly forward biased, it conducts and allows the battery power to pass through it, which ultimately turns ON the bulb and the emergency light.

The entire unit may be adjusted inside a standard AC/DC adapter box and plugged IN directly in to an existing socket.

The bulb should be kept protruding outside the box so that the illumination reaches the external surrounding amply.

The moment AC mains fails, 

Cheap Emergency Light Using a Flashlight Bulb Circuit Diagram

Parts List

R1 = 470 Ohms,
R2 = 1K,
C2 = 100uF/25V,
Bulb = Small Flashlight Bulb,
Battery = 6V, Rechargeable Type,
Transformer = 0-9V, 500 mA

Emergency Light Using a Flashlight Bulb


  1. Want to use transformer less power supply with full charged cutof for charging 6v 4.5 ah Battery and with this want to make a automatic Cheap Emergency Light Using a Flashlight Bulb (24 led).

    1. you can try this circuit


      replace the transformer with capacitor type power supply

  2. Dear sir,
    i want circuit for inverter using cheaper cost for fan and cfl bulb using as a load please send me circuit for my mail lakshminarayanacsm@gmail.com

    1. Dear Lakshminarayan,

      you can try the following design:



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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.
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