LCD-LED Display

Automatic LED Emergency Light Circuit

This is a light-sensing automatic LED emergency light circuit that is simple and inexpensive. This system is powered by the mains supply and is turned on when the mains supply is turned off. This emergency light will last for over 8 hours (depending the battery capacity and the power consumed by the LEDs).

When the power supply is turned off, the circuit detects daylight and turns on the LEDs accordingly. Even if power is lost, the circuit switches off the LEDs if the light is there. The light is sensed using an LDR (Light Dependent Resistor).

Automatic LED Emergency Light


  • Automatic Emergency Light Circuit Principle
    • Automatic Emergency Light Circuit Diagram
    • Components for Automatic LED Emergency Light Circuit
    • Working of Automatic Emergency Light Circuit
    • How to Operate Automatic Emergency Light Circuit?
    • Advantages of Automatic Emergency Light Circuit
    • Automatic Emergency Light Circuit Applications
  • Emergency Light With Battery Charger
    • Circuit Diagram
    • Circuit Components
    • Components Description
    • Working of Mobile Phone Battery Charger Circuit

Automatic Emergency Light Circuit Principle

The battery is charged through the battery charging circuit when electricity is available. When the power is out, the white LEDs attached to the MOSFET will glow depending on the light condition until the battery dies.

The resistance of LDR (Light Dependent Resistor) is significantly low when it is in light. As a result, the transistor Q2’s base voltage rises. As a result, the white LEDs connected to the MOSFET switch off.

The resistance of the LDR when the circuit is dark is on the order of mega ohms. The base of the transistor now drops low, causing transistor Q2 to turn on the white LEDs.

Automatic Emergency Light Circuit Diagram

I split the circuit into two halves. The first is the battery charging circuit, which also serves as an indicator circuit in the event that the mains power is turned off. The LED emergency light circuit is the second circuit. The emergency LEDs are turned on or off depending on the mains supply and lighting conditions.

Battery Charging Circuit

Coming to the Automatic LED Emergency Light Circuit, the following is the circuit diagram.

Components for Automatic LED Emergency Light Circuit

  • 7805 voltage regulator
  • Light Dependent Resistor – 2MΩ
  • BC548 NPN Transistor
  • Pot – 10KΩ
  • High bright LEDs – 3V@15mA
  • Red LED – 1
  • 10KΩ Resistors – 3
  • 1KΩ Resistor – 1

Working of Automatic Emergency Light Circuit

Initially, the battery charging circuit will charge the battery when the mains power is turned on. The battery charger circuit informs the Emergency Light circuit about mains power and activates the emergency lights circuits via the battery if mains power is lost.

Instead of turning on the LEDs right away, it first reads the ambient lighting using the LDR and then turns them on if the lighting is low.

How to Operate Automatic Emergency Light Circuit?

  1. Connect the wires as shown in the circuit diagram.
  2. Make sure there are no common connections between the AC and DC supply while making the connections.
  3. When you connect the circuit to the mains, you’ll see that the LEDs are no longer glowing and the battery is charging.
  4. Remove the AC power and set the circuit in the dark; the LEDs should now illuminate.
  5. When the circuit is turned on, the LEDs turn off.

Advantages of Automatic Emergency Light Circuit

  • This is very simple circuit and the cost is also very less.
  • Power is saved because the circuit switches the LEDs based on light conditions

Automatic Emergency Light Circuit Applications

  • Used in child’s study rooms to avoid the sudden power failure.
  • As an emergency lamp in homes.
  • Used in security systems to switch ON the lights automatically during the power failure.

Emergency Light With Battery Charger

This is a fairly simple circuit for a “variable power supply and charger.” It is not only handy in the event of a power outage, but it can also be utilised as a primary power source. This circuit can be used to evaluate or test your electronic projects at your workshop. These circuits can be used to charge mobile phone batteries. This circuit can be used as a backup light in the event of a power outage.

Circuit Diagram

Circuit Components

  • LM317 – 1
  • Resistor
  • R1 (220E) – 1
  • R2-R12 (220E) – 11
  • R13 (470E)
  • VR1 (100K) – 1
  • C1 (100uF) – 1
  • C2 (. 1uF) – 1
  • D1-D4 (1N4007) – 4
  • S1-S5 (on/off switch) – 5
  • LED1-LED12 – 12
  • Transformer – 1
  • Battery – 1
  • Zener diode (3.3) – 1

Components Description

  1. The LM317 is a variable voltage power supply. It’s a device with three inputs and outputs. It operates at a current of 1.5 amps and a voltage range of 1.25 V to 37 V.
  2. The resistor is in charge of controlling the flow of current in any circuit. It is, in essence, a passive gadget. There are two types of resistors on the marketVariable
  1. Fixed Resistor — a resistor with a fixed resistance value.
  2. Resistor — a resistor with a variable resistance value.

3. Capacitor is a device that stores electrical charges. It’s also a passive gadget, and there are two varieties on the market. i.e.

  1. Capacitors with polarity, i.e. capacitors with + and – terminals, such as electrolytic capacitors, are referred to as polarised capacitors.

2. Non-Polarized Capacitor — A capacitor that does not have any polarity, such as a ceramic or paper capacitor.

4. Diode – A diode is a device that allows current to flow in only one direction. It is a two-terminal passive gadget.
5. Switches – A switch is defined as a “change of state” in its literal definition. ON and OFF are the two conditions in electrical logic, and switches help to change the state of an electrical equipment from ON to OFF or reverse. To put it another way, it doesn’t switch the machine on or off; it just makes or breaks contact.

6. LED (light-emitting diode) — A semiconductor device that emits a variety of beams at its output. The forward state of a p-n junction emits a restricted spectrum of light when it is electrically biassed. LEDs are readily available in a variety of hues, including red, yellow, green, and white, orange, and others.

7. A transformer is a device that is used to change the direction of current in one circuit to another. The characteristics of the AC signal alter during the converting process. A low voltage AC, for example, can be converted to a high voltage AC and vice versa. The transformer’s operation is dependent on the magnetic field that forms around the conductor when current passes through it. Electromagnetic mutual induction is the name for this principle. Two wire coils are wrapped around a core in a transformer.

8. Battery – A battery is primarily a collection of one or more electrochemical cells in which chemical energy is converted into electrical energy. The fundamentals of operation have remained unchanged since Volta’s time. The battery’s cells are made up of two halves of cells connected in series by an electrolytic solution. While the anode and cathode make up 1/3 of the cell, positive ions from the anode travel from the electrolyte to the cathode.

9. Zener Diode – This diode operates in reverse bias mode and begins to conduct when the voltage reaches the break point. All you need to do to establish a constant voltage is connect a resistor across it so that current flow may be controlled.

Working of Mobile Phone Battery Charger Circuit

You may get the output from the circuit by simply flipping the varied number of switches (from S3, S4, and S5) in the circuit, depending on your needs.

Set switch S3 to the “on” position if you need the variable power supply as an output. A variable voltage regulator, the LM317, is utilised in the circuit to supply variable power.

The LM317 is just a three-terminal positive voltage regulator. The output voltage range supplied by the LM317 is 1.2 V to 37V.

Different range of voltage can be achieved by just  adjusting  the variable resistor that is provided in the circuit and with the help of multimeter output can be seen and the voltage which is desirable can set. The power supply range  can altar from 1.5V to  12V.

Li-ions batteries, which are commonly used in mobile phones, may be charged with the help of your mobile connectors by switching the S5 switch supplied in the circuit.

With the help of resistor R13, the charging current in the circuit can be adjusted. If you want to use the emergency light, change to switch S5. If you want to increase the intensity of the light, you can put reflectors in the circuit.

S1 and S2 are the two switches in the circuit that allow you to power your circuit either straight from the AC supply or with the help of any battery.

If you wish to use an AC power source, turn on switch S1, and if you want to use a battery power source, turn on switch S2. Solar panels can be utilised in place of AC power, and rechargeable batteries can be used to store the charge. This will not only save you money on your electric bill, but it will also help you out.


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