An automatic emergency light circuit that runs on battery power is simple yet very important because it provides light when the electricity goes out.
This circuit makes sure that a lamp turns on by itself if the main power supply fails, which is super helpful for homes, offices and other places that need extra lighting.
The battery which serves as a backup power source should preferably be a 6V lead acid battery or five 1.2V NiCd cells connected together.
The design is not only effective but also cost efficient using parts that are easy to find in stores.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors | 27Ω, 470Ω 1/4 watt | 2 |
| Capacitors | Ceramic 0.1µF | 2 |
| Electrolytic 1000µF 25V | 1 | |
| Semiconductors | IC 7809 | 1 |
| Transistor 2N2907 | 1 | |
| Diode 1N4007 | 3 | |
| Transformer | 230V AC primary, 12-0-12V secondary 500mA | 1 |
| Switch | On/Off switch | 1 |
| Lamp | 6V | 1 |
| Battery | 6V | 1 |
The circuit is built around a step down transformer, which changes the high voltage of 230V AC into a much lower voltage of 12V AC.
This alternating current is then converted into direct current by the diodes D1 and D2.
To ensure a steady output of 9V DC the circuit uses a IC1 7809 voltage regulator, which is important for the circuits function and for charging the battery.
When everything is working normally the 6V battery, gets charged through the resistor R1 and diode D3.
During this time the transistor Q1 stays off, so the 6V lamp(bulb) does not light up.
However, if there is a power failure the battery sends voltage directly to the 6V lamp through Q1 turning it on automatically.
Diode D3 is important because it stops any current from flowing back from the battery into the regulator circuit.
The switch S1 controls the whole emergency lighting system letting the user turn the circuit ON or OFF by managing the input AC supply.
When the switch is ON it allows the battery to charge while keeping the lamp off.
But when the switch is OFF the emergency light turns on using power from the battery.
The fuse is like a safety guard for the circuit.
It helps prevent electrical problems and makes sure everything works properly.
Formulas with Calculations:
To design your own Battery Operated Automatic Emergency Light Circuit the below mentioned formulas with calculations will help to understand better:
Current Limiting Resistor R1 Calculation:
The resistor R1 27Ω limits the charging current for the battery.
The current through R1 can be estimated using ohms law:
I = V / R
I = (9V – 6V) / 27Ω
I = 0.11A (110mA)
This ensures slow and safe charging of the battery.
Base Resistor R2 Calculation:
The base current for Q1 2N2907 is determined by R2 470Ω:
I_B = V / R
I_B = 6V / 470Ω
I_B = 12.7mA
This base current is sufficient to turn on the transistor and power the lamp.
How to Build:
To build a Battery Operated Automatic Emergency Light Circuit following steps are required for connections of the circuit:
- Assemble all the components mentioned in the above circuit diagram
- Connect INPUT pin 1 of IC1 to positive end of the capacitor C2 and the negative end of capacitor connect to GND of the circuit
- Connect the GND pin 2 of IC1 to GND of the circuit.
- Connect the OUTPUT pin 3 of IC1 to one end of capacitor C3 and other end of capacitor connect to GND
- Connect capacitor C1 from INPUT pin of IC1 and GND.
- Connect resistor R1 between OUTPUT pin of IC1 and anode of diode D1 and cathode of D1 connect to emitter of transistor Q1
- Connect base of transistor Q1 between one end of resistor R1 and one end of resistor R2 and other end of resistor R2 connect to GND.
- Connect collector of transistor Q1 to one end of Lamp 6V and other end of lamp connect to GND.
- Connect diodes D1 and D2 parallel to secondary of transformer, center wire of secondary transformer connect to GND.
- Connect the primary end of transformer to 230V AC through fuse and S1 ON/OFF switch
- Connect the positive end of 6V battery to OUTPUT pin of IC1 and negative of 6V battery connect to GND
Conclusion:
This Battery Operated Automatic Emergency Light Circuit is a great solution for having backup lights when the power goes out.
It works by using a basic transistor switch that turns on a lamp as soon as the main power stops.
Since it requires only a few parts and is easy to build, this circuit is really helpful in emergencies.