Without the need for a larger transformer, this article shows how to construct a simple LED emergency light.
This makes the circuit design easy to build and less expensive.
Known as an LED emergency light circuit this device uses LEDs to give light in the event of a power outage or emergency.
Since LEDs are more handy, energy-efficient and long lasting than standard light sources they are perfect for applications requiring emergency lighting.
Circuit Working:
Parts List:
| Category | Item | Quantity |
|---|---|---|
| Resistors | 1k 1/4 W CFR | 1 |
| 100Ω 1/4 W CFR | 1 | |
| 330k 1/4 W CFR | 1 | |
| Capacitors | PPC 0.47µF 400V | 1 |
| Electrolytic 1000µF 16V | 1 | |
| Semiconductors | Transistor 2N2907 | 1 |
| Diode 1N4007 | 3 | |
| Zener Diode 6V 1 Watt | 1 | |
| LEDs White Straw Hat 30mA | 5 | |
| Li-ion Battery 3.7V 2600mAh | 1 |
The transformer, rectified diode and capacitor work together to create a standard power supply.
A single PNP transistor acting as a switch is at the foundation of this design.
A ground is provided by PNP devices that act as positive potentials.
When a PNP transistors base is grounded by connecting a positive supply to it than the transistor remains off when the mains power is turned on.
Operation during Mains Power Presence:
When the mains power is on the transistors base is kept off by a positive supply.
As a result the LEDs stay off since the battery power cannot reach the LED source.
Through the power source the battery is slowly charged.
Operation during Mains Power Disruption:
The positive supply at the transistors base drops when the mains power is cut off.
The LEDs get lit when the transistor becomes forward biased through the 1k resistor and turns on quickly.
As the LEDs go dimmer diodes in the voltage circuit slowly pass..
The Transformerless Emergency Light Circuit:
Despite similarities to earlier designs the circuits efficiency is increased by removing the transformer.
These are some of its primary features:
- Because there is no transformer the circuit is incredibly small.
- A reduced cost results from less parts.
- Simple to install is made possible by the simpler design.
Safety Considerations
It is important to remember that there is a serious safety concern when the circuit is connected directly to the AC mains.
As a result when assembling its the responsivity of the maker to take the safety precautions.
Circuit Operation Details
A level of safety is created when PNP transistor T1 is kept off when the AC main is present.
C1, R1, Z1, D1 and C2 are arranged to provide a small transformerless power supply in place of the transformer.
When AC power fails the transistor switches to a biased state allowing the LEDs to be lit by the battery.
Formulas:
Below are some simple formulas for the components which are often used in electronic circuits:
Ohms Law:
Ohms Law defines the relationship between voltage V current I and resistance R:
V = I * R
Power in a Circuit:
The power P in a circuit is calculated using the following formula:
P = V * I
Another option using ohms law formula: P = I2 * R
P = V2/ R
Resistor Color Code:
For a resistor with colored bands one can use the color code to measure its resistance value.
The formula is: R = (10first color * 10second color) Ω
here,
- The third color represents the multiplier power of 10 and the fourth color represents the tolerance.
Capacitance:
The formula for the capacitance C of a capacitor is:
C = Q / V
where,
- Q is the charge stored on the capacitor and V is the voltage across it.
Time Constant in RC Circuits:
For an RC circuit the time constant (τ) is given by the product of resistance R and capacitance C:
τ = R * C
LED Current Limiting Resistor:
To calculate the resistance RLED for limiting current through an LED one can use:
RLED = Vsource − VLED / ILED
where,
- Vsource is the source voltage
- VLED is the LED voltage drop and
- ILED is the desired LED current.
Zener Diode Current Limiting Resistor:
For a Zener diode the resistor value RZ to limit current is given by:
RZ = Vsource −VZ / IZ
where,
- VZ is the Zener voltage
- IZ is the Zener current.
Power in a Transformerless Power Supply:
The power Psupply in a transformerless power supply is given by:
Psupply = V2rms / R
where,
- R stands for load resistance
- Psupply is power supply
- Vrms represents the AC supply root mean square voltage.
Note:
The following formulas help in knowing and constructing electronic circuits.
Throughout the calculation process one should check the units are accurate.
Always verify twice and use these calculations based on particular features of the circuit and its parts.
How to Build:
Building the LED Emergency Light Circuit follow the below mentioned steps:
- Make sure that every component mentioned seems available.
- Before beginning turn off all power sources.
- Put on the correct levels of protection such as gloves and safety glasses.
- Design the circuit boards layout using the schematic diagram that is supplied..
- As shown in the schematic connect the PNP transistor T1.
- Designing the transformerless power supply using parts C1, R1, Z1, D1 and C2 is important.
- As you connect the LEDs to the circuit make sure their polarity is proper.
- If a 6V battery is being used adjust the circuit as previously indicated.
- Put resistors R1 and R2 in their selected spot.
- After checking the schematic add diodes D1, D2 and D3 to the circuit.
- The rectifier diode should be connected to the circuit as instructed.
- As you connect the battery to the circuit make sure the polarity is correct.
Final Checks:
- Every connection should have its accuracy verified twice.
- Furthermore look for soldering mistakes and fix them if needed.
Power On Test:
- Connect the circuit to a power source and see how it operates.
- Confirm that when the main power is turned off the LEDs turn on.
Safety Precautions:
- A protective covering and insulation are essential for the circuit.
- When connected to the AC mains keep your hands off the circuit.
Conclusion:
This transformerless simple LED emergency light circuit requires careful soldering, component placement and safety considerations.
If you run into problems or have questions ask knowledgeable people or electronics experts for advice.
Safety should always come first throughout construction.