LED Emergency Light Circuit

Here, is small project for making a LED Emergency Light Circuit which helps, when power goes OFF and is very easy to build and does not cost much.

Also, we use these LED because it saves power and last for long time.

Circuit Working:

Parts List:

Components	Values	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

In the above circuit diagram the transformer, diode and capacitor work together to give normal power.

First, the circuits main component is a PNP transistor acting as a switch and this device provides a ground connection by functioning as a positive wire.

Moreover, when base of PNP transistor get positive from power it stay OFF and so when power is ON transistor is OFF.

When Power is ON:

If power is there transistor base get positive so transistor is OFF and because of this LED does not get battery power and so LED stays OFF.

Hence, battery charge slowly from the power.

When Power is OFF:

Furthermore, when the power fails, the transistor base loses positive voltage and connects to ground through the 1k resistor, which turns the transistor ON quickly.

Now battery gives power to LED and LED turn ON and if LED light goes dim then voltage circuit diode start working slowly.

Transformerless Emergency Light Circuit:

Also, this circuit look same like old one but there is no transformer inside so it works better.

Main Good Things:

No transformer so circuit is very small, less parts so it cost less money and is easy to make because of simple design.

Be Careful and Safety First:

This circuit connect direct to AC power which is dangerous, so person who make it must be careful and follow safety steps.

How Circuit Work:

First, when AC power is ON PNP transistor T1 stay OFF so it is safe and C1, R1, Z1, D1 and C2 make small power without transformer.

When AC power turns OFF, the transistor turns ON and biases the circuit, allowing the battery to light the LEDs.

Formulas:

Below are some easy formulas for electronics and how they help when making electronic circuits.

Ohms Law:

It show how voltage (V), current (I) and resistance (R) work together:

V = I × R

Power in Circuit:

To find power (P) use:

P = V × I

Also, we can use these formulas:

P = I² × R

P = V² / R

Resistor Color Code:

To know resistor value with color bands use this formula:

R = (10 × first color number + second color number) Ω

3rd color is the multiply number and 4th color is the tolerance how much value we can change

Capacitance (C):

Capacitor value is:

C = Q / V

• Q is the charge
• V is the voltage

Time Constant in RC Circuit:

To know time constant (τ) then use this formula:

τ = R × C

LED Resistor:

To stop too much current in LED use:

RLED = (Vsource − VLED) / ILED

• Vsource is the power voltage
• VLED is the LED drop voltage
• ILED is the LED current

Zener Diode Resistor:

To limit current for Zener diode use:

RZ = (Vsource − VZ) / IZ

• VZ is the Zener voltage
• IZ is the Zener current

Power in Transformerless Supply:

Psupply = V²rms / R

• Psupply is the power
• Vrms is the AC voltage
• R is the load resistor

Note:

Above formulas can also help to make circuits but always check units and values are right and better to check two times before use.

How to Build:

For Building the LED Emergency Light Circuit follow the below mentioned steps:

Build the Circuit:

• First, be sure all parts we have used are easy to find in market.
• Also, before starting turn OFF all power and wear safety things like gloves and safety glasses.
• Then use the circuit diagram schematic to plan how we can place parts on board.
• After that connect PNP transistor T1 like shown in the diagram and build the transformerless power supply using C1, R1, Z1, D1 and C2.
• When we add LEDs be sure positive and negative sides polarity are correct.
• Also, if using 6V battery then change circuit like told before.
• Then put resistors R1 and R2 in right place and add diodes D1, D2 and D3 after checking circuit.
• Next, connect rectifier diode like shown in instructions and when putting battery also check the + and − sides polarity are correct.

Final Checks:

• Check every wire and part are in correct place and check two times.
• Also, look for bad soldering and fix if needed.

Power On Test:

• Now connect power and see if circuit is working and also check if LEDs turn ON when main power is OFF.

Be Safe:

• Also, cover the circuit with plastic case and add insulation for safety.
• Lastly, do not touch the circuit while it is connected to AC power.

Conclusion:

Overall, this LED Emergency Light Circuit with no transformer requires careful work, so we must solder neatly and place all parts in the correct positions.

Moreover, safety is very important and if anyone gets into problem or do not understand something then ask someone who know electronics.

To conclude, always keep safety first while making this circuit.

References:

Datasheet Transistor 2N2907