This is a circuit that can make an LED light up from a dead battery!
It works with white, blue and even ultraviolet LEDs, and all you need is a battery that’s almost empty at least 1.2V.
The cool thing is, the LED can even light up with just a tiny bit of power left as low as 0.4V.
This means you can use batteries you thought were useless!
WARNING: Building circuits can be dangerous.
Only do this with adult supervision.
What is a Joule Thief Circuit:
A Joule Thief is a simple voltage booster or step up converter circuit that is designed to efficiently extract the remaining energy from a low voltage power source.
The concept behind the joule thief is to use a minimal number of components, to boost the voltage of a nearly depleted battery enabling the powering of low voltage devices even when the battery voltage is below the typical operating voltage of the device.
Parts List:
| Component | Description | Quantity |
|---|---|---|
| Resistors | 1/4 W CFR, 1k | 1 |
| Capacitors | Ceramic, 100nF | 1 |
| Semiconductors | Transistor BC547 | 1 |
| Battery | 1.5V AAA Cell | 1 |
| LED | 5mm, 20mA | 1 |
| Transformer | As explained in article | 1 |
Formulas and Calculations:
Turns in Coil (N):
N = 2 x 50 turns
Coil Wire Diameter (d):
Wire diameter: 0.05 mm to 0.2 mm
Cross-Sectional Area of Ferrite Core (A):
A ≈ 7 mm²
Operating Frequency (f):
Operating frequency: ~50 kHz
Construction:
Coil Winding:
Take a piece of ferrite core with an ring type torroidal cross section as shown above.
Wind the coil with 2 x 50 turns of thin super enameled copper wire.
Simultaneously wind both windings for efficiency.
Use a wire diameter in the range of 0.05 mm to 0.2 mm.
Core Assembly:
After winding the coil on one of the ferrite cores apply super glue to stick the cores together.
Ensure a secure bond.
Circuit Integration:
Connect the coil to the joule thief circuit.
The joule thief circuit operates on the principle of a self oscillating inverter.
Operating Frequency Adjustment:
Fine tune the circuit for an operating frequency of around 50 kHz.
This frequency is not critical but serves as a guideline for optimal performance.
Capacitor Optional:
While the circuit can function without a capacitor, you may choose to include one.
Calculate the required capacitance using the formula:
C = 1 / (2πfZ)
where,
- Z is the impedance of the circuit.
Enclosure Integration:
Repurpose a broken flashlight for the enclosure.
Remove the original miniature bulb and 2 AA batteries.
Place the constructed joule thief circuit in the space originally occupied by the second battery.
Use a single cell battery with a voltage as low as 1.5V or 1.2V.
The LED should start emitting light with a supply voltage of 0.4V.
Voltage Considerations:
LED diodes typically require a voltage drop of approximately 3V.
To cater to this, a boost converter is essential.
Operating Frequency:
The joule thief circuit operates at a frequency of around 50kHz although this is not a critical parameter.
Optional Capacitor:
While not strictly necessary, a capacitor can be incorporated into the circuit.
However, the circuit functions efficiently even without it.
Safety Measures:
- Prior to supplying power, double check your connections and always use excellent soldering techniques.
- Make use of parts whose voltage and current ratings correspond to the layout of your circuit.
- By following these safety measures, you can enjoy the extended illumination of your LED from a seemingly “dead” 1.5V battery with a Joule thief circuit.
Conclusion:
This DIY LED joule thief circuit provides an ingenious solution for powering LEDs from 1.5V low voltage batteries that might be considered unusable for conventional devices.
The construction details outlined above ensure a basic process making it accessible for electronics enthusiasts and hobbyists alike.
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