Introduction: 12V Mini Joule Thief Inverter - Power 220V AC LED Bulb With 12V Battery

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Hello, this is my first Instructables. In this Instructables i will share how i made a simple inverter to power a 12 W LED bulb.

This circuit inverts 12 V DC from battery to 220 V AC at high frequency because it used joule thief as the heart of the circuit. Since its output frequency is high (around 16-18 kHz - NOT 50 Hz), you can only power a light bulb (except incandescent), not the other electronic appliances. Its quite suitable for use when your region got a power outage.

Step 1: Schematic and Component

This joule thief inverter will need :

  1. a Perfboard or dotted PCB.
  2. an NPN power transistor. I use TIP31c.
  3. a transistor heatsink.
  4. Electrolytic Capacitor. 1 piece of 220uF and 1 piece of 2200uF with above 12V voltage rating.
  5. 1 standard diode (1N4007), and 1 fast recovery diode (UF4007 or 1N4148).
  6. Resistors. 1 220 Ohm, 1 470 Ohm, and 3 12 Ohm 20 watt.
  7. A Transformer ferrite core, or a ferrite ring.
  8. 0.2 mm and 0.7 mm magnet wire.

Step 2: Remove Old Transformer Magnet Wire

  1. Heat the ferrite core with soldering iron until the adhesive melted and it's easy to disassemble.
  2. Peel off the tape covering the magnet wire.
  3. unwind all the magnet wire leaving the ferrit core and the plastic cover.

Step 3: Wind New Magnet Wire According to the Schematic

Magnet wire is coated with thin enamel coating. Scratch the end of the wire using knife to remove the coating before soldering.

I. Wind the secondary winding using 0.2mm wire.

  1. Solder the scratched wire to the metal pin on the transformer plastic cover.
  2. wind 25 turns, and add a layer of plastic tape after 25 windings.
  3. Continue winding until it reach 200 turns. Add a layer of tape every 25 windings.
  4. After 200 windings reached, scratch the end of wire and solder to the metal pin other than pin (2)
  5. Cover with plastic tape to prevent unwind.

II. Wind the primary winding. Solder the wire to the pin, add 9 turns, and then solder other end to other pin.


III. Wind the feedback winding. Solder the wire to the pin, add 9 turns, and then solder other end to other pin.


IV. Put back the ferrite core, tape it with plastic tape.

Step 4: Put the Component Altogether on the Perfboard

It's time to solder all the component to the perfboard according to the schematic. In this picture i use toroid transformers with ferrite ring, as my square transformers ferrite core was fallen an broken into pieces. the winding process and number of turns are the same process.

Step 5: Testing

I use my 12 V scooter battery. This circuit draws about 1 Ampere when powering 12 W LED bulb with full brightness, same as if the bulb is powered by the 220 V home electrical supply.

If you want to decrease the current draw, increase the 12 Ohm resistor to 16 or 20 Ohm. The bulb will slight dim.

The inverter can also used to power 14 W fluorescent lamp but it not as bright as the LED even it draws the same 1 Ampere. It also can powered a 12 W UV Germicidal Lamp at full brightness.