Single Cell LED Inverter (Joule Thief)

About: I started this mainly to be able to share my Projects, Inventions and Experiences in the field of Electronic with others. I'm continuously adding here more and more instructions, schematics and experiments, ...

This is a simple inverter circuit or driver provides power for different types of LEDs (eg- white LED, blue LED, UV LED, but also any other LED) from 1.2 Volt or 3.7 Volt single cell or Lithium-ion battery. But the LED starts to shine when the supply voltage is only 0.4 Volt You can use low batteries (that are useless for any other equipment). Voltage drop of a LED diode is approximately 3 Volt (but in this project i used 12 volt, 5 watt LED and voltage drop approximately 7.4 volt), so it is necessary to use a boost inverter circuit or driver. The circuit is very simple and it works on the principle of self oscillating inverter.

Step 1: Watch This Video!

Watch this Video and know more...

Step 2: Components!

  1. Old Charger Transformer Ferrite Core or Toroid Core (1 pcs)
  2. Copper Wire (0.05 mm to 0.2 mm) (As per required)
  3. NPN Transistor (Like: C945, BC547, 2N2222, etc.) (1 pcs)
  4. 1k, 0.25W Resistor (1 pcs)
  5. 100nf Capacitor (1 pcs)
  6. 2 Pin Connector (2 pcs)
  7. PCB Bord (1 pcs)

Step 3: Transformer Windings!

The coil has 50 turns of 2 thin wire (about 0.05 mm to 0.2 mm) and both windings are wound simultaneously. The core consists of two pieces of Ferrite Core. After winding the coils, two pieces of Ferrite Core stick them together with a super glue.

Step 4: Circuit Diagram!

  1. In this Inverter circuit I used C945 (or BD547, 2N2222, etc.) NPN Transistor. The working frequency of the inverter circuit about 50Hz (it is not critical).
  2. In the circuit the capacitor (100nf) is not strictly necessary, the drive also works without this capacitor.

Step 5: After Soldering!



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