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Single cell (1.2 or 1.5V) LED inverter (Joule thief)

    This inverter (driver) provides power for LEDs (eg, white, blue, UV, but also any other) from 1.5 V or 1.2 V single cell (battery), but the LED starts to shine when the supply voltage is only 0.4 V! You can use low batteries, that are useless for any other equipment. Voltage drop of a LED diode is approximately 3V. Therefore it is necessary to use a boost inverter. The circuit is very simple, it works on the principle of self oscillating inverter. The coil has 2 x 50 turns of a thin wire (about 0.05 to 0.2 mm), both windings are wound simultaneously. The core consists of two pieces of ferrite core, having an L-shaped cross-section of about 7 mm2. after winding coil on one of them, stick them together with a super glue. The working frequency is about 50kHz (not critical). The capacitor is not strictly necessary, the drive works without it. Inverter with LED I built into enclosure from the broken flashlights, where was originally a miniature bulb and 2 AA batteries. Now uses a single battery and into the space remaining after the second battery I put the inverter.

Single battery cell (1.2 or 1.5V) LED inverter driver / Joule thief schematic
Single battery cell (1.2 or 1.5V) LED inverter driver / Joule thief schematic

Ferrite transformer wound on two L ferrite pieces. You do not have to do it exactly the same way, it is just for inspiration.

Operating inverter.

Inverter built into the torch - testing. The inverter starts operating at 0.4 V, the LED shines decently at 0.8 V. Space for a second 1.5 V battery was used to place the driver.

Added: 23. 1. 2005