High Efficiency Joule Thief LED Flashlight


In this electronics project, I make a high efficiency joule thief LED flashlight circuit. It became clear that the LED flashlight should work from 3 to 6 hours and guarantee long-term operation at sub-zero temperatures, and also be reliable.

It is possible to directly connect the batteries with LEDs, but I like to complicate everything. This circuit works Joule thief principle so the circuit can drive the LEDs with a single cell which is about 1.2 V to 1.5 V.

Components List

The following components are needed for this project.

Name Value Qty.
Q1: Bipolar transistor TIP120 or TIP41 1
T1: Ferrite Ring - 1
Insulated Copper Wire 0.4 mm As per required
R1: Resistor 470Ω 1
SK1: Schottky Diode SK36 1
C1: Polar Capacitor 10uF 25V 1
D1-D9: LED 5mm, White Color 9 (Up to)
V1: Single Cell 1.2-1.5V 1
Wire - As per required
Soldering Kits - 1
PCB (Optional) - 1

High efficiency Joule thief LED flashlight Circuit diagram

Schematic of high efficiency joule thief led flashlight circuit shown below. This is a normal auto generator boost converter.

Why does it need an auto generator boost converter?

The matter is that as a power source I decided to use a single cell 1.5 V battery, it has a long service life, and a minimal memory effect in comparison. But the trouble is that for the normal power supply of conventional 5-millimeter LEDs needs 3 such batteries. So the converter is used, which raises the voltage from the battery to the desired value.

Circuit explanation

In this joule thief LED flashlight circuit I used a Bipolar transistor, Schottky diode, Capacitor, Ferrite ring, LEDs and I also explain the circuit below.

Bipolar Transistor. The converter is built only on one bipolar transistor of reverse conductivity, in my case, it is a transistor TIP120. The output current of such a converter can reach up to 300 milliampere, which is more than enough to supply the number of LEDs that I use. The transistor doesn't overheat, so there is no need for a radiator.

Ferrite Ring. The step-up transformer is wound on a ferrite ring. Both windings are wound with the same copper wire and contain 20 turns each. Wire diameter is 0.4 mm; they are connected in series to form a midpoint.

Schottky Diode. The bursts of self-induction from the power winding of the transformer are rectified by a Schottky diode, in my case, it is SK36.

Capacitor. The 10uF, 50 V capacitor is smoothing voltage, which fed to the LEDs.

LED. I used 4 light-emitting white LEDs of 5 mm (this circuit can drive up to 9 LEDs). since the brightness of the LEDs will be different so it is very desirable to use equalizing resistors for each LED. But all of my LEDs from the same lot and brightness at the same supply voltage is almost the same.

Input-Output. This high-efficiency inverter starts working at an input voltage of 0.4 Volts. From 1.2 Volts consumption is about 80-90 milliampere. The correct operating voltage range is up to 3.5 Volts.

Demo & Testing - High efficiency Joule thief LED flashlight

You can see below the high brightness of this joule thief LED flashlight.