1 watt LED Driver Using a Joule Thief Circuit

A joule thief circuit is pretty popular with all electronic hobbyists, because the concept allows us to operate even the white and the blue LEDs from a 1.5V source which normally require 3V to illuminate brightly. The present article discusses one such circuit, however here we replace the traditional 5mm LED with a 1 watt LED.

The concept discussed here remains exactly identical to the usual joule thief configuration, we just replace the normally used 5mm LED with a 1 watt LED.
Of course this would mean the battery getting drained pretty much earlier than a 5mm LED, but it's still economical than using a two 1.5 cells and not including a joule thief circuit.

Let's try to understand the proposed circuity with the following points:

If you see the circuit diagram the only seemingly difficult part is the coil, rest of the parts are just too easy to configure. However if you have a suitable ferrite core and some spare thin copper wires, you would make the coil within minutes.

The coil may be wound over a T13 toroidal ferrite core using a 0.2mm or 0.3mm super enameled copper wire. About twenty turns on each side will be quite enough. In fact any ferrite core will, a ferrite rod or bar will also serve the purpose well.

After this is done, its all about fixing the parts in the shown manner.

If everything is done correctly, connecting a 1.5 V penlight cell would instantly illuminate the attached 1 watt LED very brightly.

If you find the circuit connections to be alright yet the LED not illuminating, just interchange the coil winding terminals (either the primary ends or the secondary ends) this would fix the problem immediately.

How the Circuit Functions

When the circuit is switched ON, T1 receives a biasing trigger via R1 and the associated primary winding of TR1.

T1 switches ON and pulls the entire supply voltage to ground and in the course chokes the current across the primary winding of the coil so that the biasing to T2 dries up, shutting off T1 instantaneously.

The above situation switches OFF the voltage across the secondary winding triggering a reverse emf from the coil which is effectively dumped across the connected LED. The LED illuminates!!

However the shutting of T1 instantaneously also releases the primary winding and restores it to original condition so that the supply voltage now can pass across to the base of T1. This initiates the whole process yet again and the cycle repeats at a frequency of around 30 to 50 kHz.

The connected LED also illuminates at this rate, however due to the persistence of vision we find it illuminated continuously.

Actually the LED is ON only for 50 percent of the time period, and that's what makes the unit so economical.

Also because TR1 is able to generate voltages that may be many times greater than the supply voltage, the required 3.3V to the LED is sustained even after the cell voltage has dropped to about 0.7V, keeping the LED well illuminated even at these levels.
Parts List
R1 = 1K, 1/4 watt
T1 = 8050
TR1 = see text
LED= 1 watt, high bright
Cell = 1.5V AAA penlight

The above circuit can be also driven using a DC motor. A simple diode and a filter capacitor rectification would be enough to convert the supply from the motor suitable for illuminating the LED very brightly.

If the motor rotation is sustained with the help of a turbine/propeller arrangement and operated by wind energy, the LED can be kept illuminated continuously, absolutely free of cost.
Parts List
R1 = 1K, 1/4 watt
T1 = 8050
TR1 = see text
LED= 1 watt, high bright
Cell = 1.5V Ni-Cd
D1---D4 = 1N4007
C1 = 470uF/25V

M1 = Small 12V DC motor with propeller 


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