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.

Circuit Description

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 torroidal 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.

How to wind the Torroid Coil

As can be seen in the shown joule thief circuits, the coil is ideally made over a torroid core. The details of the coil could be found in the following article. The coil structure is exactly similar and compatible with the circuits discussed on this page.

Overunity Circuit using Joule Thief Concept


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

86 thoughts on “1 watt LED Driver Using a Joule Thief Circuit

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. grate!, it works (light intensity is less) I built and tested, thank you. can we improve upon this design to increase its brightness.

  3. Thanks, one more point, i intend to use a motor to run this, we need to add few more parts, Zener 1.5V, Capacitor 1000uf 10V, diode 4007 on +VE. is this ok

  4. hy swagatam
    i want to build a 3 kv ups , so please helpme if u can with full detail of transformer, pcb design, circuit using microcontroller or without microcontroller etc

  5. Could this little divice take double the power to perse power a six volt high power led? Im just curious cause ive just started out in electronics as a hobby and im interested in learning more. Im a novice in electronics but this is effectivly a pwm circuit from what I see. Ive got so many questions bout ic chips and diodes.

    • According to the rules, power can never be doubled or increased by any means…. the voltage may be boosted at the cost of the current, the same is true for the above circuit.

  6. I have emailed you the pics and circuit diagram as you requested. There is a typo on my post above (July 2, 2013) should have 510 Ohm resistor instead of 51 Ohm (sorry, missing a zero there). Thanks.

  7. Hello Sir,
    I have two small ferrite cores from a CFL circuit, I cannot Wind 10-10 of single core Cu wire each of Pri. SEC. winding on the core so I made two 10-10 turns inductors, So can I connect it in ||el to make a resultant transformers as the desired?

  8. Hello Dada
    I try to make this circuit but I got same output I fetch in Input do the direction of the coil in which we make the turns matters in determining the output. I made the primary & secondary coil in the same direction.

  9. Hi Swagatam,

    Can I use the coil harvested from the Quart watch, not sure of the induction it has but it has only two wires as connections. Will I be able to use any iron nail etc as ferrite core into this to work this circuit.


    • Hi Gopal,
      The coil needs to have two separate winding, a single winding won't help, so I am afraid the quartz coil won't do.

      Yes you can use a nail as the core, but the number of turns will need to be increased from 20 on each side to 50 on each side.

  10. What if I connect lion 3.7v battery what will be the output voltage???
    and what to do to increase output??
    what will be output current if input current is 1 Amp??
    give me formulae for all.
    sorry if I am annoying u too much 🙁

    • with 3.7V use 5 to 10 turns on each side and check the voltage across the LED side and increase or decrease the LED side turns for optimizing the output voltage as per the requirement.

      output will be = V x I of input…always

  11. Hello sir,
    This is Sherwin.
    What is the total current consumption of this circuit(1st diagram schematic)?

    well sir, i built this circuit in a different way;
    1. i salvaged the inductor from an old computer power supply.
    2. i shorted one opposite winding with respect to start of first coil and end of second coils. i connected positive 1.5v at the tap.
    3. i connected the resistor from the transistors' base to the start of second coil.
    4. i connected the transistors collector to end of first coil.

    after making the whole circuit, i then connected a 1n4148 at the tr's collector pin and followed it with a elec. cap rated at 1000uF@25v. and finally connected the led.
    The interesting part was that the led came out to be much more brighter.
    with conclusions i can say that the led got a pure dc after rectifying the pulsed output.


    • That's great Sherwin, thanks for the update
      however, brighter LEd means more consumption….because each time the capacitor charges it draws that extra bit of more current from the battery

  12. Hi sir,
    Sherwin again.
    When i built the circuit without the 1n4148 and cap, a humming sound was clearly audible from the coil. I tried putting a capacitor across the bias resistor to check for any differences but the LED stopped glowing.
    Why is such a thing??

  13. Sir i need to run 1w led with lithium 18650 battery.
    The fully charged voltage is 4.2v
    Empty voltage cutoff is 3.0v
    I'm confused with choosing current limiting resistor..
    Help me with diagram..

  14. But bcoz of this diode, the led terminal voltage also dropping. It ll reduce brightness .
    If the led turns off at 2.7v, still my battery volt is 3.5v, i need to utilise upto 3.2v from my battery without dimming led.

    • Li-ion cells must never be discharged below 3.6v, and charged above 4.2V….so the suggested diode concept provides safety to the LED and the li-ion cell both together.

  15. Dear sir,
    can i use a fast recovery diode with a capacitor to convert the pulsating dc to smooth dc since mentioned frequency is between 30-50khz.
    i wish to drive 2-3 multicolor leds slow changing ones.

  16. Hi Swagatam, I tried this circuit . It's excellent. I want to use this circuit for powerful bicycle light.I have a spare 3.7v,2800mAH Li-Ion battery and a stepper motor much bigger than the dc motor used in this circuit.I have spare LED(12v,15 W). What modification should I make 4 using those safely.

    • Thanks Sanjoy,

      a 3.7V 2.8AH battery will be capable of handling 8 to 9 watts maximum, so I am afraid, your 15 watt LED would be a bit high for this battery.

      For the circuit you may have to increase the wire thickness to around 1mm on both the sides, but make sure you use 3 or 4 strands of 0.3mm wires in parallel instead of a single 1mm wire, and also the transistor will need to be upgraded to a TIP 122 or any other similar…

    • Thank you for your reply Swagatam.
      I will try as you said. I will post the result definitely. Btw If I use 2 Li-Ion batteries (with different mAH/ AH values same voltage) will it be able to light up the LEDs with full voltage? Should I use heat sink for the transistor and overcharge protection for the batteries in case of continuous cycling for 3-4 hrs with the circuit on?

    • I modified the coil and used TIP 122 transistor. With a single Li-Ion now the LEDs achieved 50-60% of their full brightness I guess. I am yet two include the current limiter circuit. But before I include that and complete the project
      there is one issue that needs to be sorted out. In the original circuit you used a small dc motor with two terminals whereas I am using a stepper motor with six terminals. I identified the current generating pairs(2 nos.) of the stepper.
      But I could use only a single pair as I followed the original circuit wiring and left the other pair unused. I have no idea how to wire two pairs of terminals of the stepper in the circuit. So I am not able to use the full potential of the stepper.
      Please show how to wire two pairs of terminal together.

  17. dear sir, you are giving fantastic ideas.i want some help from u. i want a circuit for 3.3vdc to 5vdc 2amp current boost converter. 5v output must be constant (like in smps)any feed back circuit needed for this? please try to give full circuit for me.circuit without induct or is preferable. if it is compulsory we can use no problem.
    thanks in advance

    • Thanks Nivas, you can easily modify the above concept for your application need.
      for the transistor use TIP142, for the transformer initially go with 5 turns on each side. check the output voltage if it's less than 5V you can increase the secondary turns a bit and vice versa.

      the wires could be a 23 SWG rated or many 30SWG in parallel.

      for feedback you can use a BC547 between the base emitter of TIP142, and link the base of the BC547 with the transformer output via a 6V zener, this will take care of the stabilization issue.

  18. I have a 12 volts 5a alternator, but I want to improve the amperage of the alternator to fast charge the battery with was fitted to my bike both of them, can you suggest me a circuit wihch was full fill my requirment

    • I don't think current can be increased because it is dependent on the wire thickness of the alternator which cannot be changed.

      however by increasing rotational speed of the alternator, the voltage output can be increased which in turn could be transformed into current through a suitable transformer or a buck converter circuit.

  19. good day sir

    can this project to be used as free energy generator by coupling a motor and generator so that a continues rotation can happen?


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