Toroidless Joule Thief

A joule thief is an oscillating device that is capable of turning on high brightness LEDs, but the wonderful thing about this circuit is that you can use 1.5v batteries from remote controls, cameras, keyboards, in short, any electronic component that still uses batteries. button type, AA, AAA, etc.

If you are a clever hobbyst you can get from 0.8 to 1.5 volts with almost any citrus and elements like zin and copper, so it could be a survival flashlight in the woods too.

A joule thief toroidal can work from 0.8 volts because it needs a minimum of 0.7 volts to work, this is due to the base-emitter junction of the transistors (B-E) where the drop is of that value to enter conduction mode.

So don't throw away your old batteries and I'll show you how you can make a joule thief, but this time without the more expensive toroidal inductor, since we'll just use an average value two pin inductor.

I'll call this project: Toroidless Joule Thief.

Supplies

These were the materials used in this built:

• 2 SOT-23 NPN Transistors (2n2222a,2n3904)
• 1.5v LR44 coin cell holder or springs.
• 3 SMD 0805 LEDS or 3-5mm leds you have available.
• 100uH or more SMD inductor (C155129)
• Slide Switch SMD.
• Custom Partial PCBA by JLCPCB.
• 100k 0805 SMD Resistor.
• 1k 0805 SMD Resistor.
• 22pF 0805 SMD Capacitor.
• Solder, Soldering iron.
• Patience.

This is the Schematic Diagram:

¿How it works?

The Joule Thief Circuit is a voltage booster circuit which converts a constant low voltage input into a periodic output of a higher voltage. This circuit can be most often seen lighting an LED with an almost dead AA battery. The peaks in voltage occur rapidly, causing the LED to flash at a very fast rate.

Son we cannot see the flashing bc is very quick for our eyes, but it does thousand of times per second.

*by removing the toroidal inductor from the circuit, it is necessary to add a second transistor to perform the oscillation, this lowers the design cost, but adds more components. which in this case does not affect the cost of the circuit, since a toroidal inductor will be more expensive than using an extra general purpose NPN transistor*

maybe you could use an chinese joule thief IC, but in some countries its difficult to find.

This is the PCB layout of the circuit.

In the design of the PCB circuit, I decided to use surface mount components (SMD) since they are more compact and faster to solder for many, this pcb measures about 3cm in diameter and is made with 2 layers (top and bottom layer) designed in EasyEDA.

The PCB could have a different shape such as: the size of an AA battery, so that a battery retainer could be connected under the pcb, but to lower the cost I decided to make some mini Bagdes PCBs that well I don't know why I was thinking of Rosewell and the ALIENS but I wanted to make it like a flying UFO but I needed more leds.

On the back of the PCB is a LR44 button cell battery clip, but cables can be removed to power it with any voltage source from 1.5 volts, such as a battery, a potato, salt and water, etc.

The complete Schematics, Gerber Files, BOM Materials, and Pick and Place materiales a re in: https://oshwlab.com/ELECTROMAN-CREW/micro-joule-thief

The SMD leds can be changed for normal leds (5mm or 3mm) and soldered on the pcb as I will show in the next step.

After completing the design, I uploaded my Gerber Files, BOM List, and Pick and place (Excel Files) on JLCPCB Quote Website selected the solder mask color which was RED and placed the order.

I choose RED Soldermask, but you could choose any color like: black, purple, yellow, blue, and the old and reliable green color.

After placing the order, I received the PCBs in a week and the PCB quality and SMT soldering is professional grade, you know... machines still do soldering better than humans.

Really loved the end result.

I ordered 5 PCB's for $2 dollars with JLCPCB using its electronic component surface mounting (SMT) service.

The things I had to solder was the 0805 encapsulated SMD leds. To solder them, first identify the anode (positive) and cathode (negative) of each led diode, which is very well shown at the bottom of each led, or on the PCB silkscreen.

Another way to identify the positive and negative of the SMD LEDs is by using the diode scale multimeter, and if when you put the tips the LED lights up slightly, it will be directly polarized, and you will have found its anode and cathode. This works if you don't have very good eyesight like me.

To solder the inductor, you can use one from 100uH to 200uH, just apply solder to each end and solder it with a fine tip soldering iron, you can also use a heat gun if you have, apply some solder. if your inductor is new add soldering to its pads and some flux where it will be soldered, apply heat at 420°C under the PCB for a few seconds and that's it, the inductor will settle into position by itself.

On the back you can fit a 1.5v LR44 battery holder, but you can also adapt some spring-loaded battery connectors that you can recycle from a toy that uses batteries.

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*I made a mistake on design, a trace between 22pF Resistor and 1k Resistor ir missing so i need to make a bridge manually, i really feel sad about it, but it was my mistake and i know how a simple circuit couldn´t run without that bridge, but you know the feeling and i don´t wanna throw away and waste my lovely PCBs. Anyway... the mistake is SOLVED in design AND GERBER FILES* so if you make this PCB Joule Thief your design will work at first time.

Now that we know that the joule thief is an oscillator, well... it has to generate a sinusoidal wave at its output, or the closest waveform.

So I used a multimeter-oscilloscope called: Pokit Meter.

This device can measure voltage, current, resistance, diodes, etc. like a common multimeter. only that it uses the screen of your cell phone to display the data.

I connected the leads of my joule thief in direct current voltage meter mode to check that the voltage at the output is approximately the same as the battery. and so, in the first image you can see the voltage on one of the leds, and because they are connected in parallel, the voltage is the same on all of them.

In the second image, use the pokit meter as an oscilloscope, and take samples of the waveform in the output signal, here I show you some screenshots of the waveform from the Pokit Meter app shows.

the circuit works fine, larger led diodes can be soldered on, and retrofitted, it can even be powered by an external solar cell, or potato battery, or lemon, salt water solution, and the circuit can be placed in a plastic bottle glass, which will make it waterproof and protect it from moisture, dust and water.

Here are some videos of the toroidless joule thief working, and as yuu can see is a simple but interesting circuit, that anyone interested in electronics must make once in life, because its simplicity and functionality. So the joule thief is a interesting circuit to understand: toroids, transistors, oscillators, and electromagnetism.

The working video you can see through YouTube:

Link Here: https://www.youtube.com/shorts/xvm43Htpuh4