Make a Joule Thief

PLJack

Watch Here: (4 minute video)
http://blog.makezine.com/archive/2007/11/make_a_joule_thief_weeken_1.html

I find this really interesting.
Anyone know the down side of this method?
Every method has pro's and con's.

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- - - PLJack - - -

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Perfection in design is not achieved when there is nothing left to add.
It is achieved when there is nothing left to take away.

metron9

I just tried it with a tiny isolation transformer and it works great. I did not have any ferrite rings. I tried using a diode and a capacitor to see how much voltage it would pump with room light and a 2V solar panel. Pumped up a 3300 uf cap very nice to 14 volts. If you do use a capacitor remember not to disconnect an led and allow it to run , if you reconnect the led the voltage in the capacitor will blow the led.

Ran a white led at 0.5V from room light on the solar panel.

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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!

Franklin

Metron9, could you show your circuit? (for us electronically challenged ones)

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- Stephen

metron9

Just replace the LED with a diode and capacitor in series

instead of

Collector

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LED>

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GND

Use

Collector

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Diode>

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Capacitor

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GND

to get a higher voltage for charging a 9V rechargable battery for example or making a flasher or one of those tiny solar bugs that use the 1/2 volt solar chips. (darn I just ordered stuff from those guys and i did not add those to the fun bag)


If you mean the transformer I got that from radio shack, There are two coils in a isolation transformer just like the wired ferrite coil it has 4 leads, connect one side of each coil to positive and the other two the same as the ferrite coil diagram. Be sure to read the technical stuff on how it works at this link.

http://www.evilmadscientist.com/article.php/joulethief

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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!

Beau Schwabe

You can also use just about any (CT) Center Tapped transformer.... including the Audio transformers sold at Radio Shack.



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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

PLJack

From the site:

Site said...
This is a simple example of a switching power supply driven by a transformer-coupled oscillator, made of only four components

That's the part I did not understand originally.

It seemed to me that if you increased the voltage of the source then the current would be reduced.
This circuit is cycling at ~40 kHz.
So the power source still maintains it normal current abilities.
Is that true?

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- - - PLJack - - -

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Perfection in design is not achieved when there is nothing left to add.
It is achieved when there is nothing left to take away.

Beau Schwabe

For driving an LED and low current applications, this circuit would probably be fine if you place a diode cap configuration that metron9 suggests.

This circuit has been around for many, many years and it always seems to recycle in popularity. I remember this circuit from an electronics kit
I had as a kid about 30 years ago.

Anyway, a couple of things about this circuit...

- It also functions well as a VCO (Voltage controlled oscillator) meaning that as the input voltage changes, so does the frequency.
- The coil/transformer used also plays a part in determining the oscillators frequency.
- The duty cycle remains at about 40% ON 60% OFF
- Interestingly, if used as a LED driver, if the input voltage is greater than or equal to the forward bias of the LED, the oscillator will fail to oscillate...The LED remains ON..

Attached is what the waveform looks like driving a Green LED from a 1.5V "AA" battery.
The Pk-Pk voltage is about 2.84V.
The measured forward bias of the LED is 1.798V
The measured current draw while driving the LED was about 38mA

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.