joule thief

Flashlight Modding and DIY Parts
1

Anyone who knows about electronics.... Can you explain how the joule thief circuit compares to the driver used in a 1.5v single AA battery light? For example I have a unregulated "powerlight" that runs off one AA... it must have a 'transformer' circuit of some kind because the 1.5v batt can light up the LED.

I understand that the joule thief circuit can get insanely long run times, much longer than any of my flashlights can give. Is that because the joule thief circuit is more efficient? Or is it because the joule thief runs the LED dimmer at the start, but for longer?

If it can be so cheaply made and so small in size, how come flashlight manufacturers aren't putting it into flashlights? Or is it already out there in some flashlights already?

I want to understand this cool little circuit better. I'd like to try combining it with a bright LED emitter to make a survival light to get a long running AA battery camping lamp.

Thoughts? Thanks guys.

2

Or would an integrated circuit chip like the ZXSC380 LED driver be a better way to go? How does it compare to the joule thief?

Also there's a PR4401 that looks to be a similar IC.

3

"Or is it because the joule thief runs the LED dimmer at the start, but for longer? "

You said it...is good for 5 mm leds at 30 mA or so , not for power leds

Edit; that light could be made with a 5 mm led 20000 mc , not much light but useful in an emergency

4

The joule thief powers the led quite hard but for only 50k of a second. The led 5mm type can take that quite happily

5

The two ICs you listed have output current between 20 and 80 mA. Those two wouldnt be enough to drive an Xr-E, Xp-G, or Xm-L LED. I suspect that is the reason you dont see them in high power LED applications. They are effiecient, but not capable of handling higher amperage LEDs.

6

I'm a little surprised that people haven't incorporated multiple emitters of different types together into a flashlight .It maybe a pure custom design but I like the concept of the light doing multiple purposes.

I'm intrigued by the joule thief and am somewhat at a loss for it's real value since I try not to by any disposable batteries any more ..eneloop eneloop eneloop

7

Finally built my first joule thief today. I used the parts I already had on hand, instead of shopping for components.

I had a couple 2n3906 PNP transistors, so I had to reverse the battery and LED polarity. I made an air core coil, because I didn't have any good ferrite cores handy this weekend. A ferrite core should help to increase the performance and decrease the size... I'll try that next weekend. I swapped out the 1k resistor with a 1k variable resistor to adjust the resistance. I added a 2.2nf ("222") ceramic disk capacitor to improve the circuit - the LED is immediately appears brighter.

I still can't find my multimeter, otherwise I'd measure the current consumption. (Time to get a new one I guess).

It's almost as bright as my 25 lumen "BLF delight" flashlights I got off Ebay.

I hear the runtime of a LED on this circuit with an AA is insanely long. This is what got me interested in the joule thief in the first place.

Next I need to work on packaging it. I'd like to make it into an angle head flashlight so I can put it into a headband for use as a headlamp with a super long runtime. Maybe add another LED for more brightness.

Took me quite a few tries to get one working, because I'm an electronics newbie. I had my coil pairs twisted wrong at the start. It turns out thats a common beginner mistake.

8

Good Job, Dimeotane! What is the current draw off the battery? Let us know how long of a runtime you get out of it.

9

Sorry for digging up this old thread... but I found a cool video which is fitting.

10

The ones they use to charge mobile phones from a single AA go form 1.5v input to 5v output.

I think they are about $3 or so on eBay.