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Another joule thief.

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Sceadwian

Banned
Here's a Joule thief I'm working on.
New xformer is on the left, old one is on the right. Current is higher from the cell when attached to the xformer on the left but I didn't test output current for efficiency. I'm just happy I got the one on the left wound.
 

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microtexan

New Member
joule thief

Tell us about the transformer. Looks fine.:eek:
 

audioguru

Well-Known Member
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My solar garden lights use a single 1.2V Ni-Cad battery cell and the voltage stepup circuit uses a small manufactured inductor that looks like a fat 1/8W resistor.
The single 3.5V white LED or 3.5V red-green-blue fading LED lights fine.
 

Mike_2545

Super Moderator
That's great! I was just wondering how small of a battery Sceadwian was using.
 

audioguru

Well-Known Member
Most Helpful Member
Key chain flashlights use a button cell to power the voltage stepup circuit. They shine for maybe 5 minutes.
 

forumlicker007

New Member
If you want to lightup an LED using a single 1.5v cell, joule thief step up circuit is the solution. will work even at low .5volt and you'll get a high bright white LED working for many hours. It will work consistently upto the last drop of power from the cell. Very efficeient.
 

colin55

Well-Known Member
The circuit posted by audioguru does not work efficiently. See the full: "Joule Thief" project on the web, for my corrected circuit or see Talking Electronics site, under LED Torch Circuits, for the theory behind its operation.
 

Sceadwian

Banned
Colin, the "LED Torch Circuit -A" is exactly the same as the schematic posted above except for the transformer winding, yours has a 1.5:1 ratio and his is 1:1. The 2nd circuit only ads a 10n cap. The 1:1 is easier to wind smaller and closer together especially on a toroidal core. I was intimidated having to wrap a toroid that small but it was very easy, I simply popped my 3X drug store reading glasses on which I use for small stuff and wound away, it's more like sewing than electronics though =)

All the other circuits on talking electronics required more transistors resistors and diodes to work, the one I made was specifically to be as small as possible, I just breadboarded it to make sure the coil worked. That charge pump IC your on your site is very nice, I wonder if there are any shops on the net that sell them one at at time.

As a side note, what's that 10n for colin, to change the frequency?
 

colin55

Well-Known Member
The 10n is the most important component in the circuit. It holds the left-side of the feedback winding steady so the energy generated in the winding can be pumped into the base of the transistor to turn it on more (so the transformer will deliver more energy during each cycle).
You can get a free sample of PR4401 from Prema. It's not a charge-pump chip but fly-back.
 

Sceadwian

Banned
If the 10n cap is the most important part of the circuit then why does it work without it? =) I was unable to replicate any increase in performance with the cap. Also I find it a little confusing that you state that you've proved that LED's are more efficient on pulsed currents vs proper DC which is completely false.
 

forumlicker007

New Member
Will the pulsed operation increase the overall efficiency? I've no idea. Talkingelectronics 3LEDs at 3V was a failure for me. I got the brightness shared over the 3(dimmed) means output is same like as single LED. I used 1N4148.
 

Sceadwian

Banned
LEDs are most efficienty when supplied FLAT DC current at the most effcient point of their light output. You can pulse them at higher currents but efficiency is thrown right out the window, because even if the apparent brightness is the same the loss to heat is higher.
 
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confounded

New Member
since i've seen yours, thought i'd show you mine :eek:

I've built a joule thief in one of those cheap torches they usually give away with stuff, where you swivel the bulb head to turn them on. The neat thing is that the LED sits in the head and is easilly replaced so you can swap colours easilly without having to mess about with soldering, and theres no switch, you just spin the head.
 

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