Joule Thief

[magpwr]

Well I ordered some parts from digikey and the postage was more than the parts cost. I had to change to the Australian website then the postage was 34 dollars, and they asked a lot of questions as to why I wanted to import the parts. Weird.

Anyway I got 20 of those 74AUC gates and some of the Schottky's MarkE suggested, some MPSA18 transistors, some 2N7000 mosfets and some 1N5819 diodes.

If I order from them again I will make sure I have the cart full. 

Thanks for the tips on the parts.

..

I'm wondering if one of the 74AUC logic gates can be used in the place of the pnp transistor in a two transistor single coil "feed back" type oscillator, then it could possibly be turned on and off by a micro to maintain the boosted output voltage level.

Or once the boosted voltage is achieved the micro could take over switching the LV transistor, or just perform "gating" to keep the output voltage stable and not allow it to go too high.

The circuits naturally "gate" in burst mode when the input voltage gets real low, so the same voltage sense could adjust output power to maintain an equilibrium, or perform controlled dumping of the boosted voltage into storage batteries.

..

hi Farmhand,

If you want free delivery from digikey you will need to order at least $100 Usd worth of item.The delivery is extremely fast.Eg:Placed order last week Friday evening and got items on Monday afternoon(less than 4 days) and i'm living in Asia-Singapore.

Need to plan list of parts and taking quantity in account before placing order if you are already serious into experimenting.

[Farmhand]

Yeah I figured it would be fast delivery so that's good, I'm ready to experiment. 

Here's a PDF with the "Application Noted for the Texas Instruments "Little Logic devices".

..

[Farmhand]

I'm testing a low voltage "boost chip" NCP1400, and i thought some might be interested in my results since there has been some
interest in them on this thread. I got the 3 volt parts for a regulated 3 volt output. It works down under 0.1 volt input. 

I put together a quick setup on a PCB since the circuit is so simple it's easiest to hand draw it. The coil I used has a bit more
inductance than is recommended at between 18 and 27 uH, mine is about 35 uH.

Anyway, with only 1 volt input and working into 2 x NiMH AAA batteries in series at 2.78 volts to charge them it is pulling about 220 mA.
It begins current limiting with about 330 mA input current at 1.3 volts in this situation, frequency varies but so far it's between 180 kHz
and 100 kHz.
It works down under 0.1 volts input which is awesome. And throughput is impressive as well.

The LED is across the output but it's just an indicator.

Considering how quickly it is charging the batteries for the input it's using the efficiency seems like it must be fairly good.
All in all a very simple and cheap circuit, but the chip is regulated as a booster.

..

[TinselKoala]

Thumbs up! I approve of the construction technique. I had to blow up the picture to find that little chip though! Maybe that's what's under Pirate Bill's mystery black blobs in the garden lights.

[Pirate88179]

Farmhand:

Nice work.  Where did you find the 1400?  (I googled it and found lots of info but no sources) I have started working in this area as well and was looking for some 0119A chips (the 4 pin chips found in solar garden lights that do NOT have the gray blob) and I found some.  A guy has a bunch of the garden light circuit boards with the inductors, the 0119A chips, resistor and the led for like $.40 ea.  I bought 40 of them.  I also bought some axial 47 mH inductors to play with as well.  This was a much better deal than paying 2 dollars ea. for the chips alone.

I have been working 11 hour days for the past month or so and have not had time to even test those boards I bought.  My hours have returned to normal so I should be able to catch up in a week or so. I like your pcb.  That smd chip, or something similar, might just be what is under the gray blobs.

TK:

Yes, it could easily be something like the chip Farmhand is using.  If one can wind a ferrite toroid and get 47 mH, why don't more folks use these axial inductors which are cheaper and much easier?  Also, how are you guys measuring the mH's of the inductors?  Is there a cheap, do it yourself kit for this?

Bill