Joule Thief

[Pirate88179]

Pirate88179,

Do you have any idea what the current draw from
the 30 Volt battery might be?

If it is only a few milliAmperes it would be possible
to make a DC to DC Boost circuit to transform a
low two cell voltage to the needed 30 Volts with
pretty good regulation.

Do you remember the TI Scientific Calculators
from the '80s (TI-30) which were powered by either
a 9 Volt battery or the rechargeable 2-cell
NiCd boost replacement?

No, I don't know what the current draw is, but, it can't be too much.  The original battery inside was just a stack of oval hearing aid type batteries, like ten of them to get the 30 volts.  I solved this by using 3 nine volt batteries in series as I saw them do on an old radio restoration site.  (Some old radios used these batteries also)

I don't recall those calculators but, if I saw one, I would bet it would ring a bell.  Your idea is a good one but the 9 volt batteries in series (outputting 28+ volts) works fine, at least in this application.

Bill

[crowclaw]

No, I don't know what the current draw is, but, it can't be too much.  The original battery inside was just a stack of oval hearing aid type batteries, like ten of them to get the 30 volts.  I solved this by using 3 nine volt batteries in series as I saw them do on an old radio restoration site.  (Some old radios used these batteries also)

I don't recall those calculators but, if I saw one, I would bet it would ring a bell.  Your idea is a good one but the 9 volt batteries in series (outputting 28+ volts) works fine, at least in this application.

Bill

There you go Bill, yet another project for the JT circuit maybe for you!! Wind a small coil rectified DC output with cap, voltage divider to achieve target voltage. Clamp the voltage with a zener diode, etc... job done.
Worth a try maybe when you've got five.

[Jeg]

Hi guys

Nice thread but huge to search for what i need. 
I'd like to ask if anybody has a JT circuit driving an ignition coil if it is possible from 1.5V Even higher supply voltage is accepted. It's time to play with this small gadget!!!

Thanks
Jeg

[crowclaw]

Hi Jeg, just give it a try... the only problem I can see if you need to reverse the primary windings if it doesn't self oscillate!  You only have three connections on these coils, the primary and secondaries are common connections. Also beware of the high secondary voltages while experimenting. Otherwise drive it with a 555 timer IC, also these coils use an iron core so frequencies are much lower.

[Pirate88179]

I took apart another garden solar light and found this board.  As you can see (hopefully) it only has an inductor on one side of the board and that black blob covering the "mystery chip" on the reverse.  I removed it from the solar cell and the photo diode and tested the amp draw while lighting the straw hat LED very brightly.  It was only drawing 8 mA's while being powered by my power supply at 1.2 volts.  (I used a meter in series and not the display on my supply)

While researching this online I found a few guys that have this type of board with a chip not covered by the epoxy and they said it had 4 leads on it and no markings.  Another fellow said that the chip does the switching and the resistance as well.  This will light an LED brightly down to .5 volts and I want to know what it is so I can make my own boards and vary the resistance to control the lighting and mA draw.

Does anyone here know anything about this mystery chip and what it might be?  I have not put it on the scope yet but, the chip and the inductor and the built in resistor work as a JT in a very small and compact package. 

Any help here would be greatly appreciated.

Thanks,

Bill

PS  Every board I have like this labels that inductor as R1 so, until someone on here pointed out that it was indeed an inductor, I always thought it was a resistor.  I am always learning something from you guys.