Re: Joule Thief - still not working....

Paul E. Schoen wrote:
"fungus" <openglMYSOCKS@xxxxxxxxxx> wrote in message news:930ccacd-9923-4403-9ad3-66851e8c8338@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Aug 8, 9:41 am, "Paul E. Schoen" <p...@xxxxxxxxxxxx> wrote:
The original reason for the "Joule Thief" was to extract the last little
bit of energy from a battery, so the efficiency and useful life of the
battery are apparently important.

There's videos on the 'net of people lighting 400 LEDs
with a single AA battery and a Joule Thief made with
the transformer from a disposable camera.

http://www.metacafe.com/watch/2319688/joule_thief_lights_400_leds_on_single_aa_battery/

The circuits are here:

http://www.overunity.com/index.php?topic=6942.0


The LM3914 is useful for its purpose of
acting as a bargraph and the single resistor control of LED current is
convenient, but it is not useful for getting longer life out of a battery.


After a bit of playing I've found another advantage
of the LM3914 - the LEDs aren't in series so I can
switch them on/off individually, either with the
chip's sensor or with external transistors. I'm still
playing around with it but it has a lot of possibilities
for decoration.

For 10 LEDs at 20 mA each and a 6 volt supply
you will be wasting 10 * 2.7 * .02 = 0.54W and
the LED power will be 0.66W for a best case
efficiency of 55%.

Batteries don't really give 1.5V ... for most of
their lifetime it's more like 1.25V. If we assume
four batteries gives 5V input that's 10*1.7*0.02
= 0.34W lost and efficiency is 66%.

If I'm mixing colors (very likely) I could run
the LM3914 and the red LEDS off three batteries
and the other colors off four. That would save
some extra Watts.

------------------------------------------------------

You might look into something like the LT3476, which can drive four strings of LEDs with separate PWM brightness modulation with efficiency of 96%. You need a separate HV supply but that can be made with a simple boost converter which can have easily 90% efficiency. Here are the details:
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1094,P24013

Yeah, every beginner can solder QFN.


Here's a little PIC project that might do what you want:
http://hackedgadgets.com/2006/11/27/pic-based-serial-controlled-rgb-led-pwm-driver/

Yeah, every beginner has a spare PIC programmer (and the ability to trouble shoot id something goes wrong).


This is an 8 channel driver in a 16 pin DIP/SOIC, for about $1:
http://focus.ti.com/lit/ds/symlink/tlc5917.pdf


Yeah, all beginners can build a micro controller system to interface with it.

This is an interesting IC:
http://cds.linear.com/docs/Data***/3783fb.pdf

Yeah, every beginner can solder DFN and TSSOP.


Also:
http://cds.linear.com/docs/Data***/1871fe.pdf

Yeah, every beginner can solder MSOP.

http://cds.linear.com/docs/Data***/3477fc.pdf

Yeah, every beginner can solder DFN and TSSOP.


And National has a tiny SOT-23 boost circuit:
http://www.national.com/ds/LM/LM3519.pdf

Not again. This is electronics.basics? Seriously, what is the point of putting up ideas that *can't* be implemented - not every beginner can solder SOT-23 either.


There are many options, and the best choice depends on what you really want to do and the cost of parts, time, size, and whether this is a one-up hobby experiment or something you might want to make in some quantity.

I made a 15-20 watt version that drives a string of 7 white LEDs at 600-700mA on a 12 VDC battery, and works from about 6V to 16V.

3 or perhaps 4 batteries was a requirement.

I'll post
details separately. It can be built on a 1" x 2" PCB and parts are about $3. Efficiency measured about 72-80%.

Good luck, and have fun!

Paul



Fungus,

If you want to know why I am down on so many of the ideas have a look at the packaging of these chips and imagine soldering on them at home. If you want to try surface mount chips I suggest you grab something cheap in the package called "SOIC" and try on that first (SOIC is the easiest/largest surface mount package).

The PIC chip is close to a good idea. Maybe you could look at the PICAXE system / chip? The software and documentation is free and includes a software simulator. A PICAXE chip programs in a simplified BASIC language and the programmer is a serial cable and two resistors which you can buy or make at home.
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