Joule Thief - still not working....

[fungus]

On Aug 5, 12:05 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

Just another interesting note on the subject of not having to pay for
postage costs getting isolated electronic parts for the joule thief. I
just opened up a BPCE13T/8 compact fluorescent bulb's base.

I just Dremeled one open to see what's inside, there's a
*lot* of parts in there...(!) I thought it would be all
microprocessor controlled, but no.

Here's a pic: http://www.artlum.com/jt/cfl.jpg

The ferrite ring on mine is tiny. It's inside a plastic
holder and when I opened it up the ring is tiny. Good
for making a really small joule thief? Is the holder
there to maintain a distance between the wires and the
ring?

There's also an inductor in the shape of a bobbin,
like this: http://www.surplustraders.net/a/mg429.gif
If I took the thick wire off and wound it with thin
wire it might also work for a JT.

There's a little transformer in there as well with a
lot of wire on it - easily enough to wind the bead.
As an aside, would a transformer not work for a joule
thief?

There's two big transistors - google doesn't know the
spec on them but I guess they're in there for switching
so they might work.

There's half a dozen diodes hidden in there as well and
plenty of capacitors - basically everything you need
for a JT!

 

[Jon Kirwan]

On Wed, 5 Aug 2009 05:20:39 -0700 (PDT), fungus
<openglMYSOCKS@artlum.com> wrote:

On Aug 5, 12:05 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
Just another interesting note on the subject of not having to pay for
postage costs getting isolated electronic parts for the joule thief. I
just opened up a BPCE13T/8 compact fluorescent bulb's base.

I just Dremeled one open to see what's inside, there's a
*lot* of parts in there...(!) I thought it would be all
microprocessor controlled, but no.

Here's a pic: http://www.artlum.com/jt/cfl.jpg

Here's what mine looks like:
http://www.infinitefactors.org/misc/images/bpce13t_1.jpg
http://www.infinitefactors.org/misc/images/bpce13t_2.jpg

The ferrite ring on mine is tiny. It's inside a plastic
holder and when I opened it up the ring is tiny. Good
for making a really small joule thief? Is the holder
there to maintain a distance between the wires and the
ring?

I'm not sure. Mine didn't have one. They just wound wire onto it and
soldered it down. Maybe you folks rate better than we do. The unit I
opened is really pretty bad -- it's a very simple (which means cheaper
to make and probably not nearly as good) unit.

There's also an inductor in the shape of a bobbin,
like this: http://www.surplustraders.net/a/mg429.gif
If I took the thick wire off and wound it with thin
wire it might also work for a JT.

Yeah. I see those in switcher supplies a lot. But not in my
particular CFL.

There's a little transformer in there as well with a
lot of wire on it - easily enough to wind the bead.

Yup. That's an inductor (usually) placed in series with the lamp. You
can see mine, as well, in the above pictures.

As an aside, would a transformer not work for a joule
thief?

Hmm? I think it's probably an inductor (two wires, if you look very
closely underneath, not more than that.) They make them 'look' like
transformers often do. But they aren't. Not in mine, anyway. So I
can't say.

There's two big transistors - google doesn't know the
spec on them but I guess they're in there for switching
so they might work.

They are often MOSFETs. If your unit is better than mine, anyway.
Mine really are BJTs. But yours may not be.

There's half a dozen diodes hidden in there as well and
plenty of capacitors - basically everything you need
for a JT!

Yup. Most everything!

Jon

 

[Paul E. Schoen]

"fungus" <openglMYSOCKS@artlum.com> wrote in message
news:7d0990b4-7dca-4325-9711-c10e09531242@o6g2000yqj.googlegroups.com...
On Aug 4, 7:37 pm, fungus <openglMYSO...@artlum.com> wrote:

I got one to light up a bunch of LEDs using only the chip
and one external resistor (which adjusts the LED current).

I'm just running a set of batteries flat through one to
see how it goes.

The bad new is ... I think it might need four batteries to
keep a full 20mA going though the 3.3V LEDs.

============================================================

It's also very inefficient. 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%. Much better to buy a dual inductor for a
dollar:
http://www.mouser.com/Search/Refine.aspx?Keyword=47680C
and make one of the circuits that I have already proven to be at least 75%
efficient, and will work down to about 1 volt.

Paul

 

[Jonathan Kirwan]

On Wed, 5 Aug 2009 15:06:29 -0700 (PDT), fungus
<openglMYSOCKS@artlum.com> wrote:

On Aug 5, 11:13 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

There's also an inductor in the shape of a bobbin,
like this:http://www.surplustraders.net/a/mg429.gif

Yeah.  I see those in switcher supplies a lot.  But not in my
particular CFL.

What's that black thing at front-left? Might be one
covered with with heatshrink.

I think it is a MOV (a high energy pulse protection device.)

As an aside, would a transformer not work for a joule
thief?

Hmm?  I think it's probably an inductor (two wires, if you look very
closely underneath, not more than that.)

Yes, you're right. I unsoldered all the components
in mine so I can see it now. It looks like a transformer,
has four legs, but only two legs are connected.

Yup. They all have these, I think -- well, at least the cheaper ones.
I don't think I've ever seen the insides of a 0.9 power factor unit,
yet. They might not use them. These are all 0.6 or less, I think.

Still, easily enough wire in there to make a joule thief.

Yup!!! Nifty, eh?

There's two big transistors - google doesn't know the
spec on them

They are often MOSFETs. If your unit is better than mine, anyway.
Mine really are BJTs.

Yours actually says "BCE" on the PCB. Mine just
says "T1" and "T2" so I don't even know for sure
which leg is which.

Lots of these use MOSFETS. Ones like mine, where they have even fewer
components than yours and are the ultimate in save-every-penny,
probably use BJTs.

Next up - try and make one using only those parts.

Yes. You might be able to use the core and wiring of the inductor and
just find a nice place to tap off of it. (And/or unwind some of it,
anyway.) It's probably got a fair bit of inductance in it, though, so
the frequency might be very slow if you leave all of the wire on it
and just tap into it.

The nice thing is that the are a bag full of just about the right
stuff. So kind of a freebee.

Jon

--
Saying religion is the source of morality is like saying
a squirrel is the source of acorns -- [JK, 2002.]

 

[fungus]

On Aug 5, 11:13 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

There's also an inductor in the shape of a bobbin,
like this:http://www.surplustraders.net/a/mg429.gif

Yeah.  I see those in switcher supplies a lot.  But not in my
particular CFL.

What's that black thing at front-left? Might be one
covered with with heatshrink.

As an aside, would a transformer not work for a joule
thief?

Hmm?  I think it's probably an inductor (two wires, if you look very
closely underneath, not more than that.)

Yes, you're right. I unsoldered all the components
in mine so I can see it now. It looks like a transformer,
has four legs, but only two legs are connected.

Still, easily enough wire in there to make a joule thief.

There's two big transistors - google doesn't know the
spec on them

They are often MOSFETs. If your unit is better than mine, anyway.
Mine really are BJTs.

Yours actually says "BCE" on the PCB. Mine just
says "T1" and "T2" so I don't even know for sure
which leg is which.


Next up - try and make one using only those parts.

 

[Jon Kirwan]

On Wed, 05 Aug 2009 21:13:31 GMT, I wrote:

snip
Hmm? I think it's probably an inductor (two wires, if you look very
closely underneath, not more than that.) They make them 'look' like
transformers often do. But they aren't. Not in mine, anyway. So I
can't say.

Well, that inductor uses #34 magnet wire (if my micrometer isn't
fooling me) and the E-core has a 2.9mm gap inside the windings with a
measured size of 6.6mm X 4.2mm core area. Pretty large gap. It was
easy to separate the two halves of the E-core -- barely glued and then
taped (no metal spring clip here.) Just removed the tape, gripped one
half with vise-grip and twisted slightly by hand to crack the glue and
loosen. Slipped apart easy, then.

Wire appears to be wound, doubled-up -- I don't know why. Maybe
because two lengths of #34 is cheaper to someone than one length of
#31 (about the same cross section area?) Given that it is, one idea
is to disconnect the ends from each other and use it as a transformer
without all the work of winding one by hand.

Jon

 

[Jon Kirwan]

Just another comment.

I've been buying bulbs from Costco. At least three varieties of them.
Small, 13W; larger 23W; and similar but envelope-enclosed 23W
varieties. They are branded "Conserv-Energy" and they come under the
numbers, BPCE13T/8, BPCE23R40/3, and BPCE23TM/4. I also have now
opened a Philips Marathon 13W "mini decorative twister."

I've had Conserv-Energy units that simply melted with black smoke all
over the place. And looking at the circuits, they use fewer expensive
parts and are more poorly (cheaply) assembled. By comparison. They
also don't seem to last long and they are definitely NOT rated to be
used within enclosures of any kind. Their shorter life always appears
(in the 4 Conserv-Energy units I've looked at, so far) to be due to a
part grossly overheating and burning up. (BJT explosively blew out
its emitter lead; two cases of a burned up resistor; and one was so
burned and melted overall that I'm not sure.)

The Philips unit that I dismantled was in excellent visual condition
and that bulb lasted quite some time, as well. Given the years of
service, the pristine appearance of the circuit itself, and the highly
darkened regions in the fluorescent bulb itself, I'm assuming for now
that it is the bulb itself changed over time until the circuit could
no longer properly drive it. But that the circuit likely still works.

Jon

 

[Jon Kirwan]

On Thu, 6 Aug 2009 20:59:45 -0700 (PDT), fungus
<openglMYSOCKS@artlum.com> wrote:

On Aug 6, 10:12 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

The Philips unit that I dismantled was in excellent visual condition
and that bulb lasted quite some time, as well.

Does the Phillips bulb still use similar components?
It all looks very low-tech to me, I expected an IC
controller at least.

The philips bulb has parts on both sides of the board, but it doesn't
appear to use a controller. (I thought the same thing, before pulling
these apart.) It includes TWO of the 200V electrolytics and none of
the parts appeared burned/damaged. All the other units I dismantled
had blown capacitors, resistors, BJTs, and/or melted inductors. It
seems like more money (or, at least, effort) went into the Philips
unit. But I have yet to find one with a controller IC (that I can
recognize as having a controller IC -- which says something about me
or the bulbs.)

Some of the newer bulbs are a *lot* smaller, I wonder
what's inside them.

Rip one open. You can always use masking tape and Elmer's glue later.
If it is in the store still, just tell them you are one of those
customers who likes to Dremmel the merchandise before considering
buying it.

Jon

 

[fungus]

On Aug 6, 10:12 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

The Philips unit that I dismantled was in excellent visual condition
and that bulb lasted quite some time, as well.

Does the Phillips bulb still use similar components?
It all looks very low-tech to me, I expected an IC
controller at least.

Some of the newer bulbs are a *lot* smaller, I wonder
what's inside them.

 

[David Eather]

Paul E. Schoen wrote:

"fungus" <openglMYSOCKS@artlum.com> wrote in message
news:7d0990b4-7dca-4325-9711-c10e09531242@o6g2000yqj.googlegroups.com...
On Aug 4, 7:37 pm, fungus <openglMYSO...@artlum.com> wrote:
I got one to light up a bunch of LEDs using only the chip
and one external resistor (which adjusts the LED current).


I'm just running a set of batteries flat through one to
see how it goes.

The bad new is ... I think it might need four batteries to
keep a full 20mA going though the 3.3V LEDs.

============================================================

It's also very inefficient. 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%. Much better to buy a dual inductor for a
dollar:
http://www.mouser.com/Search/Refine.aspx?Keyword=47680C
and make one of the circuits that I have already proven to be at least 75%
efficient, and will work down to about 1 volt.

Paul

Gee, I hope you *always* ride a bicycle - it is the most efficient form
of transport! If you don't, then perhaps you will acknowledge that there
are other valid considerations beside efficiency.

 

[Paul E. Schoen]

"David Eather" <eather@tpg.com.au> wrote in message
news:KNCdnU7I-M-BleDXnZ2dnUVZ_tWdnZ2d@supernews.com...

Paul E. Schoen wrote:
"fungus" <openglMYSOCKS@artlum.com> wrote in message
news:7d0990b4-7dca-4325-9711-c10e09531242@o6g2000yqj.googlegroups.com...
On Aug 4, 7:37 pm, fungus <openglMYSO...@artlum.com> wrote:
I got one to light up a bunch of LEDs using only the chip
and one external resistor (which adjusts the LED current).


I'm just running a set of batteries flat through one to
see how it goes.

The bad new is ... I think it might need four batteries to
keep a full 20mA going though the 3.3V LEDs.

============================================================

It's also very inefficient. 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%. Much better to buy a dual
inductor for a dollar:
http://www.mouser.com/Search/Refine.aspx?Keyword=47680C
and make one of the circuits that I have already proven to be at least
75% efficient, and will work down to about 1 volt.

Paul

Gee, I hope you *always* ride a bicycle - it is the most efficient form
of transport! If you don't, then perhaps you will acknowledge that there
are other valid considerations beside efficiency.

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. 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.

The basic Joule Thief suffers from poor regulation, which means that most
of a fresh battery's energy will be quickly depleted because of initially
high LED current, and then perhaps what remains of its life may be extended
a little by having a circuit that will still operate when the cell voltage
goes below one volt, but the LEDs will be barely lit, and not for long.

Ultimately, one could probably get the best battery life by using a PWM
current regulator and perhaps a capacitor based charge pump which can
approach 98% efficiency. And unless you want a combination heater and lamp,
any wasted power will mean less desired output (light) and shorter battery
life.

Paul

 

[fungus]

On Aug 8, 9:41 am, "Paul E. Schoen" <p...@peschoen.com> 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.

 

[Paul E. Schoen]

"fungus" <openglMYSOCKS@artlum.com> wrote in message
news:930ccacd-9923-4403-9ad3-66851e8c8338@g19g2000vbi.googlegroups.com...
On Aug 8, 9:41 am, "Paul E. Schoen" <p...@peschoen.com> 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

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/

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

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

Also:
http://cds.linear.com/docs/Datasheet/1871fe.pdf
http://cds.linear.com/docs/Datasheet/3477fc.pdf

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

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. 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

 

[David Eather]

Paul E. Schoen wrote:

"David Eather" <eather@tpg.com.au> wrote in message
news:KNCdnU7I-M-BleDXnZ2dnUVZ_tWdnZ2d@supernews.com...
Paul E. Schoen wrote:
"fungus" <openglMYSOCKS@artlum.com> wrote in message
news:7d0990b4-7dca-4325-9711-c10e09531242@o6g2000yqj.googlegroups.com...
On Aug 4, 7:37 pm, fungus <openglMYSO...@artlum.com> wrote:
I got one to light up a bunch of LEDs using only the chip
and one external resistor (which adjusts the LED current).

I'm just running a set of batteries flat through one to
see how it goes.

The bad new is ... I think it might need four batteries to
keep a full 20mA going though the 3.3V LEDs.

============================================================

It's also very inefficient. 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%. Much better to buy a dual
inductor for a dollar:
http://www.mouser.com/Search/Refine.aspx?Keyword=47680C
and make one of the circuits that I have already proven to be at least
75% efficient, and will work down to about 1 volt.

Paul
Gee, I hope you *always* ride a bicycle - it is the most efficient form
of transport! If you don't, then perhaps you will acknowledge that there
are other valid considerations beside efficiency.

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. 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.

The basic Joule Thief suffers from poor regulation, which means that most
of a fresh battery's energy will be quickly depleted because of initially
high LED current, and then perhaps what remains of its life may be extended
a little by having a circuit that will still operate when the cell voltage
goes below one volt, but the LEDs will be barely lit, and not for long.

Ultimately, one could probably get the best battery life by using a PWM
current regulator and perhaps a capacitor based charge pump which can
approach 98% efficiency. And unless you want a combination heater and lamp,
any wasted power will mean less desired output (light) and shorter battery
life.

Paul

Actually, the OP requirement was for 3 batteries to run 6 LED's at as
close to a constant 20ma as possible.

 

[Paul E. Schoen]

"David Eather" <eather@tpg.com.au> wrote in message
news:bYqdnUt8aNdgkuPXnZ2dnUVZ_uSdnZ2d@supernews.com...

Actually, the OP requirement was for 3 batteries to run 6 LED's at as
close to a constant 20ma as possible.

The modified JouleThief with output current regulation that I posted and
built will do that with 6 LEDs in series, with about $2 in a dozen parts.

But for LEDs separately controlled a simple current regulator will work
well. Just two NPN transistors and two resistors for each LED will set the
current to about 20 mA above 2.6 volts, and will still supply 6 mA at 2
volts (which is just 0.5 v over the forward voltage of the LED).

Spice model follows.

Paul

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

Version 4
SHEET 1 880 680
WIRE 80 -16 -80 -16
WIRE 256 -16 80 -16
WIRE 256 32 256 -16
WIRE 80 80 80 -16
WIRE -80 144 -80 -16
WIRE 256 176 256 96
WIRE 80 192 80 160
WIRE 176 192 80 192
WIRE 80 224 80 192
WIRE 176 224 176 192
WIRE 192 224 176 224
WIRE 176 272 144 272
WIRE 176 288 176 272
WIRE 256 288 256 272
WIRE 256 288 176 288
WIRE -80 400 -80 224
WIRE 80 400 80 320
WIRE 80 400 -80 400
WIRE 176 400 80 400
WIRE 256 400 256 368
WIRE 256 400 176 400
WIRE 176 432 176 400
FLAG 176 432 0
SYMBOL npn 192 176 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL npn 144 224 M0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL res 240 272 R0
SYMATTR InstName R1
SYMATTR Value 33
SYMBOL LED 240 32 R0
SYMATTR InstName D1
SYMATTR Value QTLP690C
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 64 64 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL voltage -80 128 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PWL(0 0 .1 5 .2 5)
TEXT -114 456 Left 0 !.tran .12 startup

 

[fungus]

On Aug 8, 11:35 pm, "Paul E. Schoen" <p...@peschoen.com> wrote:

There are many options

I noticed...

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.

This is only hobby-level, it's for people to wear in some
night-time processions in October so it has to fairly discreet
in size, I might decorate some drums as well, hence the
"respond to sound" part.

Efficiency isn't #1 priority at this stage. I want something
easy to build and play around with.

 

[Jon Kirwan]

On Sun, 09 Aug 2009 01:28:31 GMT, "Paul E. Schoen" <paul@peschoen.com>
wrote:

snip
But for LEDs separately controlled a simple current regulator will work
well. Just two NPN transistors and two resistors for each LED will set the
current to about 20 mA above 2.6 volts, and will still supply 6 mA at 2
volts (which is just 0.5 v over the forward voltage of the LED).

Couldn't you get by with fewer? Just parallel up the BJTs bases and
emitters and use their separate collectors for the LEDs. Collector
current is determined by Vbe (ignoring Early effect among other
things.) If you wanted to be a little extra careful you could add
some low-valued emitter resistors, I suppose. BJT count is then 1
plus number of LEDs, resistor count is 2 plus number of LEDs, etc.

Something like:

: Vcc Vcc Vcc
: | | |
: | | |
: \ | |
: / Rx --- ---
: \ 1k \ / D1 \ / D2
: / --- Red 2V --- White 3V
: | | |
: | | |
: +------------+--------------+---------------> etc
: | | | | |
: | | | | |
: | | |/c Q1 | |/c Q2
: | '--| '--|
: | |>e |>e
: | | |
: | | |
: | \ \
: | / R1 / R2
: | \ 10 \ 10
: | / /
: Qx c\| | |
: 2N3904 |----------+----+--------------+----------> etc
: e<| |
: | |
: | \
: | / Rz
: gnd \ (0.7V/20mA/N)
: /
: |
: |
: gnd

Rx is plenty low enough in your original schematic to drive a host of
LEDs, so I'd leave that value alone. Qx will suck away whatever isn't
needed, anyway. Rz is supposed to drop enough to drive Qx, which is
about 0.7V. At 20mA per LED, the value to be used is easy to compute.
R1, R2, ... Rn are just there to normalize out BJT variations. At 10
ohms, even a 2N2222 and 2N3904 can be paired up with good results.

Of course, Vcc needs to be enough to drive the highest-V LED, or else
the other LEDs will get a bit of a boost due to the fact that Rz's
current needs to be where it is designed to be.

Jon

 

[David Eather]

Paul E. Schoen wrote:

"fungus" <openglMYSOCKS@artlum.com> wrote in message
news:930ccacd-9923-4403-9ad3-66851e8c8338@g19g2000vbi.googlegroups.com...
On Aug 8, 9:41 am, "Paul E. Schoen" <p...@peschoen.com> 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/Datasheet/3783fb.pdf

Yeah, every beginner can solder DFN and TSSOP.

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

Yeah, every beginner can solder MSOP.

http://cds.linear.com/docs/Datasheet/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.

 

[Paul E. Schoen]

"Jon Kirwan" <jonk@infinitefactors.org> wrote in message
news:snds75da597nbbfk66rr3o4s8mha96nor1@4ax.com...

Couldn't you get by with fewer? Just parallel up the BJTs bases and
emitters and use their separate collectors for the LEDs. Collector
current is determined by Vbe (ignoring Early effect among other
things.) If you wanted to be a little extra careful you could add
some low-valued emitter resistors, I suppose. BJT count is then 1
plus number of LEDs, resistor count is 2 plus number of LEDs, etc.

Something like:

: Vcc Vcc Vcc
: | | |
: | | |
: \ | |
: / Rx --- ---
: \ 100 \ / D1 \ / D2
: / --- Red 2V --- White 3V
: | | |
: | | |
: +------------+--------------+---------------> etc
: | | | | |
: | | | | |
: | | |/c Q1 | |/c Q2
: _ '--| '--|
: \ / |>e |>e
: --- 1N4148 | |
: | | |
: - \ \
: \ / / R1 / R2
: --- 1N5818 \ 15 \ 15
: | / /
: | | |
: |-----------------+--------------+----------> etc
: |
: |
: |
: |
: gnd
:
:
:
:

Rx is plenty low enough in your original schematic to drive a host of
LEDs, so I'd leave that value alone. Qx will suck away whatever isn't
needed, anyway. Rz is supposed to drop enough to drive Qx, which is
about 0.7V. At 20mA per LED, the value to be used is easy to compute.
R1, R2, ... Rn are just there to normalize out BJT variations. At 10
ohms, even a 2N2222 and 2N3904 can be paired up with good results.

Of course, Vcc needs to be enough to drive the highest-V LED, or else
the other LEDs will get a bit of a boost due to the fact that Rz's
current needs to be where it is designed to be.

I made some changes above that are even simpler. It might not be very
stable with temperature and it is not tightly regulated, but not bad for
such a simple circuit. Germanium transistors would work at even lower
voltages, but are hard to find. A 1VDC LDO would be better than the two
diodes. There is a TI TPS71701 that can be set to 1.00 VDC or even 0.9 VDC.

The LTspice for this circuit follows.

Paul

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

Version 4
SHEET 1 880 680
WIRE 80 -16 -80 -16
WIRE 256 -16 80 -16
WIRE 448 -16 256 -16
WIRE 80 16 80 -16
WIRE 256 32 256 -16
WIRE 448 32 448 -16
WIRE -80 144 -80 -16
WIRE 80 160 80 96
WIRE 176 160 80 160
WIRE 368 160 176 160
WIRE 256 176 256 96
WIRE 448 176 448 96
WIRE 80 208 80 160
WIRE 176 224 176 160
WIRE 192 224 176 224
WIRE 368 224 368 160
WIRE 384 224 368 224
WIRE 256 288 256 272
WIRE 448 288 448 272
WIRE 80 304 80 272
WIRE -80 400 -80 224
WIRE 80 400 80 368
WIRE 80 400 -80 400
WIRE 176 400 80 400
WIRE 256 400 256 368
WIRE 256 400 176 400
WIRE 448 400 448 368
WIRE 448 400 256 400
WIRE 176 432 176 400
FLAG 176 432 0
SYMBOL npn 192 176 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL npn 384 176 R0
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL res 240 272 R0
SYMATTR InstName R1
SYMATTR Value 15
SYMBOL LED 240 32 R0
SYMATTR InstName D1
SYMATTR Value QTLP690C
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 64 0 R0
SYMATTR InstName R10
SYMATTR Value 100
SYMBOL voltage -80 128 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 3 -200 130 Left 0
SYMATTR InstName V1
SYMATTR Value PWL(0 0 .1 6 .2 6)
SYMBOL diode 64 208 R0
SYMATTR InstName D10
SYMATTR Value 1N4148
SYMBOL schottky 64 304 R0
SYMATTR InstName D11
SYMATTR Value 1N5818
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL LED 432 32 R0
SYMATTR InstName D2
SYMATTR Value LXHL-BW02
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 432 272 R0
SYMATTR InstName R2
SYMATTR Value 15
TEXT -112 456 Left 0 !.tran .12 startup

 

[fungus]

On Aug 9, 7:20 am, David Eather <eat...@tpg.com.au> wrote:

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).

I didn't look at the packages ... but yes, most of them like
they'd be unusable for beginner-hobbyist. I'm worried about
soldering directly to the legs of a LM3914 without overcooking
it.

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.

It seems like overkill, expensive too.

For this first attempt I think the LM3914 is the right chip
for the job - cheap, simple to build, few external components,
easy to obtain in small quantities without paying massive
delivery charges....

If the only thing against it is power efficiency then I don't
see any problem.

I might still use a joule thief for any places where the
LEDs are far apart and putting them in series makes the
wiring simpler.

If this thing is a success and people want more then I'll
look into doing it properly - get some proper inductors for
the JTs and maybe look into ways of optimizing the power
and/or doing fancier effects.