Joule Thief - still not working....

[fungus]

On Jul 25, 6:10 pm, default <defa...@defaulter.net> wrote:

That looks way too "clean." What is the bandwidth of your scope?

Probably not very high - it's 1970's tech, no digital storage or
dual beams or any of that stuff.

Blocking oscillators are notorious for producing overshoot,
undershoot, and ringing.

Sorry about that. I can get better ones by adjusting R1.

Here's a nicer one one across base/emitter:

http://www.artlum.com/jt/b_to_e_2.gif


And I can get this at the transistor base (relative to ground):

http://www.artlum.com/jt/base_ring.gif


Better?

 

[John Larkin]

On Sat, 25 Jul 2009 18:52:16 GMT, Jon Kirwan
<jonk@infinitefactors.org> wrote:

On Sat, 25 Jul 2009 18:38:34 GMT, Jon Kirwan
jonk@infinitefactors.org> wrote:

What I don't have handy

...is a way to measure inductance. (Never bought such a tool.) But
actually, I can approximate that by observing frequency of operation.

Jon

Got a scope?

Put a 1-ohm resistor in series with the inductor, scope that, and
connect a power supply. The slope, dI/dT, tells you the inductance.
And at some point the inductor saturates, the current jumps up, and
now you know the saturation current.

John

 

[Jon Kirwan]

On Sat, 25 Jul 2009 19:35:24 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sat, 25 Jul 2009 18:52:16 GMT, Jon Kirwan
jonk@infinitefactors.org> wrote:

On Sat, 25 Jul 2009 18:38:34 GMT, Jon Kirwan
jonk@infinitefactors.org> wrote:

What I don't have handy

...is a way to measure inductance. (Never bought such a tool.) But
actually, I can approximate that by observing frequency of operation.

Jon

Got a scope?

Put a 1-ohm resistor in series with the inductor, scope that, and
connect a power supply. The slope, dI/dT, tells you the inductance.
And at some point the inductor saturates, the current jumps up, and
now you know the saturation current.

Yes. Makes sense. V/L. Then L goes 'air-core' at saturation and V/L
gets a lot bigger.

Need to trigger when the supply is pulsed on, I suppose. What I have
are analog scopes, though. Tek2245 and HP54645D. No digitizing and
'freeze frame' of the analog.

Jon

 

[John Larkin]

On Sun, 26 Jul 2009 03:00:12 GMT, Jon Kirwan
<jonk@infinitefactors.org> wrote:

On Sat, 25 Jul 2009 19:35:24 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sat, 25 Jul 2009 18:52:16 GMT, Jon Kirwan
jonk@infinitefactors.org> wrote:

On Sat, 25 Jul 2009 18:38:34 GMT, Jon Kirwan
jonk@infinitefactors.org> wrote:

What I don't have handy

...is a way to measure inductance. (Never bought such a tool.) But
actually, I can approximate that by observing frequency of operation.

Jon

Got a scope?

Put a 1-ohm resistor in series with the inductor, scope that, and
connect a power supply. The slope, dI/dT, tells you the inductance.
And at some point the inductor saturates, the current jumps up, and
now you know the saturation current.

Yes. Makes sense. V/L. Then L goes 'air-core' at saturation and V/L
gets a lot bigger.

Need to trigger when the supply is pulsed on, I suppose. What I have
are analog scopes, though. Tek2245 and HP54645D. No digitizing and
'freeze frame' of the analog.

Jon

You can drive it with a pulsed transistor and do it periodically. The
frequency would be pretty high for the kind of inductor we're
conidering here.

John

 

[ehsjr]

Jon Kirwan wrote:

On Sat, 25 Jul 2009 05:03:52 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:


Jon Kirwan wrote:

On Fri, 24 Jul 2009 14:17:33 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:


snip
The joule thief will "chew up" batteries quickly.
snip

It's actually pretty efficient. I didn't get this from doing basic
calculations from theory, but by simply using LTSpice to do the calcs
of efficiency for me. It can be around 80-85%, or so. (It can also
be very bad, too.) At least, it seems so if there isn't 'operator
error' involved.

Jon

You snipped the content, completely. Joule thief efficiency
is not the factor. At 100% efficiency, which is of course
impossible, the op would be replacing AAA cells every 26 hours.
The math is in my post.
snip


I'll stop it here. Yes, I snipped a lot. Mostly because that line
was a lead-in towards another later on where you wrote, "If you _must_
use battery power, there are one chip solutions better than the joule
thief." I should have included that, as well. I'd read it, just
failed to quote it. The existing chip solutions aren't a whole lot
better, frankly. That was my point in writing as I did.

No, it is not a lead in to that at all. It was a lead in to
"Solution: mains power." Read the paragraph.

There are one chip solutions that are better in all three
areas I mentioned in the post: limited run time, LED brightness
will decrease over time, and cost of batteries. I put the
sentence below the three paragraphs with underscored headings
to refer to all three of them.

I don't _know_ if it qualifies as "a whole lot" better, but
available one chip solutions can meet the op's stated requirement
of keeping the current at 15-20 mA, and the joule thief cannot.

Ed

Sorry I wasn't more clear about it.

Jon

 

[ehsjr]

fungus wrote:

On Jul 25, 7:48 am, ehsjr <eh...@NOSPAMverizon.net> wrote:

The site you reference below, shows the joule thief producing
BELOW 15 mA for every datapoint.



That's because the transistor dies if I go much higher... :-(

We'll get that fixed, eventually. Here's a consideration,
in the meantime: Run 3 joule thieves, each one powering 2
series LEDs. Or, run one joule thief with three transistors
in parallel, but with 1 ohm resistors between each emitter
and ground.

Ed

 

[ehsjr]

Jon Kirwan wrote:

On Sat, 25 Jul 2009 11:19:58 -0700 (PDT), fungus
openglMYSOCKS@artlum.com> wrote:


On Jul 25, 6:23 pm, default <defa...@defaulter.net> wrote:

On Sat, 25 Jul 2009 07:48:45 -0700 (PDT), fungus

openglMYSO...@artlum.com> wrote:

I think we can definitely assume that the ferrite was
saturating or something

Probably "or something."




Iron powder usually has way more permeability than ferrite - ferrites
claim to fame is it is more permeable than air and able to handle high
frequencies with lower loss. Some iron powder alloys can go to 100's
of megahertz, but iron is usually used in the kilohertz range.

I just made another one with my thin wire and an iron powder ring.
I was hoping hoping to get a lot of turns on it to see what happened
but unfortunately it behaved like the ferrite - current started
dropping off after about ten turns and varying R1 makes no difference to the
output of the circuit.


Well, default may have been thinking about the BJT, itself. Elsewhere,
he wrote, "If the transistor heats that's where most of the waste
power is going," so that's why I think he is thinking so. And he
could be right about that. You've mentioned about the BJT heating up
a lot.

However, your new test seems to argue in support of saturation, I
think. More turns means more inductance and a lower frequency of
operation (other things similar.) It also means that Bsat is reached
at lower Ic_peak: B = mu*N*I/l_m. Assuming mu and l_m is the same in
both cores you used, and so is Bsat, then winding more N will push you
closer to Bsat.


In any event, when you select a core you are selecting for the
characteristics you need - and it is usually more accurate to say
"magnetic material, or magnetic material mix" than iron or ferrite.

Trouble is, I don't know the specs of any of these because I pulled
them out of a PSU.


Like most of us hobbyist types.

Ed has suggested pushing towards an air core. We all breathe the same
air, so you pretty much know what you have there. Have you tried
that? I'm going to.

Jon

Yes - the air core eleminates core sat from consideration
in circuit operation, and is easily repeatable in terms of
building close to identical circuits. The one I described
is not, however, the best performer. With a core you'll
gain efficiency.

Then you can try the circuit that uses an inductor,
not a transformer, one coil only. Not efficient,
but the damn thing works.

Ed

 

[fungus]

On Jul 26, 8:57 am, ehsjr <eh...@NOSPAMverizon.net> wrote:

I don't _know_ if it qualifies as "a whole lot" better, but
available one chip solutions can meet the op's stated requirement
of keeping the current at 15-20 mA, and the joule thief cannot.

Can you maybe recommend one...?

 

[fungus]

On Jul 26, 3:10 am, Jon Kirwan <j...@infinitefactors.org> wrote:

Agreed.  But it does protect the poor BJT, which in the big priority
scheme of important things to worry about comes just a little bit
ahead of worrying over power dissipation.  When jacking things up with
a higher Vin (more batteries), the whole thing goes bad real quick.

I mentioned that with my super-bead I can dial output currents using
R1 so I tried it with two batteries. I can get 15mA out from a 2.3V
input
(which is borderline acceptable...) but the transistor gets just as
hot
as when I have 15mA output with three batteries.

The problem seems to me to be that the transistor receives the
exact same current as the LEDs. As LED current rises, so does
transistor current.

The diode makes it just a bit more idiot proof.

My little transistor graveyard definitely approves of the diode.

 

[David Eather]

fungus wrote:

On Jul 26, 8:57 am, ehsjr <eh...@NOSPAMverizon.net> wrote:
I don't _know_ if it qualifies as "a whole lot" better, but
available one chip solutions can meet the op's stated requirement
of keeping the current at 15-20 mA, and the joule thief cannot.


Can you maybe recommend one...?

LM3909 - but they are hard to get hold of now

 

[Jon Kirwan]

On Sun, 26 Jul 2009 22:24:34 +1000, David Eather <eather@tpg.com.au>
wrote:

fungus wrote:
On Jul 26, 8:57 am, ehsjr <eh...@NOSPAMverizon.net> wrote:
I don't _know_ if it qualifies as "a whole lot" better, but
available one chip solutions can meet the op's stated requirement
of keeping the current at 15-20 mA, and the joule thief cannot.


Can you maybe recommend one...?

LM3909 - but they are hard to get hold of now

David, is this your recommendation for "one chip solutions can meet
the op's stated requirement of keeping the current at 15-20 mA" for
six 3.3V LEDs?

It stacks the battery voltage with only one capacitor, to double the
voltage. That's about it. And it doesn't control current over
voltage source variations.

Here is an LM3909 equivalent that works. R1 and C1 set timing. R8 is
a current limiter, such as it is:

: +1.5 +1.5 +1.5 +1.5 +1.5
: | | | | |
: | | | | |
: | \ | | |
: | / R7 | Q2 e>| |<e Q1
: | \ 410 | 2N5401 |---+---| 2N3906
: \ / | c/| | |\c
: / R8 | | | | |
: \ 12 | | | | |
: / | |/c Q4 | | |
: | +-------+---------| 2N3904 | | |
: | | | |>e | | |
: | | | | '-----+ |
: | | \ | | |
: | | / R3 | | |
: | \ \ 22k | | |
: --- / R6 / | | |
: \ / D2 \ 410 | | | |
: --- LED / | | |/c Q3 |
: | | +------------------------| |
: | | | | |>e |
: | | | | 2N3904 | |
: | C1 | \ | | |
: | || 150uF | / R4 | | |
: +------||-------+ \ 10k | | |
: | || | / | | |
: | | | | | |
: | | | | | |
: | | +-----------' | |
: | | | \ |
: | | | / R2 |
: | | \ \ 100 |
: | | / R5 / |
: | | \ 22k | |
: | | / | |
: | | | | |
: | | | | |
: | | gnd | |
: +--------------------------------------------------' |
: | | |
: | | |
: | ,--------+ |
: \ | | |
: / R1 | | 2N3904 |
: \ 10k | Q5 c\| |
: / | |--------------------------------------'
: | _|_ D1 e<|
: | /_\ BAT54 |
: | | |
: | | |
: | | |
: gnd gnd gnd

Lots of parts and it doesn't meet with Ed's comment.

Jon

 

[Jon Kirwan]

On Sat, 25 Jul 2009 20:48:54 GMT, Jon Kirwan
<jonk@infinitefactors.org> wrote:

On Thu, 23 Jul 2009 09:24:55 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

That's a horrible circuit. Too many conflicting parameters depend on
the value of R1. A proper blocking oscillator uses an RC time constant
to set the rep rate, and a separate resistor to limit the base
current.

ftp://jjlarkin.lmi.net/BlockOsc.JPG

I still can't make sense of that one. It bugs me a lot because I just
can't see why it would work well.

This one does make more sense to me, though:

,-------------------+----------,
| | |
| | |
| | |
| \ )|
| / R1 )| L2
| \ )|
| / )|o
| | |
| ,----+------+ | D8 ,-------, ,--,
--- | | | +--|>|---+ | | |
- V1 | | | | | --- | ---
--- | | )|o | | \ / D6 | \ / D3
- | | )| | | --- | ---
| | | )| L1 | | | | |
| | | )| | | | | |
| | | | | --- C1 --- | ---
| | | | |/c Q1 --- \ / D5 | \ / D2
| | | +--------| | --- | ---
| \ | | |>e | | | |
| R2 / --- C2 | | | | | |
| \ --- _|_ D7 | | --- | ---
| / | /_\ | | \ / D4 | \ / D1
| | | | | | --- | ---
| | | | | | | | |
| | | | | | '-----' |
gnd gnd gnd gnd gnd gnd gnd

Is that what you were thinking of, instead?

Jon

Well, John, you didn't respond to this one yet. However, I did play
around with a first shot at design equations for it. (Not much
different than the other concept except, as you say, I get to change
the winding ratio and take better control of the reverse Vbe on Q1 so
that I don't need D7 shown above.)

Here is the new schematic:

,-------+----------------------,
| | |
| | |
| \ )|
| / R1 )| L2
| \ )|
| / )|o
| | |
| | | DF
| | +--|>|---+-------, ,--,
--- | | | | | |
- V1 +----+------, | | --- | ---
--- | | | | | \ / D6 | \ / D3
- | | )|o | | --- | ---
| | | )| | C1 --- | | |
| | | )| L1 | --- | | |
| | | )| | | --- | ---
| | --- C2 | |/c Q1 | \ / D5 | \ / D2
| \ --- '--------| | --- | ---
| R2 / | |>e | | | |
| \ | | | | | |
| / | | | --- | ---
| | | | | \ / D4 | \ / D1
| | | | | --- | ---
| | | | | | | |
| | | | | '-----' |
gnd gnd gnd gnd gnd gnd

In this arrangement, I get to pick a winding ratio and much of the
rest falls out. If X is the winding ratio (L1/L2) and Vr is the
maximum reverse voltage you want to apply to the base of Q1
(referenced to ground, so usually negative), then:

N = (Vout + Vdf - Vcesat) / (Vin - Vcesat)
Ic_peak = 2 * Iout * (N + 1)

(Vdf is the forward voltage of diode DF.)

Then look up Ic_peak on the datasheet for picking off beta. Now to
compute the Thevenin values:

Rth = [beta * (X * (Vout + Vdf) - Vbe + Vr)] / Ic_peak
Vth = X * (Vout + Vdf - Vin) + Vr

Obviously, X must be selected so that Vth is _less_ than Vin and yet
more than what's required to start Q1 (call that 1V or more?)

At this point, we can compute:

R1 = Rth * Vin / Vth
R2 = Rth * Vin / (Vin - Vth)

Which gets one started.

I tried out the idea of an LED current of Iout=30mA, Vout=20V,
Vcesat=0.1V, Vin=4.5V, Vdf=0.35V:

N = 4.6
Ic_peak = 336 mA

The beta for a 2N2222 at that current is about 90. I selected X=(1/4)
after thinking for a moment. I used Vbe=0.85V.

Rth = 599.33 Ohms
Vth = 1.9625 V

Then,

R1 = 1374.26 Ohms
R2 = 1062.85 Ohms

I then plugged all this into LTSpice and ran the simulation. I used
C2=100pF just to put something in. (I have already set up the six LED
stack so that the current works out close to 30mA at close to 20V.) I
set up the inductances to establish the ratio X (L1=L2/X^2, which I
assume is how spice programs estimate the winding ratio of linked
inductors.)

The output of LTSpice was the following:

Ic_peak = 332 mA
Vr = -2.15V

Pretty darned good for a first shot at it!

Jon

 

[Ecnerwal]

In article <eeOdnSNC0--N1vHXnZ2dnUVZ_hVi4p2d@supernews.com>,
David Eather <eather@tpg.com.au> wrote:

fungus wrote:
On Jul 26, 8:57 am, ehsjr <eh...@NOSPAMverizon.net> wrote:
I don't _know_ if it qualifies as "a whole lot" better, but
available one chip solutions can meet the op's stated requirement
of keeping the current at 15-20 mA, and the joule thief cannot.


Can you maybe recommend one...?

LM3909 - but they are hard to get hold of now

Supertex CL2 - very easy to come by, though not every supply house
carries them. Enough do, and they are current production. Or with twice
as many parts (2) an LM317 and a resistor, in constant current mode.
Neither is the ideal in terms of batteries, as they are basically linear
"smart" variable resistors (well, I know the 317 is, and I think the CL2
works similarly, though I could be wrong) but if supplied with enough
voltage above the minimum needed, they will provide constant current
until the supply voltage drops too low, and then fizzle out quickly.

A PWM buck, boost, or buck/boost solution would be potentially the most
efficient method, but requires a few more parts and a lot more smarts to
make it actually constant current. The Joule Thief (IIUC) is essentially
a boost converter without any PWM. If starting form multiple cells, and
thus more voltage, one of the above methods (paralleled out sideways to
as many LEDs as you want to drive) is a whole lot simpler in terms of
getting the job (if the job is 20 mA drive of LEDs) done. OTOH, the JT
provides a lot of opportunities for messing about on the bench and
trying things out, which is good for keeping your brain from rotting, if
you get beyond monkey-see monkey-do and diversions into monkey doo-doo.

--
Cats, coffee, chocolate...vices to live by

 

[ehsjr]

fungus wrote:

On Jul 26, 8:57 am, ehsjr <eh...@NOSPAMverizon.net> wrote:

I don't _know_ if it qualifies as "a whole lot" better, but
available one chip solutions can meet the op's stated requirement
of keeping the current at 15-20 mA, and the joule thief cannot.



Can you maybe recommend one...?

Manufacturer chips posted below are just the first few found by a
Google search with "led boost drivers" in the search box.

National recommends their LM3410X for this.
http://www.national.com/ds/LM/LM3410.pdf

TI shows the TPS61160 meeting the requirements.
http://focus.ti.com/lit/ds/symlink/tps61161a.pdf

Onsemi has the CAT3606-D
http://www.onsemi.com/pub_link/Collateral/CAT3606-D.PDF

Linear's LT3598 will do it:
http://cds.linear.com/docs/Datasheet/3598fa.pdf

I'm not recommending any one of those over any other,
and there are other chips from those manufactures and
others that may suit your needs.

Ed

 

[Jon Kirwan]

On Sun, 26 Jul 2009 17:06:24 GMT, ehsjr <ehsjr@NOSPAMverizon.net>
wrote:

fungus wrote:
On Jul 26, 8:57 am, ehsjr <eh...@NOSPAMverizon.net> wrote:

I don't _know_ if it qualifies as "a whole lot" better, but
available one chip solutions can meet the op's stated requirement
of keeping the current at 15-20 mA, and the joule thief cannot.

Can you maybe recommend one...?

Manufacturer chips posted below are just the first few found by a
Google search with "led boost drivers" in the search box.

National recommends their LM3410X for this.
http://www.national.com/ds/LM/LM3410.pdf

$2.50-$3 each. Lots around.

TI shows the TPS61160 meeting the requirements.
http://focus.ti.com/lit/ds/symlink/tps61161a.pdf

Hmm. Cheaper. $2 each. Lots around.

Onsemi has the CAT3606-D
http://www.onsemi.com/pub_link/Collateral/CAT3606-D.PDF

Couldn't find the -D around anywhere. But did find CAT3606HV4-T2 at
Digikey for $1 (and at only two other places.) This device cannot
handle more than 4.2V input and must have at least 3V. It's designed
for Li-ion sources and can run in either 1X or 1.5X mode. I'm not
hyped on this as a 'solution.' It's a charge pump with regulation on
the current, I think.

Linear's LT3598 will do it:
http://cds.linear.com/docs/Datasheet/3598fa.pdf

Mucho expensive. I found them for over $7 each! (Some at under $5,
too.) Only a few places carry them.

.....

TI seems to be the one out of the above I'd focus more on. Looks nice
and seems to do the right job for a reasonable price and is at various
stores, as well.

Jon

I'm not recommending any one of those over any other,
and there are other chips from those manufactures and
others that may suit your needs.

Ed

 

[John Larkin]

On Sun, 26 Jul 2009 17:51:59 GMT, Jon Kirwan
<jonk@infinitefactors.org> wrote:

On Sun, 26 Jul 2009 17:06:24 GMT, ehsjr <ehsjr@NOSPAMverizon.net
wrote:

fungus wrote:
On Jul 26, 8:57 am, ehsjr <eh...@NOSPAMverizon.net> wrote:

I don't _know_ if it qualifies as "a whole lot" better, but
available one chip solutions can meet the op's stated requirement
of keeping the current at 15-20 mA, and the joule thief cannot.

Can you maybe recommend one...?

Manufacturer chips posted below are just the first few found by a
Google search with "led boost drivers" in the search box.

National recommends their LM3410X for this.
http://www.national.com/ds/LM/LM3410.pdf

$2.50-$3 each. Lots around.

TI shows the TPS61160 meeting the requirements.
http://focus.ti.com/lit/ds/symlink/tps61161a.pdf

Hmm. Cheaper. $2 each. Lots around.

Onsemi has the CAT3606-D
http://www.onsemi.com/pub_link/Collateral/CAT3606-D.PDF

Couldn't find the -D around anywhere. But did find CAT3606HV4-T2 at
Digikey for $1 (and at only two other places.) This device cannot
handle more than 4.2V input and must have at least 3V. It's designed
for Li-ion sources and can run in either 1X or 1.5X mode. I'm not
hyped on this as a 'solution.' It's a charge pump with regulation on
the current, I think.

Linear's LT3598 will do it:
http://cds.linear.com/docs/Datasheet/3598fa.pdf

Mucho expensive. I found them for over $7 each! (Some at under $5,
too.) Only a few places carry them.

....

TI seems to be the one out of the above I'd focus more on. Looks nice
and seems to do the right job for a reasonable price and is at various
stores, as well.

Jon

I'm not recommending any one of those over any other,
and there are other chips from those manufactures and
others that may suit your needs.

Ed

A TinyLogic schmitt trigger and a SOT-23 mosfet will make a nice
controllable-PWM boost thing. It only needs a 2-terminal inductor,
which simplifies life.

Sort of like this:

ftp://jjlarkin.lmi.net/Z206.pdf

John

 

[fungus]

On Jul 26, 6:18 pm, Ecnerwal
<MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:

Supertex CL2

Datasheet says 5V minimum input voltage...

 

[Jon Kirwan]

On Sun, 26 Jul 2009 13:08:45 -0700, John wrote:

snip
A TinyLogic schmitt trigger and a SOT-23 mosfet will make a nice
controllable-PWM boost thing. It only needs a 2-terminal inductor,
which simplifies life.

Um. SOT-23. I'm sure the OP will enjoy wiring that up -- if he
doesn't sneeze first.

Sort of like this:

ftp://jjlarkin.lmi.net/Z206.pdf

Nifty multiplier there. I assume the NC7S14 is just your basic 74S14
hex schmitt-trigger inverter thingy. And I thought the schottky
variety had gone obsolete some time back. Is that really an "S" part?

Which fet do you use for Q2?

And is D1 and R1 to provide an easier path when pulling high due to
poorer output drive and mosfet loading? Or something related to the
primary inductance kick via mosfet gate capacitance that I'm not aware
of? I seem to recall getting by with 7414 oscillators without those
two parts.

Thanks,
Jon

 

[fungus]

On Jul 26, 7:51 pm, Jon Kirwan <j...@infinitefactors.org> wrote:

National recommends their LM3410X for this.
http://www.national.com/ds/LM/LM3410.pdf

$2.50-$3 each.  Lots around.

TI shows the TPS61160 meeting the requirements.
http://focus.ti.com/lit/ds/symlink/tps61161a.pdf

Hmm.  Cheaper.  $2 each.  Lots around.

Maybe there's lots where you live but I don't know where
I'd get one around here, and there's none on eBay.

But ... while I was trawling eBay I found a lot of people selling
LM3914s. It's a dedicated LED driver chip, can work with 3V
input and drive up to 10 LEDs with programmable current
(up to 30mA each).

http://www.national.com/mpf/LM/LM3914.html


Even better: It has an input sensor making LED bar graphs.
I assume I could just pull the sensor high to turn on all the
LEDs but it opens up lots of fun possibilities - eg. I might be
able to make the LEDs respond to sound, which would be
very cool for processions.

Almost seems too good to be true ...

 

[John Larkin]

On Sun, 26 Jul 2009 21:20:30 GMT, Jon Kirwan
<jonk@infinitefactors.org> wrote:

On Sun, 26 Jul 2009 13:08:45 -0700, John wrote:

snip
A TinyLogic schmitt trigger and a SOT-23 mosfet will make a nice
controllable-PWM boost thing. It only needs a 2-terminal inductor,
which simplifies life.

Um. SOT-23. I'm sure the OP will enjoy wiring that up -- if he
doesn't sneeze first.

Sort of like this:

ftp://jjlarkin.lmi.net/Z206.pdf

Nifty multiplier there. I assume the NC7S14 is just your basic 74S14
hex schmitt-trigger inverter thingy. And I thought the schottky
variety had gone obsolete some time back. Is that really an "S" part?

Actually, it's single-gate CMOS. I don't know where the S comes from.

Which fet do you use for Q2?

Don't recall at the moment. It was a low-threshold SOT-23 thing. I
only built a few of these boards to demo an electro-optical modulator
thing a friend was working on. Output is 0-900 volts, essentially no
current.

And is D1 and R1 to provide an easier path when pulling high due to
poorer output drive and mosfet loading?

They tune the gate drive duty cycle, to ballpark 7% in this case. R2
sets OFF time, R1 sets ON time, mostly.

It's also not hard to close a feedback loop on schmitt trigger
frequency or duty cycle.

John