LED wiring Series or Parallel 110 or 12v (for Power Efficien

[Chris Carlton]

Building a light fixture with 54 LEDs. (me NEWBIE)

4 different LEDs used

18 - 30mA IF 3.8VF
18 - 30mA IF 1.7VF
9 - 30mA IF 2.2VF
9 - 20mA IF 3.6

for Power Efficiency...
What's the best wiring design for this?
Parallel or Series? 12V or 110V

I'm currently planning... 12V - Series
Can I mix LEDs in a Series?
Do I need anything more than 3-5 LEDs and a resistor in each series?
How do I limit amps to a series or to the fixture?
I would like to power multiple fixtures like these off of 1
transformer. Is it better to build a device to divide the amps and
plug my fixtures into it?

If this is to much to ask for free, I'd be more than happy to pay for
your knowledge. I have to solve this one way or the other.

Thank You,
Chris Carlton

 

[Rich Webb]

On Fri, 30 Dec 2011 22:43:08 -0800 (PST), Chris Carlton
<personalgrowthnow@yahoo.com> wrote:

Building a light fixture with 54 LEDs. (me NEWBIE)

4 different LEDs used

18 - 30mA IF 3.8VF
18 - 30mA IF 1.7VF
9 - 30mA IF 2.2VF
9 - 20mA IF 3.6

for Power Efficiency...
What's the best wiring design for this?
Parallel or Series? 12V or 110V

I'm currently planning... 12V - Series
Can I mix LEDs in a Series?
Do I need anything more than 3-5 LEDs and a resistor in each series?
How do I limit amps to a series or to the fixture?
I would like to power multiple fixtures like these off of 1
transformer. Is it better to build a device to divide the amps and
plug my fixtures into it?

If this is to much to ask for free, I'd be more than happy to pay for
your knowledge. I have to solve this one way or the other.

There was a long thread here back in '04 regarding regulating current to
LEDs using a current mirror and similar techniques. Give that a read for
some options:
<http://groups.google.com/group/sci.electronics.basics/browse_thread/thread/1a8547721b8950ce/ef2d171838815044?q=led+current+mirror+group:sci.electronics.basics>
or just do a search in http://groups.google.com for "led current mirror
group:sci.electronics.basics"

--
Rich Webb Norfolk, VA

 

[fungus]

On Dec 31, 7:43 am, Chris Carlton <personalgrowth...@yahoo.com> wrote:

Building a light fixture with 54 LEDs. (me NEWBIE)

What's the best wiring design for this?
Parallel or Series?

Parallel is frowned upon because individual
LEDs vary and there's no way to control how
much current goes down each path of the
circuit. ie. Some LEDs might get more than
their maximum rating.

12V or 110V

12V seems a bit small and 110V seems too
big for your LED mix.

I'm currently planning... 12V - Series

12V will work but you'll have a lot of
little strings of LEDs.

eg. You can only put three of the 3.8V
LEDs in a series. For 18 LEDs you'll
have 6 separate series.

Can I mix LEDs in a Series?

Yes, but remember that all LEDs in a series
will have the same current passing through
them so mixing 20mA and 30mA won't work.

Do I need anything more than 3-5 LEDs and a resistor in each series?

Technically, no, but see next question.

How do I limit amps to a series or to the fixture?

Option 1: Choose your resistor carefully.

Resistors have a problem though, getting
exactly 20 or 30 mA can be fiddly and if you
get it a couple of mA wrong the difference
in brightness between LEDs can be noticeable.

If this isn't a problem for you then the resistor
method will work.

Option 2: Use a LED driver. There's lots of
circuits, pre-built boards, etc. out there
which provide a fixed current from any
reasonable voltage.

You get one that matches your LED current
(eg. 30mA) then simply connect a series of
LEDs to it.

I would like to power multiple fixtures like these off of 1
transformer. Is it better to build a device to divide the amps and
plug my fixtures into it?

I'm not sure what you mean by this. When you
build your LED circuit you're going to limit the
number of amps that can pass through it. Each
circuit will have a current requirement.

So long as the total requirement for all your circuits
is within the power supply's capabilities then you
can just connect them up, nothing extra needed.

 

[Ian Field]

"Rich Webb" <bbew.ar@mapson.nozirev.ten> wrote in message
news:jl1uf7107g5c414ccltftqo1os0c6ojl79@4ax.com...

On Fri, 30 Dec 2011 22:43:08 -0800 (PST), Chris Carlton
personalgrowthnow@yahoo.com> wrote:

Building a light fixture with 54 LEDs. (me NEWBIE)

4 different LEDs used

18 - 30mA IF 3.8VF
18 - 30mA IF 1.7VF
9 - 30mA IF 2.2VF
9 - 20mA IF 3.6

for Power Efficiency...
What's the best wiring design for this?
Parallel or Series? 12V or 110V

I'm currently planning... 12V - Series
Can I mix LEDs in a Series?
Do I need anything more than 3-5 LEDs and a resistor in each series?
How do I limit amps to a series or to the fixture?
I would like to power multiple fixtures like these off of 1
transformer. Is it better to build a device to divide the amps and
plug my fixtures into it?

If this is to much to ask for free, I'd be more than happy to pay for
your knowledge. I have to solve this one way or the other.

There was a long thread here back in '04 regarding regulating current to
LEDs using a current mirror and similar techniques. Give that a read for
some options:
http://groups.google.com/group/sci.electronics.basics/browse_thread/thread/1a8547721b8950ce/ef2d171838815044?q=led+current+mirror+group:sci.electronics.basics
or just do a search in http://groups.google.com for "led current mirror
group:sci.electronics.basics"

For 120VAC the current can be controlled by a so called "wattless dropper",
this is a series capacitor who's Xc is large compared to RL.

Back in the days of hybrid TVs, Thorn consumer electronics tried this to
replace the wasteful dropper resistors in the 300mA series heater chain.

IIRC the capacitor value was 4.3uF for 300mA on 230V mains at 50Hz, you'll
also need to include some series resistance to absorb turn on surge and
spikes.

You can use 2 series chains of LEDs in inverse parallel or a single chain
after a bridge rectifier.

 

[IanM]

Chris Carlton wrote:

Building a light fixture with 54 LEDs. (me NEWBIE)

4 different LEDs used

18 - 30mA IF 3.8VF
18 - 30mA IF 1.7VF
9 - 30mA IF 2.2VF
9 - 20mA IF 3.6

for Power Efficiency...
What's the best wiring design for this?
Parallel or Series? 12V or 110V

I'm currently planning... 12V - Series
Can I mix LEDs in a Series?
Do I need anything more than 3-5 LEDs and a resistor in each series?
How do I limit amps to a series or to the fixture?
I would like to power multiple fixtures like these off of 1
transformer. Is it better to build a device to divide the amps and
plug my fixtures into it?

If this is to much to ask for free, I'd be more than happy to pay for
your knowledge. I have to solve this one way or the other.

Thank You,
Chris Carlton
I'd be inclined to go for a simple and dumb 12V arrangement. You are

dissipating under 3.7 watts in the LEDs so even if you waste 25% more
power in the series resistors they will remain fairly cool and waste
less than a watt. You avoid a lot of safety issues by NOT having high
voltage running to the fixtures.

Unless the 12V supply is very well smoothed and regulated, you want
considerable 'headroom' between the total LED Vf in each string and the
supply, otherwise the current control will be poor e.g. a 5% increase in
supply voltage causing the LED current to double. The 3.8V LEDs have too
high a Vf to place three in series from a 12V supply for this reason.

The resistor chosen for each series string handles the current limiting
and should be chosen to run the LEDs at no more than 80% of their
maximum rating if you want reasonable reliability.

I would arrange the 30mA LEDs in series strings as follows:
9 sets of 2 x 3.8V + 1 x 1.7v giving 9.3V total Vf
2 sets of 4 x 2.2V giving 8.8V total Vf
1 set of 5 x 1.7V giving 8.8V total Vf
1 set of 4 x 1.7V + 1 x 2.2V giving 9V total Vf

The 20mA LEDs cannot be mixed in the same string as the 30mA ones and 3
x 3.6V doesn't leave much headroom to stabilise the current so I'd run 4
strings of two and an odd one out which will need its resistor
calculated separately.

Each string requires its own series resistor chosen for the correct
current based on the difference between the total Vf and the supply
voltage. All the strings WITH their individual series resistors are
connected in parallel.

You need a 'transformer' (actually a DC output power supply) intended
for LED applications. An AC output one for halogen lighting is
unsuitable. You can use multiple fixtures in parallel up to the rating
of your power supply, (though it would be smart not to exceed 80% of its
rating.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL:

 

[IanM]

IanM wrote:

1 set of 5 x 1.7V giving 8.8V total Vf
CORRECTION

1 set of 5 x 1.7V giving 8.5V total Vf

Sorry about the stupid maths error. It only affects the serise resistor
for this string and doesn't make any difference to the over-all design.

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL:

 

[P E Schoen]

"Ian Field" wrote in message news_HLq.1879$Cu1.1016@newsfe21.ams2...

For 120VAC the current can be controlled by a so called "wattless
dropper", this is a series capacitor who's Xc is large compared to RL.

Back in the days of hybrid TVs, Thorn consumer electronics tried this to
replace the wasteful dropper resistors in the 300mA series heater chain.

IIRC the capacitor value was 4.3uF for 300mA on 230V mains at 50Hz,
you'll also need to include some series resistance to absorb turn on
surge and spikes.

You need to make sure the capacitor is rated for mains connection, and even
with the series resistor the turn-on surge and spikes from transients can
easily exceed the LED's maximum surge rating (usually 3 to 5 x nominal) and
cause deterioration and failure. Much better to use an inductor or ballast.
http://ace-ballast.com/Pages/Home.html

You may even be able to adapt a ballast from a small fluorescent lamp to
work on an LED string.

But probably best is an electronic switching circuit such as
http://www.supertex.com/pdf/datasheets/HV9961.pdf which is available from
Mouser and others for a dollar or so.

You can use 2 series chains of LEDs in inverse parallel or a single chain
after a bridge rectifier.

The two chains in inverse parallel have a huge problem if one of the series
fails open. Then the other string will see the full reverse voltage and one
or more devices will also fail.

You can make a constant current regulator from an LM317 or even a common
7805 regulator:
http://diyaudioprojects.com/Technical/Voltage-Regulator/

There are many drivers available pre-made for 120 VAC line use, and it may
be better (and safer) to use them. Jameco has some for less than $20, but
designed for 350 mA 1 watt LEDs:
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2006879_-1

Also please see the recent thread on LED lamp innards. There are some pearls
of wisdom and information among the swine of bickering.

Paul

 

[krw@att.bizzzzzzzzzzzz]

On Mon, 2 Jan 2012 14:33:04 -0800 (PST), Chris Carlton
<personalgrowthnow@yahoo.com> wrote:

Thanks to every response. I don't feel nearly as insane as I did a few
short days ago.

I guess to be sensible, I'll start out simple (LEDs with correct/safe
resistors) and then also experiment with LED drivers, droppers and
regulators for possible energy savings over my 1st design. It's always
nice to have "improvements" in those areas to market if I get that
chance.

My fixtures energy draw is pretty low now at less than 3.5w. Seems
great when I compare it to what it is replacing. However I can easily
see running 20-50 of these at once so it will add up.

Oh and I found some more LEDs with 30mA to replace the ones I have
that are 20mA so I would not have to mess with it and leave me cleaner
wiring in my series chains which are long because my LEDs are 3-4"
apart in most cases. Also I trying an experiment where I mixed the
20mA with some LEDs that are 40mA in a series. I averaged the mA based
on the number of each type LED. I did my resistor calculation based on
this average. So far it lights up! we'll see if it blows up!

No, you want to set the current lower than the *minimum* LED rating. They're
in series, so each gets the same current. However, you want to add the voltage
of each LED to calculate the ballast resistor.

It's unlikely that you'll need to drive them to their rated maximum. The eye
won't be able to detect the difference between 20mA and 30mA (or 10, for that
matter), anyway.

Oh I was thinking of using laptop power supplies for this projects
future. They give 19V which makes for longer LED series strings and
they are dirt cheap ($5-10) to buy because of their popularity. What I
don't know is how reliable they are for power output??? Can I trust
them??? If I make the jump to drivers that guarantee my voltage this
may be the way to go! (LED power supplies are like $70.)

They're quite reliable. Go fer it.

 

[Chris Carlton]

Thanks to every response. I don't feel nearly as insane as I did a few
short days ago.

I guess to be sensible, I'll start out simple (LEDs with correct/safe
resistors) and then also experiment with LED drivers, droppers and
regulators for possible energy savings over my 1st design. It's always
nice to have "improvements" in those areas to market if I get that
chance.

My fixtures energy draw is pretty low now at less than 3.5w. Seems
great when I compare it to what it is replacing. However I can easily
see running 20-50 of these at once so it will add up.

Oh and I found some more LEDs with 30mA to replace the ones I have
that are 20mA so I would not have to mess with it and leave me cleaner
wiring in my series chains which are long because my LEDs are 3-4"
apart in most cases. Also I trying an experiment where I mixed the
20mA with some LEDs that are 40mA in a series. I averaged the mA based
on the number of each type LED. I did my resistor calculation based on
this average. So far it lights up! we'll see if it blows up!

Oh I was thinking of using laptop power supplies for this projects
future. They give 19V which makes for longer LED series strings and
they are dirt cheap ($5-10) to buy because of their popularity. What I
don't know is how reliable they are for power output??? Can I trust
them??? If I make the jump to drivers that guarantee my voltage this
may be the way to go! (LED power supplies are like $70.)

Thanks again!

 

[John Fields]

On Mon, 2 Jan 2012 14:33:04 -0800 (PST), Chris Carlton
<personalgrowthnow@yahoo.com> wrote:

Thanks to every response. I don't feel nearly as insane as I did a few
short days ago.

I guess to be sensible, I'll start out simple (LEDs with correct/safe
resistors) and then also experiment with LED drivers, droppers and
regulators for possible energy savings over my 1st design. It's always
nice to have "improvements" in those areas to market if I get that
chance.

---
If what you're looking for is minimum power waste, then you should
implement series strings running at high voltages.

For example, if you ran the 30 mA strings you described earlier, you'd
have 18 LEDs dropping 3.8V each for a total drop of 68.4V, 18 LEDs
dropping 1.7V each for a total of 30.6V and 9 LEDs dropping 2.2V each
for a total of 19.8V.

Putting all of those 30mA LEDs in series would result in a total drop
of 68.4V + 30.6V + 19.8V ~ 119V, which is very close to nominal mains
voltage in the US, suggesting that you could full-wave rectify the
mains and run the LEDs without a current limiting resistor.

You'd need some kind of spike protection in order to protect the
string from transients, but we can address that later, if you're
interested.
---

My fixtures energy draw is pretty low now at less than 3.5w. Seems
great when I compare it to what it is replacing. However I can easily
see running 20-50 of these at once so it will add up.

Oh and I found some more LEDs with 30mA to replace the ones I have
that are 20mA so I would not have to mess with it and leave me cleaner
wiring in my series chains which are long because my LEDs are 3-4"
apart in most cases. Also I trying an experiment where I mixed the
20mA with some LEDs that are 40mA in a series. I averaged the mA based
on the number of each type LED. I did my resistor calculation based on
this average. So far it lights up! we'll see if it blows up!

---
If you run the 20mA LEDs at higher than 20mA, then their life will be
shortened.
---

Oh I was thinking of using laptop power supplies for this projects
future. They give 19V which makes for longer LED series strings and
they are dirt cheap ($5-10) to buy because of their popularity. What I
don't know is how reliable they are for power output??? Can I trust
them??? If I make the jump to drivers that guarantee my voltage this
may be the way to go! (LED power supplies are like $70.)

---
My suggestion is that you tailor your strings so that you can run them
directly off the mains using a full-wave bridge to drive the LEDs and
a small resistor and a Zener TVS to quell the spikes.

Would you like a schematic?


--
JF

 

[Chris Carlton]

On Jan 2, 7:39 pm, John Fields <jfie...@austininstruments.com> wrote:

On Mon, 2 Jan 2012 14:33:04 -0800 (PST), Chris Carlton

personalgrowth...@yahoo.com> wrote:
Thanks to every response. I don't feel nearly as insane as I did a few
short days ago.

I guess to be sensible, I'll start out simple (LEDs with correct/safe
resistors) and then also experiment with LED drivers, droppers and
regulators for possible energy savings over my 1st design. It's always
nice to have "improvements" in those areas to market if I get that
chance.

---
If what you're looking for is minimum power waste, then you should
implement series strings running at high voltages.

For example, if you ran the 30 mA strings you described earlier, you'd
have 18 LEDs dropping 3.8V each for a total drop of 68.4V, 18 LEDs
dropping 1.7V each for a total of 30.6V and 9 LEDs dropping 2.2V each
for a total of 19.8V.

Putting all of those 30mA LEDs in series would result in a total drop
of 68.4V + 30.6V + 19.8V ~ 119V, which is very close to nominal mains
voltage in the US, suggesting that you could full-wave rectify the
mains and run the LEDs without a current limiting resistor.

You'd need some kind of spike protection in order to protect the
string from transients, but we can address that later, if you're
interested.
---

My fixtures energy draw is pretty low now at less than 3.5w. Seems
great when I compare it to what it is replacing. However I can easily
see running 20-50 of these at once so it will add up.

Oh and I found some more LEDs with 30mA to replace the ones I have
that are 20mA so I would not have to mess with it and leave me cleaner
wiring in my series chains which are long because my LEDs are 3-4"
apart in most cases. Also I trying an experiment where I mixed the
20mA with some LEDs that are 40mA in a series. I averaged the mA based
on the number of each type LED. I did my resistor calculation based on
this average. So far it lights up! we'll see if it blows up!

---
If you run the 20mA LEDs at higher than 20mA, then their life will be
shortened.
---

Oh I was thinking of using laptop power supplies for this projects
future. They give 19V which makes for longer LED series strings and
they are dirt cheap ($5-10) to buy because of their popularity. What I
don't know is how reliable they are for power output??? Can I trust
them??? If I make the jump to drivers that guarantee my voltage this
may be the way to go! (LED power supplies are like $70.)

---
My suggestion is that you tailor your strings so that you can run them
directly off the mains using a full-wave bridge to drive the LEDs and
a small resistor and a Zener TVS to quell the spikes.

Would you like a schematic?

--
JF

Hey JF!!!

I may be a noobie but I was so sure that this is where I was heading.
(Resistors just seemed to be against everything I was trying to do. It
even seemed like adding another LED would be better than a resistor,
because that way all the power is being used to make light no matter
what. ???? wasn't sure if this was true.)

I found some more 30mA LEDs so they all match now, but was already
calculating things to run at reg mains. USA 110V because of the new
30mAs I have over my 110V @ 132V and wasn't sure what to do with the
extra 20V because a resistor was a billion ohms or something.

Yes I would LOVE a schematic!

Would you like a piece of my new company? Hell Yeah!! I love folks
who help get things done!

My new specs are...
3.8Fv 3.3Fv 2.2Fv 1.7Fv
30mA 30mA 30mA 30mA
15LEDs 9LEDs 9LEDs 15LEDs

 

[P E Schoen]

"John Fields" wrote in message
news:afg4g79llvk5gbh36odep1j7otn64npfu4@4ax.com...

If what you're looking for is minimum power waste, then you
should implement series strings running at high voltages.

For example, if you ran the 30 mA strings you described earlier, you'd
have 18 LEDs dropping 3.8V each for a total drop of 68.4V, 18 LEDs
dropping 1.7V each for a total of 30.6V and 9 LEDs dropping 2.2V each
for a total of 19.8V.

Putting all of those 30mA LEDs in series would result in a total drop
of 68.4V + 30.6V + 19.8V ~ 119V, which is very close to nominal mains
voltage in the US, suggesting that you could full-wave rectify the
mains and run the LEDs without a current limiting resistor.

But for a newbie, it would be much safer to use a wall-wart or laptop power
supply. They are pretty much fail-safe if overloaded or shorted, and the
voltage won't kill you (unless you try really hard).

You'd need some kind of spike protection in order to protect the
string from transients, but we can address that later, if you're
interested.

The power supply will take care of that problem, too.

If you run the 20mA LEDs at higher than 20mA, then their life will
be shortened.

My suggestion is that you tailor your strings so that you can run
them directly off the mains using a full-wave bridge to drive the
LEDs and a small resistor and a Zener TVS to quell the spikes.

Again, using a power supply is safer. And if there is a fire, the UL rating
on the PSU may be worth an awful lot. Fire inspectors don't take kindly to
homebrew gadgets across the house wiring.

Would you like a schematic?

There is a schematic, for the bulk of what is required, in the Supertex data
sheets, and they also probably have application notes. Their circuits work
from about 12 VDC to 400 VDC, but I think it's best to stay under what is
considered "safe", which is about 25-30V. Or even 50V, which is what POTS
phone lines carry, but that is current limited to 20mA or so, which is
marginally safe.

If you want to make such a device commercially, you should contract a
licensed professional engineer to make sure the design will meet UL and
other standards. Pay somebody a modest amount now so you won't have to pay a
huge lawsuit settlement later.

Don't become a statistic...

Paul

 

[fungus]

On Jan 3, 3:02 am, Chris Carlton <personalgrowth...@yahoo.com> wrote:

I may be a noobie but I was so sure that this is where I was heading.
(Resistors just seemed to be against everything I was trying to do. It
even seemed like adding another LED would be better than a resistor,
because that way all the power is being used to make light no matter
what. ???? wasn't sure if this was true.)

It's not a good idea to do this. The thing
is that the resistance of a LED isn't constant.

The resistance of a LED drops *rapidly* as the
voltage increases past the threshold voltage,
and that's precisely the voltage you're aiming
at when you design your circuit.

In a series of LEDs, the LED with least resistance
will get the most volts. Increasing the volts will
lower the resistance even further... and... do you
see where this is going?

You can probably get away with it if you're only
trying to run them at (eg.) 10mA but if you're
anywhere near their rated current then you're
taking a big risk.

 

[fungus]

On Jan 2, 11:33 pm, Chris Carlton <personalgrowth...@yahoo.com> wrote:

Oh I was thinking of using laptop power supplies for this projects
future. They give 19V which makes for longer LED series strings and
they are dirt cheap ($5-10) to buy because of their popularity. What I
don't know is how reliable they are for power output??? Can I trust
them??? If I make the jump to drivers that guarantee my voltage this
may be the way to go! (LED power supplies are like $70.)

You won't be using anywhere near their rated
maximum current so they should be quite reliable.

 

[fungus]

On Jan 2, 11:41 pm, "k...@att.bizzzzzzzzzzzz"
<k...@att.bizzzzzzzzzzzz> wrote:

It's unlikely that you'll need to drive them to their rated maximum.  The eye
won't be able to detect the difference between 20mA and 30mA (or 10, for that
matter), anyway.

Yep. Aim for a few mA less then the rating
(eg 25 instead of 30), you won't notice the
difference and it should simplify the circuitry
(or at least let you use cheaper/easier to find
components).

 

On Sun, 1 Jan 2012 21:34:40 -0500, "P E Schoen" <paul@pstech-inc.com>
wrote:

"Ian Field" wrote in message news_HLq.1879$Cu1.1016@newsfe21.ams2...

For 120VAC the current can be controlled by a so called "wattless
dropper", this is a series capacitor who's Xc is large compared to RL.

Back in the days of hybrid TVs, Thorn consumer electronics tried this to
replace the wasteful dropper resistors in the 300mA series heater chain.

IIRC the capacitor value was 4.3uF for 300mA on 230V mains at 50Hz,
you'll also need to include some series resistance to absorb turn on
surge and spikes.

You need to make sure the capacitor is rated for mains connection, and even
with the series resistor the turn-on surge and spikes from transients can
easily exceed the LED's maximum surge rating (usually 3 to 5 x nominal) and
cause deterioration and failure. Much better to use an inductor or ballast.
http://ace-ballast.com/Pages/Home.html

I disagree. I've been using capacitive reactance for lighting small
LEDs for years now with no ill effects. Use a full wave bridge, small
series resistor, and zener across the led string to limit the peak
voltage.

I concur that AC rated caps would be the better choice - but I've been
using 450 volt polyester film caps with no problems (on 120VAC).

I think PE Johnson had a circuit posted showing a pretty good
(bullet-proof) circuit for running off 120 VAC and protecting the leds
from transients..

You may even be able to adapt a ballast from a small fluorescent lamp to
work on an LED string.

Don't do it. Fluorescent lamps require a high voltage strike to
initially ionize the gas - you may still need the same protection that
running off the mains directly would require.

But probably best is an electronic switching circuit such as
http://www.supertex.com/pdf/datasheets/HV9961.pdf which is available from
Mouser and others for a dollar or so.

That does look intriguing. 8-450 VDC input.

You can use 2 series chains of LEDs in inverse parallel or a single chain
after a bridge rectifier.

The two chains in inverse parallel have a huge problem if one of the series
fails open. Then the other string will see the full reverse voltage and one
or more devices will also fail.

That's true, but the likelihood is very remote - maybe up there with
shark bite in a Kansas cornfield...

You design the best you can and make compromises. Absolute
bullet-proof starts getting expensive, and usually requires some other
trade-offs like size, complexity, efficiency.

You can make a constant current regulator from an LM317 or even a common
7805 regulator:
http://diyaudioprojects.com/Technical/Voltage-Regulator/

That would be my choice for a few high power, high cost leds.
Downside might be efficiency, and if one were using batteries to power
it....

There are many drivers available pre-made for 120 VAC line use, and it may
be better (and safer) to use them. Jameco has some for less than $20, but
designed for 350 mA 1 watt LEDs:
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2006879_-1

Also please see the recent thread on LED lamp innards. There are some pearls
of wisdom and information among the swine of bickering.

Paul

 

[Ian Field]

<default> wrote in message
news:bb36g71fhgofv4tj5pb03l4rgbtolef1o8@4ax.com...

On Sun, 1 Jan 2012 21:34:40 -0500, "P E Schoen" <paul@pstech-inc.com
wrote:

"Ian Field" wrote in message news_HLq.1879$Cu1.1016@newsfe21.ams2...

For 120VAC the current can be controlled by a so called "wattless
dropper", this is a series capacitor who's Xc is large compared to RL.

Back in the days of hybrid TVs, Thorn consumer electronics tried this to
replace the wasteful dropper resistors in the 300mA series heater chain.

IIRC the capacitor value was 4.3uF for 300mA on 230V mains at 50Hz,
you'll also need to include some series resistance to absorb turn on
surge and spikes.

You need to make sure the capacitor is rated for mains connection, and
even
with the series resistor the turn-on surge and spikes from transients can
easily exceed the LED's maximum surge rating (usually 3 to 5 x nominal)
and
cause deterioration and failure. Much better to use an inductor or
ballast.
http://ace-ballast.com/Pages/Home.html

I disagree. I've been using capacitive reactance for lighting small
LEDs for years now with no ill effects. Use a full wave bridge, small
series resistor, and zener across the led string to limit the peak
voltage.

I concur that AC rated caps would be the better choice - but I've been
using 450 volt polyester film caps with no problems (on 120VAC).

Filter caps salvaged from the mains input circuit of old
TVs/monitors/whatever are rated to take full on mains on a full time basis -
not to mention subtracting the summed Vf of a decent size string of LEDs.

I think PE Johnson had a circuit posted showing a pretty good
(bullet-proof) circuit for running off 120 VAC and protecting the leds
from transients..

You may even be able to adapt a ballast from a small fluorescent lamp to
work on an LED string.

Don't do it. Fluorescent lamps require a high voltage strike to
initially ionize the gas - you may still need the same protection that
running off the mains directly would require.

The "electronic transformer" for low voltage halogen lights is superficially
similar to a CFL circuit - the main difference is having a large toroid
transformer instead of a ferrite cored ballas in series with the tube.

However; introducing current control into this type of half-bridge converter
is not trivial.

 

[Chris Carlton]

On Jan 3, 4:35 am, fungus <to...@artlum.com> wrote:

On Jan 2, 11:41 pm, "k...@att.bizzzzzzzzzzzz"

k...@att.bizzzzzzzzzzzz> wrote:

It's unlikely that you'll need to drive them to their rated maximum.  The eye
won't be able to detect the difference between 20mA and 30mA (or 10, for that
matter), anyway.

Yep. Aim for a few mA less then the rating
(eg 25 instead of 30), you won't notice the
difference and it should simplify the circuitry
(or at least let you use cheaper/easier to find
components).

OK not just this specific post but there seems to be a lot of warning
about overloads. I want to take this seriously specially because I can
quite be sure of what the end user would "plug" these things into.
However I also am looking for maximum efficiency. I set up a
spreadsheet that allows me to combine diff LEDs @ diif quatities and
does the math based on ohms law and all that stuff and tell me what
resistor to use. I know to round up to the next available to be safe.
Are you telling me that I need to change the current/mA settings in my
spreadsheet to lower than the manufacutrer suggestion of typical mA/
current??? I don't want to loose anything if I don't have to.

I also don't want to spend the next 2 years replacing products I've
sold because the gain a history of being over-sensitive to their power
source.

Thanks for the amazing discussion. This is better (down to earth) than
any basic LED circuit design thread I've seen for sure.

Mad Props to all who have chimed in!

 

[Chris Carlton]

just want to throw in that I'm using 5mm old school LEDs because of
their low power and nm selection. I am looking at tape and other LEDs
but the total flux seems to suck so bad. I'm sure I just to learn more
about LED shopping or get the cash to make a custom order.

 

[Chris Carlton]

and now that's
9 - 30mA IF 3.3

instead of the orignial
9 - 20mA IF 3.6