Dead LEDs

[mrresp1]

" everyone touted CFL's for home lighting so I've tried a
> few... all of which have failed in slightly longer lifespans than
> incandescent bulbs "

we switched over to CFLs all over the house a couple years ago.. we actually
got a check back from the power company after about 3 months because they
had estimated our usage based on the year before.  nice.

however, after about 6~7 months or so, 95% of them died out... strangely,
the ones located outside that are subjected to northeast winters have
survived to this day.  the indoors surviving members go into a 'flicker
fits' all the time until they warm up after about 20-30mins.  .there is no
doubt in my mind that this is a waaaayy shorter life span than what i had
with incandescents for which i'm absolutely positive i still have original
bulbs installed & working fine from 17 years ago....

these CFLs (all different brands) seem to have had self-destructive thermal
problems..  certainly there's no doubt that the manufacturers knew all about
it and gambled on the usual consumer laziness not to claim their warranty
coverage ...

after all told, the manufacturers made their quick buck and we ended up
wasting money, filling up the landfills with electronic garbage, and thus
increasing our carbon footprint...

way to go world....

resp~
.
 

--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Russell McMahon]

A number of people have asked how LED lifetimes can be
inferred from limited duration test data.
This is a representative query:

Joe Bento said:
> I am most curious, and perhaps someone can answer.  You
> mention that the
> white LED might fail within a 2x magnitude of 100k hours.
> 100k hours is
> about 11.4 years.  How is MTBF estimated or calculated?  I
> don't think
> they light an LED at its recommended current and wait -
> white LEDs
> haven't been around that many years.

An excellent paper on the subject is here

        http://www.lumileds.com/pdfs/WP12.pdf

Note section 7. where they discuss the use of the Weibull
distribution to infer long period results from shorter
period data. Alas, there are 3 factors which are "derived
from experimental data" so this is most suited to large
suppliers who have the resources to do the extensive testing
needed to establish the parameters for their product ranges
AND to understand how these are affected by various other
factors.

However, from their work lumileds have provided some
excellent rule of thumb guidelines which can be applied with
due care to other manufacturers' products. See the above
paper for information - some of it quite sobering.

Also, individual manufacturers do provide long term test
results, with data occasionally updated as tests proceed. I
have some Nichia data (may not have been meant for on
copying - I could ask) which shows real results out to
around 10,000 hours under various conditions of temperature
and humidity.

In my case I have found that operating continually for
several weeks is usually a good indicator of whether a LED
is either very bad or MAY be OK. Bad LEDs have very
measurable degradation after say 300 to 500 hours. I have
some samples which have now run for almost 6 months and a
light meter is not needed to see the result. Degradations of
up to 50& are often not detectable with certainty in
isolation to the untrained eye. "This light looks a bit
dull" may or may not be the conclusion. Even in side by side
comparisons 10% to 20% is hard to see (for me anyway).

I run batches of LEDs in series at constant current AND have
a reference LED that is in series but is usually
short-circuited. When measuring I enable the reference LED.
This gives me a zero (almost) operating time comparison and
provides a sanity check for fluctuations in ambient
temperature, current. light meter health etc.

In my tests the best Chinese LEDs operated at or below rated
current and in modest ambient conditions (say 20C mean or
less) would be extremely lucky to reach 1,000 hours at above
50% initial output!!! Hence my 2 orders of magnitude
comments. Not very hard to measure in short periods and Mr
Weibull need not be invoked. (For precision testing control
of ambient temperatures is necessary. In my case the results
are clear enough that no such control is needed. Also, heat
sinking to a level similar to that to be experienced in
practice is desirable as temperature rise can play a major
part in longevity).

Note when looking at test data that in many cases LED output
RISES after a while and then begins to decline. This is said
to be due to "annealing".Whatever the cause it is often a
good indicator of a LEDs long term performance. Those that
peak super early, or not at all, can be expected to have a
poor lifetime.



            Russell

Luxeon reliability tool

        http://www.luxeon.com/technology/reliabilitytool.cfm

Summary versions of above paper

        http://www.lumileds.com/pdfs/AB07.PDF

        http://www.luxeon.com/technology/lumenmaintenance.cfm

K2 Star
70% at 50,000 hours

        http://www.luxeonstar.com/luxeon-k2-star-red-75-lumens-700ma-p-131.php

Discussion of practical applications

        http://www.electronicsworld.co.uk/asset/361/leds.pdf






 

--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[peter green-2]

> these CFLs (all different brands) seem to have had self-destructive thermal
> problems
What type of fittings do you tend to use

In my experiance the worst situation for a CFL is a small enclosed
fitting with the lampholder at the top. The heat rises to the top of the
fitting where it is trapped cooking the electronics.
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[mrresp1]

"worst situation for a CFL is a small enclosed
fitting with the lampholder at the top"

yup, "hi-hats"... as we call them...

but let's face it, they're probably one of the most popular fixtures out there and after all, these were your standard CFL R20, R30, & R40 floods ... so where exactly did they 'think' these bulbs were going to be used???... obviously not in a table top lamp....

~


----- Original Message -----
From: "peter green" <plugwash@...>
To: "Microcontroller discussion list - Public." <piclist@...>
Sent: Wednesday, July 16, 2008 9:13 PM
Subject: Re: [EE]:: Dead LEDs

>
>> these CFLs (all different brands) seem to have had self-destructive thermal
>> problems
> What type of fittings do you tend to use
>
> In my experiance the worst situation for a CFL is a small enclosed
> fitting with the lampholder at the top. The heat rises to the top of the
> fitting where it is trapped cooking the electronics.
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Dr Skip]

Apptech wrote:
>
>
> Where's the warranty document ... .

Mail to some site, my expense, possibly pay for return postage, possibly accept
a reconditioned unit in return (not my personal one), wait 10-12 weeks, their
discretion as to repair or not, blah blah blah...

And unless they changed their process, design, or sourcing, it will happen again.

>
> Quite apart from actual LED longevity, poor driving can lead
> to early failures. Driving multiple LEDs while maintaining
> efficiency is a modest challenge that many do not rise to. I
> have seen many consumer products with little or no attempts
> to provide anything like constant current drive. Most 3-cell
> battery consumer torches place LEDs in parallel and across
> the battery. Some use a single shared series resistor.

I've actually had better luck with the 3 cell units. The ones I talked about
have a surface mount controller chip and handful of components, has flash and
multiple brightnesses, etc. Certainly more development than throwing a resistor
at it...


--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Alan B. Pearce]

> Interestingly, and not directly related, some name brand
> LEDs give atrocious spectral results at very low currents
> while others are about as good across a wide range of
> currents.

So, your testing shows you get what you pay for - pay more get better
performance ??? ;))

--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Russell McMahon]

>> Interestingly, and not directly related, some name brand
>> LEDs give atrocious spectral results at very low currents
>> while others are about as good across a wide range of
>> currents.

> So, your testing shows you get what you pay for - pay more
> get better performance ??? ;))

No.
As noted, "name brand LEDs were used in both cases. Cost
in volume is uncertain but both would be comparable.

And it was hardly testing - more just observation from
simple experiment.
And most people do not want to run LEDs in the manner
concerned. What was notable was that with one supplier you
could do so and with the other you couldn't, if you wanted
white light.

Using parts from two name brand / 'top shelf' suppliers,
Nichia & Avago, the results were very different. Note that
the result would not be a problem in any "normal"
application. Note also that vendors expressly note that when
dimming LEDs they should be PWM'd so that peak PWM on
current  ~= rated current and NOT DC fed at lower levels
expressly due to the colour shift. Caveat Emptor.

When the 20 mA spec LEDs were operated in the 1 mA to 5 mA
range the Nichia LEDs still produced essentially white
light, whereas the Avago LEDs from the same batch produced
EITHER extremely yellow or extremely blue light. When a row
of the Avago LEDs were compared it appeared that they were
of two colour types. The result appeared to be a mix of two
different colours.

Few people want to run 20 mA nominal LEDs at about 1 mA. It
happens that I have a client who does. Total current is up
to about 5 mA and this was shared amongst from 1 to about 5
LEDs during development testing. Notionally the amount of
light is similar with 1 to 5 LEDs - you just get less light
per LED as you add more. But you also get colour shift.

The results are due to the LED proper being blue and the
phosphor converting a proportion of it to white so the two
are added to produce "white". Clearly different things
happen with Nichia and Avago at low current levels.

I have no business or other links to Nichia.
I have become increasingly impressed with Nichia LEDs and
their technical approach to doing business. I don't know too
much about their business side of business or even pricing.
>From what I've seen so far I'd rate them as generally too
dear for products that can get away with not using the very
best :-). There may be others, but so far Nichia are the
only company that I have seen put a chromaticity shift with
colour graph in a standard data sheet. Also from what I've
seen so far, their chromaticity binning range seems to be
tighter for comparable products than at least one other
market leader and maker of very fine products. (Name not
mentioned and not Avago - they are good in other respects so
I don't want to be seen to be criticising them here for
something which they make clear and which may well be
acceptable in some applications. .


        Russell







--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[arocholl]

But still you didn't explain how do you measure LED life time to understand
is not 100k hours but 2 orders of magnitude less.

Some mentioned CFL lasted 2-3 years. Well, that means probably lasted before
failure (or refused to start) but that doesn't mean they were providing the
same lumens for 2-3 years. A CFL radiation curve is typically 60% less after
12 months in a few datasheets. For LEDs there are interesting curves as
well, most will have only a fraction of initial radiation after 2-3k hours.
They still work, but that doesn't mean they keep the properties at the level
one specific project may need. And I saw these curves for well documented
products such as Luxeon, but cheap chinnese brands not even provide that. So
how do you know where are you on the curve and what is the expected lifetime
with your own tests?

2008/7/17 Apptech <apptech@...>:

> >> Interestingly, and not directly related, some name brand
> >> LEDs give atrocious spectral results at very low currents
> >> while others are about as good across a wide range of
> >> currents.
>
> > So, your testing shows you get what you pay for - pay more
> > get better performance ??? ;))
>
> No.
> As noted, "name brand LEDs were used in both cases. Cost
> in volume is uncertain but both would be comparable.
>
> And it was hardly testing - more just observation from
> simple experiment.
> And most people do not want to run LEDs in the manner
> concerned. What was notable was that with one supplier you
> could do so and with the other you couldn't, if you wanted
> white light.
>
> Using parts from two name brand / 'top shelf' suppliers,
> Nichia & Avago, the results were very different. Note that
> the result would not be a problem in any "normal"
> application. Note also that vendors expressly note that when
> dimming LEDs they should be PWM'd so that peak PWM on
> current  ~= rated current and NOT DC fed at lower levels
> expressly due to the colour shift. Caveat Emptor.
>
> When the 20 mA spec LEDs were operated in the 1 mA to 5 mA
> range the Nichia LEDs still produced essentially white
> light, whereas the Avago LEDs from the same batch produced
> EITHER extremely yellow or extremely blue light. When a row
> of the Avago LEDs were compared it appeared that they were
> of two colour types. The result appeared to be a mix of two
> different colours.
>
> Few people want to run 20 mA nominal LEDs at about 1 mA. It
> happens that I have a client who does. Total current is up
> to about 5 mA and this was shared amongst from 1 to about 5
> LEDs during development testing. Notionally the amount of
> light is similar with 1 to 5 LEDs - you just get less light
> per LED as you add more. But you also get colour shift.
>
> The results are due to the LED proper being blue and the
> phosphor converting a proportion of it to white so the two
> are added to produce "white". Clearly different things
> happen with Nichia and Avago at low current levels.
>
> I have no business or other links to Nichia.
> I have become increasingly impressed with Nichia LEDs and
> their technical approach to doing business. I don't know too
> much about their business side of business or even pricing.
> >From what I've seen so far I'd rate them as generally too
> dear for products that can get away with not using the very
> best :-). There may be others, but so far Nichia are the
> only company that I have seen put a chromaticity shift with
> colour graph in a standard data sheet. Also from what I've
> seen so far, their chromaticity binning range seems to be
> tighter for comparable products than at least one other
> market leader and maker of very fine products. (Name not
> mentioned and not Avago - they are good in other respects so
> I don't want to be seen to be criticising them here for
> something which they make clear and which may well be
> acceptable in some applications. .
>
>
>        Russell
>
>
>
>
>
>
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

--
Ariel Rocholl
Madrid, Spain
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[CDB-3]

Sometime ago I wandered across the schematic for a standard LED
traffic light unit, it was nothing more than 1 series resistor and a
string of LED's upto 240vac, If I recall correctly (I probably still
have the diagram somewhere) the LEDs where used as rectifiers, by
having so many on one string, pointing one way, and so many on the
other the other.

I'll see if I can find the circuit.

Colin

:: I saw this happening soon after the LED lamps were introduced in SE
:: Worchester County MA back about five years ago. Within a year a
:: number of
:: the lamps had been replaced and since then many have been replaced
:: with the
:: old incandescent type
--
cdb, colin@... on 17/07/2008
 
Web presence: www.btech-online.co.uk  
 
Hosted by:  www.1and1.co.uk/?k_id=7988359
 

 
 
 
 

--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Russell McMahon]

> But still you didn't explain how do you measure LED life
> time to understand
> is not 100k hours but 2 orders of magnitude less.

Yes, I did. You may have missed it.
See my post about 12 hours ago (the time is NZT - about GMT
+ 12)
which begins:

    From: "Apptech" <apptech@...>
    Sent: Thursday, July 17, 2008 12:52 PM
    Subject: Re: [EE]:: Dead LEDs

    A number of people have asked how LED lifetimes can be
    inferred from limited duration test data.
    This is a representative query:

Real people use the Weibull distribution to infer long term
characteristics from shorter term data. See muy post and
Philips paper.

I have not needed this degree of complexity yet. ALL chinese
LEDs tested so far reveal themselves well enough in a month
of continuous operation.

> Some mentioned CFL lasted 2-3 years. Well, that means
> probably lasted before
> failure (or refused to start) but that doesn't mean they
> were providing the
> same lumens for 2-3 years. A CFL radiation curve is
> typically 60% less after
> 12 months in a few datasheets.

Depends on manufacturer and whether you mean continuous
running.
People like Philips define their terms well.
An 8000 hour life will probably mean something like 50% of
initial at 8000 hours.

As the philips Tornado CFLs are up to 2X as efficient as
some competitors they are as good as the worst at the end of
their life.

While I have had a number of CFL early fauilures (and have
destryed many more due to mishandling etc) I generally feel
that they are up to the claims made for them when ones from
repiutable manufacturers are used.  For general lighting use
at teh 20 Watt level I buy ONLY the best - Philips Tornado.
I buy them when they are on special at about $NZ3.33
typically (3 for $10) or about $US2.70. For 40W, 60W and 100
Watt ones (:-) :-) :-) :-) :-) :-) ) I buy the brightest on
the demo display stand. I do like the 100 Watt ones !!!!.

> For LEDs there are interesting curves as
> well, most will have only a fraction of initial radiation
> after 2-3k hours.

See the detailed lumen maintenance document from Philips
referenced in the post I mention above.

Reputable manufacturers provide guaranteed degradation data.
Typically 70% of initial at 10,000 or 50,000 or 100,000
hours depending on various parameters.

> They still work, but that doesn't mean they keep the
> properties at the level
> one specific project may need. And I saw these curves for
> well documented
> products such as Luxeon,

as above

> but cheap chinnese brands not even provide that. So

Indeed. Which is what started this thread.

> how do you know where are you on the curve and what is the
> expected lifetime
> with your own tests?

As per my prior posts.
Chinese LEDs are so far bad enough that weeks of testing is
enough to see the trend.

Operate N at constant current.
Short one with a switch.
Unshort this refence only for measuringh. Allow a minute or
so to thermally stabilise before measuring.

Use light meter of choice.

I take a white plastic kitchen funnel and cut it down so
large end fits light meter dome and small end is trimmed to
fit over 10mm lEDs and bed square on PCB. tape all outside
of cone withe black tape. This makes a crude but OK
integrating radiometer. Most LED light shines onto meter
dome (which is itself an integrator) and the rest gets
reflected off cone. As the radiation patterns I am testing
are much the same for all LEDs I'm testing the errors
introduced are (IMHO) lowish.

Measure all LEDs. Turn off reference LED.
Record levels.
Repeat occasionally.

168 hours / week.
730 hours in a month.

If it drops noticeably in a week bin it.
If it drops noticeably in a month ask why.
I have some that have been running about 6 months so far.
Not a pretty sight.




        Russell

--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Olin Lathrop]

Apptech wrote:

>> A fair number of the LED traffic lights around here have
>> developed
>> blotches of dead LEDs.  Especially the white LEDs used for
>> "Walk"
>> signals, but also even RED lights.  It's sorta sad; I bet
>> someone in
>> the local DoT is unhappy that the believed the "saves
>> replacement
>> costs" spiel..
>
> Where's the warranty document ... .
>
> Quite apart from actual LED longevity, poor driving can lead
> to early failures.

That would be rather extreme poor driving.  He wasn't saying cars were
crashing into the light poles, just that the LEDs were failing in the light
fixtures.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
[phone].  Gold level PIC consultants since 2000.
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Russell McMahon]

> Sometime ago I wandered across the schematic for a
> standard LED
> traffic light unit, it was nothing more than 1 series
> resistor and a
> string of LED's upto 240vac, If I recall correctly (I
> probably still
> have the diagram somewhere) the LEDs where used as
> rectifiers, by
> having so many on one string, pointing one way, and so
> many on the
> other the other.
>
> I'll see if I can find the circuit.

Would be interesting to see.
That's an entirely valid way to do things BUT it can be done
well or poorly.

Using AC means they are often below peak value and often off
during a cycle.
This tempts people to run them over spec at peak.
Colour shift with current not a major issue probably.
Current variation with mains voltage change not trivial.

Rectifying the mains and using DC and a basic current source
would give far better control.

Say VLED on is 2V1.
Say allow 10% for series resistor.
Say VLED_very_dim = 1V7 (make own assumptions)

For 230 VAC, Vpeak = 325 Volts.
Vleds = 325 * 90% = 293 V
LEDS = 293/2v1 = 139 = 140

Vdim = 325*1v7/2v1 =~~ 263 V
Phase angle past peak V = acos(263/325) = 36 degrees

ie LEDs go from full to very dim in +/- 36 degree area
either side of peak V or 36/90 = 40% of cycle.

This drives LEDs at far far less than max and temptation is
to use high I peak, which MAY be OK.

Running from DC rectified mains gives constant current,
constant brightness. Rectifier cost is low.
Capacitor cost may be less so. At 20 mA you need 2000/V uF
where V is ripple.
At 10V ripple need 200 uF At 400 V. Electrolytic OK. Not
tiny.

Say LEDs are $0.05 x 140 = $7 of LEDs.
Cap will be less than that but a significant part of cos.
Rough current source can cost little.
Rectifier is v cheap (1N 4007).


    Russell









--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Russell McMahon]

>> Quite apart from actual LED longevity, poor driving can
>> lead
>> to early failures.

> That would be rather extreme poor driving.  He wasn't
> saying cars were
> crashing into the light poles, just that the LEDs were
> failing in the light
> fixtures.

What have you done with Olin?


                    Russell


                                                :-)

--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Ariel Rocholl]

2008/7/17 Apptech <apptech@...>:

> > But still you didn't explain how do you measure LED life
> > time to understand
> > is not 100k hours but 2 orders of magnitude less.
>
> Yes, I did. You may have missed it.


I definitely missed that. Probably my brain capacity is lower in the curve
than I expected...


>
> Real people use the Weibull distribution to infer long term
> characteristics from shorter term data. See muy post and
> Philips paper.
>

So this means you basically reuse Philips experience to measure other
brands. But I am not sure Philips provide *all* the required data to make
their test reproducible. It would be better IMHO to have ISO / ANSI / DIN
papers to measure parameters in a well stablished, fully reproducible,
neutral way. Many times manufacturers measures parameters in the most
convenient way *for them*.



>
> I have not needed this degree of complexity yet. ALL chinese
> LEDs tested so far reveal themselves well enough in a month
> of continuous operation.
>

 So I am not being critic, I am just trying to learn how feasible is to
extrapolate what Philips documents, to measure other brands' lifetime. I
think is easier to predict degradation to a certain amount of radiation but
lifetime may be different. I think is really safe for you to say "lifetime
is shorter than brand X" but giving absolute numbers looks challenging to me
(like 2 orders of magnitude less, etc).

>
> > Some mentioned CFL lasted 2-3 years. Well, that means
> > probably lasted before
> > failure (or refused to start) but that doesn't mean they
> > were providing the
> > same lumens for 2-3 years. A CFL radiation curve is
> > typically 60% less after
> > 12 months in a few datasheets.
>
> Depends on manufacturer and whether you mean continuous
> running.
> People like Philips define their terms well.
> An 8000 hour life will probably mean something like 50% of
> initial at 8000 hours.

Right. And depending on the application. For instance, I am ok with a CFL
being at 50% in the second year if it is for a kitchen.
If the application is a UVB CFL type for a reptile terrarium, you will kill
the animal by lack of D vitamin if it doesn't receive at least 75% UVB
radiation of specified for the species. So for that application, end of life
means 75% radiation. That is typically 6-8 months for best brands (8 hs/day,
25C). Not too much.



>
> typically (3 for $10) or about $US2.70. For 40W, 60W and 100
> Watt ones (:-) :-) :-) :-) :-) :-) ) I buy the brightest on
> the demo display stand. I do like the 100 Watt ones !!!!.
>


100W CFL? !!!
I've still to see that! With sun glasses anyway!

>
> I take a white plastic kitchen funnel and cut it down so
> large end fits light meter dome and small end is trimmed to
> fit over 10mm lEDs and bed square on PCB. tape all outside
> of cone withe black tape. This makes a crude but OK
> integrating radiometer. Most LED light shines onto meter
> dome (which is itself an integrator) and the rest gets
> reflected off cone. As the radiation patterns I am testing
> are much the same for all LEDs I'm testing the errors
> introduced are (IMHO) lowish.
>
> Measure all LEDs. Turn off reference LED.
> Record levels.
> Repeat occasionally.
>
> 168 hours / week.
> 730 hours in a month.
>
> If it drops noticeably in a week bin it.
> If it drops noticeably in a month ask why.
> I have some that have been running about 6 months so far.
> Not a pretty sight.

Sounds reasonably reproducible anywhere. Did you validated Philips
parameters using this method in one of their Lumileds?

Very informative. Thx

--
Ariel Rocholl
Madrid, Spain
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[CDB-3]

:::: Sometime ago I wandered across the schematic for a
:::: standard LED
:::: traffic light unit, it was nothing more than 1 series
:::: resistor and a
:::: string of LED's upto 240vac, If I recall correctly (I
:::: probably still
:::: have the diagram somewhere) the LEDs where used as
:::: rectifiers, by
:::: having so many on one string, pointing one way, and so
:::: many on the
:::: other the other.
::::
:::: I'll see if I can find the circuit.
::::
:: Would be interesting to see.

Wouldn't you know it, I can't find it on my CD backups, so I'll check
my paper folders. Even searched Gurgle, all I found was a number of
people have patented the 'a diode backwards across the LED for AC'
amazing what can be patented.

Colin
--
cdb, colin@... on 18/07/2008
 
Web presence: www.btech-online.co.uk  
 
Hosted by:  www.1and1.co.uk/?k_id=7988359
 

 
 
 

--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist