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Re: Why'd my LEDs pop?

Have a look in lm317 datasheet at constant current source
Tom

Re: Why'd my LEDs pop?

I was considering that but I'm running 12 LEDs in parallel so if one dies
the others will get more current.

Michael

Re: Why'd my LEDs pop?

Unfortunately I'm familiar with Phil's posts. Despite him this group is
still a valuable source of information.

Michael

Re: Why'd my LEDs pop?

Agreed Michael.  Pity he can't control his Tourette's. :-(

Cheers,
Alan

Re: Why'd my LEDs pop?

On Tue, 9 May 2006 10:47:56 +1000, "Michael C"

This will essentially provide the same result. To provide a seperate
constant current source to each LED would be silly, when a resistor in
series with a regulated source voltage will do just fine in your
application.

Re: Why'd my LEDs pop?

voltage

LEDs are quite different to incadescent lightbulbs in that they are
semiconductors, and the thing you need to understand is that they have a
(more or less) constant forward voltage. This isn't a bad summary of how
they work:

http://electronics.howstuffworks.com/led.htm

Without a resistor to limit the current in the circuit, putting even a
fraction higher than the forward voltage through a LED will result in the
current going through the roof and instantly blowing the LED.

All you need to do is work out what resistor you need - you can do this
empirically using an ammeter in circuit as you try different resistors, or
if you know the forward voltage and the supply voltage, you can work out
what resistor will give you the required current using Ohm's law, or an
online calculator like this one:

http://led.linear1.org/1led.wiz

Oh, and try to ignore the malcontents such as Mr Goldsmith and friend.
Unlike them, most of us are here to share and learn and are happy to do so.

Re: Why'd my LEDs pop?

For a "fraction" greanter than 1 I have measured values of "instantly"
exceeding 30 minutes and "roofs" below 150mA

I hooked a cheap, crappy red LED across my pc's 5V bus with a miliammeter in
series, current readings started at 145mA and after half an hour have dropped
to around 94mA. the LED is hot to touch, but no scorcher.

I have heard reports of LEDs operating for days with a 5v supply.

Bye.
Jasen

Re: Why'd my LEDs pop?

after just over an hour it died open circuit. (with a 20A PSU behind it I
wasn't expecting it to go the other way)

Bye.
Jasen

Re: Why'd my LEDs pop?

Brian has always been an idiot. Add him to your kill filter, its the
best thing you can do.

YOu are correct. This is basic ohms law.

A houshold lightbulb is very different. It is purely resistive
(theoretically) piece if wire where as an LED is semiconducter.

OK, the problem with putting a whole heap of LEDs in series is that
each one may be slightly different. A small imperfection cause go one
to go short circuit then the rest are going to get more current.

Add to this, if your power source varies, then so will the current
flow through your string of LED's

Before we can help you with the correct sollution, you need to tell us
all details. What is the use? What is the expected power source and
how much can it vary (tolerence). What brand LED's are you using and
what is there stated foward voltage and current.

Re: Why'd my LEDs pop?

the voltage at which they light isn't certain, and varies...

--

Bye.
Jasen

Re: Why'd my LEDs pop?

"Michael C"

** Your DC voltmeter is stuffed.

Or are you using bloody AC  ??????

.......  Phil

Re: Why'd my LEDs pop?

putting
but I
they

Test it yourself, maybe you'll learn something new.  Like I said before,
I can apply 2.5V without any current regulation to the blue LEDs that I
have (Vf=3.3).  They light up (dimly but still quite visible) and
current is apparently limited by the LED itself.

Re: Why'd my LEDs pop?

"Anthony Fremont"

**  FUCK the HELL OFF   you  STINKING  ASSHOLE .

......  Phil

Re: Why'd my LEDs pop?

I guess you tried it for yourself.  Enlightening wasn't it?

Re: Why'd my LEDs pop?

**  FUCK the  HELL OFF   you  STINKING  YANK  ASSHOLE .

......  Phil

Re: Why'd my LEDs pop?

Anthony,
Consider you've got one over Philthy Allison.
As soon as he starts swearing, you know he's lost the argument.

Cheers,
Alan

Re: Why'd my LEDs pop?

"Alan Rutlidge" wrote:

Oh, I know.  :-)  I hope he really did try it for himself.  I noticed it
quite by accident when I connected a blue LED to the output of an op-amp
to clamp the peak output to the Vf of the diode, letting the op-amp
limit the max current thru the LED.  The op-amp was biased at 2.5V and I
was sort of surprised to see the LED start glowing as soon as I plugged
it to the breadboard.  Not blindingly bright (indicating the obvious
self limiting of the current), but clearly on.  Just can't understand
why Phil has to have a conniption fit over it.

Re: Why'd my LEDs pop?

Unfortunately the occasional flashes of brilliance PA exhibits are grossly
overshadowed by incessant ramblings of incoherent spasms of abuse and foul
language.  Obvously there's a wiring mix up in his brain or needs
re-programming?

Cheers,
Alan

Re: Why'd my LEDs pop?

Maybe a "Hard reset" would work? ;-)

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
We've slightly trimmed the long signature. Click to see the full one.
Re: Why'd my LEDs pop?

Generally he refuses to answer his unit calling if the voice is
unfamiliar ... however its not that hard to gain entry if you have time .