led's

[Mr. Man-wai Chang]

1. Would a 3V LED short itself when connected to a 3V DC input?

2. If answer to (1) was "no", then why do I need a current-limiting
resistor connecting 2 3V LEDs in series to a 5V DC input？

3. If answer to (1) was "yes", then what current-limiting resistor
should I use in (1)?

--
@~@ Remain silent. Nothing from soldiers and magicians is real!
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (Fedora 19 i686) Linux 3.10.3-300.fc19.i686
^ ^ 20:57:02 up 21:22 0 users load average: 0.00 0.01 0.05
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa

 

[John Fields]

On Tue, 30 Jul 2013 21:11:06 +0800, "Mr. Man-wai Chang"
<toylet.toylet@gmail.com> wrote:

1. Would a 3V LED short itself when connected to a 3V DC input?

---
If, over a specified temperature range and with exactly 3V across it,
the current through the LED was lower than or equal to the specified
maximum, the no resistor would be needed.
---

2. If answer to (1) was "no", then why do I need a current-limiting
resistor connecting 2 3V LEDs in series to a 5V DC input?

---
If the sum of the voltage drops was less than 5V, then 5V might
overcurrent the pair.
---

3. If answer to (1) was "yes", then what current-limiting resistor
should I use in (1)?

---
Vsupply - Vled
Rs = ----------------
Iled

--
JF

 

[John Larkin]

On Tue, 30 Jul 2013 21:11:06 +0800, "Mr. Man-wai Chang"
<toylet.toylet@gmail.com> wrote:

1. Would a 3V LED short itself when connected to a 3V DC input?

There is no "3V LED"

2. If answer to (1) was "no", then why do I need a current-limiting
resistor connecting 2 3V LEDs in series to a 5V DC input?

You don't. Practically no current will flow, no visible light will be generated,
ant it will last forever!

3. If answer to (1) was "yes", then what current-limiting resistor
should I use in (1)?

See above.


ps - it would help if you learned some basic electronics.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[John Larkin]

On Tue, 30 Jul 2013 19:12:32 +0800, "Mr. Man-wai Chang"
<toylet.toylet@gmail.com> wrote:

On 30/07/2013 5:25 AM, John Larkin wrote:
They were a gift from James Arthur, and I don't know the part number.
Just browse the Avago web site, or Digikey, for high-output green
LEDs.

I was surprsded by the sub-nA light output. At roughly 100 mV/decade
current, I'd have guessed that the voltage drop would be so low that
it wouldn't have enough energy to make photons.

It would be fun to use a PMT and some signal averaging to see how
little current would still make some light.

If it's a military grade LED, then I was NOT supposed to be able to find
anything about it!

You don't make any sense.

Do you have a real name?


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[John Larkin]

On Tue, 30 Jul 2013 07:15:57 -0700 (PDT), George Herold <gherold@teachspin.com>
wrote:

On Monday, July 29, 2013 5:25:15 PM UTC-4, John Larkin wrote:
On Tue, 30 Jul 2013 01:28:23 +0800, "Mr. Man-wai Chang"

toylet.toylet@gmail.com> wrote:



On 29/07/2013 6:41 AM, John Larkin wrote:

Just 1 mA? You talking about surface-mount LEDs?



I have some Avago high-efficiency green LEDs, in T1-3/4 packages. Greens are not

just efficient, they coincide with the eye's sensitivity curve.

These are bright a 1 mA and visible in room light at 1 uA. I tried to determine

the minimum current that would produce discernable light up close, in total

darkness, dark-adapted. It was about 800 picoamps.



Do you have the picture and datasheet of that 1mA LED? Could I read them?



They were a gift from James Arthur, and I don't know the part number.

Just browse the Avago web site, or Digikey, for high-output green

LEDs.



I was surprsded by the sub-nA light output. At roughly 100 mV/decade

current, I'd have guessed that the voltage drop would be so low that

it wouldn't have enough energy to make photons.

Ahh, but it's those electrons on the far end of the exponential 'Boltzmann tail' that have enough extra thermal energy to make it into the depletion region. (I'll have to try I-V curves for LED's at low temperatures someday, dunking into LN2 should be pretty easy.)

Well, now you're talking about physics and science and stuff like that.

Seems to me that you need X volts to make a photon of X electron-volts energy.
Can thermal energy bootstrap an electron to make a photon that's more EV than
the voltage across the junction?

Modern LEDs are remarkable gadgets. It would be fun to explore the corner cases,
"someday" as you say.

We're currently experimenting with cheap (like, $12) semiconductor lasers to
find some that accidentally make clean picosecond light pulses when whacked by
one of our laser drivers. The manufacturers certainly don't know if they might.
Most laser data sheets are pitiful.

Just spent over a grand on Thorlabs hardware to hold a laser in place and get
some of its light into a fiber.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[George Herold]

On Monday, July 29, 2013 5:25:15 PM UTC-4, John Larkin wrote:

On Tue, 30 Jul 2013 01:28:23 +0800, "Mr. Man-wai Chang"

toylet.toylet@gmail.com> wrote:



On 29/07/2013 6:41 AM, John Larkin wrote:

Just 1 mA? You talking about surface-mount LEDs?



I have some Avago high-efficiency green LEDs, in T1-3/4 packages. Greens are not

just efficient, they coincide with the eye's sensitivity curve.

These are bright a 1 mA and visible in room light at 1 uA. I tried to determine

the minimum current that would produce discernable light up close, in total

darkness, dark-adapted. It was about 800 picoamps.



Do you have the picture and datasheet of that 1mA LED? Could I read them?



They were a gift from James Arthur, and I don't know the part number.

Just browse the Avago web site, or Digikey, for high-output green

LEDs.



I was surprsded by the sub-nA light output. At roughly 100 mV/decade

current, I'd have guessed that the voltage drop would be so low that

it wouldn't have enough energy to make photons.

Ahh, but it's those electrons on the far end of the exponential 'Boltzmann tail' that have enough extra thermal energy to make it into the depletion region. (I'll have to try I-V curves for LED's at low temperatures someday, dunking into LN2 should be pretty easy.)

George H.

It would be fun to use a PMT and some signal averaging to see how

little current would still make some light.





--



John Larkin Highland Technology, Inc



jlarkin at highlandtechnology dot com

http://www.highlandtechnology.com



Precision electronic instrumentation

Picosecond-resolution Digital Delay and Pulse generators

Custom laser drivers and controllers

Photonics and fiberoptic TTL data links

VME thermocouple, LVDT, synchro acquisition and simulation

 

[John Fields]

On Tue, 30 Jul 2013 08:49:21 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 30 Jul 2013 21:11:06 +0800, "Mr. Man-wai Chang"
toylet.toylet@gmail.com> wrote:


1. Would a 3V LED short itself when connected to a 3V DC input?

There is no "3V LED"

---
I don't believe that's true, since some LEDs will drop 3V at their
rated current.

--
JF

 

[John Larkin]

On Tue, 30 Jul 2013 18:33:40 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 30 Jul 2013 08:49:21 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 30 Jul 2013 21:11:06 +0800, "Mr. Man-wai Chang"
toylet.toylet@gmail.com> wrote:


1. Would a 3V LED short itself when connected to a 3V DC input?

There is no "3V LED"

---
I don't believe that's true, since some LEDs will drop 3V at their
rated current.

OK, show me a data sheet for a "3 volt LED."


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation

 

[Michael A. Terrell]

Michael Black wrote:

"But does it short out, or open up?"

Yes.

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

 

[Mr. Man-wai Chang]

On 30/07/2013 11:50 PM, John Larkin wrote:

If it's a military grade LED, then I was NOT supposed to be able to find
anything about it!
You don't make any sense.
Do you have a real name?

Just guessing....

I googled "1mA LED", not

--
@~@ Remain silent. Nothing from soldiers and magicians is real!
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (Fedora 19 i686) Linux 3.10.3-300.fc19.i686
^ ^ 21:00:02 up 1 day 21:25 0 users load average: 0.08 0.05 0.08
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa

 

[Mr. Man-wai Chang]

On 31/07/2013 9:12 PM, Mr. Man-wai Chang wrote:

On 30/07/2013 11:50 PM, John Larkin wrote:
If it's a military grade LED, then I was NOT supposed to be able to find
anything about it!
You don't make any sense.
Do you have a real name?

Just guessing....

I googled "1mA LED", not

.... and found this link:

Avago Technologies
Red non-diffuse round LED,1mA 1.6V
http://uk.rs-online.com/web/p/visible-leds/0826521/

Is it the one you were talking about?

--
@~@ Remain silent. Nothing from soldiers and magicians is real!
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (Fedora 19 i686) Linux 3.10.3-300.fc19.i686
^ ^ 21:00:02 up 1 day 21:25 0 users load average: 0.08 0.05 0.08
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa

 

[Mr. Man-wai Chang]

On 31/07/2013 7:33 AM, John Fields wrote:

There is no "3V LED"
I don't believe that's true, since some LEDs will drop 3V at their
rated current.

He might be right.... Scroll down for the table in the following link:

http://www.marutsu.co.jp/user/led.php


This link is actually quite useful to people using LEDs. Too bad it's
Japanese...

--
@~@ Remain silent. Nothing from soldiers and magicians is real!
/ v \ Simplicity is Beauty! May the Force and farces be with you!
/( _ )\ (Fedora 19 i686) Linux 3.10.3-300.fc19.i686
^ ^ 21:00:02 up 1 day 21:25 0 users load average: 0.08 0.05 0.08
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa

 

[John Fields]

On Tue, 30 Jul 2013 17:46:34 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Tue, 30 Jul 2013 18:33:40 -0500, John Fields
jfields@austininstruments.com> wrote:

On Tue, 30 Jul 2013 08:49:21 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 30 Jul 2013 21:11:06 +0800, "Mr. Man-wai Chang"
toylet.toylet@gmail.com> wrote:


1. Would a 3V LED short itself when connected to a 3V DC input?

There is no "3V LED"

---
I don't believe that's true, since some LEDs will drop 3V at their
rated current.

OK, show me a data sheet for a "3 volt LED."

---
http://www.avagotech.com/docs/AV02-1029EN


--
JF

 

[George Herold]

On Tuesday, July 30, 2013 12:00:38 PM UTC-4, John Larkin wrote:

On Tue, 30 Jul 2013 07:15:57 -0700 (PDT), George Herold <gherold@teachspin.com

wrote:
On Monday, July 29, 2013 5:25:15 PM UTC-4, John Larkin wrote:

On Tue, 30 Jul 2013 01:28:23 +0800, "Mr. Man-wai Chang"
snip previus tuff
I was surprsded by the sub-nA light output. At roughly 100 mV/decade



current, I'd have guessed that the voltage drop would be so low that

it wouldn't have enough energy to make photons.

Ahh, but it's those electrons on the far end of the exponential 'Boltzmann tail' that have enough extra thermal energy to make it into the depletion region. (I'll have to try I-V curves for LED's at low temperatures someday, dunking into LN2 should be pretty easy.)



Well, now you're talking about physics and science and stuff like that.
Grin.. well lots of electronics looks like a branch of science to me.


Seems to me that you need X volts to make a photon of X electron-volts energy.


Can thermal energy bootstrap an electron to make a photon that's more EV than

the voltage across the junction?
There was some news 'splash' from (maybe) mit of someone getting more light out of an led than power in.. at some ridiculously low current.

(The good thing about electrons is there are a whole lot of them, so there are a few with many kT's of kinetic energy.)

There's also this 'common' physics demo where they look at the led wavlength and forward voltage drop for a bunch of different color leds and plot things up to get a measure of Planck's constant. (A bit of a bogus experiment when you look at the details.)

Modern LEDs are remarkable gadgets. It would be fun to explore the corner cases,

"someday" as you say.



We're currently experimenting with cheap (like, $12) semiconductor lasers to

find some that accidentally make clean picosecond light pulses when whacked by

one of our laser drivers. The manufacturers certainly don't know if they might.

Most laser data sheets are pitiful.

Just spent over a grand on Thorlabs hardware to hold a laser in place and get

some of its light into a fiber.
Ouch.. the only thing more expensive than optics is high vacuum.

Speaking of modulating diode lasers, Cliff Stoll (who's quite a lovable 'character'.) Was visiting the other day. He does a bunch of educational outreach and uses a modulated diode laser, beam splitter, and cheap corner cube reflector to measure the speed of light. But what he needs is a cheap (fast) photodiode detector. I put him on to Phil's book... but I've been thinking it might be a nice project.

George H.

--



John Larkin Highland Technology Inc

www.highlandtechnology.com jlarkin at highlandtechnology dot com



Precision electronic instrumentation

Picosecond-resolution Digital Delay and Pulse generators

Custom timing and laser controllers

Photonics and fiberoptic TTL data links

VME analog, thermocouple, LVDT, synchro, tachometer

Multichannel arbitrary waveform generators

 

[Ian Field]

<my2004vette@gmail.com> wrote in message
news:8f401bf3-146f-419b-9d42-cad69d000802@googlegroups.com...

I need help with a way to light up my SWR meter with internal led which
would be really close to RF passing thru the SWR meter. That way it would
only light up the meter when I transmit. if anyone could point me to a
circuit that would do this, probably need two leds one on each side of the
meter, would be really grateful. I know there are ways using 12V but I
want to stay away from batteries or having to plug/unplug cables. My email
is k4wi@earthlink.net. Thanks, Cort K4WI

If you read a few Ham related articles - most operators who publish articles
put their call sign in the intro.

Its well worth googling any call signs, many operators have websites loaded
with projects & circuits.

 

[John Larkin]

On Wed, 31 Jul 2013 08:58:12 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 30 Jul 2013 17:46:34 -0700, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Tue, 30 Jul 2013 18:33:40 -0500, John Fields
jfields@austininstruments.com> wrote:

On Tue, 30 Jul 2013 08:49:21 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 30 Jul 2013 21:11:06 +0800, "Mr. Man-wai Chang"
toylet.toylet@gmail.com> wrote:


1. Would a 3V LED short itself when connected to a 3V DC input?

There is no "3V LED"

---
I don't believe that's true, since some LEDs will drop 3V at their
rated current.

OK, show me a data sheet for a "3 volt LED."

---
http://www.avagotech.com/docs/AV02-1029EN

Those are not "3 volt leds." Their typ forward drop is 3.2, but they
are still not shown as being voltage operable; they are spec'd at 20
mA.




--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation

 

[John Larkin]

On Wed, 31 Jul 2013 21:14:04 +0800, "Mr. Man-wai Chang"
<toylet.toylet@gmail.com> wrote:

On 31/07/2013 9:12 PM, Mr. Man-wai Chang wrote:
On 30/07/2013 11:50 PM, John Larkin wrote:
If it's a military grade LED, then I was NOT supposed to be able to find
anything about it!
You don't make any sense.
Do you have a real name?

Just guessing....

I googled "1mA LED", not


... and found this link:

Avago Technologies
Red non-diffuse round LED,1mA 1.6V
http://uk.rs-online.com/web/p/visible-leds/0826521/

Is it the one you were talking about?

If red is the same color as green, yes.


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation

 

[John Larkin]

On Wed, 31 Jul 2013 08:00:56 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Tuesday, July 30, 2013 12:00:38 PM UTC-4, John Larkin wrote:
On Tue, 30 Jul 2013 07:15:57 -0700 (PDT), George Herold <gherold@teachspin.com

wrote:
On Monday, July 29, 2013 5:25:15 PM UTC-4, John Larkin wrote:

On Tue, 30 Jul 2013 01:28:23 +0800, "Mr. Man-wai Chang"
snip previus tuff
I was surprsded by the sub-nA light output. At roughly 100 mV/decade



current, I'd have guessed that the voltage drop would be so low that

it wouldn't have enough energy to make photons.

Ahh, but it's those electrons on the far end of the exponential 'Boltzmann tail' that have enough extra thermal energy to make it into the depletion region. (I'll have to try I-V curves for LED's at low temperatures someday, dunking into LN2 should be pretty easy.)



Well, now you're talking about physics and science and stuff like that.
Grin.. well lots of electronics looks like a branch of science to me.


Seems to me that you need X volts to make a photon of X electron-volts energy.


Can thermal energy bootstrap an electron to make a photon that's more EV than

the voltage across the junction?
There was some news 'splash' from (maybe) mit of someone getting more light out of an led than power in.. at some ridiculously low current.

(The good thing about electrons is there are a whole lot of them, so there are a few with many kT's of kinetic energy.)

There's also this 'common' physics demo where they look at the led wavlength and forward voltage drop for a bunch of different color leds and plot things up to get a measure of Planck's constant. (A bit of a bogus experiment when you look at the details.)



Modern LEDs are remarkable gadgets. It would be fun to explore the corner cases,

"someday" as you say.



We're currently experimenting with cheap (like, $12) semiconductor lasers to

find some that accidentally make clean picosecond light pulses when whacked by

one of our laser drivers. The manufacturers certainly don't know if they might.

Most laser data sheets are pitiful.

Just spent over a grand on Thorlabs hardware to hold a laser in place and get

some of its light into a fiber.
Ouch.. the only thing more expensive than optics is high vacuum.

Speaking of modulating diode lasers, Cliff Stoll (who's quite a lovable 'character'.) Was visiting the other day. He does a bunch of educational outreach and uses a modulated diode laser, beam splitter, and cheap corner cube reflector to measure the speed of light. But what he needs is a cheap (fast) photodiode detector. I put him on to Phil's book... but I've been thinking it might be a nice project.

Phil is fond of ebay APDs, which are apparently surplus from some
expensive projects. How fast do you need? Pulse or sine wave?


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation

 

[John Fields]

On Wed, 31 Jul 2013 16:23:44 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Wed, 31 Jul 2013 08:58:12 -0500, John Fields
jfields@austininstruments.com> wrote:

On Tue, 30 Jul 2013 17:46:34 -0700, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Tue, 30 Jul 2013 18:33:40 -0500, John Fields
jfields@austininstruments.com> wrote:

On Tue, 30 Jul 2013 08:49:21 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 30 Jul 2013 21:11:06 +0800, "Mr. Man-wai Chang"
toylet.toylet@gmail.com> wrote:


1. Would a 3V LED short itself when connected to a 3V DC input?

There is no "3V LED"

---
I don't believe that's true, since some LEDs will drop 3V at their
rated current.

OK, show me a data sheet for a "3 volt LED."

---
http://www.avagotech.com/docs/AV02-1029EN

Those are not "3 volt leds." Their typ forward drop is 3.2, but they
are still not shown as being voltage operable; they are spec'd at 20
mA.

---
Well, with no voltage to drive current through the junction they
wouldn't work at all, so they are certainly "voltage operable".

Also, notice that the data sheet shows a range of from 2.8 to 3.8V
across the junction with 20 mA through it, so 3.0V dropped across the
junction with 20mA through it is certainly within the range of
possibilities.

Consequently, for that LED, connecting 3.0V to it directly will force
20mA through it.

Ergo, 3 volt LED.

--
JF

 

[Mr. Man-wai Chang]

On 1/08/2013 7:24 AM, John Larkin wrote:

On Wed, 31 Jul 2013 21:14:04 +0800, "Mr. Man-wai Chang"
Avago Technologies
Red non-diffuse round LED,1mA 1.6V
http://uk.rs-online.com/web/p/visible-leds/0826521/
Is it the one you were talking about?

If red is the same color as green, yes.

Have you ever touched a real one?

--
@~@ Remain silent. Nothing from soldiers and magicians is real!
/ v \ Simplicity is Beauty!
/( _ )\ May the Force and farces be with you!
^ ^ (x86_64 Ubuntu 9.10) Linux 2.6.39.3
不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa