Running LEDs on five volts

[Daniel Prince]

I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.
--
I used to think that most MDs were incompetent morons. I was wrong,
they are actually very intelligent and good at what they do which is
make lots of money and get lots of prestige by shoveling enormous
amounts of BS very, very rapidly.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[John Fields]

On Sun, 12 Jun 2005 15:48:01 -0700, Daniel Prince
<neutrino1@comcast.net> wrote:

I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.

--
I used to think that most MDs were incompetent morons. I was wrong,
they are actually very intelligent and good at what they do which is
make lots of money and get lots of prestige by shoveling enormous
amounts of BS very, very rapidly.

---
I see.

Here you are, a stupid fuck who has to ask for help on how to wire up
LEDs and yet, startlingly intelligent enough to be able to impugn the
education and motives of the medical community.

Fuck you, asshole, you'll get no help from me.

--
John Fields
Professional Circuit Designer

 

[Bob Eldred]

"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:7e7pa1d8rf32bj1u1apqeemd8vqr92p43c@4ax.com...

I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.
--
I used to think that most MDs were incompetent morons. I was wrong,
they are actually very intelligent and good at what they do which is
make lots of money and get lots of prestige by shoveling enormous
amounts of BS very, very rapidly.

You've got something against resistors? Maybe they're too expensive at a
couple of bucks per hundred?

 

[John Smith]

.... might just as well not help me either...

MD's which are worth a chit are few and far between--from my
observations, most have mental problems... your post suggests you might
have those qualities--have you considered becoming an MD?

John

"John Fields" <jfields@austininstruments.com> wrote in message
newsekpa19grk7p6rfibd9rlmuq9p9nv1h6hd@4ax.com...

On Sun, 12 Jun 2005 15:48:01 -0700, Daniel Prince
neutrino1@comcast.net> wrote:

I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.

--
I used to think that most MDs were incompetent morons. I was wrong,
they are actually very intelligent and good at what they do which is
make lots of money and get lots of prestige by shoveling enormous
amounts of BS very, very rapidly.

---
I see.

Here you are, a stupid fuck who has to ask for help on how to wire up
LEDs and yet, startlingly intelligent enough to be able to impugn the
education and motives of the medical community.

Fuck you, asshole, you'll get no help from me.

--
John Fields
Professional Circuit Designer

 

[Lord Garth]

"John Smith" <assemblywizard@gmail.com> wrote in message
news:nw4re.64$Xl6.3585048@news.sisna.com...

... might just as well not help me either...

MD's which are worth a chit are few and far between--from my
observations, most have mental problems... your post suggests you might
have those qualities--have you considered becoming an MD?

John

Is that a Magnetic Disc or an M.D.?

;-)

 

[Daniel Prince]

John Fields <jfields@austininstruments.com> wrote:

Here you are, a stupid fuck who has to ask for help on how to wire up
LEDs

Are you claiming that all intelligent people automatically know how
to wire LEDs?

and yet, startlingly intelligent enough to be able to impugn the
education and motives of the medical community.

I have been disabled with ME (Myalgic Encephalomyelitis): IDC 10
(International Disease Classification 10) code of G93.3 for more
than 32 years. Articles about ME have been published in the peer
reviewed medical literature since 1959. ME has been in the IDC
since 1969. The IDC classifies ME as a neurological illness.

I have probably been to more than 100 MDs. None of them knew much
about my illness. Most of them knew NOTHING about my illness. None
of them were willing to learn much about my illness. Most of them
were unwilling to learn ANYTHING about my illness.

I have been to numerous doctors who "diagnosed" me with depression
without even asking me about my mood, appetite, or enjoyment of
activities. One infectious doctor "diagnosed" me with depression
without even seeing me.

I have tried eight different antidepressants. Most of them made me
WORSE. One of them, Zoloft helped my neurally mediated hypotension
for a few months but it stopped working.

In the spring of 1993 I agreed to take the antidepressant Imipramine
because I was told that I wouldn't be allowed to see the infectious
disease specialist unless I did and I wanted to prove to the doctors
that it wouldn't help me. The drug didn't make me feel any better.
It made me feel MUCH worse. I had insomnia (especially the first
few days) and I wasn't able to do much of anything. I wasn't able
to exercise AT ALL. My libido went down substantially and I had
difficulty reaching orgasm. It also caused such severe night sweats
that I was SURE my waterbed had sprung a leak and made me feel
awful. I was on Imipramine for a total of seven weeks (two weeks at
200 mg) and I gained seven unwanted pounds which I haven't been able
to lose since.

The psychiatrist originally told me that it usually took three to
four weeks to take effect but that he would try it for a maximum of
five weeks and if it had not helped me by that time he would take me
off it. After I had been on it for more than six weeks, I called
the psychiatrist and asked him how much longer I would have to be on
this drug. He said I would have to be on it for five weeks at the
maximum dose of 300 mg. When I told him that the PDR says that the
maximum recommended outpatient dose is 200 mg and that optimum
results take one to three weeks, he said that his recommendations
were based on newer research. I thought about this for a while and
called his service and left a message asking where I could find this
research. He never returned my call even though I left him another
message several days later.

I have been in long term psychotherapy with three different
psychiatrists. I went to one for nine months and two for six months
each. This psychotherapy did not help me with my neurological
illness Myalgic Encephalomyelitis.

I once collapsed with VERY low blood pressure (78/undetectable) and
was taken to the county hospital. They kept me in the hospital for
two weeks trying to reach a diagnosis. The Internal medicine
resident called in the psychiatrists three times. He was convinced
that it MUST be mental but the psychiatrists didn't find any
evidence of mental illness. They finally decided that there was
nothing wrong with me and that my symptoms were caused by
dehydration. They didn't explain why a supposedly healthy 25 year
old would become THAT dehydrated without becoming thirsty and have
750 ml of urine in his bladder (I was unable to urinate and was
catheterized).

One doctor I went to said that he had read several journal articles
on ME and they were all "bad science" (When I asked him if it was
because they disagreed with his preconceived notions he had no
answer.)

Two different doctors have told me that I couldn't possibly have a
chronic viral infection because there was no such thing. There are
several chronic viral infections including HIV and hepatitis C.

I had one MD tell me at least three times in one office visit:
"You're much healthier than you think you are." When I asked him
how many medical journal articles he had read about my illness he
replied: "none". (There are more than 2,000.)

Doctors at one clinic told me that I had a lipid myopathy and that a
special diet would cure me. The diet did not cure me. I have since
learned that children with lipid myopathy all die in their teens. I
was in my late twenties at the time. The diet that was supposed to
cure me caused me to go from about 194 pounds to 116 pounds (I am
just under 68 inches tall). I developed a hernia because of the
diet and had to have surgery.

One MD told me that I couldn't possibly have a chronic infection
because my sedimentation rate was normal. All the medical text
books I have looked at say that the sedimentation rate is only
sometimes elevated in infections.

The first time I took my elderly, very obese mother who was cold all
the time to her MD because she was too disabled to go by herself, I
had to ask four times before the MD agreed to run a TSH test. The
MD said that she was doing it just to humor me and that there was NO
possibility of it being abnormal. About a week later we got a call
from the lab. Mother's TSH was 12.58. (At the time, normal was
less than 5.5. Since then normal has been changed to less than
3.0.)

Once I had an ENT insist that I could not have a sinus infection
because my sinus X-rays (taken 11 months earlier) were negative. I
have since learned that sinus X-rays are not a very good way to
detect sinus infections. Obviously X-rays taken eleven months
earlier could not rule out an infection on that day.

Recently a MD was ready to have my thyroid removed even though the
thyroid ultrasound and thyroid CAT scan results were not yet
available. She was sure I had thyroid cancer because I had
antithyroid antibodies and a CEA of 16.3. (CEA is a test that is
usually elevated in cancer and normal is <5.0.) I refused the
operation and insisted on a thyroid biopsy. When I got to the
hospital for the biopsy, they refused to do one because the other
thyroid tests were normal and there were no masses in my thyroid to
biopsy.

Based on these FACTS, what conclusions do you draw about the medical
profession? If these were your experiences, what would you think
about MDs?

I will change my signature to one that is less offensive to you.
--
My previous cat Rocket thought that every time I ate something he
should get some canned cat food. Marmaduke, the cat I have now,
thinks that he should get canned food and be allowed to get on the
table and eat what he wants off my plate.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[Daniel Prince]

"Bob Eldred" <nsmontassoc@yahoo.com> wrote:

"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:7e7pa1d8rf32bj1u1apqeemd8vqr92p43c@4ax.com...
I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.

You've got something against resistors? Maybe they're too expensive at a
couple of bucks per hundred?

I don't have any on hand and my VERY poor health makes it difficult
for me to go get some. If I really need some resistors, I will go
to RS and get some the next time I drag myself out of the house if I
know which ones to get.

--
My previous cat Rocket thought that every time I ate something he
should get some canned cat food. Marmaduke, the cat I have now,
thinks that he should get canned food and be allowed to get on the
table and eat what he wants off my plate.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[Lord Garth]

"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:235qa1tiiqe7sn4ke381lnrp9m8v5kh9k8@4ax.com...

<snip medical report>

Okay, so what color are the LEDs you wish to run?
How many do you wish to have on?

The USB port supplies 5 volts at a maximum of 500mA
and I wouldn't push that limit since the fuse is microscopic
if you can get into the laptop and find its location.

 

[Brian]

"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:825qa11bdcu5spr5133v8mscdl5b3l1360@4ax.com...

"Bob Eldred" <nsmontassoc@yahoo.com> wrote:


"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:7e7pa1d8rf32bj1u1apqeemd8vqr92p43c@4ax.com...
I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.

You've got something against resistors? Maybe they're too expensive at a
couple of bucks per hundred?

I don't have any on hand and my VERY poor health makes it difficult
for me to go get some. If I really need some resistors, I will go
to RS and get some the next time I drag myself out of the house if I
know which ones to get.

--
My previous cat Rocket thought that every time I ate something he
should get some canned cat food. Marmaduke, the cat I have now,
thinks that he should get canned food and be allowed to get on the
table and eat what he wants off my plate.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000
Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

You could put 2 sets of 2 LED's in series with a 56 ohm resistor (1/4
watt) and a 150 ohm resistor (1/4 watt) in series with one LED.

Brian

 

[Brian]

You could put 2 sets of 2 LED's in series with a 56 ohm resistor (1/4
watt) and a 150 ohm resistor (1/4 watt) in series with one LED.

Brian

That is, you will need two 56 ohm resistors and one 150 ohm resistor.

One string with two LED's and a 56 ohm resistor.

Another string with two LED's and a 56 ohm resistor.

Another string with one LED and a 150 ohm resistor.


Brian

 

[Don Klipstein]

In article <Ypcre.505$ks4.234@newssvr12.news.prodigy.com>, Lord Garth wrote:

"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:235qa1tiiqe7sn4ke381lnrp9m8v5kh9k8@4ax.com...

snip medical report

Okay, so what color are the LEDs you wish to run?
How many do you wish to have on?

The USB port supplies 5 volts at a maximum of 500mA
and I wouldn't push that limit since the fuse is microscopic
if you can get into the laptop and find its location.

That was something I was curious about but not badly enough to dig this
up... Thanks!!!

Meanwhile, his original post, if I remember correctly, mentioned having
a Radio Shack 20-piece grab bag of LEDs and suggested using three of them,
at least in a proposed example.

I would not put them in series, but use a resistor in series with each
one, and put the LED-resistor series combos in parallel wth each other.

In my experience, Radio Shack 20-piece LED grab bags have LEDs that sure
look like ones mostly with typical current 20 mA maximum current 30 mA,
maybe some with maximum as high as 50 mA.
I have always been able to use these LEDs at 40 mA, although with no
good idea what their life would be like. My experience with doing this is
more than a few hours but no further data, and I am guessing most likely
merely falling well short of the typically-claimed 100,000 hours.

These LEDs have voltage drop at 20 mA in the 1.6 to 2.3 volt range in my
experience, with less than 1.8 volts only for one red chemistry.
Last month I looked at the LED grab bags at Radio Shack and they looked
like the same ones of a decade or more ago, lacking blue LEDs and
apparently lacking the other colors with voltage drop closer to (usually
above) above 3 volts.

I would say design for 20 mA if you want a good chance of 100,000 hour
"typical LED life", 30 mA for a more aggressive but probably quite
tolerable design.

With 2 volts across the LED, this means 3 volts across the resistor.
For 20 mA (.02 amp), use a resistor of (3 volts /.02 amps), which is 150
ohms. For 30 mA (.03 amp), use (3/.03), which is 100 ohms.

- Don Klipstein (don@misty.com)

 

[NRen2k5]

On 6/13/2005 1:30:43 AM, Daniel Prince wrote:

"Bob Eldred" <nsmontassoc@yahoo.com> wrote:


"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:7e7pa1d8rf32bj1u1apqeemd8vqr92p43c@4ax.com...
I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.

You've got something against resistors? Maybe they're too expensive at a
couple of bucks per hundred?

I don't have any on hand and my VERY poor health makes it difficult
for me to go get some. If I really need some resistors, I will go
to RS and get some the next time I drag myself out of the house if I
know which ones to get.

--
My previous cat Rocket thought that every time I ate something he
should get some canned cat food. Marmaduke, the cat I have now,
thinks that he should get canned food and be allowed to get on the
table and eat what he wants off my plate.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

So then find yourself an online electronics vendor and order resistors or
resistor packages. Surely the mailbox isn't too far for you to move in a day?
You're already parked in front of the computer, so I know that making the
order won't be any trouble for you...

- NRen2k5

 

[Kitchen Man]

On Sun, 12 Jun 2005 22:30:43 -0700, Daniel Prince
<neutrino1@comcast.net> wrote:

I don't have any on hand and my VERY poor health makes it difficult
for me to go get some. If I really need some resistors, I will go
to RS and get some the next time I drag myself out of the house if I
know which ones to get.

Pretty much anything can be had online via mail order. Proper LED
design requires a resistor and an LED in series. Browse the web for
design ideas and equations, and order up an assortment of resistors.
It is a very rare electronic design that omits resistors.

--
Al Brennan

"If you only knew the magnificence of the 3, 6 and 9,
then you would have a key to the universe." Nicola Tesla

 

[John Smith]

MPF-102
LED 1K Resistor
POS -------|>---| |-------\/\/\/\/\---- NEG
| | |
------- |
| |
|--------------------|


The above circuit will only pass 10 ma in though the FET over a voltage
range of 5v to 25, should work well for you--the fet functions as a
current limiter...


Warmest regards,
John

"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:7e7pa1d8rf32bj1u1apqeemd8vqr92p43c@4ax.com...

I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.
--
I used to think that most MDs were incompetent morons. I was wrong,
they are actually very intelligent and good at what they do which is
make lots of money and get lots of prestige by shoveling enormous
amounts of BS very, very rapidly.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World!
100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[Daniel Prince]

Kitchen Man <nannerbac@yahoo.com> wrote:

Proper LED design requires a resistor and an LED in series.

Just out of curiosity, what would happen if I connected three in
series without a resistor? Would they draw too much current even
though the voltage across each one would be about 1.67 volts?

What would happen if I used four in series (1.25 volts)? Thank you
in advance for all replies.
--
My previous cat Rocket thought that every time I ate something he
should get some canned cat food. Marmaduke, the cat I have now,
thinks that he should get canned food and be allowed to get on the
table and eat what he wants off my plate.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[John Popelish]

Daniel Prince wrote:

Just out of curiosity, what would happen if I connected three in
series without a resistor? Would they draw too much current even
though the voltage across each one would be about 1.67 volts?

What would happen if I used four in series (1.25 volts)? Thank you
in advance for all replies.

LEDs have a very nonlinear current response to applied voltage (as all
PN junction diodes do). Something like a 60 millivolt increase will
cause about 10 times the current to pass through them. Conversely,
dropping the voltage by 60 mV will cut the current to 1/10th. The
problem is that exactly what voltage produces the rated current varies
batch to batch and with temperature.

So there is certainly some safe voltage that can be applied to an LED,
but it is safe, only because the current is certainly so low that it
is not important exactly what it is or how much it will vary, unit to
unit or versus temperature. Establishing a useful current that is
also stable and predictable unit to unit is the reason resistance (or
other current stabilizing means) is added to LED circuits.

 

[Don Klipstein]

In art. <6ph0b1l82rdktu08q8julbu90udvaki4j5@4ax.com>, Daniel Prince wrote:

Just out of curiosity, what would happen if I connected three in
series without a resistor? Would they draw too much current even
though the voltage across each one would be about 1.67 volts?

What would happen if I used four in series (1.25 volts)? Thank you
in advance for all replies.

See John Popelish's response - current varies a lot if voltage across an
LED varies little, and voltage across an LED varies little when current
varies a lot. Although in my experience most LEDs aren't quite as extreme
as 10-1 change in current for only .06 volt change in voltage reported by
John Popelish - I think more usual is .1 volt change is
typically associated with current changing by a factor of 10.

But watch out for voltage drop varying with temperature (or current
varying significantly, sometimes wildly and in the same direction as
temperature when voltage is constant). Also watch for minor voltage
variations from one piece to another, which can (but does not always) make
for major variations in current from one piece to another if the voltage
is fixed.

As for 3 in series? I think generally safe, but with very weak
possibly essentially no light output, for green, yellow, orange, and red
other than "original forumla red" (GaAsP on GaAs substrate,
non-high-brightness 660 nm peak wavelength). The "original formula red"
may draw close to typical or close to maximum current at this voltage,
possibly excessive current but then again maybe no more than "normal"
current.

As for 4 in series? I expect with 1.25 volts across each, most likely
there wil be essentially no visible output, although GaAsP on GaAs
substrate may visibly glow very dimly as in uselessly dim.

- Don Klipstein (don@misty.com)

 

[Kitchen Man]

On Wed, 15 Jun 2005 08:24:42 -0700, Daniel Prince
<neutrino1@comcast.net> wrote:

Proper LED design requires a resistor and an LED in series.

Just out of curiosity, what would happen if I connected three in
series without a resistor? Would they draw too much current even
though the voltage across each one would be about 1.67 volts?

It's like you just heard from John and Don. The results will be
unpredictable and likely ineffective and non-repeatable.

--
Al Brennan

"If you only knew the magnificence of the 3, 6 and 9,
then you would have a key to the universe." Nicola Tesla

 

[Watson A.Name - \"Watt Su]

"John Smith" <assemblywizard@gmail.com> wrote in message
news:kqsre.103$H34.4870165@news.sisna.com...

MPF-102
LED 1K Resistor
POS -------|>---| |-------\/\/\/\/\---- NEG
| | |
------- |
| |
|--------------------|


The above circuit will only pass 10 ma in though the FET over a
voltage
range of 5v to 25, should work well for you--the fet functions as a
current limiter...

I can't figure out where you came up with that lollapalooza of a
whopper. The datasheet for the MPF102 calls for an Idss of anywhere
from 2 to 20mA. That's with the gate shorted to the source. In my
experience this value varies wildly between the min and max, so probably
half of them will _never_ be able to pass 10mA. And that's with _no_
resistor; with your value of resistor, none will be able to. Many will
give only a few mA. The MPF102 varies so wildly tht you really need a
half dozen or more to find one that's about right. Use the cheaper
single resistor per LED, and you won't despair. A 150 ohm resistor will
work okay with the red LED, depending on what current you want.

Warmest regards,
John

"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:7e7pa1d8rf32bj1u1apqeemd8vqr92p43c@4ax.com...
I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have any
specifications with them. What is my best option? Thank you in
advance for all replies.
--
I used to think that most MDs were incompetent morons. I was wrong,
they are actually very intelligent and good at what they do which is
make lots of money and get lots of prestige by shoveling enormous
amounts of BS very, very rapidly.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World!
100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption
=---

 

[Watson A.Name - \"Watt Su]

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com>
wrote in message news:11b4j3ql2u1kn73@corp.supernews.com...

"John Smith" <assemblywizard@gmail.com> wrote in message
news:kqsre.103$H34.4870165@news.sisna.com...



MPF-102
LED 1K Resistor
POS -------|>---| |-------\/\/\/\/\---- NEG
| | |
------- |
| |
|--------------------|


The above circuit will only pass 10 ma in though the FET over a
voltage
range of 5v to 25, should work well for you--the fet functions as a
current limiter...

I can't figure out where you came up with that lollapalooza of a
whopper. The datasheet for the MPF102 calls for an Idss of anywhere
from 2 to 20mA. That's with the gate shorted to the source. In my
experience this value varies wildly between the min and max, so
probably
half of them will _never_ be able to pass 10mA. And that's with _no_
resistor; with your value of resistor, none will be able to. Many
will
give only a few mA. The MPF102 varies so wildly tht you really need a
half dozen or more to find one that's about right. Use the cheaper
single resistor per LED, and you won't despair. A 150 ohm resistor
will
work okay with the red LED, depending on what current you want.

As an experiment, I pulled out two dozen MPF102 JFETs from a pile of
several makers. I put them on a 5.0V power supply. With the gate
shorted to the source, all of the JFETs had Idss of between 3.9 and
8.2mA.

I'm sure if I tried several dozen more, I would hit a few of them that
would have a higher Idss. But this experiment shows me that the MPF102
makes a very poor choice for currents of more than 8mA.

Warmest regards,
John

"Daniel Prince" <neutrino1@comcast.net> wrote in message
news:7e7pa1d8rf32bj1u1apqeemd8vqr92p43c@4ax.com...
I want to run some LEDs on five volts from one of the USB ports on
my computer. Can I just use three of them in series or do I need
to
use a current limiting resister.

I want to keep it as simple as possible. The LEDs I have are a
package of 20 assorted (RS cat no. 276-1622). They do not have
any
specifications with them. What is my best option? Thank you in
advance for all replies.
--
I used to think that most MDs were incompetent morons. I was
wrong,
they are actually very intelligent and good at what they do which
is
make lots of money and get lots of prestige by shoveling enormous
amounts of BS very, very rapidly.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure
Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World!
100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption
=---