Re: 12 LED resistance circuit help


"John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:hlet615kqfu1aa3dtvru5o08oc1g0539ln@xxxxxxxxxx
> On Tue, 26 Apr 2005 19:05:10 GMT, "Anthony Fremont"
> <spam@xxxxxxxxxxxx> wrote:
>
>
> >> >> >LMAO I'm not the one
> >> >> >touting myself as a "professional circuit designer".
> >>
> >> ---
> >> Perhaps that's because you aren't.
> >
> >Well duh, that would be the appropriate thing to do wouldn't it?
>
> ---
> Precisely. My .sig reads 'Professional Circuit Designer' because
> that's what I am. Your .sig, OTOH, reads... nothing???

I guess that means my ego gets enough to eat without me feeding it.

> ---
>
> >Did I say that somewhere? Since you mentioned it, don't you find the
> >word professional to be tiny bit redundant?
>
> ---
> Not at all. 'Circuit Designer" means one thing, Professional Circuit
> Designer' means quite another. Perhaps you're miffed because you'd
> feel ridiculous using 'Professional Hobbyist' as a .sig?

Those words are mutually exclusive, so yes I'd be embarrassed to call
myself that.

> ---
>
> > Why do you feel a need to tell the world that you really do get
paid?
>
> ---
> Actually, it's more of an ad than anything else, and has brought in
> some work from time to time, so it's important in that sense.
> ---
>
> >> >Do you think that I have no other skills, or is circuit design all
> >that
> >> >is important?
> >>
> >> ---
> >> What skills you may have, other than in electronics, are of very
> >> little interest to me since, in these groups, what's important is
> >
> >Translation: Yes, you probably do know a bunch of stuff that I don't
> >know, but since I don't know it, it's not relevant.
>
> ---
> Interesting that you find it necessary to try to put words in my
> mouth. Sounds like you're so unsure of yourself that you have to
> manufacture situations in which parts of imaginary conversations fill
> in the empty spaces.

Pot, kettle black and all that.

> ---
>
> >> electronics and the ability to communicate. In seb, it's also
> >
> >Have I not communicated well enough?
>
> ---
> Obviously not well enough to put this matter to rest.
> ---
>
>
> >Modicum and acumen in the same sentence. No wonder it took you all
> >night to respond.
>
> ---
> You were up all night just waiting for my response? How sweet!
> ---
>
> >OMG, I can't believe it. That must have been really hard.
>
> ---
> For you, maybe, but not for me. Like I said before, if an apology is
> warranted i'll offer it.

I think we all could have appreciated you researching your case BEFORE
making it. Now you've gone and said all kinds of hateful, mean, and
ugly things to me just because I made one statement that really wasn't
all that bad.

> ---
>
> >Maybe we can coexist then.
>
> ---
> We'll see.
> ---
>
> >> >My comments in the original post were rhetorical, haven't you
figured
> >> >that out yet?
> >>
> >> ---
> >> Nope. Would you mind going back and dredging up those comments and
> >> explaining what made them rhetorical?
> >
> >OK, here we go:
> >
> >First I said, "Maybe I could help make amends by belittling others,
> >nit-picking posts and posting a bunch
> >of OT crap?". Then I said, "Lets see if we can't get on to the road
to
> >recovery now." That's all kinda the setup up indicating that
sarcastic
> >and rhetorical remarks may follow. And then they did. I jibed
Watson
> >since he tossed the first punch and you for what amounts to several
> >reasons (mainly your setup question when I've never slapped at you
> >before, I knew what you were trying to do and it torqued me off,
> >finally I've frankly found you to be a bit offensive lately and
without
> >cause to other people namely Larry). So while it may not have been
> >entirely rhetorical, I really didn't expect this outcome.
>
> ---
> None of it was rhetorical, in that 'rhetorical' is defined as language
> used for mere style or effect or language marked by or tending to use
> bombast.

And isn't that precisely what it did? Did you not feel personally
bombasted?

> What you were doing was using sarcasm and invective vituperatively in

There was absolutely no invective involved. I merely posed a question,
it could have been phrased nicer, but it was just a question
nonetheless. Perhaps you should rethink that statement.

> order to retaliate for your feelings of having been belittled.
> ---
>
>
>
> >> >> >At any rate, you are the one setting the precident around here
of
> >> ^^^^^^^^^
> >> precedent
> >>
> >> >> >jumping down someones throat when you don't like the accuracy
of
> >> ^^^^^^^^
> >> someone's
> >> >their posts.
> >
> >Why are spell checking my old posts now?
>
> ---
> I'm not _just_ spell checking your posts, I'm correcting your improper
> use of the language in order to allow you to communicate more
> effectively.

Perhaps I should just send you a box of characters then you can
completely construct the sentences for me. That way you'll always know
what I mean.

> And because I feel like it.
> ---
>
> >Actually I use the "F" word plenty well, I just tend to not spell it
out
> >in usenet articles. Just trying to consider the children. ;-)
>
> ---
> How sickeningly pompous. If you don't want to use '***' when you
> write, you don't have to blame it on the kids, just don't use it.

The children thing was just a joke, didn't you see the winkey?

> Besides, any "children" who hang out here have heard it all before
> just in case you've been away from the planet for a while.

Yes, well that certainly justifies it, doesn't it?

> ---
>
>
> >> ---
> >> Certainly not, but it's not about a timeline, it's about changing
> >> streams in mid-horse. What you said earlier, unconditionally, was
that
> >> you didn't feel it was necessary to make a scene, while what you're
> >
> >At the time that is how I felt. And then you changed all that when
you
> >tried to bust my chops on current vs. power or "current hogging" as
you
> >like to call it. So, you prompted the horse change, not me.
>
> ---
> SWYMMD? ROTFLMAO!!!
> ---
>
>
> >> Not at all, just a substitution used to tighten up of the sloppy
> >> construct, which included my substitution of 'power hogging' for
your
> >> "dissipate more power".
> >
> >Yes, it's all about what serves your agenda best, isn't it?
>
> ---
> Of course. I should subjugate mine and hitch my wagon to your star?
> ---
>
>
> >> I merely asked a question designed to determine whether you did, in
> >> fact, know the difference, but you took affrontery and refused to
> >> answer it directly.
> >
> >And I thought by saying "dissipate more power" that I made it
perfectly
> >clear that I knew what you were hinting at. How direct does
something
> >need to be before you can see it?
>
> ---
> I'm not sure you remember, but I didn't comment on your answer until
> you started with your diatribe after I had the _affrontery_ to hit you
> with a "trick question" and Watson _dared_ to throw that little barb

Exactly, that's the whole problem. You posted your "trick" question and
Watson saw it for what it was and made his snide remark. That directly
makes you the proximate cause of this whole fiasco. ;-)

> at you, and you're _still_ not over it. For an 'old hand' on usenet
> you sure have thin skin!

No, just a good recollection of what happened when.

> ---
>
>
>
>
> >> Nope, but then, you've got nothing to make bodacious claims about.
> >
> >See, there you go making prejudicial statements again. You have no
> >idea.
>
> ---
> Ok, then, let's hear about your bodacity

I already did my bragging in another post that you have yet to respond
to.
..
> ---
>
> >> Awww... baby demurs. And here I thought I was going to get to see
> >> some good stuff.
> >>
> >> OK, _I'll_ do it.
> >>
> >> Here's the circuit:
> >>
> >>
> >> E1
> >> |
> >> [R1]
> >> |
> >> +---->E2
> >> |
> >> [DS1]
> >> |
> >> +---->E3
> >> |
> >> [DS2]
> >> |
> >> GND
> >>
> >> Unfortunately, the data *** at the link you provided:
> >>
> >>
http://www.epitex.com/Catalog_PDF/08_Point_source_LED/L590CE-34F.PDF
> >>
> >> doesn't show Vf min, and I couldn't find any Vf min for white LEDs
so,
> >> since you said that Vf can vary 2:1, looking at a Vf max of 4.0V
for a
> >> "typical" white LED at 20mA yields a Vf min of 2.0V. Also, 100mW
> >> seems to be a pretty typical max dissipation, so if we redraw the
> >> circuit with that in mind, and with LEDs with equal low Vf's we'll
> >> get:
> >>
> >>
> >> 9.0V-+---->E1
> >> |
> >> [R1]
> >> |
> >> 4.0V-+---->E2
> >> |
> >> [DS1]
> >> |
> >> 2.0V-+---->E3
> >> |
> >> [DS2]
> >> |
> >> GND
> >>
> >>
> >> The choice of 9V for E1 is based on the assumption that E1 will be
> >> regulated and will give 1V of headroom if DS1 and DS2 are both at
Vf
> >> max.
> >>
> >> Now, since the current in a series circuit is everywhere the same,
> >> solving for R1 with 20mA of LED current yields:
> >>
> >> (E1-E2) 5V
> >> R1 = --------- = ------- = 250 ohms
> >> It 0.02A
> >>
> >>
> >> and the LEDs will each be dissipating:
> >>
> >>
> >> P = IE = 0.02A * 2V = 0.04W
> >>
> >>
> >> so everything will be fine.
> >>
> >>
> >> Now, though, let's select a high Vf LED for DS1 and see what
happens.
> >>
> >>
> >> Here's the circuit now:
> >>
> >> 9.0V-+---->E1
> >> |
> >> [250]
> >> |
> >> 6.0V-+---->E2
> >> |
> >> [DS1]
> >> |
> >> 2.0V-+---->E3
> >> |
> >> [DS2]
> >> |
> >> GND
> >>
> >>
> >> Since we now have a 3V drop across R1 the current will fall to:
> >>
> >>
> >> E 3V
> >> I = --- = ------ = 0.012A
> >> R 250R
> >>
> >>
> >> and the power being dissipated by DS1 will be:
> >>
> >>
> >> P = 0.012A * 4V = 0.048W
> >>
> >> So, if the LED is rated for 100mW max, it will be dissipating 48mW
> >> and everything will still be fine, except the light output will
> >> suffer.
> >>
> >> If we have two Vf max LEDs in the circuit it'll look like this:
> >>
> >>
> >> 9.0V-+---->E1
> >> |
> >> [250]
> >> |
> >> 8.0V-+---->E2
> >> |
> >> [DS1]
> >> |
> >> 4.0V-+---->E3
> >> |
> >> [DS2]
> >> |
> >> GND
> >>
> >>
> >> and the current in the circuit will fall to:
> >>
> >> 1V
> >> I = ------ = 0.004A
> >> 250R
> >>
> >> So, while everything will still be fine from a power dissipation
> >> viewpoint, the light output from the LEDs will be greatly degraded.
> >>
> >> Although it would be possible to fiddle with supply voltages and
> >> series resistances in order to come up with a solution which would
> >> allow a greater light output without overdriving the LEDs
regardless
> >> of the Vf spread, It would be more practical, IMO, to drive them
with
> >> a constant current.
> >
> >So there we have it, the OP has been proven wrong. His LED's could
not
> >have possibly failed.
>
> ---
> But since there _was_ a failure, if LEDs with the range of Vf's you
> said was possible were hooked up as shown and the supply voltage and
> series resistance were as shown, it would have been impossible for an
> overcurrent situation to cause one of the LEDs to fail, so _your_
> analysis of the failure mode was in error!

Oh, obviously. Yes they died after a time, but it had nothing to do
with too much dissipation. We know that, because the data*** is the
end-all authority on the reality of any situation and that all parts
meet specs. Well, I'm sure glad that's finally settled.

> In all fairness, though, I don't recall what the situation surrounding
> the failure was or anything about the circuit other than that it was a
> couple of LEDs hooked up in series with a current limiting resistor of
> some kind and a power supply. If you can supply the details we can
> get to the bottom of it.

You have access to the same material as me.

> ---
>
>
>
> >> We've already covered that.
> >
> >Yes, I'd agree that we buried your civility a good while ago.
>
> ---
> Not bad...
>
> --
> John Fields
> Professional Circuit Designer

.