EN said:The learning curve. When someone asks how to turn on a LED.
There was a space constraint to the project box as I recall.
Most of everyone thinks of a DC source,1 resistor and the LED.
Simple enough. Someone posts the actual calculations, E=IR and
W=EI . Without knowing about E=IR or W=EI, you expect to jump
into Microcontrollers? Writing uC programs ?
How long will it be before you research about PICs, build or buy a pic
programmer, learn to program a PIC. There's a big jump between
a transistor battery and a PIC project, don't you think?
To run, you 1st got to learn to crawl & stand up.
EN said:The learning curve. When someone asks how to turn on a LED.
There was a space constraint to the project box as I recall.
Most of everyone thinks of a DC source,1 resistor and the LED.
Simple enough. Someone posts the actual calculations, E=IR and
W=EI . Without knowing about E=IR or W=EI, you expect to jump
into Microcontrollers? Writing uC programs ?
How long will it be before you research about PICs, build or buy a pic
programmer, learn to program a PIC. There's a big jump between
a transistor battery and a PIC project, don't you think?
To run, you 1st got to learn to crawl & stand up.
Yeah, and as the number of elements increase: gallium, indium, antimony,
aluminum, arsenic, rat poison...
And that doesn't even get into the various phosphors they use to get
white LEDs.
Make fun if you like, but it's way more power efficient than a resistor,
even if it's not cheaper.....yet. ;-) AFAIK, even an exceptional SMPS
couldn't do it any more efficiently. IME a nano-watt PIC running at
32kHz should be ~99% efficient driving the LED with at least 10mA
average current.
How difficult would it be to beat that using another method?
Anthony Fremont said:Whoa nellie, I didn't suggest the OP do any such thing. ;-) I was only
following up on Jim's comment about PICs.
I really wish that every mention of a PIC didn't have to result in this
statement. It's sorta becoming the Godwin's law of electronics. It's
almost like saying, "everything about electronics is worth learning, no
matter how difficult or expensive, as long as it doesn't involve micros
because they are too hard and too expensive". At any rate, I didn't
suggest using one for the OP's problem, I only mentioned that it could
be quite efficient, as a response to Jims comment.
I wasn't looking to beat that dead horse again, I was only hoping that
someone could/would (if possible) show me something more efficient using
"conventional" components.
Don Klipstein said:Also consider that voltage varies surprisingly little with
wavelength/color within a given chip chemistry. For example,
less-yellowish green LEDs and red ones of the same chemistry (InGaAlP,
or GaP) have surprisingly similar voltage drop.
One thing that does usually happen is that efficiency falls bigtime if
the wavelength gets shorter to an extent that has the photon energy in
electron volts exceeds the voltage drop in volts.
Phosphors don't affect the voltage drop...
Right, sorry if I may have caused any confusion.
But most white LEDs have blue LED chips and phosphor. So white LEDs
will have the same voltage drop as related blue ones.
I noticed that some white LEDs are now using wavelengths even shorter
than blue.
Watson A.Name - "Watt Sun said:It has _nothing_ to do with "..micros because they are too hard and too
expensive". What it has to do with is deception.
Deception. If there were money being exchanged, it could be called
something illegal, like fraud. But there's no money being exchanged.
The deceiver is advocating the use of something because it's his
fervent, almost religious, belief that it's _the_ solution to all of the
OP's problems. Which may be true.
But the deceptive part is that the deceiver has not told the OP (who is
usually a neophyte and probably knows little about electronics OR pics)
that there is a price he will have to pay in up front costs for the
hardware and software to program the pic. And there is a learning curve
that the OP must go thru to learn how to program and debug the software.
It is simply NOT Plug and Play!
I have nothing against using the right tool for the job. But it's
deceptive and unfair to tell someone to use something without telling
them what they will have to pay and what they will be going thru to
complete their project.
It just so happened that microcontrollers were the subject in past
discussions. Four decades ago it could have been using a laser as a
pointer for presentations. We all know nowadays that the little
hand-held ones do an excellent job. Back then, 40 years ago, you would
have had to blow your own glass, fill it with helium and neon, and use a
high voltage power supply to excite it. If a presenter could do all
that, he could then pull out his gatling gun sized pointer and look like
the termninator as he pointed to his presentation. But it would be
deceptive to not tell him that he would have to jump thru all those
hoops to get this cool looking presentation tool.
And there is *nothing* Godwinesque about it. Deception is deception.
Anthony Fremont said:"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com>
wrote in message news:117bk88qlcead6f@corp.supernews.com... [snip]
I have nothing against using the right tool for the job. But it's
deceptive and unfair to tell someone to use something without telling
them what they will have to pay and what they will be going thru to
complete their project.
One might also consider it deceptive and unfair for someone to suggest
that micros are as difficult and unreachable as you describe.
The primary difference being that your anology is absurd. Learning
micros or purchasing the needed equipment is no where near the
difficulty you describe. Ten or twenty hours of self study and $75 for
a programmer is not quite in the same league as ramping up to make your
own LASER tubes.
deception.
If there is nothing Godwinesque about it, then why is the same old tired
argument used to shout down the micro crowd every time?
One final time, I wasn't wishing to debate this topic (as it's like
talking religion or politics to some people), I was looking for some
"Anthony Fremont" <spam@anywhere.com> wrote
[snip]
One final time, I wasn't wishing to debate this topic (as it's like
talking religion or politics to some people), I was looking for some
clever analog or digital based current source that would be more
efficient. Any ideas? ;-)
wonder?mc said:I wonder why. I thought the voltage was related to the wavelength by a
basic law of physics. Is the internal resistance also increasing, I
They're making LED chips with a whole new and different chemistry.
Glenn said:Yeah, PIC or 555. They seem to be the solution to every problem.
But I thought the LED voltage corresponded to the energy level of the
photons... don't have the equation handy but can look it up. Hence my
question about whether the internal resistance is higher now. Maybe it is.
I know what the standard values. Some people have to shop at Radio Shack,
which has 220 but not 160 or 150 available singly.
Don ...
I've noticed this effect, also. Yet a hallowed source none other than HP
has a full chapter in AN-1005 describing how a pulsed drive increases the
optical output of the lamp. I either don't understand completely what HP is
telling me or my eyes are deceiving me, which is entirely possible.
Let's take a relatively trivial example. How about we generate a square
wave to drive our lamp. Let's not worry for the moment about how we
generate it, let's simply say that we can have either a square wave or a DC
signal for drive. Let's also make the math easy and say our LED has a
forward voltage of 2 volts at 20 mA and 2.5 volts at 40 mA (real data for
HLMP-1340, typical high brightness red LED).
So in the DC case, we choose a resistor value of 150 ohms, and in the square
wave case we choose a resistor value of 62 ohms. The battery doesn't care.
It is pumping out an average power of 100 mW in either case.
However, in the DC case, the (peak) power delivered to the LED is 40 mW and
in the square wave case the (peak) power delivered to the LED is 100 mW.
And yet, to my admittedly untrained eye, they are either the same brightness
or perhaps the square wave is just the littlest bit DIMMER than the DC
drive. What's happening? My understanding of optics is that the eye is
pretty much a peak detector when the PRF is greater than the flicker rate of
24 Hz. or so, but that isn't the case in the experimental lab. Comments?
Don Klipstein said:it is.
Voltage drop across the LED is often but not always close to that of the
"electron volts" of the emitted photons.
One thing that can happen is that when an electron "drops" from the
conduction band back to the valence band, it may have an intermediate stop
on the way down, causing the descent to have more than one step - one of
which radiates a photon that has less energy than that required to push an
electron from the valence band to the conduction band.
I suspect this is what happens in InGaN green LEDs, with voltage drop
well above the "electron volts" of their emitted photons even at 10% of
the current they were designed for.
Another thing that can happen is that factors besides bandgap energy
affect the wavelength of the emitted light. For example, the chip may
have layers of such thickness that have interference effects that
reinforce a particular wavelength. Of course, efficiency may be reduced
if this is a wavelength other than that at which the chip would otherwise
emit, especially if the wavelength has photon energy greater than the
bandgap energy.
Still another thing that could happen is that an electron has more than
one mode of descending from the conduction band to the valence band - a
radiating mode and a non-radiating one.
If the radiating one has average photon energy greater than the bandgap
energy, what happens is that most photons take the non-radiating path.
Thermal agitation gives a few electrons the above-average energy needed to
take the radiating route, but thermal agitation is actually detremental as
a net by causing what I believe is "thermal quenching" - kicking electrons
onto the non-radiating route. At lower temperature, fewer electrons take
the non-radiating route, and the voltage drop is higher.
Example: GaP and InGaP green LEDs. A really efficient one with
wavelength in the upper 560's or around 570 nm - the usual "chartreuse"
color - is about 1.5-2% efficient. The "pure green" varieties of these
chemistries (wavelength around 550-555 nm, still "lime green" as in less
yellowish but still yellowish) are much less efficient - and have average
photon energy around 2.25 eV and voltage drop maybe usually 2.1 V.
- Don Klipstein (don@misty.com)
