On Feb 12, 12:35 pm, Don Lancaster <d...@tinaja.com> wrote:
Ignoramus21592 wrote:

Well, you could have put some LEDs in series on that 12V, and create a
constant current source with some FET or transistor.
This is the classic low component count LED constant current source:

k a k a k a k a
|
|---
| |---
| | select
| [ ] R for 25 mA
| |

That's a great idea, very simple and elegant. Thanks.

Also very wrong.
The efficiency would be negligible.

Greetings Don!
Perhaps you missed that there were many LEDs in series? Although
not as good as a switcher, it would be many-fold better than a single
LED resistored to 12v.

On Mon, 12 Feb 2007 14:00:59 -0600, Ignoramus21592 wrote:
On Mon, 12 Feb 2007 10:12:28 -0800, Tim Wescott <tim@seemywebsite.com

Igor, juvenile hoodlums will thank you. Leaning out of a car window
clutching a baseball bat while going fast in the dark makes it very hard
to see mailboxes. Having one lit up by LEDs would be a blessing.

I know what you mean, but so far, all my mailbox accidents were NOT due to
juvenile hoodlums. They were due to people not knowing how to drive. Once
it was a snow plow, and another time it was some odiot who left his or her
car mirror lying next to the mailbox.

So much for bad humor:

A switching power supply would be the way to go. I doubt that any are
made specifically for LED supplies, and finding one that'll be efficient
at the low power levels you're looking at will be a challenge. So you
have your work cut out for you -- but you're known to be energetic.

Thanks Tim... I am still hoping that this is a standard problem...


I don't know where you live, but in snow country I've seen mailbox posts
set back 4-6' from the shoulder, with the box on a cantilevered arm, like
a fence gate. It stays in place by ordinary friction, or maybe there's a
piece of breakaway wire. This does two things - the snowplows don't plow
the post down, and if the box gets hit, it just swings out of the way.

So, I completed putting LEDs on my trailer. (LEDs are used to
indicate power and braking status) They are current limited by simple
500 ohm resistors, to approximately 25 mA. No big deal.

That made me think: most of the power to LEDs is wasted worthlessly in
those resistors. Only a small fraction of it is used to make
light. (my guess is about 85% of power is wasted)

Are there any LED driver kinds of chips that allow LEDs to be used in
a low power usage kind of situation (as opposed to running from a
truck alternator). That replace those resistors with something smarter.

The reason for my question is that I have a mailbox that used to be
often hit by vehicles. I have changed it to a higher visibility,
swingaway mailbox:

http://igor.chudov.com/projects/Mailbox/

but I would like to also add solar powered LEDs to it based on a WHY
NOT principle. (why not do it)

For this thing to work properly, it has to use as little power as
possible, so, I would like to know how LEDs are used in low power
situations.

i

Ignoramus21592 wrote:
So, I completed putting LEDs on my trailer. (LEDs are used to
indicate power and braking status) They are current limited by simple
500 ohm resistors, to approximately 25 mA. No big deal.

That made me think: most of the power to LEDs is wasted worthlessly in
those resistors. Only a small fraction of it is used to make
light. (my guess is about 85% of power is wasted)

Are there any LED driver kinds of chips that allow LEDs to be used in
a low power usage kind of situation (as opposed to running from a
truck alternator). That replace those resistors with something smarter.

The reason for my question is that I have a mailbox that used to be
often hit by vehicles. I have changed it to a higher visibility,
swingaway mailbox:

http://igor.chudov.com/projects/Mailbox/

but I would like to also add solar powered LEDs to it based on a WHY
NOT principle. (why not do it)

For this thing to work properly, it has to use as little power as
possible, so, I would like to know how LEDs are used in low power
situations.

i


Cat# SPL05 is a solar powered, 3 LED lite -
charges in daylight, turns on automatically
at night. $4.50
http://www.allelectronics.com/

I don't think you can beat that. Even if
it is less power efficient than some pulser
or switcher design, it's a cheap "done deal"
that seems to fit your needs. Besides it
provides the solar cell you'll need if you
build one.

Ed

So, I completed putting LEDs on my trailer. (LEDs are used to
indicate power and braking status) They are current limited by simple
500 ohm resistors, to approximately 25 mA. No big deal.

That made me think: most of the power to LEDs is wasted worthlessly in
those resistors. Only a small fraction of it is used to make
light. (my guess is about 85% of power is wasted)

Are there any LED driver kinds of chips that allow LEDs to be used in
a low power usage kind of situation (as opposed to running from a
truck alternator). That replace those resistors with something smarter.

On Mon, 12 Feb 2007 12:02:25 -0600, Ignoramus21592





ignoramus21...@NOSPAM.21592.invalid> wrote:
So, I completed putting LEDs on my trailer. (LEDs are used to
indicate power and braking status) They are current limited by simple
500 ohm resistors, to approximately 25 mA. No big deal.

That made me think: most of the power to LEDs is wasted worthlessly in
those resistors. Only a small fraction of it is used to make
light. (my guess is about 85% of power is wasted)

Are there any LED driver kinds of chips that allow LEDs to be used in
a low power usage kind of situation (as opposed to running from a
truck alternator). That replace those resistors with something smarter.

The reason for my question is that I have a mailbox that used to be
often hit by vehicles. I have changed it to a higher visibility,
swingaway mailbox:

http://igor.chudov.com/projects/Mailbox/

but I would like to also add solar powered LEDs to it based on a WHY
NOT principle. (why not do it)

For this thing to work properly, it has to use as little power as
possible, so, I would like to know how LEDs are used in low power
situations.

i

There are some chips made for the purpose but they tend to be hard to
find, costly, and are primarily for high power leds.

Easiest way to save some power is to just pulse the LED with a much
higher current for a much shorter duty cycle - or use one of the
flashing LEDs or get a hold of a LM3904 and use that to flash your
leds.

Solar powered - you'd want it to shut off while light outside.
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