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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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 Posted: Sun Jan 27, 2013 10:23 am Post subject: LEDs |
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I have posted lots on this and there is always new interest. Some recent notes:
1) With regard to LED avaiation colrs, especially green, See: attached PDF--
redandgreenledpositionlights.pdf
2) With regard to LED beacons, See: aircraft_beacons_using_leds.pdf
Several cogent comments have been offered here regarding LED power supplies. My LED tail light, which (now) needs about 1A originally ran on the Luxdrive Buck Puck, but I couldn't make the power supply quiet (EMI/RFI) enough to work. The Buck Puck switch-mode supply I used was noisy because of poor design (or one might say unsuitable for my application). There are far better, far quieter supplies that you can build or buy, and let's hope Luxdrive makes some of them. Bob put in yeoman's effort to quiet the thing but by that time I had completely converted to an LM317 configured as a constant current supply. I wouldn't have tried to save the Buck Puck.
I published a simple LM317 LED constant current supply which you can build: See: Current Regulator.pdf This is carved into a little piece of copper circuit board, but I'll send you the ExpressPCB file if you email me.
See also a discussion of LEDs in series/parallel: http://forums.matronics.com/viewtopic.php?p=379712&sid=7400ff5dce844aff9fbcfd32e30328a8
So why do we need this complication to power an LED? And what's this Current Operated vs. Voltage Operated stuff?
Well, there's not much difference in operating a 10 milliAmp LED and a 1A LED except that connecting a 10 mA LED to 12V (12V*/.01A=1200 Ohms, and the watts dissipated is IxIxR=.01X.01X1200=0.12W). So the current limiting resistor is trivial, while connecting a similar 1A LED requires a really hot resistor of 12 Ohms >12 Watts. (12V/1A=12 Ohms and the dissipation is 1x1x12 Watts). Which will cost ~$20 and gets hot...and doesn't regulate the light output.
So the rule of thumb is when the current gets high, some non-resistive method of reducing the current becomes more attractive. These methods are few, and basically consist of electronically turning ON the power, then OFF real fast while storing some energy to be drained out to the load by a variety of clever methods. These are called "switch-mode". They all have the EMI/RFI problems generated by switching ON and OFF any other kind of circuit. A lot of engineering goes into making them as quiet as necessary, but no more than needed for a particular job. And the EMI/RFI specifications are complicated because frequencies and energy at those frequencies are peak, average, mathematically sampled, radiated, conducted, etc. etc. etc. One technique involves reducing the peak noise by spreading it around. Not a straightforward business.
*(Technical sorts will notice I simplified by using 12V instead of 14V-2Vf).
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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wynaire(at)citlink.net
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| Posted: Sun Jan 27, 2013 11:09 am Post subject: LEDs |
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Thanks Eric M J,
You (and others) have provided here a wealth of info that obviously will go
a long way to shortening the [my] trial and error period. Kudos to your
reply, your web page design and the info therein. Bach at you after I
"smoke" a few more LED's. 
Mike
Moab, UT
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Andrewjames
Joined: 28 Jan 2013
Posts: 2
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| Posted: Tue Jan 29, 2013 1:56 am Post subject: Re: LEDs |
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| wynaire(at)citlink.net wrote: | Thanks Eric M J,
You (and others) have provided here a wealth of info that obviously will go
a long way to shortening the [my] trial and error period. Kudos to your
reply, your web page design and the info therein. Bach at you after I
"smoke" a few more led bulb.
Mike
Moab, UT
*****************
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hello I need to buy led lights in bulk for my house. Any reliable source which can provide me best possible price
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Mon Feb 04, 2013 3:16 pm Post subject: Re: LEDs |
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One of the "Rich-man's problems" involved in designing and selling LEDs is that the technology is moving so fast, just as one cool device is ready to sell, it is obsolete.
Cree has recently announced a 200 lumen/watt LED and has published a reference design for an MR-16 design that is free to use and will almost instantly result in marketed products.
Not to be outdone, Phillips-Luxeon has released their Luxeon-M which has an enormous output (but lower efficiency than the Cree device) and furthermore works on 12VDC. It apparently will produce >1000 lumens at 12V 1000 milliamps. This is especially advantageous because it needs no (or a minimal) power supply for 12-14.5V systems.
As always YMMV.
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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Kimkest
Joined: 15 Feb 2013
Posts: 3
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| Posted: Mon Feb 18, 2013 3:14 am Post subject: Re: LEDs |
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| wynaire(at)citlink.net wrote: | Thanks Eric M J,
You (and others) have provided here a wealth of info that obviously will go
a long way to shortening the [my] trial and error period. Kudos to your
reply, your web page design and the info therein. Bach at you after I
"smoke" a few more led lighting.
Mike
Moab, UT
*****************
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Thanks for sharing detailed information about led lights. I really liked it
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