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Kitplanes article on an Elegant LED driver

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Brantel

Joined: 23 Aug 2008
Posts: 53

Posted: Thu Aug 28, 2008 4:05 am Post subject: Kitplanes article on an Elegant LED driver

I took a look at the new kitplanes article on how to build an elegant LED driver for aircraft.



Up until now I have been planning to use an off the shelf cheap constant current power supply from LEDDYNAMICs.   But people are reporting everywhere that these things are trashing the aircraft radios with RF noise.



That being said, what if any advantages would the kitplanes article driver have over one of these off the shelf drivers and would the noise problem still exist with that driver as well?



From looking at the circuit, it looks similar to what one might think the LEDDynamics one would look like inside.

echristley(at)nc.rr.com
Guest

Posted: Thu Aug 28, 2008 5:03 am Post subject: Kitplanes article on an Elegant LED driver

Brantel wrote:

 	  Quote: 	
		   That being said, what if any advantages would the kitplanes article driver have over one of these off the shelf drivers and would the noise problem still exist with that driver as well?

   

Education.

david.nelson(at)pobox.com
Guest

Posted: Fri Aug 29, 2008 5:37 am Post subject: Kitplanes article on an Elegant LED driver

Hi Bob,



I'm curious, why is such a high freq (1-2MHz) needed for an application 

such as this?  Rather, why not in high 100's of Hz given that the eye 

can't even discern above 30 Hz?



Thank you,



 	 /\/elson



~~  Lately my memory seems to be like a steel trap .... without any spring.  ~~



On Thu, 28 Aug 2008, Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   <snip>

 http://www.national.com/ds/LM/LM3404.pdf



  This is one of a host of similar one to multi-channel dimmer

  controllers. The 3404 delivers up to of constant current

  to it's companion loads.



  It's a switcher. It hums at 1 to 2 Mhz with a butt-ugly

  wave-form rich in harmonics. This device needs to be

  a very compact layout (small antenna aperture) and be fitted

  with conduction filters on the input/output wires. It

  MIGHT be okay in a plastic enclosure . . . but a metal

  one never hurts.

 <snip>

echristley(at)nc.rr.com
Guest

Posted: Fri Aug 29, 2008 6:11 am Post subject: Kitplanes article on an Elegant LED driver

David E. Nelson wrote:

 	  Quote: 	
		   

 <david.nelson(at)pobox.com>

 Hi Bob,



 I'm curious, why is such a high freq (1-2MHz) needed for an 

 application such as this?  Rather, why not in high 100's of Hz given 

 that the eye can't even discern above 30 Hz?



100's of Hz will put you in the audio range and possibly give a humm in 
	


the audio portions of the airplane.  Somewhere just above 30KHz would 

seem like the best frequency range.

david.nelson(at)pobox.com
Guest

Posted: Fri Aug 29, 2008 7:38 am Post subject: Kitplanes article on an Elegant LED driver

Hi Ernest,

Ok, 30KHz makes sense.  Although 30Hz may not be within the dynamic range 

of the audio equipment, I could definately see a square wave's odd 

harmonics (90 Hz and 150 Hz, etc IIRC) reaching up into a sensitive audio 

area.  Interesting.

So now, why the MHz freq the LM3404?

Thank you,

 	 /\/elson

~~  Lately my memory seems to be like a steel trap .... without any spring.  ~~

On Fri, 29 Aug 2008, Ernest Christley wrote:

 	  Quote: 	

 <echristley(at)nc.rr.com>

 David E. Nelson wrote:

> 

> <david.nelson(at)pobox.com>

> 

> 

> Hi Bob,

> 

> I'm curious, why is such a high freq (1-2MHz) needed for an application 

> such as this?  Rather, why not in high 100's of Hz given that the eye can't 

> even discern above 30 Hz?

> 

 100's of Hz will put you in the audio range and possibly give a humm in the 

 audio portions of the airplane.  Somewhere just above 30KHz would seem like 

 the best frequency range.

echristley(at)nc.rr.com
Guest

Posted: Fri Aug 29, 2008 9:39 am Post subject: Kitplanes article on an Elegant LED driver

David E. Nelson wrote:

 	  Quote: 	
		  

 So now, why the MHz freq the LM3404?


	


I think Bob answered that well.  Switching power supplies have an easier 

time of it at higher frequencies.  The power supply in the back of your 

computer converts the 60Hz line signal up to something like 10KHz (IIRC) 

for the same reason.  It is much easier to transform and then rectify a 

higher frequency signal to a clean output.  The components can be much 

smaller and there is less heat generated.

david.nelson(at)pobox.com
Guest

Posted: Sat Aug 30, 2008 5:29 am Post subject: Kitplanes article on an Elegant LED driver

Hi Ernest,

My apologies. My intention was not to loose site of the original question 

should this be read years from now in one of the archives. 

Take care,

 	 /\/elson

~~  Lately my memory seems to be like a steel trap .... without any spring.  ~~

On Fri, 29 Aug 2008, Ernest Christley wrote:

 	  Quote: 	

 <echristley(at)nc.rr.com>

 David E. Nelson wrote:

> 

> So now, why the MHz freq the LM3404?

 I think Bob answered that well.  Switching power supplies have an easier time 

 of it at higher frequencies.  The power supply in the back of your computer 

 converts the 60Hz line signal up to something like 10KHz (IIRC) for the same 

 reason.  It is much easier to transform and then rectify a higher frequency 

 signal to a clean output.  The components can be much smaller and there is 

 less heat generated.

david.nelson(at)pobox.com
Guest

Posted: Sat Aug 30, 2008 5:33 am Post subject: Kitplanes article on an Elegant LED driver

Hi Bob,

Thanks for the great explanation - as usual. 

Do not archive.

Take care,

 	 /\/elson

~~  Lately my memory seems to be like a steel trap .... without any spring.  ~~

On Fri, 29 Aug 2008, Robert L. Nuckolls, III wrote:

 	  Quote: 	

 <nuckolls.bob(at)cox.net>

 At 08:31 AM 8/29/2008 -0500, you wrote:

> 

> <david.nelson(at)pobox.com>

> 

> 

> Hi Bob,

> 

> I'm curious, why is such a high freq (1-2MHz) needed for an application 

> such as this?  Rather, why not in high 100's of Hz given that the eye can't 

> even discern above 30 Hz?

> 

> Thank you,

>

>         /\/elson

 Great question. The problem of selecting an operating

 frequency comes from a trade-off in reactances . . .

 in the form of inductors and capacitors. The higher

 you go in frequency, the more energy can be stored on

 a given size inductor (assuming the core is loss less).

 The higher you go in frequency, the easier it is to

 couple energy via capacitors . . . both for the purpose

 of bypassing and transfer.

 In this case, the power supply is an energy conversion

 system that stores a short pulse of current on and inductor

 and then retrieves that energy at a different voltage level.

 Given no other considerations for efficiency of the switching

 devices and losses in the magnetics, one would LIKE to operate

 at the highest possible frequency to drive down the physical

 size of components.

 Example. Step down transformers for 60 Hz AC delivered to

 the house can handle about 60 watts per pound of transformer

 core and copper. Airplanes use 400 Hz and the same transformer

 weight and volume can handle over 6 times the power  . . .

 but the iron for the transformer must be tailored for low

 losses at the higher frequency.

 The high output LEDs need about 4v per lamp (whites) but

 they're CURRENT driven devices. The really cool thing about

 switchmode power supplies is that you can take energy in

 at voltages in a much below or above the desired output

 levels and bring the energy out as either a constant current

 or constant votlage. The LM3404 is designed to operate in

 the constant-current mode.

 Batteries are not constant voltage devices . . . so the

 most efficient flashlights will have a rather sophisticated

 voltage to constant current generator that accepts battery

 voltage over the full range useful output and delivers

 a constant current to the lamp until the batteries are

 truly drained. These converters need to be tiny and

 efficient . . . highest practical operating frequency

 is a strong consideration in meeting design goals.

 Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Aug 31, 2008 9:44 am Post subject: Re: Kitplanes article on an Elegant LED driver

My two cents....



I think Jim Weir was not well-advised in publishing his article.  There are tons of DC-DC converters available for less than what it would cost you to build one, even if you forget the bench full of test gear and the years of education, and the labor required to do this job well. 



My advice--



1) Buy the supply if you need one. www.Astrodyne.com,  etc. or Google "DC-DC switcher supply"

2) Don't use a switcher supply if battery voltage DC will do. 

3) If you really MUST make one, sign onto National Semiconductor's Web Bench where they will design a supply to your specs, component list, PCB layout and all. 

4) This is not a job for the amateur. Switchers supplies are hard work, especially the quiet ones.  Here's a free million-dollars-worth of education--"Spend the extra money for a four-layer PCB". 

5) The fact is that the LED will almost certainly last longer than the power supply. This should give one pause....



"Inventor: A person who makes an ingenious arrangement of wheels,

levers and springs, and believes it civilization."

           --Ambrose Bierce

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

rgf(at)dcn.davis.ca.us
Guest

Posted: Sun Aug 31, 2008 2:06 pm Post subject: Kitplanes article on an Elegant LED driver

I fully agree.  Describing this is the same as a handyman magazine

describing how to design wall studs.  Huh?  As a kitplane builder I don't

want to design and build fundamental electrical/electronic devices.  If I

did I'd be subscribing to ARRL or similar.



Instead, Kitplanes should have electrical articles that either describe

basic technique (for the steady stream of beginners) or higher-level issues

like connecting displays/autopilots/GPSs, maybe some of the APRS stuff,

maybe electronic ignitions...



Given Mr. Weir's well-deserved reputation as an abusive hot-head in public

forums, and his poor reputation as a seller in VAF, maybe Kitplanes should

consider someone else writing the electrical articles.  Bob?



Ralph Finch 



--

mrspudandcompany(at)veriz
Guest

Posted: Mon Sep 01, 2008 10:18 am Post subject: Kitplanes article on an Elegant LED driver

<nuckolls.bob(at)cox.net>



At 10:55 PM 8/31/2008 -0400, you wrote:

 	  Quote: 	
		  

<jimw_btg(at)earthlink.net>
	


 	  Quote: 	
		  

I had a conversation with an engineer from the mfg of the Buck Puck and

the very first thing he suggested is to package the PWS in a

container.  Just going to try this?  Hope he is right.


	


   That's half the battle. Containers provide (1) attenuation

   of radiated emissions and (2) ground reference for line filters

   to attenuate conducted emissions.



   A metallic enclosure MAY be necessary. Line filters are

   the first thing to try. That's why I asked if the noise

   conduction path had been identified in an earlier post. If

   the noises are noted coming in through the antenna on

   vor/com receivers, then the filters need tailoring for vhf

   frequencies . . . MUCH smaller/easier than audio/LF

   frequencies that plague other victims by conducting noise

   out on power lines.



   One observes by the packaging of the Buck Puck that it was

   not designed to be a stand-alone product but a component

   of a more comprehensive assembly. The elegant solution

   for integrating this device into airplanes is to built

   an adapter board that also mounts a d-sub connector.

   The line filter components can be assembled on the board

   along with the connector and power supply.



   Once the filter components are wired in, you can test to

   see if the noise went away. If not, mount the assembly in

   a metal enclosure where the 'ground' side of the filters

   are connected to that enclosure.



   I'll lay out a board and get some WAG filter components

   ordered. I need to know if there is continuity between

   the LED- and Vin(-). If you can get me this bit of

   info, I'll finish the board layout and get those ordered

   too. Also, do you plan to use the CONTROL or REFERENCE

   features of these devices?



If you are going to build a board, it would be good to keep all options

open.



Roger

   Bob  . . .

Brantel

Joined: 23 Aug 2008
Posts: 53

Posted: Mon Sep 01, 2008 11:17 am Post subject: Re: Kitplanes article on an Elegant LED driver

Bob,



I am using the simple 4 wire version of the buck puck and do not intend to use the control or reference functions but it would be great if those "could" be used on this rig in the event someone wanted to strobe/dim/on-off control these things for other applications in the plane.



I checked the continuity between the Vin Minus and LED minus and it does have 100% continuity both directions (diode mode not required on meter).



I also checked the current on the input and it was 460mA (at) 12vDC using a wall wart powersupply.

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