Driver for luxeon leds

I agree with Adam that you should use a current source or at least a current regulated power supply instead of a voltage source. However, that does not explain why your current system will not flash.

Does it not turn off or does it not turn on? Also, how are you flashing the LEDs? Do you drop the voltage to 0 when they are supposed to be off? Can you describe the circuit you are using?

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail: 
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

Your thinking voltage when its better to think current. Vf of LEDs can be fairly variable, wireing then is series is fine, but you want to think of

350mA roughly at whatever the Vf settles at.

1W LS will take up to 1A at low duty cycle, look up the data sheet at Lumileds , there is an application sheet for using them as a flash for mobile phone cameras.

400mS is possibly a bit long tto go as high as an amp for longetivity but genuine Stars will take a suprising amount of abuse.

Look to use a constant current driver not voltage though.

Adam

"booth multiplier" schreef in bericht news: snipped-for-privacy@posting.google.com...

You treated the LEDs like resistors which they are not. According to the manufacturers information you always has to use a series resistor to limit the current through the LEDs. Look at:

for instance. As LEDs are current driven devices you'd better look for a current source. See simple schematic below. The 350mA you mentioned is the maximum current the LED can handle without being damaged. With a lower current the light production will slightly decrease but the life expectance of the LED will be much better. Another important thing is temperature and heat production. Too high a temperature will also decrease life expectance of the LED or may even damage it. The example below has only two LEDs but you can add more if you increase the supply voltage accordingly. T2 and R3 make up the on/off switch. A 5V on R3 removes the base current from T1 so its collectorcurrent vanishes and the LEDs go off.

+------+ 9V | | .-. V | |R2 - LED | | | '-'1k5 | | V | - LED | | | | | | | | +-----------+ |/ T1 | +----| BC635 | | |>

| Si V | R3 | - | ___ |/ T2 | .-. -|___|--| BC546 | | |R1 4k7 |> Si V | |2.2 Ohm | - '-' | | - ---------+-----------+------+ GND created by Andy´s ASCII-Circuit v1.24.140803 Beta

petrus bitbyter

--
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.802 / Virus Database: 545 - Release Date: 26-11-2004

the

limit

source.

current

light

will be

production. Too

may even

you

collectorcurrent

First off, he said 8 LSes in series, yours shows only 2 and 9V supply. For more than 28V at more than 1/3 amp, I would say that the BC635 will quickly butn up. You need a TO-220 type transistor like the TIP31 on a heatsink. The two diodes should be 1N4002 or better. Remember these Luxeon Stars are $15 or so apiece! If you give him the wrong advice and they burn up, that's well over a hundred dollars!!

"Watson A.Name - "Watt Sun, the Dark Remover"" schreef in bericht news: snipped-for-privacy@corp.supernews.com...

You're really quick with your comment but did you read what I wrote? I gave an example, not a full fledged design. The components in the example are used within the specs. If you really think I'am wrong, prove it. Nevertheless, if you want to stay on the safe side a power transistor may have its use, but a heatsink for less then 0.5W seems a little bit exaggerated to me. Both power transistor and heatsink are only required if you want to increase the power voltage wihout adding LEDs in the collector chain. I also wonder what special properties requires the 1N4002 or better. Why should a 1N4148 (for instance) not be good enough?

petrus bitbyter

--
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.802 / Virus Database: 545 - Release Date: 26-11-2004

series.

series

to

ON

OFF,0.4sec

flashing?

supply.

will

on a

these

advice and

I

example

transistor may

required if

collector

This circuit doesn't have very good current stability to start with. The LED current depends on the forward voltage drop across those two diodes; this Vf changes with temperature. Using heftier diodes with greater dissipation will give some improvement in stability.

Nope. I've been installing a PBX all day today, Neg 48V (more like -56VDC) all over the place. Ten gauge wiring, etc. Each phone line has enough current, maybe 150mA, to make a nice blue spark when you short it. Scares the hell out of some of the contractor's techs. I get a kick out of seeing them go "WHOA! What was that?" when that happens!

=:-O

I was using four 1N4002s and maybe a 1N5818 schottky in series for a dummy while I was experimenting with my LSes. Better safe than sorry at that price.

[snip]

better

supply)

stability a

by

I'm sure

in the

have

Yeah, the following commonly seen circuit, posted here many times by myself and others, is used more often than the above because it's more stable, but still not very good. As with your circuit, it has to be scaled up in current and power to meet the 350 mA needed for the Luxeon Star. Use a BD135 or TIP31 for Q1, on a heatsink if it gets too hot to touch. And the 10k to 47k needs to be lower also. With the 33 ohms changed to 2 ohms, it should give about 300 mA.

You can also use the LM317 as a current limiter, see the circuit in the datasheet.

+--------------------+------- Positive | | Supply V. | | | --- LED 10k / =====>

to 47k / === ohms | / | | / Q1 | | / Gen'l | | Purp NPN +----------------| 2N3904 or | | 2N2222A | | E Q2 Gen'l | | Purp NPN | 470 ohms | 2N3904 or |------///----+ 2N2222A | | E / | | / | 33 ohms / | for | 18ma / | | | | | | +---------------------+------- Negative Supply V.

"Watson A.Name - "Watt Sun, the Dark Remover"" schreef in bericht news: snipped-for-privacy@corp.supernews.com...

This circuit does not have a very good stability. But IMHO it's much better then connecting the LEDS in series to a battery (or other power supply) without any current limiting at all. If you want to improve it's stability a little bit you'd better first increase the current through the diodes by lowering R2 then use beefier diodes. But why make things difficult? I'm sure you can calculate and measure the variations in the LED current due to temperature changes but I doubt if you will *see* that as variations in the light with the naked eye. If you nevertheless want more control you'll have to make a different design. Maybe you have a proposal?

petrus bitbyter

--
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.802 / Virus Database: 545 - Release Date: 26-11-2004

I built a current regulator based on an LM2941 that drives one Luxeon with about 270MA from 4.2 to over 18V (as high as my bench supply goes). It's got an on/off pin that you can use for logic-level control.

[I'm building a solar powered beacon, with a PIC for control,, but don't hold your breath. 8*]

Why should it flash slowly? Using your circuit the LED will be on for one half cycle and off for the other. So, in Europe it will flash 50 times a second, in NA 60 times a second.

Any LED will flash if used on a "flashing" power supply.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail: 
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

In message , petrus bitbyter writes

I built a mains power supply for a Luxeon star as follows:-

Live / hot -------------- | | O 40 watt light bulb. | |--------------------| V luxeon A 1N4007 diode |--------------------| | | Neutral / return -----

It lights, but doesn't flash like Luxeons are meant to. At least it's not flashing slowly. It appears to be flashing very quickly at a speed that only registers with peripheral vision.

Have Luxeon had a bad batch of their LEDs or do I need to use a different light bulb? A friend says that Luxeons don't flash, but I've seen them do it in cheap disco lights so he's just talking complete rubbish.

--
Dick Endaway.

Pro electronic services for disco's done cheap.

Are you talking about these? I believe they are meant to flash at a high rate...

Now, your bulb thingy will work, but the initial current will be painful. Light bulbs start out with a very low resistance, which quickly increases as the bulb heats up. See

Thus, your luxeon is being subjected to hideous currents when you flip on the light. I just measured the resistance through an 'off' 100W light bulb (USA). The resistance was 10.3 ohms. Now, if you put 120V across

10.3 ohms, the current will be 120/10.3 = 11.65A

Once it heats up, the resistance will go up to 120^2/100 = 144 ohms. That is more than a 10x increase in resistance.

You might be able to snub the initial rush of current using a soft-start device, as outlined in Don Klipstein's tutorial given above. However, I guess it would be easier and safer just to use a 5V wall wart.

--
Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

ask Linear Technology for Application Notes and Driver circuits for Luxeon LEDs, Maybe LT1618 and LTC3441 do the job for portable Battery systems with torch and Flash functionality.

I recently designed a driver for Luxeon III, about 3400 of which are now being installed on the pyramid shaped Luxor in Las Vegas. I used the National LM2592-ADJ, with a current feedback for 850 ma Each driver is for 2 in series, but it can work with 8. Across the 2 in series is a 220 uf cap. The feedback resistors are not bypassed. There is also a 5K resistor across each LED pair to make them turn off quickly. If this is omitted, there is a visible fading "afterglow" effect as the cap discharges slowly.

The circuit turns on/off in a few millisec. Supply voltage should be more than 20% over the load voltage (this app uses 42 v anf the "HV" version of regulator)

Charles