Superflux LEDs - questions

[cantfindausername]

Hi all,

I've been pointed to some Superflux LEDs for another attempt as some custom rear/tail lights for my car.

These are the ones I've bought...

**broken link removed**

and the spec...

Source Material: AlGaInP
Emitting Colour: Red
Emitting Wavelength (nm): 620-630
Size: 7.62 x 7.62
Intensity (mcd): 1500-2500
Viewing Angle (deg): 100
Forward Voltage (mA): 1.8-2.4
Forward Current (V): 20-30

I'm a little confused about the 4 pin configuration of these LEDs.

Can someone advise on how they're connected to a normal vero board, and if I will be able to run them on a cars power supply?

Thanks,
Ant

 

[Andy1845c]

Hey Ant,

If you look closely at them you will see that the 2 pins on each side are connected internally. So you don't have a 4 pin LED, it still has 1 anode and 1 cathode like a normal T1 package LED. The 4 pins just help support it and probably help dissapate a small amout of heat. You can use an ohm meter and figure out what pins are bonded together if you can't tell visually.

You can use them with a 12v supply. You need to add current limiting resistors. And keep in mind the voltage of a running car is around 14-15v and can have nasty spikes in it. Do a search here on LED tail lights. There are alot of topics on them.

 

[cantfindausername]

Thanks Andy. I had noticed that the 4 pins were in 2 banks of 2. I wasn't sure why this was though so thanks for clearing that up for me.

Ok, I think I've figured out why things look so wrong. I copied the Tech Spec above from the advert on ebay. And I believe they have :

Forward Voltage (mA): 1.8-2.4
Forward Current (V): 20-30

around the wrong way. It should be:
Forward Voltage (V): 1.8-2.4
Forward Current (mA): 20-30

My calculations seem to make a bit more sense using these figures

if 3 LEDs use 360ohm 0.25w resistor
if 4 LEDs use 220ohm 0.25w resistor
if 5 LEDs use 120ohm 0.25w resistor

I've seen something about running at 12V using voltage regulators. Is this something thats worth looking into?

 

[Andy1845c]

That is a large spread for the Vf. I would measure a bunch of your LEDs and see what it really is. If each one measures different I would try and put them into like groups.

To measure the Vf, size a resistor for 1 led at the current you want. Then hook it up and measure the voltage on each side of the LED with a multi-meter.

Its really hard to get a stable 12v in a car. A voltage regulator needs a little more voltage on its input then its output, and a cars voltage can swing from 11.5v when the car is off, to over 14v when its running.

I made an LED project where I regulated the voltage at 9v. It allowed for a steady voltage at all times, but whe the supply is 14v, the regulator has to drop 5v and gets hot.

Do a search here, theres alot of different oppinions on the LED/car topic.

 

[cantfindausername]

Thanks again andy. I will do the measurements you have stated above, and have another search around on the topic.

 

[MrDEB]

led resistor caculator

here is a pretty simple led/resistor caculator that I use.
as far as a voltage regulator-yes to be safe use one.
put a heat sink on it. not sure if a 7812 will be right - need somewhere around a 2-3 volt difference for the regulator to work right.
not sure if a 9v regulator is even made?
good luck

 

[MrDEB]

oups forgot to paste

LED Resistor Calculator

 

[Andy1845c]

The LM7809 is a 9 volt positive regulator. Good luck trying to buy a small quantity though. I just used a LM317 set up for 9 volts. There are better choices for automotive use though.

 

[cantfindausername]

Thanks guys. I will do some digging around and see what I can find. I'd normally check what I'm doing before I start so will be back before long no doubt!

 

[MrDEB]

lm7809 = .26cents

no problem on buying them
at 26 cents each for one
lm7809

 

[HarveyH42]

One corner is notched, with the leads pointing down, and the notched corner to the lower right, the top two leads go to positive, lower got to negative. Would strongly suggest a constant current source, instead of a resistor, they fry easy. Least the ones I get from Hong Kong do. If you run them as specified, they work well. Should also share a past experience... Before I got the notch thing, I used a fairly dead 9 volt battery to briefly check which way to plug them in the PCB. Mistakenly grabbed a fresh battery once, the lense blew off, bounced off the 8' ceiling with considerable force. Figured you should know, or you might put out an eye or something.

 

[Andy1845c]

no problem on buying them
at 26 cents each for one
lm7809

Huh.... well there ya go. Cool!

 

[audioguru]

Philips Luxeon make SuperFlux LEDs, they are not a cheap Hong Kong copy. You should look at the datasheet, not at some error-prone sales sheet from E-Bay.

The max forward current is ... never mind, yours are a cheap Chinese copy because your spec's are completely different from the spec's from Philips Luxeon.

I have 36 Philips Luxeon SuperFlux red LEDs in a plastic case of a compact cassette tape. They are soldered to Veroboard. They operate at 53mA (they are spec'd at 70mA continuous max in a 25 degrees C ambient with plenty of copper around the cathode pins).
Boy oh boy oh boy they get hot. I drilled many holes in the top and bottom of the case and mounted feet on the case but they still get very hot. I had two white LEDs in there and they turned into dim blue in two days. The yellow phosphor disappeared.
It is a night light that lights a fairly long hallway.

Good luck with your cheap Chinese copies.

 

[cantfindausername]

I guess I would need to get the LM7809CT as it will work down to -40'C?

Harvey, thanks for the warning. I will definately bare that in mind.

audioguru, I will stick with my omg super cheap ebay hong kong specials until I find a good enough reason to fork out the extra money on expensive LEDs. While I'm testing and practicing though Chinese Cheapese will do.

 

[cantfindausername]

Just been looking into this a bit more. The 9v regulator, would i need 1 of them for each "string of 3(or4) LEDs? Or could I just use 1 and then patch a 9v from that to multiple strings of (3 or 4) LEDs for instance?

 

[audioguru]

I received hundreds of genuine Philips Luxeon SuperFlux LEDs for free from a nice guy on another website for helping him design a project.

The LM7809 has an output current of up to 1A if you cool it enough.
You will make strings of 3 LEDs in series and in series with a 100 ohm resistor (if all the LEDs are about 2.2V) which is a current of 24mA. The LM7809 can power up to 40 of these strings for a total of 120 LEDs.

I hope your cheap LEDs do not all fail at the same time.

 

[cantfindausername]

Thanks for that. I'm still trying to understand how it all works to be honest, but the above information will give me a good enough idea to at least crack the soldering iron and give something a go.

What sort of thing do I want to look at for cooling the regulator?

I'm also hoping the LEDs don't fail, at all even. There is going to be a lot of bench testing before I even attempt to make a live version for putting on the car.

 

[audioguru]

I would never put cheap Chinese junk on my car, especially not lights.
I don't know how many LEDs you are using so I don't know how much current will be in the regulator. If it is half an Amp and the alternator is charging the battery at 14.4V then the regulator will be heating with (14.4V -9V) x 0.5A= 2.7W. A fairly large small heatsink should be used. Bigger than this little one:

 

[cantfindausername]

So to reduce the heat build up in the regulator, could I use a 12v regulator?

My thinking here is to stop the LEDs being fried when its producing >12v, but will just allow the lights to dim a bit when producing <12v, i.e when the engine isn't running?

 

[audioguru]

So to reduce the heat build up in the regulator, could I use a 12v regulator?

My thinking here is to stop the LEDs being fried when its producing >12v, but will just allow the lights to dim a bit when producing <12v, i.e when the engine isn't running?

The LEDs will dim a lot. The 9V regulator still works when its input voltage drops to 11.1V.
An ordinary 12V regulator starts dropping its output voltage when its input drops to 14V.
A low-dropout 12V regulator still works when its input is 12.5V.
With a 12V regulator then 4 red LEDs can be connected in series, then the resistor value will need to be re-calculated.