Someone could help me building a circuit to drive some leds?
The leds are the Osram golden dragon plus white.
If I use a 2n2222a transistor to regulate the power to the leds, driving the transistor from the arduino pwm, should it work? or I will blow up?
Show your circuit including supply voltage.
And provide a link to the LED you intend to use..
I found an [u]application note[/u] for your LED.
LEDs require a constant current (or controlled current) source. With regular "small" LEDs, you can use a current limiting resistor, but that's not normally done with high power LEDs because it requires a power resistor that wastes heat and energy.
Normally, high-power LEDs are driven by a special-purpose switchmode constant-current supply. You can buy or build one, but they are tricky to build.
The whole "thing" is powered by a 12v 60w 4A power supply. Then there is a 3.3v 10A step-down that send the power to the leds. There are 8 leds placed in series each one with its transistor.
It still need that constant current supply?
Should I put a 1w resistor before (or after) the transistor?
It still need that constant current supply?
Yes.
Should I put a 1w resistor before (or after) the transistor?
No.
You need a constant current supply.
Any recommendation for those constant current supply?
Something like this could work?
congarou:
Any recommendation for those constant current supply?Something like this could work?
http://it.rs-online.com/web/p/regolatori-di-tensione-lineari/5338209/
Yes, if you connect it up right. Since it's a linear regulator, you will need to be careful of heat dissipation, same as the LED itself.
The heath dissipation it's handled by a aluminum board. for 8 leds there is a 45 cm board.
I've made a test with a single leds with my system and it worked, the led lights up, should I still going for the linear supply? I need 80 leds so it would be a bit expensive.
I trust everybody on this but I'm really interested on understanding why I need the linear regulator even with the 3.3v step down already in place.
Thanks a lot for the replies!
The linear regulator is used to make a constant current supply. You will need a constant current supply and the linear regulator in the circuit will get very hot. It will need its own heat sink.
congarou:
The whole "thing" is powered by a 12v 60w 4A power supply. Then there is a 3.3v 10A step-down that send the power to the leds. There are 8 leds placed in series each one with its transistor.
8 LED's in series would require a 16 V supply.
If they are in parallel each LED will need it's own regulator
I reiterate this.
Boardburner2:
Show your circuit including supply voltage.
It sounds like you want an 8 x 10 display but we are not clairvoyant.
The solution could have variations depending on what you are trying to do.
Hand draw your proposal and post a photograph.
You may have to take a step back and find another power supply for this depending on what you are trying to do.
So, I've attached a (very) poorly made idea of what I'm thinking.
There should be two of this (8 controlled by the pwm and 8 controlled by the digital) one board should have one led that lights up when the sequencer hit a certain step (1-8) and the other should have every led on with variable intensity depending by the value of the certain steps.
Hope it's clear.
Look you have been told many times and you seem to be ignoring us.
For the last time
YOU NEED A CONSTANT CURRENT SUPPLY - WHAT YOU HAVE DRAWN IS CRAP AND WILL MELT THINGS
Although Mike says it a bit Grumpy 
he is right. You need a led driver for each led. And if you want to power it from 12V I would use a switching led driver like this.
And although it might not be broken out to pins on this one, most of those led driver chips have some sort of dim or enable pin which you can use to dim them.
Yeah, I don't really give a fuck about the rude reply of Mike, thing is I'm not ignoring no one, I've attached my "old" scheme just to explain better what I had in mind, actually I'm really grateful for all the replies (although I would end up in flames), if some member don't understand that why I'm on the forum seeking for help is because I don't really understand what I'm talking about and just want to be rude and insult some noob like me is not my problem.
What should be the circuit to modulate the led trough pwm with a constant power supplier? Some one can make me a quick draw?
In the end I would like to understand why those kind of led need that circuitry (and when and when not utilize it) and what kind of dissipation I would need, since on the same board there would be 8 leds and 8 linear supplier and everything will go in a wooden case and I don't really know what kind of heath all those things can produce.
Thank you all (even Mike) for the help!
congarou:
What should be the circuit to modulate the led trough pwm with a constant power supplier?
Missed a part?
septillion:
And although it might not be broken out to pins on this one, most of those led driver chips have some sort of dim or enable pin which you can use to dim them.
congarou:
In the end I would like to understand why those kind of led need that circuitry (and when and when not utilize it)
A led ALWAYS needs some sort of current driver. For small leds a resistor will act like one and it's all fine. But, when the current goes up that approach isn't that great anymore. If you try to use a resistor for a higher power led to 12V is will regulate nicely but the resistor will dissipate a multiple of what the led does... Not really that great. And if you lower the voltage you apply to the led + resistor to let's say 5V (and pick a new resistor to match) you indeed use less power in the resistor (but still much) but now the current will change a lot when the voltage or resistor value changes a tiny bit. So not great either.
congarou:
and what kind of dissipation I would need, since on the same board there would be 8 leds and 8 linear supplier and everything will go in a wooden case and I don't really know what kind of heath all those things can produce.
Your led's are 1W leds and will produce roughly 1W of heat (simple isn't it). Which is already 8W you have to cool.
But DON'T go linear for the drivers. 8 x 350mA x (12V - 3V) will give you 25,2W!!!! you have to cool for the drivers alone. No way you will be able to do that in a wooden box without fan. And of course is ridiculous for driving just 8W of led.
I was thinking about modulating the linear drivers, but if you recommend a led driver directly (which make sense) I would go for that.
Something like this?
One for every single led?
Nope.
For starters it's a boost converter. Aka the output voltage is higher then the input. You have the other way around so you need a buck converter.
Second, good luck soldering WDFN packages...
And then the problem being that designing DC-DC converters is kind of a dark art (or at least has tons of pitfalls). And if you don't know why to use a switching led driver then you're certainly not up to the task of designing a DC-DC converter. Just buy an off the shelf one (like I linked) and use that.
Yep, I saw your link but they are some led spot, doesn't seems that have any kind of modulation and last but not least I need it quickly, I just a couple of days available for having that leds working I can't wait 44-59 days.
No problem for soldering I have a factory here that just wait for my files to produce the boards.
I can pay if anyone on this forum is able to create me a project for those.
congarou:
Yep, I saw your link but they are some led spot,
No, that's just an example.
congarou:
doesn't seems that have any kind of modulation
Replay 12 and 14 anyone?
congarou:
and last but not least I need it quickly, I just a couple of days available for having that leds working I can't wait 44-59 days.
Yeahh, then sorry, I can't help you. Although I know some companies sell them as modules I don't have a clue about them. And I hope you do know the famous triangle?
congarou:
No problem for soldering I have a factory here that just wait for my files to produce the boards.
Board production != board assembly. But if you let them assemble it for you as well then I guess money isn't a issue 
congarou:
I can pay if anyone on this forum is able to create me a project for those.
There's a forum section for that
You can use 10 current regulators AMC7135:
powering at 4.5~5Vdc.