What's the max voltage for a high powered LED?

I know these things need constant current but what would be the max voltage? I have a 3W and a 1W. Im trying to figure out if I should power them with 5V or 12V?

link the high powered led in question?

the data sheet will tell you the vF of the led/color..

and what max mA will be for it..

AllenI:
I know these things need constant current but what would be the max voltage? I have a 3W and a 1W. Im trying to figure out if I should power them with 5V or 12V?

It depends on the specific color type of led as they have different forward voltage drops, and if you are driving one led or wiring more then one in series. The constant current driver circuit will raise or lower it's output voltage to keep the current constant through the led(s). The CC driver's input voltage will have to be higher then that minimum amount.

Lefty

Here's the RGB:

and the white led:

the RGB page says:

Forward Voltage 2.5V/3.4V
Maximum Forward Voltage 2.8V/3.8V

(the 2.5v-2.8v is for the red die/led.... the 3.4v-3.8v is for the blue/green dies/leds)

350 mA for the green/blue.. and 400mA for the red led..

white says 3.6v for vF.. and MAX of 4.0v
750mA for the white

xl97:
the RGB page says:

Forward Voltage 2.5V/3.4V
Maximum Forward Voltage 2.8V/3.8V

(the 2.5v-2.8v is for the red die/led.... the 3.4v-3.8v is for the blue/green dies/leds)

350 mA for the green/blue.. and 400mA for the red led..

white says 3.6v for vF.. and MAX of 4.0v
750mA for the white

Well it would appear that a constant current driver with a max output voltage of 4vdc will cover any of the leds. However what the constant current driver requires for a input voltage to be able to drive up to 4vdc output is a specification specific to a specific CC driver.

You do realize that you need four independent constant current drivers to control the one RGB and one white led?

Lefty

For the RGB, when I want to have it output white, do I then add both voltage numbers? Say I just power with 5V, is it gonna make much of a difference? I know I risk damaging it, but I've heard others doing it, is this a big deal? Also what is Reverse Voltage?

AllenI:
For the RGB, when I want to have it output white, do I then add both voltage numbers? Say I just power with 5V, is it gonna make much of a difference? I know I risk damaging it, but I've heard others doing it, is this a big deal? Also what is Reverse Voltage?

Draw an post a schematic drawing of what you are proposing, as you may not be able to do what you think you can do. You effectively have four leds needing four independent CC drivers.

Lefty

You do realize that you need four independent constant current drivers to control the one RGB and one white led?

Lefty

I bought this driver:

If Im understanding this correctly, the above driver is fine for the white led alone. It's also fine for two RGB leds as long as I dont have them both output white(1.4A)

Draw an post a schematic drawing of what you are proposing, as you may not be able to do what you think you can do. You effectively have four leds needing four independent CC drivers.

Lefty

Its a fairly simple schematic, I have a 12V input source, Im using a 7805 Voltage regulator along with N-Channel mosfet's like this:

AllenI:

Draw an post a schematic drawing of what you are proposing, as you may not be able to do what you think you can do. You effectively have four leds needing four independent CC drivers.

Lefty

Its a fairly simple schematic, I have a 12V input source, Im using a 7805 Voltage regulator along with N-Channel mosfet's like this:
Usage | RGB LED Strips | Adafruit Learning System

That is showing simple transistor switches being used to control an "RGB strip" with no form of constant current control, unless current is being managed separably inside the "RGB strip".

This has nothing to do with and not applicable with your trying to power and control current through a standalone RGB led and a white led.

Lefty

AllenI:

You do realize that you need four independent constant current drivers to control the one RGB and one white led?

Lefty

I bought this driver:
Constant Current LED Driver - 700mA - 3-12 VDC | Super Bright LEDs

If Im understanding this correctly, the above driver is fine for the white led alone. It's also fine for two RGB leds as long as I dont have them both output white(1.4A)

No I don't think you understand. That one 700ma constant current driver is good to drive one white led or any one color of your RGB led, you need four such drivers.

Lefty

Yes I know, Im using a benchtop power supply with 25A, however Im transferring everything to a perfboard with its own 13.8V, 3A power supply. With that, I shouldnt need the driver, I’d have plenty of current to drive the leds. However, its alittle big and only temporary solution until I find a wall wart, which then I will use the driver I bought. The driver itself says it can handle two RGB’s in series.

AllenI:
Yes I know, Im using a benchtop power supply with 25A, however Im transferring everything to a perfboard with its own 13.8V, 3A power supply. With that, I shouldnt need the driver,
How will then control the current flow without a driver? A regulated DC power supply controls it's output voltage, not how much current is drawn from it.
I'd have plenty of current to drive the leds.
It's not just about having enough or more avalible current, but rather how to actively control the current that will flow through each led junction. Sorry but I still suspect you don't quite get how a led needs to be operated.
However, its alittle big and only temporary solution until I find a wall wart, which then I will use the driver I bought. The driver itself says it can handle two RGB's in series.
a RGB led is really three seperate leds in one package sharing either a common cathod or anode connection. Again draw out how you propose to wire up an external DC power supply, a constant current driver(s) and the leds you plan on using. I suspect you are over simplifying what is actually required, but without a drawing I can't read your mind.
Lefty

I would use a LM317 and put it into constant current driver mode. Google "LM317 constant current" you will find plenty of circuits, with different value of resisitor, you can control current limit.

However, either with LM317 or LM7805, the higher the input voltage, the more waste on the regulator itself. For example, if your input is 12V and LED needs 3.4V, where does the 8.6V go? The 8.6V votlage drop is on the LM317 or LM7805, you are wasting 71.67% of energy. With 5V supply, you have 1.6V drop and energy wasted is 32%

The less energy wasted, the less heat LM317 or LM7805 generates and safer. Believe me, it can get really hot, burn your fingers if you touch it.

Best way to go is to get buck step down driver or other efficient chip.

Just a thought.

AllenI:
I know these things need constant current but what would be the max voltage? I have a 3W and a 1W. Im trying to figure out if I should power them with 5V or 12V?

Based on the LEDs I've owned I'd say 5V with about 90% confidence level.

retrolefty:
How will then control the current flow without a driver? A regulated DC power supply controls it's output voltage, not how much current is drawn from it.
I always thought an led draws from the power source the amount of current that is needed. Is this wrong? Or are you saying the power supply can put out 3amp AT 13.8V, it wont be putting out 3amps when I use my 7805 voltage regulator.
It's not just about having enough or more avalible current, but rather how to actively control the current that will flow through each led junction. Sorry but I still suspect you don't quite get how a led needs to be operated.
They're common anode. So what exactly does the driver do for a high powered RGB, that its needed, over say a regular RGB that may only need only a max of 60mA? obviously more current, but I mean, your saying my power supply alone will not get the job done even though it can supply 3amps. I was thinking 3 amps is more than enough since both leds will at max draw 1.4 from it, but your saying that thinking is wrong.
a RGB led is really three seperate leds in one package sharing either a common cathod or anode connection. Again draw out how you propose to wire up an external DC power supply, a constant current driver(s) and the leds you plan on using. I suspect you are over simplifying what is actually required, but without a drawing I can't read your mind.
Lefty
I put up all the links above, I have it set up exactly like the Adafruit tutorial except Im using 3W leds instead of strips. GATE= PWM pin on Arduino DRAIN= 3.3V SOURCE= Ground. I'll be using a 7805 to bring down the voltage. Im not using it right now, because my benchtop has 3.3V, 5V, 12V connections.

[/quote]

AllenI:

retrolefty:
How will then control the current flow without a driver? A regulated DC power supply controls it's output voltage, not how much current is drawn from it.
I always thought an led draws from the power source the amount of current that is needed. Is this wrong?

Yes, that is wrong, once a led has voltage applied equal or greater then it's Vf rating it acts like a short circuit and will self destruct. LEDs are current operated devices and the current must be managed external of the led.

Or are you saying the power supply can put out 3amp AT 13.8V, it wont be putting out 3amps when I use my 7805 voltage regulator.

The amount of current to be drawn from a DC power supply or regulator is determined by the connected load not the power supply or the regulator, it's an ohms law thing. Power supplies and regulators just have some specific maximum current they can provide, but it's the attached load device(s) that determine how much current is drawn from a DC voltage source up to the power supplies limit where it either shuts down or burns up.

It's not just about having enough or more avalible current, but rather how to actively control the current that will flow through each led junction. Sorry but I still suspect you don't quite get how a led needs to be operated.
They're common anode. So what exactly does the driver do for a high powered RGB, that its needed, over say a regular RGB that may only need only a max of 60mA? obviously more current, but I mean, your saying my power supply alone will not get the job done even though it can supply 3amps. I was thinking 3 amps is more than enough since both leds will at max draw 1.4 from it, but your saying that thinking is wrong.

Again your power supply can supply a fixed DC voltage, it cannot control the amount of current that is attempted to be drawn from it.

a RGB led is really three seperate leds in one package sharing either a common cathod or anode connection. Again draw out how you propose to wire up an external DC power supply, a constant current driver(s) and the leds you plan on using. I suspect you are over simplifying what is actually required, but without a drawing I can't read your mind.
Lefty
I put up all the links above, I have it set up exactly like the Adafruit tutorial except Im using 3W leds instead of strips. GATE= PWM pin on Arduino DRAIN= 3.3V SOURCE= Ground. I'll be using a 7805 to bring down the voltage. Im not using it right now, because my benchtop has 3.3V, 5V, 12V connections.

I see no links?

A adafruit led 'strip' is not the same thing you are working with, standalone leds. You (or I) have no idea how the adafruit led 'strip' controls current for each individual led on the strip. But make no mistake there is some kind of current control within the strip for each led element.
Lefty

[/quote]

I see no links?

A adafruit led 'strip' is not the same thing you are working with, standalone leds. Yes, I get that, I was showing how the circuit was setup, i.e. n-channel mosfets used for switching. You (or I) have no idea how the adafruit led 'strip' controls current for each individual led on the strip. Schematic | RGB LED Strips | Adafruit Learning System
Lefty

I started with the analog strips they sell. Followed the tutorial, I have the strip in front of me. The schematic for the strip is on the next page. Tried it, worked, now I'm moving on with on high powered leds. And this statement right here is whats confusing me:

"Each segment of 3 LEDs draws approximately 20 milliAmperes from a 12V supply" Your saying this is wrong?

Here is another tutorial I followed, this is exactly how I have my circuit setup right now, but Im using mosfets instead of Darlington transistors.
http://thecustomgeek.com/2011/08/01/controlling-high-power-or-high-number-of-leds-with-an-arduino/

See why my head is kinda spinning right now

AllenI:
I see no links?

A adafruit led 'strip' is not the same thing you are working with, standalone leds. Yes, I get that, I was showing how the circuit was setup, i.e. n-channel mosfets used for switching. You (or I) have no idea how the adafruit led 'strip' controls current for each individual led on the strip. Schematic | RGB LED Strips | Adafruit Learning System
Lefty

Current Draw | RGB LED Strips | Adafruit Learning System
I started with the analog strips they sell. Followed the tutorial, I have the strip in front of me. The schematic for the strip is on the next page. Tried it, worked, now I'm moving on with on high powered leds. And this statement right here is whats confusing me:

"Each segment of 3 LEDs draws approximately 20 milliAmperes from a 12V supply" Your saying this is wrong?

In the adafruit schematic you posted, you see those resistors wired in series with the led segments? That is how they are managing the current flow through the leds. Does your high power led scheme going to use resistors of a high enough wattage rating to control the led current? Usually high power leds draw too much current to use simple resistor current control and is why constant current drivers are almost always a requirement to use on them.
Lefty

Here is another tutorial I followed, this is exactly how I have my circuit setup right now, but Im using mosfets instead of Darlington transistors.
http://thecustomgeek.com/2011/08/01/controlling-high-power-or-high-number-of-leds-with-an-arduino/

Very poor quality site to use as a design bases. Even one of the commenters asked about his lack of current control.

Hi,
I was wondering how you limit the current for the RGB Led. As far as i understood you are using 5v to power the led with no resistors.
Wouldn’t you need to limit the current to 350mA or something? Because using 255 pwm would be like applying 5v directly to the led, wouldn’t it?
Jeremy says:
December 21, 2011 at 1:40 am
Hi Leon, you are right. I did not limit the current to the RGB LED. It was a quick setup and I did not put resistors in. You should not do this, but those LED’s can take a beating, and at the same time shave off hours of lifetime..
Having said that, there was a max of 500mA supply coming from my USB port, and that’s why the LED did not go up in magic smoke.

Blind leading the blind. That is no way to learn basic electronics. Master basic DC fundementals, Ohm's law and such. Then basic semiconductor theory, then maybe you could design your own set-up, in the mean time best to copy some proven design.
Lefty

See why my head is kinda spinning right now