calculate high power led resistor

[camilozk]

Hi!

How do I calculate the resistor to be used with the following high power leds?

-3W: 3.2 - 3.4V // 500 - 700mA
-5W: 6 - 7V // 700mA

Is it good practice to use resistors for these leds or should I used an led driver?




thanks!

 

[(*steve*)]

You cannulate then the same way you do for any led.

No, I would not recommend using resistors with high power LEDs in most cases.

For more information, see our resource on LEDs

 

[camilozk]

thanks for info steve

I am normally using led drivers such as http://store3.sure-electronics.com/ps-sp12154 and http://store3.sure-electronics.com/...er-board-dc-sepic-buck-boost-5-32v-wide-input

I am testing for one project 2 different kinds of bead leds, 3W and 5W and I am using the 600mA and 700mA drivers respectively. This is the information I found on the website of the led´s manufacterer. The problem that I am facing now is that the 5W led is getting REALLY hot, and burns after some minutes. Now, I am not fully sure if it is a heat sink issue, or if I am using the wrong driver for the 5W led.

All leds are mounted on "star" heat sink.


What do you think?

 

[camilozk]

now I connected a 3W led to the 600mA driver, and after some minutes it started to flicker, and after some minutes of flickering it started to turn on and off... until dead...

The "star" heat sink is not too hot...

Are these the wrong drivers for this leds?

 

[BobK]

The "star heatsink" is not a heatsink! It is meant to be attached to a heat sink. You can get away with running 1W ones without further heatsinking, but not 3 or 5.

Bob

 

[camilozk]

ok. so that means I am really burning all of these leds because of lack of heat sink, and the drivers are actually ok.

one more question. I found inside of a goose neck lamp, an led attached to a star heat sink with a resistor: 6R2. The lamp is meant to be connected via usb, so 5V are applied to this system. Am I right to assume this is a 1W led?

 

[(*steve*)]

It's possiblly a 1W LED, although if it's Chinese, I wouldn't put it past then to have used a 1/2W LED.

Making some bold assumptions, it's drawing about 120mA and the LED is dissipating a little over 0.5W