# driving 3 w watt leds

hello
is it ok to drive 3 3 watt leds using this driver
was going top put leds in series
thanks

Yes.
That chip should be able to drive 1-6 3watt LEDs in series, depending on supply voltage.
3 LEDs on a 12volt supply, 4-5 LEDs on a 19volt laptop supply, and 6 LEDs on a 24volt supply.
If you do silly things, like one LED on a 24volt supply, then the chip will overheat.

The two R200 and R300 resistors are for the LED current.
R200 is for 500mA, and R300 for 333mA. Both give 500+333= 833mA LED current.
You can remove one if you want a lower LED current.
Leo..

leds in parrallel?

jonisonvespa:
leds in parrallel?

No, don't put power LEDs in parallel.
LED currents don't get shared equally, and a hotter LED will even get more current and getting hotter...
Leo..

Love the avatar!

Note the silly blunder in this diagram!

Thanks
OK I understand now voltage drop

Why can't you run e leds in parallel? Up to the current rating of the driver?

Because the LEDs won’t share the current equally between them. No two LEDs are identical, even if they were made in the same batch at the same factory. One will have a lower forward voltage than the other. So it will get more current. It will heat up, and it’s forward voltage will drop even further. Soon it will get most of the current, get really hot and… pop.

After that, no current will follow in that led. But the driver will increase the voltage to keep the current steady. That current will all go to through the second led… pop.

OK i see so you can onky run leds in series then.?
I don't understand how led strips work surly they are in parallel?

Yes you can, but you must have separate current control/limiting for each group of LEDs that are in parallel. So you never have to rely on them sharing current equally.

In led strips, it depends on the type of strip. If we assume a single colour 12V strip, there are normally 3 LEDs in series in each parallel group. That's why you have to cut them at the indicated marks, so you are cutting between groups of 3. Each group of 3 LEDs has a current limiting resistor of its own, you can see them as tiny black rectangular black components on the strip, one for every 3 LEDs.

So using a çonverter’ construction (with a 300 and a 200 Ohm resister for example) is not going to work long term?

Hmm, that’s a shame…

No, that's wrong.

Each led will need it's own current limiting resistor.

With only 5V supply, you might be able to put 2 red LEDs in series with a single current limiting resistor. That's because red leds have the lowest forward voltage of all LEDs (except IR LEDs). Other colours have higher forward voltages and 5V won't be enough to place two of them in series, because you need some voltage to drop across the resistor.

Not sure what you are doing with the 300R & 200R, but perhaps you were thinking of a voltage divider? If so, that's no good for powering LEDs, or anything that draws a non-trivial amount of current, and you need to read up on how voltage dividers work and what they are used for. As shown, your 200R and 300R are not forming a voltage divider. The 200R is in series with the LEDs (which should have one each) and the 300R is just wasting current for no reason.