Driving high power LEDs

[somlioy]

Hi

Got a lamp with 9pc 50W LEDs with Vf ~ 34V and If ~ 1.5A each. The nine COBs are mounted on aluminium-angles, submerged in circulating oil.
The whole unit is then to be submerged in seawater.

What I'm courious about is how should the leds be driven aswell as how should it be configured. I need to be able to dim the LEDs.
The controller(s) is to be placed above the sea in a separate cabinet.

[danadak]

Principally drive with a constant current source.

Google "led drive application note", tons of help and references.


Regards, Dana.

[mariush]

You could simply use a LED DRIVER with ability to control the brightness through a PWM pin or by setting a resistor.
Note that if the led is at quite a long distance away from the control box, you should account for the wire resistance as well ( the circuit would most likely use a low value resistor like 0.1 ohm for example to measure the current ... so if you use a few meters of AWG18 wires with 21 mOhm per meter of resistance, that can affect the 0.1 ohm value) .
If you want to be really accurate you could have the current sense resistor near the led and then you could use a couple of thinner wires or just one thinner wire to bring the actual voltage measured to the control IC.

Check out for example Richtek RT8463GQW : https://www.digikey.com/product-detail/en/richtek-usa-inc/RT8463GQW/RT8463GQWCT-ND/6205469

It can work with up to 50v and can operate in either buck mode (step-down) or boost mode (step-up)  so for example you could design your circuit to either use a 12v..24v power supply and boost the voltage to ~34v (go as high as needed to get 1.5A through the led) , or you could for example use a 48v power supply and take that down to the voltage the led requires.
The current is controlled through a current sense resistor, a 100mV drop sets the maximum current allowed through the leds.
See page 6 of the datasheet for example circuits using analogue ( 0.2v to 1.2v range for 0..100% brightness)  or pwm dimming

Another chip worth looking up (but more expensive and boost only) would be LT3952  : https://www.digikey.com/product-detail/en/linear-technology/LT3952EFE-PBF/LT3952EFE-PBF-ND/5253630

[somlioy]

Sort of forgot about this... 

Cable down to the light will be 3 cores (2+earth) at either 1.5mm^2 or 2.5mm^2 with a length of probably around 20-30 meters.

So I either has to choose between high voltage or high current, or possible something in between?

[ocset]

What driving source do you have, or rather, would you choose to have?
Is it mains 240VAC, or some DC level.

Please Tell us this , and then we can give good recomendation.