36volt 6amp power supply for LED

[Mitch311]

So this is a little off topic, but I am building a DIY projector and am having a tiny bit of difficulty with the elctronics (I got the optics down pat, but I am still learning bout electronics lol).

I am planning on using this LED http://www.better-led.com/en/product...D-200W-02.html which can take a 36volt 6 amp power supply and needs a constant power supply.

I am wondering if I can use an SMPS to power the LED? Something like the 36volt meanwell that hifimediy sells. From what I can see on the meanwell product page you can adjust the amp output from an SMPS? Otherwise the 36volt one puts out 13amp not 6.

Just looking at my options and trying to learn a bit as well.

Thanks for any replies,

Mitch

[luka]

Yes you can use smps, in fact I wouldn't use anything else... but I think you can set only the output voltage... you would need led driver or constant current regulator, that being said it could be linear or switching...

led driver is the most... well I don't know if I would say simple but... you have input voltage, that needs to be higher then what led will use, say 40-50v (if you have such led driver) and driver needs to be set to provide 6A of constant current.

next DIY thing would be linear constant regulator, that is ultra simple (can be). you need transistor and resistor and you are good to go.
switching regulator is the same as led driver, in fact this is one and the same thing, good coz it doesn't heat up no where as much as linear would

Anyway... for your led, MOST important thing is to LIMIT current to 6A (voltage doesn't mean anything here, will be as mush as it needs to be for 6A) and to keep is as cool as you can, don't run it near 100C or whatever it is rated for

[Mitch311]

Thanks for the reply Luka.

So pretty much any voltage power source will work as long as it putting out 6A ? Eg Something like so: eBay Australia: Buy new & used fashion, electronics & home d?r would do the job?

If so now I just need to find a BIg *** heatsink and rig up some fans

[luka]

well you need the power... so with switching led drivers, if you input higher voltage, less current will flow, since I x U = P and lets say that all that power goes to output.

So if you had driver that could use 48v, you wouldn't need this 48v supply to be 6A too. Yes, that 42v supply would work great... now if you can only find led driver at 6A you are golden

but I think you might need to make one... if you are up for this... if not, you will need to dissapate suppy voltage - led voltage @6A x 6A... not too much, but still something

[!]

That power supply isn't technically a switching LED driver, it isn't as suitable as the one mentioned previously. It regulates based on voltage, the current is just the peak which isn't how you want to operate one so you get good lifespan from the SMPS, instead you'd want a current margin between SMPS spec and average current consumption.

While with these they do tend to drop rail voltage as you approach or exceed the current spec for the PSU, it isn't straighforward that you can assume it would deliver 6A, not more than that, or fall out of regulation because the forward voltage vs current curve for the LED doesn't match it. If it has a voltage adjustment feature you might be able to dial in something compatible but ultimately the far better option is a method that directly limits current.

While the LED has a 33V forward voltage spec at 6A, this is at 25C junction temperature - a temperature you surely will not have unless you use active cooling (peltier, compressor, etc) and even then, a pretty good cooling subsystem for a consumer app with 200W LED.

Instead, we should probably assume the forward voltage will drop below 33V at the actual operating temp as implemented in your project. How much I do not know, this cannot be an inexpensive LED so you are justified in asking for full specs from the manufacturer, or to forward you on to the actual manufacturer if this is only a reseller for the LED.

There are probably some industrial lighting or automotive targeted ICs for current regulating high power LEDs, but this LED is unusual in having so many in series and parallel, normal LED config would be more in series, multiple channels for parallel, not 200W in a semi-symmetrical arrangement. You might ask the LED manufacturer what they suggest to drive it, surely they had some ideas before deciding on this logical die arrangement??

If all else fails, the not-so-power-conservative but generic option is you get a SMPS rated for a few volts over 33V, not much(!), rated for more than the 6A, perhaps 9A or more. It would be preferred if it had a voltage adjustment feature. Based on the highest (or steady rated if non-adjustable) voltage it supports at 9A or more, you do the standard LED resistor calculation. For example,

(PSU voltage - LED forward voltage) / current = resistance

(PSU voltage - LED forward voltage) * current = resistor wattage ... add some margin for good life and easier cooling from lower thermal density

For example, 36V PSU and 32V LED forward voltage (@ higher thermal junction temperature than 25C) and 6A drive current:

(36V - 32V) / 6A = 0.67 Ohms

4V * 6A = 24W (add as much margin above this as budget and space allow, 50W power resistor would not be unreasonable, otherwise you need a bit better, more expensive heatsink instead unless the massive one the LED is mounted to serves double duty, which it might as well do if the design allows for that)

Maybe your actual values input above (plus an adjustable PSU voltage) will allow picking a resistor that is a commonly available value, or maybe you'll need to parallel some higher ohm resistors to arrive at the right value.

This is where an adjustable PSU might really come in handy. For example, "IF" your LED's actual forward voltage at operating temperature were 32V as randomly guesstimated above for the example, you could try putting 3 x 10W, 1 ohm resistors in parallel to limit current. That gives 30W power handling, 0.33 Ohms resistance, and per the equation above:

(PSU V - 32V) / 6A = 0.33 Ohms
PSU V = 34V
2V * 6A = 12W resistor dissipation

So, "IF" your PSU can adjust down to 34V and LED Vf is 32V, this becomes reasonable, manageable, using common cheap resistor values. Obviously LED forward voltage won't be exactly, if even near 32.0V, it is just a generalization about one method it could be implemented. Certainly when you start actually powering the LED from what you have built, you'd want to set the PSU to the lowest voltage it supports, then measure the current consumption of the LED with a meter as you slowly increase the SMPS voltage... also keeping in mind there will be a little lag, as current increases it takes a while for temperature rise to normalize which will drop forward voltage a little more causing a little higher current and so on till you eventually dial in exactly what you need for PSU output.

PS - my math is not always flawless, I usually calculate things two or more times if a critical value is being chosen.

How well this could work out depends a lot on how adjustable the PSU voltage is within an appropriate range. If it were a fixed 42V you have massive amounts of heat on resistors, even 36V would cause a lot, while if you can dial down voltage till it's barely more than needed, efficiency comes pretty close to what a proper LED current regulator subcircuit would... as per the example above you "could" only have 12W resistor loss driving a 200W load while many switching LED current regulation circuits aren't even 94% efficient.

[nigelwright7557]

You need a constant current source so as to not blow up the LED.

You cant just supply LED's with a voltage they will blow up.

Look up constant current sources.

[luka]

I think he understands he can use JUST that supply, but for power it is good

[gmarsh]

You can probably buy something off the shelf that's designed specifically to drive LEDs for cheaper than you can build something.. like a Mean Well HLG-240-36:

Meanwell Power Supply Products

$110USD at Future Electronics, <$100 at Online Components, stock but a bit spendy at Mouser.

[fireworks]

A SMPS current source can be very simply made: just use the buck topology but sense the current through the inductor instead of the voltage on the load
for regulation.

[!]

^ Often they instead put the rail through a low ohm resistor after the inductor, the resistor value varied to meet the reference voltage the regulator is set to (or is fixed at) use to adjust current output.

However, either way it might not be as simple in practice as it is in theory, you'll be needing a 2nd circuit tacked on or a controller that can take the place of the original, if your voltage drop isn't sufficiently high enough for the existing regulator IC to use... though I suppose you might be able to use a voltage divider to pull the signal up towards the rail voltage some instead of down towards the ground.

... unless you had something specific in mind, parts suitable for that so the time investment isn't high enough to justify buying a ready made driver supply like gmarsh linked. The HLG-240-36 model seems a good option if Mitch doesn't already have a suitable SMPS.