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Topic: Control very high power LED (Read 1 time) previous topic - next topic

afremont


At this current and power level a switch-mode supply is not trivial to design (easy to make one that overheats!),
a series power resistor to limit current would be a simpler circuit.

I looked into driving a 100W LED array a little while back and the only high efficiency solution(*) I found involved
a MOSFET bridge driven by the LT3791, a chip that claims upto 98.5% efficiency, but needs a lot of auxiliary
components to do the job - it does have the nice property of not caring it the supply is above or below the LED
voltage.

Some of the SMPS chips allow an external MOSFET switch, which is needed for 3.5A, but I think you really need
synchronous rectification to avoid excessive losses in the schottky diode (several watts at 3.5A).


I agree that this isn't the ideal project for somebody starting out; a scaled down version is a different matter though.  Like you said, it's easy to end up with a pile of molten material, and high power parts aren't cheap.  Most of the circuitry in a SMPS is there to stop a meltdown should something be wrong.  More current requires more protection.  Turning that MOSFET on for 1mS would cook it and the inductor probably.  Her calculator is shooting for roughly 10-15uS on time per cycle.  You can get some pretty amazing efficiency once you get rid of the resistors.

You're right on that diode, good thinking there.  It's going to burning a couple of watts and that's going to need an upgrade too.

The OP should probably stick with the dropping resistor.  I just wanted to add some food for thought.
Experience, it's what you get when you were expecting something else.

MarkT

Indeed - and if anyone has a good cheap efficient solution that works for 34V and 3A (from 12V) I'd like to
know too!!
[ I won't respond to messages, use the forum please ]

Chagrin

50-100W IR led at 38Khz? Is this like a city-sized TV-B-Gone?.  :smiley-mr-green:

Linear LED current regulators (e.g. CAT4101, NUD4001) can be used in parallel for 3.5A control. Your efficiency would depend on keeping your voltage supply near your LED's Vf.

fungus


Sounds like quite a design challenge. The OP, because he asked such a basic question, is most likely not capable of such a design and construction effort?


I suspect not.

I think we need more details about his battery and why he wants to use it before we can go any further (hint...)

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

cordvision



Sounds like quite a design challenge. The OP, because he asked such a basic question, is most likely not capable of such a design and construction effort?


I suspect not.

I think we need more details about his battery and why he wants to use it before we can go any further (hint...)



First of all, thanks for all your replies :)
I'm actually just trying to find out the max range I can get with an IR LED. I don't want to give away the exact purpose yet, as I might turn it into a real product at some point in the future. My problem is that I don't know a whole lot about electronics, but I would like to at least make a working prototype before I dive deeper into it. I already have a prototype with a 5 watt IR led. I just used a simple transistor and a 12.6 V lipo battery to power it (I use lipos because I'm into RC flying and have them readily available).
I was just looking for a way to easily replace the 5W IR LED with a 100 W LED that I just bought (I don't know why it is considered a 100W led, the specs are only 16V and 3500 mA which comes out to 56 W).
I hope to cover a large area (like a basketball court) with the IR LED. The 5W LED is strong enough to cover my whole living room with a signal, but I don't know how well it scales up. I know that I could just use an RF module to get better range, but this specific project wouldn't work with RF.
Since it is just a prototype to find out how large of an area I can cover with a 100W IR led, I just need to make it work for a few minutes at the time. I'm not too concerned with durability etc. If anybody has a really simple solution, that would be perfect...

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