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[on:]

Hello Everybody
I'm trying to find out what the best way would be to control a 50-100 Watt IR led with the arduino. The IR led is pulsed at 38 khz so the switching will have to be very fast. I would like to use a 16.8 volt lipo battery as my power source. The LED itself runs of 16-19 Volts, 3500 mA.
I was thinking if there's some transistor that can handle this or what would be my best option?

[Reply #1 on:]

Use a power mosfet, preferably driven by a mosfet driver chip such as TC4420.

[Reply #2 on:]

Use a power mosfet, preferably driven by a mosfet driver chip such as TC4420.

And what will/should control the current value for the LED's ?

Lefty

[Reply #3 on:]

And what will/should control the current value for the LED's ?

Lefty

IMO, PWM and an appropriate inductor.  A 12V supply could drive it, again just my opinion.

[Reply #4 on:]

And what will/should control the current value for the LED's ?

Lefty

IMO, PWM and an appropriate inductor.  A 12V supply could drive it, again just my opinion.

Have an example circuit to post?

Lefty

[Reply #5 on:]

Here is a place to start:
http://www.ladyada.net/library/diyboostcalc.html

It will require a different MOSFET that can handle allot more current.  The inductor would have to be wound on a core, a resistor style package would never cut it.  The idea is to not actually put much current thru the MOSFET, but a safety margin will help prevent self-disintegration should something go wrong.  I would also add feedback (a simple voltage divider) so that the Arduino can shut down the PWM if the voltage rockets, such as when the LED isn't connected.  I'd probably just do that with a comparator though so as to not depend upon the software to be functioning.

[Reply #6 on:]

IMO, PWM and an appropriate inductor.  A 12V supply could drive it, again just my opinion.

A big joule thief?

[Reply #7 on:]

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).

[Reply #8 on:]

IMO, PWM and an appropriate inductor.  A 12V supply could drive it, again just my opinion.

A big joule thief?

More or less.  I tinkered with a PIC project charging some large caps to ~400V from a 12V supply, then triggering an IGBT to dump the juice thru an electromagnet coil from a Ford style starting solenoid.  I could launch little computer screws across the room.  Beware, 400V on large caps can be quite lethal.

[Reply #9 on:]

Here is a place to start:
http://www.ladyada.net/library/diyboostcalc.html

It will require a different MOSFET that can handle allot more current.  The inductor would have to be wound on a core, a resistor style package would never cut it.  The idea is to not actually put much current thru the MOSFET, but a safety margin will help prevent self-disintegration should something go wrong.  I would also add feedback (a simple voltage divider) so that the Arduino can shut down the PWM if the voltage rockets, such as when the LED isn't connected.  I'd probably just do that with a comparator though so as to not depend upon the software to be functioning.

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 would suggest he look for a purpose designed constant current LED driver that is sized for 3.5 amps of flow and that has a PWM input pin. He is dealing with a pretty high power level here and needs to be careful in how he tries to power and control the LED assembly,  50-100 watts is a significant power level.

Lefty

[Reply #10 on:]

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.

[Reply #11 on:]

Indeed - and if anyone has a good cheap efficient solution that works for 34V and 3A (from 12V) I'd like to
know too!!

[Reply #12 on:]

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

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.

[Reply #13 on:]

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...)

[Reply #14 on:]

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...