200W LED driver? - Page 1
Forum section: electronics / projects

author: Artlav
author_rank: Frequent Contributor
timestamp: October 16, 2014, 08:59:36 pm
content: I have 4 50W LEDs that i want to drive at once from a 12V battery.Each LED needs 1.4A at about 37V.What sort of a converter and arrangement is better for it?Two basic arrangements are possible - all LEDs in series, and one 150V driver, or each LED on it's own, with 4 separate 38V drivers.Both times would need a step-up converter, so it makes sense to make one rather than 4.On the other hand, i never made a converter like that for more than 100W, and it was constant voltage and getting too warm for comfort at full power.Would 4 50W 38V converters be better than 1 200W, 150V one?What kind of a converter could it be in each case, keeping in mind that they should be constant current?50W version sounds like within the realm of a boost converter, but there is no such thing as a constant current boost converter, so it would have to be followed by a buck one, quadrupling the size.If a transformer converter is to be used, then it would be about the same for either 50W or 200W, so what's the point?With a transformer converter 200W is possible, but i never tried making one that is constant current.Is that feasible?Perhaps there are other solutions?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 16, 2014, 09:46:12 pm
content: How can there be no such thing as a constant current boost..?I'd be happy with a single boost, and current balancing resistors. The resistors don't need to be nearly as large and wasteful as when running strings from a fixed voltage supply, so it doesn't hurt much. If you must, you can do individual channels. You can then get independent control, which might be handy, I don't know.Tim

author: ConKbot
author_rank: Super Contributor
timestamp: October 16, 2014, 09:58:50 pm
content: If you wanted to drive each one individually, I'd look athttp://www.taskled.com/hboost.shtml7A max input current, 6A recommended, 8-50V input range, 80V or 3.2A max out (mind your input current limit though)So it would cheerfully run your 50W LEDs. The nice macro shot of the PCB is also a good hint at where to start if you want to do your own.http://www.linear.com/product/LT3756If you want to mess around on your own for doing a 150V transformer based driver as a learning experience, I'd grab a transformer from an ATX PSU, and run it backwards(The primary will be wound for 380V not 150V, but running it as a flyback converter means that the ratio isnt *that* critical). Grab a TL-494, and a TL-431, current shunt resistor and an amplifier for it and youre off to a decent start. However I havent designed enough transformer based SMPS to give solid advice for that.

author: ovnr
author_rank: Frequent Contributor
timestamp: October 16, 2014, 10:09:28 pm
content: Really? I've got several constant current boost converters sitting here, disagreeing with you.200W boost is a bit much, but hardly aproblem. Linear has several parts which should work for you. Consider running two LEDs in series, then each string in parallel with current limiting resistors (or whatever solution you prefer). Hell, you can just boost to a suitable voltage, and use linear CC drivers.

author: Artlav
author_rank: Frequent Contributor
timestamp: October 17, 2014, 09:15:23 am
content: Quote from: ConKbot on October 16, 2014, 09:58:50 pmThat looks great.Thanks, i can use some of them, maybe for this project, definitely for some other.Quote from: T3sl4co1l on October 16, 2014, 09:46:12 pmQuote from: ovnr on October 16, 2014, 10:09:28 pmMore precisely, i have repeatedly failed to make a constant current boost converter.http://www.edaboard.com/thread300483.htmlhttps://www.physicsforums.com/threads/boost-converter-switch-node-spiking.716486/page-2#post-4543001In the end, it is just absolutely unstable:https://www.physicsforums.com/threads/constant-current-boost-converter-problems.749692/Maybe i just don't know how to make one?Quote from: T3sl4co1l on October 16, 2014, 09:46:12 pmWhat kind of resistors would it be?How do i select them?The LEDs change voltage as they heat up, from 37.4V to 37V on average. There will be unknown imbalance.I can't quite visualise how to get them balanced with resistors, at constant current supply.Quote from: ovnr on October 16, 2014, 10:09:28 pmTried that before.https://www.eevblog.com/forum/projects/linear-led-driver-avoiding-a-hot-resistor/It gets hot even when the voltages are tuned tight.But it works.That is actually a viable solution as well - 50W CV boost, and an LDO to keep the current right.

author: bookaboo
author_rank: Frequent Contributor
timestamp: October 17, 2014, 09:20:53 am
content: TI have tools to develop these sorts of drivers.http://www.ti.com/lsds/ti/analog/webench/overview.pageThough I found it easier to just buy their evaluation kit and work from there.

author: Psi
author_rank: Super Contributor
timestamp: October 17, 2014, 09:21:38 am
content: http://www.aliexpress.com/item/Freeshipping-2pcs-12V-50W-LED-Driver-for50W-30-36V-1500mA-high-Power-50w-led-chip-transformer/1843599268.html

author: DVDRW
author_rank: Newbie
timestamp: October 17, 2014, 10:34:30 am
content: I usethesefor my100W LEDs:Fan mod needed. And ~0.5 ohm resistor.If you want constant current thanthisshould be ok.37V? All 20W - 100W leds are typically 30-35V.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 17, 2014, 12:29:58 pm
content: My light (running right now, healthy) might be worth some thought:http://seventransistorlabs.com/Images/LED_Light.pngTim

author: bookaboo
author_rank: Frequent Contributor
timestamp: October 17, 2014, 12:54:36 pm
content: There should be no need for fans at all, if you are generating that much heat something is wrong with the design or component selection. Even if it's reliable it kind of defeats the purpose of efficient LEDs.

author: Marco
author_rank: Super Contributor
timestamp: October 17, 2014, 02:34:08 pm
content: Quote from: Artlav on October 17, 2014, 09:15:23 amIt's easier to just use a dedicated LED driver IC, you don't have to worry about amplifying the signal from the current shunt with the added potential for instability.PS. that Alixpress one for 8$ a driver is a pretty good deal (if they don't blow up after 6 months).

author: Artlav
author_rank: Frequent Contributor
timestamp: October 17, 2014, 06:02:39 pm
content: Just tried making a boost converter with MAX1771 - it works up to 25W, reasonably well, but it squeals and does not work well unless i'm touching the FET's tabSame circuit worked perfectly for getting 200V for tubes.All in all, i guess i'll get something from China to run their Chineese LEDs.Thanks all for the links.Quote from: DVDRW on October 17, 2014, 10:34:30 amMadeinchi Industries, i presume.At constant 35V one does 1.06A, second - 0.76A, third - 0.8A, fourth - 0.96A.Not very consistent.And quite a pain, being just out of the range of most ready-made boost modules (which go up to 32V or 35V).Also, not all big LEDs are 30-35V, i got some Cree 100W ones that are 42V.Quote from: Marco on October 17, 2014, 02:34:08 pmAny examples?

author: amyk
author_rank: Super Contributor
timestamp: October 17, 2014, 07:21:26 pm
content: Quote from: Artlav on October 17, 2014, 06:02:39 pmLEDs are constant-current devices, not constant-voltage. Also the I-V curve is exponential and sensitive to temperature as well; 50W is the sort of power levels where tiny differences in temperature can result in huge differences in voltage/current, and thermal runaway becomes more of a concern.

author: Marco
author_rank: Super Contributor
timestamp: October 17, 2014, 07:23:12 pm
content: Quote from: Artlav on October 17, 2014, 06:02:39 pmThat's just a question of bodging the output overvoltage protection IF it's present at all. The FET, Schottky and output capacitor can likely take a few more volts.QuoteGo to digikey, search for boost, select the results from LED drivers (the last two steps are a roundabout way of picking out all the boost topologies), throw away AC/DC topologies and charge pump, select for internal driver both&no, select quantity 1, sort for price ... spend some time looking for a nice part (pay attention to the feedback voltage, some use 0.5 volt which at 1.4 A will put 0.7 Watt into the shunt ... so preferably something lower).AP3021 looks okay (no current protection for the FET though, but I'm sure there are plenty which have that as well).PS. those aliexpress drivers use the XL6006 which seems a little more competetively priced than the standard integrated controllers (only available from China though AFAICS).

author: Artlav
author_rank: Frequent Contributor
timestamp: October 17, 2014, 08:18:18 pm
content: Quote from: amyk on October 17, 2014, 07:21:26 pmSomehow i doubt that LEDs on the same hunky radiator would be that different in temperature.Quote from: Marco on October 17, 2014, 07:23:12 pmNice, i haven't noticed that category before.Much more searchable than "DC DC Switching Controllers".