100A 1.9v Constant current driver? - Page 1
Forum section: electronics / projects

author: deltawars
author_rank: Contributor
timestamp: June 09, 2014, 01:45:21 pm
content: I like to build lasers and my latest build is a 3W 445nm laser but I wanted to step things up and do something different.I want to build a 100W handheld laser, but I have struck a problem, Driving the diode seems very difficult, I have spent hours looking around and reading up on the internet but I cant find anything.The diode is a 100W Continues Wave laser bar, it has a Maximum current rating of 112A and 1.9V, I want to drive it as close as possible to the max ratings.http://www.coherent.com/download/6480/Onyx-MCCP-9001-808-DS.pdfTo keep the heat wattage of a driver down to minimal I found these 2.4V Lithium Titanate battery's with a 39A Max Impluse rate < 5 sec, i plan to use 4 of them in parallel for a 156A Max Impluse rate < 5 sec.http://www.batteryspace.com/LTO-1865-Rechargeable-Cell-2.4V-1300-mAh-39A-rated-3.12Wh.aspxThe problem I have struck is finding a circuit that can drop the voltage down from 2.4V to around 1.7-1.9V(1.9V if possible) and provide a constant current of 110-112A(112A if possible), I understand that the driver will generate around 55-80W of heat, and the laser diode will generate around 93-106W of heat but it is fine I can handle it. The laser will only be powered on for around 0.5-1s.I was looking at a MOSFET Constant current circuit but every says its not possible with this amount of current, The only other thing I can think of is 112 LM317 at 1A or maybe 74 at 1.5A.If anyone has a solution for a driver that can drop 2.4V down to 1.7-1.9V and provide a constant current of 110-112A Please let me know your help will be very much appreciated.

author: fcb
author_rank: Super Contributor
timestamp: June 09, 2014, 02:21:16 pm
content: If it's only for 0.5s to 1s, then I would look at:1. using a plain old resistor with a FET switch (several FET's probably in parallel).2. building a multiple (smaller) constant current sources, then paralleling them up (much easier to prove).You will undoubtedly need a higher supply rail for the control electronics, so either have a separate 9V battery or a little boost converter.

author: nickm
author_rank: Regular Contributor
timestamp: June 09, 2014, 02:25:01 pm
content: Multiphase buck.

author: madires
author_rank: Super Contributor
timestamp: June 09, 2014, 02:26:20 pm
content: On computer mainboards there are DC-DC converters for low voltages @ 100A. Maybe such a design could be modified to constant current.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 09, 2014, 02:30:42 pm
content: That sort of voltage/current is in the same ballpark as high-end CPUs etc.You should be able to find something like a polyphase DC-DC converter designed for this - look for appnotes from people like Linear Tech.To this you'll need to add a current-sense + amplifier arrangement to make it regulate current instead of voltage. You may get away with regulating to a few hundred mV above the diode Vf and using resistive ballast, as long as the diode characteristics don't change too much, but they might.Layout, decoupling etc. at this level is very non-trival, but using a polyphase setup with multiple converters running in parallel may make some issues slightly easier.

author: mariush
author_rank: Super Contributor
timestamp: June 09, 2014, 02:38:43 pm
content: And if that's too complicated you could always make your own toroidal transformer and use 12-24v -> inverter -> transformer -> bridge rectifier -> capacitors -> current limit (some resistors).Lots of copper wire, lots of waste in the bridge rectifiers, but since you say it's for 0.5-1s.. who cares.

author: retrolefty
author_rank: Super Contributor
timestamp: June 09, 2014, 03:29:02 pm
content: I'm confused. If it's a constant current driver why are you concerned about it's output voltage value? It will raise or lower the voltage to maintain the current it was designed to hold constant, up to it's maximum possible output voltage. Ohm's Law must be obeyed.Quote

author: mariush
author_rank: Super Contributor
timestamp: June 09, 2014, 03:43:33 pm
content: Here's another idea... go on ebay and get a bunch of those supercapacitors... you can get a 2600F 2.5 supercap for about 35$, plus $15 shipping:http://www.ebay.com/itm/Boostcap-Maxwell-2600F-2-5V-Ultracapitor-/251538977795?pt=LH_DefaultDomain_0&hash=item3a90e43403You could charge the caps at 10-20A or whatever current is convenient for you (for example 2 LT1083 linear regulators will give you 15A, each can do 7.5A by itself) but there's ready made buck dc-dc converters than can do 10-20A at better efficiency... when it's charged to 2.0 - 2.5v, you can just use a beefy mosfet to power the laser for 1s with some resistors to limit the current to 100-110A.

author: rob77
author_rank: Super Contributor
timestamp: June 09, 2014, 03:50:11 pm
content: first of all... why the heck you need a 100W laser ? that's freaking DANGEROUS.but regarding the supply:as others suggested - polyphase buck converter. take a recent (max 5 years old) PC motherboard and take the whole buck converter from there - make your PCB a copy of that layout on the MB - component placement and the shape of the traces/planes is CRITICAL.forget the current sensing resistor - you have to use the Rdson of the top mosfet for that at 100Amps.

author: lapm
author_rank: Frequent Contributor
timestamp: June 09, 2014, 04:40:16 pm
content: Ok im curious. WTF are you planning on doing with 100W laser? Seriously that's dangerous. Just reflection of that beam will damage eyes permanently in fraction of second. Not to mention its ability to burn throw things... Meaning your neighbors might not appreciate your little death-ray..

author: rob77
author_rank: Super Contributor
timestamp: June 09, 2014, 05:47:14 pm
content: Quote from: deltawars on June 09, 2014, 01:45:21 pmi just noticed - you're mentioning a HANDHELD 100W laser !!!!!!!!!!!!!!!!!!!!!!!seriously.. it's more dangerous than you can imagine.. if you blind or kill yourself - then i don't give rat's ass.. but you might blind or kill someone else !!! or is that your intentionyou should seriously think about asking for help, you must be suffering from some kind of mental disease.

author: deltawars
author_rank: Contributor
timestamp: June 09, 2014, 07:59:40 pm
content: Yer well 100w has gone out the window I cant get hold of the diode any more but I can get hold of 40w and 60w, it still the same idea just a lower current.A 3W laser can blind you, heck its 6x more powerful then Class 4 laser which is the max rating, and I know laser are dangerous that's why I have laser goggles and I take precautions, for example I never use lasers outside of my house and I am always aware of my surroundings, plus I ware long sleeves now after learning that just the beam passing over your hand for less then a second hurts like hell.Anyway thanks for the help I'm just researching some drivers and components. I will be back.

author: rob77
author_rank: Super Contributor
timestamp: June 09, 2014, 08:16:34 pm
content: ok. let's assume you are not a freak going to kill people with a HANDHELD 100W laser...how on earth are you going to dissipate the 300W+ power in a handheld device ? those laser modules are designed for industrial use and they needs to be liquid cooled.what kind of lenses are you going to use ? or will you just illuminate everything around without focusing the beam ?and be aware that even a DARK surface will reflect enough light to blind you.actually i would bet on the following scenario... you somehow put it together... during the very first power on you'll blind yourself and burn the laser module.

author: deltawars
author_rank: Contributor
timestamp: June 09, 2014, 08:41:57 pm
content: Honestly i cant be bothered to argue, i have rated laser goggles and i know how to handle lasers, its not 300W+ its more like 150-180W, plus I'm going to use a 60W diode so its more like 100W.And you cant kill people with a 100W laser, its not as powerful as you think, ok maybe if you managed to get it to a pinpoint then hit them in the head loads of times until the very narrow beam hits a part of the brain that does some damage then yes there is a very small chance you could kill someone, but if I wanted to kill someone i would not waist my time fireing a laser at there head for 30mins until it damages there brain, there is something called a gun or a arrow. And they use 100W diode in hair removal laser that they use on your skin to remove hair so.... did i meantion they also use killawatt laser in cleaning devices to clean metal or strip paint away from cars. And did you know dvd drives and blue ray players have laser diodes powerful enough to burn your skin and blind you.I bet the following scenario, you sit in your bubble wrapped room scared to go outside in case you trip on a pebble and die.

author: max666
author_rank: Frequent Contributor
timestamp: June 09, 2014, 08:52:30 pm
content: I'm with deltawars on this one, he said it's not his first laser project and his last build was a 3 W laser. If he knows how to handle a 3 W laser, then he has already more experience than I do, and i presume he knows what he's getting into with a 100 W laser.Besides, a 100 W laser would be sooo much more effective for doing this:

author: Skimask
author_rank: Super Contributor
timestamp: June 09, 2014, 08:55:11 pm
content: Quote from: deltawars on June 09, 2014, 08:41:57 pmThose that don't know that they don't knowQuoteOh...OK...Everything is ok then.QuoteMath? Or lack thereof...Quote....right.....QuoteAnd those 100W diodes for hair removal and cleaning and stripping lasers likely have a helluva lot more brains behind them than your lasers.QuoteI further bet the following scenario...You sit in your room listening to your text-to-speech reader because you blinded yourself with your 100 watt laser that doesn't do any damage.

author: rob77
author_rank: Super Contributor
timestamp: June 09, 2014, 09:47:56 pm
content: Quote from: max666 on June 09, 2014, 08:52:30 pmif someone is building a FIXED 100W laser for experiments/cutting/engraving.. then it's kind of normal but still extremely dangerous. but when someone is planning to build a HANDHELD 100W laser, that's simply a sick idea. there is no real use case for such a handheld laser other than "let's try and see (till not blind) how it went".

author: rob77
author_rank: Super Contributor
timestamp: June 09, 2014, 09:59:35 pm
content: and furthermore... that 100W laser module is even more dangerous... it's 800nm wavelength => INVISIBLE for the human eyes.regarding those guys point they laser pointers at helicopters and planes - all of them should be arrested. when the pilot is temporarily blinded by the beam he can't react and he might even crash - killing people on the plane and on the ground.this is my very last comment in this thread - i won't fight stupid people.

author: ovnr
author_rank: Frequent Contributor
timestamp: June 10, 2014, 09:36:54 am
content: Well, I certainly agree with the others that you shouldn't do this.Itcertainly wouldn't(wink wink) be possible to use one ofthese babieswith a 60W laser - all you'd need is a current sense shunt (or several - parallel a couple 0.5 mOhm shunts), and something to influence the feedback loop of the DC/DC module. Since any thermal changes would be pretty slow, I'd probably just sample it with a MCU, and control it by pulling gently on the Rtrim pin.As for handheld operation, forget it.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: June 10, 2014, 01:47:02 pm
content: Maybe I am wrong but it seems to me that following solution would have good efficiency:Lead -acid or Li-Poly accu to get 12...14Vdc. The current consumption would be about 15A so You probably need to use two or three batteries in paralell. Then mosfet chopper feeding push-pull (forward) transformer with about 6.3:1 ratio (primary and secondary have taps) and then synchronous mosfet rectifier. I think that current control loop can be sensed on the primary side, on the transformer's common for simplicity.But I wouldn't recommend to try this at home.

author: rob77
author_rank: Super Contributor
timestamp: June 10, 2014, 02:49:45 pm
content: Quote from: doktor pyta on June 10, 2014, 01:47:02 pmactually that would have a terrible efficiency at 100Aapprox 100W on the diodes, transformer losses, mosfet losses...110A @ 1.9V - that's 200W of power to be delivered to the load. add your 100W @ the rectifying diodes, add your transformer losses (significant at 100Amps) and MOSFET losses and you'll get barely 50% efficiency.polyphase buck converter is the only viable solution for such high currents.(p.s. i don't consider this very post as part of the original thread)