# Understanding CREE running on 1.5VDC



## The Gadget Guru (Jan 19, 2015)

Hello CPF Community,

Please help me understand the engineering behind a CREE LED running off different voltage sources.

The CREE XP-L chip, for example, has a forward voltage of 2.95 to 3.25 VDC.

Some lights work with numerous battery options...for example: CR123A output = 3.0 VDC, 16340 output = 3.0 or 3.6 V, AA output = 1.5 V, and 14500 output = 3.7 V (all nominal).

*To run a CREE on the lower 1.5 V AA does the Cree LED driver module in the light use a DC-to-DC converter to increase the working voltage to that of the CREE chip? I'm truly interested in how the CREE chip can run on only 1.5 VDC without a voltage increase.*

My electronics GUESS is that all the magic happens in the LED driver module...from having a possible wide voltage input to being able to drive the chip with a constant current to being able to have continuously-variable outputs.

Anyway, thanks for any responses. My web searches have thus far been ineffective at answering this.

The Gadget Guru


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## reppans (Jan 19, 2015)

HKJ has a good write-up HERE


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## The Gadget Guru (Jan 20, 2015)

reppans, that's what I'm talking about! Great info..perfect explanation and exactly what I suspected but couldn't that info myself.

I'll post this separately but in case you see this...I'd be interesting in knowing how to obtain chip drivers and do some experimenting.

Eventually I'd like to, not by myself of course, design a custom torch complete with hand-selected driver, chip, and integrate the features I'd like to see. My son is a CNC/MasterCam programmer star and could draw up any design. It would be quite interesting rather than continuing to scour the Interwebs for the next best torch design! Of course, there is a LOT to doing this so like the Flux Capacitor for now it's just a vision...a vision in my head! You need sources to produce what you make and you have to decide if you are going to make 12 or 500 units (BIG difference).

I appreciate your response and I'll keep posting/reading. Great hobby! Thanks again


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## reppans (Jan 20, 2015)

Another HKJ link HERE


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## more_vampires (Jan 20, 2015)

The Gadget Guru said:


> I'd be interesting in knowing how to obtain chip drivers and do some experimenting.



Illumn Supply, Led Supply, DX.com, Mouser, Digikey...

Cheap ones are CHEAP! Expensive ones, less so. Still not bad!


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## The Gadget Guru (Jan 20, 2015)

Whoa! That is the cat's meow right there! I could read this guys stuff for ages! Me wanna play now!

I like the lights and all but I'm really into the tech that makes it all possible. Some people know their video card part number by heart...I want to know what kind of LED chip driver I'm driving around with!


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## The Gadget Guru (Jan 21, 2015)

Say reppans, who is this HKJ wizard and is there a source for his web content that I can view?

Thanks!


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## reppans (Jan 21, 2015)

HKJ is THE battery/charger guru and tester around here, check the battery sub-forum for his reviews and posts. 

http://lygte-info.dk is his website, but there's a lot more that may not be easily found from the above link. I google lygte + subject to find some stuff - never found a comprehensive site map for all his stuff yet.


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## The Gadget Guru (Jan 22, 2015)

THIS. THIS is my kind of guy! That could easily be me. I'm a test and measure junkie. I have a pretty nice setup but it is electrical mostly. I don't have (but would like to!) have the stuff to measure lumens, for example. I have o-scopes, process meters, soldering/de-soldering gear, the works.

I love testing stuff and finding out if the specs, as advertised, are true. So many times they are not. My S30R just came this week and it says 1,000 Lumens on Turbo. The paperwork with it says you can do that but ONLY with CR123A batteries and NOT the 18650 it comes with. Interesting fine point.

I used to be really into battery charging for most effective recharging and was into pulse charging techniques since pushing a constant current into a battery is not a good way to recharge a battery. Now with Lithium Ion the charging designs must be REALLY special to avoid all that energy from going into runaway.

Thanks reppans for the info! I appreciate it!


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## more_vampires (Jan 22, 2015)

The Gadget Guru said:


> THIS. THIS is my kind of guy! That could easily be me. I'm a test and measure junkie. I have a pretty nice setup but it is electrical mostly. I don't have (but would like to!) have the stuff to measure lumens, for example. I have o-scopes, process meters, soldering/de-soldering gear, the works.



Lux meter, integrating sphere. Happy searching!


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## The Gadget Guru (Jan 22, 2015)

I though Reddit was ruining my life...NOW I also have CPF competing for my time and, unfortunately, also for my money!

I can Reddit ALL DAY and not spend any money. HERE, someone will say "Hey, check out THIS crazy new torch make from Titanium with Tritium rings and all that!" and I'm wanting to bust out my wallet immediately!

My wife, on the other hand, is NOT happy I found CPF! Bwahahahaha!


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## Anders Hoveland (Jan 23, 2015)

The Gadget Guru said:


> *I'm truly interested in how the CREE chip can run on only 1.5 VDC without a voltage increase.*


If the LED emitter itself is being supplied with only 1.5v, it should not be possible for it to light up. The energy of photons with a 460nm blue wavelength is 2.695 electron-volts. That means it takes _*at least*_ 2.695 volts to be able to produce blue light from the semiconductor junction. (and a white LED is just a blue LED emitter coated with some phosphor)

The power supply is likely a constant current circuit, and is converting up the voltage.


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## The Gadget Guru (Jan 23, 2015)

Anders Hoveland said:


> If the LED emitter itself is being supplied with only 1.5v, it should not be possible for it to light up. The energy of photons with a 460nm blue wavelength is 2.695 electron-volts. That means it takes _*at least*_ 2.695 volts to be able to produce blue light from the semiconductor junction. (and a white LED is just a blue LED emitter coated with some phosphor)
> 
> The power supply is likely a constant current circuit, and is converting up the voltage.




Yea, Anders, I figured there had to be some hardware between the power supply and the chip to bump the output volts up enough to drive the chip. rappans directed me to a great site above that shows those driver circuits. Pretty cool stuff! It's amazing how those circuits are able to do so much in such smaller and smaller packages and we are talking about driving AMPS of current!

So if you are boosting the voltage you are reducing the available current for a given output wattage so really while AA and AAA batteries are small and readily-available they are not truly a suitable choice for today's newest available lights unless you accept a lower Lumens output OR sacrifice run times overall.


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## more_vampires (Jan 25, 2015)

The Gadget Guru said:


> So if you are boosting the voltage you are reducing the available current for a given output wattage so really while AA and AAA batteries are small and readily-available they are not truly a suitable choice for today's newest available lights unless you accept a lower Lumens output OR sacrifice run times overall.



15 years ago, we just didn't have the AA and AAA lights that are around now. LED has gained efficiency, runtimes increased as well as outputs. Boosting a 1.2-1.5v cell will suck it dry faster, yeah.

You picked a really good time to "catch the addiction." 200 lumens from a single AAA is no big deal. In the same battery size lion (10440 unprotected high drain,) I get ~1200 lumens at turn on for my favorite pocket rocket. Runtime at this insane level is 6 minutes total limited to 2 minute bursts because of heat. That same energy could literally last days if the light were designed with runtime in mind.

So, it's really how the light is optimized. Yeah, it's all a balance. Capacity, over-voltage, and efficiency give you more to play with. We just plain couldn't heat-out an AA/AAA sized light 15 years ago.

There's always a cost to be the boss.


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## The Gadget Guru (Jan 25, 2015)

more_vampires, I've certainly HAD this addiction for a long time and have seen the progression over the years from really early LED lights to the insanity that is coming out these days such as the Trulight TN36...that looks CRAZY COOL. It's like owning your very own LASIK machine!

I was into strobe lights as a kid big-time and now that is a standard feature of most all new lights.

Most of my various collection is WAY under the awesomeness of much of what I see here. I just got an Olight S30R and one other truly interesting light I have is a Dorcy Metal Gear XL-M Extreme 618 Lumen light that runs on 6 AA batts. It's unregulated but built really nice and has a really nice output for color temperature and tint. Unfortunately it won't run on Lithium Ion batts but otherwise is really nice.

My EDC for many years was an Inova X5 that has served well and traveled the world!

What I would LIKE to do is design a concept whereby people could build the light they want via a web site. Pick your housing and desired power supply, choose the driver chip you want (continuously-variable output versus stepped, for example), pick the chip(s), etc...You would have lots of options and, in the end, would get what you want. Want a Titanium light that puts out 6,000 Lumens? We could do that. Want a spot beam versus a floody beam? Want laser engraving? Tritium tubes? Go for it!


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## more_vampires (Jan 25, 2015)

The Gadget Guru said:


> more_vampires, I've certainly HAD this addiction for a long time and have seen the progression over the years from really early LED lights to the insanity that is coming out these days such as the Trulight TN36...that looks CRAZY COOL. It's like owning your very own LASIK machine!



Seen the Olight M2X-UT Javelot? It is rumored to be the current off-the-shelf throw king from an "official" marque. You might CPF search for "led de-doming" if you're wondering why.



The Gadget Guru said:


> What I would LIKE to do is design a concept whereby people could build the light they want via a web site. Pick your housing and desired power supply, choose the driver chip you want (continuously-variable output versus stepped, for example), pick the chip(s), etc...You would have lots of options and, in the end, would get what you want. Want a Titanium light that puts out 6,000 Lumens? We could do that. Want a spot beam versus a floody beam? Want laser engraving? Tritium tubes? Go for it!



Heh. You're wife is going to kill me. *Want to melt a black plastic trash bag?* :devil:
http://lux-rc.com/content/products/flashlights/FL33_EDC/special_offers
Bring your wallet and time. They don't roll of that line very fast, patience.

The problem with doing a site like that is the makers will be crushed and buried under a mountain of orders.. even for a light in excess of ten Benjamins.


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