Hi,
I understand that boost drivers are like DC-DC convertors, ad “step up” the input voltage to a higher voltage. But then, why is it that in their specs, they don’t specify the output voltage?
For example, in the specs for this driver from FT:
https://www.fasttech.com/products/1143101
there isn’t any spec for the output voltage?
We could assume the output is current limited so the voltage output would be what the forward current allows.
LED's are not voltage mode devices - Their forward voltage will vary from part to part and over temperature. For this reason, most LED Driver's don't specify an output voltage - they are current controlled drivers and will adjust their output voltage to supply their rated current through any (reasonable) LED.
That said, a few points of interest with a pure boost circuit.
PPtk
Unless you add an extra transistor for a load switch…
Well, yeah, sure, but that's generally not a function of the boost converter itself.. There isn't much that can't be shut off with an external switch. At that point, though, you may as well toss in another inductor and make it a buck-boost..
Hi,
Thanks for all the responses. I was kind of guessing that such a driver would output the Vf of the emitter. I think that the question that I was really heading towards was, then, could a driver like I linked above, potentially drive (even dimly):
- A single MT-G2 emitter?
Also, a kind of related question: Would the current at the emitter(s) be governed, at least roughly by the wattage on the input end vs. the wattage at the output end?
In other words, W=VI, so does:
V (in) * I (in) ~= V (out) * I (out)
and assuming we know the emitter Vf, that’s the/a way to approximate the I (out) that a boost driver would be driving to the emitter?
The answers are a bit difficult, and since you're going to have a hard time getting any real technical detail out of a china-source, you might have to try the age-old testing method of "hook it up and try it".
In theory, it should be able to boost its voltage high enough for an MT-G2. In practice? Maybe.. We don't know how high the components on the board are rated to operate at. Depending on your input voltage, you might also be into the very inefficient stage of a boost converter. Vout > 2 * Vin starts to get really ineffiicient.
Your equation is essentially correct, but don't forget to factor in losses. They can be significant. A good general purpose equation for a boost converter like this is
Vin * Iin * 0.8 = Vout * Iout
At high boost ratios, that 0.8 will get even lower.
PPtk
Hi,
Thanks for the info, and yes, my plan is to “hook it up and try it”, but wanted to get some basis before that. I have both the 800 mA and the 1000 mA one coming in from FT.
Actually, I’m most interested to see if it can drive this (3xLuxeon in series) 3up:
http://www.ledsupply.com/07007-pw740-l.php
they’re on closeout/clearance, and I bought several of them, plus the Carclo lenses.
Now, I’m trying to figure out what to do with them (power, host, etc.). Kind of bass-ackward, huh :)?
I’m currently running one of those DD with 3x10440 drained, and have some 10440 LifePO4s coming to try, in a Defiant AAA partly built, but would like to use a driver if I can find a cheap one that works, so I’m planning to try both the FT 1000 mA and 800 mA with the 3up I have now (others in transit).
Thanks. I’ll post back when I have a chance to try them out.
There may be better choices in 2013, especially if that $6.99 (plus $6.99 shipping) is the actual price (!!!) but sticking to the point…
One spec I noticed right off is, the 3up is rated at 1000ma (I’m assuming net (Series), not per-LED (Parallel)); and the driver claims it gives 1000ma with Alkaline batteries.
From their discussions:
> Here are manufacturer’s rated currents:
>
> On alkaline batteries: 960-1000mA
> On 1*Ni-MH: 1.8A max
> On 2*Ni-MH: 3.9A max
Even if it’s Ibatt, 1.8A means a rechargeable would kill your lovely old Rebels, I’m pretty sure.
Seems important…
OTOH, if the 3x turn out to actually be in parallel, nevermind…
As to Results,
> Neutral-White 3-Up Endor Star Features:
> 270 lm \ 350mA
> 486 lm \ 700mA
Is that for the whole Endor Star, or for each LED in the set? Either way, that seems strangely…
… wait for it …
Dim, Bo!
(Sorry, I’m a glutton for PUNishment!)
Hi,
By default, the populated star comes with jumpers (2 0-ohm resistors) to make the 3 emitters in series. There’s one pair of unpopulated /- pads so you feed the ~9V to the/-. As I mentioned in another thread (search “18250” here on BLF), I’ve had the 3 up running with 3x10440 where I drained the batteries using my hobby charger to about 3.5V each. I haven’t measured the current, but it’s whatever the maximum of the 3 emitters is drawing, since they’re in series.
I know that some people have removed the 0-ohm resistors and wired the 3-up so that the 3 emitters are in parallel, but I didn’t want to do that (the star is tiny, and I couldn’t picture trying to solder the jumpers that would be needed). Again, this was DD from batteries (in series, in a 3xAAA carrier).
Anyway, I think that if I could find a (boost) driver that would drive ~9V at 1000 mAh, I think that I’d be at spec for the emitters. As I said above, I haven’t measured the current with DD, but I’m thinking that it probably is > 1000 mAh.
That’s actually why I’m looking for/at boost drivers. As I said it works DD, but I have no control, or idea, what current is being driven. I’d much rather have a driver that I “know” the drive current somewhat.
As I said in the “18250” thread, this is kind of an experiment. It’s mostly a “let me see if I can make this work without killing the emitter” experiment, but actually, I’ve kind of messed up the 1 3up I have (melted the domes) earlier, but the emitters still (amazingly) work, so I’m using that 1st 3up as my “sacrificial lamb” for experimenting. I have a couple of more of them coming in, so I want to apply whatever lessons learned for those later.
Edit: Going back, the question I originally had, which I think has been answered now, was how the boost drivers behaved voltage-wise. I wasn’t sure if they were limited to 3.6-4.2V output, but if they really can boost to 9V, then it’ll be interesting to me, to see how they work with the 3up.
Edit 2: FYI, I think that the Luxeon datasheet says max current is 1000 mA. The max Vf seems to be different for different emitters, but it’s unclear exactly which emitters are on the NW 3up, so it’s hard to tell. I think some of them even go up to 3.99V max. Just a point of info.
Weeeeeelllll….
That DD battery holder still has AAA batteries in it, which don’t seem to flow a whole Amp anyway. That (IMNERHO) is one of those “beautiful things” about modern, high-current LEDs: you just stack enough Alkalines to make Vf and lead the heat away. I’m not sure even AAs can flow a whole Amp. The 10440s also seem limited to <1000mA, so you’re still in the butter zone.
It’s really worth it (again IMNERHO) to have on hand a high-wattage (to handle any current), low-ohm (to minimize footprint in a circuit) “ballast” resistor. Add one in-circuit somewhere, measure Voltage across it & get a much better read on Current. I think. Mostly it saves having to break the circuit to insert the Ammeter…
This may be one of “those” moments… The driver you mentioned looks very interesting, but the legends of the wild performance claims in these drivers are legendary. I (for one) really hope you’ll measure it carefully & report back here what you find!
I’d wager it won’t make the numbers in the ad, but if it does, the Luxeon Rebel ES is only rated to 1000mA, so I’m still thinking you’ll blow them. IFF the ad is correct, of course!!
As for me, I’d like to see one on a 14mm disc, but other than that, this might be the perfect upgrade (along with a momentary-on switch) for a Trustfire F20/Akoray K106!
Dim
Hi,
Re. “That DD battery holder still has AAA batteries in it, which don’t seem to flow a whole Amp anyway.”, I don’t understand what you mean? I haven’t/didn’t tried with 3xAA and the 3up, but rather only used the carrier with 3x10440s.
I’ll definitely test with both the 800 mA and the 1000 mA driver, that’s my intention, and I’d really love to be able to get the 3up working in a tube light like the F20 (or Convoy S3), but the problem I keep coming back to is being able to drive 9V and 1000 mA with a battery or batteries in such a host, which lead me to try the 3x10440 in the Defiant AAA body.
The thing is, even though I can DD in the Defiant AAA body with the 3x10440, the body is not exactly amenable physically for the 3up and Carclo optics. The problem is that the optics height is tiny, like less than half an inch, whereas the head of the Defiant AAA is about 2 inches long, so the front of the Carclo is more than 1.5 inches away from where the original lens was for the Defiant, i.e., no way to secure the Carclo.
So, the choices I’m considering are:
- Chop the Defiant AAA head, somehow, but that’s going to be a lot of work, I think
If either of those drivers work, then I think it’ll give me a lot more options, since I can then consider a tube light like the F20 or Convoy S3, since I can maybe use just one 18650, rather than 3 4.2V batteries.
I’m still waiting for the 2 different drivers from FT, but meanwhile, a couple of points of info:
- the 3up, DD with 2x10440 fully-charged (4.2V unloaded) + 1 dummy 10440 - tailcap current ~50 mA. The LEDs do light up, not as bright as fully driven, but much brighter than firefly or moonlight. Something like a “low-semi-low”. I couldn’t measure voltage across the star, because it was too bright (star is in a Defiant AAA).
- the 3up, DD with 3x10440 fully-charged (4.2V, unloaded) - very bright, but I couldn’t get tailcap current yet, because the emitter domes started smoking :), so I didn’t leave it on. But, the amazing thing is they still work. These Luxeons seem pretty tough!
Still waiting for the 10440 LifePO4 batteries to come in, but looks like they, and the drivers, will take another week or so to arrive.
Edited above to mention using dummy 10440 for the 2x10440 test.
First, an update to my last post. I’m still waiting for the LifePO4 10440s, but I was able to test with 3x10440 Li-Ions, discharged to 3.4V (total 10.2V) in the light, and, DD, I measured ~1.2 amps at the tailcap).
Also, I received both the 800mA and the 1000mA driver, now I’m wondering which one to test and the best way to test?
I’m thinking the 800mA one has the best chance of being able to drive the 3up, and would like the modes, but I would prefer the 1000mA driver it if can drive the 3up at 9V.
I’m also wondering how the 1000mA one will work with an Li-Ion, like a 14500 or 18650, or maybe even 2x16340 or 2x18350? Would it be able to drive 9V and 1000mA?
So where to start? Should I just try one of them with 2xEneloops?
Also, when I test, what should I have hooked up on the output end? Should I have one of the 3ups hooked up?
Sorry about all of the questions!
I did a simple test with both of the boost drivers from Fasttech with 2xEneloop AA, and neither of them could light the 3up.
I measured voltage:
800mA boost driver (high mode): 5.17V
1000MA boost driver (it’s a single mode): 5.08V
So it seems like neither of these boost drivers can boost the voltage enough to light the 3up emitter(s).
I think that maybe I need to find a boost driver that can take Li-ion input and that can boost to 9V?
Jim
Edit: I also just tested with an 18650. Emitters would not light, and output voltage from the driver was ~5.46V.
So, it seems like, for whatever reason, this “boost” driver is only able to boost to something like 5 volts, regardless of 2xAA or Li-ion 
You are lucky that this driver’s output voltage is limited to the maximum it can take. 
Many boost drivers will simply fry themselves if you do not limit the voltage properly. (like turning them on without or with to much LEDs ).
Better try a driver that is made for multiple emitters. I think DX has some of them.
Part of this thread is trying to understand/characterize boost drivers (see OP), but partly for a project I’m working on, so it was a risk that I was willing to try this time, so I’ve learned now that, generically, a boost driver isn’t going to output just any voltage, but will have some maximum/limit. As I said, in the case of the 1000 mA one, about 5V.
Edit: Going back to the OP, so then, shouldn’t these vendors also specify maximum output voltage, rather than just the output current? Why don’t they do that?
Ok, I see. 
If the driver is boost does not mean it will boost any voltage the load would permit at 1000mA or that any input voltage is acceptable to the boost driver.
Some of the specs are off and I believe it's the manufacturers that offer the poor specs.
Again, that was kind of why I originally made my original post. Reading up about boost circuits (basically DC-to-DC convertors, I think), it seemed like they always had a max output voltage, and yet most, or maybe all, of the boost drivers for lights mention only output current, and not output voltage.
It’s like the assumption is that output voltage will be in the 4.7V range, but it’s never stated. With lights like the MT-G2 (and multi-emitters), the voltage becomes important, so not knowing the max output voltage is problematic for finding a driver that would work.