I’ve been a long time member of CPF but have lately been drawn more and more to this great forum, so this is my first post here. I have searched this forum as well as CPF for an answer but haven’t really been able to come up with a definite answer so I hope you can help me.
There are a lot of P60 drop-ins that use the linear 7135 driver but this driver falls out of regulation quickly when the battery voltage drops below Vf+0.12 volts. This happens fast on one 18650 with high current draw and will happen long before battery is drained even with moderate current draw. So what really is needed to maintain constant output until the battery is drained is a buck/boost driver. This kind of driver is used in many of the more expensive flashlights (Zebralight sc600 for instance), but I have never been able to find it in a P60 module regardless of price. A buck/boost driver will reqire a coil in the circuit AFAIK so there may not be room for that in a P60, but does it exist?
Ok judging by the number of responses to this thread I guess it doesn’t exist ;-). Are there then any runtime graphs of 8x7135 driving a XM-L with one (good) 18650 battery?
Thanks
Jan
Buck/boost drivers must not be expensive, because all the AA/14500 lights have them. As you say, they need space for some sort of inductive coil device, but maybe they are not popular for lithium only lights because of poor efficiency?
The only 17mm boost driver I’ve seen is for alkaline cells and it only does 800mA out realistically. Look at the boost drivers put in 2-3A lights from the factory, they’re usually at least 20mm and crammed full of components. Plus, there’s not much room inside a P60 pill to begin with.
Boost or buck/boost driver that outputs ~500mA is easy. Buck/boost that puts out 3A or more and fits in a 17mm hole is a different story. This has been the subject of several threads already to come up with a design that could be commissioned, it always ends with 'well it's just not possible to fit the components into the given space'.
Interesting read indeed. I would however happily take 2 amp constant output until battery drained rather than one starting out at 3 amp and decreasing almost from the moment of turn on. I’m currently waiting on an Intl Outdoor P60 dropin but I suspect that the first thing I will do to it is desolder a couple of the 7135 chips to bring it down to about 2 amps. What kind of runtime in FULL regulation can I expect using a 3400 mAh protected cell with a drive current of about 2 amps?
It depends on more than just the cell's capacity. The voltage a cell can maintain under a given load has to be accounted for too. Between two cells with identical capacity the one with less sag will give longer runtime (capacity specs are usually done at only .2C and down to 2.75v, sometimes 2.50v). A cell with less capacity but less sag can in some cases give longer regulated runtime than a higher cap cell with more sag.
They don't shut off when the cell voltage falls to the point it's no longer able to supply the driver's rated current, they just get dimmer as voltage drops. The low voltage protection usually only trips way down at 2.8v, the lowest you want to go with a li-ion, and they will give you plenty of warning before they completely shut off.
Don't confuse the amount of regulated runtime with low voltage protection, they're completely different things.
Yes, they get out of regulation and draw less current as they run down, so they run longer before they trigger the shut-off than with a buck/boost circuit that kept up the current. Also, without voltage boost, the current drops away quickly near the lowest forward voltage of the led, helping to protect the cell from over-discharge.
Thanks Comfy, yes I know it depends on the voltage sag. Internal resistance differ from cell to cell. I just wanted an approx regulated runtime. hasn’t anybody made a graph of a typical setup with 1x 18650 and a number of 7135?
Intl-outdoor has a 1A buck-boost driver that is based on the TI TPS63000 IC. It is a true buck-boost driver that will provide constant output (no gradual dimming) down to the low voltage cutoff at 2.7v. They used to offer a 3-mode driver without the blinky modes but it appears they don’t have them anymore. This driver is essentially the same as Shiningbeams 3-mode perfect regulated circuit used in S-mini.
A buck-boost driver with output greater than 1A that is smaller than 17mm in diameter as far as I know of doesn’t exist.
Thanks. If only I could find a P60 module with this driver in it I would buy it instantly. Strangely though there dosen’t seem to be ANY P60 modules with truly regulated output on one 18650 - not even 1 amp ones.
Apart from the space issue inside the module, thermal transfer is another thing that can contribute to why no constant current p60 module available so far.
for XML, driver used in my light is almost like direct drive.
as for nichia 219 one, I use nanjg101 with 1.4A output.
Hi JanBLF, I have the ShiningBeam version of the 1A driver linked above and its not a boost driver, it’s just a very well regulated linear driver. It works the cell harder and harder to keep the 1A output until it’s incapable of providing the current, then drops to low mode and starts the low battery warning flashes… Also, if you like the sound of the 1A driver, ShiningBeam still stock a 1.4A regulated 3 mode driver as well. they dont advertise it as having a perfectly flat output like they did for the 1A driver, but I guess that doesn’t mean it will be any worse, either.
Can you solder? It would be very easy to swap an existing driver on a P60 drop-in to that 1A or 1.4A regulated driver you are interested in.
Edit: Hmmm according to lilkevin715 above, maybe thats not how it works? Thats how it appears to work, but I am not an EE… I dont know why its considered a boost driver, it doesn’t “boost” anything (it also has a low voltage cut-off at 2.7V) :~
Since all the commonly used LEDs have a forward voltage well above 2.7v even at the lower 1A output, if the driver is able to maintain an actual output of 1A or 1.4A all the way down to the cutoff, it's got to be a boost driver. Any other type will reduce the output as soon as the input voltage falls below the LED's Vf at whatever desired current.
If it's not a boost driver, assuming an XML2 and the 1.4A driver, the part of the run from around 3.15v down to 2.7v would not be able to do the rated 1.4A (or from 3.05v down to 2.7v for the 1A version). If you give an XML2 only 2.7v, it will only run at around 150-170mA.
I think the word 'regulated' is being used rather inaccurately to mean 'limited to no more than'. Fairly common misuse of language when it comes to drivers.
Yeah It’s so annoying when the term regulated is used when in reality the output is decreasing almost from the moment you turn on the light. It’s so easy to meassure whether it is a true constant output driver with boost, because the current draw on the battery (current at the tailcap) should INCREASE from the moment of turn on all the way to falling out of regulation.