so you're saying that every flashlight that uses a boost or buck circuit has PWM even on the highest mode?
absolutely.
I somehow seriously doubt that....
So what do you guys think for the 1.5 vs 2.5 amp dropins? I know I want one of them, not sure if I want to take the output hit from 2.5->1.5 amps... The manafont dropin has ridiculously bad runtime and pwm... Probably partially cuz I only use my 60 18650's pulled from laptops....
Absolutely incorrect.
There are quite a few flashlight drivers that are current controlled and have no PWM output at all. Fenix, Quark, Eagletac, Klarus, and many others make lights with fully regulated drivers and NO PWM. My Lumintop ED20 uses PWM only for the Low mode, and current controlled for Med and High. The PWM is at 800Hz and not noticeable until you hit a fan or running water with the light on Low. I also have a couple of Quarks that are fully current controlled, even on Low and Moonlight modes - NO PWM at all, and they have buck and boost circuits.
PWM is easier and cheaper to make, which is why you tend to see those drivers in cheaper flashlights. In more expensive flashlights you tend to find better driver circuits that do not use PWM. You can find flashlight test reviews that check for PWM and they clearly show which lights are current controlled and which use PWM to control output.
Absolutely Incorrect. What do you think a boost or buck 'driver' is? It's a SMPS - SWITCH MODE POWER SUPPLY. The SWITCHING is PWM. Just because the people who do flashlight test reviews don't have equipment to 'see' 2 MEGAHERTZ PWM, Doesn't mean it isn't there.
PPtk
We have to be careful what is the PWM signal doing. NOT every flashlight that uses a boost/buck circuit has PWM in which the output is being switched fully ON and OFF. It is true that "some" designs use PWM on the output, and some use PWM internally, but not visible on the output.
Again, not every LED driver uses PWM. Some do, not all of them. Some of the better LED drivers do accept a PWM signal as an input signal, which translates to constant current output level, and that level is variable per the duty cycle of the input PWM signal. On this type of LED driver, there is zero PWM of the output current reaching the LED, so there is zero strobe effect for humans or camera/video. The PWM is purely an input signal to set the output current level.
Some other drivers have a boost/buck (or buck/boost) and they have a constant output, and achieve dimming by using PWM on the full output signal. These unfortunately could have a strobe effect on humans, and even more so on cameras (since their shutter is much faster than the average human eye).
Will
What we associate with a visible strobe of the output based on the dimming level is in fact normally associated with PWM in which the output current reaching the LED is completely being turned ON and OFF. Again, the current goes to a max level, and then to zero, as per the duty cycle of the PWM signal in order to achieve a dimming effect since the human eye can't "see" the complete switching ON and OFF.
This PWM above is COMPLETELY different than the switching frequency of the energy storing component in a switching power supply (buck/boost or buck-boost). This PWM is an internal signal which the controller IC uses to control the charging and discharging of the storage element (most commonly an inductor). This frequency, which you correctly state is usually much higher in the 100's of Khz or low MegaHz, is absolutely NOT the same as the PWM above, as the output current in this type of LED driver does NOT go from a high value to zero, and then again to a high value and zero!. This PWM signal is seeing on the output as an output ripple, basically an AC signal, on top of the average (DC value) of the output current. This DC value of the output current is the "set" level, either based on a sense resistor, or like in my previous post, an external PWM signal or Analog voltage sets the dimming value for the controller - this external signal sets the "target" DC current.
So NO, the PWM that causes visible effects in the output is 100% completely different and has nothing do to with the internal PWM signal used by the controller IC on a DC-DC switching converter.
What makes all of this even more confusing is then you combine both: you have a DC to DC constant current driver (which uses a very high speed PWM for the switching function) AND then you apply an external PWM signal to change the set point for the output current. This type of driver gives you a non-pulsing output (output is still constant current, with a small AC component from the switching frequency) AND it also gives you dimming capability, and the human eye (or cameras) just sees a constant output throughout the output current range.
Note: The key is to keep in mind that PWM is just that - pulse width modulation, and it can be used in many ways:
- input signal
- output signal
- internal signal
PWM by itself does not always mean that the output current is being switched fully ON and OFF. Internal PWM and output PWM are completely different, one being visible to the eye, the other not.
Will
Seriously.. I give up.. How many Switch Mode (Buck/Boost) drivers have you designed? I'm going to take a wild guess and say zero.. I suggest looking up the terms "Ripple Current", "Peak Inductor Current", "Average Inductor Current", "Ripple Voltage", and "Switch Frequency". These will all take you to references which illustrate how Boost/Buck converters operate and how PWM (or FM) interacts with an inductor and an output capacitor to form a rippled output voltage. Where's my face-plam smiley....
Lets get this thread back on topic... and thanks for answering: No, this dropin has no commonly detectable PWM that will affect use. 
Deleted; Agreed - Thread back on topic.
- One PWM voltage regulated design (been selling it for about two years now).
- One really, really simple boost circuit (been selling it for about 2 months now)
- And about 2 weeks ago started the early work on a 2amp buck DC-DC converter using the LT3518.
I am likely not even close to being as experienced as you are, but I "do" understand PWM.
My reason to post is to clarify how we use the term. We can't throw the term PWM out there without clarifying how it is being used, specially since most people's idea/perception of PWM is the negative side of PWM, when it is being used to fully switch ON/OFF the output current, which yes, causes grief to some folks due to they being sensitive to it. Plus in video recording, this type of PWM at the output is usually "seen" by the camera, so it is no good.
But PWM can be part of a design and be a good thing, like the internal PWM used in the storage element, which is that creates that AC ripple. That PWM is generally not visible, and therefore not necessarily a bad thing.
My apologies for derailing the thread ...
Will
Thanks Will...that sums it up nicely. I don't know all the details of the electronics involved, but I do know that visible PWM is from the high frequency switching On/Off of the emitter, and that a current controlled output keeps the LED lit continuously and simply reduces the current to the emitter to reduce output. That's why many of the current controlled lights have slight tint changes as the output level changes.
You are welcome, but I still got carried away. My apologies to PilotPTK and everyone for the off-topic content 
No worries, we both got over-zealous.. I'm sorry about it as well. I guess we can only hope that someone can read through it and learn something... PWM - Not necessarily good, not necessarily bad - all depends on the context, the purpose and the frequency.
PPtk
Sorry I forgot about this thread and missed all the fun. It's hard to keep up with all my reviews.
First off; nobody need apologize and/or delete anything from a lively discussion that educates. Seriously - I learned more about PWM from the above exchange than I ever knew. And, while it may be unpopular to take sides, Pilot's day job kinda speaks for itself.
As an end-user, what I care about is PWM that I can see, simply by turning the light on. If it is so fast that I cannot detect it with my eyes then, PWM is well sorted on that particular module. The ubiquitous 3-mode UF XM-L (sku 5720) we all know and love has significant PWM on medium and low. If I'm taking a picture of an engine stamp under a car and need some light for the shot, I'll turn my UF/XM-L equipped L2P on low or medium and PWM shows up on the screen as a slow stobe. In fact, when I take multiple shots under these conditions, a few will be a lot darker because the camera caught it between . . . wavelengths or whatever.
That's how I discovered I could somewhat determine PWM with my camera. When held at just the right angle in front of my camera, on low or medium the UF drop-in produces a slow oscillation with smooth, fading lines seemingly spaced far apart. The same experiment with this XM-L module from IO produces fast moving lines with sharper edges that are very close together. With some drop-ins, the oscillating "waves" will take almost a second to pass fully across the LCD, with others the lines are so close together that they are barely indistinguishable.
Sorry for the ramble and I also apologize in advance if I'm getting this whole PWM thing completely wrong.
Foy
Did you end up dissecting one of these modules Foy? I’m really curious about the details concerning how they were put together. However, please don’t engage in the exercise just because I’m asking. Just, you know, if you were absolutely going to do it anyway, I’d love it if you remembered to come back here and give us the juicy details 
Thats how it looks on the inside:
Credits to Turbo-Siggi @ TLF: http://www.taschenlampen-forum.de/taschenlampen-neuigkeiten/12205-solarforce-p1-7.html#post172798
NightCrawl is the man. Saved one of my modules from certain death.
Foy
Thanks NightCrawl!
I’m trying to sign up to that forum, but it’s asking me an anti-spambot question:
Ich seh den … vor lauter Bäumen nicht. Nennen Sie das fehlende Wort!
Translated by google, it is: I see the … not from sheer trees. Name the missing word!
But, what’s the correct missing word, in german I presume?
LOL
Nevermind, “wald” (forest)!