I've been wondering about LED strips and how its individual LEDs are being powered.
My knowledge about LEDs is very basic. I know they're diodes, I know they tend to draw more current than what's good for them, hence current needs to be limited. That happens e.g. via a constant current power supply or a resistor in front of every LED. Former one, as far as I get it, only makes sense if you know exactly how much current is to be drawn, which maps to the need of knowing the exact amount of LEDs to be driven, which is is not the case for LED strips which you can cut almost everywhere. On top - at least that's what I'm assuming writing this post - individual LEDs need to be supplied with moderate voltages <= 5V, otherwise they might get damaged.
So, there's those WS28xx protocol driving LED strips, cubes, matrixes, .. where you're able to address single (groups of) LEDs individually.
And then there's those "5050" LEDs, which I understand as physical packages for (RGB(W)) LEDs having whatever control logic on top of it (e.g. implementing one of those WS28xx protocols).
There's those famous WS2812B LED strips with 5050 packages containing RGB LEDs where you can't only address every single RGB 5050 package, but also every single physical LED inside (=every color). Those strips can be cut after (almost) every 5050 package and are powered by 5V which makes sense to me, as you can "just" power each physical LED with those 5V (again, limiting current still necessary). Then there's those WS28xx strips which can be powered by 12V where however only LEDs of groups of three can be individually addressed (which probably doesn't mean the three physical LEDs (=colours) in one 5050 package, but one physical LED (=colour) in three 5050 packages). Which also sounds sane to me, as 12V/3 = 4V which probably is also fine to drive individual LEDs.
Makes me wonder though, how to cut the strips then. According to my understanding I would also only be able to cut them into groups of three, as if the last part would be only a group of two or even one 5050 package, they would receive a too high voltage of 12V/2 = 6V or even 12V/1 = 12V. But at least the dumb (=non-WS28xx) 12V/24V RGB as well as white-only strips I have here I can apparently can cut after each 5050 package.
Then there's the relatively new WS2815 RGB LED strips, which are also powered by 12V, can be cut after each 5050 package, and where every physical LED (as in: every colour within each 5050 package) can be individually addressed without any grouping.
How do those >= 12V LED strips - which can be cut after each LED / 5050 package - manage to drive the individual (physical) LEDs at non-damaging voltages?
Half-knowledge: I doubt every package has a DC-DC step down converter in it - would be too big / costly. Also, I can't imagine the remaining energy (12V-5V = 8V) just being dispersed as heat (sounds like a horrible waste of energy and I'd also wonder if those strips could even handle the heat). When looking at some (admittedly rather dodgy) datasheets of the new WS2815 strips, I can see for some there's a mention of some 2kHz PWM control as part of the 5050 package. Are those individual physical LEDs maybe PWM'ed by >=12V in a way so they don't get damaged? If not that directly(because it's still >=12V) I could imagine the PWM curve being flattened so it boils down to some reasonable voltage? This only speculation based on half knowledge, though..