How are 300 LED curtains running on only 5V USB?

[Colttt]

How is it that you can run 300 LEDs on only 5V? Any videos?

 

[brianmoooore]

Forward voltage of a white LED is about 5V, so what's the problem, as long as you keep track of the total current?

 

[Colttt]

Got it! I am understanding more each day. All you would need to do is limit the current...

So why do people still choose to use high voltage? What's the benefit of high voltage if any at all?

 

[Martin]

Higher voltages mean longer cable runs before volt drop becomes a problem. Also at 5V, the current can be high, necessitating thicker cables. So 5V is ok for short runs, but usually 12 or 24V is preferable once you get above a few metres of cable run between PSU and LED. The higher voltage LED's are usually just multiple LEDs in series. Each LED will be about 2-3V.

 

[pc1966]

Since LEDs operating point is defined by the current (light output is more or less dependent on current alone) and the forward voltage is quite temperature dependent, you want to regulate current.

By connecting a set of LEDs in series you can regulate the current in ALL of them by regulating the current from a single higher voltage supply.

Parallel operation means thicker cables (as covered above) and also some means to make sure the LEDs all share the current equally, which normally means separate regulators or (power-wasting) ballast resistors per LED.

 

[Julie.]

As above.

The situation with LEDs is very confusing, if you take the component itself (the actual LED) typically you control the current to say 20mA (0.02A) and there will be a certain voltage drop , say 1.6V for a red LED, 3.5v for a white LED and a host of voltages between for the various colours.

If you have 10, then you could put them in series, control the current to 20mA and the volt drop would be 10 x 1.6V = 16V.
( but if you have 300, then 300 x 1.6V = 480V - so not a good idea)

If you put them in parallel then the volt drop should be 1.6V, but the current would be 0.02A x 10 = 0.2A (200mA), unfortunately you can't control how much current goes through each LED this way, as one could take 100mA, another 0.0001mA, etc as long as the total is the 200mA , this would destroy the LED taking too much current, then the next and so on.
So isn't a good idea either!

The solution(s) is to make each "LED" actually a LED plus a little control circuit, so you put 5V on the LED assembly and the internal control circuit manages 20mA.

Thus you can put 300 "LED assemblies " in parallel and each would control the current through its own LED, in this case you control the voltage to a fixed value, and the "LED assembly " itself controls its own current.

There are many other ways of doing this, unfortunately in common terminology they are all just called LEDs - whilst some are (and need their own circuitry), others have an integral current control circuit - so need the voltage to be fixed, others are self-standing - such as an LED Lamp replacement for a domestic lamp, some others have a complex control circuit often used for Christmas lighting - where the colour can be controlled.

These latter devices typically known as pixel LEDs - ws2811 and so on are used for seasonal lights as you can have synchrononised lights to music, moving displays etc.

Try here Different Styles of Pixels - doityourselfchristmas.com - https://www.doityourselfchristmas.com/wiki/index.php?title=Different_Styles_of_Pixels

Or youtube search for "Christmas light display"

So a question of how to control 300 LEDs could have dozens of different answers depending on what you really mean by LED.