recently I've been wondering how so many leds can be powered by a single supply.
For example, my christmas lights have 1000 leds on them which are powered from the mains. They definatly arn't connected in series which would require ~3.3KV, so how are they powered if each one doesn't have any sort of resistor on them?
If we take a typical string such as this one made by Ningbo Laihe Christmas Gifts Co.,Ltd, the power supply is 30V (for isolation and so it can use low voltage wire). The total power is only 9W. That's about the power used by just two C6 15V incandescent lamps (series string) that were common when I was a child.
The 1000 lamps could be arranged into series strings of 8 LEDs with a single resistor (perhaps molded into the base or cord) in series with each string. There could be a resistor in series with each lamp of 1/8 the value, but that would be wasteful.
Then put 125 of those series strings in parallel to operate from the 30V source. The 30V would be produced by a switching power supply adapter similar to a phone charger or other modern mains-operated switching supply.
They're all connected in parallel, and need a low voltage high current supply. Each LED gets a ground and a voltage wire. If they are individually addressable (as some LED Strips are), each LED also gets an additional Data wire, which is passed on to the next LED in the series. Using this method we can control any number of LEDs using only 3 wires, with a low voltage, the only limiting factor being the current.
Also LEDs do not necessarily require 3.3V to operate, many operate on far lower voltages, and some have current limiting resistors built into them.
