Why different output voltages of LEDs?

[corvus]

Hello everyone,

I want to buy small 220AC to 12V DC transformers to power leds.
When I consult the specifications, I always find an output voltage range, like 6-12V or 12-18V, but never a single voltage.
I also tested one of those I received recently, and it comes out of the 8.5V, a bit weak for what I expected.

Does anyone have the explanation?

We look forward to seeing you!

Julien

[dirk pitt]

LEDs are supplied with constant current rather than voltage.

[chatelot16]

12V, it is for led lamp, which have the current regulator in the base

to power LEDs only the power supply box called "transformer" must above all provide the nominal current that the led needs ... and it is the led that will make the voltage

it is the opposite of the usual power supply where the generator turns on the power and the devices consume the current they want

a constant current power supply unit at maximum voltage: when there are several LEDs in series, the operating voltage of the LEDs must be within the expected range of the power supply unit

there are led chips with several leds in series

a white led is about 3 v

a chip with 3 LEDs in series is around 9V: often it is 9 chip in assembly 3 in parallel and 3 in series

we also see LEDs with 9 chips all in series: it's about 27V