LED Forward voltage (Vf=21)

[mdueda]

Hi,

What is the advantage of having Vf=21V in LED when compared to normal LED (vf=0.7V)

 

[DeLorean]

Your data must be for a string of LEDs. I've never seen one LED forward voltage much above 3.5 volts

 

[betwixt]

And a Vf of 0.7V refers to a silcon diode, not an LED.

There are some higher voltage LEDs but these are built using several series connected low-Vf junction in series within one package. There are some advantages and disadvantages to higher voltage types: For the same output power, the input current is lower when the voltage is increased and becasue the junctions are series connected, there is no need to use individual resistors to balance the current they draw. Given that in most applications the supply voltage will be higher than the LED voltage anyway, having to drop less voltage can simplify power supply design.

Brian.