BICOLOR LED Confusion

[daneloctober]

Hello!!!

Another newbie question here...

I haven't used bicolor LEDs before, so I've read some, and found out there were basically two kinds: the 2- and 3-legged kinds. I understand that in order for the 3rd color to come out (the combination of the original two), you have to drive the 2-legged kind by alternating the current direction through the device really fast (cause you turn on one color only, by letting current pass through in a certain direction).

But this datasheet got me confused, because I know that 3-legged bicolor LEDs have a common something (anode/cathode), and thus, you can turn on both LEDs at once.

**broken link removed**

This datasheet (it's of the 3-legged kind) says you have to PWM both colors/LEDs. But why??? Can't you just turn on BOTH LEDs so you can get the third color?...

Thaaaaaaaanks!!! =D

 

[FvM]

This datasheet (it's of the 3-legged kind) says you have to PWM both colors/LEDs.

No. It literally says

Colors between the two chips can be generated by independently pulse width modulating the LED chips.

The difference is betweeen "have to" and "can".

PWM is in fact often used for this kind of bicolor LEDS. But you can also use a static current ratio, and the datasheet doesn't opt against it.

 

[spudboy488]

You can apply a constant current to one or both sides of the LED and get 3 basic colors (LED1, LED2, and LED1+LED2). If want to vary the shade and/or the intensity of the colors, you can apply a PWM current.