TechnoGilles
New Member
Hi all,
I have an application where I use a dual color LED with only two terminals. When polarized one way, the LED is green; when polarized the other way, it's red.
So I thought I would use two MCU ports (say P[1:0]) and connect the LED through a current limiting resistor. So when P[1:0] = 10, the LED would be green and when P[1:0] = 01, the LED would be red.
The nominal current for both sides is 20mA. But the problem is that the forward voltage is different : 2.2V for the green side and 2.0V for the red side. So, as you might have guessed by now, choosing the resistor value becomes the challenge !!
At 2.0V, the green side current drops to 5mA (4 times less bright). At 2.2V, the red side current jumps to more than 50mA and the LED blows !!!
So how can I setup that LED to get 20mA in both direction ?
Needless to say that I would like to achieve that with as few parts as possible !
Thanks !
TG
I have an application where I use a dual color LED with only two terminals. When polarized one way, the LED is green; when polarized the other way, it's red.
So I thought I would use two MCU ports (say P[1:0]) and connect the LED through a current limiting resistor. So when P[1:0] = 10, the LED would be green and when P[1:0] = 01, the LED would be red.
The nominal current for both sides is 20mA. But the problem is that the forward voltage is different : 2.2V for the green side and 2.0V for the red side. So, as you might have guessed by now, choosing the resistor value becomes the challenge !!
At 2.0V, the green side current drops to 5mA (4 times less bright). At 2.2V, the red side current jumps to more than 50mA and the LED blows !!!
So how can I setup that LED to get 20mA in both direction ?
Needless to say that I would like to achieve that with as few parts as possible !
Thanks !
TG