I have a working schematic for a PCB board that has a few components including a 3V power supply, a 32 QFN, and 1 RGB LED attached to 3 PIOs on the QFN.
The schematic uses the following resistors for each color in the RGB LED.
Red ---- 360 ohms
Green ---- 180 ohms
Blue ---- 160 ohms
The LED light used (found here: http://www.osram-os.com/Graphics/XPic3/00115411_0.pdf) has the following forward voltages:
...................Min........Typ.........Max
Red....-----...1.8V.......2.05V.......2.4V
Green.-----...2.9V.......3.2V........3.7V
Blue....-----...2.9V.......3.2V.........3.7V
Assuming a current of 20mA....I try plugging these values into the Ohm's Law equation like so:
Ex. (for Red)
R = (Vsource - Vdrop)/(I)
R = (3-2.05)/20
R = 47.5 ohms
That 47.5 ohms is way different than the 360 ohms resistor used in the schematic. I have to be doing something wrong...Can anyone explain the correct calculation?
Thanks in advance.
The schematic uses the following resistors for each color in the RGB LED.
Red ---- 360 ohms
Green ---- 180 ohms
Blue ---- 160 ohms
The LED light used (found here: http://www.osram-os.com/Graphics/XPic3/00115411_0.pdf) has the following forward voltages:
...................Min........Typ.........Max
Red....-----...1.8V.......2.05V.......2.4V
Green.-----...2.9V.......3.2V........3.7V
Blue....-----...2.9V.......3.2V.........3.7V
Assuming a current of 20mA....I try plugging these values into the Ohm's Law equation like so:
Ex. (for Red)
R = (Vsource - Vdrop)/(I)
R = (3-2.05)/20
R = 47.5 ohms
That 47.5 ohms is way different than the 360 ohms resistor used in the schematic. I have to be doing something wrong...Can anyone explain the correct calculation?
Thanks in advance.