Red LEDs typically have a forward voltage of 1.8V to 2.2V. Old green LEDs typically are around 2V to 2.2V. Modern green LEDs may be a bit higher.
Blue and white LEDs typically have a forward voltage of 3V to 3.5V, but it varies depending on how much current they are operated at and the quality of the LED (some from eBay run at 3.7V for example).
Modern red, green.and blue LEDs are often bright at 1 to 5mA, unlike older LEDs which typically needed 10 to 20mA to light brightly.
The formula to calculate the value of the series current limiting resistor is:
R = (Vs - Vf)/I
Where R is resistance in ohms
Vs is the supply voltage
Vf is the LED forward voltage
I is the current you want in amps
Hence if Vs is 5V, Vf is 2V and I is 0.002A (2mA) R =1500 ohms or 1.5k
Mark
Blue and white LEDs typically have a forward voltage of 3V to 3.5V, but it varies depending on how much current they are operated at and the quality of the LED (some from eBay run at 3.7V for example).
Modern red, green.and blue LEDs are often bright at 1 to 5mA, unlike older LEDs which typically needed 10 to 20mA to light brightly.
The formula to calculate the value of the series current limiting resistor is:
R = (Vs - Vf)/I
Where R is resistance in ohms
Vs is the supply voltage
Vf is the LED forward voltage
I is the current you want in amps
Hence if Vs is 5V, Vf is 2V and I is 0.002A (2mA) R =1500 ohms or 1.5k
Mark
Statistics: Posted by 1024MAK — Thu Aug 29, 2024 6:30 pm