i am very very green when it comes to electrionics but im learning! I have a very basic question, when calculating the reistor size for leds do you use the typical forward voltage value or the max one and
do you use the typical forward current value or the max one?
I use the min voltage, as that will cause the highest current draw:
(Vs - Vmin)/Resistor = current
ex.
(5V - 3V)/100 = 20mA
(5V-3.4V)/100 = 16mA
Plan for no more than 20mA (generally) continuous current. Using the MAX for continuous will really shorten the LED life.
Many LEDs can be pulsed with higher currents, but only for very short times. The data sheet will have details of the on time and the frequency.
DmarkL:
when calculating the reistor size for led`s do you use the typical forward voltage value or the max one and
do you use the typical forward current value or the max one?
The minimum one. And round the resistor upwards.
If you want more you need to use a current controller circuit, a resistor isn't good enough.
just know the forward voltage drop and subtract it from the voltage you are supplging and given the max amount of current for your leds use ohms's law
V=IR.