I need to work out what resistor I need for a series circuit containing 3 LEDs of 2 different types, and a 9v battery. I can do the maths, but I need to check I'm doing it right as I'm trying to learn this from what I can google!
LED1 VF = 3.2V @ IF = 20mA
LED2 VF = 2.2V @ IF = 20mA
Both LEDs have a Forward Current of 20mA at these Forward Voltages.
The circuit will contain 2x LED1 and 1x LED2.
So, using R = (VS - VF) / IF, do I calculate the total VF as 3.2V + 3.2V + 2.2V, therefore VF = 8.6V?
Using the figures I have, I get:
(9 - 8.6) / (20 / 1000) = 20 ohm, so I'd need a 20Ω resistor?
Also, can anyone advise what type of resistor would be best?