I've created the following circuit for educational purposes. It's basically 2 LEDs in parallel. I've used my multimeter to measure the current and voltage of the various components and noted everything down. The idea was to come up with the formula to calculate the current flowing through the 2 LEDs. I know that the total current will be divided between the 2 LEDs but I'm having trouble calculating everything.
I'm able to use Ohms law for a simple 1 resistor/LED circuit but I'm having trouble understanding how to calculate the current flowing through the 2 LEDs in this circuit. Here's what I did :
Current for the green LED :
Here I attempted to use the basic formula to calculate the current through the green LED, but that obviously doesn't take into account that there is a another LED in parallel.
I = V/R = (5V – 2,065V drop green LED) / 270 = 10.9mA
So this is obviously wrong. I don't know what I calculated here. I guess this would have been valid if only the green LED was present, and the voltage drop would have been 2,065V.
Current for the red LED :
Here I tried to visualize the current flow, so I asssumed that the current flowing through the red LED would have to pass the 2 resistors in series (270 + 100) and used Ohms law again
I = V/R = (5V – 1.863V drop red LED) / 370 = 8,47mA
This is again incorrect but seems to correspond to the current flowing through the green LED. Don't know if this is coincidence.
I've chosen the resistor values randomly just to ensure that the 2 LEDs would be lit. This circuit is just for educational purposes.
The logic behind calculating the current is something I'm currently missing. Any help would be great.
Best Answer
The big problem is that you didn't draw the schematic properly. A good schematic always makes the things clear:
simulate this circuit – Schematic created using CircuitLab
The current is \$I = \frac{U}{I}\$
I0 = I1+I2
I0 = (5V-2.065V)/270 = 10.87037037mA
I1 = (2.065V - 1.863V)/100 = 2.02mA
I2 = I0 - I1 = 8.85037037mA