Electronic – Does resistor placement change power dissipation in simple LED circuit


Does the power dissipation in an LED and resistor change depending on the resistor placement?

Let's assume the following:

  • Supply Voltage: 3.3v (DC)
  • LED Forward Voltage: 2.1v
  • Resistor: 330 Ohm

I think my problem is that I'm thinking that the circuit "starts" at 3.3v, then goes through the resistor which restricts current and then goes through the LED which drops voltage. Alternatively, if I place the LED before the resistor, then the LED will drop the voltage (3.3v – 2.1v = 1.2v) before it reaches the resistor so the resistor is dissipating less heat?

Best Answer

The order of the components does not make any difference. The voltage is diveded on the two components in the same way, in your case 2.1V on the LED and 1.2V on the resistor. This results in 1.2V/330Ohm = 3.6mA through your series circuit. So the power dissipation is also the same in both configurations.