Hi everyone,

I am having a hard time selecting the right power rating for SMD resistors. With through hole resistors I never encountered running into problems with resistor power ratings as through hole resistors have relatively high power ratings and I was never really thinking about them when using them in my 5V Arduino's projects before.

In my project I will be using the ATMega 328P and as an example lets take this Arduino nano schematic. Let's look at pin 17 on the ATMega328P which is connected to the resistor RP2A a 1K ohm resistor array, a yellow led and ground. Lets ignore that RP2 is a 4x1K ohm resistor array for now and look at RP2A as a single resistor.

Using: V / R = I so 5V/1000 ohm = 0.005A and P = I x V so 0.005A x 5V = 0.025W = 1/40W

So the minimal power rating would be 1/40W for this resistor? So using a resistor with a 1/10W power rating (typically seen on imperial 0603 SMD package sizes) would give me a good safety margin?

What is confusing me is that when I do the same calculation for a 10K ohm resistor instead of a 1K ohm resistor I get a power rating of 1/400W (Using the same calculation as above). I was expecting power ratings to go up as the resistor value goes up. More resistance produces more heat and therefore energy right??

Kind of confused about this, hope you guys can help me out here :D