The PCB as a heatsink


While developing the Roboduino, Scott had to calculate how many amps his project could deliver to attached motors. He wrote up his findings (and how he arrived at them) as a helpful article –

As a review, the total heat generated by the regulator is just the energy in minus the energy out. This is how linear regulators work–they turn excess energy straight into heat.

heat generated = (Vin-Vout)*I

(there’s also quiescent current in there which is the current used by the regulation circuity, but this is around 50mA, so we’ll ignore it for brevity).

So, if Vin = 9V, Vout = 5V, and I = 1amp, the heat generated would be about 4W.

As it turns out, our board was only able to dissipate about 2W. A bundle of 20 1/4W resistors (100ohms, 10ohms total) was used as a dummy 1Amp load at 5V. A thermal couple measured regulator temperature at the solder joint. Current was measured before it entered the Roboduino’s input.

Plus the article continues to explain how a circuits trace width determines how much current it can handle. – PCB as a Heat Sink

[Updated – Thanks, anachrocomputer!]