The PCB as a heatsink

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!]

14 thoughts on “The PCB as a heatsink

  1. anachrocomputer says:

    When we measure Volts, we get voltage, but when we measure Amps, we get current.

  2. Collin Cunningham says:

    d’ohs! I make better :P

  3. engineer says:

    Doing double-sided copper pours with a lot of vias and no solder mask is a clever way to make a heatsink. You don’t hear about it a lot, though, because clever people use switching regulators instead.

  4. The Oracle says:

    Voltage (volts) is a measure of Electromotive Force. Amperage (amps) is a mesure of Electrical Current.

    So…what is the problem?

  5. Collin Cunningham says:

    @Oracle – in hindsight, I’m not exactly sure. I assumed I mispoke, then edited amperage from the entry – thinking now, not quite sure why. well either way best not to edit in a hurry :)

  6. anachrocomputer says:

    The problem is, the word “amperage” is simply wrong. No professional engineer would refer to current like that. It was certainly pointed out to me, at school, that the correct term was “current”. Having done a quick search on the subject, however, I find that even patents are using the term “high amperage current”, so it’s difficult to find an authoritative reference.

  7. Collin Cunningham says:

    ahh, gotcha. my professor in college had a big problem with people saying “filming” in reference to shooting video, I can still hear him whenever i notice it.

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