Hot when running at 12vdc

[hydronics]

Driving 3 ~20ma LEDs seems to overheat the 5v 32u4 when powered at 12vdc via the BAT/Vin pin. I'm assuming the regulator can't handle the voltage drop. Seems like a bit of a design flaw. Any thoughts?

[hydronics]

The cut sheet for the power supply seems to suggest a maximum power draw of ~320mW.

(12vdc-5vdc) x 0.320W = 46ma...

That's a pretty weak!

https://www.digikey.com/product-detail/ ... ND/1834779

[adafruit_support_mike]

With a 12V supply you're operating at about 40% efficiency. You'll generate 1.4W of heat in the regulator for every 1W that goes through the load.

Under those conditions, a regulator with a higher power rating would need active cooling to keep it from unsoldering itself from the PCB. Temperature is a function of power and mass, and mass decreases with the cube of size. 100-ohm 0805 resistors will melt solder at 250mW, and 0603s will do it at about 150mW.

If you need to drop 12V to 5V, it's more effective to use an external switching converter. The 3A UBEC we have in the shop is about 70% efficient:

https://www.adafruit.com/product/1385

and the Verter is around 90% efficient for loads between 10mA and 1A:

https://www.adafruit.com/product/2190

[hydronics]

Hi Mike, thanks for the quick reply. We were able to modify the design to use a USB wall wart. I appreciate the platform and continue to enjoy working with the 32u4 chip... even with its new wee regulator.

I've also started to use that new tsr-1-2450 regulator. I hope it has a long life and holds up in our museum exhibits.

[mikekscholz]

Im using a R-78E5.0 - 1.0, its tiny, and its a fully contained switching regulator and im dropping 12 down to 5v and it feels cool to the touch still, like 90% efficient or better. And its less than a half inch in all dimensions. Love it.

[adafruit_support_mike]

Hmm.. I wasn't familiar with that one, but the specs look good:

https://datasheet.octopart.com/R-78E5.0 ... 298118.pdf

Thanks for mentioning it: