I'm using a LM7805 voltage regulator(12V in, 5V out) for my arduino Yun project. Also, 330pF capacitor on the input and 100pF on the output of the LM7805, as recommended by the regulator specs.
The Yun seems to run fine for ~10-20 seconds - plugging the 5V out to the Yun Vin pin - and then emits a small hiss noise and then proceeds to power down.
I tried bypassing the voltage regulator and powering the yun via a 5V AC to DC adapter, and it ran flawlessly.
Does anyone know what's happening? Do I need a heatsink for the regulator? It does get pretty hot. I checked the V out from the regulator and it seems to stay consistently at 5V, so I don't know why the Yun keeps powering down.
The 330pF and 100pF are not recommended.
Some datasheets specify 330nF and 100nF, but normally is 100nF at input and 100nF at output. An extra capacitor of roughly 22uF to 1000uF could be added. Do you have a number of decoupling 100nF capacitors ? Everyone should have some of those.
If it gets hot, you might consider a DC-DC converter.
Most of the times at the input, but it depends if the circuit can handle a current peak when the power input is connected.
If the larger capacitor is at the input, the output is more stable at 5V if the input has gaps.
If the larger capacitor is at the output (5V), the 7805 has a current limiter that prevents current peaks when it is charged.
I use often 22uF to 470uF at both input and output. And sometimes a diode in the power input line to protect it against reverse polarity.
Hmm, I'm not sure what reverse polarity is, but I think that may be affecting something here. I've put a 470uF capacitor in both the input and output, and the Yun blinks the LED strip for about 10 repeats of the script and then it seems to just power down and the led "power" onboard fades out.
Yes, its thermal shutdown kicking in. This regulator has 2V dropout and is inefficient. Possible Solution: If you can lower the input voltage to 7.5-9V, it will make a huge difference in the heat dissipated.
This "12V supply" is probably supplying much more than 12V.
Unloaded, delivering little current, it could be near 17V.
You have to test your supply circuit before you connect it to anything important.
Throwing caution to the wind, haphazardly slapping together some conglomeration of components together and hoping for the best is just asking for it.
But, still.
What's the draw of a "Yun"? That's going to push a 7805, even if it's holding off 10V, over the edge into thermal runaway?
Back to my last post, get the regulator right, first.
Run some LEDs (I guess I have to make that LEDs with limiting resistors) and check, check and check again.
