Question Reg Capacitors

[DeTree72]

I understand that the purpose for capacitors is to filter the output and input voltages to protect against voltage spikes, but looking at the PTH08080, it looks like it already has surface mount regulators on it. What are these caps for if not filtering?

 

[Shank]

Different value capacitors are better at filtering different frequencies. Smaller caps are great at filtering out smaller spikes at higher frequencies, while larger capacitors work for larger spikes and lower frequencies. A switch mode buck converter (like the PTH08080s) creates a lot of large voltage spikes due to how it works. (More info here)
Smaller ceramic capacitors, like the ones on the board, can have tiny capacities and high voltage ratings and work for any voltage. However, having a "one size fits all" large electrolytic capacitor would be enormous, even bigger than the regulator itself. (Not to mention have a higher ESR making it less effective). Since we use the regs at a relatively low voltage, having external caps lets us use caps that work just as well for us and are much smaller than an onboard "one size fits all" capacitor would be.

 

[DeTree72]

so would it not be plausible to use similar surface mount caps? even if they were 100 microfarad and rated for 16v?

 

[Stitches]

so would it not be plausible to use similar surface mount caps? even if they were 100 microfarad and rated for 16v?

You could, but it would be ugly and have odd spacing.

 

[Shank]

You could, but it would be ugly and have odd spacing.

Naw, you can get 100uf ceramics that are about the same size as the larger ceramics on the PTH regs and stack them on those regs, but they are more expensive and overall not worth it. I successfully did it for the Kill Mii, but swapped it out for a custom PowerMii Lite.

 

[DeTree72]

So I was tinkering with it while sitting at my desk, and this is what I came up with. The resistor this one is wired to is 86.6kohm, and the caps are all 100 μF 16v. I had it running without a load on it and it put out 1.001v. If I could figure out how to clean this up a little, I feel it would be really useful for my portable

The other side has caps for another regulator, which would use the resistor that’s set right next to the one wired.

 

[Shank]

I would advise using a through hole resistor to set your voltage rather than an SMD. You can bend the legs between the inductor and ceramic cap to have it nice and clean with no wires. Then stack those ceramics on top of the stock ceramics and you are good to go.

 

[cheese]

Also, if you use through hole resistors, make sure to insulate the legs with electric tape/heatshrink so it doesn't short anything out

 

[DeTree72]

Sounds good. Thanks for the advice