Topic: Capacitance in power supplies

[Chuck]

I know that large capacitors (bypassed with smaller capacitors) in AC to DC power supplies act as filters to reduce DC ripple. I also know that adding large capacitors in battery systems, like car audio, help keep amplifiers supplied with DC. What I don't understand is how to come up with reasonable values to use for either application and why, or even if, it's a good idea to add the little film caps in parallel.

I've actually built many AC to DC power supplies and used cap values I found in other circuits and in manuals. I just never really understood how the cap values were chosen. Also, how does the type of capacitor fit in? Electrolytic vs film etc...

One reason for the questions is I'm thinking about getting one of those T-amps, www.tnt-audio.com/ampli/t-amp_e.html and  I want to build a decent 13.2 v DC power supply for it.

[pigiron]

Since all knowledge is now available on the 'net  and it's been soooooo long since I dabbled in the sparky world, I thought I'd have a quick (and short) go at this. Hopefully others with more (and more recent) experience can jump in.

Assuming you're talking about a standard full wave bridge rectified PS, and not a switcher... here's one pointer to some basics on cap values for amps http://sound.westhost.com/power-supplies.htm. But like a lot of the old electronics books it uses some generalities (you'll notice they get the cap sizing formula from a rectifier data book... which tend to stay in the "simple" realm). But it hits some of the other points needed for a good design... the components attached to those caps.

Here's another http://www.tnt-audio.com/clinica/ssps1_e.html that I have some problems with... but does touch on some of the things to look for in a filter cap... which heads toward a semi answer of your capacitor types question.

Not releated to your questions though was this gem I ran across while searching, which hits on a pet peeve of mine... coming from the old school days of having anything over 25 watts running your speakers was a big deal... and weighed a ton... so how is that now a tiny box that's light as a feather can put out a kagillion watts???  Here's the answer http://sound.westhost.com/power.htm. But this is NOT a reflection on the T-Amp... don't know anything about it and never heard it... but it does speak to the snake oil on most of the amps for sale at places like Best Buy, Circuit City, etc.