Evaluating Polymer Capacitors - Buck Converter Tests

RE: Evaluating Polymer Capacitors - Buck Converter Tests

14rhb — Fri, 07 Jun 2019 19:43:58 GMT

Hi Ralph,

I'm having a look to see what everyone else got up to on this challenge, your work here is really interesting, especially as you explore the buck circuit (and mine was a boost). A very interesting conclusion as well e.g. that the ESR can actually be too low and cause instability....something I hope to remember for future designs.

Rod

RE: Evaluating Polymer Capacitors - Buck Converter Tests

dougw — Sun, 26 May 2019 15:27:44 GMT

Nice work. Low ESR capacitive loading on control loops is one of those things that designers often overlook. I consider it for op-amp circuits but wouldn't have thought twice about putting a low ESR cap on this IC.

It sounds like adding a few inches of wire before the cap might provide a better result.

RE: Evaluating Polymer Capacitors - Buck Converter Tests

michaelkellett — Sun, 26 May 2019 08:31:58 GMT

If you had used a MLCC instead of the polymer cap I expect you would have seen the same unstable feedback loop results.

It would be nice if you could try that (if you have some MLCCs adding up to 220uF lying around [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-f9587905-84f9-42b0-a031-cc5e06f86f39/contentimage_5F00_1.png:16:16])

The LM2596 is an old fashioned switcher and runs at a fairly low frequency - it was never intended to be used with MLCC caps and

since the polymer electrolytic caps are mainly intended as replacements for MLCCs it isn't that odd for them to be a poor match for this switcher.

RE: Evaluating Polymer Capacitors - Buck Converter Tests

jw0752 — Sun, 26 May 2019 05:58:55 GMT

Hi Ralph,

I liked your experiment. It explains some of the trouble I have experienced in the past trying to improve ripple on the output of switching circuits. At the time I gave up and ascribed my poor results to magic. Since I don't believe in magic it is comforting to see a scientific explanation.

John