We're going to be doing several instruments that need isolated signal channels, so I've been researching low power dc/dc converters. I'll need floating +-5 or maybe +-12 volts.
These are really cool
They're tiny and cost around $4 at 100 pieces. There's at least one second source, Mornsun. One gotcha is that the CUI parts short-circuit protection looks tricky.
Anyhow, I want low noise injection into the isolated-common side, so I breadboarded it to play with it:
I added a cute little Bourns 500 uH common-mode choke on the input side to theortically reduce spikes kicked across from ground to the output common.
So, the output common showed 10 volts p-p noise relative to ground! Square wave! Adding a 1 nF cap from out common to ground hardly changed it at all. I measured gnd-com capacitance on another part and it's like 12 pF. Made no sense.
Well, pin 10 on the data sheet says NC, but it should say DNC. It seems to be one end of the transformer primary, and it is 10 volts p-p at 100 KHz, and I soldered it to the output common copper on my little board, just a mechanical thing I thought. Lifted, the noise on the floating common is tiny.
For $4, one could use these to generate new power rails even if isolation isn't required. There are parts that convert practically anything to +-anything else. They are proportional, not regulated.
The Bourns inductor doesn't seem to affect noise much, so I'll probably leave it out. The CUI part may need a polyfuse on the input or something, in case something on the channel side shorts out. Or maybe not.