I need a supply to produce +5V and -5V supplies from a single Li-ion cell. Current will be around 100mA.
What is your best suggestion?

 

A couple of cheapo off-the-shelf DC-DC converter modules? Or do you want to brew your own?

 

A couple of cheapo off-the-shelf DC-DC converter modules? Or do you want to brew your own?

I haven't had much luck making my own switch-mode stuff.
If I use two boost converters I suspect that It will not work if I connect the positive of one to the negative of the other unless at least one of them is isolated.

 

I suspect that It will not work if I connect the positive of one to the negative of the other unless at least one of them is isolated.

Agreed. I have no practical experience of those modules, but considering their cost maybe they aren't isolated.

 

I haven't had much luck making my own switch-mode stuff.
If I use two boost converters I suspect that It will not work if I connect the positive of one to the negative of the other unless at least one of them is isolated.

That is correct.

I did find this

But it says the negative supply must have the same load as the positive supply. That worries me, though they cannot mean that literally, can they? Hopefully, what they really mean is that the + supply must have a minimum load for the - supply to work.

 

I found this: https://www.ebay.co.uk/itm/193636331718
So I can use a 5V boost converter and the above item to generate the other supply rail

 

You could build an inverter with a suitable transformer output and then use diodes to get your positive and negative voltage. Inverters are less picky than switch-mode supplies.

 

A better plan would be either to re-work your Circuit for a single 3.3V-Supply,
or, use 4-Cells in series and 2 Linear-Regulators.

If You have no Circuit choices, a Push-Pull-Inverter will be the most reliable and stable solution.
There are plenty of dedicated, self-contained-Chips designed to push a small Transformer.
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