With careful design the noise from an isolated switching regulator will not be a problem.
Why isolated? Why not just go say 1V below the bus voltage and boost from there? (You can buy single cell to 5V boost modules dirt cheap.)
I thought we were discussing how to use a floating bias supply in connection with the control circuits of a higher output voltage power supply. This is a simple but sometimes confusing way to avoid the problem of using 5, 15, or 30 volt operational amplifiers to control a power supply with a 30 volt or higher output.
I suppose that you are suggesting inverter only for negative bias supply connected to the output of positive bias supply or to the main rectifier.
I was suggesting an alternative to using a separate 60 Hz power transformer to produce a bipolar floating power supply for the control circuits of a high voltage power supply. If you were winding your own transformer or just added a second transformer, you could have a pair of floating supplies from the same inverter.
Using sine wave instead of square has obvious advantage. Does some of inverters or low power switcher widely available use sine wave? Thanks for Coilcraft recommendation. I'm aware of their offer, they have some really nice items.
Low noise inverters may use sine wave drive. Some low noise switching power supplies use quasi-resonate operation which amounts to the same thing and has the same advantage.
I linked the Coilcraft examples because they have good availability from distributors. Other companies make similar products. Few people want to wind their own.
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