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DC-DC converter with floating ground
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electrodacus:

--- Quote from: SiliconWizard on December 27, 2023, 11:43:51 pm ---You can't do that if your only return path is through the load. As shown in the diagram.

--- End quote ---

Here I made a diagram that is maybe better than a description.
There is a DC-DC converter inside the box with positive input from battery+ and battery- trough the 100Ohm load.
This can me a max power point type that can say maintain 5V at the input and so with 5V drop on 100Ohm 50mA are available for DC-DC converter times 5V that is a respectable 0.25W witch can be used to charge the capacitor to 20V
Then when that gets to 20V the DC DC converter is disconnected and the capacitor is connected thus for a moment V2 will be 30V

Andy Chee:
I believe you are fundamentally describing a variant of a Cuk regulator or charge pump:

https://www.analog.com/en/technical-articles/differences-between-the-uk-converter-and-the-inverting-charge-pump-converter.html

It may be possible to float the switch control circuitry (the blue line in your diagram), but given you have common grounds anyway (the grey line in your diagram), why would you even bother going through the hassle?

If this is just a thought experiment, then yes, charging a capacitor in series, then flipping its direction, would indeed boost the output voltage.  The control circuitry can be made floating and it would still work.

In practice, there's no point in floating a capacitor based converter.  OTOH floating transformer based converters happens all the time.
electrodacus:

--- Quote from: Andy Chee on December 28, 2023, 01:21:53 am ---I believe you are fundamentally describing a variant of a Cuk regulator or charge pump:

https://www.analog.com/en/technical-articles/differences-between-the-uk-converter-and-the-inverting-charge-pump-converter.html

It may be possible to float the switch control circuitry (the blue line in your diagram), but given you have common grounds anyway (the grey line in your diagram), why would you even bother going through the hassle?

Are you attempting to extend this principle to a multi kilovolt generator or similar that would require such isolation?

--- End quote ---

This circuit is not useful and is just an exercise to understand that V2 can be larger than V1 (intermittently) but not continues if the ground is floating.
It is the analog of a mechanical setup that I was trying to explain but I think the electrical setup is easier to understand first.
There where people in the past that disagreed with the fact that V2 can not be continuously higher than V1 despite the floating GND.
Andy Chee:

--- Quote from: electrodacus on December 28, 2023, 01:33:45 am ---It is the analog of a mechanical setup that I was trying to explain but I think the electrical setup is easier to understand first.

--- End quote ---
Electrical analog of the hydraulic ram?

https://en.wikipedia.org/wiki/Hydraulic_ram





electrodacus:

--- Quote from: Andy Chee on December 28, 2023, 01:39:57 am ---Electrical analog of the hydraulic ram?

--- End quote ---

Yes it will be the electrical equivalent of that also.
Energy storage is used in that case to be able to pump water at higher elevation.
People seem to always remember about the frictional losses and the fact that you can not get rid of them in real world but fail to think about the energy storage witch is I will say as important.
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