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DC-DC converter with floating ground

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Andy Chee:

--- Quote from: IanB on December 29, 2023, 11:34:10 am ---
--- Quote from: electrodacus on December 28, 2023, 01:33:45 am ---There were people in the past that disagreed with the fact that V2 can not be continuously higher than V1 despite the floating GND.

--- End quote ---

You would need to provide a context for that statement, by quoting instances where "people in the past" said this.

--- End quote ---
I can provide context.

The DC-DC floating converter problem is supposed to be an electrical analogy to describe the energy interactions behind Veritasium's/Xyla's "downwind faster than wind" vehicle.

"people in the past" is a reference to people discussing the vehicle physics, as opposed to the DC-DC converter problem.  But the OP believes they are directly equivalent.  Go figure.

IanB:
I fully understand that context. I knew what this was about from the very first post in the thread, since we've been here before.

But I want electrodacus to provide a direct quote where someone said the DC-DC converter could provide a continuous step up in voltage without a third electrical connection. Otherwise he is just being disingenuous and misrepresenting people.

Because I really don't believe anyone on this forum would be likely to say that about the "DC-DC converter" picture in the first post.

Zero999:

--- Quote from: electrodacus on December 29, 2023, 05:24:17 am ---
--- Quote from: boB on December 29, 2023, 04:44:19 am ---
How about an LTspice simulation of one of the answers ?

--- End quote ---

Is this a question directed to me ?
There are two questions A) and B) in the original post with my answers in bold No and Yes.

A) Is it possible for V2 to be a constant 30V?  No
B) Is it possible for V2 to peak to 30V multiple times while V2 never drops below 5V ?  Yes

So do you not agree with one of my answers ? Or with both ?

If you say Yes to question A) the it will be you that will need to prove that as I can just use an empty box or a wire between the two points and made my case.
If you say No to second question I can describe to you how it will work but the diagram I offered as an example should be sufficient.

The capacitor will be disconnected from the two box terminals and connected to the output of a DC-DC boost converter.
The boost converter can be a max power point so one that maintain a constant voltage at the input and takes what is available.
So say DC-DC MPPT is set to 5V then the other 5V will drop across the 100Ohm resistor meaning 50mA will flow trough the circuit.
5V * 50mA = 0.25W are available with say a 70% efficient DC-DC converter 0.175W are available to charge a large electrolytic capacitor connected at the output of this DC-DC converter.
When this capacitor gets to 20V some analog trip circuit can disconnect the DC-DC and connect the capacitor between the two connection points on the green box.
Thus for a short moment V2 = 10V + 20V = 30V
It can get way more complicated than this with a microcontroller and current measurement to calculate exactly what the resistance value is and what the battery voltage is but this are unnecessary complications just to say that it can be done.

--- End quote ---
Higher voltage output pulses are possible but not a steady voltage.


--- Quote from: boB on December 29, 2023, 04:44:19 am ---How about an LTspice simulation of one of the answers ?

--- End quote ---
Here's a simulation. A capacitor is first connected in series with the supply and the load, which charges it up. It is then connected the other way round, negative plate to V1 and positive to the output. The capacitor first discharges, adding its voltage to V1, before charging in in the opposite direction. Higher voltages are possible by connecting more capacitors in parallel and then in series for the discharge cycle.

This circuit isn't practical application. It's just a theoretical demonstration. It's possible to use solid state relays connected to a microcontroller for the timing. The microcontroller could be powered via another capacitor which is charged in series with the load resistor.

electrodacus:

--- Quote from: Someone on December 29, 2023, 07:06:01 am ---
--- Quote from: electrodacus on December 29, 2023, 05:24:17 am ---A) Is it possible for V2 to be a constant 30V?  No
B) Is it possible for V2 to peak to 30V multiple times while V2 never drops below 5V ?  Yes

So do you not agree with one of my answers ? Or with both ?
--- End quote ---
Now that you have stated a somewhat clear question who has disagreed with you? No-one! So why immediately ask if every poster agrees/disagrees?

--- End quote ---

Just the comment before yours Andy Chee asked for a LTspice simulation as proof for those answers.
Should I understand you do not disagree with my answers to those two questions?
As there will be people asking the opposite of what you are asking.

electrodacus:

--- Quote from: soldar on December 29, 2023, 10:03:12 am ---
--- Quote from: SiliconWizard on December 27, 2023, 10:40:49 pm ---I'm more used to having the signal flow drawn from left to right, but whatever.
--- End quote ---
Me too. Power, voltage, signal flow from left to right and from top to bottom. I often redraw schematics that way because it helps me analyze and understand the circuit.

When I reverse engineer a circuit I start out with a schematic which resembles the PCB but I rearrange it in steps until it is easier to conceptualize.

--- End quote ---

I agree and sorry for having the diagrams drawn in a non standard way.  I was thinking that is a simple enough diagram that it will not affect anyone's ability to understand.

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