Electronics > Beginners

Curious case of the charging capacitor

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Zero999:

--- Quote from: ZeroResistance on February 20, 2019, 02:24:09 pm ---
--- Quote from: Zero999 on February 20, 2019, 01:43:38 pm ---
--- Quote from: ZeroResistance on February 20, 2019, 01:31:30 pm ---
--- Quote from: T3sl4co1l on February 20, 2019, 01:21:23 pm ---If you charge a capacitor from zero, through an ideal voltage source, ideal diode and inductor, it charges to double the input voltage at 100% efficiency. :)

Tim

--- End quote ---

What???!  :-/O
How does that work? And how does one get double the voltage??

--- End quote ---
Try simulating it in LTSpice, see attached.

--- End quote ---

Thanks for the file, did you whip that up in seconds?! That's awesome!!

So after simulating, It looks like it works with some kind of resonance?
The L and C, resonant frequency is around 50Hz or 20ms. So I would have expected the peak to reach in 1/4th of that time or 5ms, but the simulation returns 10ms as time to peak.

So does it work on resonance?!

--- End quote ---
Try using a parallel circuit and a constant current source, rather than voltage. Perhaps that might be more intuitive.

ZeroResistance:

--- Quote ---Try using a parallel circuit and a constant current source, rather than voltage. Perhaps that might be more intuitive.

--- End quote ---

The capacitor and inductor seem to start charging at the same time and then the diode turns on after the capacitor has discharged.

it seems the following may be occuring
1. Current source charges the C and L
2. Then C discharges into L
3. Then L discharges thru the diode

I don't understand why the current source only charges the C up to only 300V and why it does not infinitely charge the C?

unitedatoms:

--- Quote from: ZeroResistance on February 20, 2019, 05:25:56 am ---
2. This case is of charging a capacitor with another capacitor. Eg. If I have a 1uF capacitor charged to 10VDC and another 1uF capacitor uncharged. If I connect both of these in parallel the final derived energy is again half the energy that we started off with. So where did the other half go?
And if this is true then how come charge pumps achieve high efficiencies?

PS: Would the above cases still be true if the capacitor was charged with constant current?

--- End quote ---

Voltage is not related to energy linearly. Its is squared in capacitor energy formula.

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