Maximizing Efficiency: Comparing AC and DC Sources for Charging Capacitors

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Discussion Overview

The discussion revolves around the efficiency of charging capacitors using alternating current (AC) versus direct current (DC) sources. Participants explore the implications of using a sine wave source compared to a DC source, particularly in the context of power loss and energy transfer through various circuit components.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether a sine wave source charging a capacitor through a diode is more efficient than a DC source, referencing a specific attachment for context.
  • Another participant argues that energy transfer through a resistor to the capacitor incurs losses, suggesting that a DC source would have less loss compared to a sine wave source due to the voltage drop across the diode in forward bias.
  • A different participant expresses the need to analyze the efficiency of an AC/DC charge pump and inquires about the power loss associated with a sine wave charging a capacitor, noting that existing literature primarily addresses DC capacitor charging losses.
  • This participant references a paper proposing that high efficiency occurs when the input voltage is close to the capacitor voltage, and questions whether a specific efficiency formula for DC charging can be adapted for AC charging by substituting the input voltage with the root mean square (Vrms) value.
  • Another participant mentions the inclusion of an inductor for power factor correction, indicating that losses depend on the timing of circuit activation and the values of voltage, resistance, and capacitance. They note that minimal losses can occur under specific conditions, such as turning the circuit on at zero voltage.

Areas of Agreement / Disagreement

Participants express differing views on the efficiency of AC versus DC sources for charging capacitors, with no consensus reached on the overall efficiency or the applicability of specific formulas across different charging methods.

Contextual Notes

Participants highlight various assumptions regarding circuit conditions, such as the timing of activation and component values, which may influence the efficiency analysis. The discussion also reflects a reliance on specific mathematical models and empirical data that may not fully encompass the complexities of AC charging scenarios.

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A sine wave source charge a capacitor through a diode.

Is it more efficiency than a DC source charging a capacitor ?

base on this
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Seems the conclusions being made aren't quite right. You cannot transfer energy through a resistor to the capacitor without loss in the resistor no matter how much of the sine wave period you pass through it.

A DC source charging a capacitor will have less loss than a Sine source charging through a diode. You have a voltage drop across the diodes in the forward bias, and so energy is lost. Not exactly sure why you're comparing this to the figure you attached because that example is charging through a resistor, which holds true for sine and DC sources either way.
 
thanks for your answer

i need to analyse the efficiency of a AC/DC charge pump,

so i need to know the power loss of a sine wave charging a capacitor firstly.

but the general thesis and data is only analysis the DC/DC capacitor charging loss.

In this paper "A new visit to an old problem in switched-capacitor converters"

propose that the while Vin from voltage source keep close to the voltage of capacitor

it will have high efficiency. the formula in the paper for analysis DC capacitor charging

through resistor is efficiency=1/2(1+Vci/Vin). Vci is the capacitor initial voltage.

Can i use this formula to analysis the efficiency of AC/DC capacitor charge by replace

Vin to Vrms ? thanks
 

Attachments

usually there's inductor in series (before the diode bridge) for power factor correction purposes. With inductor you can avoid the loss.

When you are charging capacitor off sine wave through diode and resistor the loss will depend on the time when the circuit is turned on, as well as voltage and resistor and capacitor values. If the capacitor is small and resistance is very small and you turn circuit on at zero voltage, you have no losses (besides the diode's voltage drop). If you turn same circuit on at max phase, you can burn out the diode.
 

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