# An Overview of Non-Isolated Hybrid Switched-Capacitor Step-Up DC-DC Converters
## 4 The Charge Interchange between Capacitors
### Different Types of Charge Interchange  
Switched-capacitor circuits have different applications; when they are used for power conversion, there is a disadvantage from the power electronics point of view; when capacitors get connected in parallel, the current among the capacitors, what we usually call the \"charge interchange\" [34; 40; 41], is limited only by parasitic resistances in both transistors and capacitors. This produces a spike-type waveform such as the ones shown in Figure 17. The circuit in Figure 17 shows two capacitors. Let us consider that they have different voltages before being paralleled (\(V_{C1}>V_{C2}\)). The resistor \(R_{Par}\) lumps the parasitic resistances of the loop, including both capacitors of ESR and the switch-on resistance. The peak current is equal to the initial voltage difference divided over the parasitic resistance \(R_{Par}\). The current follows the classical exponential discharge. This does not make their applications \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Title** & **Reference** & **Peak Efficiency Reported** & **Power Rating of Experiment** \\ \hline Multilevel DC–DC Power Conversion System with & [102] & 98.9\% & 10 kW \\ Multiple DC Sources & & & \\ \hline Analysis and Comparison of Medium-Voltage & & & \\ High-Power DC/DC Converters for Offshore Wind & [104] & 99.1\% & 22 kW \\ Energy Systems & & & \\ \hline SiC-Based Bidirectional Multilevel High-Voltage & & & \\ Gain Switched-Capacitor Resonant Converter with & [105] & 97\% & 5 kW \\ Improved Efficiency & & & \\ \hline DC–DC High-Voltage-Gain Converters with Low & & & \\ Count of Switches and Common Ground & [107] & 91\% & 300 W \\ \hline Design and Analysis of Switched-Capacitor-Based & & [109] & 94.4\% & 100 W \\ Step-Up Resonant Converters & & & \\ \hline Multiphase Multilevel Modular DC–DC Converter & & & \\ for High-Current High-Gain TEG Application & & & \\ \hline Zero-Current-Switching Multilevel Modular & & & \\ Switched-Capacitor DC–DC Converter & & & \\ \hline Switched-Capacitor-Cell-Based Voltage Multipliers & & & \\ and DC–AC Inverters & & & \\ \hline Resonant switched-capacitor voltage multiplier with & & & \\ interleaving capability & & & \\ \hline LLC Resonant Voltage Multiplier-Based Differential & & & \\ Power Processing Converter Using Voltage Divider & & & \\ with Reduced Voltage Stress for Series-Connected & & & \\ Photovoltaic Panels under Partial Shading & & & \\ \hline Nonisolated High Step-Up Soft-Switching DC–DC & & & \\ Converter with Interleaving and Dickson & & & \\ Switched-Capacitor Techniques & & & \\ \hline Input Current Ripple Reduction in a Step-Up & & & \\ DC–DC Switched-Capacitor & & & \\ Switched-Inductor Converter & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: References of switched-capacitor converters with high efficiency. prohibited, there are many applications in power electronics for switched-capacitor circuits, and the peak current can be calculated and handled. Despite the fact that the current waveform among the capacitors does not prohibit the application of SC circuits in power conversion, it presents the following concerns and disadvantages for high-power applications:  
* If the peak current is too large, it may damage the components (transistors and capacitors). In transistors, a large current, such as the peak current in the SC converters, causes an increase in the switching losses of the transistor, increasing its junction temperature [117]. * A spike current has a larger RMS value than a flat one. It is better to have a flat current. * There is an effort to reduce parasitic resistances in new devices, transistors, and capacitors; we can expect that the peak current will be larger if we use better components. The peak of the current can be reduced if the switching frequency is high enough to prevent a large discharge of the output capacitor, leading to what we call \"partial charge interchange\" (see Figure 17), but this still is more used in low power since the switching losses of transistors may be larger.