# Influence of MOSFET Parasitic Capacitance on the Operation of Interleaved ZVS Boost Converters
## 8 Conclusions  
In this paper interleaved quasi-resonant zero-voltage switching boost converters are analyzed. A new formula for the voltage ratio is derived for a converter of any number of phases. It ties the output voltage with switching frequency and load resistance. However, its implicit form makes it necessary to use numerical methods to solve the equation for a given set of parameters.  
The analysis led to formulating the conditions for soft switching which were then further analyzed and certain characteristics of the converter could be plotted. Namely the relation between voltage ratio \(G\), normalized switching frequency \(f_{\text{s}}/f_{0}\), and normalized load resistance \(\overline{R}\) were presented as several  
Figure 15: Response of the converter with the proposed control method during sudden changes in load resistance (from 50 \(\Omega\) to 200 \(\Omega\) and back to 50 \(\Omega\)) for \(V_{\text{ref}}=400\) V.  
families of characteristics. The limiting factor of high load resistance was recognized and described as a potential problem for regulation of output voltage.  
The impact of normalized load resistance was further investigated and described. It was found that a compromise between normalized load resistance \(\overline{R}\) and characteristic impedance \(Z_{0}\) must be found in order to limit the transient currents of the converter while allowing for output voltage regulation.  
An experimental two-phase converter was built and tested. The results of the experiments were compared to the values calculated using the derived formula. A difference was recognized and a possible explanation was given. Namely parasitic output capacitance of the transistors \(C_{\mathrm{oss}}\) was pointed out as the reason for lower voltage ratio, as its influence lowers the resonant frequency.  
Output capacitance \(C_{\mathrm{oss}}\) was taken into account in calculations and compared to the previously achieved experimental results. Much closer results, with calculated and measured voltage ratio remaining within 0.05 of each other in the range of 2.4 to 4.5, were obtained. Therefore it was concluded that the derived formula is useful to predict and control output voltage of the analyzed converter topology, provided that transistors' output capacitance is considered in calculations.  
Real-life applications of such a converter require it to be able to produce a desired value of output voltage for a wide range of input voltage and load resistance values. Thus a control method for the converter was proposed and a simulation model was built to confirm its feasibility. The simulations have shown that it is indeed possible to control the output voltage but certain limitations occur. Namely at low or no load conditions the voltage ratio \(G\) rises, making the output voltage high and thus possibly leading to damage of the converter components or the supplied load itself. A possible solution was proposed, namely a \"cutoff mode\" implementation, similar to LLC resonant converters, where the transistors are switched in short \"bursts\" to keep the output voltage at a desired value.  
Further work should be done, focusing on implementing the proposed control method in a prototype converter while solving the problem of regulating the output voltage at low load conditions. Extreme high load conditions should also be analyzed and both over-current and over-voltage protection should be implemented.  
Conceptualization, P.Z. and M.K.; methodology, P.Z.; software, P.Z.; validation, P.Z., M.K. and K.K.; formal analysis, P.Z., M.K. and K.K.; investigation, P.Z. and K.K.; data curation, P.Z.; writing--original draft preparation, P.Z.; writing--review and editing, P.Z., M.K. and K.K.; supervision, M.K.; funding acquisition, P.Z. All authors have read and agreed to the published version of the manuscript.  
This research was supported by Silesian University of Technology's internal scholarship fund for the year 2020.  
The authors declare no conflict of interest.