# Influence of MOSFET Parasitic Capacitance on the Operation of Interleaved ZVS Boost Converters
## 5 Experimental Converter  
To confirm the analysis an experimental two-phase converter was constructed and \(G\) was measured as a function of \(f_{\text{s}}f_{0}\) for a set value of \(R=50\)\(\Omega\). The experimental converter was designed using the following procedure:  
1. Input data were decided: supply voltage \(V_{\text{in}}=50\) V, load resistance \(R=50\)\(\Omega\), output power \(P_{\text{o}}\) up to 1 kW, output voltage \(V_{\text{o}}\) up to 250 V, voltage ratio range \(G=2.5\)-\(5\), switching frequency range \(f_{\text{s}}=200\)-\(500\) kHz.
2. By reading Figure 4 it was deduced that for the chosen voltage ratio range a normalized load resistance value \(\overline{R}\) in the range of 1.5-2.5 and normalized switching frequency \(f_{\text{s}}f_{0}\) in the range of 0.25-0.6 is suitable. For the chosen switching frequency range this results in a required value of the resonant frequency \(f_{0}=\) ca. 800 kHz.
3. In order to keep maximum current values in the circuit possibly low it was decided that the normalized load resistance \(\overline{R}\) should be kept close to the lower boundary of the chosen range, thus \(Z_{0}\) was chosen to be 30 \(\Omega\) which would result in \(\overline{R}=1.67\).
4. Assuming \(Z_{0}=30\)\(\Omega\) and \(\omega_{0}=2\pi\)-800 kHz and using Equations (3) and (4) \(L\) and \(C\) were calculated, resulting in \(L=5.96\)\(\mu\)H and \(C=6.63\) nF.
5. By analyzing the market of available capacitors final value of capacitance \(C\) was chosen to be 6.6 nF. The final value of inductance \(L\) was set experimentally by using the available ferrite cores and litz wire to be \(L=5.8\)\(\mu\)H.  
The parameters of the converter designed with the above procedure are provided in Table 1.  
Figure 6: Plot of the voltage ratio \(G\) as a function of normalized load resistance \(\overline{R}\) for \(N=2\) and different values of normalized switching frequency \(f_{\text{s}}f_{0}\).  
Gallium nitride TPH3207 WS transistors and silicon carbide STPSC1006D diodes were used as power semiconductors. By changing the switching frequency the voltage ratio \(G\) was measured for constant values of \(V_{\text{in}}\) and \(R\). The measurements were conducted in the following conditions:  
* Frequency range: \(f_{\text{s}}\) = (200-400) kHz which corresponds to \(f_{\text{s}}\)/\(f_{0}\cong\) 0.25-0.5, with a step of 10 kHz,
* Supply voltage \(V_{\text{in}}\) = 50 V,
* Load resistance \(R\) = 50 \(\Omega\), which results in \(\overline{R}\) = 1.68.  
Temperature of the transistors was also measured to ensure that each data point was recorded at thermal steady state.  
Voltage ratio was also calculated numerically for the same sets of parameters using Equation (13). Both data sets were plotted and are presented in Figure 7. It can be seen that the experimental results differ from the calculated voltage ratio throughout the whole range of data points. The difference is lower for higher values of \(G\), but it remains at a value of around 0.2, which makes it difficult to predict the output voltage at a given value of \(V_{\text{in}}\), \(\overline{R}\), and \(f_{\text{s}}\)/\(f_{0}\).  
Figure 8 presents waveforms of the gate-source voltage and drain-source voltage of transistor T\({}_{1}\) and the current of inductor \(L_{1}\), thus showing how one of the phases operates. It can be seen that in steady-state the transistor is turned on in zero-voltage conditions.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline \(L\) & 5.8 \(\mu\)H \\ \(C\) & 6.6 nF \\ \(Z_{0}\) & 29.6 \(\Omega\) \\ \(R\) & 50 \(\Omega\) \\ \(\overline{R}\) & 1.68 \\ \(f_{0}\) & 813 kHz \\ \hline \end{tabular}
\end{table}
Table 1: Parameters of the experimental converter.  
Figure 7: Plot of the voltage ratio \(G\) as a function of normalized switching frequency for \(N=2\), \(\overline{R}\) = 1.68.