## 6 Experimental Results
### Switching Waveforms  
If no damping solutions are exploited, the switching voltage (\(v_{\text{sw}}\)), which was measured by means of a digital oscilloscope, is affected by oscillations at the \(T_{\text{HS}}\) turn-on, as shown in Figure 11 by dashed lines. More precisely, the oscillation takes place after the \(v_{\text{DS}}\) voltage has dropped off. Such an oscillation is characterized by \(f_{\text{r,on}}=62.5\,\text{MHz}\) and a \(v_{\text{sw}}\) peak equals to 69 V. At the turn-off, a negligible oscillation with \(f_{\text{r,off}}=23\,\text{MHz}\) and 50.4 V peak is superimposed onto \(v_{\text{DS}}\). To damp the turn-on oscillation, a low-side RC snubber, which was characterized by \(C_{snb}=820\,pF,R_{sub}=2.3\,\Omega\)[9], was inserted, resulting in the switching waveforms shown by dotted lines in Figure 11. The snubber effectively removes the oscillations, but it slightly slows down the \(v_{\text{DS}}\) rise during the \(T_{\text{HS}}\) turn-off. Then, the snubber was removed and a 6.6 nH air core wrapped inductor, which was the closest value available on the market to the optimal value found previously, i.e., \(L_{\text{s,opt}}=6\,\text{nH}\), was exploited as source inductance. The corresponding switching wave forms are those shown by solid lines in Figure 11. Indeed, the \(v_{\text{sw}}\) peak voltage is reduced and the oscillations are almost completely damped with respect to the undamped case. Referring to Figure 11, the \(v_{\text{DS}}\) voltage is not monotonic when the source inductance is inserted, i.e., during the Miller's plateau the high-side transistor is slowed-down by the negative feedback introduced by the source inductance. Moreover, during the turn-off no unwanted self-turn-on is present, as expected. Different values of source inductance were tested, i.e., \(2.5\,\text{nH},5\,\text{nH},8\,\text{nH},12.5\,\text{nH}\) and the magnitudes of the corresponding \(v_{\text{SW}}\) frequency spectrum in the (5, 100) MHz frequency range are plotted in Figure 12 in case of an output current equals to 3 A. When the high-side transistor is driven sharply, the peak at the \(f_{\text{r}\text{on}}\) frequency is noteworthy, on the contrary, the one related to the turn-off is not apparent. The \(v_{\text{sw}}\) spectrum comprises a secondary peak at 48 MHz, approximately 10 dB lower than the one at \(f_{\text{r}\text{on}}\), which is also related to the \(T_{\text{HS}}\) turn on. Indeed, from the \(v_{\text{sw}}\) waveform in Figure 11a in dashed line, it can been noticed that the turn-on oscillation is not purely sinusoidal, but it is distorted, meaning that higher order resonant circuits are excited. Such spectra validate the optimal value found in Section 5.2, as the peak is reduced by 20 dB. Indeed, lower \(L_{\text{s}}\) values, i.e., \(2.5\,\text{nH}\) and \(5\,\text{nH}\), result in a peak not completely removed, whereas the 8 nH spectrum is equal to the 6.6 nH one, meaning that there are no advantages in the use of a higher source inductance. Indeed, if \(L_{\text{s}}\) is further increased up to 12.5 nH, the peak at \(f_{\text{r}\text{on}}\) increases again, which is also in agreement with the simulations, as reported in Figure 8 by square markers.  
Figure 11: Measured time domain phase voltage \(v_{\text{sw}}\) (**a**) and drain-source voltage (\(v_{\text{DS}}\)) (**b**) at the \(T_{\text{HS}}\) turn-on. The dashed lines were obtained in the oscillating case, the dotted ones with the low-side snubber inserted and the continuous ones with a 6.6 nH source inductance. The use of the source inductance allows one to reduce the over-voltage affecting the \(v_{\text{sw}}\) at the turn-on.  
Figure 12: Frequency spectra of the measured switching voltage (\(v_{\text{sw}}\)) with 3 A output current and different source inductances.