## 4 Experimental Results  
A prototype driver has been built and tested for supplying an 18 W-rated T8-type LED tube lamp (EVERLIGHT FBW/T8/857/U/4 ft, ELECTRONICS Co., Ltd., New Taipei City, Taiwan), whose rated voltage and current are 60 V and 0.3 A, respectively. The components utilized in the LED tube lamp driver are shown in Table 1.  
Figure 7 presents the measured inductor current \(i_{LPFC1}\). The measured switch voltage \(v_{DS2}\) and inductor current \(i_{Lr}\) are shown in Figure 8, and the series resonant tank resembles an inductive load. The measured DC-bus voltage is shown in Figure 9, and the average value of \(V_{DC}\) is approximately 318 V. Figure 10a,b presents the measured voltages \(v_{DS1}\) and \(v_{DS2}\) and currents \(i_{DS1}\) and \(i_{DS2}\) of the power switches \(S_{1}\) and \(S_{2}\), respectively. ZVS is obviously achieved on the power switches; thus, the circuit efficiency is increased. Figure 11 shows the measured output voltage and current waveforms, and the average values of \(V_{o}\) and \(I_{o}\) are 60 V and 0.3 A, respectively. Table 2 presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages. Figure 12 shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages. In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current). According to Figure 12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively. Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively. Figure 11: Measured output voltage \(V_{o}\) (20 V/div) and current \(I_{o}\) (0.2 A/div); time scale: 2 ms/div. Figure 9: Measured DC (direct current)-bus voltage \(V_{DC}\) occurred on DC-linked capacitors (\(C_{DC1}\) and \(C_{DC2}\)) (100 V/div); time scale: 5 \(\upmu\)s/div. The measured input utility-line voltage and current are shown in Figure 13, and the input current is in phase with the input voltage. Figure 14 presents the measured input-current harmonics compared with the International Electrotechnical Commission (IEC) 61000-3-2 Class C standards under input utility-line voltages ranging from 100 V to 120 V; all measured current harmonics meet the requirements. Figure 15 shows the measured power factor (PF) and current THD at input utility-line voltages ranging from 100 V to 120 V. At a utility-line rms voltage of 110 V, the measured PF and current THD are 0.96 and 9.3%, respectively. The maximum PF is 0.97 occurred at a utility-line rms voltage of 120 V, and the minimum current THD is 6.9% occurred at a utility-line rms voltage of 100 V.  
Figure 16 shows the measured efficiency of the presented LED tube lamp driver under input utility-line voltages from 100 V to 120 V. The highest and lowest measured efficiency levels are 94.16% and 91.24%; these occurred at utility-line rms voltages of 100 V and 120 V, respectively. In addition, the efficiency which drops with increased utility-line voltages is related to the voltage gain of the LC series-resonant tank. For providing rated output power (voltage/current), the voltage gain of the LC series-resonant tank will decrease when the utility-line voltages increase, resulting in increasing the switching frequency of the power switches. Thus, the switching losses of power switches and conduction losses of power diodes will increase resulting in lowering the circuit efficiency. Figure 16: Measured efficiency of the presented LED tube lamp driver under different input utility-line voltages. Figure 14: Measured input-current harmonics compared with the IEC 61000-3-2 Class C standards.