where RL is the output load and Xp is the reactance of capacitor Cp. Equation (4.2) shows that the output voltage of the converter is load dependent. For full-load to no-load operation and against any variation in the input voltage, the output voltage of the converter is kept constant by varying the pulse width angle d. Figure 21 shows typical characteristics of the parallel resonant DC/DC converter for a varying output load and constant output voltage. The following points are derived from this figure: (1) The output current (Zs) and therefore the conduction losses are constant from full-load to no-load. Therefore, the converter efficiency suffers at reduced loads. (2) A wide range in pulse width angle (J) is required to control the output voltage from full-load to no-load. This makes it more difficult to design a control circuit with a fast dynamic response. 4.3.3 Series-Parallel Resonant Converter Topology. The series-parallel resonant DC/DC converter topology is obtained by integrating an uncontrolled AC/DC rectifier stage with the DC/AC inverter of Fig. 8. Such a converter topology is shown in Fig. 22. As discussed in Section 3.3.2, the series branch of the converter is tuned to the operating frequency to achieve a load independent output voltage. The output voltage under this condition is given by:
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