Power Electronics, A First Course, 2nd Edition

10 SOFT-SWITCHING IN DC-DC CONVERTERS AND HALF-BRIDGE RESONANT CONVERTERS

10.1 INTRODUCTION

In converters so far, we have discussed hard-switching in the switching power-pole, as described in Chapter 2. In this chapter, we will look at the problems associated with hard-switching and some of the practical circuits where this problem can be minimized with soft-switching.

10.2 HARD-SWITCHING IN SWITCHING POWER POLES

Figure 10.1a shows the switching power-pole, and Figure 10.1b shows the hard-switching waveforms, which were discussed in Chapter 2. Because of the simultaneous high voltage and high current associated with the transistor during the switching transition, the switching power losses in the transistor increase linearly proportional to the switching frequency and the sum of the times and , shown in Figure 10.1b, assuming an ideal diode,

(10.1)

FIGURE 10.1 Hard switching in a power pole.

In hard-switching converters, in addition to the switching power losses decreasing the energy efficiency, the other problems are device stresses, thermal management of power losses, and electromagnetic ...