Power Electronics, A First Course, 2nd Edition

8 SWITCH-MODE DC POWER SUPPLIES

8.1 APPLICATIONS OF SWITCH-MODE DC POWER SUPPLIES

Switch-mode DC power supplies represent an important power electronics application area with a worldwide market of several billion dollars per year. Many of these power supplies incorporate transformer isolation for reasons that are discussed below. Within these power supplies, transformer-isolated DC-DC converters are derived from non-isolated DC-DC converter topologies already discussed in Chapter 3. For short, we will refer to transformer-isolated switch-mode DC power supplies as SMPS (switched-mode power supply, sometimes called switcher), whose block diagram is shown in Figure 8.1. As shown in Figure 8.1, these supplies encompass the rectification of the utility supply, and the voltage across a large filter capacitor is the input to the transformer-isolated DC-DC converter, which is the focus of discussion in this chapter. Internally, the transformer operates at very high frequencies, typically upwards of a few hundred kHz, thus resulting in small size and weight, as discussed in the next chapter.

FIGURE 8.1 Block diagram of switch-mode DC power supplies.

8.2 NEED FOR ELECTRICAL ISOLATION

Electrical isolation by means of transformers is needed in switch-mode DC power supplies for three reasons: ...