Stabilized DC voltage is required to run electric appliances stably. That is why stabilized DC power supply exists. Currently, mode for stabilized DC power supply roughly classified into switching mode and series mode.

<< Switching mode >>
Basic block diagram of switching mode is shown in Figure 1.3 below.

Figure 1.3 Basic block diagram of switching mode

In switching mode, rectified voltage is switched (turned ON and OFF) at high speed to be converted to alternate voltage with high frequency (pulse). This alternate voltage is rectified again. By high frequency switching, transformer can be smaller　to contribute to compact equipment. Also, heat buildup becomes low to bring high efficiency. However, switching increases noises.

<< Series mode >>
Basic block diagram of series system is shown in figure 1.4 below.

Figure 1.4 Basic block diagram of series mode

In series mode, output voltage is stabilized by series regulator as input voltage changes. Noise and ripple voltage is small, but efficiency is poor to bring large and heavy transformer without high frequency conversion.

<< Comparison between switching and series mode is shown below in Table 1.1. >>

Table 1.1　Comparison between switching and series system