Switching Power Converters, 2nd Edition

3	Basic Three-Phase Inverters

3.1    HIGH-POWER DEVICES OPERATED AS SIMPLE SWITCHES

Using semiconductor devices such as bipolar transistors and MOSFETs at somewhat higher power levels in the active region yields low efficiency. A voltage regulator built with a bipolar transistor working in the active region can barely provide an efficiency of 30–40% because of the large collector–emitter voltage drop. In contrast, operation of the same device in switch mode allows efficiencies of 80–99%, depending on the converter topology and the number of passive elements. The whole idea of using switches is to operate at high frequency with a constant or variable duty cycle followed by low-pass filtering with a passive filter. The DC or low-frequency ...