Low‐power uninterruptible dc power supplies have been used widely. These are powered by several types of power sources with differing voltages, e.g., commercial ac power sources as well as batteries. A multi‐input‐type converter is developed to simplify circuit configuration and realize a low‐loss power system. This paper presents a method of designing a multiinput transformer as well as the operation principle of a multiinput‐type uninterruptible power supply and the circuit technology required for it. The power supply can be realized if the transformer primary winding‐turn ratio is designed considering the input voltage variation range and the voltage‐drop in the transformer primary circuit. The fact that the switching‐duty ratio must be changed drastically and that the switching transistor loss is inclined to increase in a multiinput‐type converter causes some problems. It is shown that the application of a collector current proportional drive circuit to the forward‐type converter or a base resistor switching circuit to the flyback‐type converter is effective in reducing the converter loss and the converter can be simplified by using most of the converter circuits in common.
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Koyashiki et al. (1986) studied this question.