A multiinput type converter for an uninterruptible dc power supply

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.