Hitachi, Ltd.

Toshikazu Okubo

Hiroyuki Shoji

Tatsumi Yamauchi

Seigou Yukutake

Takae Shimada

Junpei Uruno

A small and efficient DC-DC converter is provided. In this DC-DC converter, passive elements such as an inductor and a capacitor can be reduced in size by reducing switching loss by a soft switching technology and increasing the drive frequency of a switching element. The DC-DC converter has a main switching element, a main diode and an auxiliary circuit that discharges the electric charges of the capacitance between the ends of the main switching element. The DC-DC converter includes an auxiliary inductor magnetically coupled with the main inductor, an auxiliary switching element that stores energy in the auxiliary inductor, and an auxiliary diode that discharges energy stored in the auxiliary inductor to the direct-current power source or the output side. The auxiliary inductor is coupled with the main inductor in the direction in which backward voltage is applied to the auxiliary diode when the main inductor discharges energy.

DC-DC converter

A bi-directional DC-DC converter uses a transformer for both step-down and step-up operations. A switching frequency for operating a switching device is set separately for the step-down and step-up operations. When, for example, the switching frequency during the step-up operation is lower than the switching frequency during the step-down operation, the range in which the duty ratio in PWM control can be controlled is widened, compensating for step-up ratio insufficiency. Conversely, step-down ratio insufficiency is compensated for by making the switching frequency during the step-down operation lower than the switching frequency during the step-up operation.

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Hitachinaka, Japan

Toshikazu Okubo