In DC-DC converters, switching losses occur when switching elements are turned on and off, and thus it is desirable to suppress such losses. As a method for suppressing a switching loss, a method has been proposed as disclosed in JP 2014-236620A. JP 2014-236620A discloses a technique that relates to a soft switching method in which a switching element is operated using a zero current or a zero voltage, and specifically discloses a configuration in which a step-up/down circuit unit includes a resonance capacitor and an inductor, and a resonance phenomenon is used to perform a soft switching operation.
However, if a configuration as in the DC-DC converter disclosed in JP 2014-236620A is employed in which a resonance phenomenon is used to perform a soft switching operation, the use of the resonance phenomenon is likely to cause the problems that high voltage resistance and a complicated control system are required.
For example, when the method disclosed in JP 2014-236620A is used, an excessive resonance voltage or resonance current that instantaneously occurs needs to be dealt with, and thus the size of elements and the number of parallel connections tend to increase. Furthermore, because the resonance voltage or the resonance current need to be controlled, a complicated control system is required, and thus the number of elements tends to increase in this respect. Moreover, in the resonance method disclosed in JP 2014-236620A, because, due to the resonance, a much larger voltage than a high voltage-side voltage is applied to each element of a switching circuit, it is necessary to select, as a switching element such as an FET, a member that withstands a larger voltage than in a case where no resonance method is selected, resulting in an increase in on-resistance of the elements.
The present disclosure was made in view of the aforementioned circumstances, and it is an object thereof to realize a DC-DC converter that can suppress switching loss, with a simpler configuration and a lower withstand voltage.