Switching power supply unit and voltage converting method

A switching power supply unit comprising:

• a first bridge circuit of a full bridge type including four first switching elements and generating a first AC voltage on the basis of a DC input voltage that is input to the switching power supply unit;
• first capacitative elements each of which is connected in parallel with each of the first switching elements;
• a first inductor connected to the first bridge circuit so as to form an H bridge and configuring a first resonance circuit in cooperation with the first capacitative elements;
• a first transformer for transforming the first AC voltage to generate a second AC voltage;
• a rectifier circuit provided on a secondary side of the first transformer, including a plurality of first rectifier elements, and rectifying the second AC voltage by the plurality of first rectifier elements, thereby generating a DC output voltage that is output from the switching power supply unit;
• a second bridge circuit including a pair of second switching elements connected in series and a pair of second capacitative elements connected in series, the second bridge circuit connected in parallel with the first bridge circuit;
• a second inductor connected to the second bridge circuit so as to form an H bridge and constructing a second resonance circuit in cooperation with the second capacitative elements;
• a second transformer for transforming an input voltage from the second bridge circuit to generate an output voltage and supplying the output voltage to the rectifier circuit;
• and
• a driving circuit for driving the first and second bridge circuit so that a current flowing in the first rectifier elements due to a resonance operation of the first resonance circuit has an opposite phase to a current flowing in the first rectifier elements due to a resonance operation of the second resonance circuit.

A switching power supply unit comprising:

• a bridge circuit of a full bridge type for generating a first AC voltage by switching a DC input voltage inputted to the switching power supply unit;
• a transformer for transforming the first AC voltage to generate a second AC voltage;
• a rectifier circuit provided on a secondary side of the transformer, including a plurality of rectifier elements, and rectifying the second AC voltage by the plurality of rectifier elements, thereby generating a DC output voltage outputted from the switching power supply unit;
• a surge voltage suppressing circuit connected in parallel with the bridge circuit and injecting surge voltage suppressing energy into the rectifier circuit, wherein the surge voltage suppressing energy suppresses a surge voltage applied to the rectifier elements;
• and
• a driving circuit for driving the bridge circuit and the surge voltage suppressing circuit, wherein
• the driving circuit drives the bridge circuit and the surge voltage suppressing circuit so that the surge voltage suppressing energy has a phase opposite to that of energy which amplifies the surge voltage supplied from the bridge circuit.

A switching power supply unit comprising:

• a bridge circuit of a full bridge type for generating a first AC voltage by switching a DC input voltage inputted to the switching power supply unit;
• a transformer for transforming the first AC voltage to generate a second AC voltage;
• a rectifier circuit provided on a secondary side of the transformer, including a plurality of rectifier elements, and rectifying the second AC voltage by the plurality of rectifier elements, thereby generating a DC output voltage outputted from the switching power supply unit;
• a surge voltage suppressing circuit connected in parallel with the bridge circuit and injecting surge voltage suppressing energy into the rectifier circuit, wherein the surge voltage suppressing energy suppresses a surge voltage applied to the rectifier elements;
• and
• a driving circuit for driving the bridge circuit and the surge voltage suppressing circuit, wherein
• the driving circuit drives the bridge circuit and the surge voltage suppressing circuit so that a reverse voltage applied to the rectifier element maintains, for a predetermined period, to be lower than a voltage determined based on the DC input voltage and the primary-side and secondary-side windings of the transformer by balancing first current and second current, the first current supplied from the bridge circuit and flowing in the direction of amplifying the surge voltage, the second current flowing in the direction of suppressing the surge voltage based on the surge voltage suppressing energy.

A switching power supply unit comprising:

• a bridge circuit of a full bridge type for generating a first AC voltage by switching a DC input voltage inputted to the switching power supply unit;
• a transformer for transforming the first AC voltage to generate a second AC voltage;
• a rectifier circuit provided on a secondary side of the transformer, including a plurality of rectifier elements, and rectifying the second AC voltage by the plurality of rectifier elements, thereby generating a DC output voltage outputted from the switching power supply unit;
• a surge voltage suppressing circuit connected in parallel with the bridge circuit and injecting surge voltage suppressing energy into the rectifier circuit, wherein the surge voltage suppressing energy suppresses a surge voltage applied to the rectifier elements;
• and
• a driving circuit for driving the bridge circuit and the surge voltage suppressing circuit, wherein
• the driving circuit drives the bridge circuit and the surge voltage suppressing circuit so that a reverse voltage applied to the rectifier element rises step by step through the injection of the surge voltage suppressing energy.