Method for controlling a switching power unit using an AC/DC converter, a power factor correction unit, and a DC/DC converter unit

A method for controlling a switching power unit that converts AC input voltages of an AC source into DC voltages while improving a power-factor of the AC input voltages, the switching power unit comprising an AC/DC converter circuit that is composed of a power-factor correction unit and a current resonance converter unit, wherein at least a part of switching elements of the current resonance converter unit is shared with switching elements of the power-factor correction unit, the switching power unit includes a full-bridge type AC/DC converter circuit that includes the power-factor correction unit and the current resonance converter unit which share a first switching element and a second switching element, the method comprising:

• around a time when polarities of the AC source are switched between a positive half cycle and a negative half cycle, controlling ON-and-OFF of the switching elements as high frequency voltages applied to a primary winding of a high frequency transformer, which is a part of the current resonance converter unit, the positive half-cycle and the negative half-cycle being symmetrical in a positive and a negative relation,
• the power-factor correction unit includes:
• a series circuit comprising the first switching element and the second switching element;
• a series circuit comprising a first diode and a second diode;
• and a first smoothing capacitor that is connected in parallel with the series circuit of the first and second switching elements,
• the series circuit of the first and second switching elements and the series circuit of the first and second diodes are connected in parallel to each other,
• a booster inductor and the AC source are connected in series between the series circuits,
• the current resonance converter unit comprises:
• a full-bridge circuit where the series circuit of the first and the second switching elements and the series circuit of the third and fourth switching elements are connected in parallel to each other, and where the first and third switching elements are arranged on a high pressure side while the second and fourth switching elements are arranged on a low pressure side;
• the high frequency transformer that is driven by the full-bridge circuit;
• and a series resonance circuit that is connected to the primary winding of the high frequency transformer,
• the switching power unit further comprises:
• a PFC voltage detector that detects PFC voltages at both ends of the first smoothing capacitor of the power-factor correction unit;
• an output voltage detector that detects output voltages at both ends of a second smoothing capacitor provided on a secondary side of the high frequency transformer of the current resonance converter unit;
• a polar detector that detects polarity of the AC source;
• and a switching controller by which ON and OFF operation of the first to fourth switching elements is controlled,
• the switching controller is adapted to control the PFC voltages by changing on-duty of the first and second switching elements based on signals output from the pre-voltage detector, and
• the output voltages are controlled by changing switching cycles of the full-bridge circuit based oil signals output from the output voltage detector.