Switching power supply circuit capable of reducing switching loss and control method used therein

A switching power supply circuit comprising:

• a switching element;
• an inductance element for storing electromagnetic energy supplied from a DC power supply unit when said switching element is in ON state, in which counter electromotive force generated in said inductance element when said switching element is turned into OFF state is superimposed on an output voltage of said DC power supply unit;
• rectifying means;
• smoothing means to which the superimposed voltage is applied through said rectifying means to boost the output voltage of said DC power supply unit;
• a rectifying element connected to both ends of said switching element such that the forward direction of said rectifying element is reverse to the direction of current flowing in said switching element;
• a capacitance element connected to both ends of said switching element;
• and
• a control circuit which allows current to flow through said rectifying element in the forward direction to turn said rectifying element on and discharges said capacitance element before said switching element changes from OFF state into ON state, charges said capacitance element and turns said rectifying element off when said switching element changes from ON state into OFF state, and restricts recovery current flowing from said smoothing means through said rectifying means into said switching element when said switching element changes from OFF state into ON state.