Non-isolated DC/DC converter with 2 inductors and zero voltage switching

A switching power supply circuit that includes:

• a first switching element which turns on and off passage of a current supplied from a power input portion;
• a first inductor which stores a power input through the first switching element and which discharges the power to a power output portion;
• a rectifying diode which rectifies a current toward the power output portion;
• and a smoothing capacitor which smoothes a voltage in the power output portion, the switching power supply circuit comprising:
• a second inductor that is inserted into a path of a current which flows from the power input portion to the first switching element and the first inductor during a period in which the first switching element is on;
• a series circuit that is formed by connecting a second switching element and a voltage source in series;
• a current detection portion that detects a current flowing through the second switching element or a current flowing through the second inductor;
• and
• a control circuit that controls turning on of the first switching element and turning on of and turning off of the second switching element such that a voltage applied to both ends of the first switching element when the first switching element is turned on and a voltage applied to both ends of the second switching element when the second switching element is turned on are equal to or less than a predetermined value,
• wherein the series circuit
• is connected between a connection point between the second inductor and the first switching element and the power output portion,
• is connected between the connection point and a reference potential point having a negative terminal potential of the power input portion,
• is connected between the connection point and the power input portion or
• is connected between the connection point and a terminal of the rectifying diode, and
• the control circuit turns on the second switching element after a predetermined time has elapsed since turning off of the first switching element, thereafter turns off the second switching element at timing at which a detection current value of the current detection portion reaches a predetermined threshold value and turns on the first switching element after a predetermined time has elapsed since the timing.