Switching power supply circuit and overcurrent protection method for the switching power supply circuit

A switching power supply circuit comprising:

• a switching element provided with a source terminal, a drain terminal and a gate terminal;
• a power supply source connected to the source terminal;
• a load connected to the drain terminal;
• a control circuit connected to the gate terminal;
• an inductor disposed in a current path from the drain terminal to the load;
• a first current detection resistor for detecting a current flowing from the source terminal to the drain terminal;
• a first comparator connected to the first current detection resistor;
• a second current detection resistor disposed in a current path from the drain terminal to the ground terminal;
• and
• a second comparator connected to the second current detection resistor.

An overcurrent protection method for a switching power supply circuit having a switching element for controlling on/off state of an input power supply according to a drive pulse generated on the basis of a clock pulse having a prescribed period, wherein an electric current is allowed to flow from the input power supply to a load by controlling the switching element to be in on state, and a flywheel current is allowed to flow to the load by controlling the switching clement to be in off state;

• the overcurrent protection method comprising:
• detecting that the current flowing through the switching element has reached a first reference value;
• detecting with an overcurrent detecting means that the current flowing through the switching element has reached a first reference value;
• detecting with flywheel current detecting means that the flywheel current has reached a second reference value;
• performing an overcurrent protection operation for turning off the switching element based on a detected output of the overcurrent detecting means;
• and
• turning on the switching element during the overcurrent protection operation at a timing of the clock pulse after the flywheel current detected by the flywheel current detecting means has reached the second reference value.