Step-down/step-up DC/DC converter apparatus and method with inductor current threshold value adjusting

A switching power supply device, comprising:

• a switching converter circuit having at least one inductor, and being configured, adapted and connected to alternate repeatedly between a first state for storing power input from an input terminal in said inductor and a second state for discharging the power stored in said inductor from an output terminal, to step up or down DC voltage applied to said input terminal as a result of said repeated operation, and to output said stepped up or down voltage at said output terminal;
• a control circuit configured, adapted and connected to set said switching converter circuit into said second state when the voltage at said output terminal is higher than a target value, and returning said switching converter circuit to said second state after it has been set into the first state for a prescribed period of time when the voltage at said output terminal is lower than the target value, and to set said switching converter circuit into said second state when the current of said inductor is larger than a threshold value;
• and
• a threshold value adjusting circuit configured, adapted and connected to adjust said threshold value corresponding to the ratio or difference between the voltage at said input terminal and the voltage at said output terminal, so that the variation in the ripple voltage occurring at said output terminal in company with the variation in said ratio or difference is reduced.