Patent ID: 8199535
Filing Date: 2012-06-12
Classification: H02M,Y02B

Abstract:
1. A switching power source apparatus comprising: a series circuit connected to both ends of a DC power source and including a primary winding of a transformer and a switching element; a current detector configured to detect a current passing through one of the primary winding of the transformer and the switching element; an output rectifying-smoothing circuit configured to rectify and smooth a voltage generated by a secondary winding of the transformer and provide a DC output voltage; and a controller configured to generate a drive signal that controls an ON/OFF period of the switching element in such a way as to keep the DC output voltage at a predetermined value, the controller including: an edge detector configured to detect an edge of the drive signal when the switching element is switched from ON to OFF; a load tester configured to test, when the edge detector detects the edge of the drive signal, whether or not the switching power source apparatus is in a light load state according to a reference voltage and a voltage derived from a detection signal provided by the current detector; a bottom detector configured to detect a minimum point in a voltage across the switching element during an OFF period of the switching element; a bottom skip state tester configured to test, according to an output from the load tester, whether or not a bottom skip state has continued for a first predetermined time, the bottom skip state being asserted if the output of the load tester indicates the light load state; and a bottom skip operation tester configured to: the bottom skip state tester comprises: a variable voltage part configured to change, if the load tester indicates the light load state, a first voltage to a second voltage that is larger than the first voltage; a capacitor; a current source configured to pass a current corresponding to the second voltage set by the variable voltage part through the capacitor; and a time tester configured to determine that the bottom skip state has continued for the first predetermined time when a voltage across the capacitor charged by the current source reaches the second voltage from the first voltage.