Switching power source device and switching power source control circuit

A switching power source control circuit comprising:

• control circuit of a switching power source including a series resonant circuit which includes:
• a current resonant inductor and a current resonant capacitor, a plurality of main switch elements which switch a current path of the series resonant circuit by alternately turning ON and OFF,
• a transformer which induces a current from the series resonant circuit to a secondary side by ON-OFF controlling the main switch elements ON a primary side, and a plurality of synchronous rectification switch elements in which internal diodes are connected in parallel, and each is turned ON and OFF in response to one of the plurality of main switch elements, rectifying the secondary current of the transformer, the switching power source control circuit comprising:
• a detection unit which detects a conduction timing of the internal diodes by an inter-terminal voltage signal of the synchronous rectification switch element;
• and
• a synchronous control circuit which turns the synchronous rectification switch element ON in synchronization with the conduction timing of the internal diodes of the synchronous rectification switch element detected by the detection unit, or with the ON timing of the main switch element corresponding to the synchronous rectification switch element, whichever timing is later, and decides a maximum ON width of the synchronous rectification switch element in accordance with a delay time of the conduction timing of the internal diodes with respect to the ON timing of the main switch element,
• wherein the switching power source control circuit indicates a start timing of the maximum ON width of the synchronous rectification switch element in synchronization with the ON timing of the main switch element corresponding to the synchronous rectification switch element.