Switching Power Supply with a Measuring and Calculating Process for the Switching Times

A switching power supply comprising:

• a power converter that includes a series circuit with a boost inductor, to which an input voltage Vi is applied, and a switch, and a synchronous rectifier connected to a junction between the boost inductor and the switch, and converts the input voltage Vi to an output voltage Vo which is outputted;
• a zero current detector that includes a detection winding, which is magnetically coupled to the boost inductor and outputs a zero current detection signal whose voltage value changes in proportion to a voltage across the boost inductor, and detects zero timing at which an inductor current flowing in the boost inductor becomes zero;
• a controller that executes an on/off control process that sets the switch in an on state based on the zero timing, causes energy to accumulate in the boost inductor, switches the switch from the on state into an off state, then sets the synchronous rectifier in a synchronous rectification state to have the energy discharged from the boost inductor to cause the power converter to output the output voltage Vo;
• and
• a voltage meter that measures the input voltage Vi and the output voltage Vo,
• wherein the controller causes a second on period T2, where the synchronous rectifier is set in the synchronous rectification state, to end before the zero timing by executing:
• a first measuring process that measures a first on period T1 where the switch is set in an on state;
• a second on period calculating process that calculates, when a correction time for the second on period T2 is expressed as “Tc”, the second on period T2 according to a following expression
• T2=T1×|Vi|/(Vo−|Vi|)−Tc;
• the on/off control process that sets the synchronous rectifier in the synchronous rectification state for only the second on period T2 calculated by the second on period calculating process;
• a second measuring process that measures an elapsed time from an end of the second on period T2 to a start of the first on period T1;
• and
• a correction time changing process that changes the correction time Tc so that the elapsed time measured by the second measuring process becomes a target time set in advance.