Switching power source apparatus

A switching power source apparatus comprising:

• an input rectifying-smoothing circuit configured to rectify and smooth an AC voltage from an AC power source and provide a DC input voltage;
• a switching element connected through a primary winding of a transformer to an output end of the input rectifying-smoothing circuit;
• an output rectifying-smoothing circuit configured to rectify and smooth a voltage induced by a secondary winding of the transformer and provide a DC output voltage;
• a control circuit for controlling ON/OFF of the switching element;
• and
• a delay circuit configured to generate a predetermined delay time, wherein
• the control circuit is configured to:
• detect a peak value of the AC voltage from the AC power source;
• start a switching operation of the switching element if the peak value of the AC voltage has increased to or above a threshold value;
• and
• stop the switching operation of the switching element if the peak value of the AC voltage is lower than the threshold value and that a period during which the peak value is continuously lower than the threshold value has reached the predetermined delay time generated by the delay circuit.