Patent ID: 8488339

Claim:
A switching power supply comprising: a first auxiliary power supply for causing a secondary winding; a first auxiliary winding of a transformer to induce voltage by ON/OFF control of a switching element connected to a primary winding of the transformer, wherein the voltage induced by the secondary winding is smoothened to output a DC voltage, and the voltage induced by the first auxiliary winding is smoothened to charge a capacitor in the first auxiliary power supply; a control circuit that starts the ON/OFF control of the switching element when a voltage of the capacitor becomes greater than or equal to a first threshold value, causing the secondary winding of the transformer and the first auxiliary winding to induce voltage by the ON/OFF control, wherein the control circuit stops the ON/OFF control when the voltage of the capacitor becomes smaller than or equal to a second threshold value smaller than the first threshold value; an activation circuit for charging the capacitor with voltage from power supply input to the switching power supply; and a determination unit for determining a lifespan of the switching power supply based on the voltage of the capacitor after the voltage of the capacitor becomes greater than or equal to the first threshold value.