Switching power supply

摘要

A switching power supply includes a first auxiliary power supply (30) for causing a first auxiliary winding (N3) of a transformer to induce voltage by ON/OFF control of a switching element (S1) connected to a primary winding (N1) of the transformer. The voltage induced by the first auxiliary winding (N3) charges a capacitor in the first auxiliary power supply. The switching power supply also includes a control circuit (40) for starting and stopping the ON/OFF control of the switching element (S1) by comparing a voltage of the capacitor (C5) with a first threshold value, an activation circuit (20) for charging the capacitor (C5) with voltage from the power supply input to the switching power supply; and a determination unit (50) for determining a lifespan of the switching power supply based on the voltage of the capacitor (C5) after the voltage of the capacitor (C5) becomes greater than or equal to the first threshold values.