Power supply apparatus and electronic device

An electric device comprising:

• a DC-DC converter configured to convert an input voltage into an output voltage in accordance with a duty cycle which is decided by a difference of a third signal;
• a first photo coupler configured to output a first signal corresponding to the output voltage;
• a converter configured to convert the output voltage into a digital signal;
• and
• a second photo coupler configured to output a second signal corresponding to the digital signal;
• a memory;
• a processor coupled to the memory and configured to:
• calculate a third signal on the basis of the difference between the first signal and the second signal,
• control the DC-DC converter so that the third signal is to be zero, and
• predict a life of the first photo coupler on the basis of the first signal;
• and
• a display configured to display information of the life.