Power supply apparatus with feedback ratio calculation unit

A power supply apparatus structured to supply a power supply signal to a power supply terminal of a device via a power supply line, the power supply apparatus comprising:

• an A/D converter structured to receive, via a feedback line, an analog measurement value that corresponds to the power supply signal supplied to the power supply terminal of the device, and to analog/digital convert the analog measurement value so as to generate a digital measurement value;
• a digital calculation unit structured to generate, by means of digital calculation, a control value adjusted such that the digital measurement value received from the A/D converter matches a predetermined reference value;
• a D/A converter structured to digital/analog convert the control value to an analog power supply signal, and to supply the analog power supply signal to the power supply terminal of the device via the power supply line, wherein the analog power supply signal is proportional to the control value;
• and
• a feedback ratio calculation unit structured to calculate the ratio between the control value and the digital measurement value,
• wherein the digital calculation unit is structured to change its calculation content based on the ratio calculated by the feedback ratio calculation unit;
• and
• the analog power signal is proportional to the control value for both a stable state and a transient state.