Patent ID: 7397151

Claim:
A power supply unit, comprising a series regulator for converting an input voltage into a predetermined output voltage in a continuously controlled manner and outputting said output voltage from the output end thereof; and a switching DC-DC converter for converting said input voltage into a predetermined output voltage, said switching DC-DC converter connected at the output end thereof in parallel with the output end of said series regulator, wherein said power supply unit has a mode in which only said series regulator is operated (regulator mode) and a mode in which only said switching DC-DC converter is operated (converter mode), switching from one mode to another in response to a mode instruction signal, wherein said power supply unit has a predetermined overlapping period in which said series regulator and switching DC-DC converter are simultaneously operated for a predetermined period of time following a switching from one mode to another, wherein said switching DC-DC converter includes an error amplification circuit for controlling said output voltage in accordance with the difference between a reference voltage and a voltage representing said output voltage, said error amplification circuit having an AC and a DC feedback circuits that are switchable from said AC feedback circuit to said DC feedback circuit during said overlapping period.