Power supply unit and portable device

A power supply unit having:

• an output circuit for outputting a predetermined output voltage obtained by regulating a given power supply voltage;
• an error amplification circuit adapted to compare a feedback voltage associated with said output voltage with a reference voltage, and, based on the comparison, control said output circuit to bring said feedback voltage to said reference voltage;
• and
• a reference voltage generation circuit for generating a reference voltage, said power supply unit adapted to be controlled to assume an enabled state or a disenabled state depending on the operation command input voltage that is inputted into the operation command signal input terminal of said power supply unit and gradually rises with a predetermined time constant, said power supply unit comprising:
• a voltage level detector circuit for generating a detection signal when said operation command input voltage exceeds a first predetermined voltage level;
• and
• a level shift circuit for generating a level shift voltage lower than said operation command input voltage by shifting the level of said operation command input voltage,
• said reference voltage generation circuit further adapted to be enabled to generate said reference voltage in response to said detection signal;
• and
• said error amplification circuit adapted to be enabled in response to said detection signal to compare said level shift voltage with said feedback voltage in place of said reference voltage when said level shift voltage is lower than said reference voltage.