A power supply apparatus includes a switching transistor, a transistor
control circuit, and a reference voltage generator. The switching
transistor performs a switching operation for converting an input source
voltage to an output power voltage according to a control signal. The
transistor control circuit generates the control signal based on a
reference voltage and a feedback voltage associated with the output power
voltage. The reference voltage generator generates the reference voltage,
increases the reference voltage in a phased manner to increase the output
power voltage in a phased manner to a desired value, and decreases the
reference voltage to decrease the output power voltage. A power supply
method is also described.