Disclosed is a constant voltage power supply, which comprises an error
amplifier VEA including a transistor M3, and a transistor M4 having
the same ratio between channel width and channel length as that of the transistor
M3. The gate and source of the transistor M4 are connected to the
gate of a transistor M3 to form a current mirror circuit in conjunction
with the transistor M3. Further, the drain of the transistor M4 is
connected with a transistor M5 adapted to be switched in response to an
external control signal Sg. For example, when the transistor M5 is in ON
state, any signal amplification function of the transistor M3 is vanished
away, and the gain of the error amplifier VEA is lowered. The circuit configuration
for changing the gain of the error amplifier VEA makes it possible to strike a
balance between high-speed response characteristic in an active mode and operational
stability in a sleep mode, and reduce a circuit area required for being formed
on an integrated circuit.
