An inverting negative voltage DC-DC power supply circuit comprises a first
resistor having one end connected to an output terminal for converting a
change in output voltage into a current. A zero-volt clamp circuit is
connected to the other end of the first resistor and comprises a first
and second transistor. A current mirror circuit comprises a third and
fourth transistor and is connected to the zero-volt clamp circuit for
causing a current of the same value as that of a current flowing in the
zero-volt clamp circuit to flow. A second resistor is connected to the
current mirror circuit for converting a change in current flowing from
the zero-volt clamp circuit into a voltage.