Abstract: A step-down circuit is incorporated in a large scale integrated circuit for producing an internal power voltage from an external power voltage, and the step-down circuit comprises a reference signal generating unit for producing a reference signal indicative of a target level for the internal power voltage, first and second voltage regulating units for regulating the internal power voltage to the target level, and a monitoring unit monitoring the voltage level of the power voltage and producing an enable signal in the standby mode of operation when the external power voltage exceeds a predetermined level, wherein the first and second voltage regulating units are selectively enabled depending upon mode of the large scale integrated circuit, i.e. an active mode and a standby mode, as well as the level of the external power voltage so that power consumption of the large scale integrated circuit is improved.

Abstract: A different power sources interface circuit for connecting a first power source operating circuit for supplying complementary outputs with a second power source operating circuit having a power source for supplying a voltage higher than that of the power source of the first power source circuit comprises an input transistor circuit including first and second N channel MOS transistors which are in series connected between said second power source and a ground and have respective gates to which the complementary outputs of said first power circuit are supplied; a first inverter circuit having an input connected with a connection between both said transistors; and a second inverter circuit having an input and an output thereof which are connected with the output and input of said first inverter circuit, respectively.