To realize a circuit using step-down power supply voltage which can reduce a means current to supply a power by stepping down the power supply voltage to an electrical circuit having two states of an on state and a standby state.

The output terminal 6 of a high efficiency step-down power supply circuit 7 having a high step-down efficiency in the on state of an electric circuit 2 and the output terminal 8 of a low efficiency step-down voltage power supply circuit 5 having extremely small leakage current in the standby state of the electric circuit 2 are connected together to the power supply terminal 3 of the electric circuit 2. In the on state, power is supplied from the high efficiency step-down power supply circuit 7 to the electric circuit 2, and in the standby state, the power is supplied from the low efficiency step-down power supply circuit 5 to the electric circuit 2.

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