US Patent 7764119 Voltage control circuit

A circuit for controlling voltage includes a condenser having a first end coupled to an input node of a target circuit, and a second end coupled to a predetermined fixed potential, a constant current source coupled to the first end of the condenser, and a control circuit configured to charge or discharge the condenser by the constant current source, to measure a first time period passing from start timing of the charge or discharge to timing at which a voltage at the first end of the condenser reaches a predetermined voltage, and to change an input condition or operation condition of the target circuit upon passage of a second time period from the start timing where the second time period is responsive to the first time period.