| 摘要 |
PROBLEM TO BE SOLVED: To protect the gate-source of an MOSFET for protecting the internal circuit from an undue input voltage, and to suppress a leakage current flowing through the gate-source via a diode so as not to have an adverse effect on the internal circuit.SOLUTION: N type and P type FETs 4, 5 are connected in series between an application terminal 3 of an input voltage Vin, and a voltage measurement circuit 1 to which an applied voltage Vic is input. When the input voltage Vin exceeds the power supply voltage (VDD-VSS) of the circuit 1, one of the FETs 4, 5 is turned off to block input of an undue voltage. The input protective circuit includes Zener diodes 12, 13 connected between the gate-source of the FETs 4, 5, and a voltage shift circuit 11 for holding the gate-source voltage of the FETs 4, 5 at a fixed voltage value within the range of power supply voltage by giving the gate potential of the FETs 4, 5, while tracking to the Vic that is the input voltage Vin, between the source end of the FET 5 and the gate end of the FETs 4, 5. |
