Electronic circuit for vehicles, having a fail safe function for abnormality in supply voltage

Claim 1

An electronic circuit for use in a vehicle which is equipped with an internal combustion engine and an electrical power source, said electronic circuit consisting essentially of: a power-supply circuit for controlling a voltage supplied from said power source to a predetermined voltage; at least one electrical apparatus installed in said vehicle, said electrical apparatus being capable of changing the amount of air or fuel to be supplied to said engine; a control circuit arranged to be supplied with power from said power-supply circuit and having a central processing unit for controlling the operation of said at least one electrical apparatus, said central processing unit being susceptible to erratic operation when said voltage supplied thereto by said power-supply circuit is outside a predetermined range defined by a predetermined upper limit voltage and a predetermined lower limit voltage, said central processing unit being resettable; a detecting circuit consisting essentially of a first comparator for comparing the voltage of said power supplied from said power-supply circuit with said predetermined upper limit voltage and a second comparator for comparing the voltage of said power supplied from said power-supply circuit with said predetermined lower limit voltage, said detecting circuit being adapted to produce an output signal immediately when said power has a voltage lying out of said predetermined range determined by said upper and lower limit voltages, and to stop producing said output signal immediately when the voltage of said power supplied from said power-supply circuit is restored to a value within said predetermined range, said first comparator having an inverting input terminal and a non-inverting input terminal, the non-inverting input terminal of said first comparator being connected substantially directly to the output of said power-supply circuit, said second comparator having an inverting input terminal and a non-inverting input terminal, the inverting input terminal of said second comparator being connected substantially directly to the output of said power-supply circuit, means for applying a first predetermined voltage delimiting an upper limit of said predetermined power-supply circuit voltage range to the inverting input terminal of said first comparator, means for applying a second predetermined voltage delimiting a lower limit of said predetermined power-supply circuit voltage range to the non-inverting input terminal of said second comparator, and an OR circuit having first and second input terminals substantially directly connected to outputs of said first and second comparators respectively; and means immediately responsive to said output signal of said detecting circuit to reset said central processing unit and to keep said central processing unit reset so long as said output signal is present, whereby said central processing unit remains connected to said power-supply circuit but is temporarily and immediately rendered inoperative at those times when the voltage applied thereto from said power-supply circuit is outside said predetermined range.