Patent ID: 8643992

Claim:
An overcurrent protection apparatus for protecting a load circuit from an overcurrent, the load circuit including a power source, a load and a first semiconductor element (T 1 ) disposed between the power source and the load, a first main electrode of the first semiconductor element (T 1 ) being coupled to a positive electrode terminal of the power source and a second main electrode of the first semiconductor element (T 1 ) being coupled to a negative electrode terminal of the power source via the load, the overcurrent protection apparatus comprising: an amplifying section (AMP 1 ) that includes a non-inverting terminal which is coupled to the second main electrode of the first semiconductor element (T 1 ); a first resistor (R 1 ) that includes one end which is coupled to the first main electrode of the first semiconductor element (T 1 ) and the other end which is coupled to an inverting terminal of the amplifying section (AMP 1 ); a third resistor (R 3 ); a second semiconductor element (T 2 ) that includes a first main electrode, a second main electrode and a control electrode, the first main electrode being grounded via the third resistor (R 3 ), the second main electrode being coupled to a point a which is a coupling point between the first resistor (R 1 ) and the inverting terminal of the amplifying section, and the control electrode being coupled to an output terminal of the amplifying section; and a comparator (CMP 1 ) that includes one input terminal and the other input terminal, the one input terminal being applied with a voltage (V 3 ) at a coupling point (point e) between the second semiconductor element (T 2 ) and the third resistor (R 3 ), and the other input terminal being applied with a determination voltage (V 4 ) which is generated by dividing a voltage (V 1 ) of the first main electrode of the first semiconductor element (T 1 ) by a resistance ratio (R 4 :R 5 ), wherein in a case where a current having a current value (V 4 /m/Ron), which is obtained by dividing the determination voltage (V 4 ) by a value (m) that is obtained by dividing a resistance value of the third resistor (R 3 ) by a resistance value of the first resistor (R 1 ), by an average value (Ron) of an on-resistance of the first semiconductor element (T 1 ) flows into the first semiconductor element (T 1 ) and the on-resistance is larger than the average value (Ron) of the on-resistance, a current obtained by subtracting a current (ΔI 1 ) proportional to a deviation (ΔRon) of the on-resistance from a current (I 1 ) flowing through the first resistor at the point a is flown through the third resistor so that an output signal of the comparator (CMP 1 ) is inverted.