Heater control apparatus for exhaust gas sensor

A heater control apparatus comprising:

• an exhaust gas sensor provided in an exhaust passageway of an internal combustion engine, the exhaust gas sensor for detecting an oxygen concentration in exhaust gases;
• a heater for heating the exhaust gas sensor to a predetermined temperature;
• a power source including:
• a battery for supplying heating electric power to the heater;
• and
• a charging generator for charging this battery;
• a switching element inserted into a circuit for supplying electric power to the heater from the power source,
• a controller including a microcomputer for performing current-carrying control of the switching element to maintain a temperature of the exhaust gas sensor at a predetermined value;
• a circuit abnormal detector for detecting circuit abnormality and outputting an abnormal detection signal;
• an overvoltage detection element for outputting an abnormal detection signal when a voltage of the charging generator increases and exceeds a predetermined value;
• and
• a second switching element inserted into a circuit for supplying electric power to the heater from the power source, the second switching element for responding to the abnormal detection signal of the circuit abnormal detector, responding to the abnormal detection signal of the overvoltage detection 31 element, and breaking a current flowing through the heater.