Circuit for driving a heater at a constant power

摘要

A current-limiting resistor (5) is connected between a power-supply line and a heater (4) provided near the oxygen-detecting element (2) of limiting-current type oxygen sensor (1). A power MOSFET (6) is connected between the heater (4) and a ground line. The resistor (5) and the heater (4) have such resistances that a current I2 flowing through the resistor (5) and the heater (4) when the heater (4) has a resistance R2 is about I1 (R1/R2), where I1 is a current flowing through the resistor (5) and the heater (4) when the heater (4) has a resistance R1.