Patent ID: 7155970

Claim:
A heat-radiation type flow sensor comprising: a heater resistor, a first transistor and a first resistor, which are connected to each other in series to form a first current path to allow a first current to flow in the first current path from a power supply; and a first operational amplifier for controlling the first current flowing between an emitter and a collector of the first transistor, wherein: the emitter of the first transistor is connected to the heater resistor; the collector of the first transistor is connected to the first resistor; an electrical potential appearing at a junction between the emitter of the first transistor and the heater resistor is supplied to an inverting input terminal of the first operational amplifier; a reference voltage is supplied to a non-inverting input terminal of the first operational amplifier; an electrical potential appearing at an output terminal of the first operational amplifier is supplied to a base of the first transistor; and an electrical potential appearing at a junction between the collector of the first transistor and the first resistor is taken as an output varying with a flow amount of fluid.