Heating resistor type airflow meter

A hot-wire airflow meter for measuring airflow rate, comprising:

• a heat-generating resistor for a heating resistor type airflow meter;
• a resistance temperature detector for air temperature compensation;
• a current source that determines the ratio of currents that flow through said heat-generating resistor and said resistance temperature detector;
• and
• a current-detecting resistor for indirectly detecting the current that flows through said heat-generating resistor,
• wherein said current source comprises at least a current mirror circuit and an operational amplifier, said current mirror circuit comprising first and second transistors connected in parallel,
• wherein said first transistor and said heat-generating resistor are connected in series, said second transistor, said resistance temperature detector for air temperature compensation, and said current-detecting resistor are connected in series,
• wherein a voltage between said heat-generating resistor and said first transistor and a voltage between said resistance temperature detector for air temperature compensation and said second transistor are input to said operational amplifier, and
• wherein said first and second transistors are controlled by an output of said operational amplifier such that the current that flows through each of said resistors is controlled to maintain a predetermined ratio.

A hot-wire airflow meter for measuring airflow rate, comprising:

• a heat-generating resistor for a heating resistor type airflow meter;
• a resistance temperature detector for air temperature compensation;
• a current source that determines the ratio of currents that flow through said heat-generating resistor and said resistance temperature detector;
• and
• a current-detecting resistor for indirectly detecting the current that flows through said heat-generating resistor,
• wherein said current source comprises at least a current mirror circuit and an operational amplifier, said current mirror circuit comprising first, second, and third transistors connected in parallel,
• wherein said first transistor and said heat-generating resistor are connected in series, said second transistor and said resistance temperature detector for air temperature compensation are connected in series, and said third transistor and said current-detecting resistor are connected in series,
• wherein a voltage between said heat-generating resistor and said first transistor and a voltage between said resistance temperature detector for air temperature compensation and said second transistor are input to said operational amplifier,
• wherein said first to third transistors are controlled by an output of said operational amplifier such that the current that flows through each of said resistors is controlled to maintain a predetermined ratio, and
• wherein said heat-generating resistor, said resistance temperature detector for air temperature compensation, and said current-detecting resistor are connected in parallel via said current source that determines the current ratio.

A hot-wire airflow meter for measuring airflow rate, comprising:

• a heat-generating resistor for a heating resistor type airflow meter;
• a resistance temperature detector for air temperature compensation;
• a current source that determines the ratio of currents that flow through said heat-generating resistor and said resistance temperature detector;
• and
• a current-detecting resistor for indirectly detecting the current that flows through said heat-generating resistor,
• wherein said current source comprises at least a current mirror circuit and an operational amplifier, said current mirror circuit comprising first and second transistors connected in parallel,
• wherein said first transistor and said heat-generating resistor are connected in series, said second transistor, said resistance temperature detector for air temperature compensation, and said current-detecting resistor are connected in series,
• wherein a voltage between said heat-generating resistor and said first transistor and a voltage between said resistance temperature detector for air temperature compensation and said second transistor are input to said operational amplifier,
• wherein said first and second transistors are controlled by an output of said operational amplifier such that the current that flows through each of said resistors is controlled to maintain a predetermined ratio,
• wherein said current-detecting resistor and said resistance temperature detector for air temperature compensation are connected in series, and
• wherein these resistors and said heat-generating resistor are connected in parallel via said current source that determines the current ratio.