JPH0381621A - Automotive hot wire air flow meter - Google Patents

Abstract

PURPOSE:To protect a monolithic IC from an overcurrent providing an overcurrent protecting circuit which never increases in source voltage for securing minimum operation even when a large current is supplied to the monolithic IC from a power source for the air flowmeter. CONSTITUTION:A resistance with a high resistance value is used as the resistance 18 of the overvoltage protecting circuit. When a source voltage VB is generated and a voltage which is higher than its Zener voltage is applied to the upper terminal of a Zener diode 19, the diode 19 conducts, and consequently the base voltage of a transistor (TR) 17 is held as high as the Zener voltage of the diode 19 and never becomes higher that it. Even if the source voltage Vs becomes high, the voltage Vcc at the power source terminal 3A of an IC block 3 including the circuit principal part of a constant-temperature control circuit consisting of the monolithic IC is held higher than the voltage obtained by subtracting the base-emitter voltage VBE of the TR 17 from the Zener voltage Vz of the diode 19, so the IC block 3 which is the monolithic IC can be protected from the overvoltage by setting the VZ-VBE from the breakdown voltage of the monolithic IC.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hot-wire air flow meter for automobiles, and more particularly to a hot-wire air flow meter used in various electronic control systems of internal combustion engines for automobiles.

[Conventional technology]

A conventional example of an air flow meter is, for example, Japanese Patent Application Laid-Open No. 55-137.
There is one disclosed in Publication No. 321.

In this prior art invention, in order to prevent the intake air flow rate signal from being affected by the temperature of the intake air in the intake air flow rate measuring device, even if the intake air temperature becomes high, the temperature of the resistance element for flow rate measurement and the intake It is configured so that the difference with the air temperature is small.

By the way, in the technical content disclosed in this prior art, in FIG. 4, which shows an example of a hot wire drive circuit, it is configured such that power is supplied from the power supply +E to drive circuit elements such as an operational amplifier. In order to prevent overvoltage from being applied to each circuit element due to fluctuations in the power supply in this configuration, an overvoltage protection circuit consisting of a series circuit of a resistor and a Zener diode is connected between the power supply terminal and the ground terminal. Current is supplied to the main part of the circuit via the resistor, and a Zener diode is arranged in parallel to the main part of the circuit. According to the configuration including such an overvoltage protection circuit, even if the value of the power supply voltage +E becomes excessively large due to fluctuations in the output of the voltage generator (not shown) mounted on the vehicle, the voltage will not exceed a predetermined voltage. The Zener diode becomes conductive and can protect the main part of the circuit from overvoltage.

[Problem to be solved by the invention]

In recent years, electronic circuits installed in automobiles are increasingly being integrated into ICs from the viewpoint of miniaturization, weight reduction, and improvement in operational reliability. The electronic circuit of the hot wire flowmeter mentioned above is also a monolithic IC circuit.
There are things that have been transformed.

In the hot wire drive circuit made of a monolithic IC, when this monolithic IC circuit consumes a large amount of current and a large current flows from the power supply, according to the circuit configuration, the resistor forming the overvoltage protection circuit Since a large voltage drop occurs at , the voltage applied to the monolithic IC decreases.

In other words, according to the hot wire drive circuit having the conventional overvoltage protection circuit described above, when current consumption increases when formed using a monolithic IC, the input voltage decreases due to the connection configuration of the overvoltage protection circuit. There is a problem in that the maximum output voltage of the monolithic IC decreases accordingly.

In order to eliminate the above-mentioned problems, it is necessary to increase the minimum applied voltage value of the power supply for the air flow meter, which guarantees the operation of the electronic circuit of the air flow meter, or to increase the minimum applied voltage value of the power supply for the air flow meter, which guarantees the operation of the electronic circuit of the air flow meter, or to It is necessary to reduce the resistance value of the overvoltage protection circuit to reduce the voltage drop. However, in either case, a problem arises in that an element with a large power capacity must be used as the Zener diode of the overvoltage protection circuit that is arranged in parallel with the main part of the circuit such as the operational amplifier.

An object of the present invention is to provide a hot-wire air flow meter for an automobile that includes an electronic circuit formed of a monolithic IC, with a minimum level of operation even when a large amount of current is supplied from the power supply for the air flow meter to the monolithic IC. An object of the present invention is to provide a hot wire type air flow meter for an automobile, which has an overvoltage protection circuit that does not require a large power supply voltage and does not require a large-capacity Zener diode.

[Means to solve the problem]

The hot wire air flow meter for automobiles according to the present invention has a heating resistor disposed in an air passage, a function of controlling the temperature state of the heating resistor to a constant level, and an amount of current required for constant temperature control. In the automotive hot wire air flowmeter, the constant temperature control circuit is formed of a monolithic IC circuit. A transistor that outputs a voltage that follows a control signal given to the energization amount control terminal is provided between the first power supply terminal and the second power supply terminal of the monolithic IC circuit, and the voltage of the first power supply terminal is A circuit is provided between the resistor and the ground to limit the control signal given to the energization amount control terminal when the voltage increases, and the voltage at the second power supply terminal is configured to be limited so as not to exceed a predetermined value. .

[Effect]

According to the present invention having the above configuration, a transistor is provided as a circuit having a voltage follower function before the power supply terminal of a monolithic IC circuit, and the operation of this transistor is controlled by a control signal generated based on a resistor having a required resistance value. and the minimum operating power supply voltage is reduced by such a resistor,
Further, when an overvoltage state occurs at the first power supply terminal, this is detected and the control signal is limited, and the power supply voltage at the second power supply terminal is limited so as not to exceed a predetermined value, and the resistor conducts current. Since the amount can be reduced, the capacitance of the Zener diode included in the circuit that limits the control signal can be reduced.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention, in which reference numeral 1 indicates a power terminal to which a power supply voltage 2 is applied, and 2 is a ground terminal. The power supply terminal 1 is a terminal to which a power supply voltage for the hot wire air flow meter is applied. A block 3 indicated by a broken line is a monolithic IC circuit (hereinafter referred to as an IC block), in which a constant temperature control circuit forming a main part of the hot wire air flow meter is formed. This IC block 3 is provided with at least eight connection terminals, for example designated by symbols 3A to 3H. Reference numeral 4 denotes a heating resistor, which, as is already known, is a resistor used to measure the air flow rate, which is disposed in an air passage for air flowing into an internal combustion engine of an automobile. In terms of an electric circuit, the heating resistor 4 is connected to the heating resistor 4 between the power supply terminal 1 and the ground terminal 2, with a transistor 5 provided on the upstream side for adjusting the amount of current flowing through the heating resistor 4. The current detection resistor 6 is connected in series with a current detection resistor 6 that can detect the amount of current supplied.

A constant temperature control circuit for the heating resistor 4, transistor 5, and current detection resistor 6 is configured as follows. IC
Two operational amplifiers 7.8 and a battery 9 are provided in the block 3. The voltage between the heating resistor 4 and the current detection resistor 6 is input to one input terminal of the operational amplifier 7 via the resistor 10 and the terminal 3E, and the output of the operational amplifier 7 is input to the other input terminal. The voltage is taken out via terminal 3G and divided by resistors 11 to 13, and the divided voltage value is further transferred to terminal 3F.
input via . ■1 is a resistor for detecting air temperature. Operational amplifier 7 works as a differential amplifier. Further, a resistor 14 is connected between the terminal 3E and a terminal 3C connected to the battery 9 and for applying a reference voltage V□. This resistor 14 is used together with the resistor 10 to provide an offset voltage which is a factor determining the dynamic characteristics of the air flow meter. Two resistors 15 are connected to the heating resistor 4 in parallel.
．． 16 is connected in series with these resistors 15.
16 divides the voltage between the terminals of the heating resistor 4, and applies the divided voltage to one input terminal of the operational amplifier 8 via the terminal 3D. Further, the output voltage of the operational amplifier 7 is applied to the other input terminal of the operational amplifier 8. Operational amplifier 8 works as differential amplifier 8. The output of the operational amplifier 8 is supplied to the base of the transistor 5 via the output terminal 3B. The output current of the operational amplifier 7 adjusts the amount of current supplied by the transistor 5.

According to the above circuit configuration, when the transistor 5 is in the on state and current is flowing through the heat generating resistor 4 and the current detection resistor 6, the heat generating resistor 4 is cooled by the air flowing in the air passage, and the temperature increases. When the resistance value of the heating resistor 4 decreases, the resistance value of the heating resistor 4 increases, so this state of change is extracted as a change in the voltage between the terminals, and the constant temperature control circuit to which the extracted voltage is input increases the amount of current flowing through the transistor 5. Heat generating resistor 4
By increasing the temperature of the heating resistor 4, the temperature of the heating resistor 4 is kept constant, and the output current of the operational amplifier 8 is applied to the base of the transistor 5, so that the resistance value thereof is kept constant, thereby performing constant temperature control. When such constant temperature control is performed, when the voltage between the terminals of the current detection resistor 6 is measured, this voltage becomes a function of the air flow rate flowing through the air passage in which the heating resistor 4 is installed. This allows the serious flow rate to be measured.

The power supply terminal 3A is a terminal that supplies power to the main part of the circuit formed in the IC block 3 of the constant temperature control circuit configured as described above. Further, 3H is a ground terminal because the IC block 3 is connected to the ground terminal 2. From the power terminal 1 of the air flow meter to the power terminal 3A of the IC block 3, there is a high-voltage NPN wire that has a higher withstand voltage than that of the IC block 3.
A voltage is applied via a type transistor 17. The collector of transistor 17 is connected to power supply terminal 1, and its emitter is connected to power supply terminal 3A.

Furthermore, a resistor 18 and a Zener diode 19 are connected to the base of the transistor 17 between the power supply terminal 1 and the ground terminal 2.
By providing a series circuit of , the downstream terminals of the resistor 18 are connected. In this way, the overvoltage protection circuit according to this embodiment is composed of the transistor 17, the resistor 18, and the Zener diode 19. In this case, resistor 18
The resistance value of is set to a high value.

According to the configuration of the overvoltage protection circuit, when the voltage applied to the power supply terminal 1 is lower than the Zener voltage of the Zener diode 19, the Zener diode 19 is in a non-conductive state, and at this time, the transistor 17 functions as a diode, and the transistor A voltage approximately equal to the power supply voltage V is applied to the base of 17 as a control signal.

When the transistor 17 functions as a diode, a voltage obtained by subtracting the voltage drop as a diode from the power supply voltage V is applied to the power supply terminal 3A, and unless the Zener diode 19 is conductive, the power supply terminal 3A of the IC block 3 has no power. A voltage that changes in accordance with changes in the power supply voltage (2) of the terminal 1 is applied.

A high voltage occurs in the power supply voltage VB, and the Zener diode 19
When a voltage higher than the Zener voltage is applied to the upper terminal in the figure, the Zener diode 19 becomes conductive, and as a result, the base voltage of the transistor 17 is maintained at the Zener voltage of the Zener diode 19 and does not become higher than that. As described above, even if the power supply voltage VB becomes a high voltage, the voltage VCC at the power supply terminal 3A of the IC block 3, which includes the main circuit part of the constant temperature control circuit composed of a monolithic IC, is From the voltage v2 to the voltage ■ between the base and emitter of the transistor 17. The voltage obtained by subtracting Vz V. Therefore, by setting V2-vllE lower than the breakdown voltage of the monolithic IC, the IC block 3, which is a monolithic IC, can be protected from overvoltage.

According to the above embodiment, since the high voltage transistor 17 is provided between the power terminal 1 for the air flow meter and the power terminal 3A for the IC block 3, the transistor 17 is connected in series to the Zener diode 19. The resistance value of the resistor 18 can be increased.

Even if the resistance value of the resistor 18 is set high, the resistor 18
is not directly connected to the power supply terminal 3A, but is connected to the base of the transistor 17 connected to the power supply terminal 3A to adjust its base current, so that the drop in the voltage VCC at the terminal 3A caused by the resistor 18 is reduced. can do. In addition, since the voltage drop of the resistor 18 is reduced and the amount of current supplied to it is reduced, the overvoltage protection circuit can be implemented using the Zener diode 19 with a small power capacity without increasing the minimum voltage of the power supply voltage V that operates the air flow meter. Can be configured.

FIG. 2 shows a second embodiment of the invention, in which the Zener diode 19 is formed inside the monolithic IC, rather than outside it, between terminals 3I and 3H. Since the other configurations are the same as those of the first embodiment, the same elements are given the same reference numerals.

According to the overvoltage protection circuit according to the present invention, a Zener diode with a small power capacity can be used, so the Zener diode for the overvoltage protection circuit can be fabricated in a monolithic IC circuit. According to this configuration, the number of external parts is reduced, resulting in a simple circuit configuration.

FIG. 3 shows a third embodiment of the invention. In this example,
First, the Zener diode 19 is formed in an IC block 3 made of a monolithic IC, and furthermore, a resistor 20, 21 and a transistor 22 are additionally formed in this IC block 3. Resistors 20 and 21 are connected in series between terminal 3A and ground terminal 3H, and transistor 22 has its collector and emitter connected to terminals 3 and 3, respectively.
Connected to H. Zener diode 19 is resistor 2
It is provided between the midpoint 23 of 0.21 and the base of the transistor 22, and the cathode is connected to the midpoint and the anode is connected to the base. Furthermore, the transistors 5.17 in the first embodiment are also formed of another monolithic IC, as indicated by the broken line block 24. Furthermore, a series resistor 32 is provided at the base of the transistor 17. Their connection configuration is the same as in the previous embodiment.

According to this circuit configuration, when the voltage VCC of the power supply terminal 3A rises and the voltage at the intermediate point 23 of the resistor 20.21 becomes larger than the sum of the Zener voltage 2 and the base-emitter voltage of the transistor 22. , the transistor 22 turns on, and the base voltage of the transistor 7 decreases. This prevents the voltage VCC of the power supply terminal 3A of the IC circuit 3 from rising above a predetermined voltage. In this embodiment as well, as in the previous embodiments, when the power supply voltage (2) of the air flow meter changes to a high voltage, the voltage (2) at the terminal 3A is not increased more than necessary to protect the IC block 3. be able to. Also, according to this embodiment, the midpoint 2 of the resistors 20 and 21
Since the cathode of the Zener diode 19 is connected to the resistor 20.3, even if the Zener voltage of the Zener diode 19 cannot be arbitrarily set, the resistor 20.
By appropriately selecting each resistance value of 21, the maximum value of the voltage VCC of the power supply terminal 3A of the IC block 3 can be arbitrarily set. Furthermore, according to this embodiment, by forming the resistors 20, 21 and the transistors 5, 17, and 22 using monolithic ICs, the number of external parts can be further reduced than in the previous embodiment. Also,
If the power supply terminal 1 and the ground terminal 2 of the flowmeter are connected incorrectly, the current flowing from the base of the transistor 17 to the collector can be limited by the resistor 32.

FIG. 4 shows a fourth embodiment of the invention. In this example,
In the configuration shown in FIG. 1, a Zener diode 19, a resistor 20° 21, and a transistor 22 are formed in the IC block 3, which is a monolithic IC, as shown in FIG. A capacitor 25 is connected between the base of the transistor 17 and the base of the transistor 17 . The other configurations are the same as those of the first embodiment. According to this embodiment, since the capacitor 25 is provided between the base and emitter of the transistor 17, even if the power supply voltage V changes abruptly, the transistor 16 can follow this change with good responsiveness. make it possible.

In each of the above embodiments, NPN type transistors were used, but by slightly changing the circuit, PNP type transistors were used.
Of course, it is possible to use a type.

Next, a fifth embodiment of the present invention will be described. In this embodiment, the capacitor 25 is removed from the configuration shown in FIG.
(field effect transistor) 26 is used. According to this configuration, since a voltage is applied to the gate of the voltage-controlled FET 26 and no current is required, the resistance value of the resistor 18 connected between the drain and gate of the FET 26 is set to It can be made higher than the resistance value. Therefore, less current flows through transistor 22, while conducting FET 26 has a smaller voltage drop than a bipolar transistor, allowing the minimum operating voltage of the air flow meter's supply voltage V to be further reduced.

FIG. 6 shows a sixth embodiment of the invention. In this example,
In the configuration shown in FIG.
A differential amplifier circuit is used instead of 9. This differential amplifier circuit is composed of four transistors 27 to 30, and the voltage obtained by dividing the power supply voltage VCC by resistors 20 and 21 is applied to the base of transistor 27, while the voltage of transistor 28, which is the object of comparison, is applied to the base of transistor 27. A reference voltage output from a reference voltage source 31 is applied to the base. The output of the differential amplifier circuit is applied to the base of the transistor 22. According to the configuration of this embodiment, the reference voltage to be compared can be obtained from the stable reference voltage source 31,
Further, this reference voltage can be set arbitrarily. Therefore, it is not affected by the base-emitter voltage of the transistor 22 or the Zener voltage when a Zener diode is used, and stable and reliable operation can be performed against temperature changes.

FIG. 7 shows a seventh embodiment of the invention. In this example,
In the configuration shown in FIG. 4, the capacitor 25 is removed and a capacitor 31 is connected in parallel to the resistor 18 between the power supply terminal 1 of the air flow meter and the base of the transistor 17.

The other configurations are the same as the fourth embodiment shown in FIG. According to this embodiment, a capacitor 31 is connected in parallel to the resistor 18.
, it is possible to prevent excessive current from flowing through the resistor 18 even if the power supply voltage changes abruptly.

FIG. 8 shows an eighth embodiment of the present invention. In this example,
In the configuration shown in FIG. 3, the Zener diode 19 is removed from the base of the transistor 22, and the base is directly connected to the midpoint of the resistor 20.21, and the Zener diode 19 is connected between the emitter of the transistor 22 and the ground terminal 3H. and the cathode is connected to the emitter. According to this embodiment, when the transistor 22 is energized, its emitter current flows to the Zener diode 19, resulting in the effect that the operating voltage of the Zener diode 19 is stabilized.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a transistor is provided between the power terminal of the air flow meter and the power terminal of the monolithic IC forming the constant voltage control circuit, and this transistor functions as a voltage follower. The power supply voltage of the monolithic IC is controlled by controlling the power supply voltage of the monolithic IC, and when the overvoltage is larger than a predetermined voltage, the signal that controls the transistor is restricted so that the power supply voltage of the monolithic IC does not become larger than the predetermined value. A high resistance value can be used for the resistor that generates the signal, which reduces the voltage drop across the resistor and reduces the minimum operating voltage applied to the power supply terminal.
Moreover, a Zener diode with a small power capacity can be used. The circuit that protects the constant voltage control circuit formed by the monolithic IC of the air flow meter when an overvoltage is applied to it is formed as much as possible by the same monolithic IC as the constant voltage control circuit, which reduces the number of parts. Therefore, the circuit can be simplified and the production cost can be reduced. Since the monolithic IC's power supply voltage is detected using a voltage dividing resistor to determine whether an overvoltage condition exists, it is possible to arbitrarily set the voltage for limiting the control signal without being restricted by the Zener voltage. can.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the invention, FIG. 2 is a circuit diagram showing a second embodiment of the invention, and FIG. 3 is a circuit diagram showing a third embodiment of the invention.
A circuit diagram showing an embodiment, FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention, FIG. 5 is a circuit diagram showing a fifth embodiment of the present invention,
6 is a circuit diagram showing a sixth embodiment of the present invention, FIG. 7 is a circuit diagram showing a seventh embodiment of the present invention, and FIG. 8 is a circuit diagram showing a seventh embodiment of the present invention.
FIG. 2 is a circuit diagram showing an example. [Explanation of symbols] 1... Power terminal for air flow meter 2... Earth terminal 3... IC block formed by monolithic IC 3A... Power terminal for IC block 4... Heat generation Resistor 5...Transistor for adjusting current supply amount/Transistor for current detection 8...Operation amplifier 17...Transistor that outputs a voltage that follows the power supply voltage...Resistor with high resistance value...Zener diode 21...・Voltage dividing resistor ・Transistor for limiting the control signal of the control terminal ・Field effect transistor 18 ・ 19 ・ 20° 22 ・ 26 ・

Claims (10)

[Claims] (1) A heating resistor placed in the air passage and a constant temperature control circuit that has the function of controlling the temperature of the heating resistor to a constant level and outputs the amount of current required for constant temperature control. The constant temperature control circuit is integrated into a monolithic IC.
In a hot wire air flowmeter for an automobile formed of a circuit, a resistor is connected between a first power supply terminal and a current flow control terminal, and a transistor is provided that outputs a voltage that follows a control signal given to the current flow control terminal. , provided between the first power supply terminal and the second power supply terminal of the monolithic IC circuit, and limiting the control signal applied to the energization amount control terminal when the voltage of the first power supply terminal increases. A hot wire type air flowmeter for an automobile, characterized in that a circuit is provided between the resistor and ground, and the voltage at the second power supply terminal is limited so as not to exceed a predetermined value. (2) In claim 1, the transistor is a bipolar transistor, the resistor is connected between the base and collector of the transistor, and the circuit for limiting the control signal is connected between the base of the transistor and the ground. A hot wire air flow meter for an automobile, characterized by a Zener diode installed in the zener diode. (3) The hot wire air flow meter for an automobile according to claim 2, wherein the Zener diode is formed within the monolithic IC circuit. (4) In claim 1, the circuit for limiting the control signal divides and takes out the voltage at the second power supply terminal of the monolithic IC circuit, and detects this state when the divided voltage value exceeds a predetermined value. 1. A hot-wire air flowmeter for an automobile, comprising a detection circuit that outputs a detection signal to be detected, and receiving the detection signal and limiting the control signal given to the transistor. (5) A hot wire air flow meter for an automobile according to claim 4, wherein the detection circuit is comprised of a resistor, a Zener diode, and a transistor. (6) The hot wire air flow meter for an automobile according to claim 1 or 4, wherein at least a portion of the circuit for limiting the control signal is formed by the monolithic IC circuit. (7) A hot wire air flow meter for an automobile according to claim 1, wherein the transistor is formed on the same silicon substrate as a transistor that adjusts the heating current of the heating resistor. (8) A hot wire air flow meter for an automobile according to claim 7, wherein the resistor is formed on the same silicon substrate as a transistor that adjusts the heating current of the heating resistor. (9) The hot wire air flow meter for an automobile according to claim 1, wherein the transistor is a field effect transistor. (10) In claim 1, the circuit for limiting the control signal divides and extracts the voltage at the second power supply terminal for the monolithic IC circuit, and the divided voltage value and
It includes a differential amplifier circuit that compares reference voltage values output by reference voltage sources and outputs a detection signal to detect this state when the divided voltage value exceeds the reference voltage value, and in response to the detection signal, the transistor A hot wire air flow meter for an automobile, characterized in that the control signal given to the vehicle is limited.