JP2000314645A - Heater drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heater drive circuit by which the temperature difference between a heater temperature and an outside temperature can be made constant. SOLUTION: A fixed resistor RR and a temperature measuring resistor RR are connected across the - terminal of an operational amplifier OP2 and a ground. A heater resistor RH is connected across the + terminal of the operational amplifier OP2 and the ground. A fixed resistor Ra is connected across the + terminal of the operational amplifier OP2 and a transistor Q2. A variable resistor Rb is connected across the - terminal of the operational amplifier OP2 and the transistor Q2. When the fixed resistor RU does not exist, the potential difference between a point A and a point B becomes zero, a prescribed current flows to the heater resistor RH, and a heater is heated. In addition, when the fixed resistor RU is connected in series with the temperature measuring resistor RR, the potential difference becomes large by a portion of the inserted fixed resistance RU. As a result, the transistor Q2 increases a current to the heater resistor RH more than the prescribed current in such a way that the potential difference becomes zero, and a heater temperature rises with reference to an external temperature by a portion of the inserted fixed resistor RH.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sensor device having a heater, for example, a heater drive circuit for driving a heater of a micro flow sensor.

[0002]

2. Description of the Related Art Conventionally, for example, a micro flow sensor has been used as a flow meter. This micro flow sensor is used for measuring a heater resistance on a silicon substrate base and an ambient temperature disposed on both sides of the heater resistance. And the flow rate of gas or the like is measured by detecting a change in the temperature distribution of heat generated from the heater resistance by the temperature measuring element.

[0003] A hot wire type flow sensor is used as another flow meter.
A heater wire having a large temperature coefficient is arranged in the flow path, and the flow rate of gas or the like is measured by detecting the amount of heat radiated from the heater wire.

The heaters of these flow sensors are:
It is driven by a heater drive circuit as shown in FIG. 5 or a heater drive circuit as shown in FIG. Here, FIG.
Only the heater drive circuit shown in FIG.

The heater driving circuit includes an operational amplifier OP1 and
The transistor Q1 of the PNP type, and the resistance thermometer R _R which is connected between the inverting input terminal and ground of the operational amplifier OP1,
A fixed resistor R ₂ connected between the collector of the inverting input terminal and the transistor Q1 of the operational amplifier OP1, and a heater resistor R _H, which is connected between the non-inverting input terminal and ground of the operational amplifier OP1, a non-operational amplifier OP1 a fixed resistor R ₁ is connected between the collector of the inverting input terminal of transistor Q1, constructed and a fixed resistor R ₃ connected between the base of the output terminal and the transistor Q1 of the operational amplifier OP1.

[0006] fixed resistors R _1, the fixed resistors R _2, it forms a bridge circuit by the resistance thermometer R _R, and a heater resistor R _H.

The heater driving circuit applies a current negative feedback based on a potential difference between the inverting input terminal and the non-inverting input terminal (between A and B) of the operational amplifier OP1 to thereby provide a heater resistance R _R.
Operates so as to keep the resistance value of the constant.

Here, a relational expression of each resistance value is expressed by the following expression.

[0009] _{R H · R 2 = R R} · R 1 In other words, if the heater resistance R _R has a positive temperature coefficient, when the heater temperature is the heater resistance R _R is small low, the potential difference between the heater resistance R _R is smaller Become. For this reason,
The output of the operational amplifier OP1 swings in the negative direction, so that the base current of the transistor Q1 increases, thereby increasing the collector current. As a result, the current flowing through the bridge circuit increases, and the heater resistance _RH warms and the temperature rises, so that the heater resistance _RH increases. For this reason, the resistance value of the heater resistance _RH becomes a constant value. If the heater temperature is too high, control that is the reverse of the control when the heater temperature is low is performed.

As a conventional heater drive circuit, for example, a heater control device of a flow meter described in Japanese Patent Application Laid-Open No. 4-34315 is known. FIG. 7 shows a circuit configuration of the heater control device of the flow meter. 7, a temperature measuring resistor 103 is connected between the inverting input terminal (-) of the operational amplifier 101 and the ground, and a fixed resistor 105 is connected between the inverting input terminal of the operational amplifier 101 and the emitter of the transistor 111. ing. The fixed resistor 107 is connected between the non-inverting input terminal (+) of the operational amplifier 101 and the ground, and the output of the operational amplifier 101 is connected to the base of the transistor 111 via the fixed resistor 109. A heater resistor 113 is connected between the collector of the transistor 111 and the ground, and a fixed resistor 115 is connected between the collector of the transistor 111 and the non-inverting input terminal of the operational amplifier 101.

An operational amplifier 101, a fixed resistor 10
7, a fixed resistor 109 and a fixed resistor 115 constitute an amplifier circuit.
13 is amplified.

In the above configuration, if the resistance value of the fixed resistor 105 is set to be sufficiently larger than the resistance value of the temperature measuring resistor 103, the current flowing through the temperature measuring resistor 103 changes because the resistance value of the temperature measuring resistor 103 changes. Is also constant. At this time, the resistance
03 is the same as the temperature coefficient of the heater resistor 113, so that even if the ambient temperature changes, the heater resistance 11
The heat value of No. 3 becomes a constant value, and appropriate temperature correction is performed.

[0013]

However, in the conventional heater driving circuits shown in FIGS. 5 and 6, since the heater temperature is controlled to a constant temperature, the heater control circuit shown in FIG. Is a circuit for adjusting the power applied to the heater, and thus cannot meet the requirement that the heater temperature be higher than the external temperature by a certain temperature. That is, it is impossible to cope with a demand for making the temperature difference between the heater temperature and the external temperature constant.

It is an object of the present invention to provide a heater driving circuit capable of keeping a temperature difference between a heater temperature and an external temperature constant.

[0015]

The present invention has the following arrangement to solve the above-mentioned problems. The invention according to claim 1 is characterized in that the heater resistance, the temperature measurement resistance for measuring the ambient temperature, the first resistance, and the second resistance.
And a bridge circuit in which power is supplied to a first connection terminal of the four connection terminals and the second connection terminal is grounded, and a third of the bridge circuit A differential amplifier for amplifying the potential difference between the voltage of the connection terminal and the voltage of the fourth connection terminal; and controlling the current from the power supply to the bridge circuit so that the potential difference amplified by the differential amplifier becomes zero. It is characterized by comprising a current control unit and a fixed resistor connected in series to the temperature measuring resistor.

According to the first aspect of the present invention, when there is no fixed resistance, the potential difference becomes zero, a predetermined current flows through the heater resistance of the bridge circuit, and the heater is heated. Also,
When the fixed resistor is connected in series with the temperature measuring resistor, the potential difference increases by the amount of the fixed resistor inserted, so the current control unit controls the current to the heater resistor of the bridge circuit so that the potential difference becomes zero. increase. That is, the heater temperature rises with respect to the external temperature by an amount corresponding to the insertion of the fixed resistor. Therefore, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

According to a second aspect of the present invention, the current control section is a transistor, and the fixed resistor and the temperature measuring resistor are connected between an inverting input terminal of the differential amplifier and the ground,
The heater resistor is connected between a non-inverting input terminal of the differential amplifier and the ground, and the first resistor is connected between a non-inverting input terminal of the differential amplifier and the transistor. The second resistor is connected between the inverting input terminal of the differential amplifier and the transistor.

According to the second aspect of the present invention, the fixed resistor and the temperature measuring resistor are connected between the inverting input terminal of the differential amplifier and the ground, and the heater resistor is connected between the non-inverting input terminal of the differential amplifier and the ground. A first resistor is connected between the non-inverting input terminal of the differential amplifier and the transistor, and a second resistor is connected between the inverting input terminal of the differential amplifier and the transistor. A heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant can be realized.

According to a third aspect of the present invention, the current control section is a transistor, wherein the fixed resistor and the temperature measuring resistor are connected between a non-inverting input terminal of the differential amplifier and the transistor, and A resistor connected between a non-inverting input terminal of the differential amplifier and the ground; a first resistor connected between an inverting input terminal of the differential amplifier and the ground; The resistor is connected between the inverting input terminal of the differential amplifier and the transistor.

According to the third aspect of the present invention, the fixed resistor and the temperature measuring resistor are connected between the non-inverting input terminal of the differential amplifier and the transistor, and the heater resistor is connected between the non-inverting input terminal of the differential amplifier and the ground. And a first resistor is connected between the inverting input terminal of the differential amplifier and the ground, and a second resistor is connected between the inverting input terminal of the differential amplifier and the transistor. A heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant can be realized.

According to a fourth aspect of the present invention, the current control section is a transistor, wherein the fixed resistor and the temperature measuring resistor are connected between a non-inverting input terminal of the differential amplifier and the transistor, and A resistor connected between the inverting input terminal of the differential amplifier and the transistor; the first resistor connected between the inverting input terminal of the differential amplifier and ground; Is connected between the non-inverting input terminal of the differential amplifier and the ground.

According to the present invention, the fixed resistor and the temperature measuring resistor are connected between the non-inverting input terminal of the differential amplifier and the transistor, and the heater resistor is connected between the inverting input terminal of the differential amplifier and the transistor. A first resistor is connected between the inverting input terminal of the differential amplifier and the ground, and a second resistor is connected between the non-inverting input terminal of the differential amplifier and the ground. A heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant can be realized.

According to a fifth aspect of the present invention, the current control section is a transistor, and the fixed resistor and the temperature measuring resistor are connected between an inverting input terminal of the differential amplifier and the ground,
The heater resistance is connected between an inverting input terminal of the differential amplifier and the transistor, and the first resistance is
The transistor is connected between a non-inverting input terminal of the differential amplifier and the transistor, and the second resistor is connected between a non-inverting input terminal of the differential amplifier and the ground. .

According to the fifth aspect of the present invention, the fixed resistor and the temperature measuring resistor are connected between the inverting input terminal of the differential amplifier and the ground, and the heater resistor is connected between the inverting input terminal of the differential amplifier and the transistor. And a first resistor is connected between the non-inverting input terminal of the differential amplifier and the transistor, and a second resistor is connected between the non-inverting input terminal of the differential amplifier and the ground. A heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant can be realized.

According to a sixth aspect of the present invention, the fixed resistor does not have a temperature characteristic, and has a temperature coefficient of the first resistor and the second resistor.
Are characterized by the same temperature coefficient of resistance.

According to the sixth aspect of the present invention, the fixed resistor has no temperature characteristic, and the temperature coefficient of the first resistor and the temperature coefficient of the second resistor have the same value. Changes with respect to the external temperature.

According to a seventh aspect of the present invention, the temperature coefficient of the first resistor and the temperature coefficient of the second resistor have the same value, and the resistance value of the temperature measuring resistor is equal to the static resistance value of the temperature measuring resistor. The temperature coefficient of the heater resistance and the temperature coefficient of the temperature measurement resistor are substantially the same value, and the ratio between the static resistance value of the heater resistance and the static resistance value of the temperature measurement resistance is the first value. The ratio of the resistance value of the resistor to the resistance value of the second resistor is the same.

According to the seventh aspect of the present invention, the temperature coefficient of the first resistor and the temperature coefficient of the second resistor have the same value, and the resistance value of the temperature measuring resistor is substantially the same as the static resistance value of the temperature measuring resistor. Value
The temperature coefficient of the heater resistance and the temperature coefficient of the temperature measurement resistance are the same value, and the ratio of the static resistance value of the heater resistance to the resistance value of the temperature measurement resistance is the resistance of the first resistance and the resistance of the second resistance. By having the same value as the ratio of the heater temperature, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

The one of the first resistor and the second resistor according to the invention of claim 8 is a variable resistor, and the variable resistor allows the static resistance value of the heater resistor and the resistance value of the temperature measuring resistor to be adjusted. The ratio between the static resistance value and the resistance value of the first resistor is compared with the second resistance value.
The resistance is adjusted so as to have the same value as the ratio of the resistance to the resistance value.

According to the eighth aspect of the present invention, the ratio between the static resistance value of the heater resistance and the static resistance value of the temperature measuring resistor is determined by the variable resistance by the resistance value of the first resistance and the resistance value of the second resistance. By adjusting the ratio so as to have the same value as the ratio, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the heater driving circuit according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a heater drive circuit according to the present invention. The heater drive circuit shown in FIG. 1 controls, for example, a micro heater provided in a flow sensor.

The heater driving circuit includes an operational amplifier OP2,
A PNP transistor Q2, a fixed resistance R _U having a small resistance connected in series between the inverting input terminal of the operational amplifier OP2 and the ground, and a temperature measuring resistor R _R for measuring the ambient temperature.
And the inverting input terminal of the operational amplifier OP2 and the transistor Q
, A variable resistance Rb connected between the collector of the transistor Q2, a heater resistor R _H connected between the non-inverting input terminal of the operational amplifier OP2 and the ground, a non-inverting input terminal of the operational amplifier OP2 and the collector of the transistor Q2. configured with a fixed resistor Ra connected, and a fixed resistor R ₃ connected between the base of the output terminal and the transistor Q2 of the operational amplifier OP2 during the.

Here, a bridge circuit is composed of the fixed resistors Ra, Rb, R _U , temperature measurement resistor R _R , and heater resistor R _H. Resistance thermometer R _R is a platinum resistor disposed on the flow sensor, the resistance value is changed by a change in temperature. Here, the heater resistance R _H and the resistance thermometer R _R, the same material, for example, a platinum resistor,
Have the same temperature coefficient.

Further, the operational amplifier OP2 constitute a differential amplifier to amplify a potential difference between the fixed resistor R _U terminal voltage and the terminal voltage of the heater resistance Rh of the bridge circuit. The transistor Q2 forms a current control unit, and includes an operational amplifier O
The current from the power supply to the bridge circuit is controlled so that the potential difference amplified by P2 becomes zero.

Next, the operation of the heater driving circuit of the embodiment configured as described above will be described. First, here, without connecting the fixed resistance R _U in the resistance thermometer R _R, sets the resistance values such that the following relation.

[0036] When satisfying _{R H · Rb = Ra · R} R above equation, the potential difference between A-B is next to zero, the operational amplifier OP2 is so as not to almost operate transistors Q2, no current flows through the heater resistor R _H To
The heater is not heated. Hereinafter, the measured external temperature of the resistance thermometer R _R and Tr, the heater temperature by the heater resistance R _H and T _H.

Next, connecting fixed resistor R _U in series with the resistance thermometer R _R, by the amount insertion of the fixed resistor R _U, the potential at the point A is greater than the potential at the point B. For this reason, the output of the operational amplifier OP2 swings in the negative direction, and the base current of the transistor Q2 increases, thereby increasing the collector current. That is, an amount corresponding to the insertion of the fixed resistor R _U, the potential difference is large, the transistor Q2
Increases the current to the heater resistance _RH of the bridge circuit.

[0038] As a result, increases the current flowing through the heater resistor R _H, for a heater resistor R _H is further increased, the external temperature Te by resistance thermometer R _R, the heater resistance R _H
Heater temperature by becomes T _H = Tr + ΔT. That is, the heater temperature rises with respect to the external temperature by an amount corresponding to the insertion of the fixed resistor. Therefore, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant. In this case, depending on the magnitude of the resistance value of the fixed resistor R _U, it is possible to arbitrarily adjust the magnitude of the temperature difference ([Delta] T), depending on the desired temperature difference, by setting the fixed resistor R _U I just need.

Note that the control for making ΔT constant with respect to the temperature change of the heater resistance R _H is similar to the operation of the heater drive circuit shown in FIG. 5, and therefore the description thereof is omitted here.

Next, a theoretical calculation of constants of respective resistance values of the heater driving circuit for making the temperature difference between the external temperature and the heater temperature constant is performed. First, since the negative feedback circuit keeps the potential difference between A and B of the bridge circuit constant, R _H · Rb = (R _R + R _U ) · Ra. From the above equation, R _H = Ra · (R _R + R _U ) / Rb =
κ · R _R + κ · R _U (1)

Here, the equation (1) is modified to be decomposed as follows: R _HR = κ · R _R (2) R _HU = κ · R _U (3) κ is Ra / Rb.

If R _{HR in} equation (2) is the static resistance of the heater, then R _HR = R _HRS . R _HRS is the static resistance value of the heater. Thus, the equation (3) represents a change in resistance due to the heating of the heater. That is, the equation (3) represents the temperature difference between the external temperature and the heater temperature.

First, κ will be verified. Same value and the temperature coefficient alpha _b temperature coefficient alpha _a and Rb of Ra (α _a = α _b, first
Be designed to precondition) of, κ = Ra / Rb = R a0 · {1 + α a · (Tr-T 0)} / R b0 · {1 + α b · (Tr-T 0)} = R a0 / R b0 Becomes Tr is the external temperature, T ₀ is the reference temperature,
R _a0 and R _b0 are resistance values at the reference temperature. For this reason,
κ is constant regardless of the external temperature.

Next, represented by the following formula and the heater temperature T _H and the resistance temperature value T _R.

T _H = T ₀ + (1 / α) · (R _H / R _HS0 −1) (4) T _R = T ₀ + (1 / α) · (R _R / R _R0 −1) ) (5) wherein, R _HS0 is R _H of the static resistance of at standard temperature T _0, R _R0 is R _R o'clock reference temperature T _0.

Generally, the resistance of the temperature measuring resistor is determined by self-heating.
The resistance value may change more than the resistance value Rr converted from the actual external temperature Tr. To cope with this resistance value change by suppressing the current consumed during temperature measurement operation,
Often devised. In the present invention, assuming that the resistance value does not change in the temperature measurement operation (second precondition), R _R = Rr and T _R = Tr.

Expanding equation (4) using equation (1), T _H = T ₀ + (1 / α _H ) ｛(κRr + κR _U ) / R _HS0
-1)} kappa = so that R _HS / Rr adjusting the kappa and (adjustment condition), the above _{formula, T H = T 0 + (} 1 / α H) · {(κRr + κR U) / κRr 0 - 1)｝ = T ₀ + (1 / α _H ) · (Rr / Rr ₀ + R _U / Rr ₀ −1) Here, the temperature coefficient α _H of the heater resistance and the temperature coefficient α _R of the temperature measurement resistance are the same value. , The heater temperature T
_H is as follows.

T _H = Tr + (1 / α _H ) · R _U / Rr _{0 In} other words, the temperature ΔT of the heating portion of the heater is (1 / α _H )
R _U / Rr ₀ , and becomes a constant value if the fixed resistor R _U has no temperature characteristic (fourth precondition). First precondition α _a = α _b Second precondition R _R = R _RS (condition not _causing self-heating) Third precondition α _H = α _R Fourth precondition α _U = 0 or R _U = R _U0 adjustment condition κ = Ra / Rb = Ra ₀ / Rb ₀ = R
_HS0 / R _RS0 As described above, according to the heater driving circuit of the embodiment, the temperature difference between the heater temperature and the external temperature can be kept constant by controlling the amount of heat applied to the heater. Also,
The temperature difference between the heater temperature and the external temperature can be adjusted so as to be constant without using a large device such as a constant temperature bath, whereby an inexpensive heater drive circuit can be configured.

Conventionally, the external temperature (gas temperature) is kept constant in a constant temperature bath, and the heater temperature is kept constant in a constant temperature circuit (FIGS. 5 and 6), so that the temperature difference between the external temperature and the heater is reduced. Although the physical property value of a gas or the like was measured by the power consumption of the heater while keeping it constant, according to the microsensor using the heater drive circuit of the embodiment, the heater drive circuit sets the heater temperature to a predetermined temperature with respect to the external temperature. Since it can be set by raising only, the sensor alone without using a thermostat, etc., for example,
Physical properties such as thermal conductivity and specific heat of gas and liquid can be measured.

Further, in a micro flow sensor or a hot wire type flow rate sensor, temperature correction can be easily performed.
Thereby, the accuracy of the flow velocity measurement after the temperature correction is improved, so that the flow velocity measurement range is widened and the power consumption can be reduced.

<First Modification> FIG. 2 is a circuit diagram showing a first modification of the heater drive circuit according to the embodiment. The heater driving circuit according to the first modification includes an operational amplifier OP2,
A transistor Q2, a fixed resistor Ra connected between the inverting input terminal of the operational amplifier OP2 and the ground, a variable resistor Rb connected between the inverting input terminal of the operational amplifier OP2 and the collector of the transistor Q2, and a Heater resistor R connected between non-inverting input terminal and ground
And _H, are connected between the fixed resistor R _U and resistance thermometer R _R is connected between the collector of the non-inverting input terminal and the transistor Q2 of the operational amplifier OP2, the base of the output terminal and the transistor Q2 of the operational amplifier OP2 constructed and a fixed resistor R ₃ that.

With the heater driving circuit of the first modification, the heater temperature can be raised by a predetermined temperature with respect to the external temperature. Therefore, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

<Second Modification> FIG. 3 is a circuit diagram showing a second modification of the heater drive circuit according to the embodiment. The heater driving circuit according to the second modification includes an operational amplifier OP2,
A transistor Q2, a fixed resistor Ra connected between the inverting input terminal of the operational amplifier OP2 and the ground, a heater resistor R _H connected between the inverting input terminal of the operational amplifier OP2 and the collector of the transistor Q2, and an operational amplifier OP2.
Variable resistor R connected between the non-inverting input terminal of
and b, are connected between the fixed resistor R _U and resistance thermometer R _R is connected between the collector of the non-inverting input terminal and the transistor Q2 of the operational amplifier OP2, the base of the output terminal and the transistor Q2 of the operational amplifier OP2 constructed and a fixed resistor R ₃ that.

With the heater driving circuit of the second modification, the heater temperature can be raised by a predetermined temperature with respect to the external temperature. Therefore, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

<Third Modification> FIG. 4 is a circuit diagram showing a third modification of the heater drive circuit according to the embodiment. The heater driving circuit according to the third modification includes an operational amplifier OP2,
A transistor Q2, a fixed resistor connected between the inverting input terminal and ground of the operational amplifier OP2 R _U and the resistance thermometer R _R
And the inverting input terminal of the operational amplifier OP2 and the transistor Q
A heater resistance R _H, which is connected between the second collector, and a variable resistor Rb is connected between the non-inverting input terminal and ground of the operational amplifier OP2, and the collector of the non-inverting input terminal and the transistor Q2 of the operational amplifier OP2 configured with a fixed resistor Ra connected, and a fixed resistor R ₃ connected between the base of the output terminal and the transistor Q2 of the operational amplifier OP2 during the.

With the heater driving circuit of the third modification, the heater temperature can be raised by a predetermined temperature with respect to the external temperature. Therefore, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

It should be noted that the present invention is not limited to the heater drive circuit of the above-described embodiment. The heater driving circuit of the heater drive circuit and the first modification to the third modification of the embodiment, although the variable resistor Rb, the ratio of the static resistance of the heater resistor R _H and the resistance thermometer R _R It is not necessary to vary the variable resistor Rb if it can always be made constant. In addition, it goes without saying that various modifications can be made without departing from the technical idea of the present invention.

[0058]

According to the first aspect of the present invention, when there is no fixed resistance, the potential difference becomes zero, a predetermined current flows through the heater resistance of the bridge circuit, and the heater is heated. Also, if the fixed resistance is connected in series with the resistance temperature detector,
Since the potential difference increases by the amount of the fixed resistor inserted,
The current control unit increases the current to the heater resistor of the bridge circuit so that the potential difference becomes zero. That is, the heater temperature rises with respect to the external temperature by an amount corresponding to the insertion of the fixed resistor. Therefore, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

According to the second aspect of the present invention, the fixed resistor and the temperature measuring resistor are connected between the inverting input terminal of the differential amplifier and the ground, and the heater resistor is connected between the non-inverting input terminal of the differential amplifier and the ground. A first resistor is connected between the non-inverting input terminal of the differential amplifier and the transistor, and a second resistor is connected between the inverting input terminal of the differential amplifier and the transistor. A heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant can be realized.

According to the third aspect of the present invention, the fixed resistor and the temperature measuring resistor are connected between the non-inverting input terminal of the differential amplifier and the transistor, and the heater resistor is connected to the non-inverting input terminal of the differential amplifier and the ground. And a first resistor is connected between the inverting input terminal of the differential amplifier and the ground, and a second resistor is connected between the inverting input terminal of the differential amplifier and the transistor. A heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant can be realized.

According to the fourth aspect of the present invention, the fixed resistor and the temperature measuring resistor are connected between the non-inverting input terminal of the differential amplifier and the transistor, and the heater resistor is connected between the inverting input terminal of the differential amplifier and the transistor. A first resistor is connected between the inverting input terminal of the differential amplifier and the ground, and a second resistor is connected between the non-inverting input terminal of the differential amplifier and the ground. A heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant can be realized.

According to the fifth aspect of the present invention, the fixed resistor and the temperature measuring resistor are connected between the inverting input terminal of the differential amplifier and the ground, and the heater resistor is connected between the inverting input terminal of the differential amplifier and the transistor. And a first resistor is connected between the non-inverting input terminal of the differential amplifier and the transistor, and a second resistor is connected between the non-inverting input terminal of the differential amplifier and the ground. A heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant can be realized.

According to the sixth aspect of the present invention, the fixed resistor has no temperature characteristic, and the temperature coefficient of the first resistor and the temperature coefficient of the second resistor have the same value. Changes with respect to the external temperature.

According to the seventh aspect of the present invention, the temperature coefficient of the first resistor and the temperature coefficient of the second resistor have the same value, and the resistance value of the temperature measuring resistor is substantially the same as the static resistance value of the temperature measuring resistor. Value
The temperature coefficient of the heater resistance and the temperature coefficient of the temperature measurement resistance are the same value, and the ratio of the static resistance value of the heater resistance to the resistance value of the temperature measurement resistance is the resistance of the first resistance and the resistance of the second resistance. By having the same value as the ratio of the heater temperature, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

According to the eighth aspect of the present invention, the ratio between the static resistance value of the heater resistance and the static resistance value of the temperature measuring resistance is determined by the variable resistance by the resistance value of the first resistance and the resistance value of the second resistance. By adjusting the ratio so as to have the same value as the ratio, it is possible to realize a heater drive circuit that makes the temperature difference between the external temperature and the heater temperature constant.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a heater drive circuit according to the present invention.

FIG. 2 is a circuit diagram showing a first modification of the heater drive circuit according to the embodiment.

FIG. 3 is a circuit diagram showing a second modification of the heater drive circuit according to the embodiment.

FIG. 4 is a circuit diagram showing a third modification of the heater drive circuit according to the embodiment.

FIG. 5 is a circuit diagram showing an example of a conventional heater drive circuit.

FIG. 6 is a diagram showing a modification of the heater drive circuit shown in FIG.

FIG. 7 is a diagram showing an example of a conventional heater control device for a flow meter.

[Explanation of symbols]

Q1, Q2 transistors OP1, OP2 operational amplifier R _H heater resistance R _R resistance thermometer Ra fixed resistor Rb variable resistor R _U fixed resistance

Claims (8)

[Claims] 1. A heater resistor, a temperature measuring resistor for measuring an ambient temperature, a first resistor, and a second resistor are connected in a closed loop shape, and are connected to a first connection terminal among four connection terminals. A bridge circuit to which power is supplied and a second connection terminal is grounded; a differential amplifier for amplifying a potential difference between a voltage of a third connection terminal and a voltage of a fourth connection terminal of the bridge circuit; A current control unit configured to control a current from the power supply to the bridge circuit so that a potential difference amplified by the amplifier becomes zero; and a fixed resistor connected in series to the temperature measuring resistor. Heater drive circuit. 2. The current control section is a transistor, wherein the fixed resistor and the temperature measuring resistor are connected between an inverting input terminal of the differential amplifier and the ground, and the heater resistor is connected to the differential resistor. A first resistor connected between the non-inverting input terminal of the differential amplifier and the transistor, and a second resistor connected between the non-inverting input terminal of the differential amplifier and the transistor; 2. A transistor connected between an inverting input terminal of a dynamic amplifier and the transistor.
The heater drive circuit according to the above. 3. The current control unit is a transistor, the fixed resistor and the temperature measuring resistor are connected between a non-inverting input terminal of the differential amplifier and the transistor, and the heater resistor is A first resistor connected between the non-inverting input terminal of the differential amplifier and the ground, the first resistor connected between the inverting input terminal of the differential amplifier and the ground,
2. The heater driving circuit according to claim 1, wherein the second resistor is connected between an inverting input terminal of the differential amplifier and the transistor. 4. The current control section is a transistor, the fixed resistance and the temperature measuring resistance are connected between a non-inverting input terminal of the differential amplifier and the transistor, and the heater resistance is The first resistor is connected between an inverting input terminal of a differential amplifier and the transistor, the first resistor is connected between the inverting input terminal of the differential amplifier and ground, and the second resistor is connected to the differential amplifier. 2. The heater drive circuit according to claim 1, wherein the heater drive circuit is connected between a non-inverting input terminal of a dynamic amplifier and the ground. 5. The current control unit is a transistor, the fixed resistor and the temperature measuring resistor are connected between an inverting input terminal of the differential amplifier and the ground, and the heater resistor is connected to the differential resistor. The first resistor is connected between an inverting input terminal of an amplifier and the transistor, the first resistor is connected between a non-inverting input terminal of the differential amplifier and the transistor, and the second resistor is connected to the differential amplifier. 2. The heater drive circuit according to claim 1, wherein the heater drive circuit is connected between a non-inverting input terminal of a dynamic amplifier and the ground. 6. The fixed resistor has no temperature characteristic, and the temperature coefficient of the first resistor and the temperature coefficient of the second resistor have the same value. A heater drive circuit according to any one of the preceding claims. 7. The temperature coefficient of said first resistor and said second resistor.
The temperature coefficient of the resistance is the same value, the temperature measuring resistor indicates a resistance value due to an external temperature regardless of the temperature measuring operation, the temperature coefficient of the heater resistance and the temperature coefficient of the temperature measuring resistance are the same value, The ratio between the static resistance value of the heater resistor and the static resistance value of the temperature measuring resistor is the same as the ratio of the resistance value of the first resistor to the resistance value of the second resistor. The heater drive circuit according to any one of claims 1 to 6. 8. One of the first resistor and the second resistor is a variable resistor, and the variable resistance allows the static resistance of the heater resistor and the static resistance of the temperature measuring resistor to be changed. 8. The heater drive circuit according to claim 7, wherein the ratio is adjusted to be the same as the ratio between the resistance value of the first resistor and the resistance value of the second resistor.