JP2001188617A - Current control circuit - Google Patents

Abstract

(57) [Problem] To provide a current control circuit having a novel configuration using a general operational amplifier having a narrow response range without using a rail-to-rail type operational amplifier. SOLUTION: Load current detecting means Rc is provided at one input terminal.
A current control circuit for controlling a load current supplied to the load RL using an operational amplifier A1 to which a negative feedback voltage from s is input, wherein the other input terminal of the operational amplifier A1 is connected to a reference potential point of a power supply Vcc. A reference voltage source -Vref for providing a reference voltage within the operational range of the operational amplifier A1 is connected, and the load current detection means R is connected to the one input terminal.
A control voltage source Va for providing a control voltage for shifting the negative feedback voltage from cs to within the range of operation of the operational amplifier A1 was connected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a current control circuit, and more particularly to a current control circuit useful for a catalytic combustion type gas sensor circuit.

[0002]

2. Description of the Related Art The applicant has already proposed Japanese Patent Application Laid-Open No. Hei 9-318584 as a patent application concerning a current control circuit useful for a catalytic combustion type gas sensor circuit. JP-A-9-3
No. 18584 discloses a contact combustion type gas sensor constant current drive circuit using an operational amplifier for negative feedback control, in which a constant voltage from a positive terminal of a direct current power supply is applied to a non-inverting influential terminal of the operational amplifier. A highly reliable catalytic combustion type gas sensor constant current drive circuit that does not malfunction even if it fluctuates is disclosed.

FIG. 3 is a circuit diagram showing an example of a current control circuit used in a conventional catalytic combustion type gas sensor circuit.
In FIG. 3, the sensor current control circuit constitutes a high-side constant current drive circuit including an operational amplifier (operational amplifier) A1, and an inverting input terminal of the operational amplifier A1 is connected to a power supply Vcc via a current detection resistor Rcs. , Non-inverting input terminal is connected to the control voltage Vc. Operational amplifier A1
The output terminal is connected to the base of a PNP transistor Q1, and the negative input terminal is connected to a PNP transistor Q1.
One emitter is connected. A load RL is connected between the collector of the PNP transistor Q1 and the ground.

The load RL is a contact combustion type gas sensor circuit, and includes a temperature compensation element Rref and a contact combustion type gas sensor Rsns connected in series between the collector of the PNP transistor Q1 and ground, and a series connection of the temperature compensation element Rref and the gas sensor Rsns. An operational amplifier A2 having an inverting input terminal connected to the connection point. The reference voltage is input to the non-inverting input terminal of the operational amplifier A2.

In the load RL, that is, in the contact combustion type gas sensor circuit, a constant current is supplied to the gas sensor Rsns from a power supply Vcc via a current detection resistor Rcs, a transistor Q1, and a temperature compensation element Ref. Operational amplifier A2
Compares the above-described constant current input to the inverting input terminal with the voltage drop of the gas sensor Rsns due to the resistance of the gas sensor Rsns, and the reference voltage input to the non-inverting input terminal, and outputs a signal when a difference occurs. Generates an output signal at the terminal,
By driving an alarm buzzer, a display, and the like (not shown) connected to the subsequent stage, it is notified that gas has been detected.

A normal combustion (idle) current and a heating (detection) current determined by the specifications of the sensor must flow through the contact combustion type gas sensor Rsns. for that reason,
A normal load current IL1 to flow through the contact combustion type gas sensor Rsns and a load current IL2 (IL during heating (detection))
1 <IL2) is detected by the current detection resistor Rcs. The current detection voltage of the current detection resistor Rcs, that is, the drop voltage is input to the inverting input terminal of the operational amplifier A1 as a negative feedback voltage.

The operational amplifier A1 has a negative feedback voltage supplied to the inverting input terminal, that is, (power supply voltage Vcc-drop voltage Vcs of the current detection resistor Rcs) equal to the control voltage Va input to the non-inverting input terminal. Negative feedback control.

Therefore, a non-inverting input terminal of the operational amplifier A1 is supplied with a control combustion voltage Va as a control combustion gas sensor Rs.
A control voltage Va1 corresponding to when ns is in the normal state or a control voltage Va2 corresponding to when in ns is in the heating state is input. The control voltages Va1 and Va2 have different values, and specifically, have a relationship of Va1> Va2.

[0009]

When a general operational amplifier is used as the operational amplifier A1, the input / output response range is 0V + 1.5V to Vcc-1.5V. That is, a general operational amplifier has a voltage range from a high-side power supply voltage side to a voltage value lowered to a voltage value of 1.5 volts, and a low-side voltage range from a zero volt side to a voltage value raised to a voltage value of 1.5 volts. Cannot be used in the voltage range.

As specific operating conditions of the above-described current control circuit, for example, power supply voltage Vcc: +5 V, load resistance R
L: about 12Ω, current detection resistance Rcs: 2.5Ω, normal load current I to be passed to the catalytic combustion type gas sensor Rsns
L1: 170 mA, load current IL during heating (detection)
Consider a case of 2: 265 mA. In this case, when the load current IL is 265 mA, the voltage across the load RL rises to about 3.2 V. Therefore, the resistance value of the current detection resistor Rcs is increased, and the voltage Vcs input to the inverting input terminal of the operational amplifier A1 is It cannot be reduced below Vcc-1.5V within the response range. Therefore, under such an operating condition, a general operational amplifier cannot be used as the operational amplifier A1 because it does not fall within the response range of a general operational amplifier.

For the reasons described above, in this current control circuit example, a rail-to-rail (R
It is necessary to use an operational amplifier of the "aile to Rail" type. Since the rail-to-rail type operational amplifier has a wide response range from the power supply voltage to almost zero volt, the current detection resistor R
The operation within the response range can be performed without increasing the resistance value of cs. As described above, in the current control on the high potential (high side) side, when operating a voltage higher than Vcc-1.5 V (that is, a voltage closer to Vcc than Vcc-1.5 V), the operational amplifier that performs control A1
Rail to Rail
The operation is ensured by using a type.

However, the rail-to-rail type operational amplifier has a response range of 0 V + 1.5 V to V
Compared to a general operational amplifier with cc-1.5V,
Since the price is high, there is a problem that the cost of the entire current control circuit increases.

[0013] In order to deal with an operating voltage that does not fall within the response range of a general operational amplifier, the applicant has disclosed a technique for enabling a general operational amplifier to be used without using a rail-to-rail type operational amplifier. , Already
No. 318585. JP-A-9-31
The technology described in No. 8583 discloses a floating return potential supply circuit for shifting a signal source voltage to an operational range of an operational amplifier in an operational amplifier device in which a signal source voltage used as an input signal of the operational amplifier can be equal to or lower than an operational range of the operational amplifier. By adding such a configuration and shifting the signal source voltage to within the operation range of the operational amplifier, it is possible to operate the signal in a wide range even if a conventional operational amplifier having a narrow operation range is used.

However, the above-described technique shifts the input signal source voltage on the input side of the operational amplifier so as to correspond to the response range, but uses an operational amplifier to which the negative feedback voltage from the load current detecting means is input. In a current control circuit that controls a load current supplied to a load, it is necessary to consider a response range of an operational amplifier according to a load current value on an output side instead of an input side.

An object of the present invention is to solve the above-mentioned problems,
Without using a rail-to-rail type operational amplifier,
An object of the present invention is to provide a current control circuit having a novel configuration different from the technology proposed by the applicant by using a general operational amplifier having a narrow response range.

[0016]

SUMMARY OF THE INVENTION In view of the above object, the present invention according to claim 1 uses a first operational amplifier having one input terminal to which a negative feedback voltage from a load current detecting means is input. A current control circuit for controlling a load current to be supplied to a load, wherein a reference voltage is applied to the other input terminal of the first operational amplifier, the reference voltage being within a response range of the first operational amplifier when viewed from a reference potential point of a power supply. Connect the voltage source,
A control voltage source for supplying a control voltage for shifting a negative feedback voltage from the load current detection means to a range within which the first operational amplifier responds is connected to the one input terminal.

According to the first aspect of the present invention, there is provided a current control circuit for controlling a load current supplied to a load by using a first operational amplifier to which a negative feedback voltage from a load current detecting means is input to one input terminal. And a reference voltage source for providing a reference voltage within a response range of the first operational amplifier when viewed from a reference potential point of the power supply, to the other input terminal of the first operational amplifier. Also, one input terminal of the first operational amplifier is
Since a control voltage source for providing a control voltage for shifting the negative feedback voltage from the load current detecting means into the response range of the first operational amplifier is connected, a general operational amplifier having a small response range can be used.

According to a second aspect of the present invention, in the current control circuit according to the first aspect, the reference potential point of the power supply is a power supply voltage or zero potential.

According to the second aspect of the present invention, a current control circuit can be configured using a general operational amplifier having a narrow response range on either the high side or the low side.

The invention according to claim 3 is the invention according to claim 1 or 2
In the current control circuit described above, the control voltage source includes a second operational amplifier having one input terminal to which a negative feedback voltage from the current detection resistor is input, and a variable unit that changes a resistance value of the current detection resistor. It is characterized by being constituted by a current drive circuit.

According to the third aspect of the present invention, the control voltage source is a second operational amplifier having one input terminal to which the negative feedback voltage from the current detection resistor is input, and a variable to change the resistance value of the current detection resistor. Means, and the magnitude of the control voltage input to the other input terminal of the first operational amplifier can be easily varied by the variable means.

According to a fourth aspect of the present invention, in the current control circuit according to the third aspect, the variable means includes at least one circuit connected in parallel with the current detecting resistor and formed of a resistor and a switching means connected in series. It is characterized by the following.

According to a fourth aspect of the present invention, the variable means includes at least one circuit connected in parallel with the current detecting resistor and composed of a resistor and a switching means connected in series, and is controlled by ON / OFF control of the switching means. By changing the resistance value of the current detection resistor, as a result, the magnitude of the control voltage input to the other input terminal of the first operational amplifier can be easily changed.

According to a fifth aspect of the present invention, in the current control circuit according to any one of the first to fourth aspects, the load is:
It is a gas sensor circuit.

In the fifth aspect of the present invention, the load is:
This is a gas sensor circuit, which can control the current flowing through the gas sensor.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the current control circuit according to the present invention will be described. FIG. 1 is a circuit diagram of an embodiment of a current control circuit according to the present invention.

In FIG. 1, the sensor current control circuit has a narrow response range (for example, 0V + 1.5V to Vcc-1.
5V), a high-side constant current drive circuit including an operational amplifier A1 using a general operational amplifier having a current detection resistor R1 is connected to an inverting input terminal of the operational amplifier A1.
cs, a resistor Ru, and a non-inverting input terminal are connected to a reference voltage source -Vr connected to the power supply Vcc.
ef. The inverting input terminal of the operational amplifier A1 is also connected to a control voltage source Va via a resistor Rw. The output terminal of the operational amplifier A has a diode D
The base of the PNP transistor Q1 is connected via the terminals D1 and D2. The emitter of the PNP transistor Q1 is connected to a connection point between the current detection resistor Rcs and the resistor Ru. A load RL is connected between the collector of the PNP transistor Q1 and the ground.

The load RL is a contact combustion type gas sensor circuit, and includes a temperature compensation element Rref and a contact combustion type gas sensor Rsns connected in series between the collector of the PNP transistor Q1 and ground, and a series connection of the temperature compensation element Rref and the gas sensor Rsns. An operational amplifier A2 having an inverting input terminal connected to the connection point. The reference voltage is input to the non-inverting input terminal of the operational amplifier A2.

In the load RL, that is, in the contact combustion type gas sensor circuit, a constant current is supplied to the gas sensor Rsns from a power supply Vcc via a current detection resistor Rcs, a transistor Q1, and a temperature compensation element Ref. Operational amplifier A2
Compares the above-described constant current input to the inverting input terminal with the voltage drop of the gas sensor Rsns due to the resistance of the gas sensor Rsns, and the reference voltage input to the non-inverting input terminal, and outputs a signal when a difference occurs. Generates an output signal at the terminal,
By driving an alarm buzzer, a display, and the like (not shown) connected to the subsequent stage by this output signal, it is notified that gas has been detected.

The current detection resistor Rcs detects a normal load current IL1 to be supplied to the contact combustion type gas sensor Rsns and a load current IL2 during heating (detection). The current detection voltage of the current detection resistor Rcs, that is, the voltage drop is the resistance R
It is input as a negative feedback voltage to the inverting input terminal of the operational amplifier A1 via u.

The operational amplifier A1 has a voltage supplied to the inverting input terminal, that is, (power supply voltage Vcc-current detection resistor R
cs-the drop voltage of the resistor Ru) is the voltage input to the non-inverting input terminal, that is, Vcc-Vre
Negative feedback control is performed so as to be equal to f.

Therefore, the reference voltage source -Vref is a reference voltage applied to the non-inverting input terminal of the operational amplifier A1, that is, Vcc-Vref is the response range of the operational amplifier A1 in view of the reference potential point of the power supply Vcc, here the power supply voltage. It is set to the voltage value which becomes the voltage inside.

The control voltage source Va is a control voltage Va1 corresponding to when the contact combustion type gas sensor Rsns is in a normal state or a control voltage Va corresponding to when the contact combustion type gas sensor Rsns is in a heating state.
2 (where Va1> Va2).

Therefore, a case is considered in which a load current IL1 during normal operation and a load current IL2 during heating (detection) are supplied to the gas sensor Rsns. First, when a normal load current IL1 flows through the gas sensor Rsns, assuming that the voltage drop of the current detection resistor Rcs is Vcs1 and the currents flowing through the resistors Ru and Rw are Ia1.

Ia1 = (Vcs1-Vref) / Ru (1)

The set voltage Va1 when the normal load current IL1 flows through the gas sensor Rsns in the control voltage source Va is as follows:

Va1 = Vref−Ia1 × Rw (2)

Next, when the load current IL2 at the time of heating is passed through the gas sensor Rsns, the voltage drop of the current detection resistor Rcs is Vcs2, and the current flowing through the resistors Ru and Rw is Ia2.
Then

Ia2 = (Vcs2-Vref) / Ru (3)

When the control voltage source Va supplies the load current IL1 during heating to the gas sensor Rsns, the set voltage Va2 is as follows:

Va2 = Vref−Ia2 × Rw (4)

The current I flowing through the resistors Ru and Rw is
a (Ia1, Ia2) is the load current IL (IL1, IL
In order not to affect 2), the relationship between the resistance values of the resistors Ru and Rw and the resistance value of the current detection resistor Rcs is expressed as Rcs <Rcs <
<Ru, Rw needs to be set.

By setting the control voltage of the control voltage source Va to Va1 and Va2 in accordance with the normal operation and the heating operation of the gas sensor Rsns, the potential of the inverting input terminal of the operational amplifier A1 becomes Vc.
c-Vref (in other words, the current detection resistor Rc
The negative feedback voltage from s is shifted within the response range of the operational amplifier A1), and control can be performed so that the normal load current IL1 and the heating load current IL2 that meet the specifications of the gas sensor Rsns flow.

Next, an example of specific operating conditions of the current control circuit will be described. For example, the power supply voltage Vc
c: + 5V, load resistance RL: about 12Ω, current detection resistance R
cs: 2.5Ω, resistance Ru: 20 kΩ, resistance Rw: 5k
Ω, the normal load current IL of the contact combustion type gas sensor Rsns: 170 mA and the heating load current IL2: 2
Consider the case of 65 mA.

In this case, first, the operational amplifier A1 is connected to a general operational amplifier (for example, the input / output response range is 0V + 1.
5V to Vcc-1.5V), and the high-side power supply voltage 5.0 to the non-inverting input terminal of the operational amplifier A1.
In order to supply a voltage value which is a voltage within the response range of the operational amplifier A1 from the V side, the reference voltage source -Vre
The voltage value of f is set to -1.75 V (a minimum of -1.5 V may be used, but tolerance is taken into consideration). Therefore, the non-inverting input terminal of the operational amplifier A1 has Vcc-Vref.
= 5.0-1.75 = 3.25 volts reference voltage supplied.

Therefore, when a normal load current IL of 170 mA flows through the contact combustion type gas sensor Rsns, the current Ia1 flowing through the resistor Ru can be obtained from the above equation (1) as follows.

Ia1 = (− 0.425 V − (− 1.75)
V)) / 20000 = 66.25 μA

In the control voltage source Va, the gas sensor Rsn
s set voltage Va1 for flowing the normal load current IL1
Is obtained from the above equation (2) as follows.

Va1 = −1.75V−66.25 μA ×
5000 = −2.08125V

Next, when a heating load current IL1: 265 mA of the contact combustion type gas sensor Rsns flows, the resistance R
The current Ia2 flowing through u is obtained from the above equation (3) as follows.

Ia2 = (− 0.6625V − (− 1.7)
5V)) / 20,000 = 54.375 μA

In the control voltage source Va, the gas sensor Rsn
Set voltage Va2 for flowing load current IL2 during heating of s
Is obtained from the above equation (4) as follows.

Va2 = −1.75V−54.375 μA
× 5000 = -2.02185V

As described above, the control voltage of the control voltage source Va is set to −2.08125 V and −2.08 V in accordance with the normal operation and the heating operation of the gas sensor Rsns, respectively.
By setting to 2185V, the potential of the inverting input terminal of the operational amplifier A1 becomes Vcc-1.75V (in other words, the negative feedback voltage from the current detection resistor Rcs is shifted within the response range of the operational amplifier A1), and the gas sensor R
The control can be performed so that the normal load current IL of sns: 170 mA and the heating load current IL2 of 265 mA flow.

Next, FIG. 2 is a circuit diagram showing a more specific configuration example of the current control circuit of FIG. In FIG.
The same components as those in FIG. 1 are described with the same reference numerals.

In FIG. 2, the sensor current control circuit has a narrow response range (for example, 0V + 1.5V to Vcc-1.
5V), a high-side constant current drive circuit including an operational amplifier A1 using a general operational amplifier having a current detection resistor R1 is connected to an inverting input terminal of the operational amplifier A1.
cs, a resistor Ru, and a non-inverting input terminal are connected to a reference voltage source -Vr connected to the power supply Vcc.
ef. The inverting input terminal of the operational amplifier A1 is also connected to a control voltage source Va.

The output terminal of the operational amplifier A is connected to the base of a PNP transistor Q2 via a resistor R6. The collector of PNP transistor Q2 is grounded, and the emitter is connected to power supply Vcc via resistor R7 and to the base of PNP transistor Q1. The emitter of the PNP transistor Q1 is connected to a connection point between the current detection resistor Rcs and the resistor Ru.
A load RL is connected between the collector of the PNP transistor Q1 and the ground.

The resistors R6 and R7 and the PNP transistor Q2 correspond to the diodes D1 and D2 in FIG.

The control voltage source Va includes an operational amplifier A3 and N
PN type transistors Q3, Q4 and resistors R1, R2, R
3, R4 and R5. NPN transistor Q3
Is connected to the inverting input terminal of the operational amplifier A1, the base is connected to the inverting input terminal of the operational amplifier A3, and is grounded via the resistor R5. The reference voltage is supplied to the non-inverting input terminal of the operational amplifier A3. NPN transistor Q as switching means
4 is connected to the emitter of an NPN transistor Q3 via a resistor R4, the emitter is grounded, and the base is connected to a resistor R connected in series between a power supply Vcc and ground.
1, R2 and R3 are connected to a connection point between the resistors R2 and R3. Resistance R of the resistor voltage divider
A control signal is supplied to a connection point between R1 and R2. The operational amplifier A3, the NPN transistor Q4, and the resistor R5 constitute a constant current drive circuit, and the resistor R5 acts as a current detection resistor of the constant current drive circuit.

This circuit is particularly characterized by the configuration of the control voltage source Va, and its operation will be described below.

Therefore, a case is considered in which a load current IL1 during normal operation and a load current IL2 during heating (detection) are supplied to the gas sensor Rsns. When a normal load current IL1 flows through the gas sensor Rsns, the resistances R1 and R2 of the resistance voltage dividing circuit are used.
A high-level control signal is input to the connection point. In this case, the NPN transistor Q4 is turned on by the divided voltage at the connection point between the resistors R2 and R3 of the resistor voltage dividing circuit, and the resistor R4 is connected in parallel to the resistor R5. The parallel resistance value of the resistor R4 and the resistor R5 at this time is defined as Ra.

Next, when a load current IL2 for heating is supplied to the gas sensor Rsns, the resistances R1, R2
, A low-level control signal is input. In this case, the NPN transistor Q4 is turned off because the divided voltage at the connection point of R2 and R3 of the resistance voltage dividing circuit decreases, and the resistance R4 is not connected in parallel with the resistance R5. Assuming that the resistance value of the resistor R5 at this time is Rb, Ra
<Rb.

As described above, the resistances R1 and R
In response to a high or low level control signal input to the connection point No. 2, a circuit Rx composed of an NPN transistor Q4 as a switching means and a resistor R4 connected in series is
Acting as a variable means for varying the resistance value of the resistor R5 acting as a current detection resistor, the resistance value of the current detection resistor of the constant current drive circuit is varied to Ra or Rb.

Therefore, by appropriately selecting the resistance values of the resistors R4 and R5, the gas sensor Rsns
In order to allow the load currents IL1 and IL2 during normal operation or during heating to flow, the current detection resistor Ra is connected in parallel with the resistors R4 and R5, or the current detection resistor r is formed by the resistor R5 alone.
b, and the drop voltage is supplied from the collector of the NPN transistor Q3 to the inverting input terminal of the operational amplifier A1, so that the potential of the inverting input terminal of the operational amplifier A1 becomes Vcc-Vref (in other words, The negative feedback voltage from the detection resistor Rcs is shifted within the response range of the operational amplifier A1), and the normal load current IL1 and the heating load current IL matching the specifications of the gas sensor Rsns.
2 can be controlled to flow.

As described above, the embodiments of the present invention have been described. However, the present invention is not limited thereto, and various modifications and applications are possible. For example, diodes D1 and D2 are
This covers the narrow range of the output response of the operational amplifier A1, but is not essential to the present invention. In the embodiment, two are connected. However, one or no connection may be used.

Further, in the embodiment, as the variable means of the current detection resistor of the constant current drive circuit in the control voltage source Va, a circuit comprising a series connection of an NPN transistor Q4 and a resistor R4, which are switching means, is one in the embodiment. However, the present invention is not limited to this, and a plurality may be provided.

In the above-described embodiment, the current control circuit is configured to operate on the high side using the reference potential point of the power supply as the power supply voltage. However, the current control circuit operating on the low side using the reference potential point of the power supply as zero potential is used. It can also be configured as a control circuit.

Further, in the above-described embodiment, the case where the load RL is a gas sensor circuit has been described. However, the present invention is not limited to this and can be applied to current control of various loads.

[0069]

According to the first aspect of the present invention, rails
A low-cost and high-accuracy current control circuit can be obtained by using a general operational amplifier having a narrow response range without using a two-rail type operational amplifier.

According to the second aspect of the present invention, a general operational amplifier having a narrow response range can be used to operate on the high side using the reference potential point of the power supply as the power supply voltage, and the power supply can be used. Can be configured to operate as a current control circuit that operates on the low side with the reference potential point of zero as the zero potential.

According to the third aspect of the present invention, the control voltage source can be an inexpensive constant current drive circuit instead of a constant voltage circuit. Further, the magnitude of the control voltage input to the other input terminal of the operational amplifier can be easily varied by the variable means.

According to the fourth aspect of the present invention, the resistance value of the current detection resistor is changed by ON / OFF control of the switching means, and as a result, the magnitude of the control voltage input to the other input terminal of the operational amplifier easily. Can be varied.

According to the fifth aspect of the present invention, the load is a gas sensor circuit, and can control a current flowing through the gas sensor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of a current control circuit according to the present invention.

FIG. 2 is a circuit diagram showing a more specific configuration example of the current control circuit of FIG. 1;

FIG. 3 is a circuit diagram illustrating an example of a conventional current control circuit.

[Explanation of symbols]

 Rcs current detection resistor (load current detection means) A1 operational amplifier (first operational amplifier) RL load (gas sensor circuit) Vcc power supply Vref reference voltage source Va control voltage source CD constant current drive circuit R4 resistance R5 resistance (current detection resistance) A3 operational amplifier (Second operational amplifier) Rx variable means Q4 NPN transistor (switching means)

Claims (5)

[Claims] 1. A current control circuit for controlling a load current supplied to a load using a first operational amplifier to which a negative feedback voltage from a load current detecting means is input to one input terminal, The other input terminal of the operational amplifier is connected to a reference voltage source that supplies a reference voltage within the response range of the first operational amplifier when viewed from the reference potential point of the power supply, and the one input terminal is connected to the one input terminal from the load current detecting means. A current control circuit, comprising: a control voltage source for supplying a control voltage for shifting a negative feedback voltage to a range within which the first operational amplifier operates. 2. The current control circuit according to claim 1, wherein the reference potential point of the power supply is a power supply voltage or a zero potential. 3. The control voltage source includes a second operational amplifier having one input terminal to which a negative feedback voltage from a current detection resistor is input, and variable means for changing a resistance value of the current detection resistor. 3. The current control circuit according to claim 1, comprising a current drive circuit. 4. The current control circuit according to claim 3, wherein said variable means includes at least one circuit connected in parallel with said current detection resistor and comprising a series connection of a resistor and a switching means. 5. The current control circuit according to claim 1, wherein the load is a gas sensor circuit.