JP2003021115A - Two-wire sensor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-wire sensor circuit enabling stable action, decreasing size, and reducing a cost. SOLUTION: This two-wire sensor circuit is structured by a bridge circuit 1 having MR elements 1a to 1d sensing magnetic force as four sides, an amplifier 2 amplifying a detecting signal from the bridge circuit 1, a Darlington connecting circuit 3 connected to the amplifier 2, a light emitting diode LED1 connected to the Darlington connecting circuit 3, and a constant-current circuit 4 connected to the light emitting diode LED1. The amplifier 2 is made to be a CMOS type, and the constant-current circuit 4 is structured by a field effect transistor FET1, a resistance R1, and a variable resistance VR1, thereby decreasing a voltage drop of the constant-current circuit 4 at the time of detection by the MR elements 1a to 1d, and enabling operation of the CMOS type amplifier 2 by power source voltage lower than a constant-current range of the field effect transistor FET1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wire type sensor circuit technology, and in particular, it is applied to a two-wire type sensor circuit which is suitable for downsizing and cost reduction as a position detecting device for fluid pressure operating equipment such as a cylinder. And effective technology.

[0002]

2. Description of the Related Art Conventionally, in a position detecting device for fluid pressure actuated equipment, a monolithic IC is used, a general-purpose sensor IC and an SMD (surface mount, There is a single-function sensor configured as a device.

For example, as the latter example, there is a technique described in the utility model registration No. 2606494 previously proposed by the present inventor. The technology of this publication is
As shown in FIG. 13, a bridge circuit 1 having four sides of the MR elements 1a to 1d, an amplifier 2 for amplifying a detection signal from the bridge circuit 1, a Darlington connection circuit 3, a light emitting diode LED, and a constant current circuit 4 are provided. The transistor Q and the constant current diode ID are included. The emitter terminal of the transistor Q is connected to the signal terminal OUT, and the emitter terminal of the Darlington connection circuit 3 is the common terminal GN.
It is configured to be connected to D.

[0004]

With respect to the technology described in Japanese Utility Model Registration No. 2606494, the present inventor has found that the present fluid pressure actuating device and a position detecting device for the fluid pressure actuating device. Focusing on the demand for size reduction and cost reduction, the following improvement measures were examined.

For example, in the technique described in the above publication, a CMOS type amplifier may be considered in order to reduce power consumption and supply voltage. In this case, the internal resistance is large in the constant current circuit including the transistor and the constant current diode as shown in FIG.
Since the voltage drop due to this internal resistance also becomes large, it is conceivable that the amplifier will not operate.

Therefore, the present inventor uses a field effect transistor instead of a constant current diode as a circuit structure for reducing the internal resistance of the constant current circuit. It was conceived that the sensor circuit can operate with a low power supply voltage even when the resistance is reduced and the amplifier is of CMOS type.

Therefore, an object of the present invention is to make the amplifier a CMO.
It is an object of the present invention to provide a two-wire sensor circuit which is S-type and has a circuit configuration of a constant current circuit using a field effect transistor, which enables stable operation and can achieve downsizing and cost reduction. .

[0008]

In order to achieve the above-mentioned object, the present invention provides a bridge circuit with a detection element, an amplifier,
In the configuration of the 2-wire type sensor circuit including the Darlington connection circuit, the light emitting diode, the field effect transistor, the resistor, etc., the amplifier is of CMOS type, and the field effect transistor and the resistor reduce the voltage drop at the time of detection by the detection element to reduce the electric field. It is configured as a constant current circuit that enables a CMOS amplifier to operate with a power supply voltage lower than the constant current region of the effect transistor.

Another two-wire sensor circuit of the present invention is
In a configuration including a bridge circuit by a detection element, an amplifier, a Darlington connection circuit, a light emitting diode, a field effect transistor, a resistor, a transistor, etc., the amplifier is a CMOS type, the field effect transistor and the resistor are configured as a constant current circuit, and the transistor is The switching circuit is configured so that the CMOS type amplifier can operate by reducing the voltage drop during detection by the detection element without depending on the current characteristics of the field effect transistor.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. In all the drawings for explaining the embodiments, constituent elements having the same functions are designated by the same reference numerals, and repeated description thereof will be omitted.

(Embodiment 1) First, an example of the configuration of a two-wire sensor circuit according to Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram showing a two-wire sensor circuit of this embodiment.

The two-wire type sensor circuit of this embodiment is a two-wire type sensor having a signal terminal and a common terminal for outputting a detection signal from a bridge circuit by a detection element through an amplifier, and is sensitive to magnetic force. MR element 1a-
A bridge circuit 1 having 1d as four sides, an amplifier 2 for amplifying a detection signal from the bridge circuit 1, and an amplifier 2
To the Darlington connection circuit 3 and the light emitting diode LED1 connected to the Darlington connection circuit 3.
And a constant current circuit 4 connected to the light emitting diode LED1.

The bridge circuit 1 has a four-sided bridge structure in which MR elements 1a to 1d, which are detection elements, are connected to each side, and the intersection of the MR element 1a and the MR element 1c is the power supply voltage Vcc and the MR element 1b. The intersections of the MR elements 1d are connected to the ground voltage GND, respectively. Also, the MR element 1a
And the MR element 1b intersect at the output terminal OUT1 and MR element 1
The intersections of c and the MR element 1d are connected to the output terminal OUT2, and the output terminal OUT1 and the output terminal OUT are connected.
2 to the amplifier 2.

The amplifier 2 includes a PMOS transistor and an NM.
It is a CMOS type with OS transistors, and includes, for example, a positive input terminal (+), a negative input terminal (-), and an output terminal (OU).
T), a power supply terminal (+ V), and a ground terminal (-V). The positive input terminal (+) and the negative input terminal (-) are connected to the output terminal OUT2 and the output terminal OUT1 of the bridge circuit 1, respectively.
The capacitor C1 is connected between the negative input terminal (−) and the negative input terminal (−). The output terminal (OUT) is connected to the Darlington connection circuit 3, and the resistor R2 is connected between the output terminal (OUT) and the positive input terminal (+). Further, the power supply terminal (+ V) and the ground terminal (-V) are connected to the power supply voltage Vcc and the ground voltage GND, respectively, and the capacitor C2 is connected between the power supply terminal (+ V) and the ground terminal (-V). ing.

The Darlington connection circuit 3 is a circuit in which a plurality of transistors having the same polarity are directly connected to each other to form a single transistor having an apparently excellent characteristic. The bridge circuit 1 detects an ON state and a non-detection state. At times, it becomes an OFF state, and is composed of, for example, two NPN type transistors Q1 and Q2 and a resistor R3, and the resistor R3 is connected to the base terminal of the first stage NPN type transistor Q1.
The emitter terminal of the transistor Q1 is connected to the base terminal of the NPN transistor Q2 at the final stage, and the collector terminals of the NPN transistors Q1 and Q2 are connected. The base terminal of the first-stage NPN transistor Q1 is connected to the amplifier 2 through the resistor R3, the emitter terminal of the last-stage NPN transistor Q2 is connected to the common terminal GND, and both NPN transistor Q are connected.
The collector terminals of 1 and Q2 are connected to the light emitting diode LED1.

The light emitting diode LED1 is an indicator light which is turned on when the Darlington connection circuit 3 is ON when detected, and is turned off when the Darlington connection circuit 3 is OFF when not detected. The cathode terminal is connected to the Darlington connection circuit 3. The anode terminal is connected to the constant current circuit 4.

The constant current circuit 4 is a circuit that reduces the voltage drop during detection by the MR elements 1a to 1d and enables the CMOS type amplifier 2 to operate with a power supply voltage lower than the constant current region. For example, the field effect transistor FET1. , Resistance R
1 and the variable resistor VR1, the source terminal of the field effect transistor FET1 is at one end of the variable resistor VR1, the other end of the variable resistor VR1 is at one end of the resistor R1, and the other end of the resistor R1 is at the field effect transistor FET1. Each is connected to the gate terminal. The drain terminal of the field effect transistor FET1 is connected to the light emitting diode LED1, and the gate terminal is the bridge circuit 1
Is connected to the power supply voltage Vcc side.

In the two-wire type sensor circuit configured as described above, the drain terminal of the field effect transistor FET1 of the constant current circuit 4 is connected to the signal terminal OUT, and the emitter terminal of the Darlington connection circuit 3 is the common terminal GND.
And the gate terminal of the field effect transistor FET1 and the emitter terminal of the Darlington connection circuit 3 are connected between the power supply voltage Vcc of the bridge circuit 1 and the ground voltage GND, and the circuit voltage is applied to the bridge circuit 1. Detection is possible with the MR elements 1a to 1d. In this 2-wire sensor circuit, the signal terminal OUT and the common terminal GND are used for compensation due to external noise.
A constant voltage diode ZD1 for surge voltage countermeasure is connected between and.

The components of the two-wire sensor circuit are mounted on a printed circuit board (not shown) by using general-purpose SMD components, and are further housed in a case to serve as a position detecting device for the two-wire sensor, for example, pneumatic pressure. It is fitted and mounted in a mounting groove provided on the outer surface of a fluid pressure operating device such as a cylinder, and is used for detecting the position of the stroke end of a pneumatic cylinder.

Next, one example of the characteristics of the two-wire sensor circuit of the present embodiment will be described with reference to FIGS. 2 is a characteristic diagram of the drain current I _D -gate-source voltage V _GS of the field effect transistor, FIG. 3 is a characteristic diagram of the drain current I _D -drain-source voltage V _DS , and FIG. 4 is a circuit diagram of a constant current circuit. Figure 5 is the drain current I _D - drain-source voltage V _D
The characteristics of _S are shown respectively.

(1) CMOS type amplifier In the two-wire type sensor circuit of this embodiment, the amplifier 2 has a CM.
Since the OS type is used, it can operate even at a low voltage, and the current consumption by the MR elements 1a to 1d of the bridge circuit 1 and the amplifier 2 becomes low. For example, as an example, the MR element 1a
Resistance value of 1d = 8 kΩ, current consumption of amplifier 2 = 0.0
82V, 1.8V when the power supply voltage Vcc = 1.8V
÷ 8 kΩ + 0.082 mA = 0.3 mA consumption current. Further, as the field effect transistor FET1, I
By selecting and using the one with a small _DSS, the voltage drop due to the constant current circuit 4 also becomes small. For example, as an example,
When I _{DS S} = 1 mA and I _D = 0.3 mA, V from FIG.
_GS = 0.2V, the minimum voltage of the constant current region in FIG. 3 V _DS =
From 0.5V, the voltage drop becomes 0.2 + 0.5 = 0.7V. Therefore, when the two-wire sensor circuit is ON, the amplifier 2 can be operated without bypassing the transistor Q by the constant current diode ID as in the constant current circuit of FIG. 13 which is a premise of the present invention. You can

Further, by removing the transistor Q of the constant current circuit which is the premise of the present invention, the voltage between the power supply voltage Vcc and the ground voltage GND of the two-wire type sensor circuit is lowered by the V _BE voltage of the transistor Q1. However, there is no problem for the same reason as above.

Further, even at a voltage lower than the constant current region, the internal resistance of the constant current circuit 4 of the present embodiment is smaller and the voltage drop is smaller than that of the constant current diode ID of the constant current circuit which is the premise of the present invention. Therefore, the amplifier 2 can be stably operated. For example, as an example, the internal resistance of the constant current circuit 4 is 0.7 / 0.3 = 2.3 kΩ.

(2) Constant using a field effect transistor
Current circuit In FIG. 4, for example, as an example, a field effect transistor
Drain-source voltage V of FET 1_DSIs 2.5V
When the drain current I_DIf only 0.3 mA is applied,
Voltage across anti-R1 and variable resistor VR1, ie gate
・ Source voltage V _GSIs 0.2V, the resistance R1 + variable resistance
Set anti-VR1 to 0.2 ÷ 0.3 = 660Ω.

In this state, the drain current I_DWill increase
And the voltage drop of the resistor R1 + variable resistor VR1 becomes large.
, Gate-source voltage V_GSBecause the drain becomes larger
Current I _DIs reduced. And the drain current I_DIs reduced
Then, the voltage drop of the resistor R1 + variable resistor VR1 becomes small.
, Gate-source voltage V_GSBecomes smaller so drain
Current I_DWill increase.

As a result, constant current characteristics can be obtained. Therefore, even if the drain-source voltage V _DS of the field effect transistor FET1 changes, as shown in FIG. 5, when the drain-source voltage V _DS > 2.5 V, the change of the drain current I _D is 0.
It is constant in the range of 2 mA.

(3) Substrate occupation area comparison of constant current circuit Constant current diode ID of constant current circuit which is the premise of the present invention
Is, for example, 3.5 × 1.35≈4.7 mm
² , the constant current circuit using the field effect transistor FET1 of the present embodiment is, for example, 1.6 × 1.6 (FET1) + 0.6 × 0.3
(R1) + 1.0 × 0.5 (VR1) ≈2.7 mm ² , which is 57 by the constant current circuit 4 of the present embodiment.
% (2.4 ÷ 4.7).

As described above, in the two-wire type sensor circuit of this embodiment, for the purpose of reducing power consumption, reducing internal voltage drop, cost reduction, and size reduction, The CMOS type amplifier 2 is used to reduce the power consumption, and the constant current circuit 4 including the field effect transistor FET1 and the like is used to reduce the internal voltage drop, which is the premise of the present invention for cost reduction. It is characterized in that the constant current circuit 4 constituted by the field effect transistor FET1 and the like is adopted in order to reduce the size by removing the switching circuit including the transistor and the like shown in FIG.

That is, in the present embodiment, the power supply voltage cannot be increased because the amplifier 2 used for reducing the power consumption is a CMOS type. To solve the problem, a constant current circuit 4 composed of a field effect transistor FET1 and the like is adopted to solve the problem. Further, in order to reduce the internal voltage drop, the power supply voltage of the amplifier 2 is lowered. To solve the problem, a constant current circuit 4 composed of a field effect transistor FET1 and the like is adopted to solve the problem. Further, when the constant current circuit 4 including the field effect transistor FET1 and the like is adopted, the internal resistance is small, so that the switching circuit including the transistor and the like which is the premise of the present invention can be eliminated. Further, since the field effect transistor FET1 which is a microminiature component is adopted for the large constant current diode ID of the constant current circuit which is the premise of the present invention, miniaturization can be achieved.

Next, an example of the design of the two-wire type sensor circuit of this embodiment will be described with reference to FIGS. 2 in FIG.
FIG. 7 is an explanatory diagram of the design of the linear sensor circuit, FIG. 7 is an explanatory diagram of h _FE of the NPN type transistor, FIG. 8 is an explanatory diagram of V _BE , FIG. 9 is an explanatory diagram of V _F of the light emitting diode, and FIG. 10 is a constant current circuit. V
FIG. 11 is an explanatory diagram of _GS , and FIG. 11 is an explanatory diagram summarizing the design results.

In the present embodiment, for example, referring to FIG. 6, MR elements 1a to 1a of bridge circuit 1 are shown in FIG.
1d resistance R _MR = 8 kΩ, power supply voltage Vcc = 10 to 28
V, load current = 4 to 20 mA, leakage current = 1 mA or less.

(1) Calculation of output voltage of amplifier When the NPN transistors Q1 and Q2 are turned on within the operating range of the two-wire type sensor circuit, the minimum value of the output voltage of the amplifier 2 is calculated. At this time, h _FE of the NPN transistors Q1 and Q2 uses the values in FIG. 7 and V _BE in FIG. 8 from the data sheet, respectively.

V _ICO = V _R3 + V _BE1 + V _BE2 (Equation (1)) V _R3 = R3 × I _B1 (Equation (2)) I _C2 = h _FE1 × h _FE2 × I _B1 I _B1 = I _C2 / (H _FE1 × h _FE2 ) ... Expression (3) Substituting Expression (2) and Expression (3) into Expression (1), V _ICO = R3 × I _C2 / (h _FE1 × h _FE2 ) + V _BE1 + V _BE2 ... Formula (4). When I _C2 = 20 mA at temperature = −10 ° C., and R3 = 100 kΩ from the calculation of the resistance R3 in (2) described later, V _ICO = 100 × 10 ³ × 20 × 10 ⁻³ /(93.3) × 154) + 0.94 + 0.97≈2.05 (V).

.. When I _C2 = 4 mA at temperature = −10 ° C., V _ICO = 36 × 10 ³ × 4 × 10 ⁻³ /(93.3×136)+0.94 + 0.94≈1.89 (V) .

.. When I _C2 = 4 mA at temperature = 70 ° C., V _ICO = 36 × 10 ³ × 4 × 10 ⁻³ /(159×192)+0.62 + 0.62≈1.24 (V).

Therefore, temperature = -10 ° C., I _C2 = 20 mA
At this time, V _ICO becomes the maximum value, and the required power supply voltage Vcc at this time is Vcc = V _ICO +0.05, and Vcc =
It becomes 2.1 (v).

(2) From the calculation formula (4) of the resistance R3, R3 × I _C2 / (h _FE1 × h _FE2 ) = V _ICO −V _BE1 −V _BE2 R3 = h _FE1 × h _FE2 × (V _ICO −V _BE1 −V _BE2 ) / I _{C2 When} temperature is −10 ° C. and I _{C2 is} 20 mA, and V _{ICO is} 2 V, R3 = 93.3 × 154 × (2−0.97−0.94) / 0 0.02 = 64656.9 and the resistance R3 = 100 kΩ.

(3) Outside the operating range of the two-wire sensor circuit (N
The maximum value of the sink current of the amplifier 2 at this time is temperature = −
At 10 ° C., I _C2 = 20 mA, I _B1 = 20 × 10 ⁻³ /(93.3×154)≈1.4×10 ⁻⁶ (A) At this time, the low level output voltage of the amplifier 2 is close to 0V. Therefore, the NPN transistors Q1 and Q2 are OF
It becomes F.

(4) Calculation of internal voltage drop (when NPN transistor Q2 is ON) At this time, the value shown in FIG. 9 is used as V _{F of the} light emitting diode LED1 from the data sheet.

The internal voltage drop V _D is V _D = V _F + V _BE2 .

.. At a temperature of −10 ° C. and I _C2 = 20 mA, V _D = 2.23 + 0.97 = 3.2 (v).

.. At a temperature of −10 ° C. and I _C2 = 4 mA, V _D = 1.93 + 0.94 = 2.87 (v).

.. At a temperature of 70 ° C. and an I _{C2 of} 4 mA, V _D = 1.81 + 0.62 = 2.43 (v).

(5) Examination of constant current circuit Assuming that the power supply voltage Vcc = 2.1V, the current value I _MR flowing through the MR elements 1a to 1d of the bridge circuit 1 is I _MR = Vcc / R _MR = 2.1 / 8000 = because the circuit current of 0.26mA amplifier 2 is 0.2 mA, the current to make the constant current circuit 4 (the drain current) I _D becomes _{I D = 0.26 + 0.2 = 0.46mA} .

V _GS at this time is obtained. This V _GS is as shown in FIG.

Therefore, since V _GS varies from 0.15 to 0.84 V, it is necessary to trim the resistor R1 + variable resistor VR1 so as to have this voltage.

If R1 + VR1 = R _S , the minimum is R _S = 0.15 / 0.46 × 10 ⁻³ ≈326 Ω
Or ≈330Ω The average is R _S = 0.54 / 0.46 × 10 ⁻³ ≈1.17
The maximum kΩ is R _S = 0.84 / 0.46 × 10 ⁻³ ≈1.83.
It becomes kΩ.

(6) Results As shown in FIG. 11, in the field effect transistor FET1 with I _DSS = 5 mA, the measured voltage drop in the constant current circuit 4 is about 0.5 V in actual measurement. Therefore, the above (4)
Even if the internal voltage drop is low, as in
Since 0.5 = 1.93V, the power supply voltage of the amplifier 2 is secured. In addition, as in the above temperature range,
At load current, Vcc-0.05> _VICO , so N
The PN type transistors Q1 and Q2 can be operated. In the case of, the internal voltage drop is 70 ° C, 4 mA.
Of becomes a voltage higher than 2.43V, V _ICO is -10 ℃,
There is no problem because it becomes lower than 2.05V of 20 mA.

As described above, the MR of the bridge circuit 1
Elements 1a to 1d, amplifier 2, light emitting diode LED1,
The type and value of each circuit component such as the NPN transistors Q1 and Q2, the field effect transistor FET1, the resistor R1, the variable resistor VR1 and the like are calculated. Can be designed.

Therefore, according to the two-wire type sensor circuit of the present embodiment, the amplifier 2 is a CMOS type and the constant current circuit 4 is composed of the field effect transistor FET1, the resistor R1 and the variable resistor VR1. 1a-1d
The voltage drop of the constant current circuit 4 is reduced at the time of detection by
The CMOS amplifier 2 can be operated with a power supply voltage lower than the constant current region of the field effect transistor FET1. Furthermore, since the amplifier 2 can be operated stably, it is possible to eliminate malfunctions during switching.

Further, as compared with the two-wire type sensor circuit which is the premise of the present invention, small parts can be used,
The two-wire sensor circuit can be downsized by downsizing the parts. Furthermore, since the number of parts can be reduced, it is possible to reduce the cost by reducing the number of parts.

(Second Embodiment) An example of the configuration of a two-wire sensor circuit according to a second embodiment of the present invention will be described with reference to FIG. FIG. 12 is a circuit diagram showing the two-wire sensor circuit of this embodiment.

The two-wire type sensor circuit of the present embodiment has a two-wire type sensor circuit which has a signal terminal and a common terminal for outputting a detection signal from a bridge circuit by a detection element through an amplifier, as in the first embodiment. The sensor is different from the first embodiment in that the CMOS type amplifier can operate by reducing the voltage drop at the time of detection by the detection element without depending on the current characteristic of the field effect transistor of the constant current circuit. This is the point that a switching circuit for switching is added.
In addition, in the present embodiment, description of the components having the same functions as those in the first embodiment will be omitted.

That is, the two-wire type sensor circuit of the present embodiment has a bridge circuit 1 having four sides of MR elements 1a to 1d sensitive to magnetic force, and an amplifier 2 for amplifying a detection signal from the bridge circuit 1. And the Darlington connection circuit 3 connected to the amplifier 2 and the Darlington connection circuit 3
And a constant current circuit 4 connected to the light emitting diode LED1, a switching circuit 5 connected to the light emitting diode LED1 and the constant current circuit 4, and the like.

In particular, in the present embodiment, for the purpose of avoiding selection of the field effect transistor and lowering the internal resistance of the constant current circuit, selection of the field effect transistor is avoided and the internal resistance of the constant current circuit is reduced. This is characterized in that the switching circuit 5 is adopted in order to lower the voltage.

The switching circuit 5 enables the CMOS amplifier 2 to operate by reducing the voltage drop during detection by the MR elements 1a to 1d without depending on the current characteristic of the field effect transistor FET1 of the constant current circuit 4. Circuit, for example a PNP transistor Q3 and a resistor R
4, the base terminal of the PNP transistor Q3 is connected to one end of the resistor R4, and the other end of the resistor R4 is connected to the emitter terminal of the PNP transistor Q3. The base terminal of the PNP transistor Q3 is connected to the anode terminal of the light emitting diode LED1,
The collector terminal is the gate terminal of the field effect transistor FET1, and the emitter terminal is the field effect transistor FE.
Each of them is connected to the drain terminal of T1.

Further, in the present embodiment, the constant current circuit 4
Is a field effect transistor FET1 and a variable resistor VR1
The field effect transistor FET1 is composed of
By adding the switching circuit 5 capable of lowering the internal resistance of the constant current circuit 4 at the time of detection by the elements 1a to 1d, it is not necessary to use an object having a small I _DSS as in the first embodiment. Field effect transistor FET1
It is possible to avoid selection when using. Further, by forming the filter circuit with the capacitor C2 and the resistor R1, it is possible to prevent the oscillation phenomenon of the circuit. That is, even when the output of the amplifier 2 abnormally operates due to the fluctuation of the power supply voltage at the timing of detection by the MR elements 1a to 1d, the fluctuation of the power supply voltage is suppressed by the filter circuit, so that a countermeasure against oscillation can be incorporated. Furthermore, by connecting the constant voltage diode ZD2 between the power supply terminal (+ V) and the ground terminal (−V) of the amplifier 2, it is possible to take measures against the rise in the power supply voltage of the amplifier 2.

Therefore, according to the two-wire type sensor circuit of the present embodiment, the amplifier 2 is a CMOS type, the constant current circuit 4 is composed of the field effect transistor FET1, etc., and the PNP is used.
By adding the switching circuit 5 including the transistor Q3 and the like, the voltage drop can be reduced at the time of detection by the MR elements 1a to 1d without depending on the current characteristic of the field effect transistor FET1 of the constant current circuit 4 to reduce the CMO.
The S-type amplifier 2 can be operated. Furthermore, by incorporating circuit oscillation countermeasures, the amplifier 2 can be operated more stably, so that malfunctions at the time of switching can be eliminated.

Further, as in the case of the first embodiment, it is possible to use a smaller component than the two-wire type sensor circuit which is the premise of the present invention. It can be miniaturized. Furthermore, since the number of parts can be reduced, it is possible to reduce the cost by reducing the number of parts.

In the above-described embodiment, the case where the present invention is applied to the two-wire type sensor circuit used for detecting the position of the pneumatic cylinder has been described, but the present invention is not limited to this, and for example, a hydraulic cylinder or a rotary actuator. It can also be widely applied as a position detection device for other fluid pressure actuated devices such as, and as a sensor circuit for other devices requiring a detection function.

[0061]

As described above, according to the two-wire sensor circuit of the present invention, the voltage drop of the constant current circuit can be reduced by forming the constant current circuit using the field effect transistor. Therefore, the CMOS type amplifier can be stably operated. Furthermore, since the number of parts can be reduced and the parts used can be made smaller,
It is possible to reduce the size and cost. As a result, the two-wire sensor circuit can be stably operated, and the miniaturization and the cost reduction can be realized.

Further, according to another two-wire type sensor circuit of the present invention, by incorporating measures against circuit oscillation,
Since the amplifier can be operated stably, it is possible to eliminate malfunctions at the time of switching.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a two-wire sensor circuit according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a drain current _ID −gate-source voltage V _GS of a field effect transistor in the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a drain current I _D −drain / source voltage V _DS of a field effect transistor in the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram showing a constant current circuit in the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a drain current I _D −drain / source voltage V _DS of a field effect transistor in the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 6 is a circuit diagram for explaining the design of the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram showing h _FE of the NPN transistor in the design of the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 8 is an explanatory diagram showing V _BE of the NPN transistor in the design of the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 9 is an explanatory diagram showing V _F of the light emitting diode in designing the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 10 is an explanatory diagram showing V _GS of the constant current circuit in the design of the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 11 is an explanatory diagram showing a summary of design results of the two-wire sensor circuit according to the first embodiment of the present invention.

FIG. 12 is a circuit diagram showing a two-wire sensor circuit according to a second embodiment of the present invention.

FIG. 13 is a circuit diagram showing a two-wire sensor circuit which is a premise of the present invention.

[Explanation of symbols]

1 bridge circuit 1a to 1d MR element 2 amplifier 3 Darlington connection circuit 4 constant current circuit 5 switching circuits LED1 light emitting diode C1, C2 capacitors R1, R2, R3, R4 resistance Q1, Q2 NPN type transistor Q3 PNP type transistor FET1 field effect transistor VR1 variable resistor ZD1, ZD2 constant voltage diode OUT signal terminal GND common terminal

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H03K 17/95 G01R 33/06 R (72) Inventor Motoaki Iwata 3-2-3 Marunouchi, Chiyoda-ku, Tokyo No. Incorporated company in Koganei (72) Inventor Kiyoshi Nakaaki 9 at 249 Miyamoto, Ryuyo-cho, Iwata-gun, Shizuoka Prefecture Hamamatsu Photoelectric Co., Ltd. (72) In Hiroshi Oba 9 Hamamatsu at 249 Miyamoto, Ryoyo-cho, Iwata-gun, Shizuoka 2F077 AA49 CC02 JJ03 JJ09 JJ23 TT06 TT16 TT82 TT87 2G017 AD55 BA05 BA14 3H081 AA03 BB01 BB03 CC25 GG05 GG10 GG15 GG16 GG23 5JAEE EE23 CA36 CA37 CA87 CA92 FA01 FA10 HA02 HA10 HA19 HA20 HA25 HA29 HA44 KA01 KA12 KA47 MA06 MA08 MA21 SA01 SA15 TA01 TA02 VL07

Claims (2)

[Claims] 1. A two-wire sensor circuit used for detecting the position of a fluid pressure actuated device, comprising a signal terminal for outputting a detection signal from a bridge circuit by a detection element through an amplifier and a common terminal, the output terminal of the amplifier. A Darlington connection circuit having a base terminal connected to a light emitting diode, a light emitting diode having a cathode terminal connected to a collector terminal of the Darlington connection circuit, a field effect transistor having a drain terminal connected to an anode terminal of the light emitting diode, A resistor connected between the source and gate terminals of the effect transistor, the drain terminal of the field effect transistor is connected to the signal terminal, the emitter terminal of the Darlington connection circuit is connected to the common terminal, the electric field Gate terminal of effect transistor and said Darlington connection circuit An emitter terminal is connected between the bridge circuits to apply a circuit voltage to the bridge circuits to enable detection by the detection element, the amplifier is of CMOS type, the field effect transistor and the resistor are the The voltage drop is reduced during detection by the detection element, and the CM is operated at a power supply voltage lower than the constant current region of the field effect transistor.
A two-wire sensor circuit configured as a constant current circuit that enables an OS-type amplifier to operate. 2. A two-wire type sensor circuit used for detecting the position of a fluid pressure actuated device, comprising a signal terminal for outputting a detection signal from a bridge circuit by a detection element through an amplifier and a common terminal, the output terminal of the amplifier. A Darlington connection circuit having a base terminal connected to the light emitting diode, a light emitting diode having a cathode terminal connected to a collector terminal of the Darlington connection circuit, a field effect transistor having a drain terminal connected to an anode terminal of the light emitting diode, and the electric field A transistor connected between a source and a gate terminal of an effect transistor, a base terminal connected to an anode terminal of the light emitting diode, and a collector terminal and an emitter terminal connected to a gate terminal and a drain terminal of the field effect transistor, respectively. And a drain of the field effect transistor. The Darlington connection circuit is connected to the common terminal, the gate terminal of the field effect transistor and the emitter terminal of the Darlington connection circuit are connected between the bridge circuits. A circuit voltage is applied to the bridge circuit to enable detection by the detection element, the amplifier is a CMOS type, the field effect transistor and the resistor are configured as a constant current circuit, the transistor is the A two-wire sensor circuit, which is configured as a switching circuit that enables the CMOS amplifier to operate by reducing the voltage drop when detected by the detection element without depending on the current characteristics of the field effect transistor. .