Voltage stabilizing circuit with negative impedance characteristic and two-wire system valve positioner

Abstract

The invention provides a voltage stabilizing circuit with a negative impedance characteristic and a two-wire system valve positioner, the voltage stabilizing circuit comprises a voltage dividing unit, a shunting unit and an adjustable voltage stabilizer, the voltage dividing unit is used for dividing input voltage, the shunting unit is used for shunting input current at the input end of the voltage dividing unit, and the adjustable voltage stabilizer is used for adjusting the voltage of the two-wire system valve positioner. The regulation and control on the input voltage at the two ends of the voltage stabilizing circuit are realized; under the shunting action of the shunting unit, the input voltage is inversely proportional to the input current, so that the voltage stabilizing circuit has a negative impedance characteristic. According to the voltage stabilizing circuit provided by the invention, the input voltage is inversely proportional to the input current, so that the input power of a two-wire system instrument is increased when the input current is small, the design difficulty of low power consumption of the whole machine is reduced, the equivalent impedance is reduced when the input current is large, and the equipment applicability is improved.

Description

Technical Field

[0001] This invention relates to the field of instrumentation technology, and in particular to a voltage regulator circuit with negative impedance characteristics and a two-wire valve positioner. Background Technology

[0002] Two-wire instruments transmit power and signals simultaneously through the same pair of wires, and their system impedance directly affects system power consumption and power supply reliability. In traditional solutions, the instrument end typically uses a linear voltage regulator (such as a single Zener diode). This voltage regulation scheme based on a single Zener diode requires controlling the positioner's power consumption within a fixed range. Generally, as the input current increases, the input power also increases, and the excess input power is mainly dissipated as heat, resulting in energy waste.

[0003] In related technologies, the input power at the minimum operating current is generally increased by increasing the clamping voltage of the Zener diode, thereby improving the power supply reliability of the system and reducing the difficulty of low-power design of the whole machine. However, increasing the clamping voltage of the Zener diode will increase the equivalent impedance in two-wire instruments. The equivalent impedance includes the impedance of functions such as industrial communication and current detection. If the equivalent impedance is too high, it may cause current signal distortion problems when the system is under high current. Therefore, the equivalent impedance of the instrument should not be too high. Summary of the Invention

[0004] This invention provides a technical solution for a voltage regulator circuit with negative impedance characteristics to solve the technical problem of limited power and impedance in two-wire instrument systems.

[0005] The present invention provides a voltage regulator circuit with negative impedance characteristics, comprising:

[0006] The voltage divider unit is used to divide the input voltage.

[0007] A current shunt unit is connected to the voltage divider unit and performs current shunt processing on the input current at the input terminal of the voltage divider unit.

[0008] An adjustable voltage regulator adjusts the input voltage through the voltage divider unit and the current shunt unit;

[0009] The current shunting capability of the current shunting unit is configured such that, under the current shunting action of the current shunting unit, the input voltage is inversely proportional to the input current, so that the voltage regulator circuit has negative impedance characteristics.

[0010] In one embodiment of the present invention, the current shunt unit includes a current shunt subunit and an adjustment subunit. The current shunt subunit is connected to the voltage divider unit and performs current shunt processing on the input current at the input terminal of the voltage divider unit to generate a branch current. The adjustment subunit is connected to the current shunt subunit, samples the input current of the voltage regulator circuit, converts the sampled current into a bias voltage, and adjusts the branch current in the current shunt subunit through the bias voltage.

[0011] In one embodiment of the present invention, the voltage divider unit includes a first resistor and a second resistor. The first end of the first resistor is the first input terminal of the voltage divider unit, the second end of the first resistor is connected to the first end of the second resistor, the first end of the second resistor is the output terminal of the voltage divider unit, and the second end of the second resistor is the second input terminal of the voltage divider unit.

[0012] In one embodiment of the present invention, the shunt subunit includes a third resistor and a first PNP transistor. The first end of the third resistor is the input terminal of the shunt subunit, the second end of the third resistor is connected to the emitter of the first PNP transistor, the base of the first PNP transistor is connected to the bias voltage, the collector of the first PNP transistor is the output terminal of the shunt subunit, and the output terminal of the shunt subunit is connected to the reference terminal of the adjustable voltage regulator.

[0013] In one embodiment of the present invention, the regulating subunit includes a fourth resistor and a second PNP transistor. The first end of the fourth resistor is connected to the input terminal of the shunt subunit, the second end of the fourth resistor is connected to the emitter of the second PNP transistor, the base of the second PNP transistor outputs the bias voltage, the base of the second PNP transistor is also connected to the cathode of the adjustable voltage regulator, and the collector of the second PNP transistor is left floating.

[0014] In one embodiment of the present invention, the reference terminal of the adjustable voltage regulator is also connected to the common terminal of the first resistor and the second resistor, and the anode of the adjustable voltage regulator is connected to the second terminal of the second resistor.

[0015] In one embodiment of the present invention, the expression for the input voltage is as follows:

[0016]

[0017] In the above expression, V in Where R1 is the input voltage, R2 is the resistance of the first resistor, R3 is the resistance of the third resistor, and R4 is the resistance of the fourth resistor. ref I is the voltage at the reference terminal of the adjustable regulator. in For the input current, I refThe current at the reference terminal of the adjustable voltage regulator is denoted as .

[0018] The present invention also provides a two-wire valve positioner, the two-wire valve positioner comprising a voltage regulator circuit having negative impedance characteristics as described above.

[0019] The beneficial effects of this invention are as follows: This invention proposes a voltage regulator circuit with negative impedance characteristics and a two-wire valve positioner. The voltage regulator circuit includes a voltage divider unit, a current shunt unit, and an adjustable voltage regulator. The voltage divider unit divides the input voltage, and the current shunt unit shunts the input current at the input terminal of the voltage divider unit. The adjustable voltage regulator is connected to the voltage divider unit and the current shunt unit. By adjusting the input voltage through the voltage divider unit and the current shunt unit, the input power of the voltage regulator circuit can be controlled. Under the shunt action of the current shunt unit, the input voltage increases as the input current decreases, thereby increasing the circuit input voltage under low input current and thus increasing the input power. The input voltage decreases as the input current increases, thereby reducing the device input voltage and lowering the circuit operating impedance under high input current. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] In the attached diagram:

[0022] Figure 1 This is a schematic diagram of the impedance of a traditional valve positioner in the prior art;

[0023] Figure 2 This is a block diagram of a voltage regulator circuit with negative impedance characteristics provided in one embodiment of the present invention;

[0024] Figure 3 This is a detailed structural diagram of a voltage regulator circuit with negative impedance characteristics provided in one embodiment of the present invention.

[0025] The attached figures are labeled as follows:

[0026] 210 - Voltage divider unit; 220 - Current shunt unit; D1 - Adjustable voltage regulator; R1 - First resistor; R2 - Second resistor; R3 - Third resistor; Q1 - First PNP transistor; R4 - Fourth resistor; R5 - Fifth resistor; Q2 - Second PNP transistor; C1 - First capacitor; I in - Input current; V in - Input voltage; Vz - Clamping voltage; V T - Bias voltage. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0028] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0029] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0030] HART communication (Highway Addressable Remote Transducer) is a hybrid communication protocol widely used in industrial automation. It can superimpose digital communication onto traditional 4-20mA analog signals to achieve bidirectional data interaction, while being compatible with existing analog instrument systems. Here, milliampere is the unit of current, abbreviated as mA.

[0031] The TL431 is a programmable precision voltage reference and shunt regulator widely used in power management, voltage regulation, feedback control, and protection circuits.

[0032] A PNP transistor is a bipolar junction transistor (BJT) composed of three layers of semiconductor materials arranged in the order of P-type-N-type-P-type.

[0033] Two-wire instruments transmit power and signals simultaneously through the same pair of wires; the system impedance directly affects system power consumption and power supply reliability. In traditional solutions, such as... Figure 1 As shown, the instrument end (valve positioner end) typically uses a linear voltage regulation method (such as a single Zener diode). This voltage regulation scheme based on a single Zener diode needs to limit the power consumption of the entire system to P.max =V z Within the range of ×3.6mA, where V z This is the clamping voltage of the Zener diode; as the input current increases, the input power P... in =V z ×I in This will also increase, with excess input power being mainly consumed through heat dissipation, resulting in energy waste.

[0034] In related technologies, this is generally achieved by increasing the clamping voltage V of the Zener diode. z This is to increase the input power at the lowest operating current, thereby increasing power supply reliability and reducing the difficulty of low-power system design. However, the clamping voltage V of the Zener diode... z The increase will cause the equivalent impedance in two-wire instruments to be affected. The increase of R, of which sense Impedance required to achieve other functions (e.g., HART communication, current sensing), etc. Figure 1 As shown, due to the limitation of the controller output capability in two-wire instruments and the line impedance R... line Due to the voltage division effect (especially during long-distance transmission), the effective power supply voltage at the instrument end becomes very limited, so the equivalent impedance of the instrument cannot be too high.

[0035] like Figure 2 As shown, this application provides a voltage regulator circuit with negative impedance characteristics, comprising:

[0036] Voltage divider unit 210 is used to divide the input voltage V in Perform voltage division processing;

[0037] The current shunt unit 220 is connected to the voltage divider unit 210, and the input current I at the input terminal of the voltage divider unit 210 is... in Perform traffic diversion processing;

[0038] The adjustable voltage regulator D1 adjusts the input voltage V through the voltage divider unit 210 and the current shunt unit 220. in ;

[0039] The shunt capability of the shunt unit 220 is configured such that, under the shunt action of the shunt unit 220, the input voltage V... in With input current I in The impedance is inversely proportional, giving the voltage regulator circuit a negative impedance characteristic.

[0040] Specifically, such as Figure 2 As shown, the input voltage V is divided by the voltage divider unit 210. in Voltage division is performed, and the input current I at the input terminal of voltage divider unit 210 is divided by current divider unit 220. inThe voltage is shunted, and the input voltage V across the voltage regulator circuit is adjusted by voltage divider unit 210 and current shunter unit 220. in This is used to regulate the input power of the regulated voltage. The adjustable regulator D1 includes, but is not limited to, the TL431 model. The input voltage V across the regulator is... in With input current I in The input voltage V decreases as the input voltage increases. in With input current I in The voltage regulator circuit exhibits negative impedance characteristics as the voltage decreases and increases.

[0041] In detail, the shunt unit 220 includes a shunt subunit and a regulating subunit. The shunt subunit is connected to the voltage divider unit 210, and the input current I at the input terminal of the voltage divider unit 210 is... in The current is shunted to generate branch current; the regulating subunit is connected to the shunting subunit to regulate the input current I of the voltage regulator circuit. in Sampling is performed, and the sampled current is converted into a bias voltage V. T Through bias voltage V T Adjust the branch current in the shunt subunit.

[0042] In detail, such as Figure 3 As shown, the voltage divider unit 210 includes a first resistor R1 and a second resistor R2. The first end of the first resistor R1 is the first input terminal of the voltage divider unit 210, and the first input terminal of the voltage divider unit 210 is connected to the input voltage V. in The positive terminal of the voltage divider is connected to the second terminal of the first resistor R1, which is connected to the first terminal of the second resistor R2. The first terminal of the second resistor R2 is the output terminal of the voltage divider unit 210, and the second terminal of the second resistor R2 is the second input terminal of the voltage divider unit 210. The second input terminal of the voltage divider unit 210 is connected to the input voltage V. in The negative electrode.

[0043] In detail, such as Figure 3 As shown, the shunt subunit includes a third resistor R3 and a first PNP transistor Q1. The first terminal of the third resistor R3 is the input terminal of the shunt subunit, and the input terminal of the shunt subunit is connected to the input current I. in The input terminal of the shunt subunit is connected to the first terminal of the first resistor R1, the second terminal of the third resistor R3 is connected to the emitter of the first PNP transistor Q1, the base of the first PNP transistor Q1 is the driving terminal of the shunt subunit, and the driving terminal of the shunt subunit is connected to the bias voltage V. T The collector of the first PNP transistor Q1 is the output terminal of the shunt subunit, and the output terminal of the shunt subunit is connected to the reference terminal of the adjustable regulator D1.

[0044] More in detail, such as Figure 3As shown, the regulating subunit includes a fourth resistor R4 and a second PNP transistor Q2. The first terminal of the fourth resistor R4 is connected to the input terminal of the shunt subunit, and the first terminal of the fourth resistor R4 is connected to the input current I. in The first terminal of the fourth resistor R4 is connected to the first terminal of the third resistor R3, and the first terminal of the fourth resistor R4 is also connected to the first terminal of the first resistor R1. The second terminal of the fourth resistor R4 is connected to the emitter of the second PNP transistor Q2, and the base of the second PNP transistor Q2 outputs a bias voltage V. T The base of the second PNP transistor Q2 is connected to the driving terminal of the shunt unit, that is: the base of the second PNP transistor Q2 is connected to the base of the first PNP transistor Q1, the base of the second PNP transistor Q2 is also connected to the cathode of the adjustable voltage regulator D1, and the collector of the second PNP transistor Q2 is left floating.

[0045] like Figure 3 As shown, a fifth resistor R5 can also be set between the base of the second PNP transistor and the cathode of the adjustable regulator D1 to prevent the voltage on the adjustable regulator D1 from being too high and to limit the power on the adjustable regulator D1. The fifth resistor R5 can be omitted when the input voltage is not high or the power is not high.

[0046] It should be noted that the third resistor R3 is also placed at the base of the first PNP transistor Q1 (in order to improve the adhesion). Figure 3 Visibility, Figure 3 (not shown in the diagram), that is: the first end of the third resistor R3 is connected to the base of the first PNP transistor Q1, and the second end of the third resistor R3 is connected to the common terminal of the base of the second PNP transistor Q2 and the fifth resistor R5.

[0047] To prevent circuit oscillation, the shunt unit 220 also includes a first capacitor C1. The first end of the first capacitor C1 is connected to the collector of the first PNP transistor Q1, and the second end of the first capacitor C1 is connected to the second end of the fifth resistor R5. Phase compensation is performed through the first capacitor C1.

[0048] In detail, such as Figure 3 As shown, the reference terminal of the adjustable voltage regulator D1 is also connected to the common terminal of the first resistor R1 and the second resistor R2, and the anode of the adjustable voltage regulator D1 is connected to the second terminal of the second resistor R2.

[0049] Please see Figures 2 to 3 The working principle of the voltage regulator circuit with negative impedance characteristics provided by this invention is as follows:

[0050] like Figure 3 As shown, the input voltage V is controlled by the first resistor R1 and the second resistor R2. inVoltage division is performed. The shunt unit consisting of the third resistor R3 and the first PNP transistor Q1 is connected in parallel with the first resistor R1. The fourth resistor R4 is a sampling resistor for the input current I. in Sampling is performed by connecting the fourth resistor R4 to the second PNP transistor Q2, converting the sampling current collected by the fourth resistor R4 into a bias voltage V. T Bias voltage V T The base of the first PNP transistor Q1 is input to control the magnitude of the branch current of the shunt subunit, and the fifth resistor R5 is used for current limiting and voltage division.

[0051] When the input current I in Much greater than the current I flowing through the first resistor R1 R1 For example, when the input current I... in For I R1 100 times or 1000 times; the current I flowing through the fourth resistor R4 R4 With input current I in When the preset deviation threshold is met, i.e., I R4 ≈I in For the loop formed by the third resistor R3, the first PNP transistor Q1, the second PNP transistor Q2, and the fourth resistor R4, Kirchhoff's voltage theorem states that:

[0052] I R3 ×R3+V EB1 =I R4 ×R4+V EB2 (1)

[0053]

[0054] In expressions (1)-(2), I R3 The current flowing through the third resistor R3 is V. EB1 V is the voltage difference between the emitter and base of the first PNP transistor Q1. EB2 I represents the voltage difference between the emitter and base of the second PNP transistor Q2. R4 I is the current flowing through the fourth resistor R4, where R4 is the fourth resistor. in This is the input current.

[0055] Based on the connection point of the first resistor R1, the second resistor R2, the collector of the first PNP transistor Q1, and the reference terminal of the adjustable voltage regulator D1, Kirchhoff's current theorem states that:

[0056]

[0057] In expression (3), I R1 For the current flowing through the first resistor R1, I R2For the current flowing through the second resistor R2, I R3 R2 is the current flowing through the third resistor R3, and R2 is the second resistor. c1 I is the collector current of the first PNP transistor Q1. ref V is the reference current of the adjustable voltage regulator D1. ref β1 is the reference voltage of the adjustable regulator D1, and β1 is the current amplification factor of the first PNP transistor Q1.

[0058] Because the input terminal of the voltage divider unit 210 is the input voltage V in The input voltage V can be obtained. in As shown in expression (4):

[0059] V in =V R2 +V R1 (4)

[0060] In expression (4), V in V is the input voltage. R1 V is the voltage across the first resistor R1. R2 This is the voltage across the second resistor R2.

[0061] Since the voltage at the reference terminal of the adjustable voltage regulator D1 is equal to the voltage at the second resistor R2, we can equivalence equation (4) to obtain equation (5):

[0062] V in =V ref +R1×I R1 (5)

[0063] In expression (5), V in V is the input voltage. ref The reference voltage of the adjustable voltage regulator D1 is given by R1, and the resistance of the first resistor is given by I. R1 This is the current flowing through the first resistor R1.

[0064] Combining expressions (3) and (5), the input voltage V is calculated. in This yields expression (6):

[0065]

[0066] In expression (4), V in V is the input voltage. ref I is the reference voltage of the adjustable regulator D1. in For the input current, I ref V is the reference current of the adjustable voltage regulator D1. EB1 V is the voltage difference between the emitter and base of the first PNP transistor Q1. EB2β1 is the voltage difference between the emitter and base of the second PNP transistor Q2, β1 is the current amplification factor of the first PNP transistor Q1, R1 is the resistance of the first resistor R1, R2 is the resistance of the second resistor R2, R3 is the resistance of the third resistor R3, and R4 is the resistance of the fourth resistor R4.

[0067] Since β1 >> 1, and the first PNP transistor Q1 and the second PNP transistor Q2 are of the same type, V can be made EB1 ≈V EB2 Then expression (6) can be simplified to expression (7):

[0068]

[0069] In expression (7), V in For the input voltage, I in For the input current, I ref V is the reference current of the adjustable voltage regulator D1. ref R1 is the reference voltage of the adjustable voltage regulator D1, R2 is the resistance of the first resistor R1, R3 is the resistance of the third resistor R3, and R4 is the resistance of the fourth resistor R4.

[0070] From expression (7), it can be seen that the input voltage V in With input current I in Inversely proportional to the input voltage V in With input current I in The input voltage V decreases as the input voltage increases. in With input current I in The slope increases as the value decreases. This gives the voltage regulator circuit negative impedance characteristics.

[0071] The purpose of the voltage regulator circuit provided by this invention is twofold: First, to solve the problem of excessively low power input to the positioner under low input current, as lower input power increases the design difficulty of the positioner; this voltage regulator circuit increases the input voltage under low input current, thereby increasing the input power; the increased input power reduces the difficulty of low-power design for the entire positioner. Second, to solve the problem of excessively high equivalent impedance of the positioner under high input current, as excessively high impedance can lead to current signal distortion under high input current; this voltage regulator circuit reduces the input voltage under high input current, thereby reducing the equivalent impedance of the positioner.

[0072] The present invention also provides a two-wire valve positioner, which includes a voltage regulator circuit with negative impedance characteristics as described above, to improve the input power of the positioner at low input current and reduce the equivalent impedance at high input current.

[0073] This invention proposes a voltage regulator circuit with negative impedance characteristics and a two-wire valve positioner. The voltage regulator circuit includes a voltage divider unit and a current shunt unit. The voltage divider unit divides the input voltage, and the current shunt unit shunts the input current. These two units control the input voltage of the voltage regulator circuit, thereby adjusting the input power. Under the shunt effect of the current shunt unit, the input voltage is inversely proportional to the input current, giving the circuit a negative impedance characteristic. The voltage regulator circuit provided by this invention allows the input voltage to decrease as the input current increases, and the input voltage to increase as the input current decreases. This ensures that the input power of two-wire instruments does not increase with increasing input current, reducing power consumption and preventing energy waste. The equivalent impedance of the circuit is also prevented from becoming excessively high, enhancing system stability.

[0074] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A voltage regulator circuit with negative impedance characteristics, characterized in that, include: The voltage divider unit is used to divide the input voltage. A current shunt unit is connected to the voltage divider unit and performs current shunt processing on the input current at the input terminal of the voltage divider unit. An adjustable voltage regulator adjusts the input voltage through the voltage divider unit and the current shunt unit; The current shunting capability of the current shunting unit is configured such that, under the current shunting action of the current shunting unit, the input voltage is inversely proportional to the input current, so that the voltage regulator circuit has negative impedance characteristics.

2. The voltage regulator circuit with negative impedance characteristics according to claim 1, characterized in that, The current shunting unit includes a current shunting subunit and an adjustment subunit. The current shunting subunit is connected to the voltage divider unit and performs current shunting processing on the input current at the input terminal of the voltage divider unit to generate branch current. The regulating subunit is connected to the shunt subunit, samples the input current of the voltage regulator circuit, converts the sampled current into a bias voltage, and adjusts the branch current in the shunt subunit through the bias voltage.

3. The voltage regulator circuit with negative impedance characteristics according to claim 2, characterized in that, The voltage divider unit includes a first resistor and a second resistor. The first end of the first resistor is the first input terminal of the voltage divider unit, the second end of the first resistor is connected to the first end of the second resistor, the first end of the second resistor is the output terminal of the voltage divider unit, and the second end of the second resistor is the second input terminal of the voltage divider unit.

4. The voltage regulator circuit with negative impedance characteristics according to claim 3, characterized in that, The shunt subunit includes a third resistor and a first PNP transistor. The first end of the third resistor is the input terminal of the shunt subunit, the second end of the third resistor is connected to the emitter of the first PNP transistor, the base of the first PNP transistor is connected to the bias voltage, the collector of the first PNP transistor is the output terminal of the shunt subunit, and the output terminal of the shunt subunit is connected to the reference terminal of the adjustable voltage regulator.

5. The voltage regulator circuit with negative impedance characteristics according to claim 4, characterized in that, The regulating subunit includes a fourth resistor and a second PNP transistor. The first end of the fourth resistor is connected to the input terminal of the shunt subunit, and the second end of the fourth resistor is connected to the emitter of the second PNP transistor. The base of the second PNP transistor outputs the bias voltage. The base of the second PNP transistor is also connected to the cathode of the adjustable voltage regulator, and the collector of the second PNP transistor is left floating.

6. The voltage regulator circuit with negative impedance characteristics according to claim 5, characterized in that, The reference terminal of the adjustable voltage regulator is also connected to the common terminal of the first resistor and the second resistor, and the anode of the adjustable voltage regulator is connected to the second terminal of the second resistor.

7. The voltage regulator circuit with negative impedance characteristics according to claim 5, characterized in that, The expression for the input voltage is as follows: In the above expression, V in Where R1 is the input voltage, R2 is the resistance of the first resistor, R3 is the resistance of the third resistor, and R4 is the resistance of the fourth resistor. ref I is the voltage at the reference terminal of the adjustable regulator. in For the input current, I ref The current at the reference terminal of the adjustable voltage regulator is denoted as .

8. A two-wire valve positioner, characterized in that, The two-wire valve positioner includes a voltage regulator circuit with negative impedance characteristics as described in any one of claims 1-7.

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