Two-wire transmitter

Abstract

Power from an external circuit is effectively utilized. A two-wire transmitter connected to the external circuit via two transmission lines operates using an input voltage and a current signal supplied from the external circuit, the two-wire transmitter including a constant current circuit that controls the current signal based on a detection result of a sensor, and a shunt regulator circuit that controls a circuit voltage based on the input voltage, the shunt regulator circuit controlling the circuit voltage so that the circuit voltage becomes larger as the input voltage becomes larger.

Description

Technical Field

[0001] This invention relates to a two-wire transmitter. Background Technology

[0002] A two-wire transmitter is known, which is connected to an external circuit via two transmission lines and operates using input voltage and current signals supplied from the external circuit (see, for example, Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-99088 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In the two-wire transmitter of Patent Document 1, the circuit voltage of the internal circuit remains constant even if the input voltage changes. Therefore, when the input voltage is large (high), the power from the external circuit cannot be effectively utilized.

[0008] One aspect of the present invention provides a two-wire transmitter capable of efficiently utilizing power from an external circuit.

[0009] Methods for solving problems

[0010] One approach involves a two-wire transmitter connected to an external circuit via two transmission lines, operating using an input voltage and current signal supplied from the external circuit. The two-wire transmitter includes: a constant current circuit that controls the current signal based on sensor detection results; and a shunt regulator circuit that controls the circuit voltage based on the input voltage, such that the circuit voltage increases as the input voltage increases.

[0011] The effects of the invention

[0012] According to the present invention, power from an external circuit can be used efficiently. Attached Figure Description

[0013] Figure 1 This is a diagram illustrating an example of the schematic structure of a two-wire transmitter according to an embodiment.

[0014] Figure 2 This is a diagram illustrating an example of the circuit structure of a two-wire transmitter.

[0015] Figure 3 This is a diagram showing a modified example of the circuit structure.

[0016] Figure 4 This is a diagram showing a modified example of the circuit structure. Detailed Implementation

[0017] The embodiments will now be described with reference to the accompanying drawings. Identical elements will be labeled with the same reference numerals, and repeated descriptions will be omitted where appropriate.

[0018] Figure 1 This is a diagram illustrating an example of the schematic structure of a two-wire transmitter according to an embodiment. The two-wire transmitter 100 is used in conjunction with an external circuit 200.

[0019] The two-wire transmitter 100 is connected to the external circuit 200 via two transmission lines, L1 and L2. The connection points of the two-wire transmitter 100 to transmission lines L1 and L2 are illustrated as nodes N11 and N12.

[0020] The two-wire transmitter 100 operates using voltage and current supplied from external circuit 200. The voltage supplied from external circuit 200 to the two-wire transmitter 100 is illustrated as the input voltage Vin. The input voltage Vin is the voltage at node N11 when node N22 is used as a reference (described later). The current supplied from external circuit 200 to the two-wire transmitter 100 is illustrated as the current signal Iout. The current signal Iout is the current flowing from transmission line L1 to node N11. Details will be described later, but the current signal Iout is controlled by the two-wire transmitter 100.

[0021] External circuit 200 includes a power supply 201 and a resistor R1. In this example, power supply 201 is a voltage source with a supply voltage Eb. Power supply 201 and resistor R1 are connected in series between transmission line L1 and transmission line L2.

[0022] Additionally, connection can mean electrical connection within a non-contradictory scope. Furthermore, connection between elements can include electrical connection via other elements within a scope that does not impede the function of these elements.

[0023] A current signal Iout flows through resistor R1, generating a voltage in R1. The magnitude of the current signal Iout, controlled by the two-wire transmitter 100, is detected by measuring this voltage. Thus, information is transmitted from the two-wire transmitter 100 to the external circuit 200 using the current signal Iout.

[0024] The two-wire transmitter 100 includes: a sensor 1, an input voltage measurement circuit 2, a signal processing circuit 3, a constant current circuit 4, a reference voltage processing circuit 5, a shunt regulator circuit 6, and a comparator circuit 7. Alternatively, the sensor 1 can also be located externally to the two-wire transmitter 100.

[0025] Sensor 1 detects a physical quantity. Examples of physical quantities include pressure, temperature, and flow rate. Examples of sensor 1 include pressure sensors, temperature sensors, and flow sensors, and examples of the two-wire transmitter 100 include pressure transmitters, temperature transmitters, and flow transmitters. Sensor 1 generates and outputs a sensor signal S1 corresponding to the detection result. For example, the voltage of sensor signal S1 increases as the detected value of sensor 1 increases.

[0026] Input voltage measuring circuit 2 measures the voltage corresponding to the input voltage Vin. In this example, input voltage measuring circuit 2 is connected between node N11 and node N22 (described later), generating a voltage signal Vd corresponding to the input voltage Vin. The voltage signal Vd is sent from input voltage measuring circuit 2 to signal processing circuit 3 and is input to signal processing circuit 3.

[0027] The signal processing circuit 3 is configured to perform various signal processing operations. As an example, after performing linear correction and other processing on the sensor signal S1 from the sensor 1, the signal processing circuit 3 generates the current control signal S2, which will be described later. The signal processing circuit 3 can be a dedicated circuit design or it can be configured to include a general-purpose microcontroller, etc. Figure 1 In the example shown, signal processing circuit 3 generates various signals for controlling constant current circuit 4, reference voltage processing circuit 5, and shunt regulator circuit 6.

[0028] The control of the constant current circuit 4 is described below. The signal processing circuit 3 generates a current control signal S2 based on the sensor signal S1 from the sensor 1, which enables the constant current circuit 4 to control the current signal Iout. The current control signal S2 is sent from the signal processing circuit 3 to the constant current circuit 4 and is input to the constant current circuit 4.

[0029] The constant current circuit 4 controls the magnitude of the current signal Iout based on the current control signal S2 from the signal processing circuit 3, that is, based on the sensor signal S1, or more specifically, the detection result of the sensor 1. For example, the current signal Iout is controlled within the range of 4mA to 20mA. When the detection value of the sensor 1 is 0% of the set span, the current signal Iout is controlled at 4mA. When the detection value of the sensor 1 is 100% of the set span, the magnitude of the current signal Iout is controlled at 20mA. In other words, the signal processing circuit 3 generates the current control signal S2 to enable the constant current circuit 4 to control the current signal Iout in this way.

[0030] exist Figure 1In the example shown, the constant current circuit 4 is connected between nodes N11 and N12 and the signal processing circuit 3, the reference voltage processing circuit 5, the shunt regulator circuit 6, and the comparator circuit 7. The nodes opposite to nodes N11 and N12, separated by the constant current circuit 4, are referred to as nodes N21 and N22 in the diagram. The sensor 1, signal processing circuit 3, reference voltage processing circuit 5, shunt regulator circuit 6, and comparator circuit 7 are connected in parallel between nodes N21 and N22.

[0031] Additionally, the signal processing circuit 3, constant current circuit 4, reference voltage processing circuit 5, shunt regulator circuit 6, and comparator circuit 7 are sometimes referred to as internal circuits. Sensor 1 can also be one of the internal circuits.

[0032] Node N22 provides a common reference potential (COM) to the internal circuitry. The voltage at node N21 with reference to node N22 is illustrated as circuit voltage V1. Circuit voltage V1 provides the operating voltage for the internal circuitry. The operating voltage of the internal circuitry can be either the circuit voltage V1 itself or a voltage obtained by stepping down the circuit voltage V1 using a DC-DC converter or similar means. Furthermore, current corresponding to the current signal Iout flows from the constant current circuit 4 to node N21. That is, the internal circuitry operates using these voltages and currents. Additionally, when sensor 1 is located outside and connected to the two-wire transmitter 100, voltage and current are supplied from circuit voltage V1 to the external sensor 1.

[0033] This section describes the control of the reference voltage processing circuit 5 and the shunt regulator circuit 6 based on the signal processing circuit 3. The signal processing circuit 3 generates a voltage control signal Vs1 based on the voltage signal Vd from the input voltage measurement circuit 2, which is used to control the circuit voltage V1 of the reference voltage processing circuit 5 and the shunt regulator circuit 6. The voltage control signal Vs1 is sent from the signal processing circuit 3 to the reference voltage processing circuit 5 and is input to the reference voltage processing circuit 5.

[0034] The reference voltage processing circuit 5 generates a reference voltage signal Vref based on the voltage control signal Vs1 from the signal processing circuit 3. The reference voltage signal Vref is sent from the reference voltage processing circuit 5 to the shunt regulator circuit 6 and is input to the shunt regulator circuit 6.

[0035] The shunt regulator circuit 6 controls the circuit voltage V1 based on the voltage measured by the input voltage measuring circuit 2. In this example, the shunt regulator circuit 6 controls the circuit voltage V1 based on the reference voltage signal Vref, that is, based on the voltage control signal Vs1, the voltage signal Vd, and more specifically, the magnitude of the input voltage Vin. Specifically, the shunt regulator circuit 6 controls the circuit voltage V1 based on the comparison between the reference voltage signal Vref and the circuit voltage V1. The shunt regulator circuit 6 controls the circuit voltage V1 so that the circuit voltage V1 increases as the input voltage Vin increases. In other words, the reference voltage processing circuit 5 generates the reference voltage signal Vref, and the signal processing circuit 3 generates the voltage control signal Vs1, so that the shunt regulator circuit 6 controls the circuit voltage V1.

[0036] Comparator circuit 7 is used for detecting abnormalities in circuit voltage V1. Details will be provided later. Figure 2 Please provide an explanation.

[0037] In the two-wire transmitter 100 described above, the shunt regulator circuit 6 controls the circuit voltage V1 of the internal circuit so that the circuit voltage V1 increases as the input voltage Vin increases. If the circuit voltage V1 increases, the power available to the internal circuit also increases accordingly. Therefore, power from the external circuit 200 can be utilized effectively.

[0038] In the two-wire transmitter of Patent Document 1, the circuit voltage V1 is determined such that the operation of the internal circuit is achieved when the power supply voltage Eb of the power supply 201 of the external circuit 200 is minimized. Even if the power supply voltage Eb increases and the input voltage Vin increases, the value of the circuit voltage V1 remains constant. Therefore, the portion of power that increases with the input voltage Vin, more specifically, the power difference between the power based on the input voltage Vin and the power based on the circuit voltage V1, is consumed, for example, only as heat in the transistor (equivalent to transistor Q4 described later) within the constant current circuit 4. Even if the input voltage Vin increases, the power available to the internal circuit does not increase. This problem is addressed by the two-wire transmitter 100 according to the embodiment.

[0039] refer to Figure 2 An example illustrating the specific circuit structure of the two-wire transmitter 100.

[0040] Figure 2 This diagram illustrates an example of the circuit structure of a two-wire transmitter. It shows the circuit structure of the input voltage measurement circuit 2, the constant current circuit 4, the reference voltage processing circuit 5, and the shunt regulator circuit 6. Furthermore, the two-wire transmitter 100 includes a diode D1 and a reference voltage source P. R1Furthermore, the two-wire transmitter 100 can operate even without diode D1, and furthermore, even if the reference voltage source P... R1 Without resistors R6 and R7 (described later), the amplifier can operate simply by connecting the inverting terminal of Q2 to the reference potential (COM).

[0041] Diode D1 is a reverse current prevention diode connected between transmission line L1 and node N11, allowing current to flow from transmission line L1 to node N11. Reference voltage source P R1 Output reference voltage V R1 Reference voltage V R1 From the reference voltage source P R1 The current supplied to constant current circuit 4 is divided by resistors R6 and R7 (described later) and input to the inverting terminal of amplifier Q2.

[0042] The input voltage measurement circuit 2 includes resistors R15 and R16, and an analog-to-digital (A / D) converter 21. Resistors R15 and R16 are used to divide the input voltage Vin, and are connected in series between nodes N11 and N22. The input voltage Vin is divided by resistors R15 and R16 to become voltage Vdiv. Voltage Vdiv is input to the A / D converter 21. The A / D converter 21 converts the analog voltage Vdiv into a digital voltage signal Vd and outputs it. As described above, the voltage signal Vd is sent from the input voltage measurement circuit 2 to the signal processing circuit 3 and is input to the signal processing circuit 3.

[0043] By inputting voltage Vdiv to AD converter 21, the input withstand voltage of AD converter 21 can be reduced compared to directly inputting input voltage Vin to AD converter 21. Even when the input withstand voltage of AD converter 21 is greater than the input voltage Vin, the input voltage Vin can still be directly input to AD converter 21. Alternatively, a voltage divider for the input voltage Vin can be omitted, thus eliminating the need for resistors R15 and R16.

[0044] Furthermore, the function of the AD converter 21 can also be included in the signal processing circuit 3. In this case, the voltage Vdiv is directly input to the signal processing circuit 3, and the voltage signal Vd is obtained within the signal processing circuit 3. Alternatively, the AD converter 21 can be omitted without the conversion required by the AD converter 21. If resistors R15 and R16, as well as the AD converter 21, are not present, the input voltage measurement circuit 2 can also be constructed solely by the wiring connecting node N11 and the signal processing circuit 3.

[0045] Although Figure 2The capacitor is not shown, but it can also be connected in parallel with resistor R16. This can reduce noise and other noise contained in the input voltage Vin and suppress short-term voltage fluctuations input to the AD converter 21.

[0046] The constant current circuit 4 includes: a DA converter 41, resistors R3 to R8, amplifier Q2, transistor Q3, transistor Q4, and diode 42. Alternatively, diode 42 can be omitted, and this part can be directly connected to the reference potential (COM).

[0047] The DA converter 41 converts the digital current control signal S2 from the signal processing circuit 3 into an analog voltage signal Va and outputs it. Resistor R4 is connected between the DA converter 41 and the non-inverting terminal of amplifier Q2. Resistor R5 is connected between the connection point of resistor R4 and the non-inverting terminal of amplifier Q2 and node N12. Resistor R3 is a feedback resistor for amplifier Q2, connected between resistors R5 and R7 on the opposite side of amplifier Q2, separated by resistors R5 and R7. The voltage signal Va output by the DA converter 41 is divided by resistors R4, R5, and R3 and input to the non-inverting terminal of amplifier Q2.

[0048] Resistor R6 is connected to the reference voltage source P R1 Resistor R7 is connected between the inverting terminal of amplifier Q2 and node N22. The voltage source is P. R1 The reference voltage V R1 The voltage is divided by resistors R6 and R7 and input to the inverting terminal of amplifier Q2.

[0049] Amplifier Q2 is an error amplifier that detects the voltage obtained by dividing the voltage signal Va through resistors R4, R5, and R3, and the voltage obtained by dividing the reference voltage V through resistors R6 and R7. R1 The voltage difference (error) is obtained by voltage division. Based on this error, amplifier Q2, along with transistors Q3 and Q4, controls the current flowing through the internal circuitry.

[0050] Transistor Q3 is an NPN bipolar transistor. The base of transistor Q3 is connected to the output of amplifier Q2. The collector of transistor Q3 is connected to the base of transistor Q4. The emitter of transistor Q3 is connected to node N12 via diode 42. Diode 42 is connected between the emitter of transistor Q3 and node N12 to allow current to flow from the emitter of transistor Q3 to node N12.

[0051] Transistor Q4 is a PNP bipolar transistor. Transistor Q4 is connected between transmission line L1 and shunt regulator circuit 6, allowing current to flow between its collector and emitter from transmission line L1 to shunt regulator circuit 6. The base of transistor Q4 is connected to the collector of transistor Q3. The collector of transistor Q4 is connected to node N21. The emitter of transistor Q4 is connected to node N11. The voltage between the collector and emitter of transistor Q4 is referred to as voltage Vce in the diagram. The circuit voltage V1 is only slightly less than the input voltage Vin by voltage Vce.

[0052] Resistor R8 is connected between the collector and emitter of transistor Q4. Resistor R8 is connected in parallel with transistor Q4 and is used as a starting resistor to start the internal circuit.

[0053] The magnitude of the current signal Iout is controlled by controlling the emitter current of transistor Q4. The emitter current of transistor Q4 is controlled by the base current of transistor Q4. The base current of transistor Q4 is controlled by the collector current of transistor Q3. The collector current of transistor Q3 is controlled by the base current of transistor Q3. The base current of transistor Q3 is controlled by amplifier Q2. A voltage signal Va, which corresponds to the current control signal S2, the sensor signal S1, and more specifically, the voltage corresponding to the detection value of sensor 1, is input to the non-inverting terminal of amplifier Q2. For example, with such a circuit structure, the current signal Iout is controlled based on the detection value of sensor 1.

[0054] The reference voltage processing circuit 5 includes: a DA converter 51, an amplifier Q5, resistors R10 and R11. As described above, a voltage control signal Vs1 from the signal processing circuit 3 is supplied to the reference voltage processing circuit 5. The voltage control signal Vs1 is used to control the circuit voltage V1 via the shunt regulator circuit 6 so that the voltage Vce of transistor Q4 becomes a specified voltage at which transistor Q4 does not saturate. The specified voltage can be a constant voltage (e.g., 2V) or a variable voltage. The voltage control signal Vs1 can also be limited so that the circuit voltage V1 does not exceed the withstand voltage of the internal circuitry.

[0055] The DA converter 51 converts the digital voltage control signal Vs1 from the signal processing circuit 3 into an analog voltage control signal Vs2 and outputs it. The voltage control signal Vs2 is input to the non-inverting terminal of the amplifier Q5 and to the inverting terminal of the comparator Q8 of the comparator circuit 7, which will be described later.

[0056] Resistors R10 and R11 are connected in series between the output terminal of amplifier Q5 and node N22. Resistors R10 and R11 are also connected to the inverting terminal of amplifier Q5. Thus, amplifier Q5 provides negative feedback amplification of the voltage control signal Vs2. The voltage output by amplifier Q5 is illustrated as the reference voltage signal Vref. The reference voltage signal Vref is input to the non-inverting terminal of amplifier Q6 in the shunt regulator circuit 6, which will be described later.

[0057] In this example, the shunt regulator circuit 6 controls the circuit voltage V1 so that the voltage Vce of transistor Q4 is a specified voltage (e.g., 2V), and makes the circuit voltage V1 smaller than the input voltage Vin than the voltage Vce of transistor Q4. The shunt regulator circuit 6 includes resistors R13 and R14, amplifier Q6, and transistor Q7.

[0058] Resistors R13 and R14 are connected in series between nodes N21 and N22. Resistor R13 is connected between node N21 and the inverting terminal of amplifier Q6. Resistor R14 is connected between the inverting terminal of amplifier Q6 and node N22. The circuit voltage V1 is divided by resistors R13 and R14 and input to the inverting terminal of amplifier Q6, and also input to the non-inverting terminal of comparator Q8 in comparator circuit 7.

[0059] The reference voltage signal Vref from amplifier Q5 of reference voltage processing circuit 5 is input to the non-inverting terminal of amplifier Q6. Amplifier Q6 is an error amplifier, which controls the circuit voltage V1 together with transistor Q7 based on the difference (error) between the voltage obtained by dividing the circuit voltage V1 through resistors R13 and R14 and the reference voltage signal Vref.

[0060] Transistor Q7 is a PNP bipolar transistor or field-effect transistor (FET), specifically a PNP MOS (Metal-Oxide-Semiconductor) FET in this example. The gate (G) of transistor Q7 is connected to the output terminal of amplifier Q6. The source (S) of transistor Q7 is connected to node N21. The drain (D) of transistor Q7 is connected to node N22. The circuit voltage V1 increases as the current flowing through transistor Q7 (the current between the source and drain) decreases. The current flowing through transistor Q7 is controlled by its gate voltage. The gate voltage of transistor Q7 is controlled by amplifier Q6. A reference voltage signal Vref, corresponding to the voltage control signals Vs2, Vs1, and Vd (more specifically, the input voltage Vin), is input to the non-inverting terminal of amplifier Q6. For example, with this circuit structure, the circuit voltage V1 is controlled based on the input voltage Vin.

[0061] More specifically, the circuit voltage V1 increases as the input voltage Vin increases. As a result, the power available to the internal circuitry of the two-wire transmitter 100 increases. For example, the power obtained by multiplying the circuit voltage V1 by the current signal Iout can be utilized. As described above, in the internal circuitry, the circuit voltage V1 can be used, for example, after being converted by a DC-DC converter (not shown). In this case, the current on the output side (secondary side) of the DC-DC converter increases, and the available power increases accordingly.

[0062] Comparator circuit 7 includes comparator Q8. The non-inverting terminal of comparator Q8 receives a voltage obtained by dividing the circuit voltage V1 using resistors R13 and R14. The inverting terminal of comparator Q8 receives a voltage from reference voltage processing circuit 5; in this example, a voltage control signal Vs2 is input. Alternatively, a reference voltage signal Vref can be used instead of the voltage control signal Vs2. Comparator Q8 compares these voltages and outputs a voltage corresponding to the comparison result (e.g., low voltage or high voltage). The output voltage of comparator Q8 is input to signal processing circuit 3.

[0063] If the circuit voltage V1 decreases, the voltage input to the non-inverting terminal of comparator Q8 decreases, and the output voltage of comparator Q8 inverts. Signal processing circuit 3 detects the decrease (abnormality) of circuit voltage V1 by detecting the inversion of the output voltage of comparator Q8. For example, if the circuit voltage V1 continues to decrease, the internal circuitry may malfunction or stop. Signal processing circuit 3 performs pre-emptive measures to address such situations, such as maintaining the current value of sensor signal S1.

[0064] Since the two-wire transmitter 100 includes an input voltage measurement circuit 2, the signal processing circuit 3 can also detect abnormalities in the input voltage Vin. For example, if the input voltage Vin is above the withstand voltage of the constant current circuit 4, an abnormality in the input voltage Vin is detected. The detection result of the abnormal input voltage Vin can be notified (alarm notification) from the two-wire transmitter 100 to the external circuit 200. This notification can be made using the current signal Iout. If the voltage signal Vd is detected to be above the withstand voltage value, the signal processing circuit 3 controls the current signal Iout to make its magnitude outside the normal range of 4mA to 20mA (e.g., 3mA). The external circuit 200 detects the current signal Iout outside the normal range, thereby notifying the external circuit 200 of the abnormal input voltage Vin. By stopping the supply of voltage and current from the external circuit 200 to the two-wire transmitter 100, or by reducing the input voltage Vin below the withstand voltage value, the time when the abnormal input voltage Vin is applied to the constant current circuit 4 can be shortened. This results in an effect such as reducing the probability of failure of the two-wire transmitter 100.

[0065] As described above, in the two-wire transmitter 100, if the input voltage Vin increases, the circuit voltage V1 of the internal circuit also increases, thus enabling efficient utilization of power from the external circuit 200. An example of the calculation will be explained.

[0066] <Example of calculation>

[0067] The conditions are as follows.

[0068] (a) The minimum value of the power supply voltage Eb is 16.6V, and the maximum value is 42V.

[0069] (i) The resistance value of resistor R1 is 250Ω.

[0070] (ウ) The resistance of resistor R3 is 100Ω.

[0071] (エ) The forward voltage of diode D1 = 1V

[0072] (o) The ratio of the resistance value of resistor R15 to the resistance value of resistor R16 is 9:1 (Vdiv = Vin / 10)

[0073] (a) The resistance value of resistor R10 is sufficiently small compared to the resistance value of resistor R11 (gain of amplifier Q5 = 1).

[0074] (キ) The ratio of the resistance value of resistor R13 to the resistance value of resistor R14 is 9:1 (V1 = 10Vref)

[0075] (ク) The voltage Vce used for unsaturated transistor Q4 is 2V.

[0076] The voltage Vce of transistor Q4 is calculated by subtracting the circuit voltage V1 from the input voltage Vin, as shown in equation (1).

[0077] Vce = Vin - V1 (1)

[0078] The input voltage Vin is calculated using the voltage Vdiv as shown in equation (2) below.

[0079] Vin = Vdiv × 10 (2)

[0080] Since the gain of amplifier Q5 in reference voltage processing circuit 5 is 1, the voltage control signal Vs2 is equal to the reference voltage signal Vref. In addition, since the gain of shunt regulator circuit 6 is 10, the circuit voltage V1 is calculated using the voltage control signal Vs2 as shown in equation (3) below.

[0081] V1=Vs2×10 (3)

[0082] If we substitute equations (2) and (3) into equation (1) above, and further substitute Vce = 2V, then the voltage control signal Vs2 is calculated as shown in equation (4) below.

[0083] Vs2 = Vdiv - 0.2 (4)

[0084] Signal processing circuit 3 generates and outputs a voltage control signal Vs1 so that the voltage control signal Vs2 of equation (4) above can be obtained. Thus, while maintaining voltage Vce = 2V, the circuit voltage V1 can be increased proportionally to the input voltage Vin.

[0085] Calculate the available power. With a power supply voltage Eb = 16.6V (minimum) and a current signal Iout = 4mA, the input voltage Vin is calculated as shown in equation (5) below. In the equation, Eb_min is the minimum value of the power supply voltage Eb. R1 and R3 are the resistance values ​​of resistor R1 and resistor R3, respectively.

[0086] Vin=Eb_min-Iout×(R1+R3)-1V (5)

[0087] If the values ​​shown in the above conditions are substituted into equation (5) above, the input voltage Vin is 14.2V. The circuit voltage V1 is controlled to be 12.2V. At this time, the available power is 48.8mW (=V1×Iout). The same applies to the technology in Patent Document 1.

[0088] On the other hand, with the power supply voltage Eb = 42V (maximum value) and the current signal Iout = 4mA, according to the above formula (5), the input voltage Vin is 39.6V. The circuit voltage V1 is controlled to be 37.6V. The available power is 150.4mW (=V1×Iout). The available power increases. In the technology of Patent Document 1, even if the power supply voltage Eb increases, the circuit voltage V1 remains unchanged, so the available power is still 48.8mW. According to the two-wire transmitter 100 of the embodiment, the available power can be increased by about 3 times compared with the technology of Patent Document 1.

[0089] If the same calculation is performed with the current signal Iout = 20mA, the usable power when the power supply voltage Eb is at its minimum value is 172mW in both the two-wire transmitter 100 according to the embodiment and the technology of Patent Document 1. On the other hand, the usable power when the power supply voltage Eb is at its maximum value is 680mW in the two-wire transmitter 100 according to the embodiment, and still 172mW in the technology of Patent Document 1. According to the two-wire transmitter 100 according to the embodiment, the usable power can be increased by approximately four times compared to the technology of Patent Document 1.

[0090] The circuit structure of the two-wire transmitter 100 is not limited to that described above. Figure 2 The structure is described. Several variations are illustrated.

[0091] <First Variation>

[0092] Figure 3 This is a diagram showing a modified example of the circuit structure. Figure 3 The two-wire transmitter 100 shown is similar to the one described above. Figure 2 Compared to the previous structure, it has the following differences: it does not include the reference voltage processing circuit 5, the input voltage measurement circuit 2 includes a reference voltage source REF to replace the resistor R15, and on the other hand, it does not include the AD converter 21. The voltage Vdiv from the input voltage measurement circuit 2 is input to the non-inverting terminal of the amplifier Q6, and the inverting terminal of the amplifier Q6 is connected to node N21.

[0093] The voltage of the reference voltage source REF is illustrated as the reference voltage VREF. In this example, the reference voltage source REF is a Zener diode. The reference voltage VREF can be the same as the voltage Vce of transistor Q4 described earlier. A voltage Vdiv is generated that is smaller than the input voltage Vin than the reference voltage VREF. The voltage Vdiv is input to the non-inverting terminal of amplifier Q6 in shunt regulator circuit 6.

[0094] The amplifier Q6 in the shunt regulator circuit 6 controls the circuit voltage V1 so that the circuit voltage V1 becomes the voltage Vdiv. For example, if the reference voltage VREF is 2V, then while keeping the voltage Vce of transistor Q4 at 2V, the circuit voltage V1 can be increased proportionally to the input voltage Vin.

[0095] In addition, Figure 3 In the example shown, the voltage control signal Vs2 is directly generated by signal processing circuit 3. However, as described above... Figure 2 Similarly, signal processing circuit 3 can also generate voltage control signal Vs1. This is achieved by placing a DA converter (equivalent to...) between signal processing circuit 3 and comparator circuit 7. Figure 2 The voltage control signal Vs1 can be converted into voltage control signal Vs2 by the DA converter 51, and then input to the inverting terminal of comparator Q8 of comparator circuit 7.

[0096] according to Figure 3 The two-wire transmitter 100 shown does not require the same features as the one referenced earlier. Figure 1 as well as Figure 2 As described above, the shunt regulator circuit 6 is controlled by the signal processing circuit 3 via the reference voltage processing circuit 5. Therefore, the reference voltage processing circuit 5 is not required. Furthermore, the AD converter 21 of the input voltage measurement circuit 2 is also not required. Figure 2 This achieves the effect of component reduction.

[0097] <Second Variation>

[0098] Figure 4 This is a diagram showing a modified example of the circuit structure. Figure 4 The two-wire transmitter 100 shown is similar to the one described above. Figure 2 Compared to the previous structure, it has the following differences: it does not include the reference voltage processing circuit 5, the input voltage measurement circuit 2 does not include the AD converter 21, and the voltage Vdiv from the input voltage measurement circuit 2 is input to the non-inverting terminal of the amplifier Q6 of the shunt regulator circuit 6.

[0099] The circuit voltage V1 is controlled by changing the gain of the input voltage measuring circuit 2, i.e., the ratio of the resistance values ​​of resistor R15 and resistor R16, and the gain of the shunt regulator circuit 6, i.e., the ratio of the resistance values ​​of resistor R13 and resistor R14.

[0100] For example, if the input voltage Vin is set to 10V, the ratio of the resistance values ​​of resistor R15 and resistor R16 is set to 9:1, and the ratio of the resistance values ​​of resistor R13 and resistor R14 in the shunt regulator circuit 6 is set to 7:1, then the voltage Vdiv, circuit voltage V1, and voltage Vce are calculated as follows (6) to (8).

[0101] Vdiv=Vin×1 / 10=1V (6)

[0102] V1 = Vdiv × 8 = 8V (7)

[0103] Vce=Vin-V1=2V (8)

[0104] The voltage Vce of transistor Q4 is 2V, and the circuit voltage V1 is controlled to be 2V lower than the input voltage Vin. Figure 4 The structure of the two-wire transmitter 100 shown is similar to that described above. Figure 3 Compared to the previous structure, this design reduces the input voltage of amplifier Q6 in the shunt regulator circuit 6. Consequently, lower voltage-rated components can be used.

[0105] <Other variations>

[0106] Regarding the generation of each signal, the method is not limited to the above-described embodiment and various methods can be used. For example, in the above embodiment, the use of DA converter 41 and DA converter 51 in the generation of voltage signal Va and voltage control signal Vs2 is described as an example. However, instead of DA converter 41 and DA converter 51, for example, PWM (Pulse Width Modulation) control and LPF (Low Pass Filter) as shown in Patent Document 1 can be used, or various other known methods can be used. The functions of DA converter 41 and DA converter 51 can also be implemented within the signal processing circuit 3.

[0107] For example, the technology described above can be defined as follows. One of the disclosed technologies is a two-wire transmitter 100. (See reference...) Figure 1 As explained, the two-wire transmitter 100 is connected to the external circuit 200 via two transmission lines L1 and L2, and operates using the input voltage Vin and current signal Iout supplied from the external circuit 200. The two-wire transmitter 100 includes a constant current circuit 4 that controls the current signal Iout based on the detection result of the sensor 1, and a shunt regulator circuit 6 that controls the circuit voltage V1 based on the input voltage Vin. The shunt regulator circuit 6 controls the circuit voltage V1 so that the circuit voltage V1 increases as the input voltage Vin increases.

[0108] According to the two-wire transmitter 100 described above, the circuit voltage V1 increases as the input voltage Vin increases. If the circuit voltage V1 increases, the power available to the internal circuit also increases accordingly. Therefore, power from the external circuit 200 can be utilized effectively.

[0109] For reference Figure 1 , Figure 2 as well as Figure 4 As explained, the two-wire transmitter 100 includes an input voltage measuring circuit 2 that measures the voltage corresponding to the input voltage Vin, and the shunt regulator circuit 6 can control the circuit voltage V1 based on the voltage measured by the input voltage measuring circuit 2. For example, the circuit voltage V1 can be controlled using the voltage measurement result based on such an input voltage measuring circuit 2.

[0110] For reference Figure 2 As explained, the constant current circuit 4 includes a transistor Q4 connected between the transmission line L1 and the shunt regulator circuit 6, allowing current between the collector and emitter to flow from the transmission line L1 to the shunt regulator circuit 6. The shunt regulator circuit 6 controls the circuit voltage V1 so that the collector-emitter voltage Vce of the transistor Q4 in the constant current circuit 4 becomes a predetermined voltage, and makes the circuit voltage V1 smaller than the collector-emitter voltage Vce of the transistor Q4 than the input voltage Vin. This suppresses saturation of the transistor Q4 and controls the circuit voltage V1.

[0111] For reference Figure 3 As explained, the input voltage measuring circuit 2 generates a voltage Vdiv that is smaller than the input voltage Vin by a specified voltage (e.g., the reference voltage VREF of the reference voltage source REF). The shunt regulator circuit 6 can control the circuit voltage V1 so that the circuit voltage V1 becomes the voltage Vdiv generated by the input voltage measuring circuit 2. Therefore, for example, the reference voltage processing circuit 5, which supplies the reference voltage signal Vref to the shunt regulator circuit 6, is not required. Furthermore, the AD converter 21 of the input voltage measuring circuit 2 is also unnecessary. This results in a reduction of components. Additionally, in Figure 4 In this way, the reference voltage processing circuit 5 and the AD converter 21 are not required, and the component reduction effect can be achieved.

[0112] Explanation of reference numerals in the attached figures

[0113] L1 transmission line

[0114] L2 transmission line

[0115] 100 dual-line transmitter

[0116] 1 sensor

[0117] 2 Input Voltage Measurement Circuit

[0118] R15 resistor

[0119] R16 resistor

[0120] 21AD converter

[0121] REF reference voltage source

[0122] 3. Signal processing circuit

[0123] 4. Constant Current Circuit

[0124] 41DA converter

[0125] R4 resistor

[0126] R5 resistor

[0127] R6 resistor

[0128] R7 resistor

[0129] Q2 amplifier

[0130] Q3 transistor

[0131] Q4 transistor

[0132] R8 resistor

[0133] 42 diodes

[0134] 5. Reference Voltage Processing Circuit

[0135] 51DA Converter

[0136] Q5 amplifier

[0137] R10 resistor

[0138] R11 resistor

[0139] 6-way regulator circuit

[0140] R13 resistor

[0141] R14 resistor

[0142] Q6 amplifier

[0143] Q7 transistor

[0144] 7 Comparator Circuit

[0145] Q8 comparator

[0146] 200 external circuits

[0147] 201 power supply

[0148] R1 resistor

Claims

1. A two-wire transmitter connected to an external circuit via two transmission lines, operating using an input voltage and a current signal supplied from the external circuit, the two-wire transmitter comprising: a constant current circuit that controls the current signal in accordance with a detection result of a sensor; and a shunt regulator circuit that controls a circuit voltage in accordance with the input voltage, the shunt regulator circuit controls the circuit voltage so that the circuit voltage becomes larger as the input voltage becomes larger, the constant current circuit includes a transistor connected between the transmission lines and the shunt regulator circuit so that a current flowing through the transistor flows from the transmission lines to the shunt regulator circuit, the shunt regulator circuit controls the circuit voltage so that a voltage between terminals of the transistor of the constant current circuit becomes a prescribed voltage, and so that the circuit voltage is smaller than the input voltage by the prescribed voltage, and the prescribed voltage is a voltage at which the transistor does not become a saturation state.

2. The two-wire transmitter according to claim 1, wherein the two-wire transmitter includes an input voltage measurement circuit that measures a voltage corresponding to the input voltage, and the shunt regulator circuit controls the circuit voltage based on the voltage measured by the input voltage measurement circuit.

3. The two-wire transmitter according to claim 2, wherein the input voltage measurement circuit generates a voltage that is smaller than the input voltage by the prescribed voltage, and the shunt regulator circuit controls the circuit voltage so that the circuit voltage becomes the voltage generated by the input voltage measurement circuit.

4. The two-wire transmitter according to claim 2, wherein the two-wire transmitter further includes a signal processing circuit that detects an abnormality of the input voltage based on the voltage measured by the input voltage measurement circuit. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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