Dynamic power supply circuit and two-wire electromagnetic flowmeter

Abstract

The present invention provides a dynamic power supply circuit and a two-wire electromagnetic flowmeter. In the dynamic power supply circuit provided by the present invention, while providing voltage to the outside through a closed-loop electronic circuit, the output voltage can also be compensated and corrected through feedback regulation of the closed-loop electronic circuit, so that the output voltage remains stable, effectively improving the output voltage stability; the closed-loop energy storage subcircuit can dynamically store the electric energy that is shunted and wasted in the current loop, fully utilizing the energy of the output current of the current loop, and effectively improving the power supply performance and efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of instruments and meters, and in particular to a dynamic power taking circuit and a two-wire electromagnetic flowmeter. Background Art

[0002] The characteristics of two-wire instruments indicate that only two cables are required for external connections. These cables provide both 24VDC power distribution and 4-20mA current output. The instrument's overall load current is also reflected in these two cables. If the instrument's overall load current exceeds 4mA, this current will flow through these two cables, and the instrument's 4-20mA current loop will not be able to output 4mA (generally, 4mA represents the lower limit of the instrument's measurement range). To address this issue, the industry's general approach is to control the overall load current of two-wire instruments to around 3.5 (less than 4) mA. If the full 4mA is not reached, a 0.5mA reserve is reserved for alarm output.

[0003] To control the instrument's load current to around 3.5mA, instrument functionality must be simplified. Typically, two-wire instruments only feature a 4-20mA current output and HART communication. Furthermore, high-power devices such as highly flexible dot-matrix displays and high-performance A / D converters cannot be used. When the 4-20mA current loop output current (X mA (X not greater than 20)) exceeds 4mA, in addition to the 3.5mA consumed by the instrument itself, the remaining (X - 3.5)mA is shunted through this loop and wasted. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a dynamic power supply technical solution to solve the above-mentioned technical problems.

[0005] To achieve the above and other related objectives, the present invention provides a dynamic power extraction circuit for extracting and storing power from a current loop, comprising:

[0006] A closed-loop electronic circuit is connected to the current loop and provides a first voltage and a first current to an external load;

[0007] The closed-loop energy storage subcircuit is connected to the current loop and the closed-loop electronic circuit, and dynamically adjusts and stores the first current according to the current in the current loop.

[0008] Optionally, the closed-loop electronic circuit includes an NPN transistor; the NPN transistor is connected to the current loop, the collector of the NPN transistor is connected to the positive pole of the power supply in the current loop through a first resistor, and the emitter of the NPN transistor is grounded through a second resistor.

[0009] Optionally, the closed-loop electronic circuit further includes:

[0010] a first operational amplifier, the output end of which is connected to the base of the NPN transistor;

[0011] a third resistor, one end of which is connected to the collector of the NPN transistor and the other end of which is connected to the non-inverting input terminal of the first operational amplifier;

[0012] a fourth resistor, one end of which is grounded and the other end of which is connected to the non-inverting input terminal of the first operational amplifier;

[0013] a fifth resistor, one end of which is connected to the second voltage and the other end of which is connected to the inverting input terminal of the first operational amplifier;

[0014] The closed-loop electronic circuit provides the first voltage and the first current to the external load through the collector of the NPN transistor and the ground.

[0015] Optionally, the positive power supply terminal of the first operational amplifier is connected to the collector of the NPN transistor, and the negative power supply terminal of the operational amplifier is grounded.

[0016] Optionally, the third voltage and the first voltage satisfy the relationship:

[0017] Wherein, V1 represents the first voltage, V2 represents the second voltage, R3 represents the third resistor, and R4 represents the fourth resistor.

[0018] Optionally, the closed-loop energy storage subcircuit includes a PMOS tube and a capacitor, the source of the PMOS tube is connected to the collector of the NPN transistor, the drain of the PMOS tube is connected to one end of the capacitor, and the other end of the capacitor is grounded; the gate voltage of the PMOS tube is adjusted to control the magnitude of the first current flowing through the PMOS tube.

[0019] Optionally, the closed-loop energy storage subcircuit further includes:

[0020] a sixth resistor;

[0021] a second operational amplifier, an output end of which is connected to the gate of the PMOS transistor via the sixth resistor;

[0022] a seventh resistor, one end of which is connected to the emitter of the NPN transistor and the other end of which is connected to the inverting input terminal of the second operational amplifier;

[0023] an eighth resistor, one end of which is connected to the inverting input terminal of the second operational amplifier and the other end of which is connected to the output terminal of the second operational amplifier;

[0024] a ninth resistor, one end of which is connected to the collector of the NPN transistor and the other end of which is connected to the non-inverting input terminal of the second operational amplifier;

[0025] A tenth resistor has one end connected to the non-inverting input terminal of the second operational amplifier and the other end grounded.

[0026] Optionally, the output voltage of the second operational amplifier satisfies the following relationship:

[0027]

[0028] Among them, V3 represents the collector voltage of the NPN transistor, V4 represents the output voltage of the second operational amplifier, R7 represents the seventh resistor, R8 represents the eighth resistor, R9 represents the ninth resistor, and R10 represents the tenth resistor.

[0029] Optionally, R7=R8=R9=R10.

[0030] In addition, to achieve the above-mentioned purpose and other related purposes, the present invention also provides a two-wire electromagnetic flowmeter, which includes the dynamic closed-loop power supply circuit described in any one of the above-mentioned items.

[0031] As described above, the dynamic power supply circuit of the present invention has the following beneficial effects:

[0032] While providing the first voltage and the first current to the outside through the closed-loop electronic circuit, the first current can also be dynamically adjusted and stored according to the current in the current loop through a closed-loop energy storage subcircuit connected to the current loop and the closed-loop electronic circuit, and the wasted current in the current loop can be effectively transferred to the first current for storage and application, thereby improving the utilization efficiency of the output current in the current loop. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Shown is a dynamic power supply circuit diagram of the 4-20mA current loop of the electromagnetic flowmeter in an embodiment of the present invention.

[0034] Description of Reference Numerals

[0035] C capacitor

[0036] R1 first resistor

[0037] R2 Second resistor

[0038] R3 third resistor

[0039] R4 fourth resistor

[0040] R5 fifth resistor

[0041] R6 Sixth resistor

[0042] R7 seventh resistor

[0043] R8 eighth resistor

[0044] R9 ninth resistor

[0045] R10 tenth resistor

[0046] R11 eleventh resistor

[0047] R12 equivalent resistance

[0048] Q1, Q3 NPN transistors

[0049] Q2 PMOS tube

[0050] U1 first operational amplifier

[0051] U2 Second operational amplifier

[0052] V1 first voltage

[0053] V2 Second voltage

[0054] V3 Collector voltage of NPN transistor Q1

[0055] V4 Output voltage of the second operational amplifier U2

[0056] I1 first current

[0057] 1 Output of the first operational amplifier U1

[0058] 2 Inverting input of the first operational amplifier U1

[0059] 3. The non-inverting input of the first operational amplifier U1

[0060] 4 Negative power supply terminal of the first operational amplifier U1

[0061] 8 Positive power supply terminal of the first operational amplifier U1

[0062] 5. The non-inverting input of the second operational amplifier U2

[0063] 6 The inverting input of the second operational amplifier U2

[0064] 7 Output of the second operational amplifier U2 DETAILED DESCRIPTION

[0065] As mentioned in the background section, the industry generally limits the overall power consumption of two-wire instruments (such as two-wire electromagnetic flowmeters) to less than 3.5mA. Regardless of the output state of the 4-20mA current loop, the two-wire instrument itself maintains a current consumption of approximately 3.5mA, with the excess being shunted and wasted. Therefore, the performance of two-wire instruments is generally weaker than that of their four-wire counterparts.

[0066] Based on this, the present invention proposes a dynamic power-collection solution that dynamically stores the current diverted from the current loop and dynamically controls the charging current based on the output current of the current loop, aiming to maximize the utilization of the current loop output current. This stored energy is then used to increase the processing power of the electromagnetic flowmeter, based on its actual needs, thereby improving the overall performance of the two-wire electromagnetic flowmeter.

[0067] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0068] See also Figure 1 . It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner, so the diagrams only show the electronic components related to the present invention rather than being drawn according to the type, number and layout of the components during actual implementation. During actual implementation, the type, quantity and layout of each electronic component can be changed at will, and the layout type may also be more complicated. The structural form, quantity and layout of the electronic components illustrated in the diagrams attached to this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which the present invention can be implemented. Therefore, they have no technical significance. Any modification or simple addition or subtraction of the structural electronic components should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0069] like Figure 1 As shown, the present invention provides a dynamic power supply circuit for supplying power from a current loop and storing the power, which includes:

[0070] Closed loop electronic circuit ( Figure 1 The portion indicated by the dotted line box on the left side of the middle circuit is connected to the current loop and provides a first voltage V1 and a first current I1 to an external load;

[0071] Closed-loop energy storage subcircuit ( Figure 1 The portion shown by the dotted box on the right side of the middle circuit is connected to the current loop and the closed-loop electronic circuit, and dynamically adjusts and stores the first current I1 according to the current in the current loop.

[0072] In detail, such as Figure 1 As shown, the closed-loop electronic circuit includes an NPN transistor Q1; the NPN transistor Q1 is connected to the current loop, the collector of the NPN transistor Q1 is connected to the positive pole (such as 24V+) of the power supply in the current loop through the first resistor R1, and the emitter of the NPN transistor Q1 is grounded through the second resistor R2.

[0073] In more detail, Figure 1 As shown, the closed-loop electronic circuit also includes:

[0074] The first operational amplifier U1 has an output terminal 1 connected to the base of the NPN transistor Q1;

[0075] A third resistor R3, one end of which is connected to the collector of the NPN transistor Q1 and the other end of which is connected to the non-inverting input terminal 3 of the first operational amplifier U1;

[0076] A fourth resistor R4, one end of which is grounded and the other end of which is connected to the non-inverting input terminal 3 of the first operational amplifier U1;

[0077] a fifth resistor R5, one end of which is connected to the second voltage V2 and the other end of which is first connected to the inverting input terminal 2 of the operational amplifier U1;

[0078] The closed-loop electronic circuit provides a first voltage V1 and a first current I1 to the outside through the collector of the NPN transistor Q1 and the ground.

[0079] In more detail, Figure 1 As shown, the positive power supply terminal 8 of the first operational amplifier U1 is connected to the collector of the NPN transistor Q1, and the negative power supply terminal 4 of the operational amplifier Q1 is grounded.

[0080] In detail, such as Figure 1 As shown, when the entire closed-loop electronic circuit is normally connected and powered on, for the first operational amplifier U1, according to the "virtual short circuit", the second voltage V2 and the first voltage V1 satisfy the relationship:

[0081]

[0082] According to the above relationship, the value of the first voltage V1 is determined by the values of the second voltage V2, the third resistor R3 and the fourth resistor R4. By adjusting the values of the second voltage V2, the third resistor R3 and the fourth resistor R4, the value of the first voltage V1 can be effectively adjusted, which can be flexibly selected according to design requirements.

[0083] Optionally, in one embodiment of the present invention, a first voltage V1 of +12V needs to be provided externally; correspondingly, the provided second voltage V2 is +2.5V, the third resistor R3 is 300KΩ, and the fourth resistor R4 is 82KΩ.

[0084] In detail, such as Figure 1 As shown, the closed-loop energy storage subcircuit includes a PMOS transistor Q2 and a capacitor C. The source of the PMOS transistor Q2 is connected to the collector of the NPN transistor Q1, the drain of the PMOS transistor Q2 is connected to one end of the capacitor C, and the other end of the capacitor C is grounded. The gate voltage of the PMOS transistor Q2 is adjusted to control the magnitude of the first current I1 flowing through the PMOS transistor Q2.

[0085] Among them, capacitor C is the main storage capacitor and its capacitance is very large, generally not less than 2200uF, and the stored electrical energy is The turn-on voltage of PMOS tube Q2 is V GS =-2.7V.

[0086] In detail, such as Figure 1 As shown, the closed-loop energy storage subcircuit also includes:

[0087] a sixth resistor R6;

[0088] The second operational amplifier U2 has an output terminal 7 connected to the gate of the PMOS transistor Q2 via a sixth resistor R6, and applies the output voltage V4 to the gate of the PMOS transistor Q2;

[0089] a seventh resistor R7, one end of which is connected to the emitter of the NPN transistor Q1 and the other end of which is connected to the inverting input terminal 6 of the second operational amplifier U2;

[0090] an eighth resistor R8, one end of which is connected to the inverting input terminal 6 of the second operational amplifier U2, and the other end of which is connected to the output terminal 7 of the second operational amplifier U2;

[0091] a ninth resistor R9, one end of which is connected to the collector of the NPN transistor Q1 and the other end of which is connected to the non-inverting input terminal 5 of the second operational amplifier U2;

[0092] The tenth resistor R10 has one end connected to the non-inverting input terminal 5 of the second operational amplifier U2 and the other end grounded.

[0093] In detail, such as Figure 1 As shown, when the entire closed-loop energy storage subcircuit is normally connected and powered on, for the second operational amplifier U2, according to the "virtual short", the output voltage V4 of the second operational amplifier satisfies the following relationship:

[0094]

[0095]

[0096] Among them, V3 represents the collector voltage of the NPN transistor Q1 (that is, the voltage across the second resistor R2), V4 represents the output voltage of the second operational amplifier U2, R7 represents the seventh resistor, R8 represents the eighth resistor, R9 represents the ninth resistor, and R10 represents the tenth resistor.

[0097] Alternatively, in one embodiment of the present invention, R7=R8=R9=R10, then:

[0098] V4 = V1 - V3;

[0099] In detail, such as Figure 1 As shown, the negative electrode of the power supply (such as 24V-) in the current loop is grounded after passing through the eleventh resistor R11.

[0100] In detail, the capacitor C is connected in parallel with the external load. In one embodiment of the present invention, Figure 1 As shown, capacitor C is connected in parallel with the electromagnetic flowmeter's total load equivalent resistor R12. A first current I1 exceeding the electromagnetic flowmeter's total load current (e.g., 3.5 mA) is stored in capacitor C. Capacitor C then outputs the first current I1 to the electromagnetic flowmeter's total load equivalent resistor R12. The magnitude of the first current I1 is controlled by adjusting the gate voltage of the PMOS transistor Q2. The electromagnetic flowmeter's total load equivalent resistor R12 primarily includes the electromagnetic flowmeter's excitation load and measurement load.

[0101] The working principle of the entire circuit will be analyzed in detail below.

[0102] For closed-loop electronic circuits, Figure 1 As shown, in the closed-loop electronic circuit, the third resistor R3, the fourth resistor R4, the first operational amplifier U1 and the NPN transistor Q1 form a complete closed-loop system, which can effectively perform feedback regulation on the output first voltage V1. The feedback regulation logic is as follows:

[0103] 1) The current flowing through the equivalent resistance R12 of the electromagnetic flowmeter's load increases → the first voltage V1 decreases → the input voltage of the non-inverting input terminal 3 of the first operational amplifier U1 decreases → the output voltage of the output terminal 1 of the first operational amplifier U1 decreases → the base input voltage of the NPN transistor Q1 decreases → the collector-emitter junction on-resistance of the NPN transistor Q1 increases → the current flowing through the collector-emitter junction of the NPN transistor Q1 decreases → the first voltage V1 increases;

[0104] 2) The current flowing through the equivalent resistance R12 of the electromagnetic flowmeter's entire load decreases → the first voltage V1 increases → the input voltage of the non-inverting input terminal 3 of the first operational amplifier U1 increases → the output voltage of the output terminal 1 of the first operational amplifier U1 increases → the base input voltage of the NPN transistor Q1 increases → the collector-emitter junction on-resistance of the NPN transistor Q1 decreases → the current flowing through the collector-emitter junction of the NPN transistor Q1 increases → the first voltage V1 decreases.

[0105] It can be seen that the negative feedback process based on the closed-loop electronic circuit can keep the value of the first voltage V1 relatively stable.

[0106] When the entire circuit is connected normally and powered on, Figure 1 As shown, the V / I conversion circuit, the NPN transistor Q3, the NPN transistor Q1, the second resistor R2 and the eleventh resistor R11 form a current loop, and the NPN transistor Q3, the NPN transistor Q1, the second resistor R2 and the eleventh resistor R11 form a shunt path.

[0107] In order to enable the two-wire electromagnetic flowmeter to have the basic function of outputting 4mA current, the load current of the electromagnetic flowmeter is generally controlled at around 3.5mA. Figure 1 This 3.5mA current essentially flows only through the electromagnetic flowmeter's load (i.e., equivalent resistor R12) and ultimately returns to the negative terminal of the power supply, "24V-," completing a complete circuit. At this point, the current flowing through the shunt path formed by NPN transistor Q3, NPN transistor Q1, second resistor R2, and eleventh resistor R11 is very small (<0.5mA).

[0108] When the output current of the current loop is greater than 4mA (denoted as XmA), since the load current of the entire electromagnetic flowmeter is still about 3.5mA, that is, the current flowing through the equivalent resistor R12 is still 3.5mA, the remaining (X-3.5)mA current must return to the negative pole "24V-" of the power supply through the shunt path composed of the NPN transistor Q3, the NPN transistor Q1, the second resistor R2 and the eleventh resistor R11, forming a current loop and being directly wasted.

[0109] The main purpose of the present invention is to store this part of the diverted (X-3.5) mA current in the capacitor C first, and then use this part of the electric energy to further improve the working performance of the electromagnetic flowmeter.

[0110] For the closed-loop energy storage sub-circuit, the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9, the tenth resistor R10, the second operational amplifier U2, and the PMOS transistor Q2 form a closed-loop feedback control system. When the shunt current passes through the second resistor R2 (the sampling resistor of the shunt path), a sampling voltage V3 (i.e., the collector voltage of the NPN transistor Q1) is generated. The closed-loop feedback control system then generates a driving voltage V4 (i.e., the output voltage of the second operational amplifier U2) to control the on-resistance of the PMOS transistor Q2, thereby regulating the charging current of the capacitor C2 (i.e., the first current I1). When the output current of the current loop is 4 mA, the PMOS tube Q2 is in the cut-off state and the capacitor C is not charged. The capacitor C is charged only when the output current of the current loop is greater than 4 mA, and the magnitude of the charging current (i.e., the first current I1) is directly related to the output state of the current loop. The larger the output current of the current loop, the larger the charging current (i.e., the first current I1), and the smaller the output current of the current loop, the smaller the charging current (i.e., the first current I1).

[0111] In detail, such as Figure 1 As shown, according to the formula V4=V1-V3, when the output current of the current loop increases, the current flowing through the shunt path will increase, and the collector voltage V3 of the NPN transistor Q1 will also increase accordingly, then the gate voltage V4 of the PMOS tube Q2 (that is, the output voltage of the second operational amplifier U2) will decrease. When the source input voltage of the PMOS tube Q2 is constant at the first voltage V1, the smaller its gate voltage V4 is, the smaller its gate-source voltage V GS The more negative the voltage increases, the smaller the on-resistance of the PMOS tube Q2 will be, causing the first current I1 (i.e., the charging current) to increase. Conversely, when the output current of the current loop decreases, the first current I1 (i.e., the charging current) will eventually decrease. When the output current of the current loop is 4 mA, the current flowing through the shunt path is zero, V3 = 0, V4 = V1, the PMOS tube Q2 is in the cut-off state, and the capacitor C is not charged.

[0112] It can be seen that the negative feedback process based on the above-mentioned closed-loop energy storage sub-circuit can monitor the current in the shunt path in real time, and dynamically adjust the first current I1 (i.e., charging current) according to the current in the shunt path, and "transfer" the current in the shunt path to the first current I1 (i.e., charging current) and store it in the capacitor C, which can maximize the utilization of the energy of the current loop output current and effectively improve the power supply performance and efficiency.

[0113] Meanwhile, the specific structures of the V / I conversion circuit and the current loop can refer to the existing technology and will not be described in detail here.

[0114] In addition, to achieve the above-mentioned purpose and other related purposes, the present invention also provides a two-wire electromagnetic flowmeter, which includes the above-mentioned dynamic power supply circuit, and the above-mentioned closed-loop electronic circuit can provide a stable operating voltage for the two-wire electromagnetic flowmeter; through the closed-loop energy storage sub-circuit, the electric energy wasted by the diversion in the current loop can be dynamically stored, and the energy of the current loop output current can be fully utilized, thereby effectively improving the performance of the two-wire electromagnetic flowmeter.

[0115] To sum up, in the dynamic power supply circuit provided by the present invention, while providing voltage to the outside through the closed-loop electronic circuit, the output voltage can also be compensated and corrected through the feedback adjustment of the closed-loop electronic circuit, so that the output voltage remains stable, effectively improving the output voltage stability; the closed-loop energy storage sub-circuit can dynamically store the electric energy that is shunted and wasted in the current loop, fully utilizing the energy of the output current of the current loop, and effectively improving the power supply performance and efficiency.

[0116] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may 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 one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A dynamic power circuit that draws power from a current loop and stores it, characterized in that: include: A closed-loop electronic circuit is connected to the current loop and provides a first voltage and a first current to an external load; a closed-loop energy storage subcircuit, connected to the current loop and the closed-loop electronic circuit, and dynamically adjusting and storing the first current according to the current in the current loop; The closed-loop electronic circuit includes an NPN transistor Q1; the NPN transistor Q1 is connected to the current loop, the collector of the NPN transistor Q1 is connected to the positive electrode of the power supply in the current loop through a first resistor, and the emitter of the NPN transistor Q1 is grounded through a second resistor; The closed-loop electronic circuit further comprises: A first operational amplifier, an output terminal of which is connected to the base of the NPN transistor Q1; a third resistor, one end of which is connected to the collector of the NPN transistor Q1 and the other end of which is connected to the non-inverting input terminal of the first operational amplifier; a fourth resistor, one end of which is grounded and the other end of which is connected to the non-inverting input terminal of the first operational amplifier; a fifth resistor, one end of which is connected to the second voltage and the other end of which is connected to the inverting input terminal of the first operational amplifier; The closed-loop electronic circuit provides the first voltage and the first current to the external load through the collector of the NPN transistor Q1 and the ground; The positive power supply terminal of the first operational amplifier is connected to the collector of the NPN transistor Q1, and the negative power supply terminal of the operational amplifier is grounded; The closed-loop energy storage subcircuit includes a PMOS transistor and a capacitor, the source of the PMOS transistor is connected to the collector of the NPN transistor Q1, the drain of the PMOS transistor is connected to one end of the capacitor, and the other end of the capacitor is grounded; the gate voltage of the PMOS transistor is adjusted to control the magnitude of the first current flowing through the PMOS transistor; The closed-loop energy storage subcircuit further includes: a sixth resistor; a second operational amplifier, an output end of which is connected to the gate of the PMOS transistor via the sixth resistor; a seventh resistor, one end of which is connected to the emitter of the NPN transistor Q1 and the other end of which is connected to the inverting input terminal of the second operational amplifier; an eighth resistor, one end of which is connected to the inverting input terminal of the second operational amplifier and the other end of which is connected to the output terminal of the second operational amplifier; a ninth resistor, one end of which is connected to the collector of the NPN transistor Q1 and the other end of which is connected to the non-inverting input terminal of the second operational amplifier; a tenth resistor, one end of which is connected to the non-inverting input terminal of the second operational amplifier and the other end of which is grounded; Wherein, when the closed-loop electronic circuit is normally connected and powered on, the first operational amplifier and the second operational amplifier meet the virtual short condition; The current loop includes a V / I conversion circuit, an NPN transistor Q3, an NPN transistor Q1, a second resistor R2, and an eleventh resistor R11. The base of the NPN transistor Q3 is connected to the V / I conversion circuit, the collector of the NPN transistor Q3 is connected to the positive electrode of the power supply, the emitter of the NPN transistor Q3 is connected to the collector of the NPN transistor Q1, the first end of the eleventh resistor R11 is grounded, and the second end of the eleventh resistor R11 is connected to the negative electrode of the power supply.

2. The dynamic power supply circuit according to claim 1, characterized in that: The second voltage and the first voltage satisfy the relationship: V2= Wherein, V1 represents the first voltage, V2 represents the second voltage, R3 represents the third resistor, and R4 represents the fourth resistor.

3. The dynamic power supply circuit according to claim 1, characterized in that: The output voltage of the second operational amplifier satisfies the following relationship: Among them, V3 represents the collector voltage of the NPN transistor Q1, V4 represents the output voltage of the second operational amplifier, R7 represents the seventh resistor, R8 represents the eighth resistor, R9 represents the ninth resistor, and R10 represents the tenth resistor.

4. The dynamic power supply circuit according to claim 3, characterized in that: R7=R8=R9=R10.

5. A two-wire electromagnetic flowmeter, characterized in that: The invention comprises the dynamic power supply circuit described in any one of claims 1 to 4.

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