Coil driving circuit of fluxgate current sensor

Abstract

The invention is applicable to the technical field of fluxgates, and provides a coil driving circuit of a fluxgate current sensor, which comprises a stabilized power supply output module and a coil control module, the voltage-stabilized power supply module is used for outputting a constant first reference voltage and a constant second reference voltage from an input power supply voltage; the coil control module is used for driving the ZCT coil. Compared with the existing other schemes, the application has the outstanding advantages that the scheme provides a relatively stable excitation waveform; the requirement on the operational amplifier driving capability is reduced; the stable Vref can be provided for a user, so that a more stable overturning threshold value and a more stable measurement range are achieved, and the consistency of products is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluxgates, and in particular relates to a coil driving circuit of a fluxgate current sensor. Background Art

[0002] A fluxgate sensor is a high-precision magnetic field sensor with a complex structure and operating principle. The sensor primarily consists of an iron core, an excitation coil, an induction coil, a drive circuit, and a signal processing circuit. The drive circuit controls the current in the excitation coil, causing the iron core to undergo periodic magnetization. The signal processing circuit amplifies and processes the signal output by the induction coil to extract information about the target magnetic field.

[0003] In existing residual current protection modules using fluxgate technology, the driving circuit typically uses an op amp and peripheral circuits to form a voltage hysteresis comparator. The op amp's non-inverting input is typically connected to the power supply VDD, the op amp's output voltage, and the ground network GND, combined with different resistors to produce two different voltage thresholds, forming a hysteresis comparator. The inverting input is connected to the voltage signal on a sampling resistor connected in series with the transformer coil. The voltage on the sampling resistor is compared with the voltage on the non-inverting input. The op amp's output is directly connected to the other end of the transformer coil to drive the coil. Because the op amp's output changes the voltage threshold on the non-inverting input, the comparator alternates between outputting VDD and GND. A reference voltage Vref, generated by dividing the VDD voltage, is connected to the other end of the coil, generating an alternating current in the coil, causing the ZCT coil to alternately saturate in both directions.

[0004] However, when the primary current is very high, a large current is induced in the secondary coil. Since the op amp output directly drives the ZCT coil, the ZCT coil requires a large drive current, which is limited by the drive capability of the component itself. Once the demand exceeds the output capability of the op amp, the op amp output will be pulled low. In the hysteresis comparator, VDD and Vref are important reference voltages. Changes in VDD and Vref directly affect the two voltage thresholds of the hysteresis comparator, thereby affecting the measurement results.

[0005] Therefore, it can be seen that the current technology has problems such as low stability of the excitation flip threshold voltage and poor stability and accuracy of the output reference voltage. Summary of the Invention

[0006] The purpose of the embodiments of the present application is to provide a coil drive circuit for a fluxgate current sensor, aiming to solve the problems of low stability of the excitation flip threshold voltage and poor stability and accuracy of the output reference voltage.

[0007] The embodiment of the present application is implemented by providing a coil drive circuit for a fluxgate current sensor, the circuit comprising: Regulated power supply output module and coil control module; The voltage-stabilized power supply module is used to output a constant first reference voltage and a second reference voltage from the input power supply voltage; The coil control module includes a comparator T3, a comparator T4, and a ZCT coil. The input end of the first reference voltage is connected to the first end of the sampling resistor Rshut, the second end of the sampling resistor Rshut is connected to the first end of the ZCT coil and the inverting input end of the comparator T3, the positive input end of the comparator T3 is connected to the first end of the resistor R6, the second end of the resistor R6 is connected to the input end of the second reference voltage and the first end of the resistor R7, the second end of the resistor R7 is grounded, the positive input end of the comparator T3 is connected to the first end of the resistor R8, the second end of the resistor R8 is connected to the output end of the comparator T3 and the positive input end of the comparator T4, the two ends of the resistor R9 are respectively connected to the inverting input end and the output end of the comparator T4, and the output end of the comparator T4 is also connected to the second end of the ZCT coil.

[0008] Preferably, the regulated power supply output module includes: a power input terminal, wherein the power input terminal is connected to a first end of a resistor R1, a second end of the resistor R1 is connected to a cathode of a Zener diode ZD1 and a first end of a resistor R2, an anode of the Zener diode ZD1 is connected to a second end of the resistor R3 and then to ground, a second end of the resistor R2 is connected to a first end of the resistor R3 and to a reference voltage terminal of the Zener diode ZD1, a second end of the resistor R2 is further connected to a positive input terminal of a comparator T1, a negative input terminal of the comparator T1 is connected to a first end of a resistor R4, a second end of the resistor R4 is connected to an output terminal of the comparator T1, and an output of the output terminal of the comparator T1 is a first reference voltage; The second end of the resistor R1 is connected to the positive input end of the comparator T2, the negative input end of the comparator T2 is connected to the first end of the resistor R5, the second end of the resistor R5 is connected to the output end of the comparator T2, and the output end of the comparator T2 is the second reference voltage.

[0009] Preferably, the input power supply voltage is 5V, the first reference voltage is 2.5V, and the second reference voltage is 4V.

[0010] Preferably, the first end and the second end of the ZCT coil are further connected to the first end and the second end of a diode ZD5 respectively, and the diode ZD5 is a bidirectional diode.

[0011] Preferably, the circuit further comprises a diode ZD4 and a diode ZD3; The anode of the diode ZD3 is connected to the first end of the ZCT coil, and the cathode of the diode ZD3 is connected to the input end of the power supply voltage; The cathode of the diode ZD4 is connected to the first end of the ZCT coil, and the anode of the diode ZD4 is grounded.

[0012] Preferably, the diode ZD4 and the diode ZD3 are both voltage stabilizing diodes.

[0013] Preferably, the circuit further comprises a diode ZD6 and a diode ZD7; The anode of the diode ZD7 is connected to the second end of the ZCT coil, and the cathode of the diode ZD7 is connected to the input end of the power supply voltage; The cathode of the diode ZD6 is connected to the second end of the ZCT coil, and the anode of the diode ZD6 is grounded.

[0014] Preferably, the diode ZD6 and the diode ZD7 are both voltage stabilizing diodes.

[0015] Preferably, the resistance ratio of the resistor R6, the resistor R7 and the resistor R8 is 24:40:15.

[0016] The embodiment of the present application provides a coil driving method for a fluxgate current sensor, which has the outstanding advantage that, compared with previous solutions, this solution provides a relatively stable excitation waveform; reduces the requirements for the operational amplifier driving capability; and can provide users with a stable Vref, thereby having a more stable flip threshold and a more stable measurement range, thereby improving product consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A circuit diagram of a coil control module of a fluxgate current sensor provided in an embodiment of the present application; Figure 2 A circuit diagram of a voltage-regulated power supply output module of a fluxgate current sensor provided in an embodiment of the present application; Figure 3 A schematic diagram of the voltage waveform at both ends of a ZCT coil provided in an embodiment of the present application; Figure 4 A schematic diagram of the voltage waveform across a sampling resistor Rshut provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] It will be understood that the terms "first," "second," and the like, used herein may be used to describe various components, but unless otherwise specified, these components are not limited by these terms. These terms are used solely to distinguish a first unit or module from another unit or module. For example, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor without departing from the scope of this application.

[0020] In one embodiment, a coil drive circuit for a fluxgate current sensor is provided. The circuit may include: Regulated power supply output module and coil control module; The voltage-stabilized power supply module is used to output a constant first reference voltage and a second reference voltage from the input power supply voltage; The coil control module includes a comparator T3, a comparator T4, and a ZCT coil. The input end of the first reference voltage is connected to the first end of the sampling resistor Rshut, the second end of the sampling resistor Rshut is connected to the first end of the ZCT coil and the inverting input end of the comparator T3, the positive input end of the comparator T3 is connected to the first end of the resistor R6, the second end of the resistor R6 is connected to the input end of the second reference voltage and the first end of the resistor R7, the second end of the resistor R7 is grounded, the positive input end of the comparator T3 is connected to the first end of the resistor R8, the second end of the resistor R8 is connected to the output end of the comparator T3 and the positive input end of the comparator T4, the two ends of the resistor R9 are respectively connected to the inverting input end and the output end of the comparator T4, and the output end of the comparator T4 is also connected to the second end of the ZCT coil.

[0021] In the embodiments of this application, a ZCT (Zero Current Transformer) refers to a zero-sequence current transformer. Researchers in this application have discovered that existing mainstream solutions are limited by the drive capabilities of the components themselves. Once the demand exceeds the output capability of the op amp, the op amp output will be pulled low, affecting the measurement results. Therefore, the solution provided in this application is suitable for a fluxgate drive circuit that automatically flips to generate alternating current and is built using a hardware circuit, eliminating the need for a single-chip microcomputer to control the flipping.

[0022] In this embodiment, the voltage-regulated power supply output module uses a voltage reference chip to generate two stable voltages: a first reference voltage, Vref, and a second reference voltage, Vo. Compared to existing solutions that generate Vref by dividing the VDD voltage, both Vref and Vo in this solution are stable and do not change with changes in VDD. This results in a more stable output, significantly improving overall system performance.

[0023] Coil control module part such as Figure 1As shown in Figure 1, one end of the ZCT coil is connected to the follower output, and the other end is connected to the sampling resistor Rshut. The comparator compares the voltage across the sampling resistor Rshut with the voltage at the non-inverting input terminal. If V+ > Vshut, the comparator outputs a high level, otherwise it outputs a low level.

[0024] In the embodiment of the present application, one end of the ZCT coil is connected to the follower output, and the other end is connected to the sampling resistor Rshut. The voltage at the follower output is as follows: Figure 3 As shown, the voltage across the sampling resistor Rshut is as follows: Figure 4 As shown. When the op amp outputs a high level, the ZCT coil is charged, and Vshut gradually increases. When Vshut rises to, for example, 3.75V, the comparator outputs a high level, which is then controlled by the combinational logic circuit to invert and output a low level. At this time, the ZCT coil discharges the comparator, and Vshut gradually decreases. When the Vshut voltage drops to, for example, 1.25V, the comparator controls the op amp again after the combinational logic circuit to invert and output a high level. At this point, the entire system completes a working cycle. This reciprocating process achieves the purpose of alternating saturation of the ZCT coil. Since the comparator does not need to directly drive the ZCT coil, it has a stable square wave output. Since the Zener diode provides a stable Vo, the comparator's flip thresholds of 1.25V and 3.75V are also stable.

[0025] In the solution provided by this application, a voltage follower is placed behind the comparator that controls the alternating current direction in the ZCT coil. This serves as an isolation device to prevent the comparator from directly driving the ZCT coil. Although direct drive of the ZCT coil is theoretically possible, the ZCT coil requires a large drive current when measuring high currents. Even voltage fluctuations on the follower do not affect the flip threshold of the upper-level comparator, providing a stable flip threshold and ZCT coil measurement range.

[0026] In a preferred embodiment, Figure 2 As shown, the regulated power supply output module includes: a power input terminal, wherein the power input terminal is connected to a first end of a resistor R1, a second end of the resistor R1 is connected to a cathode of a Zener diode ZD1 and a first end of a resistor R2, an anode of the Zener diode ZD1 is connected to a second end of the resistor R3 and then to ground, a second end of the resistor R2 is connected to a first end of the resistor R3 and to a reference voltage terminal of the Zener diode ZD1, a second end of the resistor R2 is further connected to a positive input terminal of a comparator T1, a negative input terminal of the comparator T1 is connected to a first end of a resistor R4, a second end of the resistor R4 is connected to an output terminal of the comparator T1, and an output of the output terminal of the comparator T1 is a first reference voltage; The second end of the resistor R1 is connected to the positive input end of the comparator T2, the negative input end of the comparator T2 is connected to the first end of the resistor R5, the second end of the resistor R5 is connected to the output end of the comparator T2, and the output end of the comparator T2 is the second reference voltage.

[0027] In a preferred embodiment, the input power supply voltage is 5V, the first reference voltage is 2.5V, and the second reference voltage is 4V.

[0028] In the embodiment of the present application, in this scheme, the power input terminal is VDD, VDD uses 5V, and the first reference voltage Vref=2.5V; the second reference voltage Vo is obtained through R2 and R3 (preferably, R2=12K, R3=20K), Vo=4V.

[0029] In a preferred embodiment, the first end and the second end of the ZCT coil are further connected to the first end and the second end of a diode ZD5 respectively. The diode ZD5 is a bidirectional diode.

[0030] In the embodiment of the present application, the diode ZD5 can suppress the high voltage spike during the coil switching process and protect the comparator output stage.

[0031] In a preferred embodiment, the circuit further comprises a diode ZD4 and a diode ZD3; The anode of the diode ZD3 is connected to the first end of the ZCT coil, and the cathode of the diode ZD3 is connected to the input end of the power supply voltage; The cathode of the diode ZD4 is connected to the first end of the ZCT coil, and the anode of the diode ZD4 is grounded.

[0032] In a preferred embodiment, the diode ZD4 and the diode ZD3 are both voltage stabilizing diodes.

[0033] In an embodiment of the present application, a set of forward and reverse voltage clamping protections is provided to suppress the transient high voltage generated during the coil switching process, protect core components such as comparators and power modules from damage, and improve the safety and reliability of the device.

[0034] In a preferred embodiment, the circuit further comprises a diode ZD6 and a diode ZD7; The anode of the diode ZD7 is connected to the second end of the ZCT coil, and the cathode of the diode ZD7 is connected to the input end of the power supply voltage; The cathode of the diode ZD6 is connected to the second end of the ZCT coil, and the anode of the diode ZD6 is grounded.

[0035] In a preferred embodiment, the diode ZD6 and the diode ZD7 are both voltage stabilizing diodes.

[0036] In an embodiment of the present application, another set of forward and reverse voltage clamping protection is provided to suppress the transient high voltage generated during the coil switching process, protect core components such as comparators and power modules from damage, and improve the safety and reliability of the device.

[0037] In a preferred embodiment, the resistance ratio of the resistor R6 , the resistor R7 , and the resistor R8 is 24:40:15.

[0038] In this embodiment, the resistor values can be as follows: R6 = 12K, R7 = 20K, and R8 = 7.5K. At this point, when comparator T3 outputs 0V, the non-inverting input terminal behaves as if R7 were first connected in parallel with R8 and then in series with R6. V+ = Vo / (R6 + R8 / / R7) * R8 / / R7, yielding V+ = 1.25V. When the comparator outputs 5V, the non-inverting input terminal behaves as if R6 were first connected in parallel with R8 and then in series with R7. (5V - V+) / R7 + (4V - V+) / R8 = V+ / R9, yielding V+ = 3.75V. Therefore, the two V+ values are 1.25V and 3.75V, respectively. This precisely meets the device's operating requirements.

[0039] It should be understood that, although each step in the flow chart of each embodiment of the present application is shown in sequence according to the indication of the arrow, these steps are not necessarily performed in sequence according to the order indicated by the arrow. Unless there is clear explanation in this article, the execution of these steps does not have strict order restriction, and these steps can be performed in other orders. Moreover, at least a portion of the steps in each embodiment may include a plurality of sub-steps or a plurality of stages, and these sub-steps or stages are not necessarily performed at the same time, but can be performed at different times, and the execution order of these sub-steps or stages is not necessarily performed in sequence, but can be performed in turn or alternately with at least a portion of other steps or sub-steps or stages of other steps.

[0040] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0041] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A coil drive circuit for a fluxgate current sensor, characterized in that: The circuit comprises: Regulated power supply output module and coil control module; The voltage-stabilized power supply module is used to output a constant first reference voltage and a second reference voltage from the input power supply voltage; The coil control module includes a comparator T3, a comparator T4, and a ZCT coil. The input end of the first reference voltage is connected to the first end of the sampling resistor Rshut, the second end of the sampling resistor Rshut is connected to the first end of the ZCT coil and the inverting input end of the comparator T3, the positive input end of the comparator T3 is connected to the first end of the resistor R6, the second end of the resistor R6 is connected to the input end of the second reference voltage and the first end of the resistor R7, the second end of the resistor R7 is grounded, the positive input end of the comparator T3 is connected to the first end of the resistor R8, the second end of the resistor R8 is connected to the output end of the comparator T3 and the positive input end of the comparator T4, the two ends of the resistor R9 are respectively connected to the inverting input end and the output end of the comparator T4, and the output end of the comparator T4 is also connected to the second end of the ZCT coil.

2. The coil drive circuit of a fluxgate current sensor according to claim 1, characterized in that: The voltage-stabilized power supply output module includes: a power input terminal, wherein the power input terminal is connected to a first end of a resistor R1, a second end of the resistor R1 is connected to a cathode of a Zener diode ZD1 and a first end of a resistor R2, an anode of the Zener diode ZD1 is connected to a second end of the resistor R3 and then to ground, a second end of the resistor R2 is connected to a first end of the resistor R3 and to a reference voltage terminal of the Zener diode ZD1, a second end of the resistor R2 is further connected to a positive input terminal of a comparator T1, a negative input terminal of the comparator T1 is connected to a first end of a resistor R4, a second end of the resistor R4 is connected to an output terminal of the comparator T1, and an output of the output terminal of the comparator T1 is a first reference voltage; The second end of the resistor R1 is connected to the positive input end of the comparator T2, the negative input end of the comparator T2 is connected to the first end of the resistor R5, the second end of the resistor R5 is connected to the output end of the comparator T2, and the output end of the comparator T2 is the second reference voltage.

3. The coil driving circuit of a fluxgate current sensor according to claim 1, characterized in that: The input power supply voltage is 5V, the first reference voltage is 2.5V, and the second reference voltage is 4V.

4. The coil driving circuit of a fluxgate current sensor according to claim 1, characterized in that: The first end and the second end of the ZCT coil are also connected to the first end and the second end of the diode ZD5 respectively. The diode ZD5 is a bidirectional diode.

5. The coil driving circuit of a fluxgate current sensor according to claim 1, characterized in that: The circuit further includes a diode ZD4 and a diode ZD3; The anode of the diode ZD3 is connected to the first end of the ZCT coil, and the cathode of the diode ZD3 is connected to the input end of the power supply voltage; The cathode of the diode ZD4 is connected to the first end of the ZCT coil, and the anode of the diode ZD4 is grounded.

6. The coil driving circuit of a fluxgate current sensor according to claim 5, characterized in that: The diode ZD4 and the diode ZD3 are both voltage-stabilizing diodes.

7. The coil driving circuit of a fluxgate current sensor according to claim 1, characterized in that: The circuit further includes a diode ZD6 and a diode ZD7; The anode of the diode ZD7 is connected to the second end of the ZCT coil, and the cathode of the diode ZD7 is connected to the input end of the power supply voltage; The cathode of the diode ZD6 is connected to the second end of the ZCT coil, and the anode of the diode ZD6 is grounded.

8. The coil driving circuit of a fluxgate current sensor according to claim 7, characterized in that: The diode ZD6 and the diode ZD7 are both voltage-stabilizing diodes.

9. The coil driving circuit of a fluxgate current sensor according to claim 1, characterized in that: The resistance ratio of the resistor R6 , the resistor R7 , and the resistor R8 is 24:40:15.

Images