Current sensor circuit

Abstract

A current sensor circuit (1) is provided with: a detection coil (N1) configured such that the inductance changes according to a direct current; a resonant capacitor (C1); a phase adjustment circuit (10) that receives a feedback signal from the resonant capacitor and outputs a drive signal; a switching circuit (20) including a plurality of switching elements (Q1, Q2) forming a half-bridge circuit or a full-bridge circuit, the switching circuit (20) supplying an AC signal to the detection coil and the resonant capacitor by switching the plurality of switching elements in accordance with the pulse period of the drive signal; a signal conversion circuit (40) that converts the drive signal output from the phase adjustment circuit into a detection signal indicating a change in the DC current; and a detection terminal (DCSIG) that outputs a detection signal to the outside.

Description

Technical Field

[0001] The invention relates to a current sensor circuit for detecting direct current. Background Art

[0002] As a current sensor for detecting a direct current in a non-contact manner, there is a current sensor using a Hall element. However, this current sensor has a problem in that it cannot accurately detect the current when noise is superimposed on the current detection signal.

[0003] Patent Document 1 below discloses a current sensor capable of measuring the direction of a detected current without using a Hall element. This current sensor comprises: a magnetic core that allows magnetic flux based on the detected current to pass through it; a resonant circuit comprising a winding wound around the magnetic core; an oscillator that applies a signal of a predetermined frequency to the resonant circuit; an output circuit connected to the resonant circuit that outputs an electrical signal corresponding to the direction of the detected current based on changes in the characteristics of the resonant circuit that vary with the direction of the detected current; and a magnetic field bias unit that applies a magnetic field bias to the magnetic core.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-37508 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, the above-mentioned current sensor has room for improvement in current detection accuracy.

[0009] The present invention provides a current sensor circuit technology capable of suppressing the influence of noise and detecting a direct current with high precision.

[0010] Solutions for solving problems

[0011] According to the present invention, a current sensor circuit is provided that can detect a DC current flowing through a detected conductive line. The current sensor circuit includes: a detection coil having an inductance that changes in accordance with the DC current; a resonant capacitor that, together with the detection coil, forms a series resonant circuit; a phase adjustment circuit that receives a feedback signal from the resonant capacitor and outputs a drive signal; a switching circuit including a plurality of switching elements forming a half-bridge circuit or a full-bridge circuit, the switching circuit switching the plurality of switching elements in accordance with a pulse cycle of the drive signal to thereby supply an AC signal to the detection coil and the resonant capacitor; a signal conversion circuit that converts the drive signal output from the phase adjustment circuit into a detection signal representing a change in the DC current; and a detection terminal that outputs the detection signal externally. The phase adjustment circuit sets the pulse cycle of the drive signal based on a phase difference between the feedback signal and the drive signal so that the frequency of the AC signal flowing through the detection coil and the resonant coil tracks the resonant frequency of the series resonant circuit, which changes in accordance with a change in the inductance of the detection coil.

[0012] Effects of the Invention

[0013] According to the above aspect, it is possible to provide a current sensor circuit technology capable of suppressing the influence of noise and detecting a direct current with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 : is a circuit diagram of a current sensor circuit in this embodiment.

[0015] Figure 2 This is a diagram conceptually showing a configuration example of a detection coil in this embodiment.

[0016] Figure 3 This is an example of a circuit diagram of a pulse conversion circuit.

[0017] Figure 4 This is a graph showing the relationship between changes in the inductance of the detection coil, changes in the pulse frequency of the drive signal, and the DC bias current.

[0018] Figure 5 1 is a diagram showing signal waveforms at points A, B, C, and D of the current sensor circuit in this embodiment.

[0019] Figure 6 This is a diagram conceptually showing the structure of a detection coil in a modified example.

[0020] Figure 7 4 is a circuit diagram of a current sensor circuit in a modified example. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present invention will be described. However, the embodiments listed below are for illustration only, and the present invention is not limited to the structures of the following embodiments.

[0022] 〔Circuit Structure〕

[0023] Figure 1 : is a circuit diagram of the current sensor circuit 1 in this embodiment.

[0024] The current sensor circuit 1 includes a phase adjustment circuit 10 , a switch circuit 20 , a detection circuit 30 , a feedback rectification circuit 40 , a signal conversion circuit 50 , a detection terminal 60 , a magnetic field bias unit, and the like.

[0025] The detection circuit 30 is composed of a resistance element R1, a detection coil N1, and a resonant capacitor C1 connected in series. Therefore, the detection circuit 30 becomes a series resonant circuit due to the flow of an AC signal of a resonant frequency.

[0026] The detection coil N1 is configured such that its inductance changes in response to a direct current (sometimes also referred to as a detected current) flowing through a detected conductor of a system under measurement.

[0027] Figure 2 This is a diagram conceptually showing a configuration example of the detection coil N1 in this embodiment.

[0028] like Figure 2 As shown, the windings of the detection coil N1 are wound around a magnetic core 32 through which the detected conductor TL passes. With this structure, the magnetic flux within the magnetic core 32 changes in response to the magnetic field generated around the detected conductor TL by the DC current I flowing through the detected conductor TL. This change in magnetic flux causes the inductance of the detection coil N1 wound around the magnetic core 32 to change as well.

[0029] The core 32 may be made of any material other than ferrite or electromagnetic steel sheets as long as it fulfills the above function.

[0030] in addition, Figure 2 The illustrated magnetic core 32 is a ring-shaped core called a toroidal core, and the detection conductor TL passes through the center of the magnetic core 32 . However, as long as the above-mentioned function is achieved, the structure is not limited to this one.

[0031] Furthermore, a bias coil N2 is wound around the magnetic core 32. The bias coil N2 constitutes a magnetic field bias unit that applies a magnetic field bias to the magnetic core 32 to bring it into a magnetic saturation region. The details of the magnetic field bias unit will be described later.

[0032] When the detected current I flows in a direction that generates a magnetic flux in the same direction (superimposed direction) as the magnetic flux in the magnetic core 32 generated by the DC bias current Ib flowing through the bias coil N2, the inductance of the detection coil N1 becomes smaller. Conversely, when the detected current I flows in a direction that generates a magnetic flux in the opposite direction (cancelled direction) as the magnetic flux in the magnetic core 32 generated by the DC bias current Ib flowing through the bias coil N2, the inductance of the detection coil N1 becomes larger.

[0033] In this embodiment, the direction of the detected current I when the inductance of the detection coil N1 decreases is defined as a positive direction (+I), and the direction of the detected current I when the inductance of the detection coil N1 increases is defined as a negative direction (-I).

[0034] The switch circuit 20 includes a drive circuit 22 , two transistors Q1 and Q2 , and the like.

[0035] The transistors Q1 and Q2 in this embodiment are FETs (Field Effect Transistors), which can be described as switching elements.

[0036] exist Figure 1 In the example shown, transistors Q1 and Q2 are N-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) forming a half-bridge circuit. Detection circuit 30 is connected between the source and drain of transistor Q2.

[0037] The drive circuit 22 is capable of applying a gate-source voltage (hereinafter sometimes referred to as V GS voltage) is connected to transistors Q1 and Q2.

[0038] The driving circuit 22 alternately applies a voltage V exceeding the threshold voltage to the transistors Q1 and Q2. GS The voltage alternately switches the on / off states of transistors Q1 and Q2 (performing a switching operation). At this time, drive circuit 22 periodically switches the on / off states of transistors Q1 and Q2 in accordance with the pulses of the drive signal from phase adjustment circuit 10. As a result, an AC signal having a frequency corresponding to the period of the drive signal from phase adjustment circuit 10 flows through detection circuit 30. The pulse period of the drive signal from phase adjustment circuit 10 is controlled so that an AC signal having a resonant frequency flows through detection circuit 30. Details will be described later.

[0039] The feedback rectifier circuit 40 performs half-wave rectification on the feedback signal from the detection circuit 30 . Specifically, the feedback rectifier circuit 40 performs half-wave rectification on the AC voltage waveform applied to the resonant capacitor C1 and sends the half-wave rectified voltage waveform to the phase adjustment circuit 10 .

[0040] Phase adjustment circuit 10 receives a feedback signal from detection circuit 30 and outputs a drive signal. Specifically, phase adjustment circuit 10 sets the pulse period of the output drive signal based on the phase difference between the signal (feedback signal) obtained by half-wave rectification of the AC voltage waveform applied to resonant capacitor C1 and the drive signal, so that the frequency of the AC signal flowing through detection circuit 30 tracks the resonant frequency of detection circuit 30 (series resonant circuit).

[0041] The phase adjustment circuit 10 includes a feedback pulse generation circuit 11 , a PLL (Phase Locked Loop) circuit 16 , and the like.

[0042] Feedback pulse generation circuit 11 includes a NOT circuit 12, a variable resistor 13, a capacitor 14, and the like. NOT circuit 12 converts the half-wave rectified waveform from feedback rectifier circuit 40 into a pulse waveform using a threshold voltage. The RC filter formed by variable resistor 13 and capacitor 14 corrects for variations in the shaping of this pulse waveform. The feedback pulse signal (SIG pulse) obtained by conversion of the half-wave rectified waveform from feedback rectifier circuit 40 by feedback pulse generation circuit 11 is transmitted to PLL circuit 16.

[0043] The PLL circuit 16 compares the phase of the feedback pulse signal (SIG pulse) sent from the feedback pulse generating circuit 11 with the phase of the drive signal (REF pulse) and adjusts the pulse period of the drive signal (PLLout) as the output signal to eliminate the phase difference. The PLL circuit 16 can have the structure of a known single-loop PLL circuit, for example, consisting of a frequency divider, a phase comparator, a filter, and a voltage-controlled oscillator (VCO). The drive signal output from the PLL circuit 16 is sent to the switching circuit 20 and the signal conversion circuit 50, respectively. Meanwhile, the drive signal is also circulated and used as a reference signal (REF pulse).

[0044] The signal conversion circuit 50 converts the drive signal output from the phase adjustment circuit 10 into a detection signal indicating a change in the DC current flowing through the detection target conductor TL. The detection signal is output to the outside through the detection terminal DCSIG.

[0045] The signal conversion circuit 50 includes a pulse conversion circuit 51, a resistor 52, a capacitor 53, and other components. The pulse conversion circuit 51 converts the drive signal output from the phase adjustment circuit 10 into a pulse frequency modulated (PFM) signal. The resistor 52 and capacitor 53 form an RC filter, smoothing the PFM signal output from the pulse conversion circuit 51 into a voltage waveform. This voltage waveform becomes a detection signal representing changes in the DC current flowing through the detected conductor line TL.

[0046] Figure 3 This is an example of a circuit diagram of the pulse conversion circuit 51.

[0047] exist Figure 3 In the example shown, pulse conversion circuit 51 is a monostable multivibrator circuit composed of a resistor 511, a capacitor 512, a NOT circuit 513, and an AND circuit 514. In pulse conversion circuit 51, the rising timing of the input drive signal pulse is shifted by resistor 511 and capacitor 512, inverted by NOT circuit 513, and the input drive signal is input to AND circuit 514. This outputs a PFM signal having a fixed pulse width and a duty cycle that varies proportionally with the pulse period of the drive signal.

[0048] However, the structure of the pulse conversion circuit 51 is not limited to Figure 3 The structural example shown may also be a monostable multivibrator circuit having another structure.

[0049] The magnetic field bias unit includes the bias coil N2 (see Figure 2 ) and a DC power supply (not shown) that causes a constant current to flow through the bias coil N2. The DC power supply supplies DC power to the bias coil N2 whose winding is wound around the magnetic core 32 (in Figure 1 In the example, +5 V is applied to the magnetic core 32 to bias the magnetic field so that the core 32 reaches the magnetic saturation region. This shifts the inductance characteristics of the detection coil N1 wound around the core 32 to a region where the inductance changes linearly.

[0050] Figure 4 Graph showing the relationship among the change in inductance of the detection coil N1 , the change in the pulse frequency of the drive signal, and the DC bias current Ib. Figure 4 The horizontal axis represents the detected current I, Figure 4 The vertical axis represents the pulse frequency (the inverse of the pulse period) of the driving signal.

[0051] pass Figure 2 In the illustrated structure, the inductance of the detection coil N1 changes according to the detected current I. Figure 4As shown, as the positive detected current I increases, the inductance of detection coil N1 decreases. When the negative detected current I increases, the inductance of detection coil N1 increases. Furthermore, as the inductance of detection coil N1 decreases, the resonant frequency of detection circuit 30 increases, and accordingly, the pulse frequency of the drive signal also increases (the pulse period shortens). Conversely, as the inductance of detection coil N1 increases, the resonant frequency of detection circuit 30 decreases, and accordingly, the pulse frequency of the drive signal also decreases (the pulse period lengthens).

[0052] On the other hand, the inductance change of the detection coil N1 is not completely linear. Therefore, in this embodiment, the bias coil N2 is wound around the magnetic core 32 together with the detection coil N1, and a DC bias current is passed through the bias coil N2. This eliminates the nonlinear region in the inductance characteristic of the detection coil N1 and shifts it to the linear region.

[0053] Therefore, the output of the DC power supply of the magnetic field bias unit is set so that the inductance of the detection coil N1 changes in a linear region within the measurable range of the detected current I (the range from -Imax to +Imax), and the inductance value of the detection coil N1 when no detected current I flows (zero ampere) becomes the central value of the linear change region.

[0054] 〔action〕

[0055] Next, use Figure 5 The operation of the current sensor circuit 1 having the above-described circuit configuration will be described. Figure 5 : is a diagram showing the signal waveforms at points A, B, C, and D of the current sensor circuit 1 in this embodiment. Figure 1 In addition, Figure 5 (a) shows the signal waveform when the detected current I does not flow (at 0 (A)). Figure 5 (b) shows the signal waveform when the detected current I is +10 (A). Figure 5 (c) shows the signal waveform when the detected current I is -10 (A).

[0056] When no current flows in the detected conductor TL ( Figure 5 In (a), the switching circuit 20 switches the transistors Q1 and Q2 according to the pulse cycle of the drive signal output from the phase adjustment circuit 10, so that the detection circuit 30 enters a resonant state.

[0057] At this time, the AC voltage waveform (base signal) applied to the resonant capacitor C1 of the detection circuit 30 becomes a waveform of the resonant frequency, and this waveform signal is half-wave rectified by the feedback rectifier circuit 40 . Figure 5The waveform at point A in (a) is a half-wave rectified waveform output from the feedback rectifier circuit 40 .

[0058] This core signal (half-wave rectified waveform) is converted into a pulse waveform using a threshold voltage in the feedback pulse generating circuit 11 of the phase adjustment circuit 10, and subjected to deviation correction. The waveform is then sent as a feedback pulse signal to the PLL circuit 16. The PLL circuit 16 compares the phase of the feedback pulse signal with the phase of the drive signal, and adjusts the pulse period of the drive signal (PLLout), which is the output signal, so that the phase difference is eliminated. Figure 5 The waveform at point B in (a) is the waveform of the drive signal output from the phase adjustment circuit 10 .

[0059] At this time, since no current flows through the detection conductor TL, there is almost no phase difference, and the pulse period of the drive signal is maintained to correspond to the resonant frequency of the detection circuit 30 .

[0060] The drive signal is sent to the switch circuit 20 and also to the signal conversion circuit 50 , and is converted into a PFM signal in the pulse conversion circuit 51 . Figure 5 The waveform at point C in (a) is the PFM signal waveform.

[0061] The PFM signal is smoothed by the RC filter of the resistor 52 and the capacitor 53 in the signal conversion circuit 50 to become a voltage level waveform, and can be output to the outside from the detection terminal DCSIG. Figure 5 The waveform at point D in (a) is the voltage level waveform, and indicates the voltage level corresponding to the case where the detected current I is 0 (A).

[0062] When a detected current I of +10(A) flows through the detected wire TL ( Figure 5 In (b)), the inductance of detection coil N1 decreases compared to when no current is flowing. Consequently, the resonant frequency in detection circuit 30 increases, leaving the resonant state. As a result, a phase difference occurs between the feedback pulse signal and the drive signal, which are compared in PLL circuit 16 of phase adjustment circuit 10. PLL circuit 16 shortens the pulse period of the drive signal (setting the pulse frequency higher) to reduce this phase difference. Figure 5 The waveform at point B in (b) shows the waveform of the drive signal after adjustment in this manner.

[0063] By switching transistors Q1 and Q2 in accordance with the pulse period of the drive signal adjusted in this manner through the switching circuit 20, the frequency of the AC signal flowing through the detection circuit 30 follows the resonant frequency of the detection circuit 30 that changes in accordance with the reduction in the inductance of the detection coil N1.

[0064] The drive signal adjusted in this way is converted into a PFM signal in the pulse conversion circuit 51 ( Figure 5 The PFM signal is smoothed by the RC filter of the resistor element 52 and the capacitor 53 in the signal conversion circuit 50 and becomes a voltage level waveform ( Figure 5 (b) The voltage level waveform shows the voltage level corresponding to the case where the detected current I is +10 (A).

[0065] When the detected current I of -10(A) flows through the detected wire TL ( Figure 5 In (c)), the inductance of detection coil N1 increases compared to when no current is flowing. Consequently, the resonant frequency in detection circuit 30 decreases, leaving the resonant state. As a result, a phase difference occurs between the feedback pulse signal and the drive signal, which are compared in PLL circuit 16 of phase adjustment circuit 10. PLL circuit 16 extends the pulse period of the drive signal (setting the pulse frequency to a lower level) to reduce this phase difference. Figure 5 The waveform at point B in (c) shows the waveform of the drive signal after adjustment in this manner.

[0066] By switching transistors Q1 and Q2 in accordance with the pulse period of the drive signal adjusted in this manner through the switching circuit 20, the frequency of the AC signal flowing through the detection circuit 30 follows the resonant frequency of the detection circuit 30 that changes in accordance with the increase in the inductance of the detection coil N1.

[0067] The drive signal adjusted in this way is converted into a PFM signal in the pulse conversion circuit 51 ( Figure 5 The PFM signal is smoothed by the RC filter of the resistor element 52 and the capacitor 53 in the signal conversion circuit 50 and becomes a voltage level waveform ( Figure 5 (c) The voltage level waveform shows the voltage level corresponding to the case where the detected current I is -10 (A).

[0068] As described above, in this embodiment, the magnitude of the detected current I is captured based on changes in the inductance of the detection coil N1 and changes in the resonant frequency of the detection circuit 30, and the resonant frequency is tracked using the phase adjustment circuit 10, and a detection signal is generated based on the drive signal output from the phase adjustment circuit 10.

[0069] As described above, in this embodiment, the circuit is operated to track the resonant frequency of detection circuit 30, thereby suppressing its response to external noise frequencies. Furthermore, in this embodiment, noise immunity is improved by deriving a detection signal from a PFM signal corresponding to the pulse duty cycle.

[0070] Therefore, according to this embodiment, the detection level of the direct current can be maintained with high accuracy without being easily affected by noise.

[0071] In addition, in this embodiment, there is a nonlinear change region in the inductance characteristics of the detection coil N1, but by winding the winding of the bias coil N2 on the magnetic core 32 on which the winding of the detection coil N1 is wound and allowing the DC bias current Ib to flow through the bias coil N2, this nonlinear change region is eliminated, and the inductance of the detection coil N1 is changed within the linear change region.

[0072] Thus, the magnitude of the detected current I can be detected with high accuracy.

[0073] In addition, the PFM signal output from the pulse conversion circuit 51 is as follows: Figure 5 As shown in the waveform at point C of FIG, the drive signal (waveform at point B) is synchronized with the rising timing of the pulse and has a constant pulse width regardless of the pulse period of the drive signal. Specifically, the drive signal output from the phase adjustment circuit 10 has a constant duty cycle and a pulse width proportional to the pulse period (pulse frequency). In contrast, the PFM signal has a constant pulse width and a duty cycle proportional to the pulse period (pulse frequency).

[0074] By converting into such a PFM signal, the smoothed signal can be made into a signal whose level rises and falls according to the pulse period (pulse frequency), thereby making it possible to make a detection signal indicating a change in the detected current I.

[0075] [Modification]

[0076] The contents of the above-described embodiment can be modified appropriately.

[0077] For example, if the current sensor circuit 1 can detect whether a DC current, or a DC current exceeding a predetermined current value, is flowing through the detected conductor TL at a detection current level that causes a change in the inductance of the detection coil N1, it need not include a magnetic bias unit. Furthermore, the signal conversion circuit 50 is not limited to the above configuration as long as it can convert the drive signal output from the phase adjustment circuit 10 into a detection signal that represents changes in the detected current. For example, the signal conversion circuit 50 may generate a detection signal without converting it into a PFM signal.

[0078] In the above embodiment, the magnetic bias unit includes the bias coil N2 and a DC power supply, but the magnetic bias unit may also include a bias magnet. In this case, the bias coil N2 and the DC power supply (+5V) are not required.

[0079] Figure 6 This is a diagram conceptually showing the configuration of the detection coil N1 in a modified example.

[0080] While the aforementioned embodiment has a winding of the detection coil N1 wound around the magnetic core 32 and a detected conductor TL passing through the magnetic core 32, this variation does not include a winding of the bias coil N2. Instead, a bias magnet BM is provided in the magnetic core 32. Specifically, in this variation, the magnetic core 32 is formed into a partially interrupted C-shape, with the bias magnet BM embedded in the gaps in the interruption, forming a ring-shaped body as a whole.

[0081] The bias magnet BM applies a magnetic field bias to the magnetic core 32 to bring it into a magnetic saturation region. That is, the bias magnet BM has a magnetic force that can shift the inductance of the detection coil N1 to a region where the inductance changes linearly (linear change region).

[0082] Even if the magnetic bias unit has such a structure, the same operational effects as those of the above-described embodiment can be obtained.

[0083] Figure 7 2 is a circuit diagram of a current sensor circuit 1 according to a modified example.

[0084] like Figure 7 As shown, the switching circuit 20 described above can be modified to include a plurality of transistors Q1 , Q2 , Q3 , and Q4 forming a full-bridge circuit.

[0085] In this modification, the drive circuit 22 is configured to apply a gate-source voltage (V GS The driving circuit 22 is connected to the transistors Q1, Q2, Q3, and Q4 in the form of a voltage exceeding the threshold voltage. In addition, the driving circuit 22 alternately applies a voltage exceeding the threshold voltage V to the pair of transistors Q1 and Q4 and the pair of transistors Q2 and Q3 according to the pulse cycle of the driving signal from the phase adjustment circuit 10. GS The voltage is applied, thereby alternately switching the on and off states of the pair of transistors Q1 and Q4 and the pair of transistors Q2 and Q3 (performing a switching operation).

[0086] Thus, similarly to the above-described embodiment, an AC signal having a frequency corresponding to the pulse period of the drive signal from the phase adjustment circuit 10 can flow through the detection circuit 30 .

[0087] A part or all of the above-mentioned embodiment and modified examples can also be defined as follows. However, the above-mentioned embodiment and modified examples are not limited to the following description.

[0088] <1>

[0089] A current sensor circuit is capable of detecting a DC current flowing through a detected conductor, the current sensor circuit comprising:

[0090] a detection coil configured such that its inductance changes according to the DC current;

[0091] a resonant capacitor, which forms a series resonant circuit together with the detection coil;

[0092] a phase adjustment circuit, which receives a feedback signal from the resonant capacitor and outputs a driving signal;

[0093] a switching circuit comprising a plurality of switching elements forming a half-bridge circuit or a full-bridge circuit, wherein the plurality of switching elements are switched according to a pulse period of the driving signal, thereby providing an AC signal to the detection coil and the resonant capacitor;

[0094] a signal conversion circuit that converts the drive signal output from the phase adjustment circuit into a detection signal indicating a change in the DC current; and

[0095] a detection terminal, which outputs the detection signal to the outside,

[0096] In which, the phase adjustment circuit sets the pulse period of the drive signal according to the phase difference between the feedback signal and the drive signal, so that the frequency of the AC signal flowing through the detection coil and the resonant coil follows the resonant frequency of the series resonant circuit that changes accordingly with the inductance change of the detection coil.

[0097] <2>

[0098] according to <1> The current sensor circuit, wherein:

[0099] The signal conversion circuit includes a pulse conversion circuit that converts the drive signal output from the phase adjustment circuit into a PFM (Pulse Frequency Modulation) signal, and obtains the detection signal representing the magnitude of the DC current in terms of voltage based on the PFM signal.

[0100] <3>

[0101] according to <1> or <2> The current sensor circuit, wherein:

[0102] The detection coil winding is wound around the magnetic core, and the detection conductor passes through the magnetic core.

[0103] <4>

[0104] according to <3> The current sensor circuit, wherein:

[0105] The device further comprises a first magnetic field bias unit or a second magnetic field bias unit, wherein the first magnetic field bias unit comprises a bias coil wound around the magnetic core and a DC power supply for passing a constant current through the bias coil, and the second magnetic field bias unit comprises a bias magnet.

[0106] In the first magnetic field bias unit, the DC power supply flows the constant current through the bias coil so as to shift the inductance characteristic of the detection coil to a region where the inductance changes linearly.

[0107] In the second magnetic field bias unit, the bias magnet has a magnetic force capable of causing the inductance characteristic of the detection coil to shift to a region where the inductance changes linearly.

[0108] Description of Reference Numerals

[0109] 1: Current sensor circuit; 10: Phase adjustment circuit; 11: Feedback pulse generation circuit; 12: NOT circuit; 13: Variable resistance element; 14: Capacitor; 16: PLL circuit; 20: Switch circuit; 22: Drive circuit; 30: Detection circuit; 32: Magnetic core; 40: Feedback rectifier circuit; 50: Signal conversion circuit; 51: Pulse conversion circuit; 52: Resistance element; 53: Capacitor; 60: Detection terminal; 511: Resistance element; 512: Capacitor; 513: NOT circuit; 514: AND circuit; N1: Detection coil; N2: Bias coil; Q1, Q2, Q3, Q4: Transistors; R1: Resistance element; C1: Resonance capacitor; TL: Detected wire; BM: Bias magnet.

Claims

1. A current sensor circuit capable of detecting a DC current flowing through a detected conductor, the current sensor circuit comprising: a detection coil configured such that its inductance changes according to the DC current; a resonant capacitor, which forms a series resonant circuit together with the detection coil; a phase adjustment circuit, which receives a feedback signal from the resonant capacitor and outputs a driving signal; a switching circuit comprising a plurality of switching elements forming a half-bridge circuit or a full-bridge circuit, wherein the plurality of switching elements are switched according to a pulse period of the driving signal, thereby providing an AC signal to the detection coil and the resonant capacitor; a signal conversion circuit that converts the drive signal output from the phase adjustment circuit into a detection signal indicating a change in the DC current; and a detection terminal, which outputs the detection signal to the outside, In which, the phase adjustment circuit sets the pulse period of the drive signal according to the phase difference between the feedback signal and the drive signal, so that the frequency of the AC signal flowing through the detection coil and the resonant capacitor follows the resonant frequency of the series resonant circuit that changes accordingly with the inductance change of the detection coil.

2. The current sensor circuit according to claim 1, wherein: The signal conversion circuit includes a pulse conversion circuit that converts the drive signal output from the phase adjustment circuit into a pulse frequency modulation signal (PFM signal), and obtains the detection signal representing the magnitude of the DC current in terms of voltage based on the PFM signal.

3. The current sensor circuit according to claim 1 or 2, wherein: The detection coil winding is wound around the magnetic core, and the detection conductor passes through the magnetic core.

4. The current sensor circuit according to claim 3, wherein: The device further comprises a first magnetic field bias unit or a second magnetic field bias unit, wherein the first magnetic field bias unit comprises a bias coil wound around the magnetic core and a DC power supply for passing a constant current through the bias coil, and the second magnetic field bias unit comprises a bias magnet. In the first magnetic field bias unit, the DC power supply flows the constant current through the bias coil so as to shift the inductance characteristic of the detection coil to a region where the inductance changes linearly. In the second magnetic field bias unit, the bias magnet has a magnetic force capable of causing the inductance characteristic of the detection coil to shift to a region where the inductance changes linearly.

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