阅读说明：本技术 一种磁通门磁饱和保护电路及磁饱和检测方法 (Fluxgate magnetic saturation protection circuit and magnetic saturation detection method ) 是由 不公告发明人 于 2021-07-30 设计创作，主要内容包括：本发明涉及磁通门设计领域,特别涉及一种磁通门磁饱和保护电路及磁饱和检测方法,磁通门磁饱和保护电路,包括：桥式震荡电路、磁环、频率采样电路以及信号处理电路。当磁通门发生磁饱和现象时,体现出来的特征为驱动频率的突然增加,通过频率采样电路,采样系统的震荡频率,信号处理电路判断出高频状态下系统处于磁饱和状态,并输出保护信号,从而有效解决当下磁通门磁饱和工作异常的问题。(The invention relates to the field of fluxgate design, in particular to a fluxgate magnetic saturation protection circuit and a magnetic saturation detection method, wherein the fluxgate magnetic saturation protection circuit comprises: bridge type oscillating circuit, magnetic ring, frequency sampling circuit and signal processing circuit. When the fluxgate generates the magnetic saturation phenomenon, the characteristic is that the driving frequency is suddenly increased, the oscillation frequency of the system is sampled through the frequency sampling circuit, the signal processing circuit judges that the system is in the magnetic saturation state under the high-frequency state and outputs the protection signal, and therefore the problem that the fluxgate works abnormally under the magnetic saturation state is effectively solved.)

1. A fluxgate saturation protection circuit for connection with an earth leakage protector, comprising: the magnetic circuit comprises a bridge type oscillating circuit, a magnetic ring, a frequency sampling circuit and a signal processing circuit;

the bridge type oscillating circuit comprises a bridge type switching circuit and a detection coil connected with the output end of the bridge type switching circuit, and the detection coil surrounds the magnetic ring;

the frequency sampling circuit is used for acquiring the frequency of a driving signal of the bridge type switching circuit or the oscillation frequency of the current of the detection coil and outputting a frequency acquisition signal reflecting the frequency of the driving signal or the oscillation frequency of the current;

and the signal processing circuit judges whether the magnetic ring is in a magnetic saturation state or not according to the frequency acquisition signal, and if so, outputs a control signal to control the leakage protector to be disconnected.

2. The fluxgate saturation protection circuit of claim 1 wherein the frequency sampling circuit comprises: an RC filter circuit, a reference power supply, a comparator U1 and a low-pass filter circuit,

the input end of the RC filter circuit is connected with a driving signal of the bridge type switching circuit, and the output end of the RC filter circuit is connected with the positive input end of the comparator U1;

the inverting input end of the comparator U1 is connected with the reference power supply, and the output end of the comparator U1 is connected with the low-pass filter circuit;

the signal processing circuit comprises a threshold generating circuit, a comparator U2, a comparator U3, a first diode, a second diode, a timing circuit and a comparator U4,

the threshold generation circuit is used for generating a first threshold voltage and a second threshold voltage;

the positive input end of the comparator U2 is connected with the output end of the low-pass filter circuit, the negative input end of the comparator U2 is connected with a first threshold voltage, and the output end of the comparator U2 is connected with the positive input end of the comparator U4 through the first diode;

the negative input end of the comparator U3 is connected with the output end of the low-pass filter circuit, the positive input end of the comparator U3 is connected with a second threshold voltage, and the output end of the comparator U3 is connected with the positive input end of the comparator U4 through the second diode;

one end of the timing circuit is connected with the positive input end of the comparator U4, and the other end of the timing circuit is connected with the ground.

3. The fluxgate saturation protection circuit according to claim 2, wherein the RC filter circuit comprises a resistor R1 and a capacitor C1, one end of the resistor R1 is connected to the driving signal of the bridge switch circuit, and the other end is connected to one end of the capacitor C1 and the positive input port of the comparator U1; the other end of C1 is grounded; the negative input port of the comparator U1 is connected with a reference power supply;

the low-pass filter circuit is provided with a resistor R2, a capacitor C2 and a resistor R3, the output end of the comparator U1 is connected with one end of a resistor R2, the other end of the resistor R2 is respectively connected with a positive input end of the capacitor C2, a resistor R3, a positive input end of the comparator U2 and a negative input end of the comparator U3, and the other ends of the resistor R3 and the capacitor C2 are connected with a reference power supply;

the threshold generation circuit is provided with a voltage source, a resistor R4, a resistor R5 and a resistor R6, one end of the resistor R4 is connected with the voltage source, the other end of the resistor R5 is connected with one end of the resistor R5 and the negative input end of the comparator U2, the other end of the resistor R5 is respectively connected with the positive input end of the comparator U3 and one end of the resistor R6, and the other end of the resistor R6 is grounded;

the timing circuit comprises a capacitor C3 and a resistor R7, the output end of the comparator U2 is respectively connected with the anode of a diode D1, the cathode of the diode D1 is connected with the cathode of a diode D2, one end of a capacitor C3, one end of a resistor R7 and the positive input end of the comparator U4; the output end of the comparator U3 is connected with the anode of a diode D2; the other ends of the capacitor C3 and the resistor R7 are connected together and grounded; the negative input of the comparator U4 is connected to the reference power supply.

4. The saturation protection circuit according to claim 3, wherein the frequency of the driving signal of the bridge switch circuit is selected by setting the magnitudes of the resistor R2 and the capacitor C2.

5. The fluxgate saturation protection circuit according to claim 3, wherein the frequency range of the frequency acquisition signal is set by setting the sizes of the resistor R4, the resistor R5 and the resistor R6.

6. The fluxgate saturation protection circuit according to claim 3, wherein the control of the magnetic saturation recovery time is realized by setting the sizes of the resistor R7 and the capacitor C3.

7. The fluxgate saturation protection circuit according to claim 2, wherein the comparator U1 is a drive shaping isolation comparator, and the comparator U1 isolates the drive signal of the bridge switching circuit to prevent the latter circuit from interfering with the drive circuit; comparator U2 and comparator U3 constitute a window comparator.

8. A magnetic saturation detection method for a fluxgate, the fluxgate comprising: the magnetic saturation detection method comprises the following steps of:

acquiring the frequency of a driving signal of the bridge type switching circuit or the oscillation frequency of the current of the detection coil, and outputting a frequency acquisition signal reflecting the frequency of the driving signal or the oscillation frequency of the current;

and judging whether the magnetic ring is in a magnetic saturation state or not according to the frequency acquisition signal, and if so, outputting a control signal to control the leakage protector to be disconnected.

9. The magnetic saturation detecting method for the fluxgate as claimed in claim 8, wherein the frequency of the driving signal of the bridge switching circuit is collected and the frequency collecting signal reflecting the frequency of the driving signal is outputted accordingly, comprising the steps of:

the driving signal is input into a comparator U1, the driving signal is isolated by a comparator U1, and the output of the comparator U1 obtains a ripple signal reflecting the frequency of the driving signal through a resistor R2 and a capacitor C2, wherein the ripple signal is the frequency acquisition signal of which the ripple amplitude is reduced along with the increase of the frequency of the driving signal.

10. The method as claimed in claim 9, wherein the frequency acquisition signal is compared with a threshold of a window comparator, and if the frequency acquisition signal is smaller than the threshold of the window comparator, the magnetic ring is determined to be in a magnetic saturation state.

Technical Field

The invention relates to the field of design of fluxgates, in particular to a fluxgate magnetic saturation protection circuit and a magnetic saturation detection method.

Background

Referring to fig. 1, a conventional B-type leakage protector mainly includes a fluxgate current detection circuit (hereinafter, referred to as fluxgate), a threshold determination circuit, and an electromagnet. The fluxgate is a most core part and is used for detecting an input current to be detected (namely leakage current), and the output voltage of the fluxgate can accurately restore the waveform of the current to be detected; the threshold value judging circuit is used for detecting the amplitude of the detected current output by the fluxgate, and when the detected current exceeds a standard specified value, the threshold value judging circuit can control the electromagnet to work, so that the leakage protector cuts off a power supply loop, and the leakage dangerous event is prevented.

The existing fluxgate comprises a magnetic ring, a bridge type oscillation circuit (half bridge or full bridge), a sampling resistor, a sampling circuit and a filter circuit, wherein the bridge type oscillation circuit consists of a switching tube Q1, a switching tube Q3 and a detection coil. When the bridge type oscillating circuit works, the bridge type oscillating circuit works in a peak current control mode (bridge arm current is detected, the bridge arms are switched when the bridge arm current reaches a threshold value), and when the voltage on the sampling resistor reaches a certain threshold value, one bridge arm in the bridge type oscillating circuit is controlled to be switched off and the other bridge arm in the bridge type oscillating circuit is controlled to be switched on (namely, when the switch tube Q1 is switched off, the switch tube Q3 is switched on, and when the switch tube Q1 is switched on, the switch tube Q3 is switched off).

Under normal conditions, when the magnetic ring is in a non-magnetic saturation state, the inductance of the detection coil is large, the oscillation frequency of the exciting current of the detection coil is low (namely the frequency of the driving signal of the switching tube Q1 or the switching tube Q3 is low), and the flux gate outputs normally; when the magnetic ring is saturated, the inductance of the detection coil is reduced rapidly, the oscillation frequency of the exciting current of the detection coil is high, and at the moment, the output of the fluxgate is abnormal.

In order to better understand the relationship between the fluxgate saturation phenomenon and the excitation frequency, the fluxgate saturation phenomenon is specifically described as follows:

when the measured current is large, the magnetic flux generated by the detection coil and the excitation current of the detection coil are shown in fig. 2(a) and 2(b), respectively. Ideally, we would like the saturation region to be in any case positive-negative symmetric, and the interval of the saturation region to be as small as possible. However, the peak current is controlled by the peak current, the peak current is not changed, but the saturation point is biased to one side, so that the positive-negative asymmetry degree of the saturation region is increased when the measured current is large, and the detection accuracy is influenced.

If the measured current is increased continuously, the platform of the excitation current (when a constant excitation voltage is applied to the magnetic core, the slope of the unsaturated current of the magnetic core is lower, the slope is higher after saturation, and the waveform unsaturated current shows a platform state) exceeds I_PEAKIt may cause the operation of the fluxgate to be abnormal. The normal fluxgate operation process is that saturation and non-saturation alternately occur. When the current to be measured is more than I after the turn ratio is equivalent_PEAKWhen the magnetic field is applied, its working state is shown in 3, and the measured current can produce a negative magnetic flux, and when the coil is positively excited, it must be reached to B_RE-The magnetic ring will exit the saturation state but not reach B_RE-The peak current in the forward direction is reached, so the inductance of the detection coil in the forward excitation is L₀It is obvious that the inductance of the detection coil is also L when reversely excited₀. When the magnetic field is excited in two directions, L0, the exciting frequency can be increased to more than ten times rapidly, the detecting function is lost, the output voltage can gradually return to zero along with the increase of the measured current, and the phenomenon is the saturation phenomenon of the fluxgate magnet.

However, the leakage protector in the current sensor product in the existing market has no magnetic saturation protection function, and constitutes a potential danger for power application, that is, when the magnetic ring is magnetically saturated, the detected current (leakage current) is already large to an extreme state, but the leakage protector fails. The invention provides a technical scheme for solving the problem of magnetic saturation.

Disclosure of Invention

Therefore, the technical problem to be solved by the invention is to provide a fluxgate magnetic saturation protection circuit, which can enable the fluxgate circuit not to influence the output of the later stage when the fluxgate circuit is in magnetic saturation under the condition of achieving the same beneficial effects.

The invention conception is as follows: by analyzing the magnetic saturation phenomenon, it is recognized that the oscillation frequency is increased to more than 10 times of the normal frequency, and thus a magnetic saturation protection signal can be given at a high frequency by acquiring the oscillation frequency of the system.

The technical scheme for solving the technical problems is as follows:

a fluxgate saturation protection circuit for connection to an earth leakage protector, comprising: the magnetic circuit comprises a bridge type oscillating circuit, a magnetic ring, a frequency sampling circuit and a signal processing circuit;

the bridge type oscillating circuit comprises a bridge type switching circuit and a detection coil connected with the output end of the bridge type switching circuit, and the detection coil surrounds the magnetic ring;

the frequency sampling circuit is used for acquiring the frequency of a driving signal of the bridge type switching circuit or the oscillation frequency of the current of the detection coil and outputting a frequency acquisition signal reflecting the frequency of the driving signal or the oscillation frequency of the current according to the frequency acquisition signal;

the signal processing circuit judges whether the magnetic ring is in a magnetic saturation state or not according to the frequency acquisition signal, and if so, outputs a control signal to control the leakage protector to be disconnected.

In one embodiment, a frequency sampling circuit includes: an RC filter circuit, a reference power supply, a comparator U1 and a low-pass filter circuit,

the input end of the RC filter circuit is connected with a driving signal of the bridge type switching circuit, and the output end of the RC filter circuit is connected with the positive input end of the comparator U1;

the inverting input end of the comparator U1 is connected with a reference power supply, and the output end of the comparator U1 is connected with a low-pass filter circuit;

the signal processing circuit comprises a threshold generating circuit, a comparator U2, a comparator U3, a first diode, a second diode, a timing circuit and a comparator U4,

the threshold generating circuit is used for generating a first threshold voltage and a second threshold voltage;

the positive input end of the comparator U2 is connected with the output end of the low-pass filter circuit, the negative input end of the comparator U2 is connected with a first threshold voltage, and the output end of the comparator U2 is connected with the positive input end of the comparator U4 through a first diode;

the negative input end of the comparator U3 is connected with the output end of the low-pass filter circuit, the positive input end of the comparator U3 is connected with the second threshold voltage, and the output end of the comparator U3 is connected with the positive input end of the comparator U4 through a second diode;

one end of the timing circuit is connected to the positive input of the comparator U4, and the other end is connected to ground.

In one embodiment, the RC filter circuit includes a resistor R1 and a capacitor C1, one end of the resistor R1 is connected to the driving signal of the bridge switch circuit, and the other end is connected to one end of the capacitor C1 and the positive input port of the comparator U1; the other end of C1 is grounded; the negative input port of the comparator U1 is connected with a reference power supply;

the low-pass filter circuit is provided with a resistor R2, a capacitor C2 and a resistor R3, the output end of the comparator U1 is connected with one end of a resistor R2, the other end of the resistor R2 is respectively connected with a positive input end of the capacitor C2, a resistor R3, a positive input end of the comparator U2 and a negative input end of the comparator U3, and the other ends of the resistor R3 and the capacitor C2 are connected with a reference power supply;

the threshold generation circuit is provided with a voltage source, a resistor R4, a resistor R5 and a resistor R6, one end of the resistor R4 is connected with the voltage source, the other end of the resistor R5 is connected with one end of the resistor R5 and the negative input end of the comparator U2, the other end of the resistor R5 is respectively connected with the positive input end of the comparator U3 and one end of the resistor R6, and the other end of the resistor R6 is grounded;

the timing circuit comprises a capacitor C3 and a resistor R7, the output end of the comparator U2 is respectively connected with the anode of a diode D1, the cathode of the diode D1 is connected with the cathode of a diode D2, one end of a capacitor C3, one end of a resistor R7 and the positive input end of the comparator U4; the output end of the comparator U3 is connected with the anode of a diode D2; the other ends of the capacitor C3 and the resistor R7 are connected together and grounded; the negative input of the comparator U4 is connected to the reference power supply.

In one embodiment, the frequency of the drive signal for the bridge switch circuit is selected by setting the size of resistor R2 and capacitor C2.

In one embodiment, the frequency range of the frequency acquisition signal is set by sizing the resistor R4, the resistor R5, and the resistor R6.

In one embodiment, control of the magnetic saturation recovery time is achieved by sizing the resistor R7 and the capacitor C3.

In one embodiment, the comparator U1 is a drive shaping isolation comparator, and the comparator U1 isolates the drive signal of the bridge switching circuit to prevent the latter circuit from interfering with the drive circuit; comparator U2 and comparator U3 are window comparators, respectively.

The present invention also provides a magnetic saturation detection method for a fluxgate, the fluxgate including: the magnetic saturation detection method comprises the following steps of:

acquiring the frequency of a driving signal of a bridge type switching circuit or the oscillation frequency of current of a detection coil, and outputting a frequency acquisition signal reflecting the frequency of the driving signal or the oscillation frequency of the current according to the frequency acquisition signal;

and judging whether the magnetic ring is in a magnetic saturation state or not according to the frequency acquisition signal, and if so, outputting a control signal to control the leakage protector to be disconnected.

In one embodiment, the step of acquiring the frequency of the driving signal of the bridge switching circuit and accordingly outputting a frequency acquisition signal reflecting the frequency of the driving signal comprises the following steps:

inputting a driving signal into a comparator U1, isolating the driving signal through a comparator U1, and obtaining a ripple signal reflecting the frequency of the driving signal through the output of a comparator U1 through a resistor R2 and a capacitor C2; the ripple signal is the frequency acquisition signal with the ripple amplitude decreasing with the increase of the frequency of the driving signal.

In one embodiment, the frequency acquisition signal is compared with a threshold of a window comparator, and if the frequency acquisition signal is smaller than the threshold of the window comparator, the magnetic ring is judged to be in a magnetic saturation state.

The fluxgate magnetic saturation protection principle is that when a fluxgate circuit generates a magnetic saturation phenomenon, the characteristic is that the driving frequency is suddenly increased (after the magnetic material is saturated, the inductance suddenly changes, and therefore the oscillation frequency suddenly increases), that is, the frequency of a driving signal Vgs of a bridge type switching circuit is increased, a square wave with the same frequency as Vgs1 is formed by Vgs of the bridge type switching circuit, Vgs1 is filtered by low pass filters R2, C2 and R3 to form a frequency sampling signal Vgs2 with a reduced ripple amplitude, and the frequency sampling signal Vgs2 cannot reach the threshold of a comparator U2 and a comparator U3, so that the output is a low level, at this time, the positive input port of the comparator U4 is a low level, so the output of the comparator U4 is a low level, and the low level is a magnetic saturation state. Otherwise, the output high level is in a non-magnetic saturation state.

The working principle of the invention will be analyzed and explained by combining with the specific embodiment, and the invention can be used for solving the problem of abnormal magnetic saturation operation of the current fluxgate circuit.

Drawings

FIG. 1 is a schematic structural diagram of a B-type earth leakage protector;

FIG. 2(a) is a schematic diagram showing the variation of magnetic flux generated by the detection coil when the measured current is large;

FIG. 2(b) is a schematic diagram of the current generated by the detection coil when the measured current is large;

FIG. 3 is a diagram of the saturation operating condition of the fluxgate magnet;

FIG. 4 is a schematic structural diagram of a fluxgate saturation protection circuit according to a first embodiment of the present invention;

FIG. 5 is a circuit diagram of a frequency sampling circuit and a signal processing circuit in the fluxgate saturation protection circuit of the present invention;

FIG. 6 is a waveform illustrating operation of the first embodiment of the present invention;

FIG. 7 is a schematic diagram of a fluxgate saturation protection circuit according to a second embodiment of the present invention;

FIG. 8 is a schematic diagram of a saturation protection circuit of fluxgate according to a third embodiment of the present invention;

FIG. 9 is a schematic diagram of a saturation protection circuit of fluxgate according to a fourth embodiment of the present invention;

fig. 10 is a schematic structural diagram of a fluxgate saturation protection circuit according to a fifth embodiment of the present invention.

Detailed Description

In order to make the invention more clearly understood, the invention is further described in detail below with reference to the attached drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

First embodiment

Referring to fig. 4 and 5, the invention provides a fluxgate saturation protection circuit, which includes a bridge oscillator circuit, a frequency sampling circuit 1, a magnetic ring 2, a signal processing circuit 3 and a sampling resistor.

The bridge type oscillating circuit comprises a bridge type switching circuit consisting of a switching tube Q1 and a switching tube Q3 and a detection coil 11 connected with the output end of the bridge type switching circuit, wherein the detection coil 11 surrounds the magnetic ring 2.

The frequency sampling circuit 1 is used for acquiring the frequency of a driving signal of the bridge switching circuit or the oscillation frequency of the current of the detection coil, and outputting a frequency acquisition signal reflecting the frequency of the driving signal or the oscillation frequency of the current according to the frequency acquisition signal. In this embodiment, the frequency sampling circuit 1 acquires a frequency acquisition signal by acquiring a frequency of a driving signal of the bridge switching circuit.

The signal processing circuit 3 is used for judging whether the magnetic ring 2 is in a magnetic saturation state according to the frequency acquisition signal, and if so, outputting a control signal to control the leakage protector to be disconnected.

The frequency sampling circuit 1 includes: an RC filter circuit, a reference power supply Vref, a comparator U1, and a low pass filter circuit.

The input end of the RC filter circuit is connected with a driving signal of the bridge type switching circuit, and the output end of the RC filter circuit is connected with the positive input end of the comparator U1; the inverting input terminal of the comparator U1 is connected to the reference power Vref, and the output terminal is connected to the low-pass filter circuit. In this embodiment, the RC filter circuit has a resistor R1 and a capacitor C1, one end of the resistor R1 is connected to the driving signal of the bridge switch circuit, and the other end is connected to one end of the capacitor C1 and the positive input port of the comparator U1; the other end of the capacitor C1 is grounded; the negative input port of the comparator U1 is connected to a reference supply Vref. In this embodiment, the comparator U1 is a drive shaping isolation comparator, and the comparator U1 isolates the drive signal to prevent the interference of the subsequent circuit with the drive circuit.

The low-pass filter circuit is provided with a resistor R2, a capacitor C2 and a resistor R3, the output end of the comparator U1 is connected with one end of a resistor R2, the other end of the resistor R2 is respectively connected with a positive input end of the capacitor C2, the resistor R3, the positive input end of the comparator U2 and the negative input end of the comparator U3, and the other ends of the resistor R3 and the capacitor C2 are connected with a reference power supply Vref together. The driving signal frequency of the bridge switching circuit can be converted into a ripple signal (i.e., a frequency acquisition signal) by setting the sizes of the resistor R2 and the capacitor C2.

The signal processing circuit 3 includes a threshold generation circuit, a comparator U2, a comparator U3, a first diode, a second diode, a timing circuit, and a comparator U4. The comparator U2 and the comparator U3 form a window comparator.

The threshold generation circuit is provided with a voltage source, a resistor R4, a resistor R5 and a resistor R6, one end of the resistor R4 is connected with the voltage source VCC, the other end of the resistor R5 is connected with one end of the resistor R5 and the negative input end of the comparator U2, the other end of the resistor R5 is respectively connected with the positive input end of the comparator U3 and one end of the resistor R6, and the other end of the resistor R6 is grounded. Wherein the junction of the resistor R4 and the negative input of the comparator U2 generates a first threshold voltage UI-INN (window comparator threshold); the junction of the resistor R6 and the positive input of the comparator U3 produces a second threshold voltage U2-INP (window comparator threshold). The invention sets the frequency range of the frequency acquisition signal by setting the sizes of the resistor R4, the resistor R5 and the resistor R6.

The positive input terminal of the comparator U2 is connected with the output terminal of the low-pass filter circuit, and the output terminal of the comparator U2 is connected with the positive input terminal of the comparator U4 through a diode D1. The negative input end of the comparator U3 is connected with the output end of the low-pass filter circuit, and the output end of the comparator U3 is connected with the positive input end of the comparator U4 through a diode D2.

The timing circuit comprises a capacitor C3 and a resistor R7, the output end of the comparator U2 is respectively connected with the anode of a diode D1, the cathode of the diode D1 is connected with the cathode of a diode D2, one end of a capacitor C3, one end of a resistor R7 and the positive input end of the comparator U4; the output end of the comparator U3 is connected with the anode of a diode D2; the other ends of the capacitor C3 and the resistor R7 are connected together and grounded; the negative input of the comparator U4 is connected to the reference power supply Vref. The invention realizes the control of the magnetic saturation delay time by setting the sizes of the resistor R7 and the capacitor C3. When the voltage of a frequency acquisition signal Vgs2 is at VCC/2 when a magnetic saturation phenomenon occurs, the output of each of the comparators U2 and U3 is at a low level, and when the resistor R7 discharges the capacitor C3 to be below a reference power supply Vref, the output of the comparator U4 is at a low level, which is a magnetic saturation protection signal. The magnetic saturation delay time refers to the delay to the comparator U4 outputting a low level when the system enters magnetic saturation.

The magnetic saturation control method adopted by the fluxgate magnetic saturation protection circuit in the embodiment is as follows: when the fluxgate circuit generates the magnetic saturation phenomenon, the characteristics are that the driving frequency is suddenly increased (the inductance of the detection coil is suddenly increased after the magnetic material is saturated, and therefore, the oscillation frequency of the current of the detection coil is suddenly increased), that is, the frequency of the driving signal Vgs is increased, the square wave signal Vgs1 is a square wave having the same frequency as the driving signal Vgs, the square wave signal Vgs1 is filtered by the low pass filter composed of R2 and C2, and then the frequency acquisition signal Vgs2 with the wave amplitude being increased and decreased relative to the frequency of the square wave signal Vgs1 is output, at this time, Vgs1 is a high frequency signal, so the amplitude of the frequency acquisition signal Vgs2 cannot reach the first threshold voltage input to the comparator U2 and the second threshold voltage input to the comparator U3, therefore, the outputs of the comparators U2 and U3 are both low level, at this time, the resistor R7 exists, the positive input port of the comparator U4 is low level, and therefore, the output of the comparator U4 is low level, and the low level is in the magnetic saturation state, the earth leakage protector is controlled to be disconnected. Otherwise, the output high level is in a non-magnetic saturation state.

Referring to fig. 6, fig. 6 is a working waveform diagram of the first embodiment of the present invention, where Iin is an input measured current to be input to the fluxgate, Vgs1 is a fluxgate oscillation frequency, i.e. a frequency acquisition signal of the magnetic saturation circuit, Vgs2 is an output of the low-pass filter circuit, and it can be seen from the waveform that when Iin current is between 2A to 0.6A, -0.6A and-2A, Vgs1 is high in frequency, Vgs2 is small in oscillation amplitude, and vo (ctr) is that the low-level fluxgate has undergone a magnetic saturation phenomenon; in the range of-0.6A to 0.6A, the Vgs1 frequency is low, the Vgs2 oscillation amplitude is large, the first threshold voltage and the second threshold voltage of the comparators U2 and U3 are triggered, and vo (ctr) is high level, which indicates that the fluxgate works normally.

In conclusion, when the fluxgate is normal, the magnetic saturation protection signal is at a high level, and when the fluxgate is in a magnetic saturation state, the magnetic saturation protection signal is at a low level, so that the problem that the fluxgate is abnormal when the fluxgate is in the magnetic saturation state is solved.

Second embodiment

Fig. 7 is a schematic diagram of a fluxgate saturation protection circuit according to a second embodiment of the present invention. The difference from the first embodiment is that: frequency sampling is achieved by sampling the drive signal of the switching tube Q1.

Third embodiment

Fig. 8 is a schematic diagram of a fluxgate saturation protection circuit according to a third embodiment of the present invention. The difference from the first embodiment is that: frequency sampling is achieved by sampling the drain-source voltage of the switching tube Q3.

Fourth embodiment

Fig. 9 is a schematic diagram of a fluxgate saturation protection circuit according to a fourth embodiment of the present invention. The difference from the first embodiment is that: frequency sampling is achieved by sampling resistors.

Fifth embodiment

Fig. 10 is a schematic diagram of a fluxgate saturation protection circuit according to a fifth embodiment of the present invention. The difference from the first embodiment is that: the frequency sampling point is realized by sampling the current of the magnetic ring auxiliary winding.

The invention has various circuit form changes, and the working principle of the second embodiment to the fifth embodiment is that the magnetic saturation protection signal is output when the fluxgate oscillation frequency is suddenly increased by collecting the fluxgate oscillation frequency.

The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiment should not be considered as limiting the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and these modifications and adaptations should be considered within the scope of the invention.