CN117394674A - Electromagnetic interference filter and electronic equipment - Google Patents

Abstract

The application discloses an electromagnetic interference filter, which comprises a signal processing module and a passive filtering module, wherein the input end of the signal processing module and the input end of the passive filtering module are commonly connected with an external power grid, and the output end of the signal processing module is connected with the input end of the passive filtering module; the signal processing module comprises a sampling circuit and a signal injection circuit, wherein the sampling circuit is used for collecting common-mode voltage signals, and the signal injection circuit is used for generating common-mode current signals according to the common-mode voltage signals so as to counteract common-mode noise in a circuit where the electromagnetic interference filter is located. By additionally arranging the signal processing module between the passive filtering module and the external power grid, common-mode voltage signal sampling is carried out from the external power grid, and the common-mode current signal obtained through processing is input back to the passive filtering module, so that common-mode noise signals in a circuit are eliminated, the volume, weight, cost and copper loss of common-mode inductance in the passive filtering module are reduced, and finally the aim of improving the safety of the circuit is achieved.

Description

Electromagnetic interference filter and electronic equipment

Technical Field

The application relates to the technical field of electronic circuits, in particular to an electromagnetic interference filter and electronic equipment.

Background

A large number of switching devices controlled by PWM, PDM, PFM and transient switches exist in a power electronic system, and electromagnetic interference (EMI) mainly comprising common mode noise can be generated due to voltage and current transients existing in the process of rapidly switching on and off the switching devices.

In order to reduce electromagnetic interference of the power electronic system to the outside, a passive EMI filter is generally used to filter out common mode noise. The passive EMI filter filters common mode noise through the common mode inductance and the Y capacitor, the volume, weight, cost and copper loss of the required common mode inductance are high, and the leakage current of the system to the ground caused by the Y capacitor is large. In the case of using only a passive EMI filter, the volume of the common-mode inductance increases with an increase in power of the power electronic device main body, and the power loss and the occupied volume of the filter itself are hardly reduced.

Disclosure of Invention

The application provides an electromagnetic interference filter and electronic equipment.

The electromagnetic interference filter comprises a signal processing module and a passive filtering module, wherein the input end of the signal processing module and the input end of the passive filtering module are commonly connected with an external power grid, and the output end of the signal processing module is connected with the input end of the passive filtering module;

the signal processing module comprises a sampling circuit and a signal injection circuit, wherein the sampling circuit is used for collecting common-mode voltage signals, and the signal injection circuit is used for generating common-mode current signals according to the common-mode voltage signals so as to counteract common-mode noise in a circuit where the electromagnetic interference filter is located.

Thus, according to the embodiment of the application, the signal processing module is additionally arranged between the passive filtering module and the external power grid, common-mode voltage signal sampling is carried out from the external power grid, and the common-mode current signal obtained through processing is input to the passive filtering module, so that common-mode noise signals in a circuit are eliminated through mutual cancellation of opposite-phase signals, dependence on common-mode inductance in the passive filtering module is reduced, inductance of the common-mode inductance is reduced, and therefore the volume, weight, cost and copper loss of the common-mode inductance are reduced, and finally the purposes of reducing capacitance of a Y capacitor in the passive filtering module and reducing leakage current of a filter to the ground are achieved, so that the circuit safety is improved.

In some embodiments, the signal processing module further includes an inverter circuit and a signal conversion circuit, wherein an input end of the sampling circuit is connected with the external power grid, the sampling circuit, the inverter circuit, the signal conversion circuit and the signal injection circuit are sequentially connected in series, and an output end of the signal injection circuit is connected with an input end of the passive filtering module.

In this way, the embodiment of the application can process the collected common-mode voltage signal sequentially through the sampling circuit, the inverting circuit, the signal conversion circuit and the signal injection circuit in the signal processing module, so as to obtain a common-mode current signal for eliminating common-mode noise.

In some embodiments, the sampling circuit includes a first high-pass filtering sub-circuit, a notch filtering sub-circuit, a second high-pass filtering sub-circuit and an impedance matching sub-circuit, wherein an input end of the first high-pass filtering sub-circuit is connected with the external power grid, the first high-pass filtering sub-circuit, the notch filtering sub-circuit, the second high-pass filtering sub-circuit and the impedance matching sub-circuit are sequentially connected in series and are all grounded, and an output end of the impedance matching sub-circuit is connected with the inverting circuit.

In some embodiments, the first high-pass filter sub-circuit includes one or more first capacitors and a first resistor, the number of the first capacitors is determined according to a connection mode between the external power grid and the input end of the signal processing module, the anode of the first capacitor is connected to the external power grid, the cathode of the first capacitor is connected to the first end of the first resistor and the notch filter sub-circuit, and the second end of the first resistor is grounded.

In some embodiments, the notch filter sub-circuit includes a second resistor, a first induction coil, and a second capacitor, a first end of the second resistor is connected to the first high-pass filter sub-circuit, a second end of the second resistor is connected to the first induction coil and the second high-pass filter sub-circuit, and the first induction coil is further connected to the second capacitor in series with ground.

In some embodiments, the second high-pass filter sub-circuit includes a third capacitor, a third resistor, and a fourth resistor, where the third capacitor, the third resistor, and the fourth resistor are serially connected to ground in sequence, an anode of the third capacitor is connected to the notch filter sub-circuit, and a cathode of the third capacitor is connected to the first end of the third resistor.

In some embodiments, the impedance matching sub-circuit includes a first transient voltage suppressor, an operational amplifier, and an external power supply matched with the operational amplifier, wherein a first end of the first transient voltage suppressor is connected to a second end of the third resistor and a first input end of the operational amplifier, a second end of the first transient voltage suppressor is grounded, and an output end of the operational amplifier is connected to the inverter circuit.

In this way, in the sampling circuit in the embodiment of the application, the high-frequency signal component and the low-frequency signal component in the common-mode voltage signal are filtered respectively through the two groups of high-pass filter sub-circuits, and meanwhile, the resonance phenomenon of the passive filter module is eliminated through the notch filter sub-circuits, and the impedance matching sub-circuits are utilized to protect the sampling circuit and the whole electronic interference filter when the circuit has the surge phenomenon. Meanwhile, the sampling circuit can also adjust the number and the connection mode of the first capacitors in the first high-pass filtering sub-circuit according to the connection mode of an external power grid connected with the electromagnetic interference filter so as to adapt to circuits with different connection modes.

In some embodiments, the signal injection circuit includes a clamp protection sub-circuit, a surge protection sub-circuit, and a signal injection sub-circuit, where the clamp protection sub-circuit, the surge protection sub-circuit, and the signal injection sub-circuit are serially connected in sequence, the surge protection sub-circuit is grounded, and an output end of the signal injection sub-circuit is connected with an input end of the passive filter module.

In some embodiments, the clamp protection sub-circuit includes a first clamp diode, a second clamp diode, and an external power supply used in a matched manner, where the external power supply is further used to support the operation of the sampling circuit; the positive pole of first clamp diode and the negative pole of second clamp diode are connected jointly the input of signal injection circuit, the negative pole of first clamp diode is connected the first end of external power supply, the positive pole of second clamp diode is connected the second end of external power supply, the electric potential of external power supply first end is higher than the electric potential of external power supply second end.

In some embodiments, the surge protection sub-circuit includes a fifth resistor, a sixth resistor, and a second transient voltage suppressor, wherein a first end of the fifth resistor is connected to the clamp protection sub-circuit, a second end of the fifth resistor is connected to the signal injection sub-circuit, and the sixth resistor and the second transient voltage suppressor are connected in parallel between the second end of the fifth resistor and ground.

In some embodiments, the signal injection sub-circuit includes one or more fourth capacitors, the number of the fourth capacitors is determined according to a connection mode between the external power grid and the input end of the signal processing module, an anode of the fourth capacitor is connected with the surge protection sub-circuit, and a cathode of the fourth capacitor is connected with the input end of the passive filter module.

Therefore, the signal injection circuit in the embodiment of the application can protect the signal injection circuit and the electromagnetic interference filter through means such as clamping voltage and transient voltage control under the condition that the circuit is in a surge state by arranging the clamping protection sub-circuit and the surge protection sub-circuit, and meanwhile, the number and the connection mode of the fourth capacitors in the signal injection sub-circuit can be adjusted according to the connection modes of the signal processing module, the passive filtering module and an external power grid so as to adapt to the circuits in different connection modes.

The electronic device of the embodiment of the application comprises the electromagnetic interference filter.

Additional aspects and advantages of embodiments of the application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of embodiments of the application.

Drawings

The foregoing and/or additional aspects and advantages of the present application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:

fig. 1 is a schematic block diagram of an electromagnetic interference filter according to an embodiment of the present application;

fig. 2 is a schematic diagram of a signal processing module according to an embodiment of the present application;

fig. 3 is a schematic circuit diagram of a sampling circuit according to an embodiment of the present application;

fig. 4 is a schematic circuit diagram of a signal injection circuit according to an embodiment of the present application;

wherein: r1, a first resistor; r2, a second resistor; r3, a third resistor; r4, a fourth resistor; r5, a fifth resistor; r6, a sixth resistor; l1, a first induction coil; TVS1, a first transient voltage suppressor; TVS2, a second transient voltage suppressor; a1, an operational amplifier; c1 (C1 ', C1", C1'") a first capacitance; c2, a second capacitor; c3, a third capacitor; c4 (C4 ', C4", C4'") a fourth capacitance; d1, a first clamping diode; d2, a second clamping diode.

Detailed Description

Embodiments of the present application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are exemplary only for explaining the embodiments of the present application and are not to be construed as limiting the embodiments of the present application.

As shown in fig. 1, the electromagnetic interference filter in the embodiment of the application includes a signal processing module and a passive filtering module, wherein an input end of the signal processing module and an input end of the passive filtering module are commonly connected with an external power grid, and an output end of the signal processing module is connected with an input end of the passive filtering module;

the signal processing module comprises a sampling circuit and a signal injection circuit, wherein the sampling circuit is used for collecting common-mode voltage signals, and the signal injection circuit is used for generating common-mode current signals according to the common-mode voltage signals so as to counteract common-mode noise in a circuit where the electromagnetic interference filter is located.

Electromagnetic interference filters, i.e., EMI filters, are widely used in various types of circuits to remove common mode noise signals generated by circuit hopping. EMI filters are generally classified into active EMI filters requiring external power support and passive EMI filters requiring external power support. In order to reduce electromagnetic interference of the power electronic system to the outside, a passive EMI filter is generally used to filter out common mode noise. The passive EMI filter filters common mode noise through the common mode inductance and the Y capacitor, the volume, weight, cost and copper loss of the required common mode inductance are high, and the leakage current of the system to the ground caused by the Y capacitor is large. In order to improve the working performance of the EMI filter, the embodiment of the application provides an EMI filter, which is modified based on a passive EMI filter.

Specifically, the electromagnetic interference filter comprises a signal processing module and a passive filtering module, wherein the passive filtering module is a passive electromagnetic interference filter, and the input end of the passive filtering module is directly connected with an external power grid. The signal processing module is additionally arranged between the external power grid and the passive filtering module, the input end of the signal processing module is connected with the external power grid, and the output end of the signal processing module is connected with the input end of the passive filtering module.

Because the external power grid is generally an ac circuit, especially a three-phase ac circuit is used in many cases, the external power grid and the electromagnetic interference filter can be connected in various ways. The situation shown in fig. 1 is a connection mode of an external power grid and an electromagnetic interference filter under the condition of three-phase three-wire system connection, wherein the input end of the signal processing module and the input end of the passive filtering module are respectively connected with three phase lines introduced by the external power grid. In addition to the situation shown in fig. 1, in the three-phase four-wire connection mode, the input end of the signal processing module and the input end of the passive filtering module are respectively connected with three phase lines and a neutral line introduced by an external power grid. In the single-phase connection mode, the input end of the signal processing module and the input end of the passive filtering module are respectively connected with a phase line and a neutral line which are introduced by an external power grid. In particular, in a single-wire connection mode, the input end of the signal processing module and the input end of the passive filtering module are respectively connected with a phase line or a neutral line introduced by an external power grid. That is, the electromagnetic interference filter in the embodiment of the application can adapt to the connection modes of various alternating current circuits, and effectively expands the application range of the electromagnetic interference filter for various different current supply scenes.

And for the signal processing module, in order to eliminate common mode noise existing in the circuit through common mode voltage signals and common mode current signals, a sampling circuit and a signal injection circuit are arranged in the signal processing module, the sampling circuit is used for directly obtaining common mode voltage signals from electric signals introduced into the electromagnetic interference filter, the common mode current signals are obtained after being processed by the signal processing module, and then the common mode current signals are injected into the passive filter module through the signal injection circuit, so that the common mode noise existing in the electric signals introduced by the passive filter module is counteracted. In order to ensure the technical effects, the input end of the signal processing module is the input end of the sampling circuit, the output end of the signal processing module is the output end of the signal injection circuit, and the connection mode of the signal processing module depends on the circuit connection mode of an external power grid.

For passive EMI filter, the filtering effect of the filter on the electric signal is to filter the common mode noise through the LC filter circuit composed of the common mode inductance coil and the Y capacitor, the filtering effect generally depends on the inductance value of the common mode inductance, so the requirements on the volume, weight, cost and copper loss of the common mode inductance are high. In the embodiment of the application, the common mode voltage signal and the common mode current signal are utilized to preprocess the electric signal introduced into the passive filtering module through the signal processing module, so that the amount of common mode noise in the electric signal is reduced in advance. The passive filtering module receives the electric signal processed by the signal processing module, then filters the electric signal, and outputs the electric signal to other loads (not shown in the figure) in the circuit at the output end. When the common mode noise frequency is low and the noise voltage is relatively large, the magnetic flux density of the common mode inductance core is increased, so that the requirement on the magnetic flux density of the common mode inductance core is reduced under the condition of filtering the common mode noise in advance, which brings the following two benefits: (1) Inexpensive magnetic core materials with low saturation magnetic flux density can be used, thereby reducing cost; (2) The low-frequency noise can be reduced, the magnetic flux requirement on the magnetic core is lower, the size of the magnetic core can be reduced, and the volume of the common-mode inductance can be reduced, so that the weight, the cost and the copper loss of the common-mode inductance are reduced.

In addition, because the coil needs to be wound on the magnetic core during the production of the common-mode inductor, the processing error of the wound coil is large, and the parameter consistency among the common-mode inductor monomers is far lower than that of semiconductor devices such as operational amplifiers, transistors and the like. Because the magnetic permeability of the magnetic core material is greatly affected by temperature, the temperature stability of the common-mode inductance is lower than that of semiconductor devices such as operational amplifiers, transistors and the like. The passive electromagnetic interference filter circuit in the related art relies on only the common mode inductance and the Y capacitor to filter out common mode noise. Therefore, in the electromagnetic interference filter provided by the embodiment of the application, the signal processing module mainly utilizes the semiconductor device to offset common mode noise by injecting the common mode current with opposite phases in advance, so that the difference deviation between the single elements of the filter circuit device can be reduced, and the consistency and the temperature stability between the single elements of the circuit are improved. In addition, common mode noise is restrained or eliminated through common mode current signals in advance, the requirement on the capacitance value of the Y capacitor in the passive filter module is reduced, and therefore the Y capacitor with smaller capacitance value can be adopted in the passive filter module, the capacitance value of the Y capacitor in the passive filter module is reduced, leakage current of the filter to the ground is reduced, and therefore circuit safety is improved.

Thus, according to the embodiment of the application, the signal processing module is additionally arranged between the passive filtering module and the external power grid, common-mode voltage signal sampling is carried out from the external power grid, and the common-mode current signal obtained through processing is input to the passive filtering module, so that common-mode noise signals in a circuit are eliminated through mutual cancellation of opposite-phase signals, dependence on common-mode inductance in the passive filtering module is reduced, inductance of the common-mode inductance is reduced, and therefore the volume, weight, cost and copper loss of the common-mode inductance are reduced, and finally the purposes of reducing capacitance of a Y capacitor in the passive filtering module and reducing leakage current of a filter to the ground are achieved, so that the circuit safety is improved.

In some embodiments, the signal processing module further includes an inverter circuit and a signal conversion circuit, wherein an input end of the sampling circuit is connected with an external power grid, the sampling circuit, the inverter circuit, the signal conversion circuit and the signal injection circuit are sequentially connected in series, and an output end of the signal injection circuit is connected with an input end of the passive filtering module.

Referring to fig. 2, fig. 2 schematically illustrates the operation of the signal processing module. After the signal processing module acquires a common-mode voltage signal through an input end (input) connected with an external power grid, the first-stage high-pass filtering sub-circuit (HPF 1) is used for filtering the acquired common-mode voltage signal, and then the voltage signal which is opposite to the common-mode voltage signal in phase and is larger than the common-mode voltage signal in amplitude is obtained through the inversion processing (I O) of the inversion circuit and the amplification stage processing (K). Then, the voltage signal is converted into a current signal through a voltage-to-current Converter (Vto I Converter), and then the current signal is filtered through a second-stage high-pass filter sub-circuit (HPF 2), so that a common-mode current signal is finally obtained, and the common-mode current signal is transmitted back to each phase line or neutral line of an external power grid through an output terminal (output), so that noise signal parts in the connected electric signals are offset. The signal processing module may be capable of achieving the above-mentioned effects in principle, and it is not necessary to construct the signal processing module by taking analog circuit components such as an operational amplifier, and the signal processing module may be formed by digital circuits such as a DSP, and the above-mentioned effects may be achieved.

On the basis of the principle and the embodiment, in order to process the common-mode voltage signal acquired by the sampling circuit to obtain a common-mode current signal, the signal processing module is further provided with an inverting circuit and a signal conversion circuit. After the sampling circuit acquires the common-mode voltage signal, in order to cancel out common-mode noise in the electric signal input to the passive filter module by the common-mode current signal generated from the common-mode voltage signal, the acquired common-mode voltage signal needs to be subjected to an inversion process so that the phase of the common-mode voltage signal becomes a state opposite to the original phase. In addition, in order to facilitate signal conversion, in some examples, an amplifying stage sub-circuit is further provided in the inverting circuit, and the obtained common-mode voltage signal can be amplified while the phase of the input common-mode voltage signal is inverted.

Then, in order to obtain the common-mode current signal, the inverted common-mode voltage signal is also required to be converted into the common-mode current signal, so the inverted common-mode voltage signal is converted into the common-mode current signal by the arrangement of the signal conversion circuit.

The sampling circuit, the inverting circuit, the signal converting circuit and the signal injection circuit are arranged in series in order to realize the elimination of common mode noise in the order of sampling, inverting, signal converting and signal injection.

In this way, the embodiment of the application can process the collected common-mode voltage signal sequentially through the sampling circuit, the inverting circuit, the signal conversion circuit and the signal injection circuit in the signal processing module, so as to obtain a common-mode current signal for eliminating common-mode noise.

In some embodiments, the sampling circuit includes a first high-pass filtering sub-circuit, a notch filtering sub-circuit, a second high-pass filtering sub-circuit and an impedance matching sub-circuit, wherein an input end of the first high-pass filtering sub-circuit is connected with an external power grid, the first high-pass filtering sub-circuit, the notch filtering sub-circuit, the second high-pass filtering sub-circuit and the impedance matching sub-circuit are sequentially connected in series and are all grounded, and an output end of the impedance matching sub-circuit is connected with the inverting circuit.

In some embodiments, the first high-pass filter sub-circuit includes one or more first capacitors C1 and a first resistor R1, the number of the first capacitors C1 is determined according to a connection manner between an external power grid and an input end of the signal processing module, an anode of the first capacitor C1 is connected to the external power grid, a cathode of the first capacitor C1 is connected to a first end of the first resistor R1 and the notch filter sub-circuit, and a second end of the first resistor R1 is grounded.

In some embodiments, the notch filter sub-circuit includes a second resistor R2, a first induction coil L1, and a second capacitor C2, a first end of the second resistor R2 is connected to the first high-pass filter sub-circuit, a second end of the second resistor R2 is connected to the first induction coil L1 and the second high-pass filter sub-circuit, and the first induction coil L1 is further connected to the ground in series with the second capacitor C2.

In some embodiments, the second high-pass filter sub-circuit includes a third capacitor C3, a fourth resistor R4, and a fifth resistor R5, where the third capacitor C3, the third resistor R3, and the fourth resistor R4 are serially connected to ground in sequence, a first end of the third capacitor C3 is connected to the notch filter sub-circuit, and a second end of the third capacitor C3 is connected to the first end of the third resistor R3.

In some embodiments, the impedance matching sub-circuit includes a first transient voltage suppressor TVS1, an operational amplifier A1, and an external power supply matched with the operational amplifier A1, where a first end of the first transient voltage suppressor TVS1 is connected to a second end of the third resistor R3 and a first input end of the operational amplifier A1, a second end of the first transient voltage suppressor TVS1 is grounded, and an output end of the operational amplifier A1 is connected to an inverter circuit.

Referring to fig. 3, fig. 3 (a) shows a circuit structure of a sampling circuit in a three-phase three-wire system connection mode. For other connection modes, only the input end of the sampling circuit needs to be adaptively adjusted. Next, a sampling circuit shown in fig. 3 will be described as an example.

In some examples, the sampling circuit is divided into four parts, namely a first high-pass filtering sub-circuit, a notch filtering sub-circuit, a second high-pass filtering sub-circuit and an impedance matching sub-circuit, wherein the input end of the first high-pass filtering sub-circuit is directly connected with three phase lines of an external power grid, each phase line is correspondingly connected with the anode of one first capacitor C1/C1', the cathodes of the three first capacitors are commonly connected with one end of a first resistor R1, and the other end of the first resistor R1 is grounded. In order to ensure the normal operation of the electromagnetic interference filter, the external power grid should also be grounded. In the first high-pass filter sub-circuit configured according to the above connection method, a group of RC filter circuits is configured for each phase line, that is, 3 first capacitors are provided in total in the three-phase three-wire system connection method. The high-frequency component of common mode noise in the electric signal connected to the sampling module is filtered through setting the parameters of the first capacitor C1/C1' and the first resistor R1.

In addition, as shown in fig. 3 (b), for the three-phase four-wire connection mode, the input end of the first high-pass filter sub-circuit is directly connected with three phase lines and one neutral line of the external power grid, each phase line or each neutral line is correspondingly connected with the anode of one first capacitor, that is, 4 first capacitors are arranged in total in the three-phase four-wire connection mode, the cathodes of the four first capacitors are commonly connected with one end of the first resistor R1, and the other end of the first resistor R1 is grounded.

As shown in fig. 3 (c), for the single-phase connection mode, the input end of the first high-pass filter sub-circuit is directly connected to one phase line and one neutral line of the external power grid, and each phase line or neutral line is correspondingly connected to the anode of one first capacitor, that is, 2 first capacitors are arranged in the single-phase connection mode, the cathodes of the two first capacitors are commonly connected to one end of the first resistor R1, and the other end of the first resistor R1 is grounded.

As shown in fig. 3 (d), for the single-wire connection mode, the input end of the first high-pass filter sub-circuit is directly connected to a phase line or a neutral line of the external power grid, and the phase line or the neutral line is correspondingly connected to the anode of the first capacitor, that is, only a single first capacitor is arranged in the single-wire connection mode, the cathode of the first capacitor is connected to one end of the first resistor R1, and the other end of the first resistor R1 is grounded.

In some examples, the notch filter subcircuit is connected to the output of the first high pass filter subcircuit. However, the notch filter sub-circuit can be installed at any position in the signal processing module or the passive filter module except for the connection of the notch filter sub-circuit, and only the notch filter sub-circuit needs to be ensured to be capable of inhibiting or eliminating the resonance phenomenon of the passive filter module. When the passive filter module is at the resonance frequency, the impedance of the electromagnetic interference filter can become 0 or infinity, so that the electromagnetic interference filter can not work normally. Specifically, for the frequency of the electrical signal that can be suppressed or eliminated by the notch filter sub-circuit, the parameter values of the second resistor R2, the first induction coil L1, and the second capacitor C2 can be adjusted adaptively.

For the second high-pass filter sub-circuit, a group of RC filter circuits are formed by the third capacitor C3 and the third resistor R4, and the low-frequency components in the common-mode noise signals are filtered by adjusting circuit parameters of the third capacitor C3, the third resistor R3 and the fourth resistor R4.

Finally, the impedance matching sub-circuit is mainly divided into two parts, wherein the first part comprises a first transient voltage suppressor TVS1, and the main purpose of the impedance matching sub-circuit is to suppress or eliminate the surge energy connected to the electromagnetic interference filter under the conditions of lightning stroke, starting and stopping of high-power equipment, circuit line faults and the like, so that the safety of each equipment in the electromagnetic interference filter and a load connected with the electromagnetic interference filter is protected to the greatest extent, and equipment damage is prevented.

The second part comprises an operational amplifier A1 and an external power supply matched with the operational amplifier A1, wherein the external power supply comprises a positive power supply VCC and a negative power supply VEE which are respectively connected to two external power supply terminals of the operational amplifier A1.

In addition to the case shown in fig. 3, the external power supply used in combination with the operational amplifier A1 may be provided as a single positive power supply VCC. In the case where the external power supply is the equal positive power supply VCC and the negative power supply VEE, the midpoint voltage at the output end of the operational amplifier A1 is 0. In the case of the single positive power supply VCC, the midpoint voltage at the output terminal of the operational amplifier A1 is 1/2VCC.

The operational amplifier A1 mainly functions as a follower for impedance matching. Since the level of the common-mode noise electric signal is generally in millivolt level, and the voltage of the external power grid is hundreds of volts, the voltage value of the first capacitor C1/C1' input into the first high-pass filtering sub-circuit can be reduced by improving the input impedance of the operational amplifier A1, so that the power supply voltage collected by the sampling circuit is attenuated, and the adjustment space for setting the frequency characteristic and attenuation characteristic of the electric signal of the input filter is further enlarged.

After passing through the first high-pass filter sub-circuit, the notch filter sub-circuit, the second high-pass filter sub-circuit and the impedance matching sub-circuit, the electromagnetic interference filter obtains a common-mode voltage signal processed by the sampling circuit.

In this way, in the sampling circuit in the embodiment of the application, the high-frequency signal component and the low-frequency signal component in the common-mode voltage signal are filtered respectively through the two groups of high-pass filter sub-circuits, and meanwhile, the resonance phenomenon of the passive filter module is eliminated through the notch filter sub-circuits, and the impedance matching sub-circuits are utilized to protect the sampling circuit and the whole electronic interference filter when the circuit has the surge phenomenon. Meanwhile, the sampling circuit can also adjust the number and the connection mode of the first capacitors C1 in the first high-pass filter sub-circuit according to the connection mode of an external power grid connected with the electromagnetic interference filter so as to adapt to circuits with different connection modes.

In some embodiments, the signal injection circuit includes a clamp protection sub-circuit, a surge protection sub-circuit, and a signal injection sub-circuit, which are serially connected in sequence, the surge protection sub-circuit is grounded, and an output end of the signal injection sub-circuit is connected to an input end of the passive filter module.

In some embodiments, the clamp protection sub-circuit includes a first clamp diode D1, a second clamp diode D2, and an external power supply for supporting operation of the sampling circuit; the anode of the first clamping diode D1 and the cathode of the second clamping diode D2 are connected with the input end of the signal injection circuit together, the cathode of the first clamping diode D1 is connected with the first end of the external power supply, the anode of the second clamping diode D2 is connected with the second end of the external power supply, and the potential of the first end of the external power supply is higher than that of the second end of the external power supply.

In some embodiments, the surge protection sub-circuit includes a fifth resistor R5, a sixth resistor R6, and a second transient voltage suppressor TVS2, the first end of the fifth resistor R5 is connected to the clamp protection sub-circuit, the second end of the fifth resistor R5 is connected to the signal injection sub-circuit, and the sixth resistor R6 and the second transient voltage suppressor TVS2 are connected in parallel between the second end of the fifth resistor R5 and ground.

In some embodiments, the signal injection sub-circuit includes one or more fourth capacitors C4, the number of the fourth capacitors C4 is determined according to the external power grid and the connection mode between the input ends of the signal processing module, the anode of the fourth capacitor C4 is connected with the surge protection sub-circuit, and the cathode of the fourth capacitor C4 is connected with the input end of the passive filtering module.

Referring to fig. 4, fig. 4 (a) shows a circuit structure of the signal injection circuit in a three-phase three-wire system connection mode, and for other connection modes, only the output end of the signal injection circuit needs to be adaptively adjusted. Next, a signal injection circuit shown in fig. 4 will be described as an example.

Specifically, the signal injection circuit comprises a clamping protection sub-circuit, a surge protection sub-circuit and a signal injection sub-circuit, wherein the output end of the signal injection sub-circuit is directly connected with the input end of the passive filter module and three corresponding phase lines, each phase line is correspondingly connected with the cathode of one fourth capacitor C4/C4', the anodes of the three fourth capacitors are commonly connected with the surge protection sub-circuit, namely, 3 fourth capacitors are commonly arranged in a three-phase three-wire system connection mode. The signal formed according to the connection mode is injected into the sub-circuit, and the processed common mode current signal is input into each phase line, so that the common mode noise on each line in the circuit is suppressed or eliminated.

In addition, as shown in fig. 4 (b), for the three-phase four-wire connection mode, the output end of the signal injection sub-circuit is directly connected with the input end of the passive filter module and the corresponding three phase lines and one neutral line, each phase line and each neutral line is correspondingly connected with the cathode of one fourth capacitor, that is, 4 fourth capacitors are arranged in total in the three-phase four-wire connection mode, and the anodes of the four fourth capacitors are commonly connected with the surge protection sub-circuit.

As shown in fig. 4 (c), for the single-phase connection mode, the output end of the signal injection sub-circuit is directly connected to the input end of the passive filter module and a corresponding phase line and a corresponding neutral line, each phase line and each neutral line is correspondingly connected to the cathode of a fourth capacitor, that is, 2 fourth capacitors are arranged in the single-phase connection mode, and the anodes of the two fourth capacitors are commonly connected to the surge protection sub-circuit.

As shown in fig. 4 (d), for the single-wire connection mode, the output end of the signal injection sub-circuit is directly connected to the input end of the passive filter module and a corresponding phase line or a neutral line, and the phase line or the neutral line is connected to the cathode of the fourth capacitor, that is, only a single fourth capacitor is arranged in the single-wire connection mode, and the anode of the fourth capacitor is connected to the surge protection sub-circuit.

For the clamp protection sub-circuit, the first clamp diode D1 and the second clamp diode D2 are respectively connected to an external power supply matched with the operational amplifier A1 in a reverse direction, wherein the cathode of the first clamp diode D1 is connected to a positive power supply of the external power supply, and the anode of the second clamp diode D2 is connected to a negative power supply of the external power supply. The purpose of this is that when the circuit is in surge, the two clamping diodes clamp the output terminal voltage of the signal processing module to the positive power supply voltage VCC or the negative power supply voltage VEE according to the signal direction of the surge, so as to protect the operational amplifier A1 and other components in the circuit.

And for the surge protection sub-circuit, the surge energy connected to the electromagnetic interference filter is restrained or eliminated under the conditions of lightning stroke, starting and stopping of high-power equipment, circuit line faults and the like, the safety of each equipment in the electromagnetic interference filter and a load connected with the electromagnetic interference filter is protected to the maximum extent, equipment damage is prevented, and the surge protection sub-circuit is mainly realized through a second transient voltage suppressor TVS 2.

Therefore, the signal injection circuit in the embodiment of the application can protect the signal injection circuit and the electromagnetic interference filter through means such as clamping voltage and transient voltage control under the condition that the circuit is in a surge state by arranging the clamping protection sub-circuit and the surge protection sub-circuit, and meanwhile, the number and the connection mode of the fourth capacitors C4 in the signal injection sub-circuit can be adjusted according to the connection modes of the signal processing module, the passive filtering module and an external power grid so as to adapt to the circuits in different connection modes.

An electronic device of an embodiment of the present application includes the electromagnetic interference filter described above.

In the description of the present specification, reference to the terms "certain embodiments," "in one example," "illustratively," and the like, means that a particular feature, structure, material, or characteristic described in connection with the embodiments or examples is included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and further implementations are included within the scope of the preferred embodiment of the present application in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the embodiments of the present application.

While embodiments of the present application have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the present application, and that variations, modifications, alternatives, and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the present application.

Claims (12)

1. The electromagnetic interference filter is characterized by comprising a signal processing module and a passive filtering module, wherein the input end of the signal processing module and the input end of the passive filtering module are commonly connected with an external power grid, and the output end of the signal processing module is connected with the input end of the passive filtering module;

the signal processing module comprises a sampling circuit and a signal injection circuit, wherein the sampling circuit is used for collecting common-mode voltage signals, and the signal injection circuit is used for generating common-mode current signals according to the common-mode voltage signals so as to counteract common-mode noise in a circuit where the electromagnetic interference filter is located.

2. The electromagnetic interference filter of claim 1, wherein the signal processing module further comprises an inverter circuit and a signal conversion circuit, wherein an input end of the sampling circuit is connected with the external power grid, the sampling circuit, the inverter circuit, the signal conversion circuit and the signal injection circuit are sequentially connected in series, and an output end of the signal injection circuit is connected with an input end of the passive filter module.

3. The electromagnetic interference filter of claim 2, wherein the sampling circuit comprises a first high-pass filter sub-circuit, a notch filter sub-circuit, a second high-pass filter sub-circuit and an impedance matching sub-circuit, wherein an input end of the first high-pass filter sub-circuit is connected with the external power grid, the first high-pass filter sub-circuit, the notch filter sub-circuit, the second high-pass filter sub-circuit and the impedance matching sub-circuit are sequentially connected in series and are all grounded, and an output end of the impedance matching sub-circuit is connected with the inverting circuit.

4. The electromagnetic interference filter of claim 3 wherein the first high pass filter sub-circuit comprises one or more first capacitors and a first resistor, the number of the first capacitors being determined by the connection between the external power grid and the input of the signal processing module, the anodes of the first capacitors being connected to the external power grid, the cathodes of the first capacitors being connected to the first end of the first resistor and the notch filter sub-circuit, the second ends of the first resistors being grounded.

5. The electromagnetic interference filter of claim 3 wherein the notch filter sub-circuit comprises a second resistor, a first inductor coil, and a second capacitor, a first end of the second resistor connected to the first high pass filter sub-circuit, a second end of the second resistor connected to the first inductor coil and the second high pass filter sub-circuit, the first inductor coil further coupled in series with the second capacitor.

6. The electromagnetic interference filter of claim 3 wherein the second high pass filter sub-circuit comprises a third capacitor, a third resistor and a fourth resistor, the third capacitor, the third resistor and the fourth resistor being serially connected in series, an anode of the third capacitor being connected to the notch filter sub-circuit and a cathode of the third capacitor being connected to the first end of the third resistor.

7. The emi filter of claim 6 wherein the impedance-matching sub-circuit comprises a first transient voltage suppressor, an operational amplifier, and an external power source associated with the operational amplifier, the first transient voltage suppressor having a first end coupled to the second end of the third resistor and the first input of the operational amplifier, the second end of the first transient voltage suppressor being coupled to ground, the operational amplifier having an output end coupled to the inverting circuit.

8. The electromagnetic interference filter of claim 2, wherein the signal injection circuit comprises a clamp protection sub-circuit, a surge protection sub-circuit, and a signal injection sub-circuit, the clamp protection sub-circuit, the surge protection sub-circuit, and the signal injection sub-circuit are serially connected in sequence, the surge protection sub-circuit is grounded, and an output terminal of the signal injection sub-circuit is connected to an input terminal of the passive filter module.

9. The emi filter of claim 8, wherein the clamp protection subcircuit includes a first clamp diode, a second clamp diode, and an external power source for use therewith, the external power source further configured to support operation of the sampling circuit; the positive pole of first clamp diode and the negative pole of second clamp diode are connected jointly the input of signal injection circuit, the negative pole of first clamp diode is connected the first end of external power supply, the positive pole of second clamp diode is connected the second end of external power supply, the electric potential of external power supply first end is higher than the electric potential of external power supply second end.

10. The emi filter of claim 8, wherein the surge protection subcircuit includes a fifth resistor having a first end connected to the clamp protection subcircuit, a sixth resistor having a second end connected to the signal injection subcircuit, and a second transient voltage suppressor connected in parallel between the second end of the fifth resistor and ground.

11. The emi filter of claim 8, wherein the signal injection sub-circuit includes one or more fourth capacitors, the number of the fourth capacitors being determined according to a connection between the external power grid and the input terminal of the signal processing module, an anode of the fourth capacitor being connected to the surge protection sub-circuit, and a cathode of the fourth capacitor being connected to the input terminal of the passive filter module.

12. An electronic device, characterized in that it comprises an electromagnetic interference filter according to any of claims 1-11.