CN216437057U - Power supply filter circuit capable of inhibiting information leakage of power line - Google Patents

Abstract

The utility model belongs to electromagnetic information safety field relates to and provides a can carry out the power filter circuit that information leakage restraines to the power line, characterized by: the circuit comprises common-mode inductors L1, L2 and L3, two groups of common-mode capacitors CY1, CY2, CY3 and CY4, differential-mode capacitors CX1 and CX2, and common-mode inductors L1, L2 and L3; the 2 groups of common mode capacitors CY1, CY2, CY3 and CY4 and the differential mode capacitors CX1 and CX2 are fixedly welded on the PCB, and a common ground E on the PCB is electrically connected with the shielding shell through a spring piece and then is limited and fixed in the shielding shell. The power supply filter circuit is a power supply filter circuit which can restrain information leakage of a power line in a frequency band of 150 kHz-100 MHz aiming at a generalized computer system.

Description

Power supply filter circuit capable of inhibiting information leakage of power line

Technical Field

The utility model belongs to electromagnetic information safety field relates to and provides a power filter circuit that can carry out information leakage to the power line and restrain.

Background

With the rapid development of computer technology, a single computer device has evolved into a generalized computer system (a computer, a computer peripheral device, a network device, etc.), and as the operating frequency band of the generalized computer system is wider and wider, the capacity of information transmission is larger and larger, and the applications are more and more, the problem of electromagnetic information security is brought. Research proves that electromagnetic conduction and electromagnetic radiation generated when a generalized computer system works carry a lot of working information and can be intercepted and even restored under certain conditions, so that information leakage is caused, and information safety is influenced.

The traditional passive filter device can maintain good filtering characteristics in a lower frequency band range, but if the frequency band range is too large and generally exceeds 20MHz frequency, the filtering performance of the traditional LC filter device is sharply reduced in a high frequency band due to the influence of inductance and capacitance high-frequency parasitic parameters of the traditional LC filter device, and meanwhile, the high-frequency parasitic parameters of the traditional LC filter device are also uncontrollable due to the adoption of a manual welding mode. Finally, the traditional grounding mode of the LC filter device circuit and the filter device shell generally adopts the near single-point grounding of the element device pins, and the grounding mode causes the grounding impedance of the filter device circuit to be overlarge and the high-frequency performance of the filter device to be reduced.

SUMMERY OF THE UTILITY MODEL

The utility model provides a power supply filter circuit design method for the information leakage suppression of power lines in 150 kHz-100 MHz frequency band aiming at generalized computer system.

The utility model aims at realizing like this, a can carry out the power filter circuit that information leakage restraines to the power line, characterized by: the circuit comprises common-mode inductors L1, L2 and L3, two groups of common-mode capacitors CY1, CY2, CY3 and CY4, differential-mode capacitors CX1 and CX2, and common-mode inductors L1, L2 and L3; the 2 groups of common mode capacitors CY1, CY2, CY3 and CY4 and the differential mode capacitors CX1 and CX2 are fixedly welded on the PCB, and a common ground E on the PCB is electrically connected with the shielding shell through a spring piece and then is limited and fixed in the shielding shell.

A power line L, N network sequentially passes through common mode inductors L1, L2 and L3 which are connected in series, differential mode capacitors CX1 and CX2 are respectively connected in parallel at front and rear ports of the common mode inductor L1, and common mode capacitors CY1 and CY2 are sequentially connected in parallel between common mode inductors L1, L2 and L3 on a loop of the power line L and a common ground E; common-mode capacitors CY3 and CY4 are connected in parallel between common-mode inductors L1, L2 and L3 on a loop of a power line N and a common ground E in sequence, and common-mode inductors L1 and L3 are wound on a magnetic core; the other end of the common mode inductor L3 is electrically connected to the load.

The common ground E is connected with the shielding shell through a spring piece conductor.

The common ground E is connected with the shielding shell through the conductor spring leaf, so that the common ground E and the shielding shell are kept at one position through the connection of the conductor spring leaf so as to keep the consistency of parameters

The common-mode inductors L1, L2 and L3 are flat inductors, the flat inductors comprise copper wires and magnetic materials, the magnetic materials are ferrites, the directions of coils wound by the two groups of copper wires on the same magnetic core are opposite, and the number of winding turns is 18-30 turns, so that the magnetic core is not afraid of saturation. The copper wire is a rectangular enameled wire, the thickness of the rectangular enameled wire is 0.1-1 mm, and the width of the rectangular enameled wire is 1-3 mm.

The utility model has the advantages that: the utility model discloses a flat inductance, this inductance compare in ordinary inductance has following advantage: winding the flat coil, wherein turns are tightly and flatly arranged; the effective sectional area of the wire is increased, the limited assembly space of the magnetic core is fully utilized, and the number of turns required by the flat inductor is small under the condition of the same inductance, so that the parasitic capacitance between adjacent turns of the inductor is less, and the high-frequency characteristic of the inductor is favorably improved; meanwhile, the shape of the magnetic core is completely matched with the design of the coil, the leakage of a magnetic field is reduced to the minimum, the magnetic core is formed by casting a ferrite material, the magnetic loss is reduced to the minimum, and the magnetic core has the characteristic of saturation current which cannot be surpassed by the traditional inductor.

Drawings

The invention will be further explained with reference to the drawings of the embodiments:

FIG. 1 is a circuit form of a broadband LC power filter device;

FIG. 2 is a schematic diagram of a grounding structure;

FIG. 3 is a common mode filter equivalent circuit diagram;

FIG. 4 is a simplified circuit for common mode filtering;

FIG. 5 is a differential mode filtering equivalent circuit;

FIG. 6 is a simplified circuit for differential mode signal output;

FIG. 7 is a high frequency equivalent of a common mode circuit;

FIG. 8 is a high frequency equivalent of a differential mode circuit;

FIGS. 9A and 9B are a comparison of conventional inductors and flat inductor turns;

FIG. 10 shows the insertion loss of the broadband LC power filter device between 150kHz and 30 MHz;

FIG. 11 shows the insertion loss of the broadband LC power filter device in the range of 30MHz to 100 MHz.

Detailed Description

As shown in fig. 1, an LC power filter circuit capable of suppressing information leakage from a power line is characterized in that: the circuit comprises common- mode inductors 2, 5 and 7, two groups of common- mode capacitors 3, 6, 8 and 9, differential- mode capacitors 1 and 4 and common- mode inductors 2, 5 and 7; two groups of common mode capacitors 3, 6, 8, 9 and differential mode capacitors 1 and 4 are fixedly welded on a PCB, a common ground 1 on the PCB is conductively connected with a shielding shell 3 through a spring piece 2, and then is limited and fixed in the shielding shell.

The power line L, N network sequentially passes through common mode inductors 2, 5 and 7 connected in series, differential mode capacitors 1 and 4 are respectively connected in parallel at the front and rear ports of the common mode inductor 2, and common mode capacitors 3 and 6 are sequentially connected in parallel between the common mode inductors 2, 5 and 7 on the loop of the power line L and the PCB common ground 2; common- mode capacitors 8 and 9 are sequentially connected in parallel between common- mode inductors 2, 5 and 7 on a loop of a power line N and a common ground 2 of the PCB, and the common- mode inductors 2, 5 and 7 are wound on a magnetic core; the other end of the common mode inductor 7 is electrically connected with the load.

As shown in fig. 2, the common ground 2 and the shield shell 3 are connected by the conductor spring plate 1, so that the common ground 2 and the shield shell 3 are connected by the conductor spring plate 1 and kept at a position so as to keep the parameters consistent. The common- mode inductors 2, 5 and 7 are flat inductors, the flat inductors comprise copper wires and magnetic materials, the magnetic materials are ferrites, the directions of coils wound by the two groups of copper wires on the same magnetic core are opposite, and the number of winding turns is 18-30, so that the magnetic core is not afraid of saturation. The copper wire is a rectangular enameled wire, the thickness of the rectangular enameled wire is 0.1-1 mm, and the width of the rectangular enameled wire is 1-3 mm.

Leakage inductance of the common mode inductor at high frequencies of 2, 5 and 7 can play a role of differential mode inductance and play a certain role in inhibiting differential mode signals. Low-frequency interference and leakage signals firstly pass through the passive electromagnetic leakage protection module, and are reflected by using an impedance mismatch principle to be prevented from being transmitted into a power line network; and the high-frequency interference cannot be ideally grounded due to the passive electromagnetic leakage protection module, and part of signals can be transmitted to a power grid through the filter. For this purpose, an active noise injection module is used, and the leaked electromagnetic signals are "submerged" to realize blocking due to broadband interference noise with a certain amplitude, so that the electromagnetic leakage information cannot be detected.

For a power supply system, the differential mode inductance is easy to generate heating and magnetic saturation phenomena under a lower frequency, so the differential mode problem is generally solved by the differential mode inductance of the common mode choke coil. I.e. the rejection of common and differential modes at low frequency bands in the low pass passive filter arrangement may all employ common mode chokes. The high-frequency band filtering considers the bypass effect of the capacitor, and the differential mode capacitor is bridged between the line L (N) and the line N for differential mode signals, and the common mode capacitor is bridged between the line L (N) and the line E for common mode signals. The Y capacitor has a capacitance which is not too large because the leakage current is not too large. In addition, considering that the low frequency band has almost no attenuation at 50Hz or 60Hz, and the attenuation is more than 50dB at the stop band, the insertion loss curve edge is very steep, so that a high-order number of filtering devices are used. Namely, it is considered to split the differential mode capacitance and the common mode choke into two stages of filter circuits. The resulting circuit form of the filter device is shown in fig. 1.

After the form of the broadband LC power supply filter circuit is determined, common-mode equivalent analysis needs to be carried out on the circuit. The common-mode equivalent circuit of the broadband LC power filter circuit can be obtained by analyzing the common-mode equivalent circuit of the broadband LC power filter circuit as shown in fig. 3.

In FIG. 3, L_CM＝L₁+L₂+L₃，C_CM＝C_Y1+C_Y2，Z_SIs the equivalent impedance of the common mode signal, Z_tIs the impedance of the linear network. At signal angular frequency of

The circuit diagram of fig. 3 can then be simplified to fig. 4, where V_s,cmIs an equivalent signal voltage, V_o,cmIs the level value after the signal has passed the filter means. From fig. 4, the calculation of the cut-off frequency of the anti-common mode part of the filter device can be obtained:

the following formula can be obtained:

in the actual design process, C is selected firstly_CMValue such that it meets the high frequency loss requirement while determining the cut-off frequency f of the filter circuit_cm. Then the common mode capacitance C is connected_CMSubstituting the value into a leakage current calculation formula, and checking the magnitude of the leakage current to enable the leakage current to meet the safety requirement. Finally, the common mode choke coil L can be obtained by substituting the cut-off frequency and the common mode capacitance value into the formula_CMThe inductance value of (c).

The utility model discloses a broadband LC power filter circuit needs to carry out the equivalent circuit analysis to the differential mode filtering in this circuit.

The equivalent circuit form shown in fig. 5 can be obtained by the broadband LC power supply filter circuit form. The frequency of the differential mode signal satisfies 1/(omega. C)_Y2/2)＞＞Z_t,1/(ω·C_X1)＜＜Z_sUnder which fig. 5 can be converted into a circuit form as shown in fig. 6.

Wherein L is_eThe leakage inductance of the common mode choke coil is 0.5% -2% of the self inductance value under the general condition. Namely L_e＝L_CM×2％。

Wherein C is_DM＝C_X1+C_X2+C_Y1/2+C_Y2/2. The calculation formula of the cut-off frequency of the anti-differential mode part of the filter device can be obtained:

in the actual calculation process, the common mode choke L is determined by the calculation common mode filter device_CML is determined by a calculation formula of leakage inductance_eWhile determining the cut-off frequency f of the filter circuit_DMIs prepared by mixing L_eAnd f_DMSubstituting into the above formula to calculate C_DMThe value of (c).

From above two parts calculate, can obtain the utility model discloses common mode inductance 2, 5, 7 among the broadband LC power filter circuit, two sets of common mode electric capacity 3, 6, 8, 9 and differential mode electric capacity 1 and 4 parameters.

Generally, at high frequencies, the inductance and the capacitance are influenced by high-frequency parasitic parameters, so that the inductance and the capacitance respectively show capacitance and inductance characteristics at high frequencies. The capacitance is not ideal, the residual inductance of the leads causes parasitic inductance ESL, and the proximity of the leads creates parasitic capacitance EPC. The characteristics of the actual capacitor are different from those of the ideal capacitor. Also the inductance is not ideal and inductive. Adjacent windings form many small capacitors that, when added together, can form a significant capacitance value.

The following analysis the utility model discloses broadband LC power filter's common mode/differential mode circuit high frequency equivalent circuit. In a common-mode equivalent circuit diagram of the broadband LC power filter device, at high frequency, a parasitic capacitor EPC is generated between each turn of coils of two common-mode chokes and connected with an inductor in parallel, and a pin connected with a shell of the filter device by a Y capacitor generates a parasitic inductor ESL which is connected with the capacitor in series. Fig. 7 is a common mode circuit high frequency equivalent.

Similarly, in a differential-mode equivalent circuit diagram of the broadband LC power filter device, at high frequency, a parasitic capacitor EPC is generated between each turn of leakage inductance of the two common mode chokes and is connected with the inductor in parallel, and a parasitic inductor ESL is generated at a pin connected with an X capacitor and an N (L) line and is connected with the capacitor in series. Fig. 7 shows that the high-frequency equivalent circuit research of the differential mode circuit shows that the high-frequency characteristic of the common winding inductor becomes prominent after the frequency reaches 20 MHz. In order to design a filter device with broadband characteristics, a flat inductor is used instead of a conventional wire-wound inductor.

Because the current required to flow by the power supply filter device is larger, the selected wire diameter is larger, and the number of turns which can be wound on the magnetic core is smaller. Therefore, it is considered that a flat enameled wire is used, and as shown in fig. 9A and 9B, the thickness of the flat enameled wire is smaller than that of a round enameled wire under the condition of the same sectional area, and the number of turns that can be wound in the same magnetic ring is increased.

Through the analysis the utility model discloses the flat inductance of chooseing for use, this inductance compare in ordinary inductance and have following advantage: the flat coil is wound, turns are tightly and flatly arranged, the effective sectional area of the wire is increased, the limited assembly space of the magnetic core is fully utilized, and the number of turns required by the flat inductor is small under the condition of the same inductance, so that the parasitic capacitance between adjacent turns of the inductor is less, and the high-frequency characteristic of the inductor is favorably improved; meanwhile, the shape of the magnetic core is completely matched with the design of the coil, the leakage of a magnetic field is reduced to the minimum, the magnetic core is formed by ferrite die casting, the magnetic loss is reduced to the minimum, and the magnetic core has the characteristic of saturation current which cannot be surpassed by the traditional inductor.

For the traditional filter device installation, the method of directly welding the pins of the filter element and the shell of the filter device nearby and directly winding and welding the pins of the element device is generally adopted, and the production method of the traditional filter device can cause the high-frequency parasitic parameters of the filter device to become uncontrollable, so that the frequency band of the filter device cannot be widened, and simultaneously, the deviation of the high-frequency performance of each filter device after production and the actual predicted performance is overlarge, and the high-frequency performance of each filter device is inconsistent.

The utility model discloses a filtering component mounting means adopt PCB base plate installation, and wave-soldering's mode is adopted to this kind of mounting means, reduces manual operation for the filtering device's that produces component pin is extremely short, the effectual parasitic parameter of high frequency that has reduced. Meanwhile, the PCB substrate is adopted for installation, so that the filtering devices can be automatically produced, and the high-frequency performance deviation between every two filtering devices can be prevented from being overlarge. The utility model discloses a PCB base plate installation filter element can effectual improvement filter equipment's high frequency performance for filter equipment possesses the broadband characteristic.

The conventional filter device usually adopts a grounding mode of connecting a single point with a housing of the filter device, and the grounding mode uses a long grounding wire, and the grounding area is too small due to the single point grounding. This will result in deterioration of the high frequency characteristics of the filter device, degrading the filtering performance. The longer grounding wire leads to a higher grounding impedance at high frequencies of the filter device, and particularly, the grounding impedance is extremely high near the frequency of distributed inductance and distributed capacitance resonance. On the other hand, the single-point grounding is adopted, so that the grounding area is too small, and the filtering device is also poor in grounding. Therefore, it is necessary to use an efficient grounding method.

The utility model discloses a reed ground connection mode, this ground connection mode compare in traditional filter's single-point ground connection mode have following advantage: because the reed is directly pressed with the shell of the filter device, the grounding length of the filter circuit can be almost ignored, the ground wire impedance is greatly reduced, and the high-frequency characteristic of the filter device is effectively improved; meanwhile, the grounding area of the filter circuit can be larger by adopting a reed compression joint mode, so that filtered signals can flow into the ground, the performance of the filter device at high frequency is more excellent, and the bandwidth is represented as a broadband characteristic; and finally, the grounding mode of the reeds is convenient for the installation and production of the filter device, and meanwhile, uncertain factors caused by manual welding are reduced.

The insertion loss test of this filter device was carried out, and the results are shown in FIG. 10 for 150 kHz-30 MHz and FIG. 11 for 30 MHz-100 MHz. The insertion loss of the filter device is more than or equal to 50dB in the broadband range of 150 kHz-100 MHz, and the filter device has good broadband characteristics.

Claims (5)

1. A power filter circuit capable of suppressing information leakage on a power line, characterized in that: the circuit comprises common-mode inductors L1, L2 and L3, two groups of common-mode capacitors CY1, CY2, CY3 and CY4, differential-mode capacitors CX1 and CX2, and common-mode inductors L1, L2 and L3; the 2 groups of common mode capacitors CY1, CY2, CY3 and CY4 and the differential mode capacitors CX1 and CX2 are fixedly welded on the PCB, and a common ground E on the PCB is conductively connected with the shielding shell through a spring piece and then is limited and fixed in the shielding shell.

2. The power filter circuit according to claim 1, wherein the power filter circuit is configured to suppress leakage of information from the power line, and further comprises: a power line L, N network sequentially passes through common mode inductors L1, L2 and L3 which are connected in series, differential mode capacitors CX1 and CX2 are respectively connected in parallel at front and rear ports of the common mode inductor L1, and common mode capacitors CY1 and CY2 are sequentially connected in parallel between common mode inductors L1, L2 and L3 on a loop of the power line L and a common ground E; common-mode capacitors CY3 and CY4 are connected in parallel between common-mode inductors L1, L2 and L3 on a loop of a power line N and a common ground E in sequence, and common-mode inductors L1 and L3 are wound on a magnetic core; the other end of the common mode inductor L3 is electrically connected to the load.

3. The power filter circuit according to claim 2, wherein the power filter circuit is configured to suppress leakage of information from the power line, and further comprises: the common ground E is connected with the shielding shell through a spring piece conductor.

4. The power filter circuit according to claim 2, wherein the power filter circuit is configured to suppress leakage of information from the power line, and further comprises: the common ground E is connected with the shielding shell through the conductor spring leaf, so that the common ground E and the shielding shell are kept in one position through the conductor spring leaf connection, and the consistency of parameters is kept.

5. The power filter circuit according to claim 1, wherein the power filter circuit is configured to suppress leakage of information from the power line, and further comprises: the common-mode inductors L1, L2 and L3 are flat inductors, the flat inductors comprise copper wires and magnetic materials, the magnetic materials are ferrites, the directions of coils wound by the two groups of copper wires on the same magnetic core are opposite, and the number of winding turns is 18-30 turns, so that the magnetic core is not afraid of saturation; the copper wire is a rectangular enameled wire, the thickness of the rectangular enameled wire is 0.1-1 mm, and the width of the rectangular enameled wire is 1-3 mm.

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