A filter for a medical frequency converter

Abstract

The utility model discloses a filter for medical frequency converter, including connector J1 and connector J2, the one foot of connector J1 is connected respectively piezo -electric resistance MOV1, piezo -electric resistance MOV3, inductance L1 one foot, electric capacity C2 and electric capacity C3, piezo -electric resistance MOV1 other end connects inductance L1 three feet, piezo -electric resistance MOV3 other end connects gas discharge tube and piezo -electric resistance MOV2 respectively, gas discharge tube ground connection, piezo -electric resistance MOV2 other end connects inductance L1 three feet, electric capacity C2 other end connects electric capacity C1, electric capacity C1 ground connection, electric capacity C3 other end ground connection, inductance L1 two feet connects electric capacity C5, electric capacity C4, resistance R1 and inductance L2 one foot respectively, electric capacity C4 other end ground connection, resistance R1 other end connects electric capacity C10, electric capacity C10 ground connection, electric capacity C5 other end connects inductance L1 four feet.

Description

Technical Field

[0001] This utility model relates to the field of EMC design, and in particular to a filter for medical frequency converters. Background Technology

[0002] EMI filters utilize the impedance mismatch principle to suppress electromagnetic interference and are widely used in various electronic devices to ensure their electromagnetic compatibility. Internally, filters typically employ wideband nickel-zinc ferrite, manganese-zinc ferrite, amorphous materials, and capacitors to achieve good filtering characteristics across a wide frequency range. EMI filters suffer from large size and insufficient low-frequency attenuation: the lower the frequency, the larger the inductor volume for the same inductance, resulting in a larger filter size; according to Q=ω0L / R_dc (where L is the filter's inductance value, and R_dc is the equivalent series resistance (ESR) in the resonant circuit, including the inductor's wire resistance, the capacitor's equivalent resistance, and any resistive components that consume energy), a large inductor results in a high Q value when suppressing low-frequency interference. Combined with the incremental negative resistance characteristic of the PWM converter, this means the system is not consuming energy but increasing it, resulting in gain rather than suppression. This highlights the challenge of balancing low-frequency attenuation with the incremental negative resistance of the PWM converter.

[0003] In order to improve attenuation, the Y capacitance is increased, which leads to excessive leakage current and makes it difficult to balance the attenuation and leakage current problems.

[0004] Low-frequency magnetic field coupling problem: Low-frequency magnetic fields mainly propagate through electromagnetic induction near-field coupling, and interference cannot be suppressed by traditional LC filtering. Utility Model Content

[0005] Purpose of the utility model: The technical problem to be solved by this utility model is to provide a filter for medical frequency converters, which addresses the shortcomings of the existing technology.

[0006] To solve the above-mentioned technical problems, this utility model discloses a filter for a medical frequency converter, including connector J1 and connector J2. One pin of connector J1 is connected to varistor MOV1, varistor MOV3, one pin of inductor L1, capacitor C2, and capacitor C3. The other end of varistor MOV1 is connected to the third pin of inductor L1. The other end of varistor MOV3 is connected to a gas discharge tube and varistor MOV2, with the gas discharge tube grounded. The other end of varistor MOV2 is connected to the third pin of inductor L1. The other end of capacitor C2 is connected to capacitor C1, which is grounded. The other end of capacitor C3 is grounded. Two pins of inductor L1 are connected to capacitor C5, capacitor C4, resistor R1, and one pin of inductor L2, with the other end of capacitor C4 grounded. The other end of resistor R1 is connected to capacitor C10. The other end of capacitor C5 is connected to the four pins of inductor L1. The two pins of inductor L2 are connected to capacitor C8, capacitor C12, transient voltage suppressor diode TVS1, and the two pins of connector J2, respectively. The other end of capacitor C8 is connected to the four pins of inductor L2. The other end of capacitor C12 is connected to resistor R3. Resistor R3 is connected to the four pins of inductor L2. The other end of transient voltage suppressor diode TVS1 is connected to the four pins of inductor L2. One pin of connector J2 is connected to the four pins of inductor L2. The three pins of inductor L2 are connected to resistor R2, capacitor C5, capacitor C6, and the four pins of inductor L1, respectively. Resistor R2 is connected to capacitor C11. Capacitor C11 is connected to capacitor C6. Capacitor C6 is grounded. The three pins of cable L1 are connected to capacitor C1, capacitor C2, varistor MOV1, varistor MOV2, and fuse F1, respectively. Fuse F1 is connected to the two pins of connector J1.

[0007] In this invention, the inductor L1 is placed inside the cavity, and the surface of the cavity is provided with a permalloy layer.

[0008] In this invention, the inductor L1 is wound with a magnetic core made of iron-based nanocrystalline soft magnetic alloy material.

[0009] In this invention, the inductor L2 is wound with a ferrite core.

[0010] In this invention, the capacitance of capacitors C1, C3, C4 and C6 is 1 nF; the capacitance of capacitors C2, C5 and C8 is 2.2 uF; the capacitance of capacitors C10 and C11 is 2.2 nF; and the capacitance of capacitor C12 is 4.7 uF.

[0011] In this invention, the inductance of inductor L1 is 50mH and the inductance of inductor L2 is 5mH.

[0012] In this invention, the resistance values ​​of resistors R1 and R2 are 270Ω, and the resistance value of resistor R3 is 3Ω.

[0013] Beneficial effects: 1. Permalloy and low-frequency inductors can increase low-frequency attenuation by 50% (10kHz-1MHz).

[0014] 2. Low-frequency inductance improves leakage current: unweighted leakage current to ground is reduced by 80%.

[0015] 3. The high permeability iron-based nanocrystalline soft magnetic alloy material reduces the volume: Compared with ordinary low-frequency filters, the volume of this utility model is reduced by 30%.

[0016] 4. The damping circuit consisting of R1, R2, R3, C10, C11, and C12 effectively suppresses the resonant frequency of the filter, eliminating any obvious resonant frequency. Attached Figure Description

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0018] Figure 1 It is a circuit schematic;

[0019] Figure 2 This is a structural diagram;

[0020] Figure 3 This is a schematic diagram of conducted interference data without a filter;

[0021] Figure 4 This is a schematic diagram of conducted interference data of this utility model. Detailed Implementation

[0022] like Figure 1 This product consists of a pre-stage protection circuit, an interference suppression circuit, and a damping circuit. The protection circuit consists of MOV1, MOV2, GDT1, and TVS1; the interference suppression circuit consists of C1, C3, C4, C6 (1nF), C2, C5, C8 (2.2uF), L1 (50mH), and L2 (5mH); and the damping circuit consists of R1-R2 (270Ω), R3 (3Ω), C10-C11 (2.2nF), and C12 (4.7uF).

[0023] The varistors MOV1 and MOV2 are model 561KD14 varistors. The gas discharge tube is model 2RM600L-8. The transient suppression diode is model 5KE440CA.

[0024] Specifically addressing the issue of excessive low-frequency performance, a common-mode inductor L1 is wound with a core made of a special iron-based nanocrystalline soft magnetic alloy. By adjusting the material and composition ratio of the core, it exhibits high magnetic saturation strength and high permeability at a specific single frequency point, achieving an initial permeability on the order of 8*10⁴ and a maximum permeability on the order of 40*10⁴. This allows for high low-frequency inductance within a small size, abandoning the conventional requirement of high impedance within a certain bandwidth. Similarly, considering that the operating frequency of frequency converters is typically in the kHz range, the high inductance value of the common-mode inductor at this frequency point can block high-frequency leakage current from being discharged through the AC power line, thereby significantly reducing the leakage current of the frequency converter.

[0025] like Figure 2 To solve the near-field coupling problem of low-frequency magnetic fields, a cavity is made inside the filter housing, and a layer of permalloy is attached to the surface of the cavity where the nanocrystalline inductor is located to block the propagation and coupling of low-frequency magnetic fields and improve the attenuation capability of low-frequency magnetic fields.

[0026] Given the characteristics of inverter switching power supplies, the unweighted leakage current to ground is relatively large at the operating frequency. It is necessary to further increase the permeability of the nanocrystals at the kHz frequency to achieve a high inductance value at the kHz operating frequency point, so as to block the leakage current from being discharged through the AC power line, thereby significantly reducing the leakage current of the inverter.

[0027] To increase high-frequency attenuation, an L2 common-mode inductor is wound with a ferrite core to achieve interference suppression over a wide frequency band.

[0028] Common-mode inductance and Y-capacitor, along with their parasitic parameters, can induce resonance, leading to gain at specific frequencies under extreme conditions and amplifying interference. Adding a common-mode RC series circuit can dampen the filter at the resonant frequency, limiting its impedance. Connecting a series RC damping network in parallel with the capacitor is the most common and effective passive damping method. A branch consisting of a resistor R_damp and a capacitor C_damp connected in series is connected in parallel with the main filter capacitor. The value of C_damp is much larger than the main capacitor C (typically 3 to 10 times C). Thus, at the resonant frequency, the impedance of the damping branch is primarily determined by R_damp. The value of R_damp is calculated using a formula, with the goal of reducing the filter's Q value to below 1 (typically between 0.5 and 1).

[0029] like Figure 3 and Figure 4 The switching frequency of this medical frequency converter is 120KHz. It is obvious that its operating frequency and harmonics exceed the standard. At the same time, the leakage current is 20mA after testing.

[0030] Adding a filter to the front end of this medical frequency converter clearly shows that the operating frequency and its harmonics are suppressed. Simultaneously, the leakage current also decreases to 3mA.

[0031] It is evident that there is no resonant frequency, indicating that the Q value has been effectively reduced.

[0032] This utility model provides a concept and method for a filter used in medical frequency converters. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of this utility model. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of this utility model, and these improvements and modifications should also be considered within the scope of protection of this utility model. All components not explicitly stated in this embodiment can be implemented using existing technology.

Claims

1. A filter for medical frequency converters, characterized in that, The connectors include connectors J1 and J2. One pin of connector J1 is connected to varistor MOV1, varistor MOV3, one pin of inductor L1, and capacitors C2 and C3. The other pin of varistor MOV1 is connected to the third pin of inductor L1. The other pin of varistor MOV3 is connected to a gas discharge tube and varistor MOV2, with the gas discharge tube grounded. The other pin of varistor MOV2 is connected to the third pin of inductor L1. The other pin of capacitor C2 is connected to capacitor C1, which is grounded. The other pin of capacitor C3 is grounded. The second pin of inductor L1 is connected to capacitors C5 and C4, resistor R1, and one pin of inductor L2, with the other pin of capacitor C4 grounded. The other pin of resistor R1 is connected to capacitor C10, which is grounded. The other pin of capacitor C5 is connected to the fourth pin of inductor L1. The inductor L2 is connected to two of the following terminals: capacitor C8, capacitor C12, transient voltage suppressor diode TVS1, and connector J2. The other end of capacitor C8 is connected to the fourth terminal of inductor L2. The other end of capacitor C12 is connected to resistor R3, which is connected to the fourth terminal of inductor L2. The other end of transient voltage suppressor diode TVS1 is connected to the fourth terminal of inductor L2. One terminal of connector J2 is connected to the fourth terminal of inductor L2. The third terminal of inductor L2 is connected to resistor R2, capacitor C5, capacitor C6, and the fourth terminal of inductor L1. Resistor R2 is connected to capacitor C11, and capacitor C11 is connected to capacitor C6. Capacitor C6 is grounded. The third terminal of cable L1 is connected to capacitor C1, capacitor C2, varistor MOV1, varistor MOV2, and fuse F1. Fuse F1 is connected to two of the following terminals of connector J1.

2. The filter for a medical frequency converter according to claim 1, characterized in that, Inductor L1 is placed inside the cavity, and the surface of the cavity is provided with a permalloy layer.

3. A filter for a medical frequency converter according to claim 1, characterized in that, Inductor L1 is wound with a core of iron-based nanocrystalline soft magnetic alloy material.

4. A filter for a medical frequency converter according to claim 1, characterized in that, Inductor L2 is wound with a ferrite core.

5. A filter for a medical frequency converter according to claim 1, characterized in that, The capacitance of capacitors C1, C3, C4, and C6 is 1 nF; the capacitance of capacitors C2, C5, and C8 is 2.2 uF; the capacitance of capacitors C10 and C11 is 2.2 nF; and the capacitance of capacitor C12 is 4.7 uF.

6. A filter for a medical frequency converter according to claim 1, characterized in that, The inductance of inductor L1 is 50mH, and the inductance of inductor L2 is 5mH.

7. A filter for a medical frequency converter according to claim 1, characterized in that, The resistance of resistors R1 and R2 is 270Ω, and the resistance of resistor R3 is 3Ω.

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