An internal anti-interference circuit and transformer

Abstract

The application provides an internal anti-interference circuit and a transformer, the internal anti-interference circuit is connected in parallel at two ends of a winding of the transformer, and is composed of a state energy absorption module, an impedance resonance suppression branch and an integrated planar electromagnetic suppression structure; the energy absorption module adopts a structure in which a buffer capacitor is connected in parallel with a bidirectional clamping unit, two branches are respectively matched with a fast recovery device, a voltage-dependent resistor, an isolation diode and a voltage stabilizing tube to realize bidirectional voltage clamping; the resonance branch is connected in parallel with the absorption module, and LC series resonance parameters are matched according to a winding parasitic oscillation frequency; the planar electromagnetic suppression structure is arranged on a ferrite substrate, and a lead is arranged as a differential microstrip line, a distributed common-mode impedance is formed under the action of a magnetic medium, a common conductive plane is matched to construct a common-mode bypass channel, and multi-layer control of voltage spikes, resonance oscillation and electromagnetic noise is completed.

Description

Technical Field

[0001] This application belongs to the field of circuits, and in particular relates to an internal anti-interference circuit and a transformer. Background Technology

[0002] With the rapid development of modern power electronics technology, high frequency, miniaturization, and high power density have become important development directions for transformers and various switching power supply equipment. However, in complex and ever-changing actual operating environments, transformers are susceptible to the combined effects of electromagnetic interference and transient shocks. During the frequent high-frequency switching of circuit switching transistors, or when encountering abnormal operating conditions such as sudden changes in grid voltage or lightning surges, transient voltage spikes with high amplitude and steep rise times are easily generated at the ends of the transformer windings. If such transient energy cannot be absorbed and discharged in time, it will create overvoltage stress on the insulation system of the transformer windings, shorten the service life of the equipment, and in severe cases, even cause insulation breakdown. At the same time, parasitic parameters such as leakage inductance and stray capacitance are commonly found in transformer structures. Under the action of external high-frequency excitation, these parasitic parameters are prone to generate continuous high-frequency parasitic oscillations inside the windings. Such oscillations not only bring additional power losses and reduce power conversion efficiency, but may also propagate outward in the form of electromagnetic radiation, further deteriorating the electromagnetic compatibility performance of the system.

[0003] Besides differential-mode spikes and parasitic oscillations, transformers, as key components for electrical isolation and energy transfer, are also important channels for common-mode noise propagation and coupling. Traditional anti-interference designs typically rely on external discrete components to address these issues, such as adding surge protectors, resistor-capacitor buffer networks, and bulky common-mode chokes outside the transformer. However, this traditional approach, relying on external discrete components, has shortcomings: firstly, it increases the overall circuit board area and device size, hindering miniaturization; secondly, long or complex interconnections between discrete components introduce new parasitic inductances, leading to decreased anti-interference effectiveness at high frequencies. Furthermore, conventional fixed-parameter protection circuits have limited adaptability to complex interference conditions where amplitude, frequency, and duration can vary, making it difficult to synergistically suppress multiple types of electromagnetic interference. Therefore, an anti-interference solution is needed that can be integrated within the transformer, possess state-response capabilities, and simultaneously handle multi-dimensional electromagnetic interference problems such as transient energy surges, high-frequency parasitic resonances, and common-mode noise coupling. Summary of the Invention

[0004] According to a first aspect of the present invention, an internal anti-interference circuit is provided to solve the problems of multidimensional electromagnetic interference such as transient energy surges, high-frequency parasitic resonances, and common-mode noise coupling, comprising: The first and second connection terminals of the transformer winding are connected in parallel to the two ends of the transformer winding. The internal anti-interference circuit of the transformer includes a state energy absorption module, an impedance resonance suppression branch and an integrated planar electromagnetic suppression structure. The state energy absorption module includes a buffer capacitor and a bidirectional clamping unit connected in parallel. The bidirectional clamping unit consists of a first clamping branch and a second clamping branch connected in reverse parallel. The first clamping branch includes a fast recovery diode, a thermistor, and a varistor connected in series. The threshold voltage of the varistor is higher than the operating peak voltage of the transformer winding. The second clamping branch includes an isolation diode, a fixed resistor, and a Zener diode connected in series. The impedance resonance suppression branch is connected in parallel with the state energy absorption module. The impedance resonance suppression branch is composed of a resonant inductor and a resonant capacitor connected in series. The series resonant frequency of the impedance resonance suppression branch is set according to the parasitic oscillation frequency of the transformer winding. The integrated planar electromagnetic suppression structure is constructed on a ferrite substrate that is located close to and insulated from the transformer core. The leads of the first and second connection ends are arranged as differential fused microstrip line pairs on the ferrite substrate. The differential fused microstrip line pairs exhibit distributed common-mode impedance under the action of the magnetic medium of the ferrite substrate. A common conductive plane is provided on the ferrite substrate. The distributed capacitance formed between the differential fused microstrip line pairs and the common conductive plane constitutes a common-mode noise bypass path.

[0005] Optionally, the bidirectional clamping unit is composed of a first clamping branch and a second clamping branch connected in reverse parallel, including: The first clamping branch and the second clamping branch achieve current shunting according to the voltage polarity at both ends of the transformer winding; When a forward overvoltage occurs at both ends of the transformer winding and exceeds the threshold voltage of the varistor, the fast recovery diode is forward-biased and guides the forward surge current to the first clamping branch for energy absorption. When a reverse overvoltage occurs at both ends of the transformer winding and its absolute value exceeds the breakdown voltage of the Zener diode, the isolation diode conducts in the forward direction, guiding the reverse surge current to the second clamping branch for energy absorption.

[0006] Optionally, the first clamping branch includes a fast recovery diode, a thermistor, and a varistor connected in series, wherein the threshold voltage of the varistor is higher than the operating peak voltage of the transformer winding, including: The varistor exhibits a high resistance state when the voltage across its terminals is lower than the threshold voltage of the varistor, and a low resistance state when the threshold voltage is reached or exceeded, thereby limiting the amplitude of the forward overvoltage. The thermistor is a positive temperature coefficient thermistor. Under normal operating temperature, it has an initial low resistance value. When the first clamping branch continuously absorbs surge energy and the temperature reaches the Curie temperature, the resistance value increases nonlinearly, limiting the continuous fault current flowing through the first clamping branch to achieve thermal protection.

[0007] Optionally, the second clamping branch includes an isolation diode, a fixed resistor, and a Zener diode connected in series, comprising: The isolation diode is used to prevent the second clamping branch from conducting in reverse when a forward voltage is applied. The Zener diode has a Zener voltage that is higher than the absolute value of the peak reverse working voltage of the transformer winding and lower than the threshold voltage of the varistor. It is used to enter the avalanche breakdown state when a reverse transient overvoltage occurs, and to clamp and reduce the reverse voltage in combination with a fixed resistor. When the reverse transient overvoltage disappears and the voltage recovers to below the Zener diode's voltage regulation value, it automatically returns to the reverse cutoff state.

[0008] Optionally, the impedance resonance suppression branch is composed of a resonant inductor and a resonant capacitor connected in series, and the series resonant frequency of the impedance resonance suppression branch is set according to the parasitic oscillation frequency of the transformer winding, including: The resonant inductor and resonant capacitor form a low-impedance series resonant circuit to absorb interference signals from parasitic oscillation frequencies. When a transient surge occurs with an equivalent frequency lower than the series resonant frequency, the resonant capacitor exhibits high impedance based on its capacitive reactance characteristics, limiting the transient surge current spike and protecting the resonant inductor.

[0009] Optionally, the leads of the first and second connection terminals are arranged as differential fused microstrip line pairs on the ferrite substrate. These differential fused microstrip line pairs exhibit distributed common-mode impedance under the influence of the magnetic medium of the ferrite substrate, including: The differential fused microstrip lines are arranged symmetrically in parallel to reduce the differential mode current loop area and constrain the differential mode magnetic field to diffuse outward, thereby reducing the concentrated effect of differential mode interference on the local magnetic flux density of the ferrite substrate. When a high-frequency common-mode interference current flows through a differentially fused microstrip line pair in the same direction, the differentially fused microstrip line pair forms a common-mode current channel relative to the common conductive plane, and exhibits distributed common-mode impedance under the action of the magnetic medium of the ferrite substrate, which, together with the distributed capacitance, guides the high-frequency common-mode interference current to bypass and discharge.

[0010] Optionally, a common conductive plane is provided on the ferrite substrate, and the distributed capacitance formed between the differential fused microstrip line pair and the common conductive plane constitutes a common-mode noise bypass path, including: The common conductive plane is electrically connected to the protective grounding terminal, the metal shielding shell, or a reference grounding structure that meets the isolation safety requirements via a grounding terminal; in an isolation transformer, the common conductive plane is not directly short-circuited to the secondary side cold ground; The differential fused microstrip line pairs are isolated from the common conductive plane by an insulating dielectric layer and form an equivalent distributed grounding capacitor. The distributed grounding capacitor and the distributed common-mode impedance of the distributed common-mode fusion section together constitute a low-pass filter network to bypass and discharge high-frequency common-mode noise to the corresponding grounding reference body.

[0011] According to a second aspect of the present invention, a transformer is provided, comprising: Internal anti-interference circuits as described in any of the above.

[0012] Preferably, the bidirectional clamping unit is composed of a first clamping branch and a second clamping branch connected in reverse parallel, including: The first clamping branch and the second clamping branch achieve current shunting according to the voltage polarity at both ends of the transformer winding; When a forward overvoltage occurs at both ends of the transformer winding and exceeds the threshold voltage of the varistor, the fast recovery diode is forward-biased and guides the forward surge current to the first clamping branch for energy absorption. When a reverse overvoltage occurs at both ends of the transformer winding and its absolute value exceeds the breakdown voltage of the Zener diode, the isolation diode conducts in the forward direction, guiding the reverse surge current to the second clamping branch for energy absorption.

[0013] Preferably, the first clamping branch includes a fast recovery diode, a thermistor, and a varistor connected in series, wherein the threshold voltage of the varistor is higher than the operating peak voltage of the transformer winding, including: The varistor exhibits a high resistance state when the voltage across its terminals is lower than the threshold voltage of the varistor, and a low resistance state when the threshold voltage is reached or exceeded, thereby limiting the amplitude of the forward overvoltage. The thermistor is a positive temperature coefficient thermistor. Under normal operating temperature, it has an initial low resistance value. When the first clamping branch continuously absorbs surge energy and the temperature reaches the Curie temperature, the resistance value increases nonlinearly, limiting the continuous fault current flowing through the first clamping branch to achieve thermal protection.

[0014] Preferably, the second clamping branch includes an isolation diode, a fixed resistor, and a Zener diode connected in series, comprising: The isolation diode is used to prevent the second clamping branch from conducting in reverse when a forward voltage is applied. The Zener diode has a Zener voltage that is higher than the absolute value of the peak reverse working voltage of the transformer winding and lower than the threshold voltage of the varistor. It is used to enter the avalanche breakdown state when a reverse transient overvoltage occurs, and to clamp and reduce the reverse voltage in combination with a fixed resistor. When the reverse transient overvoltage disappears and the voltage recovers to below the Zener diode's voltage regulation value, it automatically returns to the reverse cutoff state.

[0015] Preferably, the impedance resonance suppression branch is composed of a resonant inductor and a resonant capacitor connected in series, and the series resonant frequency of the impedance resonance suppression branch is set according to the parasitic oscillation frequency of the transformer winding, including: The resonant inductor and resonant capacitor form a low-impedance series resonant circuit to absorb interference signals from parasitic oscillation frequencies. When a transient surge occurs with an equivalent frequency lower than the series resonant frequency, the resonant capacitor exhibits high impedance based on its capacitive reactance characteristics, limiting the transient surge current spike and protecting the resonant inductor.

[0016] Preferably, the leads of the first and second connection terminals are arranged as differential fused microstrip line pairs on the ferrite substrate. The differential fused microstrip line pairs exhibit distributed common-mode impedance under the influence of the magnetic medium of the ferrite substrate, including: The differential fused microstrip lines are arranged symmetrically in parallel to reduce the differential mode current loop area and constrain the differential mode magnetic field to diffuse outward, thereby reducing the concentrated effect of differential mode interference on the local magnetic flux density of the ferrite substrate. When a high-frequency common-mode interference current flows through a differentially fused microstrip line pair in the same direction, the differentially fused microstrip line pair forms a common-mode current channel relative to the common conductive plane, and exhibits distributed common-mode impedance under the action of the magnetic medium of the ferrite substrate, which, together with the distributed capacitance, guides the high-frequency common-mode interference current to bypass and discharge.

[0017] Preferably, a common conductive plane is provided on the ferrite substrate, and the distributed capacitance formed between the differential fused microstrip line pair and the common conductive plane constitutes a common-mode noise bypass path, including: The common conductive plane is electrically connected to the protective grounding terminal, the metal shielding shell, or a reference grounding structure that meets the isolation safety requirements via a grounding terminal; in an isolation transformer, the common conductive plane is not directly short-circuited to the secondary side cold ground; The differential fused microstrip line pairs are isolated from the common conductive plane by an insulating dielectric layer and form an equivalent distributed grounding capacitor. The distributed grounding capacitor and the distributed common-mode impedance of the distributed common-mode fusion section together constitute a low-pass filter network to bypass and discharge high-frequency common-mode noise to the corresponding grounding reference body.

[0018] This invention enhances the anti-interference capability and operational stability of transformers through the synergistic cooperation of a state energy absorption module, an impedance resonance suppression branch, and an integrated planar electromagnetic suppression structure. Specifically, the state energy absorption module utilizes anti-parallel bidirectional clamping units, combined with thermistors and varistors, to perform bidirectional clamping and energy absorption when transient overvoltages or energy surges occur at the winding ends, reducing the risk of winding insulation damage. The impedance resonance suppression branch bypasses and attenuates high-frequency resonant energy by using a series resonant inductor and resonant capacitor that match the parasitic oscillation frequency. The integrated planar electromagnetic suppression structure utilizes differentially fused microstrip line pairs, a common conductive plane, and their distributed capacitance on a ferrite substrate to form a common-mode noise bypass path, thereby enhancing the common-mode interference suppression effect and improving structural integration. Attached Figure Description

[0019] Figure 1 This is the overall topology diagram of the anti-interference circuit inside the transformer; Figure 2 This is a schematic diagram of the state energy absorption module; Figure 3 This is a schematic diagram of the impedance resonance suppression branch; Figure 4 This is a schematic diagram of the equivalent circuit of an integrated planar electromagnetic suppression structure. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In the first embodiment, the present invention proposes an internal anti-interference circuit, comprising: S1 is connected in parallel to the first and second connection terminals at both ends of the transformer winding. The internal anti-interference circuit of the transformer includes a state energy absorption module, an impedance resonance suppression branch, and an integrated planar electromagnetic suppression structure.

[0022] The first and second connection terminals are led out via pins or copper pads and connected in parallel to the taps of the primary or secondary winding of the transformer, achieving the shortest path absorption and discharge of interference signals at the winding ports. The state energy absorption module, impedance resonance suppression branch, and integrated planar electromagnetic suppression structure are arranged in parallel in the circuit topology and are highly integrated into the spare space on the side of the transformer frame or on an additional printed circuit board at the bottom. Through modular parallel collaborative operation, they provide a full-band, multi-mode anti-interference network against high-energy transient surges, high-frequency parasitic oscillations, differential-mode noise, and spatial radiated and conducted common-mode noise, achieving purification of the internal electromagnetic environment of the transformer without altering the main magnetic circuit characteristics. The overall topology of the transformer's internal anti-interference circuit is as follows: Figure 1 As shown.

[0023] S2, the state energy absorption module includes a buffer capacitor and a bidirectional clamping unit connected in parallel. The bidirectional clamping unit is composed of a first clamping branch and a second clamping branch connected in reverse parallel. The first clamping branch includes a fast recovery diode, a thermistor and a varistor connected in series. The threshold voltage of the varistor is higher than the operating peak voltage of the transformer winding. The second clamping branch includes an isolation diode, a fixed resistor and a Zener diode connected in series.

[0024] During normal operation or when encountering low-energy, low-amplitude high-frequency spikes, the parallel buffer capacitors preferentially form a high-frequency bypass channel to absorb and discharge high-frequency transient currents. When the transformer encounters high-energy, high-voltage transient impacts such as lightning surges, the voltage instantaneously exceeds the high threshold of the varistor, causing the first clamping branch to conduct instantly. The fast recovery diode ensures unidirectional rapid discharge in this branch to prevent oscillation. Simultaneously, the series-connected positive temperature coefficient thermistor uses a low initial resistance pulse-type thermistor, primarily for thermal protection during continuous overcurrent, rather than as the main current-limiting element during surge transients. This prevents the varistor from being damaged by thermal breakdown due to continuous overcurrent, achieving coarse-adjustment absorption and self-protection against high energy. When the transformer encounters a switching reverse peak voltage with relatively small reverse energy but extremely rapid voltage changes, the first clamping branch does not conduct due to polarity cutoff or threshold limitation. The Zener diode or TVS diode in the second clamping branch enters the breakdown conduction state with a nanosecond-level response speed. The isolation diode is used to prevent reverse leakage current under normal AC waveforms, while the fixed resistor is used to limit the peak current flowing through the Zener diode, achieving precise clamping of residual spikes. The two are connected in reverse parallel to form a stepped energy discharge for abnormal states in both positive and negative half-cycles. The internal circuit structure of the state energy absorption module is as follows: Figure 2 As shown.

[0025] In an optional embodiment, the bidirectional clamping unit is composed of a first clamping branch and a second clamping branch connected in anti-parallel, including: The first clamping branch and the second clamping branch achieve current shunting according to the voltage polarity at both ends of the transformer winding; When a forward overvoltage occurs at both ends of the transformer winding and exceeds the threshold voltage of the varistor, the fast recovery diode is forward-biased and guides the forward surge current to the first clamping branch for energy absorption. When a reverse overvoltage occurs at both ends of the transformer winding and its absolute value exceeds the breakdown voltage of the Zener diode, the isolation diode conducts in the forward direction, guiding the reverse surge current to the second clamping branch for energy absorption.

[0026] Taking the rated AC operating voltage of a transformer as an example, when its effective value is 220V, the peak value is approximately 311V. The threshold voltage of the varistor can be set to 1.5 to 2 times the peak operating voltage, preferably 470V. The breakdown voltage of the Zener diode is set to be higher than the absolute value of the reverse operating peak voltage but lower than the threshold voltage of the varistor, for example, 350V. Fast recovery diodes with a reverse recovery time of less than 50ns can be selected, and isolation diodes with a reverse withstand voltage of not less than 1000V can be selected. When a forward lightning surge or operational overvoltage occurs, the fast recovery diode conducts forward, allowing the forward surge exceeding the varistor threshold voltage to enter the first clamping branch, where the varistor and related series devices absorb the energy with their high current-carrying capacity. The surge current magnitude is determined by the external surge source impedance, the varistor clamping voltage, the fast recovery diode voltage drop, and the transient initial impedance of the thermistor. The listed surge discharge current of the varistor only indicates the device's withstand level under the standard 8 / 20μs test waveform and does not imply that the first clamping branch will necessarily flow with this peak current under actual port overvoltage conditions. When the transformer winding is subjected to reverse transient overvoltage, such as a reverse -400V transient spike, the fast recovery diode is cut off due to reverse polarity, blocking the first clamping branch, while the isolation diode conducts forward. Since the absolute value of the reverse voltage exceeds the breakdown threshold of the Zener diode, the Zener diode enters avalanche breakdown state, guiding the reverse surge current to the second clamping branch for energy absorption. The above clamping mechanism utilizes the unidirectional conduction characteristic of the diode to achieve the shunt discharge of forward and reverse surges without the need for an active control signal.

[0027] In an optional embodiment, the first clamping branch includes a fast recovery diode, a thermistor, and a varistor connected in series, wherein the threshold voltage of the varistor is higher than the operating peak voltage of the transformer winding, including: The varistor exhibits a high resistance state when the voltage across its terminals is lower than the threshold voltage of the varistor, and a low resistance state when the threshold voltage is reached or exceeded, thereby limiting the amplitude of the forward overvoltage. The thermistor is a positive temperature coefficient thermistor. Under normal operating temperature, it has an initial low resistance value. When the first clamping branch continuously absorbs surge energy and the temperature reaches the Curie temperature, the resistance value increases nonlinearly, limiting the continuous fault current flowing through the first clamping branch to achieve thermal protection.

[0028] The first clamping branch uses a zinc oxide varistor. When the leakage current is less than 10μA below the 470V threshold voltage, it exhibits a high-resistance state, not affecting the normal operation of the transformer. When encountering a positive transient surge exceeding the threshold, the resistance drops rapidly, enabling it to withstand high-energy short-time pulses and clamp the overvoltage amplitude below a safe level. The surge discharge capability of the varistor is preferably selected according to the standard 8 / 20μs pulse test conditions, for example, using devices with a rated peak pulse current of 4500A. This rating is used to characterize the device's withstand capability and is not used as a fixed calculation current for the voltage drop across the series thermistor. The positive temperature coefficient thermistor connected in series is composed of a low-resistance pulse-type device and is installed near the varistor via thermal coupling. Under normal operating conditions (25℃), the initial resistance of this PTC thermistor is preferably 5mΩ to 50mΩ, for example, 10mΩ, to reduce the additional voltage generated during short-time surges and not hinder the discharge of transient high-frequency surge currents.

[0029] When a continuous power frequency overvoltage fault causes the varistor to continuously operate and generate heat, the heat is conducted to the PTC thermistor. Once the PTC body temperature reaches the set Curie temperature, a phase transition occurs at the internal grain boundary barrier, and the resistance increases non-linearly during the device's thermal response time. The high resistance value after PTC operation is selected based on the continuous fault voltage and the target current limit value, preferably above 50kΩ, and more preferably above 100kΩ. When the continuous fault current is within 10mA as the current limit target, the resistance value after PTC operation meets the matching requirements between the continuous fault voltage and the target current limit value. The high resistance state limits the fault current flowing through the first clamping branch within a preset safe range, avoiding the risk of thermal perforation or even fire caused by continuous overcurrent of the varistor.

[0030] In an optional embodiment, the second clamping branch includes an isolation diode, a fixed resistor, and a Zener diode connected in series, comprising: The isolation diode is used to prevent the second clamping branch from conducting in reverse when a forward voltage is applied. The Zener diode has a Zener voltage that is higher than the absolute value of the peak reverse working voltage of the transformer winding and lower than the threshold voltage of the varistor. It is used to enter the avalanche breakdown state when a reverse transient overvoltage occurs, and to clamp and reduce the reverse voltage in combination with a fixed resistor. When the reverse transient overvoltage disappears and the voltage recovers to below the Zener diode's voltage regulation value, it automatically returns to the reverse cutoff state.

[0031] The isolation diode configured in the second clamping branch is a high-voltage fast recovery diode or fast rectifier with a reverse withstand voltage of not less than 1000V. During the forward AC voltage cycle, the reverse leakage current is controlled below 5μA to ensure that the second clamping branch is in a high-resistance cutoff state under forward high voltage. The avalanche breakdown voltage of the Zener diode, such as a TVS transient voltage suppressor diode, is preferably designed to be higher than the absolute value of the peak reverse working voltage of the transformer winding and lower than the threshold voltage of the varistor. In the example of a 220V effective working voltage, the avalanche breakdown voltage is preferably designed to be between 320V and 400V. In the example, 350V is selected. This value is higher than the absolute value of the peak reverse working voltage corresponding to the 220V effective working voltage (approximately 311V) and lower than the 470V threshold voltage of the varistor of the first clamping branch. This is used to ensure that there is no false triggering under normal reverse working voltage and to promptly enter the avalanche breakdown state when a reverse transient overvoltage occurs. The fixed resistor is a 5W high-power non-inductive wire-wound resistor or a thick-film resistor, with a preferred resistance value of 5 to 20Ω, 10Ω in this example. When the absolute value of the reverse surge voltage exceeds 350V, the Zener diode enters avalanche breakdown within nanoseconds. At this time, the surge current flows through the 10Ω fixed resistor, which limits the peak amplitude of the reverse surge current and reduces the junction temperature impact on the Zener diode caused by the large reverse current by utilizing the current limiting and energy dissipation effect of the resistor. When the transient reverse energy is exhausted and the terminal voltage drops below 350V, the avalanche effect of the Zener diode terminates, automatically returning to a reverse cutoff state of megaohms or higher, and the entire second clamping branch is turned off without generating freewheeling current.

[0032] S3, the impedance resonance suppression branch is connected in parallel with the state energy absorption module. The impedance resonance suppression branch is composed of a resonant inductor and a resonant capacitor connected in series. The series resonant frequency of the impedance resonance suppression branch is set according to the parasitic oscillation frequency of the transformer winding.

[0033] The leakage inductance of a specific transformer winding can be obtained by measuring with an impedance analyzer or by using three-dimensional electromagnetic field simulation software such as Maxwell. Interlayer / Interturn distributed capacitance The high-frequency ringing frequency caused by these parasitic parameters was calculated. A high-frequency inductor with controlled equivalent series damping is selected as the resonant inductor. And select a high-frequency thin-film capacitor or a ceramic capacitor as the resonant capacitor. According to the formula × = × The configuration parameters ensure that the inherent resonant frequency of the series LC branch is precisely aligned with the parasitic oscillation frequency of the winding. When ringing noise occurs at this specific frequency, the series branch exhibits a low-impedance but non-zero-impedance damped resonance characteristic at the resonant point, acting like a "notch filter" or "damped bypass channel" at a specific frequency. This introduces high-frequency differential-mode resonant energy into the resonance suppression branch, where it is attenuated through the winding resistance of the resonant inductor, core losses, the equivalent series resistance of the capacitor, or the equivalent damping losses within the branch. At the fundamental frequency during normal transformer operation, the branch exhibits a high-impedance state, reducing voltage ringing at the switching moment without significantly dissipating fundamental energy. The equivalent circuit structure of the impedance resonance suppression branch is as follows: Figure 3 As shown.

[0034] In an optional embodiment, the impedance resonance suppression branch is composed of a resonant inductor and a resonant capacitor connected in series. The series resonant frequency of the impedance resonance suppression branch is set according to the parasitic oscillation frequency of the transformer winding, including: The resonant inductor and resonant capacitor form a low-impedance series resonant circuit to absorb interference signals from parasitic oscillation frequencies. When a transient surge occurs with an equivalent frequency lower than the series resonant frequency, the resonant capacitor exhibits high impedance based on its capacitive reactance characteristics, limiting the transient surge current spike and protecting the resonant inductor.

[0035] The inherent high-frequency parasitic oscillation phenomenon in transformer windings caused by leakage inductance and distributed capacitance typically occurs in the 500kHz to 2MHz frequency range. The impedance resonance suppression branch uses a matching resonant inductor. and resonant capacitor The value of makes the series resonant frequency The frequency is consistent with the measured parasitic oscillation frequency. For example, if the measured center frequency of the parasitic oscillation of the transformer is 1MHz, then select... =25.3μH, using a high-frequency inductor with controlled core loss or equivalent series damping, and matched =1nF, a high-frequency stable ceramic capacitor using C0G / NP0 dielectric. At an interference frequency of 1MHz, the total inductive reactance and capacitive reactance of the series LC circuit cancel each other out, and the branch exhibits damped resonance characteristics with low impedance but non-zero impedance. The equivalent series damping can be set in the range of 1Ω to 10Ω according to the requirements for suppressing the resonance peak. It can bypass and absorb the 1MHz parasitic oscillation interference like a "notch filter" and attenuate it through the equivalent damping of the branch. When the circuit suffers transient lightning strikes or operational surges with an equivalent frequency much lower than 1MHz, and the energy spectrum is mainly concentrated between 10kHz and 100kHz, the 1nF resonant capacitor exhibits high capacitive reactance in this low-frequency range. For example, the capacitive reactance is about 1.59kΩ at 100kHz, which makes the entire series branch turn into a high-impedance state, blocking the inductor from being fed into the resonant branch with large-energy low-frequency surge current, and reducing the risk of low-frequency surges burning out the resonant inductor.

[0036] S4, the integrated planar electromagnetic suppression structure is constructed on a ferrite substrate that is located close to the transformer core and is insulated and fixed to the transformer core. The leads of the first connection end and the second connection end are arranged as differential fused microstrip line pairs on the ferrite substrate. The differential fused microstrip line pairs exhibit distributed common-mode impedance under the action of the magnetic medium of the ferrite substrate. A common conductive plane is provided on the ferrite substrate. The distributed capacitance formed between the differential fused microstrip line pairs and the common conductive plane constitutes a common-mode noise bypass path.

[0037] The leads of the first and second connection terminals are laid on the surface of the ferrite substrate to form a differentially coupled microstrip line pair with a small spacing and parallel to each other. When the normal differential mode operating current flows, the two microstrip lines form a mutually coupled differential mode transmission path, which helps to reduce the differential mode current loop area and reduce the degree of differential mode magnetic field diffusion. When the common mode noise current in the same direction flows, the two microstrip lines form a common mode propagation path with respect to the common conductive plane. The magnetic dielectric characteristics of the ferrite substrate make this path exhibit distributed common mode impedance, thereby suppressing high-frequency common mode current. A common conductive plane is set on the bottom or inner layer of the ferrite substrate. The common conductive plane can be electrically connected to the transformer metal shield shell, protective grounding terminal, or grounding reference body that meets the isolation safety requirements through metallized vias, low parasitic inductance connection structures, or other equivalent connection structures. When the transformer is used as an isolated power supply, the common conductive plane is not directly short-circuited to the secondary side cold ground. An insulating dielectric layer is set between the microstrip line pair and the common conductive plane, and the insulating dielectric layer forms an equivalent distributed grounding capacitance as a distributed common mode bypass section. Therefore, the distributed common-mode impedance and distributed grounding capacitance together constitute a common-mode noise suppression network, enabling high-frequency common-mode noise to be discharged to the corresponding grounding reference body along the bypass path, thereby improving the transformer's high-frequency electromagnetic shielding and common-mode interference immunity. The equivalent circuit corresponding to the integrated planar electromagnetic suppression structure is as follows: Figure 4 As shown.

[0038] In an optional embodiment, the leads of the first and second connection terminals are arranged as differentially fused microstrip line pairs on the ferrite substrate. These differentially fused microstrip line pairs exhibit distributed common-mode impedance under the influence of the magnetic medium of the ferrite substrate, including: The differential fused microstrip lines are arranged symmetrically in parallel to reduce the differential mode current loop area and constrain the differential mode magnetic field to diffuse outward, thereby reducing the concentrated effect of differential mode interference on the local magnetic flux density of the ferrite substrate. When a high-frequency common-mode interference current flows through a differentially fused microstrip line pair in the same direction, the differentially fused microstrip line pair forms a common-mode current channel relative to the common conductive plane, and exhibits distributed common-mode impedance under the action of the magnetic medium of the ferrite substrate, which, together with the distributed capacitance, guides the high-frequency common-mode interference current to bypass and discharge.

[0039] The distributed common-mode fusion section uses nickel-zinc ferrite or composite high-frequency ferrite suitable for the target high-frequency band as the substrate. Within the 10MHz to 100MHz frequency band, the effective complex permeability of the ferrite material is determined based on the material's frequency characteristic curve. Its effective relative permeability no longer uses the initial permeability value at low frequencies, but rather preferably selects a material capable of providing stable impedance loss in the target frequency band. The differential fusion microstrip line pair consists of two copper-clad traces with a linewidth of 1mm, a thickness of 35μm, and a parallel spacing of 0.5mm printed on the front surface of the ferrite substrate. The effective trace length is preferably 40mm to 80mm, with an example of 60mm. During normal power transmission, when the power frequency current or low-frequency differential mode interference is equal in magnitude but opposite in direction, a controlled near-field coupling region is formed between the two traces. This reduces the differential mode current loop area and confines the differential mode magnetic field mainly near the microstrip line pair, thereby reducing electromagnetic interference caused by its diffusion into the external space. At the same time, by controlling the line width, line spacing, trace length, and ferrite substrate thickness, the local magnetic flux density of the ferrite substrate is kept within the allowable range, avoiding local magnetic saturation caused by continuous operating current.

[0040] When the system is subjected to high-frequency common-mode interference in the 10MHz to 100MHz range, and the interference current flows in the same direction and phase on both microstrip lines, the two traces together form a common-mode current path relative to the common conductive plane. The ferrite substrate provides frequency-dependent magnetic impedance to this common-mode current path, effectively forming a distributed common-mode impedance within the target frequency band. This distributed common-mode impedance can be obtained through impedance analysis or electromagnetic field simulation. For example, it presents an equivalent common-mode impedance of approximately 100Ω to 300Ω at 30MHz. If this distributed common-mode impedance is equivalently characterized according to the impedance characteristics under the target frequency band, it can correspond to an equivalent common-mode inductive reactance of a certain order of magnitude, rather than being limited to fixed inductance parameters under low-frequency conditions. This distributed common-mode impedance blocks the propagation of common-mode current to the transformer winding in the tens of megahertz frequency band; at the same time, it generates a cooperative impedance transformation with the distributed capacitance within the structure, allowing the high-frequency common-mode interference current to be discharged along the bypass capacitor path with lower impedance, thus achieving isolation and current diversion for high-frequency common-mode interference.

[0041] In an optional embodiment, a common conductive plane is provided on the ferrite substrate, and the distributed capacitance formed between the differential fused microstrip line pair and the common conductive plane constitutes a common-mode noise bypass path, including: The common conductive plane is electrically connected to the protective grounding terminal, the metal shielding shell, or a reference grounding structure that meets the isolation safety requirements via a grounding terminal; in an isolation transformer, the common conductive plane is not directly short-circuited to the secondary side cold ground; The differential fused microstrip line pairs are isolated from the common conductive plane by an insulating dielectric layer and form an equivalent distributed grounding capacitor. The distributed grounding capacitor and the distributed common-mode impedance of the distributed common-mode fusion section together constitute a low-pass filter network to bypass and discharge high-frequency common-mode noise to the corresponding grounding reference body.

[0042] The common conductive plane is composed of a solid copper-clad layer covering the back or inner layer of the ferrite substrate, with a thickness of up to 70 μm. This copper-clad layer is electrically connected to the metal shielding shell of the transformer, the protective grounding terminal PE, or the grounding reference body that meets the isolation safety requirements through a wide flat copper strip with a width greater than 5 mm and a parasitic inductance of less than 5 nH or an equivalent low parasitic interconnection structure. When the common conductive plane is located near the isolation boundary between the primary and secondary sides, its connection method, creepage distance, electrical clearance and withstand voltage level are set according to the corresponding safety requirements, and the secondary cold ground and protective ground are not directly short-circuited.

[0043] Ferrite substrates are not directly used as high-voltage safety insulating dielectric layers. A polyimide, ceramic, epoxy fiberglass, or high-dielectric-constant insulating dielectric layer is placed between the differential fused microstrip line pairs and the common conductive plane. The withstand voltage rating, thickness, creepage distance, and clearance of this insulating dielectric layer meet the isolation requirements between the primary and secondary sides of the transformer and the protective ground. Utilizing the dielectric properties of this insulating dielectric layer, a numerically stable distributed grounding capacitance is obtained between the differential fused microstrip line pairs on the front side and the common conductive plane on the back side. The capacitance value of this distributed grounding capacitance is determined by the trace length, copper overlap area, insulating dielectric layer thickness, and the relative permittivity of the insulating dielectric, preferably ranging from 47pF to 470pF. For example, when the linewidth of the two microstrip lines is 1mm and the effective trace length is 60mm, the total equivalent overlap area is approximately 120mm². 2 When the thickness of the insulating dielectric layer is 0.2 mm and the relative permittivity is selected to be around 80, a distributed grounding capacitance of several hundred picofarads can be obtained, for example, 470 pF.

[0044] The distributed grounding capacitor, together with the distributed common-mode impedance generated by the aforementioned distributed common-mode fusion section, constitutes a second-order low-pass filter network. For a 470pF distributed grounding capacitor, its capacitive reactance near 10MHz, 30MHz, and 100MHz is approximately 34Ω, 11Ω, and 3.4Ω, respectively, thus forming a low-impedance high-frequency bypass path in the tens to hundreds of megahertz frequency band. A low-impedance high-frequency discharge channel is formed between the differential trace and the back ground reference, allowing high-frequency common-mode noise energy to be discharged to the corresponding ground reference via a bypass path. The entire structure can provide broadband attenuation control for common-mode noise above 30MHz based on measured or simulation results.

[0045] In a second embodiment, the present invention also proposes a transformer, comprising: Internal anti-interference circuits as described in any of the above.

[0046] The above description represents the preferred embodiments of the present invention. It should be noted that, for those skilled in the art, various improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. An internal anti-interference circuit, characterized in that, include: The first and second connection terminals of the transformer winding are connected in parallel to the two ends of the transformer winding. The internal anti-interference circuit of the transformer includes a state energy absorption module, an impedance resonance suppression branch and an integrated planar electromagnetic suppression structure. The state energy absorption module includes a buffer capacitor and a bidirectional clamping unit connected in parallel. The bidirectional clamping unit consists of a first clamping branch and a second clamping branch connected in reverse parallel. The first clamping branch includes a fast recovery diode, a thermistor, and a varistor connected in series. The threshold voltage of the varistor is higher than the operating peak voltage of the transformer winding. The second clamping branch includes an isolation diode, a fixed resistor, and a Zener diode connected in series. The impedance resonance suppression branch is connected in parallel with the state energy absorption module. The impedance resonance suppression branch is composed of a resonant inductor and a resonant capacitor connected in series. The series resonant frequency of the impedance resonance suppression branch is set according to the parasitic oscillation frequency of the transformer winding. The integrated planar electromagnetic suppression structure is constructed on a ferrite substrate that is located close to and insulated from the transformer core. The leads of the first and second connection ends are arranged as differential fused microstrip line pairs on the ferrite substrate. The differential fused microstrip line pairs exhibit distributed common-mode impedance under the action of the magnetic medium of the ferrite substrate. A common conductive plane is provided on the ferrite substrate. The distributed capacitance formed between the differential fused microstrip line pairs and the common conductive plane constitutes a common-mode noise bypass path.

2. The internal anti-interference circuit according to claim 1, characterized in that, The bidirectional clamping unit consists of a first clamping branch and a second clamping branch connected in reverse parallel, including: The first clamping branch and the second clamping branch achieve current shunting according to the voltage polarity at both ends of the transformer winding; When a forward overvoltage occurs at both ends of the transformer winding and exceeds the threshold voltage of the varistor, the fast recovery diode is forward-biased and guides the forward surge current to the first clamping branch for energy absorption. When a reverse overvoltage occurs at both ends of the transformer winding and its absolute value exceeds the breakdown voltage of the Zener diode, the isolation diode conducts in the forward direction, guiding the reverse surge current to the second clamping branch for energy absorption.

3. The internal anti-interference circuit according to claim 2, characterized in that, The first clamping branch includes a fast recovery diode, a thermistor, and a varistor connected in series. The threshold voltage of the varistor is higher than the operating peak voltage of the transformer winding, and includes: The varistor exhibits a high resistance state when the voltage across its terminals is lower than the threshold voltage of the varistor, and a low resistance state when the threshold voltage is reached or exceeded, thereby limiting the amplitude of the forward overvoltage. The thermistor is a positive temperature coefficient thermistor. Under normal operating temperature, it has an initial low resistance value. When the first clamping branch continuously absorbs surge energy and the temperature reaches the Curie temperature, the resistance value increases nonlinearly, limiting the continuous fault current flowing through the first clamping branch to achieve thermal protection.

4. The internal anti-interference circuit according to claim 1, characterized in that, The second clamping branch includes an isolation diode, a fixed resistor, and a Zener diode connected in series, comprising: The isolation diode is used to prevent the second clamping branch from conducting in reverse when a forward voltage is applied. The Zener diode has a Zener voltage that is higher than the absolute value of the peak reverse working voltage of the transformer winding and lower than the threshold voltage of the varistor. It is used to enter the avalanche breakdown state when a reverse transient overvoltage occurs, and to clamp and reduce the reverse voltage in combination with a fixed resistor. When the reverse transient overvoltage disappears and the voltage recovers to below the Zener diode's voltage regulation value, it automatically returns to the reverse cutoff state.

5. The internal anti-interference circuit according to claim 1, characterized in that, The impedance resonance suppression branch is composed of a resonant inductor and a resonant capacitor connected in series. The series resonant frequency of the impedance resonance suppression branch is set according to the parasitic oscillation frequency of the transformer winding, including: The resonant inductor and resonant capacitor form a low-impedance series resonant circuit to absorb interference signals from parasitic oscillation frequencies. When a transient surge occurs with an equivalent frequency lower than the series resonant frequency, the resonant capacitor exhibits high impedance based on its capacitive reactance characteristics, limiting the transient surge current spike and protecting the resonant inductor.

6. The internal anti-interference circuit according to claim 1 or 5, characterized in that, The leads of the first and second connection terminals are arranged as differential fused microstrip line pairs on the ferrite substrate. These differential fused microstrip line pairs exhibit distributed common-mode impedance under the influence of the magnetic medium of the ferrite substrate, including: The differential fused microstrip lines are arranged symmetrically in parallel to reduce the differential mode current loop area and constrain the differential mode magnetic field to diffuse outward, thereby reducing the concentrated effect of differential mode interference on the local magnetic flux density of the ferrite substrate. When a high-frequency common-mode interference current flows through a differentially fused microstrip line pair in the same direction, the differentially fused microstrip line pair forms a common-mode current channel relative to the common conductive plane, and exhibits distributed common-mode impedance under the action of the magnetic medium of the ferrite substrate, which, together with the distributed capacitance, guides the high-frequency common-mode interference current to bypass and discharge.

7. The internal anti-interference circuit according to claim 1, characterized in that, A common conductive plane is provided on the ferrite substrate, and the distributed capacitance formed between the differential fused microstrip line pair and the common conductive plane constitutes a common-mode noise bypass path, including: The common conductive plane is electrically connected to the protective grounding terminal, the metal shielding shell, or a reference grounding structure that meets the isolation safety requirements via a grounding terminal; in an isolation transformer, the common conductive plane is not directly short-circuited to the secondary side cold ground; The differential fused microstrip line pairs are isolated from the common conductive plane by an insulating dielectric layer and form an equivalent distributed grounding capacitor. The distributed grounding capacitor and the distributed common-mode impedance of the distributed common-mode fusion section together constitute a low-pass filter network to bypass and discharge high-frequency common-mode noise to the corresponding grounding reference body.

8. A transformer, characterized in that, Includes the internal anti-interference circuit as described in any one of claims 1-7.

9. The transformer according to claim 8, characterized in that, The bidirectional clamping unit consists of a first clamping branch and a second clamping branch connected in reverse parallel, including: The first clamping branch and the second clamping branch achieve current shunting according to the voltage polarity at both ends of the transformer winding; When a forward overvoltage occurs at both ends of the transformer winding and exceeds the threshold voltage of the varistor, the fast recovery diode is forward-biased and guides the forward surge current to the first clamping branch for energy absorption. When a reverse overvoltage occurs at both ends of the transformer winding and its absolute value exceeds the breakdown voltage of the Zener diode, the isolation diode conducts in the forward direction, guiding the reverse surge current to the second clamping branch for energy absorption.

10. The transformer according to claim 8, characterized in that, The first clamping branch includes a fast recovery diode, a thermistor, and a varistor connected in series. The threshold voltage of the varistor is higher than the operating peak voltage of the transformer winding, and includes: The varistor exhibits a high resistance state when the voltage across its terminals is lower than the threshold voltage of the varistor, and a low resistance state when the threshold voltage is reached or exceeded, thereby limiting the amplitude of the forward overvoltage. The thermistor is a positive temperature coefficient thermistor. Under normal operating temperature, it has an initial low resistance value. When the first clamping branch continuously absorbs surge energy and the temperature reaches the Curie temperature, the resistance value increases nonlinearly, limiting the continuous fault current flowing through the first clamping branch to achieve thermal protection.

Images