Detecting transformer saturation in switched mode power supply

Abstract

The invention relates to detecting transformer saturation in a switched mode power supply. According to an embodiment, a flyback converter includes a transformer, a power switch coupled to a primary winding of the transformer, and a controller. The controller includes a voltage dependent current source, a reference capacitor, a comparator, and logic circuitry. The controller estimates a primary inductance of the transformer based on a voltage across the reference capacitor, detects a saturation condition based on the estimated inductance and the primary current, and in response implements a protection mechanism. The controller may distinguish between true overload conditions and potential magnetic tampering attempts. The protection mechanism may include increasing the switching frequency. The controller may include an adjustable transconductance to set a saturation detection threshold and to implement a delay prior to activation of protection. This allows more targeted protection against core saturation and magnetic disturbances while maintaining normal operation under high load conditions.

Description

Technical Field

[0001] This disclosure generally relates to power controllers, and in certain embodiments, to detecting transformer saturation in a switch-mode power supply. Background Technology

[0002] Switch-mode power supplies (SMPS) are widely used in a variety of electronic devices due to their high efficiency and compact size. Among the different topologies of SMPS, flyback converters are particularly common in low- to medium-power applications, such as battery chargers, LED drivers, and auxiliary power supplies in industrial equipment.

[0003] In a flyback converter, the transformer plays a role in energy transfer and electrical insulation between the primary and secondary sides. The proper operation of the converter depends on the characteristics of the transformer, particularly its primary inductance. However, the magnetic properties of the transformer core can be affected by various factors, including temperature, operating conditions, and external magnetic fields.

[0004] One concern in flyback converter design is the possibility of core saturation. When the transformer core saturates, its ability to store magnetic energy decreases, leading to a rapid increase in primary current. If left unchecked, this can result in reduced efficiency, increased electromagnetic interference (EMI), and potential damage to switching components.

[0005] In applications such as energy metering, core saturation can become problematic. In these situations, deliberate attempts at magnetic tampering may be made to disrupt the normal operation of the meter, potentially leading to energy theft. Magnetic tampering typically involves placing a strong external magnet near the transformer, which can prematurely saturate the core and cause power failure or shutdown.

[0006] To address these challenges, power supply designers have traditionally employed various methods to prevent core saturation and magnetic tampering. These methods typically involve increasing transformer size, using magnetic shielding, or implementing frequency doubling techniques when the converter approaches overload conditions. However, under normal operating conditions, these solutions can lead to increased cost, larger form factor, or poor performance. Summary of the Invention

[0007] The technical advantages are largely achieved through embodiments of this disclosure, which describe the detection of transformer saturation in a switch-mode power supply.

[0008] The first aspect relates to a flyback converter including a transformer having a primary winding and a secondary winding; a power switch coupled to the primary winding, wherein a primary current flows through the primary winding of the transformer; and a controller coupled to the power switch. The controller includes a voltage-dependent current source, a reference capacitor coupled to the voltage-dependent current source, a first comparator configured to compare a voltage across the reference capacitor with a saturation threshold voltage, a second comparator configured to compare a sensed voltage representing the primary current with an overcurrent protection threshold voltage, and a logic circuit system configured to generate a trigger signal based on the outputs of the first and second comparators. The controller is configured to estimate the primary inductance of the transformer based on the voltage across the reference capacitor, detect a saturation condition based on the estimated primary inductance and primary current, and implement a protection mechanism in response to the detected saturation condition.

[0009] The second aspect relates to a controller for a flyback converter. The controller includes a voltage-dependent current source; a reference capacitor coupled to the voltage-dependent current source; a first comparator configured to compare a voltage across the reference capacitor with a saturation threshold voltage; a second comparator configured to compare a primary current representing a primary current with an overcurrent protection threshold, wherein the primary current flows through the primary winding of a transformer of the flyback converter; a logic circuit system configured to generate a trigger signal based on the outputs of the first and second comparators; and a control circuit system configured to: estimate the primary inductance of the transformer based on the voltage across the reference capacitor, detect a saturation condition based on the estimated primary inductance and primary current, and implement a protection mechanism in response to the detected saturation condition.

[0010] The third aspect relates to a method for operating a flyback converter. The method includes monitoring the primary current of a transformer; estimating the primary inductance of the transformer based on the voltage across a reference capacitor; comparing the estimated primary inductance with a saturation threshold; comparing the primary current with an overcurrent protection threshold; detecting a saturation condition based on the comparison of the estimated primary inductance with the primary current; and implementing a protection mechanism in response to the detected saturation condition.

[0011] The implementation can be carried out in hardware, software, or any combination thereof. Attached Figure Description

[0012] To gain a more complete understanding of this disclosure and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, wherein:

[0013] Figure 1 This is a simplified schematic diagram of a flyback converter;

[0014] Figure 2 This is a schematic diagram of an embodiment controller used to monitor the primary inductance of a transformer;

[0015] Figure 3 This is a schematic diagram of the controller in the embodiment;

[0016] Figure 4 This is a schematic diagram of a flyback converter with saturation detection capability; and

[0017] Figure 5 This is a flowchart of an embodiment of a method for operating a converter to detect saturation conditions and implement a protection mechanism. Detailed Implementation

[0018] This disclosure provides numerous applicable inventive concepts that can be embodied in a wide variety of specific contexts. Specific embodiments are merely illustrative of particular configurations and do not limit the scope of the claimed embodiments. Unless otherwise stated, features of different embodiments can be combined to form other embodiments. Various embodiments are illustrated in the accompanying drawings, wherein identical parts and elements are identified by the same reference numerals, and repeated descriptions are omitted for brevity.

[0019] The variations or modifications described in one embodiment may also be applied to other embodiments. Furthermore, various changes, substitutions, and modifications may be made without departing from the spirit and scope of this disclosure as defined by the appended claims.

[0020] While the inventive aspects are primarily described in the context of flyback converters operating in quasi-resonant (QR) mode or discontinuous conduction mode (DCM), it should be understood that these inventive aspects can also be applied to other switch-mode power supply topologies. In particular, aspects of this disclosure can be similarly applied to forward converters, push-pull converters, and other isolated DC-DC converter topologies where transformer saturation detection facilitates reliable operation.

[0021] In the embodiments, techniques for estimating inductance and detecting saturation in switch-mode power supplies are disclosed, particularly in flyback converters operating in quasi-resonant (QR) mode or discontinuous conduction mode (DCM). The disclosed techniques can distinguish between genuine overload conditions and potential magnetic tampering attempts, allowing for more targeted protection strategies.

[0022] In this disclosure, during the power switch's on-time, the capacitor is charged with a current proportional to the input voltage. The voltage across the capacitor at the end of the on-time can be used to estimate the transformer's primary inductance. By comparing the voltage across the capacitor with a predetermined threshold, the system can detect whether the inductance has dropped below a certain level, which can indicate core saturation.

[0023] In this embodiment, the disclosed method utilizes the auxiliary winding of a flyback converter to generate a current proportional to the input voltage, eliminating the need for direct high-voltage sensing. This method simplifies implementation and improves safety in high-voltage applications.

[0024] Embodiments of this disclosure may include a saturation trigger circuit that compares an estimated inductance with a threshold. When the estimated inductance is below the threshold and the primary current approaches a cycle-by-cycle current limit, the system may activate protective measures. These measures may include increasing the switching frequency, decreasing the maximum duty cycle, initiating controlled shutdown of the converter, or a combination thereof.

[0025] The disclosed technology offers advantages over traditional saturation protection methods. By providing more accurate detection of core saturation, the system can avoid unnecessary intervention during normal operation while providing robust protection against magnetic tampering attempts.

[0026] The embodiments disclosed herein address weaknesses in energy metering systems that account for magnetic tampering. Positioning a strong magnet near the transformer of a power supply is a common method for tampering with energy meters to steal energy. This tampering forces the converter to activate overload conditions, potentially causing the meter to shut down. While existing protections can activate when the power supply approaches its power limits, these typically cannot distinguish between a genuine overload and a magnetic attack.

[0027] Conversely, the techniques described in this disclosure can provide solutions to differentiate between these scenarios. By estimating the actual inductance of the transformer, the system can determine whether the near power limit is due to actual overload conditions or magnetic tampering. This capability allows for more targeted and effective protection strategies, potentially reducing energy theft while maintaining normal operation under truly high load conditions.

[0028] This disclosure may also include methods for setting and adjusting saturation detection thresholds based on system parameters and operating conditions. This flexibility allows protection schemes to be tailored to specific application requirements and transformer characteristics. These and other details are further provided below.

[0029] Figure 1 A simplified schematic diagram of a flyback converter 100 is shown. The flyback converter 100 includes a controller 102, a power switch (Q1) 104, and an input capacitor (C). IN 106. Transformer; 108. Output capacitor (C) OUT 110. Output diode (D) OUT )112, RCD clamping circuit 114 and sensing resistor (R SRCD clamping circuit 114 includes resistor (R) 116, capacitor (C) 118, and diode (D) 120. Flyback converter 100 may include additional components not shown, such as a load at the output.

[0030] Controller 102 controls the operation of flyback converter 100. Controller 102 generates necessary control signals (typically pulse width modulation (PWM)) to regulate the output voltage (V). OUT (or current). Controller 102 monitors the output and adjusts the switching frequency or duty cycle to maintain a stable output under varying load and input conditions.

[0031] Power switch (Q1) 104 (typically a metal-oxide-semiconductor field-effect transistor (MOSFET)) is the main switching element of flyback converter 100. Controller 102 drives power switch (Q1) 104 to turn it on and off at a specific frequency and duty cycle. When power switch (Q1) 104 is on, energy is stored in the primary winding (P) of transformer 108. When power switch (Q1) 104 is off, the stored energy is transferred to the secondary winding (S) of transformer 108 and then to the output.

[0032] Sensing resistor (R) S 122 is placed in series with power switch (Q1) 104 to monitor the current flowing through the primary winding when power switch (Q1) 104 is enabled. A sense resistor (R) is used. S The voltage across 122 (V) SENSE The information is fed to controller 102, which uses it as a feedback signal to operate power switch (Q1) 104.

[0033] In this embodiment, the flyback converter 100 can operate in two different modes: quasi-resonant (QR) mode and discontinuous conduction mode (DCM). Each mode offers specific advantages in terms of efficiency and reduction of electromagnetic interference (EMI), and the controller 102 can be configured to switch between these modes based on load conditions and design requirements.

[0034] In DCM operation, power switch (Q1) 104 is turned on when the current in the primary winding 204 has dropped to zero and all the energy stored in transformer 108 has been transferred to the secondary side. This ensures that no current flows in the primary winding at the beginning of each switching cycle. Controller 102 typically uses a fixed switching frequency in DCM, adjusting the duty cycle to regulate the output voltage.

[0035] The QR mode is based on DCM operation, but utilizes the inherent resonance between the primary inductance of transformer 108 and parasitic capacitances in the circuit (including the output capacitance of power switch (Q1) 104). After energy transfer to the secondary side is completed and the secondary current drops to zero, the voltage across power switch (Q1) 104 oscillates due to this resonance.

[0036] In QR operation, controller 102 monitors the voltage across power switch (Q1) 104 and waits for the oscillating voltage to reach its minimum value before turning on power switch (Q1) 104. This technique, known as valley switching, reduces switching losses and EMI compared to conventional fixed-frequency DCM operation.

[0037] Depending on load conditions, the flyback converter 100 can dynamically switch between QR and DCM modes. QR operation can be maintained under higher loads, taking advantage of its higher efficiency. As the load decreases, the time between switching cycles in QR mode will naturally increase. The controller 102 can switch to DCM with a higher fixed switching frequency under light loads to maintain good regulation and transient response.

[0038] Input capacitor (C) IN The 106 smooths the input voltage and provides a local energy reservoir for high-frequency switching current. This helps reduce electromagnetic interference (EMI) and improves the overall efficiency of the converter.

[0039] Transformer 108 provides input voltage (V) IN ) and output voltage (V OUT Electrical isolation between the two sides. It also stores energy (in its primary winding) during the ON state of the power switch (Q1) 104 and releases energy to the load of the flyback converter 100 during the OFF state of the low-side switch (Q1) 104 (i.e., through its secondary winding).

[0040] Output capacitor (C) OUT )110 is located after the secondary winding of transformer 108. It filters out high-frequency switching ripple, ensuring a stable and smooth DC output voltage (V). OUT The stored energy also provides instantaneous power to the load during transient conditions.

[0041] Output diode (D) OUT )112 allows current to flow from the secondary winding of transformer 108 to the output during the off phase of power switch (Q1) 104 and blocks the current during the on phase to ensure unidirectional current flow at the output.

[0042] The RCD clamping circuit 114, or resistor-capacitor-diode clamping circuit, is a protective circuit system used to manage voltage spikes that may occur due to the leakage inductance of transformer 108. Resistor (R) 116 helps dissipate energy, capacitor (C) 118 absorbs voltage spikes, and diode (D) 120 provides a return path for leaked energy, ensuring that voltage spikes do not exceed safe levels and thus protecting power switch (Q1) 104.

[0043] Operationally, the flyback converter 100 controls the switching of the power switch (Q1) 104. When the power switch (Q1) 104 is on, energy is stored in the primary winding of the transformer 108. When the power switch (Q1) 104 is off, the stored energy is transferred to the secondary winding of the transformer 108, which is rectified, filtered, and supplied to the load at the output of the flyback converter 100.

[0044] The controller 102 continuously adjusts the operation of the flyback converter 100 based on feedback from the output to ensure that the desired output voltage (V) is maintained. OUT (or current.) The RCD clamping circuit 114 ensures that any potential voltage spikes are managed and do not damage the converter components.

[0045] Transformer 108 provides electrical isolation between the primary and secondary sides. It allows voltage to be increased or decreased based on the ratio between the number of turns in the primary and secondary windings.

[0046] When current flows through the primary inductance of transformer 108 (i.e., the inductance measured across the primary winding), the magnetic flux density ( B According to the following equation and the magnetic field ( H Increase proportionally: ,in It is the magnetic permeability of the core material.

[0047] The properties of the ferrite magnetic material used in the core of transformer 108 impose constraints on this relationship. Magnetic flux density ( B ) cannot be increased indefinitely, and the magnetic field ( H There are limitations; beyond these limits, the magnetic flux density ( B The magnetic flux density in this state no longer increases. This phenomenon is called saturation magnetization, and the magnetic flux density in this state is called the saturation magnetic flux density. B SAT ).

[0048] As the core approaches saturation, the magnetic field (i.e., The rate of change of magnetic flux density related to ) decreases. When the core is fully saturated, the magnetic flux density at saturation ( dBSAT The incremental change in is close to zero, causing the primary inductor to behave almost like a short circuit. This behavior can be expressed as ,in It is the voltage across the primary winding. n It is the number of turns in the primary winding. A e It is the effective cross-sectional area of ​​the primary winding core. t It's about timing. It's important to note that, due to the non-zero saturation permeability of the core material, a small amount of residual inductance is maintained to prevent a complete short circuit in the primary winding.

[0049] The saturation effect affects the operation of the flyback converter 100 because it can limit the amount of energy stored in the magnetic field and, if not properly managed, can lead to a rapid increase in current. Specifically, the primary inductance decreases rapidly due to core saturation. At a given inductor current ( I L Under these conditions, the energy stored in the primary winding 104 ( E L The energy decreases according to the equation Provide, and L It is the inductance of the primary winding.

[0050] If a strong magnet is placed near the magnetic core, the saturation magnetic flux density ( B SAT The value may be reduced. As a result, the induced current required to saturate the core is also reduced, which forms the basis for potential magnetic tampering in the power supply system. Placing a strong magnet near the transformer is often sufficient to cause core saturation of the transformer used in the power stage. Therefore, the power delivered to the output by the converter is reduced, and the meter may shut down due to the activation of overload protection. This weakness creates an opportunity to steal energy through magnetic tampering.

[0051] The economic impact of such tampering can be substantial. Each year, utility providers lose significant sums of money due to energy theft, often caused by magnetic tampering that leads to power stage failures in meters. This pervasive problem necessitates robust countermeasures to protect the integrity of utility providers and energy distribution systems. To address this challenge, silicon suppliers can implement specific functionalities to protect power supplies from core saturation, thereby preventing failures in the event of a tampering attack.

[0052] Several technical solutions have been developed to address the problems of core saturation and magnetic interference in power converters. One approach involves protecting transformer 108 from external magnetic interference by using metallic shielding. Magnetic shielding can reduce the transformer's sensitivity to external magnetic fields, thereby reducing the likelihood of premature core saturation.

[0053] Another approach involves increasing the primary inductance of transformer 108 to ensure sufficient residual inductance even under saturation conditions. This method ensures that the converter maintains sufficient residual inductance, thus maintaining adequate power capacity even when the core begins to saturate.

[0054] Another approach involves implementing a frequency multiplication function. For example, the switching frequency is doubled when the converter approaches overload conditions. This allows the converter to handle reductions in transformer inductance of up to 50% caused by external magnetization interference.

[0055] While these technical solutions can provide some protection against core saturation and magnetic interference, they also introduce some drawbacks. Using metal shielding or increasing the size of the primary inductor can increase the cost of magnetic components, potentially making the overall converter more expensive to manufacture.

[0056] Furthermore, conventional methods may cause the converter to operate under non-optimal conditions. For example, in normal operation, an excessively large primary inductance may increase losses when no additional inductor is required.

[0057] With frequency doubling technology, the switching frequency increases not only during magnetic interference events but also during actual overload conditions. As a result, the converter may need to be designed with much higher overpower protection (OPP) limits. This may necessitate an increase in the electrical and thermal dimensions of the converter components, leading to increased cost and size of the overall system.

[0058] In addition, the frequency doubling method may not be able to distinguish between actual overload conditions and overload conditions caused by magnetic interference, potentially leading to an unnecessary increase in the switching frequency and related losses in cases where such an increase is neither beneficial nor necessary.

[0059] Figure 2 A schematic diagram of an embodiment controller 200 for monitoring the primary inductance of a transformer is shown. The controller 200 can be implemented as follows: Figure 1 The controller 102 is included. The controller 200 includes a voltage-dependent current source 202, a switch (Q2) 204, and a capacitor (C). REF 206, which may (or may not) be arranged as shown. Controller 200 may include additional components not shown.

[0060] During the on-time of power switch (Q1) 104, capacitor (C) REF )206 is charged by voltage-dependent current source 202. Capacitor (C) REF The charging process of 206 and the input voltage (V) of voltage-dependent current source 202. IN ) and transconductance (g mIt is directly related to the conduction time. As the conduction time progresses, the capacitance across the capacitor (C) increases. REF The voltage across 206 (V) CREF )Increase.

[0061] After the on-time period, when the power switch (Q1) 104 is turned off, the capacitor (C) is... REF The voltage across 206 (V) CREF The charging current reaches its peak value. This peak value is determined by the charging current (which is determined by the transconductance and input voltage), the duration of the conduction time, and the capacitance (C). REF The capacitance of 206 is a function of the capacitance. This relationship can be expressed as: V CREF It is the time across the capacitor (C) at the end of the conduction period. REF The voltage across 206, g m It is the transconductance of voltage-dependent current source 202, V IN It is the input voltage, T ON It is the duration of the conduction time, and C REF It is a capacitor (C) REF A 206 capacitor.

[0062] During DCM or QR mode, the on-time of power switch (Q1) 104, peak primary current (I0) P ), primary inductor (L M ) and input voltage (V IN They are interconnected based on the following equations: .

[0063] By comparing this equation with the previously established transcapacitor (C) REF The voltage across 206 (V) CREF By combining the relationships between capacitors (C) and capacitors, a system can be established that integrates the capacitors across capacitors (C). REF The voltage across 206 (V) CREF ) directly with the primary inductor (L M The associated new equation: The derived equations reveal the behavior of the flyback converter. They prove the assumption of a peak primary current (I0). P It is known that the capacitor (C) is trans-capacitor. REF The voltage across 206 (V) CREF ) and primary inductance (L M It is directly proportional to the transconductance (g). The proportionality constant is determined by the transconductance (g) m ) and capacitor (C REF The ratio of the capacitance of 206 is determined.

[0064] It is worth noting that the transcapacitor (C REF The voltage across 206 (V)CREF ) and primary inductance (L M The relationship between the capacitors (C) and the switching frequency is independent of the converter's operating conditions (e.g., input voltage and switching frequency). This independence allows the capacitors (C) to switch independently of the converter's operating conditions. REF The voltage across 206 (V) CREF This becomes an ideal parameter for monitoring the primary inductance, and by extension, it can be used to detect core saturation, regardless of changes in input voltage or switching frequency that may occur during normal operation or under different load conditions.

[0065] Therefore, across capacitor (C REF The voltage across 206 (V) CREF It provides information about the primary inductance of transformer 108 and enables controller 200 to identify potential core saturation or tampering attempts.

[0066] Switch (Q2) 204 controls the capacitor (C) at the beginning of each switching cycle. REF )206 discharge to reset capacitor (C) REF 206. The reset operation ensures accurate measurement of the primary inductance in each cycle. Specifically, when switch (Q2) 204 is closed, it is for capacitor (C) REF The 206 provides a low-impedance path to ground, quickly releasing any voltage accumulated from the previous cycle. This action prepares the capacitor (C) for the new charging cycle. REF )206, which allows it to start from a known state (fully discharged) at the beginning of each on-time of power switch (Q1) 104.

[0067] Switch (Q2) 204 remains in the closed position throughout the entire on-time of power switch (Q1) 104, allowing capacitor (C) to... REF )206 is charged during this period. Then, switch (Q2) 204 is turned off at some point between the end of the current on-time and the beginning of the next on-time. This ensures that at the beginning of each new on-time cycle, capacitor (C) is charged. REF )206 is fully discharged. This allows the capacitor (C) to be fully discharged. REF )206 begins each on-time cycle in a discharge state, preparing to accumulate charge during the next on-time of power switch (Q1) 104.

[0068] The capacitor (C) facilitated by switch (Q2) 204 REF The 206-cycle reset and charge operation ensures cross-capacitor (C) operation. REF The voltage across 206 (V) CREF It accurately reflects the primary inductance of the current cycle, without being affected by residual charge from previous cycles.

[0069] Figure 3 A schematic diagram of the embodiment controller 300 is shown, which can be implemented as follows: Figure 1 The controller 102 is configured to detect and respond to transformer saturation conditions.

[0070] The controller 300 includes a voltage-dependent current source 202, a switch (Q2) 204, and a capacitor (C). REF The controller 200 may include a first comparator 302, a second comparator 304, and an optional AND gate 306, which may (or may not) be arranged as shown. The controller 200 may include additional components not shown.

[0071] As previously discussed in the discussion of controller 200, voltage-dependent current source 202, switch (Q2) 204 and capacitor (C) REF )206 forms part of the saturation detection mechanism. These components work together to generate and measure the capacitance (C) across the capacitor. REF The voltage across 206 (V) CREF This voltage is proportional to the primary inductance of transformer 108. For the sake of brevity, the detailed operation of these components will not be repeated here, as their functions are consistent with the preceding explanation. Instead, this description will focus on the additional components in the overall saturation detection and protection scheme of controller 300 and their functions.

[0072] The controller 300 employs two comparators for its decision-making process. The first comparator 302 will cross the capacitor (C... REF The voltage across 206 (V) CREF ) and the predetermined saturation threshold voltage (V SAT The comparison results indicate whether the inductance of transformer 108 has decreased to the level indicating core saturation.

[0073] In the context of transformer saturation, an equivalent inductance (L) is introduced. SAT The concept of equivalent inductance (L) is useful. SAT An inductor can be defined as a constant-value inductor that stores the same amount of energy in each switching cycle as an inductor operating under saturation conditions. In a saturated conductor, the actual inductance value varies with the current flowing through it. The equivalent inductance (L...) SAT It provides a simplified model that maintains energy equivalence using a fixed inductance value.

[0074] In the embodiment, the saturation current (I) SAT This provides a safety margin regarding the converter's current limiting threshold. For example, the saturation current (Is) SAT The maximum allowable drain current (I) of the power switch (Q1) 104 can be set. DLIMThe percentage of ). Intentional settings ensure that the saturation detection mechanism can be triggered before the converter reaches its absolute current limit.

[0075] By defining the equivalent inductance (L) SAT ) and saturation current (I SAT The control system can effectively monitor saturation conditions while maintaining a buffer before reaching critical current levels. This method allows for more refined and proactive protection strategies. It enables the converter to respond to potential saturation events before they lead to complete loss of regulation or trigger hard current limit protection.

[0076] It is important to note that the capacitor (C) REF The voltage across 206 (V) CREF ) and primary inductance (L M The associated equations assume the primary inductance (L) M The primary inductance (L) remains constant. However, during saturation events, the primary inductance (L) increases. M The value of the primary inductance (L) is not constant, but varies as a function of the current passing through it. In other words, the primary inductance (L) M ) becomes a variable primary inductor (L M (i)), where i It represents electric current.

[0077] To simplify calculations in the context of a flyback converter that transfers energy in each switching cycle, an equivalent inductance (L) is introduced. SAT The concept of equivalent inductance (L) is convenient. As mentioned earlier, the equivalent inductance (L) SAT This is not an actual inductance, but a mathematical construct. It represents a constant-value inductor, which stores the actual variable primary inductance (L) under saturation conditions in each switching cycle. M (i)) The same energy.

[0078] Equivalent inductance (L) SAT The use of ) allows for more direct energy calculations and behavioral modeling of the transformer 108 under saturation conditions. Using this equivalent constant inductance maintains energy equivalence while simplifying the equations used in subsequent calculations. When the peak current reaches the saturation current (I SAT This method can be particularly useful when analyzing the operation of the converter at specific points.

[0079] For the case of variable inductors: .

[0080] For the case of equivalent constant inductance: .

[0081] By equivalence of these two energy storage expressions, the equivalent inductance (L) SAT The formula for ) can be derived: .

[0082] This equation allows for the application of variable primary inductance (L) M (i) Calculate the equivalent inductance (L) based on its behavior near saturation. SAT Equivalent inductance (L) SAT It can accurately represent the behavior of a transformer under saturation conditions, enabling more effective detection and response to potential core saturation or tampering attempts.

[0083] The second comparator 304 will pass through the sensing resistor (R) S The sensed voltage (V) across 122 SENSE The primary current (I) P ) and overcurrent protection threshold voltage (V OCP This is compared to ensure that the primary current remains within safe limits. In an embodiment, the overcurrent protection threshold voltage (V) is used. OCP The value is set to be less than or equal to the sensing resistor (R). S )122 resistor (R SENSE The maximum allowable drain current (I) of the power switch (Q1) 104. DLIM The product of (i.e., ).

[0084] After each on-time period of the power switch (Q1) 104, the controller 300 evaluates the outputs of the first comparator 302 and the second comparator 304 to determine if a potential saturation condition exists. Specifically, the controller 300 checks the cross capacitor (C... REF The voltage across 206 (V) CREF Has it dropped to the predetermined saturation threshold voltage (V)? SAT Below, and check across the sensing resistor (R) S The sensed voltage (V) across 122 SENSE Has the voltage risen to meet or exceed the overcurrent protection threshold voltage (V)? OCP When both conditions are met simultaneously, a response from controller 300 is triggered.

[0085] These conditions (i.e., and The simultaneous occurrence of ) causes the controller 300 to assume the current primary inductance (L) M The value has been reduced to below the defined equivalent saturation inductance (L). SAT ).

[0086] Therefore, in this embodiment, the protection circuit employs two comparators that work together to ensure optimal and safe transformer operation. The first comparator 302 detects core saturation by identifying when the inductance drops below a predetermined, selectable threshold. This detection prevents excessive current flow and potential damage to the transformer. Simultaneously, the second comparator 304 monitors whether the inductance value (even during saturation conditions) remains sufficient to support the current output load requirements. The synergy between the two comparators allows the circuit's protection mechanism to trigger protective measures in response to two conditions: the inductance has dropped to a level indicating core saturation (as detected by the first comparator 302), and the reduced inductance is insufficient to maintain appropriate output voltage regulation for a given load (as determined by the second comparator 304). This dual-check system ensures that protection is precisely activated when needed, striking a balance between preventing core damage and maintaining consistent power output.

[0087] In one embodiment, the controller 300 activates protective measures (i.e., counter-action) or issues an alarm upon detecting this condition. One such counter-action could include increasing the switching frequency of the converter. The increased switching frequency can help mitigate the effects of reduced inductance by allowing less time for current accumulation in each cycle, potentially preventing further saturation and maintaining better control over power delivery.

[0088] It is important to note that increasing the switching frequency is only one possible response. Depending on the specific design and requirements of the power system, the controller 300 may employ other strategies or combinations of methods, such as increasing the drain current (I) of the power switch (Q1) 104. DLIM Alternatively, increase the switching frequency and increase the drain current (I) of the power switch (Q1) 104. DLIM The combination of these countermeasures is designed to maintain the safe operation of the converter and protect it from potential damage or malfunction due to core saturation or tampering attempts.

[0089] In this embodiment, the controller 300 allows the transconductance (g) of the voltage-dependent current source 202 to pass through. m The protection threshold can be flexibly adjusted. This flexibility allows the controller 300 to maintain a consistent protection level under various operating conditions. The transconductance (g) of the voltage-dependent current source 202 m The relationship between the saturation parameter and the saturation parameter can be derived from this equation. According to this equation, the transconductance (g) of the voltage-dependent current source 202 is... m ) can be represented as: ,in It is defined as The time constant.

[0090] In the embodiment, the time constant ( This includes known system parameters determined during the design phase. It can be combined with capacitors (C). REF ), current sensing resistor ( R SENSE ) and saturation voltage threshold ( V SAT ) and overcurrent protection threshold voltage ( V OCP The ratio of ).

[0091] The importance of this formula lies in its independence from variable operating conditions (such as input voltage (V)). IN ) and switching frequency (F SW Once the transconductance (g) of the voltage-dependent current source 202 is set based on these prior known system parameters... m This method ensures that the intervention point of the protection mechanism is ideally independent of fluctuating operating factors. It guarantees that saturation detection and protection function consistently over a wide range of input voltage and load conditions, providing robust and reliable operation in various applications.

[0092] In an embodiment, the result of each of the first comparator 302 and the second comparator 304 is fed into an AND gate 306. When the first comparator 302 and the second comparator 304 indicate the capacitor (C... REF The voltage across 206 (V) CREF The voltage has dropped to the predetermined saturation threshold voltage (V). SAT ) below and if across the sensing resistor (R S The sensed voltage (V) across 122 SENSE The voltage has risen to or exceeded the overcurrent protection threshold voltage (V). OCP When ), AND gate 306 provides a trigger signal (V). TRIGGER Trigger signal (V) TRIGGER It can activate various protection mechanisms implemented by the drive signal provided by the controller 300 to the power switch (Q1) 104, such as frequency multiplication, duty cycle reduction, or controlled shutdown.

[0093] In the embodiments, although AND gate 306 is described as being used to combine the outputs of the first comparator 302 and the second comparator 304, it should be understood that other logic circuitry or combinations thereof may be used to process these outputs.

[0094] For example, when the first comparator 302 detects an inductance below a threshold, when the second comparator 304 detects a current exceeding the overcurrent protection threshold, and when both conditions occur simultaneously, the system can implement separate logic paths to send signals individually. This can be achieved using combinations of logic gates (e.g., OR gates, NAND gates, or more complex programmable logic devices).

[0095] This implementation allows the system to distinguish between different events (e.g., low inductance only, overcurrent only, or both) and potentially trigger different responses based on specific detected conditions. The flexibility in this logical implementation enables finer-grained detection and response strategies, potentially improving the system's ability to differentiate genuine overload conditions from magnetic tampering attempts.

[0096] In this embodiment, when the converter approaches its maximum output power capability, it enters a state known as Output Power Limit (OLP). Regardless of the underlying reason, this state is typically triggered in conventional systems when the primary current reaches a predetermined threshold. However, the controller 300 can go beyond simple current-based detection by incorporating inductance estimation into the decision-making process.

[0097] In this embodiment, the controller 300 includes a mechanism to distinguish between genuine overload conditions and potential tampering attempts, particularly when the flyback converter enters output power limiting (OLP protection) mode. This distinction allows for the maintenance of power supply integrity and reliability, especially in applications such as energy metering, where tampering is a critical concern.

[0098] Under true overload conditions, the primary current increases, but the inductance of transformer 108 remains relatively stable. Conversely, during tampering attempts involving magnetic interference, the primary current increases, and the effective inductance of transformer 108 decreases due to core saturation.

[0099] For example, if the comparison result at the output of the second comparator 304 indicates that the current at the primary winding of the transformer 108 has reached its limit, but the comparison result at the output of the first comparator 302 indicates that the estimated inductance is within the normal range, the controller 200 provides a trigger signal (V) indicating the actual overload condition. TRIGGER ).

[0100] On the other hand, if the comparison result at the output of the second comparator 304 indicates that the current at the primary winding of the transformer 108 has reached its limit, and at the same time the comparison result at the output of the first comparator 302 indicates that the estimated inductance has significantly decreased, the controller 300 provides a trigger signal (V) indicating a potential tampering attempt. TRIGGER This situation suggests that core saturation may be caused by external magnetic interference (a common method used in energy theft attempts).

[0101] By continuously monitoring the primary current and estimating the inductance, the controller 300 can distinguish between normal high-load conditions and core saturation events that may be caused by magnetic tampering. This allows for more targeted and effective protection strategies, enhancing power supply reliability in critical applications such as energy metering.

[0102] Furthermore, continuous monitoring and analysis of parameters over time enhances the ability to differentiate between these conditions. A sudden change in inductance occurring concurrently with an output power limiting event is more likely to indicate tampering, while a gradual change leading to an output power limit may suggest a legitimate load increase or other non-malicious factors affecting converter operation.

[0103] By employing a two-parameter approach that monitors both current and inductance, the controller 300 achieves greater accuracy in identifying the true nature of output power limiting events. This advanced discrimination capability allows for more appropriate and targeted responses to different situations, enhancing the safety and reliability of the power supply system.

[0104] The primary inductance can be estimated for saturation detection in both QR and DCM modes. The capacitance (C) across the capacitor can be measured at the end of each on-time of the power switch (Q1) 104. REF The voltage across 206 (V) CREF This is proportional to the primary inductance. This allows the saturation detection mechanism to function effectively, regardless of whether the converter is operating in QR or DCM mode.

[0105] In the embodiments, as long as the primary cycle-by-cycle current limit (I) is applied... P Maintain below the drain current limit threshold (I) DLIM This configuration allows the controller 300 to maintain output voltage regulation even when the transformer 108 begins to saturate. This behavior is consistent regardless of input voltage fluctuations or changes in operating mode between continuous conduction mode (CCM) and discontinuous conduction mode (DCM).

[0106] By continuously monitoring the primary current and estimating the inductance, the controller 300 can effectively distinguish between normal high-load conditions and potentially harmful saturation events, including those that may be caused by intentional external disturbances. This capability enables the controller to implement targeted protection strategies, enhancing the overall reliability and safety of the power system.

[0107] In this embodiment, the system incorporates a mechanism for adjusting the threshold at which saturation is detected, providing flexibility to adapt to different operating conditions and transformer characteristics. This adjustability can be achieved by modifying the transconductance (g) of the voltage-dependent current source 202. m )accomplish.

[0108] By changing the transconductance, the system can effectively change the measured transcapacitance (C). REF The relationship between the voltage across 206 and the estimated primary inductance. This adjustment allows for fine-tuning of the saturation detection sensitivity without modifying other hardware components.

[0109] Threshold adjustment can be based on a known set of system parameters, including the capacitor (C). REF 206. Sensing Resistor (R) S )122 and saturation threshold voltage (V SAT ) and overcurrent protection threshold voltage (V OCP The ratio of transconductance to saturation inductance threshold (L). These parameters can be combined to form a ratio of transconductance to saturation inductance threshold (L). SAT The associated time constant (T) SAT ).

[0110] By modifying the transconductance, system designers can set the desired saturation inductance threshold (L). SAT At this threshold, the protection mechanism will be triggered. Adjustability ensures that saturation detection remains effective under a wide range of input voltage and load conditions, maintaining a consistent protection level throughout the converter's operating range.

[0111] Furthermore, this adaptable threshold allows the system to be optimized for different transformer designs and application requirements. For example, in applications where higher tolerance for inductance variations is acceptable, the threshold can be set lower to reduce the likelihood of false triggering. Conversely, in applications requiring more stringent control over inductance variations, a higher threshold can be used for more sensitive detection.

[0112] Threshold adjustment capability enhances the versatility of the protection system, making it suitable for a wide range of switch-mode power supply designs and applications. It provides designers with powerful tools to balance robust protection and operational flexibility, customizing the system's response to the specific needs of each implementation.

[0113] In this embodiment, an optional delay mechanism can be implemented between detecting saturation conditions and triggering protective measures. This delay can enhance the system's robustness to transient conditions that may trigger unnecessary protective actions.

[0114] The delay mechanism operates by introducing a time interval between the moment when both comparators indicate a potential saturation condition and the actual activation of the protection scheme. During the delay period, the system can continue to monitor the outputs of both comparators. In an embodiment, if the condition persists throughout the entire delay period, the system only triggers protective measures (e.g., increasing the switching frequency or decreasing the maximum duty cycle).

[0115] In this embodiment, the duration of the delay can be adjusted based on the specific requirements of the application. A longer delay may be suitable for systems experiencing frequent, brief transients. A shorter delay may be suitable for applications where a rapid response to potential threats is critical.

[0116] It is important to note that while this delay mechanism adds an extra layer of protection against erroneous triggering, it is not mandatory. The system can still function effectively by triggering protection measures immediately upon detecting a saturation condition. The delay can be an optional feature that is implemented or omitted based on the specific needs of the application.

[0117] Optional delay mechanisms can further enhance the flexibility and adaptability of the protection system, allowing it to be fine-tuned for optimal performance across a wide range of operating conditions and application requirements.

[0118] Figure 4 A schematic diagram of a flyback converter 400 with saturation detection capability according to an embodiment of the present disclosure is shown. The flyback converter 400 includes a primary side and a secondary side, which are electrically isolated from each other by a transformer 402 having a primary winding (P), a secondary winding (S), and an auxiliary winding (A), which may (or may not) be arranged as shown.

[0119] The flyback converter 400 includes a controller 420, a power switch (Q1) 104, and an input capacitor (C). IN 106. Transformer 402. Output capacitor (C) OUT 110. Output diode (D) OUT 112. RCD clamping circuit; 114. Sensing resistor (R S 122. Resistor (R) SAT 410 and 412, which may (or may not) be arranged as shown. The RCD clamping circuit 114 includes a resistor (R) 116, a capacitor (C) 118, and a diode (D) 120. The flyback converter 400 may include additional components (e.g., load at the output) not shown.

[0120] In practical implementation, the voltage-dependent current source 202 can be implemented using the auxiliary winding of transformer 402. This method provides a simple and efficient way to generate a current proportional to the input voltage without requiring direct high-voltage sensing.

[0121] The auxiliary winding (which is commonly found in many flyback converter designs for control and synchronization purposes) provides a convenient means of sampling the input voltage. During the on-time of the main power switch, the voltage across the auxiliary winding is proportional to the input voltage, and this proportion is determined by the turns ratio between the auxiliary and primary windings.

[0122] The auxiliary winding of transformer 402 is coupled to resistor (R). SAT 404. This combination provides a voltage proportional to the input voltage during the on-time of the power switch (Q1) 104. (Trans resistor (R)) SAT The voltage across 404 is converted into current (I). FF ), and is mirrored and scaled by the current-dependent current generator 414.

[0123] The controller 420 can implement QR mode by using an auxiliary winding to detect the valley in the drain voltage of the power switch (Q1) 104. The voltage across the auxiliary winding is proportional to the voltage across the power switch (Q1) 104, allowing the controller 420 to accurately time the turn-on event of the power switch (Q1) 104.

[0124] In one embodiment, for the input voltage (V) IN The dependence of ) can be monitored by monitoring the auxiliary voltage (V) across the auxiliary winding. AUX This is achieved. During the on-time of power switch (Q1) 104, the auxiliary voltage (V) is... AUX ) and input voltage (V IN The ratio is proportional to the primary-secondary turns ratio, which is determined by the auxiliary-primary turns ratio. This relationship allows for the use of a resistor (R) SAT )410 Current-dependent current generator coupled to auxiliary winding 414 Replaces voltage-dependent current source 202.

[0125] Flow through resistor (R) SAT )410 current (I FF ) can be represented as ,in N AUX and N PRI These are the number of turns in the auxiliary winding and the primary winding, respectively. This relationship results in the number of turns in the trans-capacitor (C). REF The voltage across 206 (V) CREF Modification of the original equation: .

[0126] In addition, the voltage-dependent current source 202 (i.e., transconductance (g) m The equation was adjusted to The time constant is defined as .

[0127] Time constant ( It consists of known system parameters, including capacitance (C). REF ), saturation threshold voltage (V) SAT ), current sensing resistor (R)SENSE ), scaling factor (Ko) and overcurrent protection threshold voltage (V) OCP By utilizing these relationships, the flyback converter 400 can maintain its effectiveness over varying input voltages, while relying on parameters that are known a priori or can be precisely controlled in the design.

[0128] Flow through resistor (R) SAT )410 current (I FF The current can be mirrored and scaled by a current-dependent current generator 414. The scaled current is relative to the capacitor (C). REF )206 is charged, generating a voltage proportional to the primary inductance, as described in the original concept.

[0129] This implementation allows for modification of the resistor (R) SAT Instead of directly changing the transconductance of the voltage-dependent current source 202, the saturation detection threshold is adjusted.

[0130] This method offers several advantages. It eliminates the need for a high-voltage sensing circuit system, improving safety and reducing complexity. It also utilizes existing components in the flyback converter, minimizing additional costs. Furthermore, it maintains the system's independence from input voltage variations, ensuring consistent protection across the converter's operating range.

[0131] Figure 5 A flowchart of an embodiment method 500 for operating a converter to detect saturation conditions and implement protection mechanisms is shown. Note that all steps outlined in the flowchart of method 500 are not required and may be optional. Furthermore, similarly, changes to the arrangement of steps, the removal of one or more steps and path connections, and the addition of steps and path connections are contemplated.

[0132] In step 502, the system is initialized and necessary parameters are set, including inductance and current thresholds. Additionally, comparators, logic gates, and other circuit components can be initialized to their appropriate initial states, ready to begin monitoring and protection.

[0133] In this embodiment, the system sets a saturation inductance threshold (L). SAT ) and overcurrent protection threshold voltage (V OCP Saturation inductance threshold (L) SAT This value can be determined based on the known characteristics of the transformer and the desired sensitivity level for saturation detection. It represents the minimum acceptable inductance before the system considers the transformer to be nearing saturation.

[0134] Overcurrent protection threshold voltage (V) OCP ) is set such that the equivalent current threshold (I) OCPThe current is set below the maximum allowable drain current (I) of the power switch. DLIM The value of ) is usually the drain current (I DLIM This is a percentage of the total current. This provides a safety margin to allow the system to react before reaching critical current levels.

[0135] In the embodiment, the transconductance (g) of the current source m The capacitor is initialized to adjust the saturation detection sensitivity. In this embodiment, the capacitor is discharged to ensure it starts from a known state. The converter's switching frequency is set to its initial operating value, and any counters or timers used for optional delay features are reset.

[0136] If the system includes recording or alarm capabilities for potential magnetic attacks, these features can also be initialized in step 502. In embodiments, the controller may include internal registers or be coupled to external memory to facilitate the recording of alarms and events. The registers or memory may store information such as timestamps of detected saturation events, duration of protection mechanism activation, frequency of occurrence, and specific parameter values ​​at the time of detection (e.g., estimated inductance, primary current)). Recording capabilities allow the system to maintain a historical record of potential tampering attempts or anomalous operating conditions. The stored data is valuable for post-event analysis, helping system operators identify patterns of tampering attempts, assess the effectiveness of protection mechanisms, and potentially improve the overall security and reliability of the power system.

[0137] In some implementations, the controller may also include a communication interface that allows the recorded data to be transmitted to an external monitoring system for real-time or periodic analysis, further enhancing the system’s ability to detect and respond to short-term threats and long-term trends in power operation as well as potential tampering attempts.

[0138] In step 504, the system monitors the primary current of the transformer and estimates the primary inductance. This estimation can be performed using the voltage across the capacitor.

[0139] In step 506, the estimated inductance is compared with a predetermined threshold. Simultaneously or independently of step 506, in step 508, the system compares the primary current with an overcurrent protection threshold.

[0140] At decision point 510, method 500 determines whether two conditions (i.e., whether the estimated inductance is below a threshold and whether the primary current exceeds the overcurrent protection threshold) are met. If neither condition is met, method 500 returns to step 504 to continue monitoring. If both conditions are met, method 500 proceeds to step 512.

[0141] In step 512, the system triggers a protection mechanism. This may involve increasing the switching frequency of the converter. A brief delay may be implemented before the protection mechanism is triggered to avoid responding to transient conditions. While the protection mechanism is active, the system can continue to monitor the conditions. Ongoing monitoring allows the system to determine when normal operation can resume.

[0142] The system can check whether the saturation condition has been resolved. This may involve reassessing the inductance and current levels relative to their respective thresholds. If the saturation condition persists, the system can maintain and monitor the protection mechanisms. If the condition has been resolved, the system can disable the protection mechanisms and restore normal operation of the converter.

[0143] After completing step 512, regardless of whether the protection mechanism is disabled or still active, method 500 returns to step 504 to continue the regular monitoring cycle.

[0144] This disclosure offers several advantages over conventional technologies in terms of power supply protection and tamper protection. One advantage is the precise activation of tamper protection. The controller can trigger protection only when true saturation occurs and the inductance drops below a user-adjustable threshold. This targeted approach ensures that protection is activated only under genuine threats, avoiding unnecessary intervention. Notably, even if some saturation occurs, as long as the remaining inductance (L...) remains below a certain threshold... M Exceeding the defined saturation threshold (L) SAT This means the protection will remain inactive. This feature allows the converter to maintain output regulation without premature protection activation.

[0145] Furthermore, embodiments of this disclosure can reduce the size and cost of magnetic components. By more accurately detecting true saturation events, the converter eliminates the need for excessively large transformers or excessive magnetic shielding often required in prior art solutions.

[0146] Furthermore, embodiments of this disclosure eliminate the need to increase the converter size to accommodate additional power capacity during true overload conditions. Advantageously, the optimization results in a more efficient and cost-effective design without compromising protection.

[0147] The distinguishing factor of the disclosed embodiments is the ability to differentiate between attempted magnetic attacks and actual overload conditions. Unlike prior art solutions that activate protection whenever the converter approaches an overload state, the two-parameter method considers both current level and inductance measurement, but not inductance value. This allows for a finer and more accurate response, enhancing security and operational efficiency against tampering under legitimate high-load conditions.

[0148] In this embodiment, a technique is provided for distinguishing between true overload conditions and magnetic attacks in switch-mode power supplies, particularly in flyback converters operating in quasi-resonant (QR) mode or discontinuous conduction mode (DCM). This distinction is advantageous, especially in applications such as energy metering, where magnetic tampering may be a significant concern.

[0149] In this embodiment, two comparators evaluate different aspects of the converter's operation. The first comparator monitors the estimated primary inductance of the transformer, while the second comparator monitors the primary current. By simultaneously analyzing the outputs of the two comparators, a true overload condition and a potential magnetic tampering attempt can be distinguished.

[0150] The true overload condition is determined when the output of the first comparator is low (indicating normal inductance) and the output of the second comparator is high (indicating high current). In this case, the converter can respond using standard overload protection measures.

[0151] Conversely, when the output of the first comparator is high (indicating reduced inductance) and the output of the second comparator is low, a potential magnetic attack is identified. This situation indicates that the transformer's inductance has been damaged, possibly due to external magnetic interference, but the current has not yet reached an overload level.

[0152] The ability to differentiate between these conditions allows for more targeted and effective protection strategies. In the event of a true overload, standard protection measures can be implemented. However, in the event of a detected magnetic attack, specific anti-tampering measures can be activated, such as increasing the switching frequency, to maintain proper operation despite inductor damage.

[0153] Advantageously, in applications where magnetic tampering is dangerous (e.g., in energy metering systems), this distinguishing capability significantly enhances the reliability and security of the power supply. It allows the power supply to respond appropriately to threats, maintain optimal performance under normal conditions, while providing robust protection against intentional interference.

[0154] In addition to triggering protective measures, the system can also record or alarm when a potential magnetic attack is detected. This feature provides valuable information to system operators and enhances the overall safety of the power supply.

[0155] For example, the system can generate a log entry or trigger an alert when it detects a potential magnetic tampering attempt. Log entries can include relevant information such as the event's timestamp, key parameter values ​​at the time of detection, and the duration of the suspected attack. This logging capability allows for post-event analysis and helps identify patterns of tampering attempts over time.

[0156] Alarm mechanisms can take various forms depending on specific application requirements. These may include sending signals to connected monitoring systems, activating visual or auditory alarms, or sending notifications to remote operators. Real-time alerting capabilities enable rapid investigation and response to potential security threats.

[0157] By combining logging and alarm signatures, the system resists immediate threats and provides valuable data for long-term security analysis and improvement. For energy providers, this information is advantageous in tracking and preventing energy theft attempts and in enhancing the overall resilience of their metering systems against magnetic tampering.

[0158] The first aspect relates to a flyback converter including a transformer having a primary winding and a secondary winding; a power switch coupled to the primary winding, wherein a primary current flows through the primary winding of the transformer; and a controller coupled to the power switch. The controller includes: a voltage-dependent current source; a reference capacitor coupled to the voltage-dependent current source; a first comparator configured to compare a voltage across the reference capacitor with a saturation threshold voltage; a second comparator configured to compare a sensed voltage representing the primary current with an overcurrent protection threshold voltage; and a logic circuit system configured to generate trigger signals based on the outputs of the first and second comparators. The controller is configured to estimate the primary inductance of the transformer based on the voltage across the reference capacitor, detect a saturation condition based on the estimated primary inductance and primary current, and implement a protection mechanism in response to the detected saturation condition.

[0159] In a first embodiment of the flyback converter, according to the first aspect, the transformer further includes an auxiliary winding coupled to a voltage-dependent current source.

[0160] In a second embodiment of the flyback converter, according to the first aspect itself or any of the foregoing embodiments of the first aspect, the flyback converter further includes a resistor coupled between the auxiliary winding and the voltage-dependent current source.

[0161] In a third embodiment of the flyback converter, the protection mechanism includes increasing the switching frequency of the power switch, according to the first aspect itself or any of the foregoing embodiments of the first aspect.

[0162] In a fourth implementation of the flyback converter, depending on the first aspect itself or any of the aforementioned implementations of the first aspect, the controller is further configured to distinguish between a genuine overload condition and a magnetic tampering attempt based on the outputs of the first and second comparators.

[0163] In a fifth embodiment of the flyback converter, the controller is further configured to implement a delay between detecting saturation conditions and implementing a protection mechanism, depending on the first aspect itself or any of the aforementioned implementations of the first aspect.

[0164] In a sixth embodiment of the flyback converter, the controller is further configured to generate a log entry or alarm when a potential magnetic tampering attempt is detected, depending on the first aspect itself or any of the foregoing implementations of the first aspect.

[0165] The second aspect relates to a controller for a flyback converter. The controller includes a voltage-dependent current source; a reference capacitor coupled to the voltage-dependent current source; a first comparator configured to compare a voltage across the reference capacitor with a saturation threshold voltage; a second comparator configured to compare a primary current representing a primary current with an overcurrent protection threshold, wherein the primary current flows through the primary winding of a transformer of the flyback converter; a logic circuit system configured to generate trigger signals based on the outputs of the first and second comparators; and a control circuit system configured to: estimate the primary inductance of the transformer based on the voltage across the reference capacitor, detect a saturation condition based on the estimated primary inductance and primary current, and implement a protection mechanism in response to the detected saturation condition.

[0166] In a first embodiment of the controller, according to the second aspect, the voltage-dependent current source includes an adjustable transconductance for setting a saturation detection threshold.

[0167] In a second embodiment of the controller, the control circuit system is further configured to distinguish between a genuine overload condition and a magnetic tampering attempt based on the outputs of the first and second comparators, depending on the second aspect itself or any of the foregoing embodiments of the second aspect.

[0168] In a third implementation of the controller, the control circuitry is further configured to implement a delay between detecting saturation conditions and implementing a protection mechanism, depending on the second aspect itself or any of the aforementioned implementations of the second aspect.

[0169] In a fourth implementation of the controller, the protection mechanism, based on the second aspect itself or any of the aforementioned implementations of the second aspect, includes increasing the switching frequency of the power switch coupled to the transformer, increasing the drain current of the power switch, or a combination thereof.

[0170] In a fifth embodiment of the controller, according to the second aspect itself or any of the foregoing embodiments of the second aspect, the control circuitry is further configured to generate a log entry or alarm when a potential magnetic tampering attempt is detected.

[0171] In a sixth implementation of the controller, a voltage-dependent current source is configured to be coupled to an auxiliary winding of the transformer, depending on the second aspect itself or any of the aforementioned implementations of the second aspect.

[0172] The third aspect relates to a method for operating a flyback converter. The method includes monitoring the primary current of a transformer; estimating the primary inductance of the transformer based on the voltage across a reference capacitor; comparing the estimated primary inductance with a saturation threshold; comparing the primary current with an overcurrent protection threshold; detecting a saturation condition based on the comparison of the estimated primary inductance with the primary current; and implementing a protection mechanism in response to the detected saturation condition.

[0173] In a first implementation of the method, according to the third aspect, the method further includes distinguishing between genuine overload conditions and magnetic tampering attempts based on a comparison of estimated primary inductance and primary current.

[0174] In a second implementation of the method, the protection mechanism, based on the third aspect itself or any of the aforementioned implementations of the third aspect, includes increasing the switching frequency of the power switch coupled to the transformer, increasing the drain current of the power switch, or a combination thereof.

[0175] In a third implementation of the method, depending on the third aspect or any prior implementation of the third aspect, the method further includes implementing a delay between detecting the saturation condition and implementing the protection mechanism.

[0176] In a fourth implementation of the method, depending on the third aspect itself or any of the foregoing implementations of the third aspect, the method further includes generating a log entry or alarm when a potential magnetic tampering attempt is detected.

[0177] In a fifth embodiment of the method, according to the third aspect itself or any of the foregoing embodiments of the third aspect, the method further includes adjusting the transconductance of a voltage-dependent current source coupled to a reference capacitor to set a saturation detection threshold.

[0178] Although this specification has been described in detail, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure as defined by the appended claims. In the various drawings, the same elements are indicated by the same reference numerals. Furthermore, the scope of this disclosure is not intended to be limited to the specific embodiments described herein, as it will be readily understood from this disclosure by those skilled in the art that existing or future processes, machines, manufactures, compositions of matter, means, methods, or steps can perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein. Therefore, the appended claims are intended to include such processes, machines, manufactures, compositions of matter, means, methods, or steps within their scope.

[0179] Therefore, the specification and drawings are to be regarded only as a description of the present disclosure as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations or equivalents falling within the scope of the present disclosure.

Claims

1. A flyback converter, comprising: A transformer has a primary winding and a secondary winding; A power switch is coupled to the primary winding, wherein primary current flows through the primary winding of the transformer; as well as A controller, coupled to the power switch, the controller comprising: Voltage-dependent current source A reference capacitor is coupled to the voltage-dependent current source. A first comparator is configured to compare the voltage across the reference capacitor with a saturation threshold voltage. A second comparator is configured to compare a sensed voltage representing the primary current with an overcurrent protection threshold voltage, and A logic circuit system is configured to generate a trigger signal based on the outputs of the first comparator and the second comparator. The controller is configured as follows: The primary inductance of the transformer is estimated based on the voltage across the reference capacitor. Based on the estimated primary inductance and the primary current, the saturation condition is detected, and A protection mechanism is implemented in response to the detected saturation condition.

2. The flyback converter of claim 1, wherein the transformer further comprises an auxiliary winding, and wherein the voltage-dependent current source is coupled to the auxiliary winding.

3. The flyback converter according to claim 2 further includes a resistor coupled between the auxiliary winding and the voltage-dependent current source.

4. The flyback converter according to claim 1, wherein the protection mechanism includes increasing the switching frequency of the power switch.

5. The flyback converter of claim 1, wherein the controller is further configured to: distinguish between a genuine overload condition and a magnetic tampering attempt based on the outputs of the first comparator and the second comparator.

6. The flyback converter of claim 1, wherein the controller is further configured to implement a delay between detecting the saturation condition and implementing the protection mechanism.

7. The flyback converter of claim 1, wherein the controller is further configured to generate a log entry or alarm upon detecting a potential magnetic tampering attempt.

8. A controller for a flyback converter, the controller comprising: Voltage-dependent current source; A reference capacitor is coupled to the voltage-dependent current source; A first comparator is configured to compare the voltage across the reference capacitor with a saturation threshold voltage. A second comparator is configured to compare a primary current with an overcurrent protection threshold, wherein the primary current flows through the primary winding of the transformer of the flyback converter. as well as A logic circuit system is configured to generate a trigger signal based on the outputs of the first comparator and the second comparator; and The controller is configured as follows: The primary inductance of the transformer is estimated based on the voltage across the reference capacitor. Based on the estimated primary inductance and the primary current, the saturation condition is detected, and A protection mechanism is implemented in response to the detected saturation condition.

9. The controller of claim 8, wherein the voltage-dependent current source includes an adjustable transconductance for setting a saturation detection threshold.

10. The controller of claim 8, wherein the controller is further configured to: distinguish between a genuine overload condition and a magnetic tampering attempt based on the outputs of the first comparator and the second comparator.

11. The controller of claim 8, wherein the controller is further configured to implement a delay between detecting the saturation condition and implementing the protection mechanism.

12. The controller of claim 8, wherein the protection mechanism comprises: Increase the switching frequency of the power switch coupled to the transformer, increase the drain current of the power switch, or a combination thereof.

13. The controller of claim 8, wherein the controller is further configured to generate a log entry or alarm upon detecting a potential magnetic tampering attempt.

14. The controller of claim 8, wherein the voltage-dependent current source is configured to be coupled to an auxiliary winding of the transformer.

15. A method for operating a flyback converter, the method comprising: Monitor the primary current of the transformer; The primary inductance of the transformer is estimated based on the voltage across the reference capacitor. The estimated primary inductance is compared with the saturation threshold; The primary current is compared with the overcurrent protection threshold; The saturation condition is detected by comparing the estimated primary inductance with the primary current. as well as A protection mechanism is implemented in response to the detected saturation condition.

16. The method of claim 15, further comprising: Based on the comparison between the estimated primary inductance and the primary current, a true overload condition is distinguished from an attempt to tamper with the magnetic inductance.

17. The method of claim 15, wherein implementing the protection mechanism comprises: Increase the switching frequency of the power switch coupled to the transformer, increase the drain current of the power switch, or a combination thereof.

18. The method of claim 15, further comprising: A delay is implemented between detecting the saturation condition and implementing the protection mechanism.

19. The method of claim 15, further comprising: When a potential magnetic tampering attempt is detected, a log entry or alert is generated.

20. The method of claim 15, further comprising: Adjust the transconductance of the voltage-dependent current source coupled to the reference capacitor to set the saturation detection threshold.

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