Flux detection circuit for sensing magnetic flux via magnetic flux probe and method thereof

Abstract

A flux detection circuit for sensing magnetic flux via a magnetic flux probe and a method thereof are presented herein. A magnetic flux probe includes circuit elements and forms a loop around a magnetic core, the magnetic flux probe enabling interconnection of flux sensitive traces over a winding window. The flux detection circuit is configured to measure an electromotive force (emf) of one or more elements of the loop; and at least one of the circuit elements may be adjustable (e.g., may include a variable resistance). In this manner, the flux probe and flux detection circuit may be calibrated to accurately detect a signal proportional to the time-varying flux and provide a signal over the winding window.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 610,775, filed on December 15, 2023, which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present invention relates to a circuit method for sensing a time-varying magnetic field by utilizing Faraday's law. Background Art

[0004] Many electronic devices, such as mobile phones, laptop computers, etc., are powered by direct current (dc) power sourced from a power supply. Conventional wall outlets typically deliver high voltage alternating current (ac) power that needs to be converted to regulated dc power to be used as a power source for consumer electronic devices. Switch-mode converters (also known as switching power supplies) are widely used because of their high efficiency, small size, and low weight to convert high voltage ac power to regulated dc power.

[0005] A switching power supply may also include a magnetic circuit for transferring energy. A magnetic circuit is analogous to an electric circuit. For example, a magnetic circuit provides a path for magnetic flux; and an applied magnetomotive force (analogous to electromotive force) forces the magnetic flux along the magnetic circuit path. Brief Description of the Drawings

[0006] Non-limiting and non-exhaustive embodiments of a flux detection circuit for sensing magnetic flux are described with reference to the following drawings, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0007] Figure 1A Illustrated is a magnetic flux probe according to one embodiment.

[0008] Figure 1B Illustrated is a magnetic flux probe according to another embodiment.

[0009] Figure 2A Illustrated is a top perspective view of a magnetic core according to one embodiment and the interconnect routing for receiving probe signals.

[0010] Figure 2B Illustrated is a top perspective view of a magnetic core according to another embodiment and the interconnect routing for receiving probe signals.

[0011] Figure 2C Illustrated is a top perspective view of a magnetic core according to one embodiment and the interconnect routing for receiving one or more probe signals.

[0012] Figure 2D Illustrates a top perspective view of a magnetic core according to another embodiment and the interconnection wiring for receiving one or more probe signals.

[0013] Figure 3A Illustrates a schematic diagram including a magnetic flux probe according to one embodiment.

[0014] Figure 3B Illustrates a schematic diagram including a magnetic flux probe according to another embodiment.

[0015] Figure 4A Illustrates a schematic diagram of a flyback converter according to one embodiment.

[0016] Figure 4B Illustrates a schematic diagram of a flyback converter according to another embodiment.

[0017] Figure 4C Illustrates a schematic diagram of a flyback converter according to another embodiment.

[0018] Figure 4D Illustrates a schematic diagram of a flyback converter according to another embodiment.

[0019] Figure 5A Illustrates a three-dimensional (3D) top perspective view of a flyback converter according to one printed circuit board (PCB) embodiment.

[0020] Figure 5B Illustrates according to Figure 5A the embodiment of a three-dimensional (3D) top perspective view of a flyback converter.

[0021] Figure 5C Illustrates according to Figure 5A the embodiment of a three-dimensional (3D) top perspective view of a flyback converter.

[0022] Figure 6A Illustrates the interconnection wiring of the magnetic flux probe and according to Figure 5A the embodiment of the interconnection wiring.

[0023] Figure 6B Illustrates the interconnection wiring of the magnetic flux probe and the interconnection wiring according to another embodiment.

[0024] Figure 7A Illustrates according to Figure 6A the embodiment of a schematic diagram of a flyback converter.

[0025] Figure 7B Illustrates according to Figure 6A the embodiment of a schematic diagram of a flyback converter.

[0026] Figure 8A Illustrates a waveform in accordance with the teachings herein.

[0027] Figure 8B Illustrates a waveform in accordance with the teachings herein.

[0028] Figure 9 Illustrates a conceptual flowchart for controlling a synchronous rectifier during a switching cycle.

[0029] In all of the several views of the drawings, corresponding reference characters indicate corresponding parts. Those skilled in the art will understand that the elements in the drawings are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the drawings may be exaggerated relative to other elements to help improve understanding of the various embodiments of the teachings herein. In addition, common but well-understood elements that are useful or necessary in a commercially viable embodiment are typically not depicted so as to facilitate a less obstructed view of these various embodiments of the flux detection circuit. Detailed Description

[0030] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the flux detection circuit. However, it will be apparent to one of ordinary skill in the art that practicing the teachings herein does not require the use of these specific details. In other instances, well-known materials or methods have not been described in detail to avoid obscuring the present disclosure.

[0031] In the context of the present disclosure, electrical power can be transferred from an input (e.g., primary) side to an output (e.g., secondary) side via an energy transfer element (e.g., a transformer) according to a switching cycle. For example, a primary switch can be switched according to the switching cycle, whereby a winding (i.e., a primary winding) receives input power within a portion of the switching cycle and one or more secondary windings provide power within another portion of the switching cycle. The energy transfer element can also be an energy storage element, since energy from an input source can be stored in the element during one portion of the switching cycle and the stored energy can be transferred to the output during another portion of the switching cycle. A magnetic energy storage element can have only a single winding, since energy from the circuit can be stored in the element during one portion of the switching cycle and the stored energy can be removed from the element during another portion of the switching cycle, not necessarily being transferred to the output.

[0032] In accordance with the teachings herein, when a transistor is in an "off state" or "off", the transistor blocks current and / or substantially does not conduct current. Conversely, when the transistor is in an "on state" or "on", the transistor is capable of substantially conducting current. By way of example, in one embodiment, a high voltage transistor includes an N-channel metal oxide semiconductor (NMOS) field effect transistor (FET), where a high voltage is supported between a first terminal (drain) and a second terminal (source). In some embodiments, an integrated controller circuit can be used to drive a power switch when adjusting the energy provided to a load. Further, for the present disclosure, "ground" or "ground potential" refers to a reference voltage or potential with respect to which all other voltages or potentials of an electronic circuit or integrated circuit (IC) are defined or measured.

[0033] A switched-mode power supply can include magnetic components. In the context of the present disclosure, magnetic components can be energy transfer elements and / or magnetic energy storage elements.

[0034] The switched-mode power supply can further include a magnetic circuit to transfer energy. Further, the magnetic circuit can channel a magnetic field and / or magnetic flux in a magnetic core (e.g., a transformer or inductor core).

[0035] Traditionally, magnetic components (e.g., energy transfer elements, embedded transformers, coupled inductors, etc.) can be placed separately from circuit components (e.g., power transistors, controllers, analog circuit systems, digital circuit systems, etc.) to isolate sensitive signals (e.g., relatively small voltage signals) from magnetic interference. However, with the trend of miniaturizing switched-mode power supplies, there is a need to remove this constraint by integrating magnetic components (energy transfer elements) with circuit components.

[0036] For example, a magnetic core can be embedded in a multilayer printed circuit board (PCB), whereby windings are formed by traces surrounding the core. Additionally, there can be a window (e.g., a space) within the core called a winding window.

[0037] Traditionally, as a best practice, sensitive traces (e.g., circuit traces carrying sensitive signals) can be routed around or away from the winding window to avoid magnetic interference and / or half-winding effects. Unfortunately, this constraint conflicts with the need to integrate and miniaturize switched-mode power supplies. Therefore, there is a need to develop methods for transmitting sensitive signals through the winding window without degrading circuit performance.

[0038] This document presents a flux detection circuit and method for sensing magnetic flux via a magnetic flux probe. A magnetic flux probe includes circuit elements and forms a loop around a magnetic core, and the magnetic flux probe implements the interconnection of flux-sensitive traces on a winding window. The flux detection circuit is configured to measure the electromotive force (emf) of one or more elements of the loop; and at least one of the circuit elements can be adjustable (e.g., can include a variable resistor). In this way, the magnetic flux probe and the flux detection circuit can be calibrated to accurately detect a signal proportional to the time-varying magnetic flux and provide the signal on the winding window. As disclosed herein, an example use of such a signal is to provide an alternative method for detecting a time-varying current in a magnetic transfer element and using this information to control the operation of circuit elements within a power converter in a manner less susceptible to interference than more traditional control methods. As disclosed herein, a specific example application of the magnetic flux probe is to control the switching of a synchronous rectifier switch on the secondary side of a switched-mode power converter.

[0039] Figure 1A Illustrated is a magnetic flux probe 50 according to one embodiment. The magnetic flux probe 50 includes resistor R1, resistor R2, interconnect 61a, and interconnect 61b. Resistors R1 - R2 are electrically coupled to interconnects 61a - 61b to form a loop (i.e., a "loop" according to circuit and network theory).

[0040] Also illustrated is a magnetic core 102 (e.g., a ferrite core) and a winding 60 (e.g., a primary winding). The magnetic core 102 can be a part of the "E" section (e.g., an E-core) of an embedded transformer, and the winding 60 can be formed using printed circuit board (PCB) traces (e.g., copper PCB traces). The magnetic core 102 includes outer legs 49a, outer leg 49b, and a center leg 49c.

[0041] Due to the current within the winding 60, a magnetic flux density B can be generated within the magnetic core 102. The magnetic flux probe 50 forms a loop that encircles the magnetic core 102; and an electromotive force (emf) and a current ILOOP can be induced in response to the time-varying magnetic flux density B.

[0042] Although the magnetic flux probe 50 is illustrated as surrounding the center leg 49c of the magnetic core 102, other configurations are possible. For example, the magnetic flux probe 50 can surround (i.e., encircle) any part of the magnetic core 102 that guides the magnetic flux density B (e.g., outer leg 49a, outer leg 49b). Additionally, other magnetic core types are possible.

[0043] For example, Figure 1B Illustrated is a magnetic flux probe 50 according to another embodiment. Figure 1BThe embodiments of Figure 1A may be similar to those of Figure 1A , except that it illustrates a single-phase core type configuration having a magnetic core 102, a winding 60 (e.g., a primary winding), and a winding 99 (e.g., a secondary winding). Additionally, similar to

[0044] Similar to Figure 1A , the core 102 may be a ferrite core configured to maintain (direct) the magnetic flux density B generated by the current ISW within the winding 60. Additionally, the core 102 may include a gap having a dimension LG to improve core saturation characteristics; and the windings 60, 99, and interconnects 61a - 61b may be implemented using a wire (e.g., a copper wire).

[0045] Additionally, similar to Figure 1A , the magnetic flux probe 50 forms a loop around the magnetic core 102; and a current ILOOP may be induced in response to the time - varying magnetic flux density B. Thus, the magnetic flux probe 50 may provide a probe signal in response to the time - varying magnetic flux density B.

[0046] Figure 2A And Figure 2B illustrates a top - down perspective view of the magnetic core 102 according to multiple embodiments and the interconnect wiring for receiving the probe signal VR1. The top - down perspective view shows the magnetic core 102 as an E - shaped core having outer legs 49a, outer legs 49b, and a center leg 49c. The magnetic flux density B is shown as entering the center leg 49c by an "X" vector symbol and as leaving the outer legs 48a - 48b by a "dot" vector symbol.

[0047] As described herein, the magnetic flux density B may be generated in accordance with a time - varying signal (e.g., current ISW) within a winding (e.g., winding 60).

[0048] The magnetic flux probe 50 surrounds the center leg 49c. According to the laws of electromagnetic induction (e.g., Faraday's law and Lenz's law), an electromotive force (emf) may be induced in the magnetic path probe 50 in response to the time - varying magnetic flux density B and alternatively in response to the time - varying magnetic flux Φ. The magnetic flux probe 50 encloses the magnetic flux Φ, which is a scalar determined by the vector surface integral (i.e., the dot - product surface integral) of the total magnetic flux density B over the enclosed surface area of the center leg 49c.

[0049] Also illustrated are interconnects 62a, interconnects 62b, and a comparator 120. The interconnect 62a is electrically coupled to the interconnect 61a at a node N1, and the interconnect 62b is electrically coupled to the interconnect 61b at a node N2.

[0050] Comparator 120 can monitor and / or measure a probe signal VR1 that is determined at least in part based on a time-varying magnetic flux Φ, a resistance RV1 of resistor R1, and a resistance RV2 of resistor R2. As illustrated, the probe signal VR1 can be an electromotive force (emf) induced across resistor R1 (i.e., the voltage of resistor R1).

[0051] Additionally, the measured value (i.e., the value of the probe signal VR1 as seen by comparator 120) may also depend on the placement of interconnects 62a - 62b. As illustrated, interconnects 62a - 62b are arranged such that the probe information VR1 (as seen by comparator 120) can be given by Equation EQ.1 in terms of the resistance RV1, the total loop resistance RTOT, and the time rate of change of the flux Φ enclosed by the magnetic flux probe 50.

[0052]

[0053] The sign (positive or negative) of the probe signal VR1 can depend in part on the time rate of change (i.e., the derivative) of the flux Φ and the corresponding direction of the induced current ILOOP.

[0054] When the interconnect resistance of interconnects 61a - 61b is negligible compared to the resistances RV1 and RV2, then the total resistance RTOT can be given by the sum of the resistances RV1 and RV2; and Equation EQ.1 can be rewritten as Equation EQ.2 below.

[0055]

[0056] Accordingly, by adjusting one or both of the resistances RV1 and RV2, the voltage magnitude of the probe signal VR1 can be fine-tuned to a selected value. For example, resistor R2 can be a variable or adjustable resistor. This can advantageously allow for fine-tuning the voltage magnitude of the probe signal VR1 such that the comparator output changes state (i.e., changes the detection signal VO) in accordance with the fine-tuned target value.

[0057] Figure 2B The embodiment of Figure 2A is similar to the embodiment of Figure 2A and Figure 2B except that node N1 can be connected to ground GND such that the measured voltage of the probe signal VR1 is referenced to ground GND. Although

[0058] In addition, other configurations for measuring the probe signal VR1 and providing a detection signal VO may be possible. The other configurations may include one or more magnetic flux probes to provide the probe signal to a comparator and / or other circuitry (e.g., operational amplifier).

[0059] For example, Figure 2C illustrates a top perspective view of the magnetic core 102 according to one embodiment and the interconnect wiring for receiving one or more probe signals VR1, VR4. Different from the Figure 2A and Figure 2B embodiments, Figure 2C and Figure 2D the embodiments include additional magnetic flux probes 55, circuitry 220, and circuitry 221.

[0060] The magnetic flux probe 55 includes resistors R3, R4, interconnects 65a, and interconnects 65b. The resistors R3 - R4 are electrically coupled to the interconnects 65a - 65b to form a loop; and the discussion above regarding the operation of the magnetic flux probe 50 and resistors R1 - R2 is also applicable to the magnetic flux probe 55.

[0061] Different from the Figure 2A and Figure 2B embodiments, Figure 2C the embodiments include circuitry 220 instead of the comparator 120. Similar to the comparator 120, the circuitry 220 can receive the probe signal VR1. The circuitry 220 may include active and / or passive components that, in response to the probe signal VR1, allow the circuitry 220 to provide a detection signal VO1. For example, the circuitry 220 may include an operational amplifier and / or passive components that provide the detection signal VO1 as a continuous analog signal. Alternatively, the circuitry 220 may include digital components, including but not limited to an analog - to - digital converter, logic gates, a digital signal processor, etc.

[0062] Also illustrated are the interconnects 65a and 65b, which are coupled to nodes N4 and N3 respectively for providing the probe signal VR4 (e.g., the electromotive force induced on resistor R4) to the circuitry 221. The circuitry 221 may be similar to the circuitry 220 and provide a detection signal VO2 in response to the probe signal VR4.

[0063] Figure 2D Also illustrated is a top perspective view of the magnetic core 102 with one or more magnetic flux probes 50, 55 and the interconnect wiring according to another embodiment. Figure 2D The embodiments of Figure 2C are similar to the Figure 2DEmbodiments include comparator 120, and comparator 120 receives probe signal VSENSE via interconnects 62b and 65b. As illustrated, comparator 120 may provide detection signal VO in response to the potential between nodes N2 and N3.

[0064] Figure 3A and Figure 3B Illustrated are schematic diagrams 301a - 301b including magnetic flux probe 50. Schematic diagrams 301a - 301b include magnetic core 102, winding 60 (e.g., primary winding), and comparator 120. Winding 60 may receive time - varying current ISW provided from signal source 30. In turn, magnetic flux density B may be generated in magnetic core 102.

[0065] As depicted in schematic diagram 301a, magnetic flux probe 50 includes partial - turn winding fT1, partial - turn winding fT2, resistor R1, and resistor R2. Partial - turn winding fT1 and resistor R2 are electrically coupled between nodes N1 and N2; and partial - turn winding fT2 and resistor R1 are electrically coupled between nodes N1 and N2.

[0066] As illustrated, partial - turn windings fT1, fT2 and resistors R1, R2 may represent a loop surrounding magnetic core 102 including nodes N1, N2. For example, the circuit path from node N1 to node N2 including partial - turn winding fT2 and resistor R1 may depict interconnects 61a, interconnects 61b, and resistor R1 that are routed through the winding window between outer leg 49a and center leg 49c. Similarly, the circuit path including partial - turn winding fT1 and resistor R2 may depict interconnects 61a, interconnects 61b, and resistor R2 that are routed through the winding window between outer leg 49b and center leg 49c.

[0067] As illustrated by schematic diagram 301a, comparator 120 is configured to measure (i.e., receive) probe signal VR1 from magnetic flux probe 50. Additionally, probe signal VR1 may be the voltage across resistor R1. For example, as discussed above with respect to Figure 2A When interconnects 62a and 62b are routed such that they do not enclose time - varying magnetic flux density B, comparator 120 may receive probe signal VR1 (i.e., the voltage across resistor R1). In this way, the inverting input and non - inverting input of comparator 120 may be coupled (i.e., electrically coupled) to nodes N2 and N1, respectively, such that the comparator measures probe signal VR1 as the voltage across resistor R1.

[0068] As in Figure 3BAs illustrated by schematic diagram 301b, comparator 120 can be configured to measure (i.e., compare) probe signal VR1 and reference voltage Vref (e.g., zero point one (0.1) volts). Node N1 can be connected to ground GND; thus, the inverting input of comparator 120 can receive the probe signal VR1X relative to the node with respect to ground GND. Additionally, the non-inverting input of comparator 120 can receive the reference voltage Vrefx relative to the node with respect to ground GND.

[0069] In addition, different from schematic diagram 301a, resistor R2 of schematic diagram 301b can have variable resistance RV2. As discussed above with respect to Figure 2A and Figure 2B , resistor R2 can be tuned and / or adjusted to achieve a target value (i.e., the target voltage of probe signal VR1) for which comparator 120 will change state.

[0070] Figure 4A Illustrates a schematic diagram of an isolated flyback converter 400a according to one embodiment. Flyback converter 400a can receive input power including input voltage VIN and current ISW (e.g., switching current). During the switching cycle of primary switch 152, winding 60 (e.g., primary winding) receives current ISW, and in response, magnetic flux density B is generated within magnetic core 102. Due to magnetic flux density B, power is transferred in the form of output power including output voltage VO1 and load current IL1 to winding 99 (e.g., secondary winding) and load 142.

[0071] In addition, the input power signal (e.g., input voltage VIN) can be with respect to primary ground (e.g., ground GND), while the output power signal (e.g., output voltage VO1) can be with respect to secondary ground (e.g., secondary ground RTN). For example, as illustrated, primary controller 109 is referenced to ground GND, while secondary controller 108 and load 142 are referenced to current-isolated secondary ground RTN.

[0072] As illustrated, flyback converter 400a includes primary controller 109, primary switch 152, and winding 60 (e.g., primary winding). Primary controller 109 can drive primary switch 152 using gate signal VCS such that winding 60 receives current ISW according to the switching cycle. In response to current ISW in winding 60, magnetic flux density B can be generated within magnetic core 102.

[0073] The peak value of the current ISW can be determined in part based on the sense signal SENS. As illustrated, the sense signal SENS can be provided to the primary controller 109 via the sense element 454. When the current ISW reaches the target peak value, then the primary controller can turn off the primary switch 152 in response to the sense signal SENS.

[0074] Additionally, the flyback converter 400a can include a secondary controller 108, a synchronous rectifier 126, a feedback network 140, and a winding 99 (e.g., a secondary winding). The winding 99 can be electrically coupled to the synchronous rectifier 126 (e.g., an NFET having a gate, source, and drain) (at the drain) at the node NFW (e.g., the secondary winding node).

[0075] The secondary controller 108 can receive the feedback signal FB1 and, in response, transmit information to the primary controller 109 via the signal FL. For example, if the feedback signal FB1 indicates that the load requires more power (e.g., the output voltage VO1 is decreasing), then the secondary controller 108 can provide a pulse via the signal FL. In response, the primary controller 109 can provide the gate signal VCS such that the primary switch 152 turns on.

[0076] Thus, when the load current IL1 varies with the load demand, the power delivered to the load 142 can be regulated to a specific output voltage VO1. Additionally, the output capacitor C1 can be used to filter the output ripple.

[0077] As illustrated, the synchronous rectifier 126 can be implemented as an N-channel field-effect transistor (NFET). During each switching cycle of the primary switch 152, the synchronous rectifier 126 can receive the control signal Vcr from the secondary controller 108. As described herein, the control signal Vcr can be provided to the synchronous rectifier 126 based in part on the switching state of the primary switch 152.

[0078] For example, if the primary switch 152 transitions from on to off, then the secondary controller 108 can provide the control signal Vcr to turn on the synchronous rectifier 126 such that the winding 99 (e.g., the secondary winding) can maintain the secondary current IS. This can advantageously allow power to be efficiently transferred to the load 142 while there is a magnetic flux density B within the magnetic core 102.

[0079] Additionally, if the secondary current IS decreases during the switching cycle such that the flyback converter operates in discontinuous mode (DCM); then once the secondary current decreases to substantially zero, the secondary controller 108 can turn off the synchronous rectifier 126.

[0080] In addition, in accordance with the teachings herein, the flux probe 50 can advantageously provide a probe signal VR1 indicative of the switching state and operating mode (e.g., DCM) of the primary switch. For example, when the primary switch 152 is turned off, then the rate of change of the magnetic flux density B may suddenly change sign (e.g., from positive to negative). Accordingly, the probe signal VR1 may suddenly change sign, indicating the transition of the primary switch 152.

[0081] Additionally, the voltage magnitude of the probe signal VR1 can indicate when the magnetic flux density B has decreased below a target magnitude. Accordingly, the probe signal VR1 can also indicate the start of DCM and ringing.

[0082] As described herein, the secondary controller 108 can also provide a control signal Vcr to the synchronous rectifier 126 based at least in part on a detection signal VO from the flux detection circuit 153.

[0083] As illustrated, the flux detection circuit 153 can include a comparator 120 that, similar to Figure 3A the comparator, measures (i.e., compares) the probe signal VR1 as the differential voltage between the non-inverting input terminal and the inverting input terminal. Accordingly, the comparator 120 can provide the detection signal VO based on the value of the probe signal VR1. The secondary controller 108 can then provide the control signal Vcr based at least in part on the detection signal VO to turn on and / or turn off the synchronous rectifier.

[0084] Figure 4B A schematic diagram of a flyback converter 400b according to another embodiment is illustrated. The flyback converter 400b is similar to the flyback converter 400a, except that the node N1 can be electrically coupled to the secondary ground RTN such that the inverting input terminal of the comparator 120 can receive the probe signal VR1X that is relative to the node with respect to the secondary ground RTN. Additionally, the non-inverting input terminal of the comparator 120 can receive a reference voltage Vrefx that is relative to the node with respect to the secondary ground RTN such that the comparator 120 can compare the probe signal VR1 with the reference voltage Vref.

[0085] Figure 4C A schematic diagram of a flyback converter 400c according to another embodiment is illustrated. The flyback converter 400c is similar to the flyback converter 400b, except that the flyback converter 400c includes an additional partial turn winding fT3. As described herein, the partial turn winding fT3 can represent a partial turn that does not completely encircle the magnetic core. As illustrated, the partial turn winding fT3 can be coupled to the secondary ground RTN and the wired secondary ground RTNX.

[0086] In addition, as presented herein, the secondary ground RTNX of the wiring and the secondary ground RTN can be physically located on opposite sides of a winding window (e.g., a winding window defined by outer stanchion 49a and center stanchion 49c). As can be understood by those skilled in the art, a partial turn winding fT3 can cause a half-winding effect and / or result in an undesired change in the winding turn ratio between the primary turns TP and the secondary turns TS. For example, when the synchronous rectifier 126 is conducting, the partial turn winding fT3 can be effectively coupled to the winding 99 (e.g., the secondary winding), thereby introducing additional partial turns.

[0087] Under certain operating conditions and configurations, if the partial turn winding fT3 becomes part of a loop around the core 102, this can change the effective secondary turns TS. For example, if additional interconnects and / or external wires are connected to the secondary ground RTN and the secondary ground RTNX of the wiring, the loop can include the partial turn winding fT3. Ideally, the layout can follow best practices such that the partial turn winding fT3 is not part of the loop; in these best practice conditions, the secondary ground RTN and the secondary ground RTNX of the wiring can be substantially equal without magnetic interference.

[0088] Thus, when the partial turn winding fT3 is not part of a loop around the core (e.g., the center stanchion 49c), the node-relative reference voltage Vrefx and the node-relative probe signal VR1X of the flyback converter 400c can be equivalent to the node-relative reference voltage and the node-relative probe signal of the flyback converter 400b.

[0089] Figure 4D A schematic diagram of a flyback converter 400d according to another embodiment is illustrated. The flyback converter 400d is similar to the flyback converter 400b, except that the node N2 can be electrically coupled to the node NFW (e.g., the secondary winding node) such that the node-relative probe signal VR1X is referenced to the winding voltage VFW rather than the secondary ground RTN.

[0090] The winding voltage VFW can vary during a switching cycle and is a function of the switching state of the synchronous rectifier 126. When the synchronous rectifier 126 is conducting, then the winding voltage VFW can be substantially equal to or less than the value of the secondary ground RTN (e.g., zero volts). For example, due to the drain-to-source voltage of the synchronous rectifier 126, the winding voltage VFW can be less than the voltage of the secondary ground RTN. Thus, when the synchronous rectifier 126 is conducting, the node-relative probe signal VR1X can vary at least in part due to the drain-to-source voltage of the synchronous rectifier 126. Accordingly, in an embodiment of the flyback converter 400d, the comparator 120 can provide a detection signal VO based at least in part on the drain-to-source voltage of the synchronous rectifier 126 and the node-relative probe signal VR1X.

[0091] Figure 5A Illustrated is a three-dimensional (3D) top-down perspective view of a portion of a flyback converter 500 according to one printed circuit board (PCB) embodiment. The flyback converter 500 includes a magnetic core 102, a synchronous rectifier 126, a resistor R1, a resistor R2, and a secondary controller 108. The magnetic core 102 can be an EI core. According to the teachings herein, there can be a magnetic flux density B generated within the magnetic core 102; and there can be a need to turn on and off the synchronous rectifier 126 based at least in part on the switching state (e.g., the switching state of the primary switch) and / or based on the operating mode (e.g., DCM).

[0092] Figure 5B Illustrated is according to Figure 5A an embodiment of a three-dimensional (3D) top-down perspective view of a portion of the flyback converter 500. In Figure 5B this view, a portion of the magnetic core 102 (e.g., the I-shaped section) has been removed to show more of the underlying traces and interconnects. Figure 5B This view shows the interconnect 61a, the trace PT_Vcr, and the trace PT_RTN. The interconnect 61a is electrically coupled to the resistor R1 and the resistor R2. The synchronous rectifier 126 can be an NFET that includes a gate electrically coupled to the trace PT_Vcr, and the trace PT_RTN can be electrically coupled to the secondary ground RTN.

[0093] Figure 5C Illustrated is according to Figure 5A an embodiment of a three-dimensional (3D) top-down perspective view of a portion of the flyback converter 500. In Figure 5CIn the top view, material has been removed to show the flux probe 50 with respect to the magnetic core 102 and with respect to the winding 99 (e.g., secondary winding). The flux probe 50 includes interconnects 61a, interconnects 61b, resistor R1, and resistor R2. As illustrated, the flux probe 50 can form a loop around the central leg 49c of the magnetic core 102. Additionally, as described herein, the flux probe 50 can provide a probe signal VR1 in response to a time-varying magnetic flux density B.

[0094] In an example implementation, the interconnect 61a can include printed circuit board (PCB) vias to route the interconnect 61a on more than one layer of the PCB. Additional PCB vias can route the interconnect 61a at the node NFW and electrically couple the node NFW to the interconnect 61a.

[0095] Furthermore, the interconnect 61b can be electrically coupled to the resistor R2 and the resistor R1 using vias. This can allow the interconnect 61b to be routed on a second layer separate from the layer of the PCB that includes the resistors R1, R2.

[0096] Figure 6A Illustrated is the interconnect routing of the flux probe 50 and the interconnect routing according to Figure 5A the implementation. The flux probe 50 includes interconnects 61a, interconnects 61b, resistor R1, resistor R2, and can form a loop around the central leg 49c of the core 102. The synchronous rectifier 126 can be an N-type field effect transistor (NFET) having a drain electrically coupled to the node NFW (e.g., secondary winding node), a source electrically coupled to the secondary ground RTN, and a gate electrically coupled to the trace PT_Vcr.

[0097] According to the teachings herein, the flux probe 50 can provide a probe signal VR1. As illustrated, the probe signal VR1 can be due to the voltage of the trace PT_RTN with respect to the routed secondary ground RTNX, the trace PT_RTN being routed across the winding window between the outer leg 49a and the central leg 49c. As discussed above with respect to Figure 4C when the trace PT_RTN is excluded from the loop surrounding the core 102, the routed secondary ground RTNX can be equivalent to the secondary ground RTN.

[0098] Comparator 120 can compare the node-relative probe signal VR1X with the node-relative reference voltage Vrefx and provide a detection signal VO in response. Additionally, similar to flyback converter 400d, the node-relative probe signal VR1X can be relative to the winding voltage VFW. The node-relative reference voltage Vrefx can be, for example, negative zero point three volts (-0.3V) relative to the secondary ground RTNX of the wiring. Thus, according to the operation of comparator 120, the detection signal VO can be high when the node-relative probe signal VR1X is less than negative zero point three volts (-0.3V) and low when the node-relative probe signal VR1X is greater than -0.3V.

[0099] Figure 6B Illustrates the interconnection wiring of flux probe 50 and the interconnection wiring according to another embodiment. Figure 6B The embodiment of can be similar to Figure 6A The embodiment of, except that node N2 is neither connected to a fixed potential (e.g., return ground RTN) nor connected to node NFW. As illustrated, the probe signal VR1 can be obtained from the voltage across resistor R1. Thus, the detection signal VO can be high when the probe signal VR1 plus the reference voltage Vref is greater than zero and low when the probe signal VR1 plus the reference voltage Vref is less than zero.

[0100] Figure 7A and Figure 7B Illustrates a schematic diagram of flyback converter 500 according to the embodiment of Figure 6A The flyback converter 500 can be similar to flyback converter 400d, except that the flux probe 50 and the flux detection circuit 153 can be wired according to the configuration of Figure 6A ; and the resistor R2 can include a fixed resistance. Figure 7B Includes a partial-turn winding fT4 to schematically represent a trace PT_Vcr across the winding window between the outer leg 49a and the center leg 49c.

[0101] As discussed herein, if the trace PT_Vcr is excluded from the loop enclosing the time-varying magnetic flux B (i.e., not part of the loop enclosing the magnetic core 102), the control signal Vcr can drive the control terminal (i.e., the gate) of the synchronous rectifier 126 without magnetic interference from the core.

[0102] Figure 8AWaveforms 801 - 804 are illustrated in accordance with the teachings herein. Waveform 801 may correspond to the current ISW in winding 60 during the switching cycle of primary switch 152. Waveform 802 may correspond to the secondary current IS in winding 99 during the switching cycle of primary switch 152. Waveform 803 may correspond to the magnetic flux Φ in core 102 during the switching cycle of primary switch 152; and waveform 804 may correspond to the detection signal VO and / or the control signal Vcr.

[0103] From time tx0 to time tx1 and from time tx3 to time tx4, the current ISW in winding 60 increases, thereby generating a magnetic flux Φ in core 102. Thus, the magnetic flux Φ may increase from time tx0 to time tx1 and from time tx3 to time tx4.

[0104] From time tx1 to time tx2 and from time tx4 to time tx5, the current ISW is zero, such that there is no current in winding 60. Thus, the magnetic flux Φ may decrease from time tx1 to time tx2 and from time tx4 to time tx5. As the magnetic flux Φ decreases, the secondary current IS may be provided to winding 99 in accordance with waveform 802 while the magnetic flux Φ decreases in core 102.

[0105] In addition, as illustrated, the switching period TSW is depicted from time tx1 to time tx4; and from time tx2 to time tx3, the magnetic flux Φ may be reduced to zero or substantially zero during discontinuous conduction mode (DCM). Thus, the secondary current IS may be reduced to zero or substantially zero in winding 99.

[0106] In accordance with the teachings herein, the magnetic flux probe 50 may provide a probe signal VR1 in response to the time derivative of waveform 803 (i.e., in response to the time - varying magnetic flux Φ). In response to the probe signal VR1, the flux detection circuit 153 may provide the detection signal VO, and the secondary controller 108 may provide the control signal Vcr in accordance with waveform 804.

[0107] Figure 8B Waveforms 801 - 805 are illustrated in accordance with the teachings herein. According to one embodiment using the node - referenced probe signal VR1X (e.g., Figure 4D and / or Figure 7B ), waveform 805 may correspond to the difference between the node - referenced probe signal VR1X and the routed secondary ground RTNX. As illustrated, the difference between the node - referenced probe signal VR1X and the routed secondary ground RTNX may be reduced below zero volts at times tx1, tx4 and may increase towards zero volts at times tx2, tx5, such that waveform 804 transitions high at times tx1, tx4 and transitions low at times tx2, tx5.

[0108] Figure 9 Illustrates the conceptual flowchart 900 for controlling the synchronous rectifier 126 during the switching cycle TSW. Step 901 may correspond to measuring the time-varying magnetic flux using the magnetic flux probe 50. Step 902 may correspond to receiving the probe signal VR1 from the first resistor R1 of the magnetic flux probe 50. Step 903 may correspond to using the flux detection circuit 153 to provide a detection signal VO in response to the probe signal VR1; and step 904 may correspond to driving the synchronous rectifier (i.e., providing the control signal Vcr) in response to the detection signal VO.

[0109] Conclusion

[0110] The above description of the illustrated embodiments of the present disclosure, including what is described in the abstract, is not intended to be exhaustive or limiting of the exact forms disclosed. Although specific implementations and embodiments of a flux detection circuit and method for sensing magnetic flux via a magnetic flux probe are described herein for illustrative purposes, various equivalent modifications are possible without departing from the broader spirit and scope of the present disclosure. Indeed, it should be understood that specific example voltage, current, frequency, power range values, times, etc. are provided for purposes of explanation and that other values may also be employed in other implementations and embodiments in accordance with the teachings herein.

[0111] The previous description may refer to elements or features as being "connected" or "coupled" together. As used herein, unless otherwise expressly stated, "connected" means that one element / feature is directly or indirectly connected to another element / feature, and not necessarily mechanically connected. Similarly, unless otherwise expressly stated, "coupled" means that one element / feature is directly or indirectly coupled to another element / feature, and not necessarily mechanically coupled. Thus, although the various schematic diagrams shown in the figures depict example arrangements of elements and components, additional intermediate elements, devices, features, or components may exist in the actual implementation (assuming the functionality of the depicted circuit is not adversely affected).

[0112] In addition, reference throughout this specification to "one embodiment", "an embodiment", "one example" or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of a flux detection circuit and method for sensing magnetic flux via a magnetic flux probe. Thus, the phrases "in one embodiment", "in an embodiment", "one example", or "an example" that appear throughout this specification do not necessarily all refer to the same embodiment or example. In addition, the particular features, structures, or characteristics may be combined in any suitable combination and / or sub-combination in one or more embodiments or examples. The particular features, structures, or characteristics may be included in an integrated circuit, an electronic circuit, a combinatorial logic circuit, or other suitable components that provide the described functionality. Additionally, it should be understood that the accompanying drawings are for illustrative purposes for those of ordinary skill in the art and are not necessarily drawn to scale.

[0113] Furthermore, conditional language used herein, such as, among other things, "can", "could", "might", "may", "e.g.", "for example", "such as", etc., unless specifically stated otherwise or otherwise understood within the context in which it is used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and / or states. Thus, such conditional language is generally not intended to imply that one or more embodiments are in any way required to include the features, elements, and / or states, or that one or more embodiments must include logic for determining whether such features, elements, and / or states are included in any particular embodiment or are to be performed in any particular embodiment.

[0114] Although certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. For example, although the disclosed embodiments are presented in a given arrangement, alternative embodiments may perform similar functions with different components and / or circuit topologies, and some elements may be deleted, moved, added, subdivided, combined, and / or modified. Each of these elements may be implemented in a variety of different ways. Any suitable combination of the elements and acts of the various embodiments described above may be combined to provide further embodiments. Accordingly, the scope of the invention is defined only by reference to the appended claims.

[0115] Although the claims presented herein are in a single dependent format for filing with the United States Patent and Trademark Office (USPTO), it should be understood that any claim may depend from any prior claim of the same type, unless that is clearly technically infeasible.

Claims

1. A switching power supply, comprising: an energy transfer element including a primary winding, a secondary winding, and a core; a primary switch electrically coupled to the primary winding and configured to generate magnetic flux within the core in accordance with a switching cycle; a magnetic flux probe comprising a first resistor and a second resistor, wherein the magnetic flux probe is configured to form a loop enclosing the magnetic flux and to provide a probe signal proportional to a time derivative of the magnetic flux; and A synchronous rectifier (SR) is electrically coupled to the secondary winding and is configured to receive a control signal based at least in part on the probe signal.

2. The switching power supply according to claim 1, wherein the switching power supply is a flyback converter.

3. The switching power supply of claim 1, wherein the energy transfer element is a magnetic component. The switching power supply according to claim 3 , wherein the magnetic component is an embedded transformer.

5. The switching power supply of claim 1, wherein the synchronous rectifier is an N-type field effect transistor (NFET).

6. The switching power supply of claim 1 wherein the magnetic flux probe includes a first node electrically coupled to the first resistor.

7. The switching power supply of claim 1, wherein the probe signal is determined at least in part based on an electromotive force (emf) of the first resistor.

8. The switching power supply of claim 1, wherein the probe signal is proportional to the resistance of the first resistor and inversely proportional to the total resistance of the flux probe.

9. The switching power supply of claim 8, wherein the total resistance of the flux probe comprises a resistance of the first resistor and a resistance of the second resistor.

10. The switching power supply of claim 1, wherein the second resistor is a variable resistor.

11. The switching power supply of claim 1, wherein the second resistor is an adjustable resistor.

12. The switching power supply of claim 1 wherein the magnetic flux probe includes a first node electrically coupled to the secondary winding.

13. The switching power supply of claim 12, wherein the first node is electrically coupled to the synchronous rectifier.

14. The switching power supply according to claim 1, further comprising: A flux detection circuit is configured to provide a detection signal in response to the probe signal, wherein the synchronous rectifier is configured to receive a control signal based at least in part on the detection signal. 15 . The switching power supply of claim 14 , wherein the flux detection circuit comprises a comparator configured to provide the detection signal in response to a comparison of the probe signal with a reference voltage.

16. The switching power supply of claim 15, wherein the reference voltage has a magnitude of zero point one volt (0.1V) to zero point five volts (0.5V).

17. The switching power supply according to claim 1, wherein the magnetic flux probe further comprises: At least one interconnect is electrically coupled between the first resistor and the second resistor.

18. The switching power supply of claim 17, wherein the at least one interconnect comprises a printed circuit board trace.

19. The switching power supply of claim 17, wherein the at least one interconnect comprises a wire.

20. A method of controlling a synchronous rectifier during a switching cycle, comprising: Use a flux probe to measure time-varying magnetic flux; receiving a probe signal from a first resistor of the flux probe; using a flux detection circuit to provide a detection signal in response to the probe signal; and The synchronous rectifier is driven in response to the detection signal.

21. The method according to claim 20, further comprising: Adjust the variable resistor to determine the size of the probe signal.

22. The method of claim 20, wherein the synchronous rectifier is an N-type field effect transistor (NFET).

23. The method of claim 20, wherein providing the detection signal in response to the probe signal using the flux detection circuit further comprises: The probe signal is compared to a reference voltage using a comparator.

24. The method of claim 23, wherein the reference voltage has a magnitude between zero point one volt (0.1 V) and zero point five volts (0.5 V).

25. The method of claim 20, wherein the switching cycle is a power converter switching cycle.

26. The method of claim 25, wherein the power converter is a flyback converter.

27. The method of claim 20, wherein the magnetic flux probe surrounds the time-varying magnetic flux of a core.

28. The method of claim 27, wherein the core is an energy transfer element core.

29. The method of claim 27, wherein the core is an embedded transformer core.

Images