Magnetic saturation detectors with single and multiple transverse windings

Abstract

This document presents a magnetic saturation detector for a power converter. An energy transfer element has an input power winding wound around a central leg. One or more transverse windings are positioned perpendicular to the input power winding and coupled to receive a transverse current, which provides a transverse magnetic flux density within the energy transfer element. The transverse magnetic flux density generates a transverse voltage waveform. A voltage detection circuit is configured to receive the transverse voltage waveform and detect a change in the sign of the slope of the transverse voltage waveform. This change in the sign of the slope indicates magnetic saturation. The voltage detection circuit is configured to detect the occurrence of an extreme value in the transverse voltage waveform. The extreme value indicates a change in the sign of the slope.

Description

[0001] This application claims the benefit of U.S. Provisional Application No. 62 / 887,810, filed August 16, 2019, which is incorporated herein by reference in its entirety.

[0002] Related applications

[0003] This patent application is related to patent application 62 / 888,194, entitled "Core Assemblies for Magnetic Saturation Detector without Requirement for DC Bias," and patent application 62 / 888,089, entitled "Energy Transfer Element Including a Communication Element," each of which was filed on the same date as the present application, is assigned to a common assignee, and has a common inventor. Each of the related applications is hereby incorporated by reference in its entirety. Background of the Invention

[0004] Field of the Invention

[0005] The present invention relates generally to magnetic energy transfer elements and, more particularly, to magnetic energy transfer elements in power converters.

[0006] Discussion of related technologies

[0007] Electronic devices run on electricity. Switched-mode power supplies are commonly used to power the electronic circuits in many of today's products because of their high efficiency, small size, and light weight. A conventional wall outlet provides a source of high-voltage alternating current (AC). In a switching power supply, a power converter receives a high-voltage alternating current (AC) input, which is converted to provide a generally well-regulated direct current (DC) output at a typically lower voltage suitable for electronic circuits. In operation, the switches in the switched-mode power converter are controlled to vary the duty cycle, switching frequency, or average number of pulses per unit time, to produce the desired output of the power supply.

[0008] Switched-mode power converters typically use at least one magnetic component that stores energy from an input and delivers energy to one or more outputs. Such magnetic components are often referred to as magnetic energy transfer elements.

[0009] Magnetic energy transfer elements typically rely on the properties of magnetically active materials, such as ferrites and metal alloys, to reduce the physical volume required to accommodate stored energy. The materials direct the magnetic field from an electric current to areas where energy can be stored at high density. Magnetically active materials typically possess their desired properties only when the strength of the magnetic field is less than a threshold magnitude known as the saturation flux density. When the strength of the magnetic field exceeds the saturation flux density, the desired properties of the magnetically active material decrease rapidly as the magnetic field increases. This loss of desired magnetic properties as the magnetic field increases reduces the amount of energy that the magnetic component can store from a given current and, therefore, can allow rapid increases in current that can damage electrical components.

[0010] It is desirable to know when the magnetic field in a magnetic energy storage element reaches its saturation flux density so that the power converter can safely operate at its maximum power capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0012] Figure 1A is a schematic diagram of an example power supply including a switch-mode power converter with a magnetic saturation detector according to an embodiment of the present disclosure.

[0013] Figure 1B is a schematic diagram of an example power system with galvanic isolation including a magnetic saturation detector according to an embodiment of the present disclosure.

[0014] Figure 2A is a perspective view of an example energy transfer element that may be included in a magnetic saturation detector according to an embodiment of the present disclosure.

[0015] Figure 2B According to the embodiments of the present disclosure Figure 2A Exploded perspective view of an example energy transfer element with the upper and lower pieces separated to show the lateral windings passing through the center post of each piece.

[0016] Figure 3A is a graph of magnetic flux density in an example magnetic energy transfer element versus current in a power winding of the energy transfer element, according to an embodiment of the present disclosure.

[0017] Figure 3Bis a graph of magnetic flux density in an example magnetic energy transfer element versus current in a power winding of the energy transfer element when the energy transfer element includes permanent magnets to provide an offset flux density, according to an embodiment of the present disclosure.

[0018] Figure 4 is a graph showing the waveform of the current in the power winding of the energy transfer element and the waveform of the voltage on the transverse winding of the energy transfer element according to an embodiment of the present disclosure.

[0019] Figure 5 is a diagram showing more details of an embodiment according to the present disclosure Figure 4 An enlarged portion of the graph of .

[0020] Figure 6 is a flow chart illustrating steps in the operation of an example power converter having a magnetic saturation detector using transverse windings in an energy transfer element, according to an embodiment of the present disclosure.

[0021] Figure 7 is a schematic diagram illustrating another example power supply including a switch-mode power converter with a magnetic saturation detector according to an embodiment of the present disclosure.

[0022] Figure 8 is a schematic diagram illustrating yet another example power supply including a switch-mode power converter with a magnetic saturation detector according to an embodiment of the present disclosure.

[0023] Figure 9A is a perspective view of an example energy transfer element using a modified standard magnetic core configuration that may be included in a magnetic saturation detector according to an embodiment of the present disclosure.

[0024] Figure 9B is a perspective view of an example energy transfer element using a standard magnetic core configuration that may be included in a magnetic saturation detector according to an embodiment of the present disclosure.

[0025] In all several views of the accompanying drawings, corresponding reference characters indicate corresponding parts. It will be understood by those skilled in the art 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 present invention. In addition, common but easily understood elements that are useful or necessary in commercially feasible embodiments are generally not depicted so as to less obstruct viewing of these various embodiments of the present invention. DETAILED DESCRIPTION

[0026] In the following description, many specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that it is not necessary to adopt these specific details to practice the present invention. In other cases, well-known materials or methods are not described in detail to avoid obscuring the present invention.

[0027] References throughout this specification to "one embodiment," "an embodiment," "one example," or "an example" mean that the particular features, structures, or characteristics described in connection with that embodiment or example are included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment," "in an embodiment," "one example," or "an example" appearing in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and / or subcombinations in one or more embodiments or examples. The particular features, structures, or characteristics may be included in an integrated circuit, an electronic circuit, a combinational logic circuit, or other suitable components that provide the described functionality. In addition, it will be understood that the figures provided herewith are for explanation purposes to persons of ordinary skill in the art and that the figures are not necessarily drawn to scale.

[0028] Figure 1A is a schematic diagram 100A of an example power supply configured to operate with a magnetic saturation detector. Figure 1A The example power supply receives an input voltage V relative to the input return line 104 IN 102 and provides a regulated output to a load 148. The regulated output may be a voltage V relative to the output return line 144. O 154. Current I O 146 or a combination of both.

[0029] Figure 1A The example power supply uses a flyback power converter to generate an output that is isolated from the input current. In other words, a voltage applied between the input return 104 and the output return 144 will generate negligible current. Figure 1A The flyback power converter in the example power supply includes an energy transfer element L1 120 having an input power winding P1 118, an output power winding P2 122, a first lateral winding T1 128, and a second lateral winding T2 126. Power windings P1 118 and P2 122 primarily participate in energy transfer between input and output, while lateral windings T1 128 and T2 126 primarily participate in magnetic saturation detection.

[0030] Figure 1AThe symbols representing energy transfer element L1 120 in FIG. 1 use the dot convention to indicate voltage polarity on the windings. The circular dots on power windings P1 118 and P2 122 indicate that the dotted ends of the windings have the same voltage polarity relative to the non-dotted ends of the same winding. For example, if the dotted end of one power winding is positive relative to the non-dotted end, the dotted ends of all power windings are positive relative to their non-dotted ends. Similarly, the square dots on transverse windings T1 128 and T2 126 indicate that the dotted ends of the transverse windings have the same voltage polarity relative to the non-dotted end of the same transverse winding. The dots on the power windings have a different shape than the dots on the transverse windings to indicate that the polarity of the power windings is not necessarily the polarity of the transverse windings, as will become apparent from the description of the construction of energy transfer element L1 120 later in this disclosure.

[0031] The clamp circuit 106 is coupled in parallel to the input power winding P1 118. The input switch S1 110 is coupled between the input power winding P1 118 and the input return 104.

[0032] In operation, the input-referenced controller 104 receives a signal from the output-referenced controller 152 through the galvanic isolator 134 to generate a drive signal 112 that opens and closes the input switch S1 110. An open switch cannot conduct current, while a closed switch can conduct current. The input-referenced controller 132 generates a current I in the input switch S1 110. S1 108 is sensed as a current sensing signal 114. In one operating mode, when the current I S1 When 108 reaches a threshold, the reference input controller 132 may open the input switch S1 110. In another mode of operation, the reference input controller 132 may open the input switch S1 110 when the energy transfer element L1 120 reaches a state of impending magnetic saturation.

[0033] The switching of switch S1 110 generates a pulsating current I in the respective power windings P1 118 and P2 122 of energy transfer element L1 120 . P1 116 and I P2 124, and the ripple voltages V1 and V2 across those respective windings. The clamp circuit 106 prevents excess voltage on the input power switch S1 110 when the switch is open. The output winding current I from the output power winding P2 122 P2 124 is rectified by diode 136 and output capacitor C O138 is filtered to generate an output voltage V at the load 148 O 154 and output current I O 146. Output voltage V O 154. Output current I O 146 or a combination of the two can be sensed by the reference output controller 152 as an output sense signal 150. The reference output controller compares the sensed output quantity with the reference value and can communicate with the reference input controller 132 through the galvanic isolator circuit 134 to appropriately switch the input switch S1 110 to obtain the desired output value. The galvanic isolator circuit 134 can include any of many known methods for coupling signals between galvanically isolated circuits using optical, magnetic, and capacitive techniques.

[0034] exist Figure 1A In the example power supply, the transverse winding T2 126 receives the transverse current I from the controller 152 of the reference output T 142. Transverse current I T 142 is a generally constant current that provides a transverse magnetic flux density within the energy transfer element L1 120, thereby generating a transverse voltage V across the respective transverse windings T1 128 and T2 126. T1 130 and V T2 140 to indicate magnetic saturation. Since the transverse windings T1 128 and T2 128 are galvanically isolated, the controller 132 of the reference input or the controller 152 of the reference output can sense the corresponding transverse voltage V T1 130 and V T2 140 to provide detection of magnetic saturation, and either controller can provide a transverse current in one of the transverse windings. Figure 1A In an embodiment, the reference input controller 132 and the reference output controller 152 are components of a regulator that maintains the output of the power supply by providing an appropriate drive signal 112 based on the input of the current sense signal 114, the output sense signal 150, and any one of the transverse voltages 130 and 140.

[0035] Control circuits require a bias voltage to power their operation. It's often preferable to provide the transverse current from a controller that operates with a lower bias voltage to reduce power dissipation in the controller. Therefore, since power supplies typically produce an output voltage significantly lower than the input voltage, and power supplies typically control switches on the input, it can be advantageous in practice for the controller referenced to the output to provide the transverse current and the controller referenced to the input to have circuitry that observes the transverse voltage to detect magnetic saturation.

[0036] Figure 1Bis a schematic diagram 100B of an example power system with galvanic isolation including a magnetic saturation detector. Figure 1B The example power system of uses energy transfer element L1 120 to control power from input source 156 to output load 158. Figure 1A In the embodiment of FIG. 1 , the input source 156 has an input return 104 that is galvanically isolated from the output load 158 having an output return 144. Figure 1A In the example power supply, the energy transfer element L1 120 has an input power winding P1 118, an output power winding P2 122, a first transverse winding T1 128, and a second transverse winding T2 126. The power windings P1 118 and P2 122 are primarily involved in energy transfer between the input and output, while the transverse windings T1 128 and T2 126 are primarily involved in detecting magnetic saturation. Figure 1B In the embodiment, the reference input controller 132 and the reference output controller 152 are components of a regulator that maintains the output of the power system by providing an appropriate input power control signal 160 based on the input of the output sense signal 150 and either of the transverse voltages 130 and 140.

[0037] In operation, the reference input controller 132 receives a signal from the reference output controller 152 through the galvanic isolator 134 to generate an input power control signal 160 that applies a time-varying current I in the input winding P1 118. P1 116 is a time-varying voltage V1.

[0038] Applying a voltage V1 to the input power winding P1 118 generates a voltage V2 at the output power winding P2 122 , which can cause a time-varying current I in the output winding P2 122 . P2 Output current I P2 124 delivers power to the output load 158 along with the output voltage V2. The reference output controller 152 senses the output quantity as an output sense signal 150, compares the sensed output quantity with a reference value, and communicates with the reference input controller 132 via the galvanic isolator circuit 134 to appropriately switch the input switch S1 110 to obtain the desired output value. The galvanic isolator circuit 134 can include any of many known methods for coupling signals between galvanically isolated circuits using optical, magnetic, and capacitive techniques.

[0039] exist Figure 1B In the example power supply, the transverse winding T2 126 receives the transverse current I from the controller 152 of the reference output T 142. Transverse current I T142 is a generally constant current that provides a transverse magnetic flux density within the energy transfer element L1 120, thereby generating a transverse voltage V across the respective transverse windings T1 128 and T2 126. T1 130 and V T2 140 to indicate magnetic saturation. Since the transverse windings T1 128 and T2 128 are galvanically isolated, the controller 132 of the reference input or the controller 152 of the reference output can sense the corresponding transverse voltage V T1 130 and V T2 140 to provide detection of magnetic saturation, and either controller can provide a lateral current in one of the lateral windings.

[0040] Figure 2A and Figure 2B Salient features of the construction of an example energy transfer element that may be included in a power supply operating with a magnetic saturation detector are illustrated. Figure 2A is a perspective view 200A showing an upper core piece, such as an upper magnetic core half 205, assembled on a lower core piece, such as a lower magnetic core half 215. Each magnetic core half has a central column 225 surrounded by a winding 218 representing one or more power windings, such as Figure 1A 118 and P2 122. In a practical component, the turns of the power windings will usually be placed on a separate spool, sometimes called a bobbin or coil former, which will fit over the center post to facilitate assembly. Figure 2A A gap 245 is shown in the center column of the assembled core halves. The size of this gap is typically selected along with the number of turns on the power winding to set the desired electrical parameters for the specific application. In some applications, the gap contains a permanent magnet to provide a flux density offset to the flux density generated by the current in the power winding. In some embodiments, the gap 245 can be distributed between the three vertical segments by inserting physical spacers of appropriate material between the core halves so that each vertical segment has a gap of the desired size.

[0041] Figure 2A Also shown are transverse windings 226 and 228, which pass through apertures 235 in the center leg 225 of each core half such that they are perpendicular to the power winding 218. Each transverse winding is typically a single turn, although a transverse winding may include more than one turn to amplify the voltage produced by the winding. Figure 2B yes Figure 2A200B is a perspective view of an example energy transfer element, wherein the upper and lower core halves 205 and 215 are separated to show transverse windings 226 and 238 passing through an opening in the lower core half 215. It should be understood that the transverse windings do not have to be geometrically perpendicular to the power windings. Any conductor that completely passes through a turn of the power winding at any angle in one direction can be a transverse winding.

[0042] Those skilled in the art will appreciate that magnetic assemblies and parts of magnetic assemblies can be described by a variety of terms that are not necessarily technically accurate and precise. For example, almost any piece of magnetic material can be referred to as a magnetic core. A complete assembly of several magnetic components excluding windings can also be generally referred to as a magnetic core. An assembly of a magnetic core typically includes two core pieces. In many magnetic core assemblies, such as in Figure 2A In the embodiment of the present invention, the two core members can be almost identical. Therefore, each core member can be generally referred to as a core member or a core half. In fact, the gap in the central column, such as Figure 2A The gap 245 in the assembly can be formed by removing material from the center column of only one of the two identical half-cores. Even though the piece forming the gap is no longer the same as the piece from which the material was not removed, each core piece is still referred to as a half-core. The assembly can also be referred to as a core pair. In the present disclosure, the term half-core can be used to refer to one of two nearly identical pieces in an assembly to distinguish the assembly from an alternative assembly that includes significantly different pieces. For example, an assembly of two E-shaped pieces can have the same geometric features and magnetic properties as an assembly using one E-shaped piece and one I-shaped piece. Although each assembly includes two core members, the EE assembly includes two half-cores, while the EI assembly does not. It should be noted that in the practice of this field, each of the core pieces, core members, core elements, magnetic half-cores, and core assemblies can be referred to as a magnetic core.

[0043] Figure 3A and Figure 3B The relationship between the magnetic flux density in the energy transfer element and the current in the power winding of the energy transfer element is graphically illustrated. Figure 3A is a graph 300A showing the power winding current relative to the horizontal axis—such as, for example Figure 1A I in the power supply P1 ——The magnetic flux density plotted on the vertical axis. Figure 3A The example energy transfer element has no flux density offset from the permanent magnets, so when the current is at zero, the flux density is at zero. The flux density from the transverse windings is typically low enough to have a negligible contribution to the behavior illustrated in the graph.

[0044] Figure 3AThe magnetic flux density curve 305 in FIG. 3 highlights several distinguishing features. Curve 305 takes positive and negative values ​​symmetrically about the origin on two axes. For positive current, there is a positive flux density, and for negative current, there is a negative flux density. The positive values ​​of current are emphasized in the graph because Figure 1A The current in the example circuit is in one direction only. P1 When increasing from zero, the energy transfer element is in the quasi-linear region B. QL 335 until the current reaches a maximum value I corresponding to the upper boundary 325 of the quasi-linear region. MAX In the quasi-linear region 335, the slope of the curve 305 is positive and relatively constant. In other words, the flux density increases at a nearly constant rate as the current increases. MAX The slope of the flux density curve 305 decreases when the flux density is greater than the value corresponding to the saturation flux density B. SAT 315 saturation current I SAT The current reaches a relatively low constant value. It is important to detect the saturation flux density B SAT 315, because operation at higher flux density values ​​may generate currents that can damage switching devices and other components in the power supply. MAX Quasi-linear region B QL 335 becomes almost constant at currents greater than I SAT Where its slope is much lower and almost constant, there is a region where the slope changes rapidly between two relatively constant values. Where the slope of the flux density changes most rapidly I MAX and I SAT The current between is identified as I KNEE , because it corresponds to a relatively sharp bend in the flux density curve 305. The magnetic saturation detector can indicate that the current I KNEE Operation at a flux density greater than I SAT Operation at current.

[0045] Figure 3B is a graph 300B showing the power winding current relative to the horizontal axis—such as, for example Figure 1A I in the power supply P1 ——The magnetic flux density plotted on the vertical axis. Figure 3A Compared with the curve graph, Figure 3B Graph of an example energy transfer element having a flux density offset from a permanent magnet.

[0046] The flux density offset from the permanent magnet causes Figure 3AThe curve 305 moves to the right on the horizontal axis, as shown by Figure 3B As shown by the curve 355 in FIG. QL 335 and saturation flux density B SAT The values ​​of 315 on the vertical axis are unchanged because they are intrinsic properties of the core's magnetic material. A flux density offset can change the relationship between flux density and external excitation, but it cannot change the intrinsic properties of the magnetic material. Figure 2A The flux density of the permanent magnet in the gap 245 of the assembly illustrated in FIG is offset by Figure 3B Shown as B OFFSET , the B OFFSET The current I on the horizontal axis P1 When is zero, a negative flux density 345 is generated in the energy transfer element. Figure 3A In , the flux density from the transverse windings is typically low enough to have a negligible contribution to the behavior illustrated in the graph.

[0047] The flux density offset increases to reach the quasi-linear region B QL 355 upper boundary 325, saturation value B SAT 315 and the current I required for the flux density where the slope of the curve changes most rapidly P1 In other words, Figure 3A The current I MAX , I SAT and I KNEE exist Figure 3B were added to I MAXBIAS , I SATBIAS and I KNEEBIAS Thus, in an energy transfer element using a permanent magnet to provide a flux density offset, a magnetic saturation detector may indicate a current corresponding to the current I KNEEBIAS Operation at a flux density greater than I SATBIAS Operation at current.

[0048] Figure 4 is a graph 400 showing the Figure 1A The waveform of the current in the power winding and the waveform of the voltage on the transverse winding of the example energy transfer element operating in the example power supply. P1 is plotted on the vertical axis 410, and the transverse voltage V T1 are plotted on the vertical axis 420 , both relative to time on the horizontal axis.

[0049] Current is the input voltage V across the power winding P1 118 of the energy transfer element L1 120 when the switch S1 110 is closed and opened. IN102. The transverse voltage V on the transverse winding T1 128 T1 160 is derived from the well-known mechanism of using the magnetic saturation properties of magnetic materials to generate voltages across the transverse windings. The saturation properties describe the behavior of the total flux density, which is the vector sum of two components: the principal component of the flux density generated by the current in the power winding and the transverse component of the flux density generated by the current in the transverse winding. The vectors of the two components are perpendicular to each other in the magnetic material. An increase in the current in the power winding forces the magnitude of the principal component to increase, even when the total flux density approaches the saturation value. Since the saturation properties limit the increase in the sum of the two vectors, the increase in the principal component forces the transverse component to decrease when the total flux density approaches the saturation value, even though the transverse component can be generated by a constant transverse current. The forced decrease in the transverse components of the flux density generates voltages across all transverse windings. When the total flux density is in the quasi-linear region ( Figure 3A and Figure 3B B in QL 355), the transverse flux density is almost independent of the main flux density, and the current in the power winding generates almost no voltage on the transverse winding. Therefore, the characteristics of the time-varying voltage on the transverse winding can be interpreted to detect magnetic saturation in the energy transfer element.

[0050] In order to produce Figure 4 An example waveform of Figure 1A The switch S1 110 in the example power supply is closed at time t1. Between time t1 and time t2, the current I P1 Increments from zero to value I MAX 430, and when the controller 132 of the reference input opens the switch, the flux density increases from zero to Figure 3A The quasi-linear region B of the flux density characteristic shown in QL 335 has an upper boundary 325. If the flux density curve 305 is completely linear, the voltage V T1 The current will remain at zero between time t1 and time t2. A slight deviation from zero near time t2 is when the current is in the quasi-linear region B. QL 335 ends close to I MAX When the switch S1 110 is turned off at time t2, the current in the power winding P1 118 changes from I MAX changes to zero, while the current in the power winding P2 122 increases from zero to maintain the current I corresponding to the current in the power winding P1 118 MAX The required value of the flux density. The transverse voltage V T1 At time t2 the polarity is changed because the flux density that produces the change in voltage across the winding decreases after the switch is opened and increases when the switch is closed. Figure 4In the embodiment of FIG. 5 , the flux density decreases to zero between time t2 and time t3.

[0051] When the switch S1 110 is closed again at time t3, the current I P1 Increase again from zero to more than I MAX 430 and I KNEE 440 both, before the controller 132 of the reference input opens the switch, I SAT 450. When the current I increases P1 More than I MAX At 430, the flux density leaves the quasi-linear range B QL 335, and the lateral voltage V T1 It quickly becomes more negative with a substantial negative slope 460. The lateral voltage V T1 The maximum negative value 480 is reached at time t4, which corresponds to I KNEE The current I at 440 P1 When the current I P1 After I KNEE And at time t5, it is close to I SAT When the final value of 450 is reached, the lateral voltage V T1 With a relatively large positive slope 470 becoming less negative, at time t5, the controller 132 referenced to the input opens the switch. When the flux density decreases to zero between time t5 and time t6, the transverse voltage V T1 becomes more positive and reaches a maximum positive value.

[0052] Figure 5 yes Figure 4 5, which shows more detail around times t4 and t5. The zoom emphasizes the nature of the transverse voltage waveform that allows the circuit to detect magnetic saturation by observing the voltage across the transverse winding.

[0053] Figure 5 Shows that when the current I P1 In the value I KNEE At 440°, the transverse voltage V T1 The extreme value 480 in the waveform. Figure 5 The example is valley, but it can be simply changed by interchanging the two ends of the winding at the voltage sensing terminal or by making the transverse current I T The direction of 142 is reversed so that the extremes are peaks rather than valleys to reverse the polarity of the voltage on the transverse winding.

[0054] A polarity-independent characteristic of an extreme value is the change in sign of the slope of the waveform from before time t4 to after time t4. Figure 5A negative slope is shown in section 460 before t4 and a positive slope is shown in section 470 after t4. The change in sign of the slope of the voltage across the transverse winding is an indicator of magnetic saturation. If the polarity of the transverse winding is reversed, the slope will be positive before t4 and negative after t4. The change in sign of the slope is also independent of the magnitude of the extreme values. Because the slope of the transverse voltage waveform changes sign—from positive to negative or negative to positive—it must cross zero. Therefore, a zero-crossing detector that observes the voltage across the transverse winding can detect magnetic saturation. A controller that opens the switch in the power winding in response to the zero-crossing detector sensing the voltage across the transverse winding can control the power supply to operate at its maximum power capacity without damage. In practice, to avoid false indications of magnetic saturation, the zero-crossing detector can be selected to observe the voltage across the transverse winding only after the switch has been closed for a threshold time, or alternatively, only when the current in the switch is greater than a threshold current.

[0055] The foregoing embodiments have illustrated the application of a magnetic saturation detector in a power supply having a power converter operating in discontinuous conduction mode (DCM). That is, within each switching cycle, the current in the power winding and the flux density in the energy transfer element (without a flux density offset) start with a value of zero and end with a value of zero. In contrast, under different conditions of input voltage, output voltage and load, the power supply can operate its power converter in continuous conduction mode (CCM). That is, in CCM, the current in the power winding and the flux density (still without a flux density offset in the energy transfer element) do not start and end with a value of zero within each switching cycle. When the flux density is in the quasi-linear region B within each switching cycle, the current in the power winding and the flux density in the energy transfer element (without a flux density offset) do not start and end with a value of zero within each switching cycle. QL The operation of the magnetic saturation detector in CCM is the same as that in DCM, starting and ending within 335.

[0056] Known magnetic saturation detectors compare the magnitude of the transverse voltage to a reference value to provide an indication of magnetic saturation in the energy transfer element. Using the magnitude of the transverse voltage to detect magnetic saturation is subject to inaccuracies and uncertainties due to variations in flux density with temperature and the relationship of the voltage across the transverse winding to the voltage across the power winding.

[0057] The voltage across the power winding establishes the rate of change of the power flux density and is therefore a multiplier of the voltage appearing across the transverse winding. A magnetic saturation detector that compares the magnitude of the transverse voltage to a reference voltage to indicate magnetic saturation in the power supply must adjust the reference voltage to be proportional to the input voltage of the power supply. The proportionality factor is difficult to calculate and must usually be determined after constructing the energy transfer element. In addition, the relationship between flux density and current in the power winding has a strong dependence on temperature. Although the significant features of this relationship are maintained over a wide temperature range, some characteristics such as the quasi-linear region B are not readily apparent.QL 335, the upper end of the quasi-linear region 325 and the saturation flux density B SAT The specific properties of 315 vary greatly with temperature in a way that is difficult to characterize. The saturation flux density of magnetic materials used in power converters generally has a strong dependence on temperature, decreasing at higher temperatures.

[0058] The magnetic saturation detector described in this disclosure overcomes the limitations of known methods because detecting a change in the sign of the slope of the transverse voltage, or equivalently, detecting a zero crossing of the slope of the transverse voltage, is a direct indication of saturation at all input voltages and temperatures. Although the magnitude of the transverse voltage can vary by unpredictable amounts with input voltage and temperature, the zero crossing of the slope will always be an accurate indication of magnetic saturation.

[0059] Figure 6 is exemplified by being included in, for example, Figure 1A Flowchart 600 of steps in the operation of an example magnetic saturation detector in an energy transfer element of a power supply. The electronic circuitry in controller 132 references the input and can observe the transverse voltage V T1 130 and responds with a signal indicative of magnetic saturation to control the switch S1 110 .

[0060] After starting at step 605, the circuit may de-assert the logic signal indicating magnetic saturation in step 610. In step 615, the circuit may receive a signal from the transverse winding of the energy transfer element. The signal received from the transverse winding is typically a voltage. In step 620, the controller may begin a switching cycle, followed by closing the switch that stores energy in the energy transfer element in step 625. In step 630, the controller may monitor the signal from the transverse winding. The signal from the transverse winding may be conditionally gated by time, current, or other operating parameters to prevent false indications of magnetic saturation. In step 635, the circuit may examine the signal from the transverse winding to detect the occurrence of extreme values ​​in its magnitude over time.

[0061] If the circuit does not detect an extreme value in step 635, the process can return to step 630 where the circuit continues to monitor the signal from the transverse winding. If the circuit detects an extreme value in step 635, the circuit can assert a logic signal for magnetic saturation in step 640, open a switch storing energy in the energy transfer element in step 645, and then return to step 610 to deassert the logic signal after the switch is opened.

[0062] Figure 1AThe example power supply uses two transverse windings to obtain the benefit of galvanic isolation between the circuit that provides the transverse current and the circuit that senses the transverse voltage. It is often desirable to provide current from a relatively low voltage, typically at the output of the power supply, in contrast to the relatively high voltage that may be the only power source available at the input of the power supply. In applications where two transverse windings are not required, the magnetic saturation detector can use a single transverse winding, as in Figure 7 exemplified in .

[0063] Figure 7 is a schematic diagram 700 of an example power supply configured to operate with a magnetic saturation detector using only a single transverse winding. Figure 7 The example power supply receives an input voltage V relative to the input return line 704 IN 702 and provides a regulated output to a load 748. The regulated output may be a voltage V relative to the output return line 744. O 754. Current I O 746 or a combination of both. Figure 7 An example power supply is similar to Figure 1A The example power supply, except Figure 7 The example power supply includes a magnetic saturation detector with only a single transverse winding.

[0064] Figure 7 The example power supply uses a flyback power converter to generate an output that is isolated from the input current. In other words, a voltage applied between the input return 704 and the output return 744 will generate negligible current. Figure 7 The flyback power converter in the example power supply includes an energy transfer element L1 720 having an input power winding P1 718, an output power winding P2 722, and a single transverse winding T1 728. Power windings P1 718 and P2 722 primarily participate in energy transfer between the input and output, while transverse winding T1 728 primarily participates in detecting magnetic saturation. A clamp circuit 706 is coupled in parallel to input power winding P1 718. An input switch S1 710 is coupled between input power winding P1 718 and input return line 704.

[0065] In operation, the reference input controller 732 receives a signal from the reference output controller 752 through the galvanic isolator 734 to generate a drive signal 712 to open and close the input switch S1 710. An open switch cannot conduct current, while a closed switch can conduct current. The reference input controller 732 controls the current I in the input switch S1 710. S1 708 is sensed as a current sensing signal 714. In one operating mode, when the current I S1When 708 reaches the threshold, the reference input controller 732 may open the input switch S1 710. In another mode of operation explained earlier in this disclosure, the reference input controller 732 may open the input switch S1 710 when the energy transfer element L1 720 reaches a state of impending magnetic saturation.

[0066] The switching of switch S1 710 generates a pulsating current I in the corresponding power windings P1 718 and P2 722 in the energy transfer element L1 720. P1 716 and I P2 724, and the ripple voltages V1 and V2 across those respective windings. The clamp circuit 706 prevents excess voltage on the input power switch S1 710 when the switch is open. The output winding current I P2 724 is rectified by diode 736 and output capacitor C O 738 is filtered to generate an output voltage V at the load 748 O 754 and output current I O 746. Output voltage V O 754. Output current I O 746 or a combination of the two can be sensed by the reference output controller 752 as an output sense signal 750. The reference output controller compares the sensed output quantity with the reference value and communicates with the reference input controller 732 through the galvanic isolator 734 to appropriately switch the input switch S1 710 to obtain the desired output value. The galvanic isolator circuit 734 can include any of many known methods for coupling signals between galvanically isolated circuits using optical, magnetic, and capacitive techniques.

[0067] exist Figure 7 In the example power supply, the transverse winding T1 728 receives the transverse current I from the controller 732 referenced to the input T 742. Transverse current I T 742 is a generally constant current that provides a transverse magnetic flux density within the energy transfer element L7 120, thereby generating a transverse voltage V across the transverse winding T1 728. T1 730 to indicate magnetic saturation.

[0068] In some applications of magnetic saturation detectors, it may be desirable to provide current to the lateral windings directly from a relatively low voltage circuit, without the complexity of circuitry included in an integrated controller. Figure 8 is a schematic diagram 800 of yet another example power supply including a switch-mode power converter configured to operate with a magnetic saturation detector, Figure 8The embodiment uses only resistors on the output of the power supply to provide current to the lateral winding.

[0069] Figure 8 The example power supply receives an input voltage V relative to the input return line 804 IN 802 and provides a regulated output to a load 848. The regulated output may be a voltage V relative to the output return line 844. O 854, Current I O 846 or a combination of both.

[0070] Figure 8 The example power supply uses a flyback power converter to generate an output that is isolated from the input current. In other words, a voltage applied between the input return 804 and the output return 844 will generate negligible current. Figure 8 The flyback power converter in the example power supply includes an energy transfer element L1 820 having an input power winding P1 818, an output power winding P2 822, a first transverse winding T1 828, and a second transverse winding T2 826. Power windings P1 818 and P2 822 primarily participate in energy transfer between the input and output, while transverse windings T1 828 and T2 826 primarily participate in detecting magnetic saturation. A clamp circuit 806 is coupled in parallel to input power winding P1 818. An input switch S1 810 is coupled between input power winding P1 818 and input return line 804.

[0071] In operation, the controller 856 with galvanic isolation receives the output sense signal 850 of the reference output and the current sense signal 814 of the reference input to generate a drive signal 812 for opening and closing the input switch S1 810. An open switch cannot conduct current, while a closed switch can conduct current. The controller 856 controls the current I in the input switch S1 810. S1 808 is sensed as a current sensing signal 814. In one operating mode, when the current I S1 When 808 reaches the threshold, the controller 856 may open the input switch S1 810. In another mode of operation explained earlier in this disclosure, the controller 856 may open the input switch S1 810 when the energy transfer element L1 820 reaches a state of impending magnetic saturation.

[0072] The switching of switch S1 810 generates a pulsating current I in the respective power windings P1 818 and P2 822 of energy transfer element L1 820. P1 816 and I P2824, and the ripple voltages V1 and V2 across those respective windings. The clamp circuit 806 prevents excess voltage on the input power switch S1 810 when the switch is open. The output winding current I from the output power winding P2 822 P2 824 is rectified by diode 836 and output capacitor C O 838 is filtered to generate an output voltage V at the load 848 O 854 and output current I O 846. Output voltage V O 854. Output current I O 846 or a combination of the two can be sensed by the controller 856 as an output sense signal 850. The reference output portion of the controller 856 compares the sensed output quantity with the reference value and communicates with the reference input portion of the controller 856 through the internal galvanic isolator circuit to appropriately switch the input switch S1 810 to obtain the desired output value. The galvanic isolator circuit within the controller 856 can include any of many known methods for coupling signals between galvanically isolated circuits using optical, magnetic, and capacitive techniques.

[0073] exist Figure 8 In the example power supply, the transverse winding T2 826 is connected through the resistor R T 858 output voltage V O 854 receives the transverse current I T 842. Transverse current I T 842 is generally a relatively constant current that provides a transverse magnetic flux density within the energy transfer element L1 820, thereby generating a transverse voltage V across the respective transverse windings T1 828 and T2 826. T1 830 and V T2 840 indicates magnetic saturation. Transverse voltage V T2 840 is usually greater than the output voltage V O 854 is much lower, so that when the output voltage V O Near its regulated value, the transverse voltage V T2 840 pairs of transverse current I T 842 has negligible impact.

[0074] Figure 2A and Figure 2B The magnetic core in is presented as a general embodiment to illustrate the salient features of the construction of an energy transfer element including a transverse winding for a magnetic saturation detector. Figure 9A is a perspective view 900A of an example energy transfer element using a standard magnetic core configuration modified to include transverse windings that may be used in a magnetic saturation detector. Figure 9Bis a perspective view 900B of an example energy transfer element using a standard magnetic core configuration that does not require modification to include transverse windings that may be used in a magnetic saturation detector.

[0075] Figure 9A The example energy transfer element in FIG is constructed from two standard EE-type ferrite core halves, upper core 905A and lower core 915A. An example power winding 918A is shown wrapped around the center post. A hole 935A must be drilled in the center post of each standard core half to create openings for the transverse windings 926A and 928A.

[0076] Figure 9B The example energy transfer element in FIG. 1 is constructed from two standard RM-type ferrite core halves—upper core 905B and lower core 915B. An example power winding 918B is shown wrapped around the center post. A hole 935B in the center of each core half's center post is a readily available option for accommodating a ferrite block to adjust the inductance of the power winding after assembly. In accordance with the teachings of the present invention, transverse windings 926B and 928B can be inserted across the adjustment holes in place of the ferrite block to provide a magnetic saturation detector.

[0077] Embodiments of the present disclosure include a saturation detector in which a magnetic energy transfer element includes at least one transverse winding and at least one power winding. One of the transverse windings conducts current to establish a transverse flux density in the magnetic energy transfer element. Current in the power winding generates a main flux density that is substantially perpendicular to the transverse flux density. A saturation detector circuit senses a voltage across the transverse winding and indicates a magnetic saturation condition at an extreme value of the time-varying voltage across the transverse winding.

[0078] The above description of the illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the precise forms disclosed. Although specific embodiments and embodiments for the present invention are described herein for illustrative purposes, various equivalent modifications are possible without departing from the broader spirit and scope of the present invention. Indeed, it should be understood that specific example voltages, currents, frequencies, power range values, times, etc. are provided for illustrative purposes, and other values ​​may be used in other embodiments and examples in accordance with the teachings of the present invention.

[0079] Although the invention is defined in the claims, it will be appreciated that the invention may alternatively be defined according to the following embodiments:

[0080] Embodiment 1: A magnetic saturation detector comprises: an energy transfer element having a central column; an input power winding wound around the central column; and a first transverse winding perpendicular to the input power winding and coupled to receive a transverse current, the transverse current providing a transverse magnetic flux density within the energy transfer element, wherein the transverse magnetic flux density produces a transverse voltage waveform; and a voltage detection circuit configured to receive the transverse voltage waveform and detect a change in the sign of the slope of the transverse voltage waveform, wherein the change in the sign of the slope indicates magnetic saturation.

[0081] Embodiment 2: The magnetic saturation detector according to embodiment 1, wherein the voltage detection circuit is further configured to detect the occurrence of an extreme value in the transverse voltage waveform.

[0082] Embodiment 3: The magnetic saturation detector according to embodiment 1, further comprising: a second transverse winding, perpendicular to the input power winding and configured to sense the transverse magnetic flux density and generate the transverse voltage waveform.

[0083] Embodiment 4: A controller configured to detect magnetic saturation, the controller comprising: a magnetic saturation detector, including, an energy transfer element having a central column, an input power winding wound around the central column, a first transverse winding perpendicular to the input power winding and coupled to receive a transverse current, the transverse current providing a transverse magnetic flux density within the energy transfer element, wherein the transverse magnetic flux density generates a transverse voltage waveform, and a voltage detection circuit configured to receive the transverse voltage waveform and detect a change in the sign of the slope of the transverse voltage waveform, wherein the change in the sign of the slope indicates magnetic saturation; and a regulator coupled to the first transverse winding and configured to compare an output sense signal with a reference value and generate a switching signal and the transverse current.

[0084] Embodiment 5: The controller of embodiment 4, wherein the voltage detection circuit is configured to detect the occurrence of an extreme value in the transverse voltage waveform.

[0085] Example 6: A controller according to Example 5, wherein the magnetic saturation detector is further configured to generate the output sensing signal, and the regulator includes: a controller of a reference input coupled to the transverse winding; and a controller of a reference output coupled to the transverse winding, wherein one of the controller of the reference input and the controller of the reference output is configured to generate the transverse current.

[0086] Embodiment 7: The controller according to embodiment 6, the regulator further comprising: a galvanic isolator coupled to receive the switching signal from the controller of the reference output and transmit the switching signal to the controller of the reference input.

[0087] Embodiment 8: The controller according to embodiment 7, further comprising: a second transverse winding perpendicular to the input power winding and configured to sense the transverse magnetic flux density and generate the transverse voltage waveform.

[0088] Embodiment 9: The controller of Embodiment 8, wherein the controller of the reference output is configured to generate the transverse current in the second transverse winding, and the controller of the reference input is configured to monitor the transverse voltage.

[0089] Embodiment 10: The controller according to embodiment 4, the magnetic saturation detector further comprising an output power winding perpendicular to the second transverse winding, wherein the controller of the reference output is coupled to the second transverse winding and configured to generate the transverse current.

[0090] Embodiment 11: The controller of Embodiment 10, wherein the energy transfer element is included in a power converter.

[0091] Embodiment 12: The controller of Embodiment 11, wherein the power converter is a flyback converter.

[0092] Example 13: A method for detecting magnetic saturation, the method comprising: monitoring a transverse voltage waveform from a transverse winding coupled to an energy transfer element; closing a switch that stores energy in the energy transfer element; detecting a change in sign of the slope of the transverse voltage waveform from the transverse winding, the change in sign indicating magnetic saturation; and opening the switch in response to the change in sign of the slope of the transverse voltage waveform from the transverse winding.

[0093] Embodiment 14: The method of embodiment 13, wherein detecting a change in the sign of the slope comprises detecting the occurrence of an extreme value in the transverse voltage waveform.

[0094] Embodiment 15: The method of embodiment 13, further comprising gating the transverse voltage waveform from the transverse winding according to operating parameters, the parameters selected to prevent false indications of magnetic saturation.

[0095] Embodiment 16: The method of embodiment 15, wherein the operating parameter is selected from the group consisting of time and current.

[0096] Embodiment 17: The method of Embodiment 15, wherein gating the transverse voltage waveform comprises comparing the output sense signal to a reference value and generating a switching signal based on the comparison.

[0097] Embodiment 18: The method according to embodiment 17 further includes receiving a transverse current.

[0098] Embodiment 19: The method of Embodiment 18, wherein the transverse current is provided by a controller coupled to a reference input of the transverse winding.

[0099] Embodiment 20: The method of Embodiment 18, wherein the transverse current is provided by a controller coupled to a reference output of the transverse winding.

Claims

1. A magnetic saturation detector, comprising: an energy transfer element having a central column; an input power winding wound around the central post; as well as a first transverse winding, perpendicular to the input power winding and coupled to receive a transverse current that provides a transverse magnetic flux density within the energy transfer element, wherein the transverse magnetic flux density generates a transverse voltage waveform; as well as a voltage detection circuit configured to receive the transverse voltage waveform and detect a change in the sign of the slope of the transverse voltage waveform, A change in the sign of the slope indicates magnetic saturation. 2 . The magnetic saturation detector of claim 1 , wherein the voltage detection circuit is further configured to detect the occurrence of an extreme value in the transverse voltage waveform.

3. The magnetic saturation detector according to claim 1 , further comprising: A second transverse winding is perpendicular to the input power winding and is configured to sense the transverse magnetic flux density and generate the transverse voltage waveform.

4. A controller configured to detect magnetic saturation, the controller comprising: Magnetic saturation detectors, including, An energy transfer element having a central column, The input power winding, wound around the central column, a first transverse winding, perpendicular to the input power winding and coupled to receive a transverse current that provides a transverse magnetic flux density within the energy transfer element, wherein the transverse magnetic flux density produces a transverse voltage waveform, and a voltage detection circuit configured to receive the transverse voltage waveform and detect a change in the sign of the slope of the transverse voltage waveform, wherein a change in the sign of the slope indicates magnetic saturation; as well as A regulator is coupled to the first lateral winding and configured to compare an output sense signal with a reference value and generate a switching signal and the lateral current. 5 . The controller of claim 4 , wherein the voltage detection circuit is configured to detect the occurrence of an extreme value in the transverse voltage waveform.

6. A power converter comprising the controller according to claim 5, wherein the magnetic saturation detector is further configured to generate the output sense signal, and the regulator comprises: a controller reference input coupled to the first lateral winding; as well as a controller having a reference output coupled to the first lateral winding, wherein the input of the power converter and the output of the power converter are galvanically isolated, One of the controller of the reference input and the controller of the reference output is configured to generate the transverse current.

7. The power converter according to claim 6, wherein the regulator further comprises: A galvanic isolator is coupled to receive the switching signal from the controller of the reference output and transmit the switching signal to the controller of the reference input.

8. The power converter of claim 7, wherein the controller further comprises: A second transverse winding is perpendicular to the input power winding of the energy transfer element and is configured to sense the transverse magnetic flux density and generate the transverse voltage waveform. 9 . The power converter of claim 8 , wherein the controller of the reference output is configured to generate the transverse current in the second transverse winding, and the controller of the reference input is configured to monitor the transverse voltage. 10 . The power converter of claim 8 , the energy transfer element further comprising an output power winding perpendicular to the second lateral winding, wherein the controller of the reference output is coupled to the second lateral winding and configured to generate the lateral current. 11 . The power converter of claim 10 , wherein the input power winding and the output power winding of the energy transfer element are configured to transfer energy between an input and an output of the power converter.

12. The power converter of claim 10, wherein the power converter is a flyback converter.

13. A method for detecting magnetic saturation, the method comprising: monitoring a transverse voltage waveform from a transverse winding coupled to an energy transfer element; closing a switch that stores energy in the energy transfer element; detecting a change in sign of a slope of the transverse voltage waveform from the transverse winding, the change in sign indicating magnetic saturation; as well as The switch is opened in response to a change in the sign of the slope of the transverse voltage waveform from the transverse winding.

14. The method of claim 13, wherein detecting a change in the sign of the slope comprises detecting the occurrence of an extrema in the transverse voltage waveform.

15. The method of claim 13, further comprising gating the transverse voltage waveform from the transverse winding according to operating parameters, the parameters selected to prevent false indications of magnetic saturation.

16. The method of claim 15, wherein the operating parameter is selected from the group consisting of time and current.

17. The method of claim 15, wherein gating the transverse voltage waveform comprises: The output sense signal is compared with a reference value, and a switching signal is generated based on the comparison. The method of claim 17 , further comprising receiving a transverse current.

19. The method of claim 18, wherein the transverse current is provided by a controller coupled to a reference input of the transverse winding, and wherein an input of a power converter and an output of the power converter are galvanically isolated.

20. The method of claim 18, wherein the transverse current is provided by a controller coupled to a reference output of the transverse winding, and wherein an input of a power converter and an output of the power converter are galvanically isolated.

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