Power system

Abstract

The circuit (100) includes a transformer (104) having first and second transformer inputs and first and second transformer outputs. The first transformer output may be adapted to be coupled to a first input of an output stage (106) via a capacitor. The second transformer output may be adapted to be coupled to a second input of the output stage (106). The circuit (100) also includes a switching system (102) having first and second inputs and first and second switching outputs. The first input may be configured to receive a switching signal. The second input may be configured to receive an input voltage. The first and second switching outputs may be coupled to the first and second transformer inputs, respectively.

Description

Technical Field

[0001] This description generally relates to electronic circuits, and more particularly to power systems.

Background Art

[0002] Power circuits can be implemented in a variety of different ways. Examples of power circuits include synchronous rectifier power converters, asynchronous rectifier power converters, resonant power converters, and any of a variety of other types of switching power converters. Thus, a typical power circuit can operate one or more switches to convert an input voltage to an output voltage. A typical power circuit can implement another transformer to deliver an output voltage to a secondary winding of a transformer from a square-wave input voltage applied to a primary winding of the transformer by such a switch. In the case of an ideal transformer (e.g., zero leakage inductance and zero winding resistance), when the secondary voltage is rectified, the DC output voltage is equal to the input voltage multiplied by the turns ratio of the transformer. However, introducing a physical separation between the primary and secondary windings of a transformer due to high insulation requirements can introduce a large leakage inductance into the transformer.

[0003] As the output current of the transformer increases, a voltage drop occurs across the impedance of the leakage inductance, and thus the output voltage decreases. Therefore, the output voltage depends on the output current. To eliminate the effect of load current fluctuations on the output voltage, a typical power circuit includes a resonant capacitor in series with the primary winding of the transformer to resonate with the leakage inductance. When the switching frequency of the converter is equal to the resonant frequency of the leakage inductance and the resonant capacitor, the impedances of these components are equal and opposite and cancel each other out. Thus, there is no voltage drop associated with the load current, and the output voltage of the converter is independent of the load current.

[0004] However, in practice, there are large tolerances in both the resonant frequency of the capacitor and the leakage inductance, as well as the switching frequency of the power converter. As a result, the resonant frequency and the switching frequency can be significantly different, and this mismatch As a result, the impedances no longer cancel each other out, and the output voltage's output load dependency becomes unacceptable. When the switching frequency of the converter is lower than the resonance frequency, a voltage is generated that significantly increases the output voltage of the converter due to the interaction between the resonance capacitor and the magnetization inductance of the transformer.

Summary of the Invention

[0005] A certain circuit has first and second transformer inputs and first and second transformer outputs. The first transformer output is adapted to be coupled to the first input of the output stage via a capacitor. The second transformer output is adapted to be coupled to the second input of the output stage. This circuit also includes a switching system having first and second inputs and first and second switching outputs. The first input is configured to receive a switching signal. The second input is configured to receive an input voltage. The first and second switching outputs are each coupled to the first and second transformer inputs.

[0006] A switching power supply system includes a switching system having a switching input and a switching output. The switching system can be configured to close in response to a switching signal at the switching input. The switching system can be configured to provide a first voltage at the switching output in response to closing the switch. This system also includes a transformer having a primary winding and a secondary winding. The primary winding can be coupled to the switching output and can be configured to receive the first voltage. The secondary winding can be configured to provide a second voltage in response to the first voltage. This system also includes a capacitor coupled to the secondary winding. This system further includes an output stage coupled to the capacitor. The output stage can be configured to generate an output voltage by rectifying the second voltage.

[0007] A switching power supply system includes a switching system having first and second inputs and first and second switching outputs. The first input may be configured to receive a switching signal having a switching frequency. The second input may be configured to receive an input voltage. The system also includes a transformer having a primary winding and a secondary winding. The primary winding may have first and second transformer inputs. The secondary winding may have first and second transformer outputs, the first transformer input being coupled to the first switching output and the second transformer input being coupled to the second switching output. The system also includes an output stage having first and second voltage inputs and a voltage output. The second voltage input may be coupled to the second transformer output. The output stage may be configured to provide an output voltage at the voltage output in response to the first and second voltage inputs and. The system further includes a capacitor coupled between the first transformer output and the first voltage input, the capacitor and the secondary winding having a resonance frequency higher than the switching frequency.

Brief Description of the Drawings

[0008]

Figure 1

[0009]

Figure 2

[0010]

Figure 3

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Figure 4

[0012]

Figure 5

[0013]

Figure 6

[0014]

Figure 7

[0015]

Figure 8

DETAILED DESCRIPTION OF THE INVENTION

[0016] This description generally relates to electronic circuits, and more particularly to a power supply system. The power supply system can be implemented as a switching power supply system that includes a transformer that inductively transfers voltage from a primary winding (or windings) to a secondary winding to generate an output voltage based on an input voltage. The power supply system includes a switching stage that includes a set of switches that are operated to provide a square wave input voltage to the primary winding of the transformer. Accordingly, a secondary voltage based on the input voltage is generated in the secondary winding of the transformer. For example, the switching stage can be configured as one of a half-bridge switching circuit, a full-bridge switching circuit, a push switching circuit, or any of a variety of other types of switching circuits. The power supply system also includes an output stage that is configured to provide an output voltage based on the secondary voltage. For example, the output voltage can be made approximately equal to the input voltage multiplied by the turns ratio of the transformer. For example, the output stage can be configured as a rectifier circuit (e.g., a full-wave rectifier) such that a positive amplitude of the output voltage is provided at each of the opposite polarities of the secondary voltage.

[0017] For example, some resonant power supply systems include a resonant capacitor in series with the primary winding of a transformer to resonate with the leakage current of the transformer reflected in the primary inductor. In such a power supply system, if the switching frequency corresponding to the frequency of the bidirectional voltage pulse through the primary winding is equal to the resonant frequency of the leakage inductance and the resonant capacitor, the voltages at both ends of the resonant capacitor and the leakage inductance are equal in amplitude and opposite in phase, and cancel each other out. However, in such a power supply system, if the switching frequency is not equal to the resonant frequency of the leakage inductance and the resonant capacitor, this cancellation is not equal to each other and not in antiphase, so the voltage cancellation difference is subtracted from the amplitude of the output voltage. For example, when operating at a switching frequency higher than the resonant frequency, the output voltage becomes lower than at resonance. As another example, when the switching frequency is lower than the resonant frequency, the voltage across the resonant capacitor increases the voltage across both ends of the primary winding, and as a result, the amplitude of the output voltage becomes larger than the amplitude of the output voltage when the switching frequency is equal to the resonant frequency.

[0018] To reduce errors in the output voltage, such as an undesirable increase in the amplitude of the output voltage, the power supply system may include a resonant capacitor arranged in series with the secondary winding of the transformer. The resonant capacitor can resonate with the leakage inductance of the transformer reflected in the secondary winding. Therefore, the leakage inductance of the transformer and the resonant capacitor can exhibit a resonant frequency. Since the power supply system described herein includes a resonant capacitor in series with the secondary winding of the transformer, it can provide soft switching of the switching system at both a switching frequency higher and lower than the resonant frequency of the resonant capacitor and the leakage inductance of the transformer. Therefore, the switching system can be operated at a switching frequency lower than the resonant frequency without affecting the amplitude of the output voltage. Therefore, to adapt to manufacturing tolerances that can affect the frequency of the switching frequency without causing a harmful increase in the amplitude of the output voltage, the switching frequency can be set to a frequency less than the resonant frequency.

[0019] FIG. 1 shows an example of a switching power supply system 100. The power supply system 100 can be implemented in any of a variety of circuit applications for efficiently providing an output voltage V IN based on an input voltage V OUT . The power supply system 100 includes a switching system 102 that includes at least one switch that is periodically operated in response to a switching signal SW. For example, the switching signal SW, hereinafter referred to as the "switching frequency," may correspond to a clock signal provided at a controlled frequency, which is described in more detail herein. Accordingly, in this specification, the terms "switching frequency" and "frequency of the switching signal SW" are used interchangeably. For example, the switching system 102 may include an array of transistors (e.g., metal oxide semiconductor field effect transistors (MOSFETs)) that are operated by different phases of the switching signal SW. For example, the switching system 102 may be arranged as a full bridge, half bridge, push-pull circuit, or any of a variety of other switching circuits.

[0020] The power supply system 100 also includes a transformer 104 that includes a primary winding L PRI and a secondary winding L SEC . For example, the switches of the switching system 102 may be operated to provide the input voltage V PRI as a square wave to the primary winding L PRI to provide a primary voltage V IN to the primary winding L PRI . As shown in the example of FIG. 1, the primary voltage V PRI may reverse polarity in each switching cycle of the switches of the switching system 102. Accordingly, the transformer 104 induces a secondary voltage V PRI in the secondary winding L PRI in response to the primary voltage V SEC being provided to the primary winding L SEC .

[0021] The power supply system 100 also provides an output voltage V SEC based on the secondary voltage V OUTincludes an output stage 106 that can provide. For example, the output voltage V OUT may have an amplitude approximately equal to the input voltage V IN multiplied by the turns ratio of the transformer 104. As described above, since the primary voltage V PRI can reverse its polarity, the secondary voltage V SEC can also reverse its polarity in each switching cycle of the switching frequency. Therefore, the output stage 106 is configured as a rectifier (e.g., a full-wave rectifier) that provides the positive amplitude of the output voltage V PRI inductively from each phase of the primary voltage V SEC between each phase of the secondary voltage V OUT . For example, other arrangements of the output stage 106 (e.g., as a voltage doubler) are also possible. The output voltage V OUT can be provided to the load, for example, via an output capacitor. As will be described in more detail herein, the switching frequency can be variable and can be load-based.

[0022] The power supply system 100 further includes a resonance capacitor C SEC coupled to the secondary winding L RES of the transformer 104. Therefore, the resonance capacitor C RES and the leakage inductance of the transformer reflected in the secondary winding L SEC can form a resonator (hereinafter referred to as a "secondary resonator") having a certain resonance frequency on the secondary side of the transformer 104. Based on coupling the resonance capacitor C RES to the secondary winding L SEC to form a secondary resonator, the power supply system 100 can be configured to operate at the frequency of the switching signal SW below the resonance frequency of the secondary resonator while maintaining a substantially constant target amplitude of the output voltage V OUT . As described herein, the term "substantially" can include some deviation (e.g., ±5%) from the exact value.

[0023] For example, the polarity of the primary voltage V PRI changes at the switching frequency, and the primary winding L PRIThe amplitude of the primary current passing through is approximately equal to zero between each phase of the switching signal SW. Therefore, the secondary voltage V SEC also changes its polarity at the switching frequency in the same way, and the amplitude of the current passing through the secondary winding L SEC is approximately equal to zero between each phase of the switching signal SW. When the secondary voltage V SEC changes its polarity at a switching frequency lower than the resonance frequency of the secondary resonator, the resonance capacitor C RES may have a residual voltage (e.g., less than the output voltage V OUT ) between each phase of the switching signal SW. When the current passing through the secondary winding L SEC has an amplitude that is approximately zero between each phase of the switching signal SW, the output stage 106 can separate the resonance capacitor C RES from the output of the power supply system 100 (e.g., based on the rectifier of the output stage 106). Therefore, the output stage 106 can act as an open circuit between the resonance capacitor C RES and the low voltage rail. Thus, no current resonates back to the leakage inductance reflected in the secondary winding L RES from the resonance capacitor C SEC , and therefore, the voltage across the resonance capacitor C SEC does not change when the amplitude of the current passing through the secondary winding L RES is approximately zero. Therefore, the output voltage V OUT also does not change at the zero amplitude of the current passing through the secondary winding L SEC between the phases of the switching signal SW.

[0024] As a result, unlike some alternative resonant power supply systems, the output voltage V OUT can be maintained at a substantially constant amplitude at a frequency of the switching signal SW equal to or lower than the resonance frequency of the secondary resonator. Therefore, regardless of the inherent variations that may be caused by the manufacturing tolerances and errors of the frequency of the switching signal SW and / or the resonance frequency of the secondary resonator, the switching signal SW can be set to a frequency lower than the resonance frequency of the secondary resonator to provide a constant amplitude of the output voltage V OUT . Therefore, in the power supply system 100, the output voltage V OUTThe amplitude error can be reduced.

[0025] For example, some alternative resonant power supply systems include a resonant capacitor in series with the primary winding of a transformer to resonate with the leakage inductance of the transformer reflected in the primary winding. In such a power supply system, when the switching frequency corresponding to the frequency of the bidirectional current pulse through the primary winding is equal to the resonant frequency of the leakage inductance and the resonant capacitor, the voltage across the leakage inductance is sent to both ends of the resonant capacitor at the resonant frequency with equal magnitude but opposite polarities. However, in such a power supply system, when the switching frequency is not equal to the resonant frequency of the primary winding and the resonant capacitor, the output voltage may exhibit an error. For example, when operating at a switching frequency higher than the resonant frequency, the load regulation may deteriorate. As another example, when the switching frequency is lower than the resonant frequency, the switches of some alternative converters continue to apply a voltage to the resonant capacitor through the magnetizing inductance of the transformer even after the current in the secondary winding has dropped to zero, thereby resulting in overcharging. The overcharging of the resonant capacitor increases the voltage of the resonant capacitor, and as a result, the output voltage of such a converter increases significantly.

[0026] Therefore, unlike some alternative converters, the power supply system 100 includes a resonant capacitor C PRI in series with the secondary winding L SEC rather than in series with the primary winding L RES . By providing the resonant capacitor C RES in series with the secondary winding L PRI (rather than in series with the primary winding L SEC ), after the current in the secondary winding L SEC has dropped to zero, no current can flow through the resonant capacitor C RES , thereby preventing the resonant capacitor C RES from being overcharged and the output voltage V OUT from increasing at a switching frequency below the resonant frequency.

[0027] The relationship between the frequency of the switching signal SW and the resonance frequency is shown in the example of FIG. 2. FIG. 2 shows an exemplary diagram 200 of a frequency / gain graph. Diagram 200 shows a first graph 202 that can correspond to an alternative power supply system. The first graph 204 plots the gain of the power supply system as a function of the switching frequency for the power supply system, and is the resonance frequency of the resonator formed by the resonance capacitor and the leakage inductance of the transformer (e.g., the ideal resonance frequency or the component rated resonance frequency), which is the frequency f RES is shown. The switching frequency of the first graph 202 is the frequency f RES which is the resonance frequency of the resonator formed by the resonance capacitor and the leakage inductance of the transformer. Large values along the X-axis are values of the switching frequency of the power supply system, and thus are higher than the resonance frequency f RES Small values along the X-axis are values of the switching frequency of the power supply system, and thus are lower than the resonance frequency f RES . The gain of the first graph 202 includes the unity gain "1" corresponding to the desired design amplitude of the output voltage. Large values along the Y-axis are values of the gain of the power supply system, which are greater than 1, and thus the amplitude of the desired output voltage is large. Small values along the Y-axis are values of the gain of the power supply system, which are less than 1, and thus the amplitude of the desired output voltage is small.

[0028] As described above, operating at a switching frequency higher than the resonance frequency f RES formed by the resonance capacitor and the leakage inductance in the power supply system can deteriorate the load regulation, and the output voltage can depend on variations in the switching frequency and the values of the resonance capacitance and the leakage inductance of the transformer. Therefore, the first graph 202 shows that the gain of the power supply system decreases at a switching frequency of the power supply system higher than the resonance frequency f RES . Also, as described above, when the switching frequency is the resonance frequency f RESAs the [resonant capacitor] experiences an overvoltage between consecutive half - switching cycles in response to [being lower], this overvoltage is added to the voltage of the primary winding of the transformer in the next switching cycle, thereby increasing the output voltage. Thus, the first graph 202 shows that at the switching frequency of the power supply system which is less than the resonant frequency f RES the gain increases significantly, so that the output voltage is boosted to an unacceptable level. Therefore, the switching frequency of the power supply system is set to approximately the resonant frequency f RES .

[0029] As described above, the switching frequency and / or the resonant frequency may be affected by inherent variations that can result from manufacturing tolerances and errors. In the example of FIG. 2, the inherent variations in the switching frequency and / or the resonant frequency are shown as a window bounded by the resonant frequency f RES which is equal but opposite to f sw+ and f sw- . Thus, if the switching frequency of the power supply system deviates or drifts from the resonant frequency f sw+ and f sw- within the inherent variations defined by the window bounded by them, the gain of the power supply system can vary significantly, and as a result, an error occurs in the desired output voltage V RES . OUT

[0030] FIG. 200 includes a second graph 204 that plots the gain of the power supply system 100 as a function of the switching frequency of the power supply system 100. For example, the gain may correspond to the gain of the output voltage V OUT , and the switching frequency may correspond to the frequency of the switching signal SW. The switching frequency of the second graph 204 includes the frequency f RES which is the resonant frequency of the secondary resonator (e.g., the ideal resonant frequency or the component - rated resonant frequency). Large values along the X - axis are values of the frequency of the switching signal SW and are thus higher than the resonant frequency f RES , and small values along the X - axis are values of the frequency of the switching signal SW and are thus lower than the resonant frequency f​RES is lower. The gain of the second graph 204 includes the unity gain "1" corresponding to the desired design amplitude of the output voltage V OUT . Large values along the Y-axis are the gain values of the power supply system 100, greater than 1, and thus the amplitude of the desired output voltage V OUT is large, and small values along the Y-axis are the gain values of the power supply system 100, less than 1, and thus the amplitude of the desired output voltage V OUT is small.

[0031] The second graph 204 shows that the gain of the power supply system 100 decreases at a frequency of the switching signal SW higher than the resonance frequency f RES . However, based on coupling the resonance capacitor C RES to the secondary winding L SEC to form a secondary resonator (different from the resonance capacitor coupled to the primary winding like the alternative converter related to the first graph 202), the second graph 204 also shows that the gain of the power supply system 100 is constant at a frequency of the switching signal SW below the resonance frequency f RES . Thus, the power supply system 100 can be configured to operate at a frequency of the switching signal SW below the resonance frequency f RES while maintaining the unity gain of the power supply system 100, and thus the desired amplitude of the output voltage V OUT is maintained.

[0032] For example, regardless of the inherent variations that may result from manufacturing tolerances and errors in the frequency of the switching signal SW and / or the resonance frequency, the switching signal SW can be set to a frequency lower than the resonance frequency f OUT to provide a constant amplitude of the output voltage V RES . For example, the frequency of the switching signal SW can be set to a frequency f RES lower than the resonance frequency f sw . In the example of FIG. 2, the inherent variations in the frequency of the switching signal SW and / or the resonance frequency are equal to but opposite f sw and f sw+ and fsw- is shown as a window bounded by. As a result, the frequency of the switching signal SW is such that f sw+ and f sw- is defined within a unique variation bounded by a window such that the switching frequency f sw deviates or drifts from, the gain of the power supply system 100 can remain unity, and thus, the error in the desired output voltage V OUT can be reduced. Therefore, the second graph 204 shows that if the power supply circuit 300 is designed such that the maximum possible frequency of the switching signal SW is lower than the minimum possible resonance frequency f RES (e.g., taking into account all variations), the output voltage V OUT becomes independent of the variation in the frequency of the switching signal SW and the actual resonance frequency of the secondary resonator.

[0033] FIG. 3 illustrates an example of a switching power supply circuit 300. The power supply circuit 300 can be implemented in any of a variety of circuit applications for efficiently providing an output voltage V IN based on an input voltage V OUT . The power supply circuit 300 can correspond to the power supply system 100 in the example of FIG. 1. Therefore, in the following description of the example of FIG. 3, reference is made to the examples of FIGS. 1 and 2.

[0034] The power supply circuit 300 includes a switching system 302 that includes a set of MOSFET switches that are periodically actuated in response to a switching signal SW. In the example of FIG. 3, the switching system 302 includes a first N-channel FET (NFET) N1 and a second NFET N2. The first NFET N1 receives the input voltage V INinterconnects with the first switching node 304, and the second NFET N2 interconnects the first switching node 304 with a low voltage rail (e.g., ground). The second NFET N2 is controlled at the gate by a switching signal SW, and the first NFET N1 is controlled at the gate by the inverted switching signal SW via an inverter 306. The switching system 302 also includes a third NFET N3 and a fourth NFET N4. The third NFET N3 interconnects an input voltage V IN with the second switching node 308, and the fourth NFET N4 interconnects the second switching node 308 with the low voltage rail. The fourth NFET N4 is controlled at the gate by the delayed switching signal SW provided via a delay element 310, and the third NFET N3 is controlled at the gate by the inverted delayed switching signal SW via an inverter 312.

[0035] Accordingly, the NFETs N1 to N4 are arranged as a full bridge. For example, the switching signal SW may correspond to a clock signal provided at a switching frequency. The delay element 310 may provide a static delay of the state transition of the switching signal SW (e.g., about half of the period of the resonance frequency of a secondary resonator). The power supply circuit 300 also includes a transformer 314 including a primary winding L PRI and a secondary winding L SEC . The primary winding L PRI is coupled to the first switching node 304 and the second switching node 308. Accordingly, the NFETs N1 to N4 can be sequentially actuated (e.g., turned on and off) by the switching signal SW to couple the input voltage V PRI to the primary winding L IN as a square wave and provide a primary voltage V PRI to the primary winding L PRI .

[0036] Based on the full-bridge arrangement of the switching system 302 and based on the delay provided by the delay element 310, the activation sequence of NFETs N1-N4 may result in four states of the switching system 302. In a first state, NFET N1 and NFET N4 are both activated. In a second state, NFET N3 and NFET N2 are both activated. In a third state, NFET N1 and NFET N3 are both activated. In a fourth state, NFET N2 and NFET N4 are both activated. Thus, in the third and fourth states, the primary winding L PRI is shorted and the primary voltage V PRI becomes zero. As described in more detail herein, the third and fourth states of the switching system 302 may facilitate load regulation of the power supply circuit 300.

[0037] As described above, in each switching cycle of the NFETs N1-N4 in the switching system 302 provided by the switching signal SW, the primary voltage V PRI The polarity of the primary voltage V PRI is the primary winding L PRI In response to being provided to the secondary winding L SEC At the secondary voltage V SEC This induces a secondary voltage V SEC Similarly, the first and second states of the NFETs N1-N4 in the switching system 302 are reversed in polarity in each switching cycle as provided by the switching signal SW.

[0038] The power supply circuit 300 also supplies a secondary voltage V SEC Based on the load resistor R L The output voltage across the load, denoted as V OUT 3, the output stage 316 includes an anode coupled to a first node 318 and a load resistor R Lincluding a first diode D1 having a cathode coupled to , and including a second diode D2 having an anode coupled to a low voltage rail (e.g., isolated from a low voltage rail in a switching system 302) and a cathode coupled to a first node 318. The output stage 316 also includes a third diode D3 having an anode coupled to a second node 320 and a cathode coupled to a load resistor R L and including a fourth diode D4 having an anode coupled to the low voltage rail and a cathode coupled to the second node 320. Thus, the output stage 316 is arranged as a full-wave rectifier that provides a positive amplitude of the output voltage V PRI between respective phases of the bidirectional secondary voltage V SEC induced from respective phases of the bidirectional primary voltage V OUT . The output stage 316 is shown by way of example in the example of FIG. 3 and can be arranged in any of a variety of different ways (e.g., as a voltage doubler) to provide the output voltage V SEC based on the secondary voltage V OUT .

[0039] The power supply circuit 300 further includes a resonant capacitor C SEC coupled to the secondary winding L RES of the transformer 314. Thus, as described above, the resonant capacitor C RES and the secondary winding L SEC can form a secondary resonator. As described above in the examples of FIGS. 1 and 2, based on coupling the resonant capacitor C RES to the secondary winding L SEC to form a secondary resonator, the power supply system 300 can be configured to operate at a frequency of the switching signal SW below the resonant frequency of the secondary resonator while maintaining the target amplitude of the output voltage V OUT . For example, between respective phases of the primary voltage V PRI for the primary winding L PRI , the current in the secondary winding L SEC is substantially zero. However, the current in the secondary winding L SECWhen the current of has substantially zero amplitude between each phase of the switching signal SW, the output stage 106 can isolate the resonant capacitor C (e.g., based on the rectifiers D1 - D4 of the output stage 316) from the output of the power supply circuit 300. Therefore, the output stage 316 can act as an open circuit between the resonant capacitor C and the low - voltage rail, and prevent the change in the voltage of the resonant capacitor C at the zero amplitude of the current of the secondary winding L. Thus, unlike an alternative resonant power supply system, the output voltage V RES can be maintained at a substantially constant amplitude at a frequency of the switching signal SW equal to or lower than the resonant frequency of the secondary resonator. Therefore, the switching signal SW is set to a frequency (e.g., f RES in the example of FIG. 2) lower than the resonant frequency of the secondary resonator (e.g., f SEC in the example of FIG. 2), and a constant amplitude of the output voltage V RES is provided. As a result, in the power supply circuit 300, the error in the amplitude of the output voltage V OUT can be reduced. RES ) such that the output voltage V sw can be maintained at a substantially constant amplitude. Therefore, the switching signal SW is set to a frequency (e.g., f OUT ) lower than the resonant frequency of the secondary resonator (e.g., f OUT ) of the secondary resonator, and a constant amplitude of the output voltage V

[0040] FIG. 4 illustrates an example of a switching power supply circuit 400. The power supply circuit 400 can be implemented in any of various circuit application examples for efficiently providing an output voltage V IN based on an input voltage V OUT . The power supply circuit 400 can correspond to the power supply system 100 in the example of FIG. 1. Therefore, in the following description of the example of FIG. 4, reference is made to the examples of FIGS. 1 and 2.

[0041] The power supply circuit 400 includes a switching system 402 that includes a set of MOSFET switches that are periodically actuated in response to a switching signal SW. In the example of FIG. 4, the switching system 402 includes a first NFET N1 and a second NFET N2. The first NFET N1 is connected to the input voltage V INinterconnects with the first switching node 404, and the second NFET N2 interconnects the first switching node 404 with a low voltage rail (e.g., ground). The second NFET N2 is controlled at its gate by the switching signal SW, and the first NFET N1 is controlled at its gate by the inverted switching signal SW via the inverter 406. The switching system 402 also includes a first capacitor C1 and a second capacitor C2. The first capacitor C1 interconnects the input voltage V IN with the second switching node 408, and the second capacitor C2 interconnects the second switching node 408 with the low voltage rail.

[0042] Accordingly, the NFETs N1 and N2, and the capacitors C1 and C2 are arranged as a half bridge. For example, the switching signal SW may correspond to a clock signal provided at a switching frequency. The power supply circuit 400 also includes a transformer 410 including a primary winding L PRI and a secondary winding L SEC . The primary winding L PRI is coupled to the first switching node 404 and the second switching node 408. Accordingly, the NFETs N1 and N2 can be sequentially actuated by the switching signal SW to couple the input voltage V PRI to the primary winding L IN as a square wave and provide a primary voltage V PRI to the primary winding L PRI . Based on the half bridge arrangement of the switching system 402, the actuation sequence of the NFETs N1 and N2 can result in two states of the switching system 402. In the first state, the NFET N1 is actuated. In the second state, the NFET N2 is actuated.

[0043] The switching system 402 also includes NFET N5 and NFET N6, each controlled by a signal SHT. NFET N5 is coupled to the first switching node 404 and NFET N6, and NFET N6 is coupled to the second switching node 408 and NFET N5. Thus, the signal SHT is provided to simultaneously activate NFET N5 and N6 so that the primary winding L PRI is short-circuited. For example, the signal SHT can be provided from a logic or state machine that periodically (e.g., in each cycle or many cycles of the switching signal SW) asserts the signal SHT, so that the amplitude of the primary voltage V PRI becomes zero and the primary winding L PRI is short-circuited. As will be described in more detail herein, short-circuiting the primary winding L PRI can facilitate load regulation of the power supply circuit 400.

[0044] As described above, in each switching cycle of NFET N1 and N2 in the switching system 402 provided by the switching signal SW, the polarity of the primary voltage V PRI is alternately reversed. Thus, in response to the primary voltage V PRI being provided to the primary winding L PRI , the transformer 410 induces a secondary voltage V SEC in the secondary winding L SEC . The secondary voltage V SEC similarly reverses its polarity in each switching cycle of NFET N1 and N2 in the switching system 402 provided by the switching signal SW.

[0045] The power supply circuit 400 also includes an output stage 412 that can provide an output voltage V SEC across the load shown as the load resistor R L based on the secondary voltage V OUT . In the example of FIG. 4, the output stage 412 includes a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4, and is thus arranged substantially the same as the output stage 316 in the example of FIG. 3.

[0046] The power supply circuit 400 further includes a resonance capacitor C coupled to the secondary winding L of the transformer 410. SEC coupled to the secondary winding L of the transformer 410. RES Thus, the resonance capacitor C RES and the secondary winding L SEC are arranged the same as those described above in the example of FIG. 3. Thus, the switching signal SW is set to a frequency (e.g., f in the example of FIG. 2) lower than the resonance frequency of the secondary resonator formed to provide a constant amplitude of the output voltage V OUT (e.g., f in the example of FIG. 2). As a result, in the power supply circuit 400, the error in the amplitude of the output voltage V RES can be reduced. sw )). As a result, in the power supply circuit 400, the error in the amplitude of the output voltage V OUT can be reduced.

[0047] FIG. 5 illustrates an example of a switching power supply circuit 500. The power supply circuit 500 can be implemented in any of various circuit application examples for efficiently providing an output voltage V based on an input voltage V IN based on an input voltage V OUT . The power supply circuit 500 can correspond to the power supply system 100 in the example of FIG. 1. Thus, in the following description of the example of FIG. 5, reference is made to the examples of FIGS. 1 and 2.

[0048] The power supply circuit 500 includes a switching system 502 that includes a set of MOSFET switches that are periodically activated in response to a switching signal SW. In the example of FIG. 5, the switching system 502 includes a first NFET N1 and a second NFET N2. The first NFET N1 interconnects a first switching node 504 and a low voltage rail (e.g., ground), and the second NFET N2 interconnects a second switching node 506 and the low voltage rail. The second NFET N2 is controlled at its gate by the switching signal SW, and the first NFET N1 is controlled at its gate by the inverted switching signal SW via an inverter 508.

[0049] Accordingly, NFETs N1 and N2 are arranged as a push-pull circuit. For example, the switching signal SW may correspond to a clock signal provided at a switching frequency. The power supply circuit 500 also includes a transformer 510 including a primary winding L PRI and a secondary winding L SEC . The input voltage IN is provided to the center tap of the primary winding L PRI , and the primary winding L PRI is coupled to a first switching node 504 and a second switching node 506. Accordingly, NFETs N1 and N2 can be sequentially actuated by the switching signal SW such that the primary voltage V IN is provided to the primary winding L PRI from the input voltage V PRI . Based on the push-pull arrangement of the switching system 502, the actuation sequence of NFETs N1 and N2 can result in two states of the switching system 502. In the first state, NFET N1 is actuated. In the second state, NFET N2 is actuated.

[0050] Also, the switching system 502 includes NFETs N5 and N6 each controlled by a signal SHT. NFET N5 is coupled to the first switching node 504 and NFET N6, and NFET N6 is coupled to the second switching node 506 and NFET N5. Accordingly, the signal SHT is provided to simultaneously actuate NFETs N5 and N6 such that the primary winding L PRI is short-circuited. For example, the signal SHT may be provided from a logic or state machine that asserts the signal SHT periodically (e.g., at each cycle or many cycles of the switching signal SW), so that the primary winding L PRI is short-circuited such that the amplitude of the primary voltage V PRI becomes zero. As will be described in more detail herein, the short-circuit of the primary winding L PRI can facilitate the load regulation of the power supply circuit 500.

[0051] As described above, in each switching cycle of NFETs N1 and N2 of the switching system 502 provided by the switching signal SW, the polarity of the primary voltage V PRI is alternately reversed. Therefore, in response to the primary voltage V PRI being provided to the primary winding L PRI , the secondary winding L SEC induces a secondary voltage V SEC . Similarly, the secondary voltage V SEC reverses its polarity in each switching cycle of NFETs N1 and N2 of the switching system 502 provided by the switching signal SW.

[0052] The power supply circuit 500 also includes an output stage 512 that can provide an output voltage V SEC across the load shown as the load resistor R L based on the secondary voltage V OUT . In the example of FIG. 5, the output stage 512 includes a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4, and is thus arranged substantially the same as the output stage 316 in the example of FIG. 3.

[0053] The power supply circuit 500 further includes a resonance capacitor C SEC coupled to the secondary winding L RES of the transformer 510. Therefore, the arrangement of the resonance capacitor C RES and the secondary winding L SEC is the same as that described above in the example of FIG. 3. Therefore, the switching signal SW can be set to a frequency (e.g., f RES in the example of FIG. 2) less than the resonance frequency of the secondary resonator (e.g., f sw in the example of FIG. 2), thereby providing a constant amplitude of the output voltage V OUT . As a result, in the power supply circuit 500, the error in the amplitude of the output voltage V OUT can be reduced.

[0054] FIG. 6 illustrates another example of a switching power supply system 600. The power supply system 600 has an input voltage VIN Based on the output voltage V OUT can be implemented in any of a variety of circuit applications for efficiently providing. The power supply system 600 includes a switching system 602 including at least one switch that is periodically operated in response to a switching signal SW. For example, the switching system 602 may correspond to any of the switching systems 302, 402, and 502 described above in each of the examples of FIGS. 3 to 5.

[0055] The power supply system 600 also includes a primary winding L PRI and a secondary winding L SEC a transformer 604 including, and an output voltage V OUT an output stage 606 that can provide. The power supply system 600 further includes a resonance capacitor C SEC coupled to the secondary winding L of the transformer 604 RES including. Accordingly, the power supply system 600 is configured to provide the output voltage V OUT in the manner described above with respect to the examples of FIGS. 1 to 5. In particular, the switching system 602 can operate the switch at a switching frequency less than the resonance frequency of the secondary resonator and can maintain the unity gain of the power supply system 600.

[0056] In the example of FIG. 6, the power supply system 600 also includes a load regulator 608. The load regulator 608 receives a primary current I PRI corresponding to the current from the switching system 602 through the primary winding L PRI and is shown to provide a switching signal SW and a signal SHT to the switching system 602. For example, the load regulator 608 may sample the amplitude of the primary current I PRI when the primary winding I PRI is short-circuited (e.g., during the third or fourth phase of the full-bridge switching system 302 in the example of FIG. 3, or in response to the operation of the signal SHT in the switching systems 402 and 502 in the examples of FIGS. 4 and 5, respectively). The load regulator 608 is for a load (e.g., the load R in the examples of FIGS. 3 to 5 Lconfigured to modify the frequency of the switching signal SW based on the resistance).

[0057] For example, the primary current I PRI is provided in each direction as a half-sine wave current pulse through the primary winding L PRI and, therefore, the secondary voltage V SEC is provided as a half-sine wave current pulse to the load resistor R L The average of the sine half-wave pulses is equal to the direct current provided to the load resistor R OUT shown as the output current I L in the example of FIG. 6. When the frequency of the switching signal SW is kept constant, the amplitude of the primary current I L and thus the secondary voltage V PRI increase in response to an increase in the load resistor R SEC Accordingly, the voltage drop across the equivalent resistance equal to the load resistor R L in series can increase, and as a result, the output voltage V OUT decreases.

[0058] As a result, the load regulator 608 can be configured to sample the primary current I L to adapt to the full value of the load resistor R L and adjust the frequency of the switching signal SW in response to a decrease in the load resistor R PRI to maintain the primary current I PRI at its peak value. Sampling of the primary current I PRI can occur when the primary current is approximately at its peak value. As described above, in the example of FIG. 3, the delay time of the delay element 310 can be set to approximately half the period of the resonance frequency of the secondary resonator. Accordingly, the primary winding L PRI is short-circuited at the alternating intervals between the alternating polarities of the primary current I PRI and the primary current I PRI is sampled at the peak amplitude of the primary current I PRI Similarly, the load regulator 608 can assert the signal SHT at appropriate intervals to sample the peak amplitude of the primary current I PRI For example, the load regulator can sample the primary current I PRICompare the peak amplitude with a reference value, and maintain the half-sine current pulse at the peak amplitude of the full-load resistance R L such that, for all values of the load resistance R L the voltage drop is made substantially equal across the total equivalent resistance in series with the load resistance R L . Thus, the load regulator 608 can adjust the frequency of the switching signal SW to adapt to changes in the value of the load resistance R L .

[0059] FIG. 7 illustrates another example of a power supply circuit 700. The power supply circuit 700 can be implemented in any of a variety of circuit applications for efficiently providing an output voltage V IN based on an input voltage V OUT . The power supply circuit 700 can correspond to the power supply system 600 in the example of FIG. 6. Thus, in the following description of the example of FIG. 7, reference is made to the example of FIG. 6

[0060] . The power supply circuit 700 includes a switching system 702 that includes a set of MOSFET switches that are periodically actuated in response to a switching signal SW. In the example of FIG. 7, the switching system 702 includes an NFET N1, a second NFET N2, a third NFET N3, and a fourth NFET N4. The switching system also includes a switching node 704, an inverter 706, a switching node 708, a first delay element 710, and an inverter 712. Thus, the switching system 702 is arranged as a full bridge as described above in the example of FIG. 3. The power supply circuit 700 also includes a primary winding I PRI that is part of a transformer (omitted for simplicity in the example of FIG. 7). For example, the primary winding L PRI can be coupled to a secondary winding L RES that provides a secondary voltage V SEC to a resonant capacitor C SEC and an output stage that provides an output voltage V L to a load resistance R OUT as described above in the examples of FIGS. 3-6

[0061] In the example of FIG. 7, the power supply circuit 700 also includes a load regulator 714. The load regulator 714 is coupled to a loop that provides the input voltage V IN to sample the primary current I PRI from the switching system 702. In the example of FIG. 7, the input voltage V IN is generated by a voltage source 718. The load regulator 714 includes an NFET N7 coupled to the connection 716 and the sampling capacitor C SMPL . The NFET N7 is controlled at its gate by the signal SMPL, and thus the NFET N7 is actuated by the signal SMPL to sample the peak amplitude of the primary current I PRI as a sampling voltage V SMPL across the sampling capacitor C SMPL . Accordingly, the sampling voltage V SMPL may have an amplitude proportional to the peak amplitude of the primary current I PRI through the primary winding L PRI . Accordingly, the amplitude of the sampling voltage V SMPL may likewise be proportional to the amplitude of the direct current I L through the load resistor R OUT as described above in the example of FIG. 6.

[0062] The sampling capacitor C SMPL is coupled to an error amplifier 720 configured to compare the sampling voltage V SMPL to a reference voltage V REF . The reference voltage V REF is shown as being generated by a voltage source 722 and provided through a resistor R1 in the example of FIG. 7. For example, the reference voltage V REF may be adjusted to represent the peak amplitude of the primary current I L for the full load of the load resistor R PRI . The error amplifier 720 is shown as having a feedback connection of the capacitor C FB and the resistor R FB , and thus the error amplifier 720 compares the sampling voltage V SMPL to the reference voltage V REFBased on the difference from, the control voltage V CTRL can be provided. The control voltage V CTRL is provided to the voltage controlled oscillator (VCO) 722 via the limiter circuit 724. The VCO 722 is configured to generate the switching signal SW at a frequency based on the amplitude of the control voltage V CTRL , and the limiter circuit 724 provides the upper and lower limits of the control voltage V CTRL to provide the respective maximum and minimum values of the frequency of the switching signal SW. Accordingly, as described above, the switching signal SW for controlling the NFETs N1 to N4 is provided to the switching system 702.

[0063] In the example of FIG. 7, the load regulator 714 further includes a derivative detector 726. The derivative detector 726 is configured to receive the primary current I PRI at the input and generate the signal SMPL at the output. For example, the derivative detector 726 may include analog or digital capabilities for determining the derivative of the amplitude of the primary current I PRI . Accordingly, the derivative detector 726 can monitor the derivative of the amplitude of the primary current I PRI . Accordingly, in response to determining the zero crossing of the derivative of the amplitude of the primary current I PRI , the derivative detector 726 can determine that the primary current I PRI has reached the peak amplitude. In response thereto, the derivative detector 726 can assert the signal SMPL to activate the NFET N7 to sample the peak amplitude of the primary current I PRI in each polarity of the flow of the bidirectional primary current I PRI through the primary winding L PRI .

[0064] In this way, the load regulator 730 adapts to the full value of the load resistor R L and adjusts the frequency of the switching signal SW based on the VCO 722 in response to the decrease of the load resistor R L to maintain the primary current I PRI at the peak value, the primary current I PRIcan be configured to sample. For example, the load regulator 722 samples the primary current I PRI and regulates the voltage V SMPL corresponding to the sampled peak amplitude of I to an amplitude level of the reference voltage V L corresponding to the total load resistance R REF so as to maintain the peak amplitude of the primary current I L regardless of the dynamic load resistance R PRI . Thus, the voltage loss across the series element at the output of the power supply circuit 700 can be maintained at a value independent of the load R L , thereby providing load regulation for the power supply circuit 700.

[0065] An example of the arrangement of the load regulator 714 is provided. However, other arrangements of the load regulator 714 can also be implemented to provide regulation of the frequency of the switching signal SW based on the load resistance R L . In the example of FIG. 7, the load regulator 714 is provided to operate, for example, with the switching system 702 arranged as a full-bridge circuit. Alternatively, other examples of the load regulator 714 for operating using a half-bridge and / or push-pull switching circuit, such as the switching circuits 402 and 502 described above in the respective examples of FIGS. 4 and 5, can also be implemented. For example, such a load regulator can include a logic and / or state machine configured to activate the signal SHT to cause a short circuit of the primary winding L PRI to facilitate sampling of the primary current I PRI . Thus, the load regulator 714 can be arranged in various manners.

[0066] FIG. 8 illustrates another example of a power supply circuit 800. The power supply circuit 800 can be implemented in any of various circuit application examples for efficiently providing the output voltage V IN based on the input voltage V OUT . The power supply circuit 800 can correspond to the power supply system 600 in the example of FIG. 6. Thus, in the following description of the example of FIG. 8, reference is made to the example of FIG. 6.

[0067] The power supply circuit 800 includes a switching system 802 that includes a set of MOSFET switches that are periodically actuated in response to a switching signal SW. In the example of FIG. 8, the switching system 802 includes NFET N1, a second NFET N2, a third NFET N3, and a fourth NFET N4. The switching system also includes a switching node 804, an inverter 806, a switching node 808, a first delay element 810, and an inverter 812. Thus, the switching system 802 is arranged as a full bridge, as described above in the example of FIG. 3. The power supply circuit 800 also includes a primary winding I that is part of a transformer PRI (omitted for simplicity in the example of FIG. 8). For example, the primary winding L PRI is coupled to a resonant capacitor C, similar to that described above in the examples of FIGS. 3-6, RES and a secondary winding L that provides a secondary voltage V SEC to a secondary winding L that provides an output voltage V SEC to a load resistor R L and an output stage that provides an output voltage V OUT can be coupled.

[0068] In the example of FIG. 8, the power supply circuit 800 also includes a load regulator 814. The load regulator 814 is coupled to a loop that provides an input voltage V IN shown at 816 to sample the primary current I PRI from the switching system 802. In the example of FIG. 8, the input voltage V IN is generated by a voltage source 818. The load regulator 814 includes an NFET N7 that is coupled to the connection 816 and a sampling capacitor C SMPL . The NFET N7 is controlled at its gate by a signal SMPL, and thus the NFET N7 is actuated by the signal SMPL to sample the peak amplitude of the primary current I PRI as a sampling voltage V SMPL for the sampling capacitor C SMPL . Thus, the sampling voltage V SMPL is the primary current I through the primary winding L PRI ​PRI may have an amplitude proportional to the peak amplitude of. Therefore, the amplitude of the sampling voltage V SMPL is also, as described above in the example of FIG. 6, proportional to the amplitude of the direct current I L through the load resistor R OUT .

[0069] The sampling capacitor C SMPL is coupled to an error amplifier 820 configured to compare the sampling voltage V SMPL with a reference voltage V REF . The reference voltage V REF is shown, in the example of FIG. 8, to be generated by a voltage source 822 and provided through a resistor R1. For example, the reference voltage V REF can be adjusted to represent the peak amplitude of the primary current I L for the full load of the load resistor R PRI . The error amplifier 820 is shown to have a feedback connection of the capacitor C FB and the resistor R FB , and thus the error amplifier 820 can provide a control voltage V SMPL based on the difference between the sampling voltage V REF and the reference voltage V CTRL . The control voltage VCTRL is provided to a voltage controlled oscillator (VCO) 822 through a limiter circuit 824. The VCO 822 is configured to generate a switching signal SW at a frequency based on the amplitude of the control voltage V CTRL , and the limiter circuit 824 provides upper and lower limits of the control voltage V CTRL to provide respective maximum and minimum values of the frequency of the switching signal SW. Therefore, as described above, a switching signal SW for controlling the NFETs N1 to N4 is provided to the switching system 802.

[0070] The switching signal SW is also provided to a third delay element 828 via a second delay element 826 and an inverter 830. For example, the second delay element 826 and the third delay element 828 can be set to have a delay approximately equal to 1 / 4 of the period of the resonance frequency of the secondary resonator. The second delay element 826 provides a signal DLY1 which is the switching signal SW delayed, and the third delay element 828 provides a signal DLY2 which is the switching signal SW inverted and delayed. The signals DLY1 and DLY2 are provided to an OR gate 832. The OR gate 832 is configured to generate a signal SMPL based on the signals DLY1 and DLY2. Based on the delay provided by the first delay element 810 and the delays provided by the delay elements 826 and 828, the OR gate 832 is for the primary winding L PRI through which the bidirectional primary current I PRI flows, the NFET N7 can be operated to sample the peak amplitude of the primary current I PRI at each polarity of the flow.

[0071] Thus, the load regulator 830 adapts to the full value of the load resistor R L and, in response to a decrease in the load resistor R L , adjusts the frequency of the switching signal SW based on the VCO822 so as to sample the primary current I PRI to maintain it at the peak value. For example, the load regulator 822 regulates a voltage V PRI corresponding to the sampled peak amplitude of the primary current I PRI to an amplitude level of a reference voltage V SMPL corresponding to the full load resistor R L so as to maintain the peak amplitude of the primary current I REF regardless of the dynamic load resistor R L . Thus, the voltage loss for the series element at the output of the power supply circuit 800 can be maintained at a value independent of the load R PRI , thereby providing load regulation of the power supply circuit 800. L Thereby, the voltage loss for the series element at the output of the power supply circuit 800 can be maintained at a value independent of the load R

[0072] The arrangement of the load regulator 814 is provided as an example. However, for providing regulation of the frequency of the switching signal SW based on the load resistance R L other arrangements of the load regulator 814 may also be implemented. In the example of FIG. 8, the load regulator 814 is provided to operate, for example, with the switching system 802 arranged as a full-bridge circuit. Alternatively, other examples of the load regulator 814 for operating using a half-bridge and / or push-pull switching circuit, such as the switching circuits 402 and 502 described above in the respective examples of FIGS. 4 and 5, may be implemented. For example, such a load regulator may include a logic and / or state machine configured to activate the signal SHT to cause a short circuit of the primary winding L PRI in order to facilitate sampling of the primary current I PRI . Thus, the load regulator 814 may be arranged in various manners.

[0073] In this description, the term "coupled" may include a connection, communication, or signal path that enables a functional relationship not inconsistent with this description. For example, if device A generates a signal for controlling device B to perform a certain operation, (a) in a first example, device A is directly coupled to device B, or (b) in a second example, device A is indirectly coupled to device B via an intervening component C, where the second example is a case where the intervening component C does not substantially change the functional relationship between device A and device B, such that device B is controlled by device A via the control signal generated by device A.

[0074] In this description, a device “configured” to perform a certain task or function can be configured (e.g., programmed and / or wired) by a manufacturer during manufacture to perform that function and / or can be configurable (or reconfigurable) by a user after manufacture to perform that function and / or other additional or alternative functions. Such configuration can be made via the firmware and / or software programming of the device, via the construction and / or layout of the hardware components, and / or via the interconnection of the device, or a combination thereof. Also, a circuit or device described herein as including certain components can instead be configured to couple to these components to form the described circuit elements or device. For example, a structure described herein as including one or more semiconductor elements (such as transistors), one or more passive elements (such as resistors, capacitors, and / or inductors), and / or one or more supply sources (such as voltage and / or current sources) can instead include only semiconductor elements within a single physical device (e.g., a semiconductor die and / or an integrated circuit (IC) package) and can be configured, either during or after manufacture, to couple to at least some of the passive elements and / or supply sources to form the described structure, for example, by an end user and / or a third party.

[0075] Within the scope of the claims, modifications to the described embodiments are possible and other embodiments are possible.

Claims

1. A circuit comprising: a transformer having a first transformer input, a second transformer input, a first transformer output adapted to be coupled to a first input of an output stage via a capacitor, and a second transformer output adapted to be coupled to a second input of the output stage; a switching system having a first input configured to receive a switching signal, a second input configured to receive an input voltage, a first switching output coupled to the first transformer input, and a second switching output coupled to the second transformer input, the switching system including a switch controlled by the switching signal; a load regulator having a first input configured to sample a current through a primary winding of the transformer and a first output configured to provide the switching signal to the first input of the switching system in response to a peak amplitude of the current; a derivative detector having an input configured to receive a signal indicative of an amplitude of the current through the primary winding and an output; a sampling switch coupled to the output of the derivative detector, the sampling switch configured to close in response to detecting a zero crossing of a derivative of the current to enable sampling of the peak amplitude of the current; the load regulator including; the circuit including.

2. The circuit according to claim 1, wherein the switching signal has a frequency less than a resonance frequency of the capacitor and a secondary winding of the transformer.

3. The circuit according to claim 1, wherein the switching system is arranged as one of a full bridge switching system, a half bridge switching system, and a push pull switching system.

4. The circuit according to claim 1, wherein the switching system further includes at least one switch configured to close to short circuit the first transformer input and the second transformer input, and the load regulator further has a second output configured to provide a short circuit signal to the at least one switch.

5. The circuit according to claim 1, wherein the load regulator includes a voltage controlled oscillator (VCO) having an input and an output corresponding to the first output of the load regulator. An input configured to receive a control signal proportional to the amplitude of the current, and a frequency adjustment component having an output coupled to the input of the VCO. A circuit further comprising. **Claim 6** The circuit according to claim 5, The load regulator further includes an amplifier having a first input configured to receive a reference voltage, a second input configured to receive a voltage proportional to the peak amplitude of the current, and an output configured to provide the control signal. A circuit. **Claim 7** A switching power supply system, A switching system having a switching input and a switching output, including a switch configured to close in response to a switching signal at the switching input, and configured to provide a first voltage at the switching output in response to closing the switch. The switching system, A transformer including a primary winding coupled to the switching output and configured to receive the first voltage, and a secondary winding configured to provide a second voltage in response to the first voltage. A capacitor coupled to the secondary winding, An output stage coupled to the capacitor and configured to generate an output voltage by rectifying the second voltage. The output stage, A load regulator configured to sample the amplitude of the current to adjust the frequency of the switching signal based on the peak amplitude of the current through the primary winding, A derivative detector having an input configured to receive a signal indicating the amplitude of the current through the primary winding and an output, A sampling switch coupled to the output of the derivative detector and configured to close so that the load regulator samples the peak amplitude of the current in response to detecting a zero crossing of the derivative of the current through the primary winding. The sampling switch, Including the load regulator, A switching power supply system including. **Claim 8** The switching power supply system according to claim 7, The switching power supply system, wherein the switching signal has a frequency less than the resonance frequency of the capacitor and the secondary winding of the transformer. **Claim 9** The switching power supply system according to claim 7, The load regulator is, A frequency adjustment component configured to generate a control voltage proportional to the amplitude of the current; A voltage controlled oscillator (VCO) configured to generate the switching signal at a frequency proportional to the control voltage; A switching power supply system further comprising.

10. The switching power supply system according to claim 9, wherein The load regulator is A sampling capacitor configured to sample a sampling voltage proportional to the peak amplitude of the current; An amplifier configured to compare the sampling voltage with a reference voltage and generate a control signal in response to the comparison; A switching power supply system further comprising.

11. A switching power supply system, comprising A transformer including a primary winding having first and second transformer inputs and a secondary winding having first and second transformer outputs; A switching system having a first input configured to receive a switching signal having a switching frequency, a second input configured to receive an input voltage, a first switching output coupled to the first transformer input, and a second switching output coupled to the second transformer input, the switching system including a switch controlled by the switching signal; A load regulator having a first input configured to sample the current through the primary winding of the transformer and a first output configured to provide the switching signal to the first input of the switching system in response to the peak amplitude of the current; A derivative detector having an input and an output, configured to receive a signal indicative of the amplitude of the current through the primary winding; A sampling switch coupled to the output of the derivative detector, configured to close so that the load regulator samples the peak amplitude of the current in response to detecting a zero crossing of the derivative of the current; A load regulator including; An output stage having a first voltage input, a second voltage input coupled to the second transformer output, and a voltage output configured to provide an output voltage in response to the first and second voltage inputs; A capacitor coupled between the first transformer output and the first voltage input; Including A switching power supply system in which the capacitor and the secondary winding have a resonance frequency higher than the switching frequency.

12. The switching power supply system according to claim 11, wherein the switching system further includes at least one switch configured to short-circuit the first transformer input and the second transformer input, and the load regulator further has a second output configured to provide a short-circuit signal to the at least one switch.

13. The switching power supply system according to claim 11, wherein the load regulator includes a voltage controlled oscillator (VCO) having an input and an output corresponding to the first output of the load regulator, and a frequency adjustment component having an input configured to receive a control signal related to the amplitude of the current and an output coupled to the input of the VCO. The switching power supply system further includes.

14. The switching power supply system according to claim 13, wherein the load regulator further includes an amplifier having a first input configured to receive a reference voltage, a second input configured to receive a voltage proportional to the peak amplitude of the current, and an output configured to provide the control signal.

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