Isolated capacitive power transfer

Abstract

This application relates to isolated capacitive power transfer. A method and apparatus for providing isolated power transfer to a low power load across a capacitor of a series resonant circuit is shown. The method includes comparing an output voltage received via a feedback loop to a desired output voltage. In response to determining that the output voltage is not equal to the desired output voltage, the method determines a sub-harmonic order of a resonant frequency of the series resonant circuit to use as a switching frequency, and switches the series resonant circuit substantially at the determined sub-harmonic order of the resonant frequency.

Description

[0001] Information related to divisional application

[0002] This case is a divisional application. The parent application of this divisional application is the invention patent application filed on October 21, 2016, with application number 201610920582.4 and entitled "Isolated Capacitive Power Transfer".

[0003] Priority claims and related patent applications

[0004] This non-provisional application claims priority based on the following prior U.S. provisional patent application: (i) U.S. Application No. 62 / 244,224, filed October 21, 2015, entitled “Harmonic Capacitive Power Transfer,” in the names of Lei Chen, Rajash Mukhopadhyay, and Mark W. Morgan; the entire contents of which are hereby incorporated by reference. Technical Field

[0005] The disclosed embodiments generally relate to the field of power transmission. More specifically, and not in any way, the present invention relates to improving the efficiency of low-power capacitive power transmission. Background Technology

[0006] In industrial sensor applications, such as those for temperature or pressure detection, isolation between the power supply and the analog front end is necessary for safety and equipment protection. The power interface requires resistance to common-mode transients that may exceed 100 kV / μs, making high-voltage isolation devices, such as transformers / capacitors, essential. In this setup, efficiency is difficult to maintain above 50% in the output power range below 50 mW, especially when significant parasitic resistance and capacitance are present in the high-voltage device. Additionally, for example, less than approximately 3 × 3 mm... 2 Furthermore, in some cases, a form factor of less than approximately 2 mm in width is crucial for sensor applications such as field emitters. However, the use of high-voltage transformers typically incurs significant area costs.

[0007] Currently, most (if not all) existing options in the isolated power supply market are transformer-based. These existing options cannot meet the aforementioned size requirements due to the significant space required to implement transformers, with several isolated power supply units having dimensions ranging from 7×7mm. 2 Up to 15×15mm 2 The dimensions vary. Additionally, existing options lack power efficiency in low-power regions, where efficiency varies from 10% to 40% at 25mW. Summary of the Invention

[0008] This patent application discloses a method and apparatus for improving the efficiency of a power converter that provides isolated power for low-power applications (e.g., 50mW or less). The applicant notes that 50mW is not an upper limit for the use of the disclosed method. If the tank impedance is sufficiently low, the technology does not have an upper limit on the output power level. However, the disclosed method has a more significant advantage for operation in low-power regions. The resonant power converter uses a series resonant circuit that provides an output voltage across a high-voltage capacitor, which is a component of the series resonant circuit. A feedback circuit includes isolated transmission of a feedback voltage from the receiver circuit to the power converter. The series resonant circuit operates at a subharmonic order of the resonant frequency to improve power transmission efficiency. Using feedback, a controller selects the largest subharmonic order of the resonant frequency that provides the necessary power output, and then fine-tunes one or both of the frequency and the input voltage to the series resonant circuit to achieve the desired output voltage. Both the subharmonic order and the input voltage can be adjusted during operation of the power converter to adapt to changing loads.

[0009] On one hand, an embodiment of an electronic device for providing isolated capacitive power transfer to a low-power load is disclosed. The electronic device includes: an inductor connected to a first terminal of a first capacitor to form a series resonant circuit across the first capacitor to provide an alternating current (AC) voltage to the low-power load; and a switching circuit connected to provide a switching voltage to the series resonant circuit at a subharmonic of the resonant frequency of the series resonant circuit.

[0010] On the other hand, an embodiment of a method for providing isolated power transfer to a low-power load via a capacitor across a series resonant circuit is disclosed. The method includes: determining whether an output voltage received via a feedback loop is equal to a desired output voltage; in response to determining that the output voltage is not equal to the desired output voltage, determining a subharmonic order of the resonant frequency of the series resonant circuit as a switching frequency; and switching the series resonant circuit substantially at the determined subharmonic order of the resonant frequency.

[0011] In another aspect, an embodiment of a method for providing isolated power transfer to a low-power load via a capacitor across a series resonant circuit is disclosed. The method includes: determining whether an output voltage received via a feedback loop is equal to a desired output voltage; in response to determining that the output voltage is not equal to the desired output voltage, determining a combination of an input voltage and a subharmonic order of the resonant frequency of the series resonant circuit that will provide the desired output voltage with maximum efficiency when used as a switching frequency; and in response to the determination, setting the input voltage to a determined value and setting the switching frequency to the determined subharmonic order of the resonant frequency.

[0012] The advantages of the disclosed operation include at least the following:

[0013] • When using high-voltage capacitors, the form factor of the entire isolated power delivery solution can be significantly reduced. In at least one embodiment, the chip area for the power delivery stage is reduced by more than 70% compared to a transformer-based solution;

[0014] • In harmonic operation, the resonant power converter can deliver up to 15 to 25 mW of power with 60% efficiency across a functional isolation barrier of 0.5 to 1 kV. This represents a 30% improvement in functional efficiency compared to basic operation.

[0015] • By eliminating the high-voltage transformer and utilizing a smaller die area, the overall solution cost is significantly reduced; and

[0016] Real-world feedback allows for adjustments to the load. Attached Figure Description

[0017] The embodiments of the invention are illustrated in the accompanying drawings by way of example rather than limitation, wherein similar element symbols indicate similar elements. It should be noted that different references to a “one” or “a” embodiment in the invention do not necessarily refer to the same embodiment, and such references may indicate at least one. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it should be assumed that implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge of those skilled in the art.

[0018] The accompanying drawings, incorporated in and forming a part of the specification, illustrate one or more exemplary embodiments of the invention. Various advantages and features of the invention will be understood from the following detailed description taken in conjunction with the appended claims and with reference to the accompanying drawings, wherein:

[0019] Figure 1 Examples of systems for isolated power conversion according to embodiments of the present invention are described;

[0020] Figure 2An example embodiment of a power output stage of a system for isolated power conversion according to an embodiment of the present invention is described;

[0021] Figure 3A D describes the various properties of the signal in the series resonant circuit of the power output circuit revealed;

[0022] Figure 4 Describes the maximum output power of an example system according to an embodiment of the present invention;

[0023] Figure 5A B describes some aspects of the decisions made to determine the switching frequency of the instance system;

[0024] Figure 6A The subharmonic order is described up to C as being related to switching frequency, power loss, and circuit efficiency;

[0025] Figure 7A To B, describe the effect of increasing the input voltage on the switching frequency and power loss in an example system according to an embodiment of the present invention;

[0026] Figure 8 A feedback circuit for use with a power output stage according to an embodiment of the present invention is described;

[0027] Figure 9A B describes a method for providing isolated capacitive power transfer across a capacitor in a series resonant circuit according to an embodiment of the present invention; and

[0028] Figures 10A to 10B A method for providing isolated capacitive power transfer across a series resonant circuit according to an embodiment of the present invention is described. Detailed Implementation

[0029] Reference will now be made to specific embodiments of the invention illustrated in the accompanying drawings. Numerous specific details are set forth in the following detailed description of embodiments of the invention to provide a more thorough understanding of the invention. However, those skilled in the art will appreciate that the invention can be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0030] Now refer to the diagram, and more specifically, refer to Figure 1 This diagram illustrates an example system 100 for power transfer across an isolation barrier according to an embodiment of the present invention. In system 100, a buck converter 102 receives an input voltage (not specifically shown) that is stepped down to a level usable by a series resonant circuit 103 of the power transfer system. This stepped-down voltage V is provided. IN This serves as the input to the 0° driver 108A and the 180° driver 108B. Driver 108 will switch the voltage V.LX A series resonant circuit 103 is provided, which includes inductors 104A and 104B and capacitors 106A and 106B. Capacitor 106 provides an isolation barrier across its power transmission. Parasitic capacitor C is also shown in this description. PAR1 C PAR2 Each of the inductors 104 is connected between the corresponding driver 108 and the corresponding capacitor 106 to provide an alternating current (AC) voltage across the capacitor 106. On the receiving side of the power transfer, the transferred voltage is received at a rectifier 114, which rectifies the voltage V... OUT The power supply is provided to the load (not specifically shown). The output voltage level is detected at output sensor 116 and provided to feedback controller 110 via feedback capacitor 112, which provides isolation in the feedback circuit. Feedback controller 110 can adjust the clock signal (CLK) and voltage V supplied to driver 108. IN Both. In at least one embodiment of this circuit, the input voltage to the buck converter 102 is in the range of 6 to 80 V. In at least one embodiment, the output voltage is 3.3 V, and the current output varies from 4 to 20 mA.

[0031] Figure 2 The diagram discloses the layout of an example of a power transmission circuit 200 according to an embodiment of the invention. This diagram is given primarily to demonstrate the small size achievable using the disclosed embodiment. As seen in the diagram, both the power transmission (chip 1) and receiver (chip 2) circuits are only about 2mm × 3mm in size. Inductors 204A and 204B are external inductors that can be included in the overall package without increasing the size. External inductors are used in this embodiment because of their higher Q factor; however, the disclosed device can also use internal inductors if a sufficiently high Q factor can be provided by internal inductors. In at least one embodiment, capacitor 206 is an internal capacitor. Figure 2 In the embodiments shown, capacitor 206 is, for example, a printed capacitor printed on top of the chip passivation layer using 3D printing technology. In at least one embodiment, capacitor 206 has a breakdown voltage of 1 kV and a capacitance of 12.5 pF / mm². 2 The capacitance density is such that the bare die area is less than 3.5 mm². 2 The base plates of capacitors 206 are connected to inductors 204, while the top plate wires of these capacitors are connected to the input pads of chip 2.

[0032] Before examining the operation of the power transmission system 100, we will quickly review some known factors that affect the resonant circuit. Figure 3A To D depict Figure 1 The signal V of the series resonant circuit 103LX Its various properties. Figure 3A In the middle, we see as from Figure 1 Two signals V LX+ and V LX- The sum of the resonant signals V LX V LX Having from V IN to -V IN Voltage swing and its switching frequency f SW The reciprocal period. In Figure 3B In the middle, the signal V LX Transforming into the frequency domain, we can see that: signal V LX The largest component appears at the switching frequency, while the smaller components are found at odd harmonic frequencies, such as 3f. SW 5f SW 7f SW And so on. Although this diagram is not drawn to scale, on 3f SW The power provided at this point is approximately one-third of the power at the switching frequency; at 5f SW The power at the switching frequency is about one-fifth of the power at the switching frequency, and so on. Therefore, as one moves to a higher harmonic of the switching frequency, the maximum available power decreases. Figure 3C The illustration shows a Bode plot of the magnitude of the transfer function of the resonant circuit, which peaks at the switching frequency and decreases rapidly in both directions. Figure 3D This illustrates the current spectrum of a resonant circuit that appears only at the switching frequency. These plots illustrate how a series inductor-capacitor (LC) assembly (e.g., series resonant circuit 103) allows signals at the resonant frequency to pass through and blocks signals of any other frequency from reaching the load.

[0033] Figure 4 The circuit plotted with harmonic order comparison to obtain power has maximum power output P. OUTThe diagram illustrates the harmonic order, which reflects the ratio of the resonant frequency to the switching frequency. It can be seen that if power is obtained at the third harmonic (i.e., the switching frequency is one-third of the resonant frequency), the circuit shown has a usable power slightly higher than 160mW. If power is obtained at the fifth harmonic (where the switching frequency is one-fifth of the resonant frequency), the same circuit has a usable power of approximately 60mW; and if power is obtained at the eleventh harmonic (where the switching frequency is one-eleventh of the resonant frequency), the usable power is approximately 15mW. A question might arise: why would anyone then want to operate the resonant circuit at any frequency lower than the resonant frequency? The applicant has realized that although the usable power decreases significantly when the switching frequency is a sub-harmonic of the resonant frequency, the circuit efficiency is significantly improved. Therefore, when the required power output is low, it is advantageous to operate the circuit at a sub-harmonic frequency of the resonant frequency to achieve circuit efficiency.

[0034] Figure 5A Section B is used to illustrate the operation of the disclosed circuit at two different sub-harmonic levels. In this example of operation, the series resonant circuit is designed to operate at a resonant frequency f of 30 MHz. R Instead of tuning the series resonant circuit to the switching frequency f. SW =f R The series resonant circuit is tuned to the fifth sub-harmonic, thus providing a switching frequency of 6MHz. The switching frequency will still be based on f... R Obtain the output; in this case, f R It is 5*f SW In one instance, operating at this level would provide 25mW, which might be sufficient for a given load. However, if the load changes, such that (for example) the output in the diagram is higher than f... R The curve indicates that 50mW is currently required on the output side, which may not be sufficient for operation at the fifth harmonic. To provide additional power, the circuit changes the switching frequency to operate at the third harmonic, which can supply the necessary output. Operation at the third harmonic is less efficient than operation at the fifth harmonic, as will be discussed below, but it still provides higher efficiency than the previous solution.

[0035] Figure 6AThis diagram illustrates the frequency response to various subharmonic orders for a specific resonant circuit designed with a resonant frequency of 29.4 MHz. In one embodiment, the inductor L = 720 nH, the series capacitance Cs = 10 pF (due to area constraints), and the parasitic capacitance Cp = 33 pF. If the circuit operates at the third harmonic, the switching frequency drops to just below 10 MHz, while operating at the fifth harmonic results in a switching frequency of approximately 6 MHz. Further frequency reductions are observed at higher harmonic orders. Because higher-order subharmonics require smaller switching, switching losses decrease with increasing subharmonic order. Figure 6B The graph illustrates the correlation between power loss and subharmonic order. As the frequency moves from the fundamental frequency to the third, seventh, eleventh, and fifteenth subharmonic orders, the power loss decreases progressively from 35mW to approximately 13mW, 5.7mW, 3.75mW, and 2.5mW, respectively. Figure 6C This illustrates the efficiency achieved when using larger subharmonic orders. At the fifth subharmonic order, the efficiency is approximately 53%; at the seventh subharmonic order, the efficiency increases to approximately 57%; at the ninth subharmonic order, the efficiency is approximately 59%; and at the eleventh subharmonic order, the efficiency is approximately 61%.

[0036] Figure 7A Explain the input voltage V IN The relationship between the subharmonic order and the resonant circuit allows it to operate on the subharmonics while maintaining constant power. This is confirmed by the graph, where V... IN An increase in input power allows for the use of a lower switching frequency while maintaining output power. Those skilled in the art will understand from this that if the subharmonic order remains constant, a larger input voltage will provide an increase in output power. The applicant has recognized that this relationship can be utilized in several ways. In at least one embodiment, adjusting the input power provides a way to fine-tune the circuit after the subharmonic order has been selected. In at least one embodiment, a larger increase in input power allows the circuit to operate at a higher subharmonic order, thereby providing additional savings in switching losses. Methods associated with these two embodiments will be discussed below. Figure 7B This is the final graph confirming the power loss attributable to both switching and conduction losses in the revealed circuit. Conduction losses are due to the loss of current circulating in the resonant circuit, while switching losses are attributable to the power loss each time the switch is operated. The graph clearly shows that as the subharmonic order increases, conduction losses rise very slowly, while switching losses decrease significantly, making it desirable to operate at higher subharmonic orders whenever possible.

[0037] Figure 8An example feedback circuit 800 for use with the disclosed capacitive power transfer is disclosed. In at least one embodiment, feedback is obtained from the receiver chip rather than directly from the circuitry of the series resonant circuit. In this embodiment, capacitor 812 provides isolation between the chip containing the power supply (chip 1) and the chip containing the receiver (chip 2). By measuring the output voltage at the receiver, rather than the output voltage on the output side, this circuit is able to provide an accurate picture of the actual operating voltage at the load and make the circuit more responsive to changes in the load. In the illustrated example, hysteresis comparator 816 receives the voltage V experienced by the load. OUT The square wave output is provided to modulator 817, which in turn provides the modulated AC voltage to the first terminal of capacitor 812. The second terminal of capacitor 812 is connected to demodulator 811, which provides the demodulated signal to integrator 810. The output of integrator 810 is used to adjust the digitally controlled oscillator (DCO) that provides the clock to the switching circuit, and to adjust the input voltage provided to the switching circuit (not specifically shown). Adjusting the DCO may involve changing a subharmonic of the resonant frequency at which the DCO is operating, or providing a smaller adjustment to the frequency to fine-tune the operating frequency of the series resonant circuit.

[0038] Figure 9A Method 900, disclosed in section B, provides isolated capacitive power transfer across a capacitor in a series resonant circuit according to an embodiment of the present invention. Figure 9A In this method, 900A begins by determining whether the output voltage of the (905) series resonant circuit is equal to the desired output voltage. If the two voltages are equal, the method continues to monitor the output voltage until action is required. If the two voltages are not equal, adjustments need to be made to the subharmonic order corresponding to the resonant frequency used as the switching frequency or to the input voltage supplied to the switching circuit. The method determines an appropriate subharmonic order of the (910) resonant frequency to be used as the switching frequency. It should be noted that if the voltage change is small, the current subharmonic order may still be appropriate, requiring only minor adjustments to the switching frequency or the input voltage. For larger voltage changes, a change to the subharmonic order may be necessary. Once the appropriate subharmonic order is determined, the method switches the (915) series resonant circuit at the determined switching frequency. Figure 9B In this method, 900B determines (920) whether fine-tuning of the output voltage is required. If fine-tuning is indeed required, the method fine-tunes at least one of the switching frequency and the input voltage (925).

[0039] Figure 10A Method 1000, which discloses an alternative embodiment of the invention, provides isolated capacitive power transfer across a series resonant circuit using a capacitor. Figure 10AIn this method 1000A, the process begins by determining (1005) whether the output voltage of the series resonant circuit is equal to the desired output voltage. If the two voltages are equal, the method continues to monitor the output voltage until action is required. If the two voltages are not equal, the method determines (1010) the combination of the input frequency and the subharmonic order of the resonant frequency, which will be used as the switching frequency to provide the desired power with maximum efficiency. If the voltage change is small, the current combination may still be appropriate, requiring only minor adjustments to the switching frequency or the input voltage. For larger voltage changes, it may be necessary to modify the combination of the input voltage and the subharmonic order. Once the appropriate subharmonic order is determined, the method sets the input voltage (1015) to a determined value and sets the switching frequency (1020) to the determined subharmonic order. The series resonant circuit is then operated (1025) using the determined values. Figure 10B In method 1000B, it is determined (1030) whether the output voltage needs to be fine-tuned. If no fine-tuning of the output is required, then the method fine-tunes at least one of the switching frequency and the input voltage (1035).

[0040] Although various embodiments have been shown and described in detail, the claims are not limited to any particular embodiment or instance. The detailed description above should not be construed as implying that any particular component, element, step, action, or function is necessary to be included within the scope of the claims. References to elements in the singular do not necessarily mean "one and only one," but rather "one or more" unless expressly stated otherwise. All structural and functional equivalents of the elements of the embodiments described above, known to those skilled in the art, are expressly incorporated herein by reference and are intended to be covered by these claims. Therefore, those skilled in the art will recognize that the exemplary embodiments described herein can be practiced with various modifications and variations within the spirit and scope of the appended claims.

Claims

1. An electronic device, the electronic device comprising: A clock that has an output; A first phase driver has an input and an output, the input of the first phase driver being connected to the output of the clock, and the output of the first phase driver being configured to couple to a first terminal of a capacitor-based resonant circuit having a resonant frequency, the first phase driver being configured to provide a first signal having a frequency based on a subharmonic of the resonant frequency at the first terminal to transmit power via the resonant circuit, wherein the frequency of the first signal is less than the resonant frequency. as well as A second phase driver having an input and an output, the input of the second phase driver being connected to the output of the clock, and the output of the second phase driver being configured to couple to a second terminal of the resonant circuit, the second phase driver being configured to provide a second signal having the frequency for transmitting power via the resonant circuit.

2. The electronic device according to claim 1, further comprising: A rectifier connected to the second terminal of a first capacitor and the second terminal of a second capacitor provides a rectified voltage to a load, wherein the first terminal of the first capacitor is coupled to the output of the first phase driver, and the first terminal of the second capacitor is coupled to the output of the second phase driver.

3. The electronic device according to claim 2, further comprising: A feedback circuit, wherein the feedback circuit is configured to change the subharmonic of the resonant frequency in response to a change in the load, and the first phase driver and the second phase driver operate with the subharmonic.

4. The electronic device of claim 3, wherein the feedback circuit receives voltage information across a feedback capacitor, the feedback capacitor having a capacitance smaller than that of the first capacitor.

5. The electronic device according to claim 4, further comprising: A buck converter configured to provide an input voltage to the first phase driver.

6. The electronic device of claim 5, wherein the feedback circuit is further configured to fine-tune the frequency of one or both of the first signal and the second signal.

7. The electronic device of claim 6, wherein the feedback circuit is further configured to adjust the input voltage provided by the buck converter.

8. The electronic device of claim 7, wherein the first capacitor is located on top of a silicon chip containing the electronic device.

9. The electronic device according to claim 8, wherein the resonant circuit is an external resonant circuit.

10. The electronic device of claim 9, wherein the feedback circuit comprises: A hysteresis comparator configured to receive the rectified voltage; A modulator configured to receive an output from the hysteresis comparator and provide a digital signal reflecting the rectified voltage to a first terminal of the feedback capacitor; A demodulator configured to receive the digital signal at the second terminal of the feedback capacitor; as well as An integrator configured to receive the output of the demodulator and control the switching frequency and input voltage of the first phase driver and the second phase driver.

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