Charge pump using tunable capacitor

Abstract

A voltage supply circuit generates a voltage on a voltage supply node. The voltage supply circuit includes an adjustable capacitor, an AC voltage source, a charge source, and an adjustment circuit. The voltage on the first capacitor terminal also becomes low when the AC voltage on the second capacitor terminal transitions to low, and the charge source provides charge to the first capacitor terminal of the tunable capacitor. When the AC voltage on the second capacitor terminal transitions to high, the voltage on the first capacitor terminal also becomes high, and thereby charges are pumped from the first capacitor terminal to the voltage supply node. The adjustment circuit periodically samples a voltage on the voltage supply node and adjusts a capacitance of the adjustable capacitor to increase or decrease the voltage.

Description

Technical Field

[0001] The present application relates to the field of voltage supply circuits, and in particular, to a charge pump for such a circuit, wherein the charge pump is regulated using an adjustable capacitor to provide an appropriate charge, thereby providing an appropriate voltage. Background Art

[0002] Electronic circuits often include transistors, which act as electronic switches that regulate or control the flow of current in part of the circuit. One type of transistor is a field effect transistor, in which a voltage is applied to a gate terminal to turn the transistor on and off. A semiconductor channel region is disposed between a drain terminal and a source terminal. When the transistor is turned on, current flows through the semiconductor channel region between the source terminal and the drain terminal. When the transistor is turned off, less or no current flows through the semiconductor channel region between the source terminal and the drain terminal. A gate terminal is disposed across the semiconductor channel region between the source terminal and the drain terminal. The voltage on the gate terminal creates a field that affects whether the semiconductor channel region conducts current, hence the term "field effect transistor."

[0003] However, there are other types of transistors. In each transistor, when the transistor is turned on by applying a sufficient voltage to the control node, current flows from the input node to the output node through the channel. For example, in a field effect transistor, the control node will be the gate terminal, the input node will be one of the source or drain terminals, and the output node will be the other of the source or drain terminals.

[0004] Typical transistors are used for amplification and switching purposes in electronic circuits. Power transistors, on the other hand, are used to carry larger amounts of current, have higher voltage ratings, and may be more typically used in power supplies, battery charging, etc. Power transistors may typically operate at currents greater than 1 ampere up to a hundred amperes or even greater. Power transistors may carry power from greater than 1 watt to several hundred watts or even greater.

[0005] Thus, a power transistor may have a specific power safety rating at which the power transistor may safely operate normally for an extended period of time. However, a power transistor may operate in an overdrive mode in which the power transistor may operate above its specified power safety rating for a short period of time without causing significant damage to the power transistor. A power transistor may be pushed into an overdrive mode by, for example, applying a higher control voltage to its control node that is greater than a sufficient control voltage to turn on the power transistor so that the power transistor operates normally.

[0006] The subject matter claimed herein is not limited to implementations that solve any disadvantages or that operate only in environments such as described above. Rather, this background is merely provided to illustrate one example technology area in which some implementations described herein may be practiced. Summary of the invention

[0007] This summary is provided to introduce some concepts in a simplified form that are further described in the following detailed description. This summary is not intended to identify key features or essential features of the described subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0008] Embodiments described herein relate to a voltage supply circuit that generates a voltage on a voltage supply node. As a specific example, the voltage supply circuit can use the voltage generated on the voltage supply node to control the operation of a power transistor (e.g., a field effect transistor). For example, the voltage supply circuit can cause the power transistor to be turned off (e.g., by applying 0V to a control node of the power transistor), turned on (e.g., by applying 6V), or put into an overdrive mode (e.g., by applying 8V). However, the principles described herein are not limited to how the voltage generated on the voltage supply node is used.

[0009] The voltage supply circuit includes an adjustable capacitor, an AC voltage source, and a charge source. The adjustable capacitor has two capacitor terminals. One of the capacitor terminals (referred to herein as the "first capacitor terminal") is coupled to a voltage supply node and a charge source. The opposite terminal (referred to herein as the "second capacitor terminal") is connected to an AC voltage source that provides an AC voltage to the second capacitor terminal, wherein the AC voltage alternates in a repeating cycle, each cycle including a transition low and a transition high.

[0010] When the AC voltage on the second capacitor terminal changes to low, the voltage on the first capacitor terminal is connected to the charge source, which provides charge to the first capacitor terminal of the adjustable capacitor. On the other hand, when the AC voltage on the second capacitor terminal changes to high, the first terminal is coupled to the voltage supply node, and charge is thereby pumped from the first capacitor terminal to the voltage supply node. Thus, the adjustable capacitor, the AC voltage source, and the charge source can be used to supplement the voltage generated on the voltage supply node by pumping charge to the voltage supply node in each cycle.

[0011] In order to supplement the correct amount of voltage to the voltage supply node in each cycle, the voltage supply circuit further includes a regulating circuit. The regulating circuit periodically (e.g., once per AC voltage cycle) samples the voltage on the voltage supply node and determines whether the voltage on the voltage supply node is too low below the specified voltage or too high above the specified voltage. If the regulating circuit determines that the voltage on the voltage supply node is too low below the specified voltage, the regulating circuit adjusts the capacitance of the adjustable capacitor upward. Increasing the capacitance of the adjustable capacitor increases the amount of charge pumped to the voltage supply node by the adjustable capacitor in one cycle. Therefore, by increasing the capacitance of the adjustable capacitor, the voltage generated on the voltage supply node can be increased to be closer to the specified voltage.

[0012] In addition, if the regulation circuit determines that the voltage on the voltage supply node is too high above the specified voltage, the regulation circuit adjusts the capacitance of the adjustable capacitor downward. Reducing the capacitance of the adjustable capacitor reduces the amount of charge that the adjustable capacitor pumps to the voltage supply node in one cycle. Therefore, by reducing the capacitance of the adjustable capacitor, the voltage generated on the voltage supply node can be reduced to be closer to the specified voltage.

[0013] Thus, by adjusting the capacitance of the adjustable capacitor upward or downward depending on whether the sampled voltage on the voltage supply node is less than or greater than the specified voltage, respectively, the voltage supply circuit is able to accurately generate the specified voltage on the voltage supply node (or carefully control the voltage). In addition, frequent automatic capacitance adjustments allow the voltage supply circuit to continue to accurately generate the specified voltage on the voltage supply node, continuously compensating for changes such as aging of components in the voltage supply circuit, operating temperature changes, or other sudden or gradual environmental changes. In addition, because the capacitance will be adjusted during normal operation, fine-tuning the capacitance of the adjustable capacitor to account for device-to-device manufacturing deviations or defects can be avoided.

[0014] Additional features and advantages will be given in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present technology. The features and advantages of the present invention can be realized and obtained by the instruments and combinations particularly pointed out in the appended claims. The features of the present invention will become more apparent from the following description and the appended claims, or can be learned through the practice of the present invention as described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to describe the manner in which the advantages and features of the systems and methods described herein can be obtained, a more particular description of the embodiments briefly described above will be rendered by reference to specific embodiments thereof illustrated in the accompanying drawings. Understanding that these drawings depict only typical embodiments of the systems and methods described herein and are therefore not to be considered limiting of their scope, certain systems and methods will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:

[0016] Figure 1 A voltage supply circuit is illustrated in which the principles described herein may be practiced and is merely one example of a voltage supply circuit consistent with the principles described herein;

[0017] Figure 2 Description Figure 1 A flow chart of an example method of operation of a voltage supply circuit during a single cycle of an alternating voltage;

[0018] Figure 3 Explained as Figure 1An adjustable capacitor bank of an example of an adjustable capacitor;

[0019] Figure 4 illustrates a voltage supply circuit which is Figure 1 An example of a voltage supply circuit;

[0020] Figure 5 illustrates a voltage supply circuit which is Figure 1 The voltage supply circuit and Figure 4 An example of a voltage supply circuit; and

[0021] Figure 6 The control node is connected to different voltage sources (including internally generated voltage sources) to repeatedly alternate Figure 5 A signal diagram of an example simulation of a voltage supply circuit. DETAILED DESCRIPTION

[0022] Embodiments described herein relate to a voltage supply circuit that generates a voltage on a voltage supply node. As a specific example, the voltage supply circuit can use the voltage generated on the voltage supply node to control the operation of a power transistor (e.g., a field effect transistor). For example, the voltage supply circuit can cause the power transistor to be turned off (e.g., by applying 0V to a control node of the power transistor), turned on (e.g., by applying 6V), or put into an overdrive mode (e.g., by applying 8V). However, the principles described herein are not limited to how the voltage generated on the voltage supply node is used.

[0023] The voltage supply circuit includes an adjustable capacitor, an AC voltage source, and a charge source. The adjustable capacitor has two capacitor terminals. One of the capacitor terminals (referred to herein as the "first capacitor terminal") is coupled to a voltage supply node and a charge source. The opposite terminal (referred to herein as the "second capacitor terminal") is connected to an AC voltage source that provides an AC voltage to the second capacitor terminal, wherein the AC voltage alternates in a repeating cycle, each cycle including a transition low and a transition high.

[0024] When the AC voltage on the second capacitor terminal turns to low, the first capacitor terminal is coupled to the charge source, and the charge source provides charge to the first capacitor terminal of the adjustable capacitor. On the other hand, when the AC voltage on the second capacitor terminal turns to high, the first capacitor terminal can be decoupled from the charge source and coupled to the voltage supply node, and charge is thereby pumped from the first capacitor terminal to the voltage supply node. Therefore, the adjustable capacitor, the AC voltage source, and the charge source can be used to supplement the voltage generated on the voltage supply node by pumping charge to the voltage supply node in each cycle.

[0025] In order to supplement the correct amount of voltage to the voltage supply node in each cycle, the voltage supply circuit further includes a regulating circuit. The regulating circuit periodically (e.g., once per AC voltage cycle) samples the voltage on the voltage supply node and determines whether the voltage on the voltage supply node is too low below the specified voltage or too high above the specified voltage. If the regulating circuit determines that the voltage on the voltage supply node is too low below the specified voltage, the regulating circuit adjusts the capacitance of the adjustable capacitor upward. Increasing the capacitance of the adjustable capacitor increases the amount of charge pumped to the voltage supply node by the adjustable capacitor in one cycle. Therefore, by increasing the capacitance of the adjustable capacitor, the voltage generated on the voltage supply node can be increased to be closer to the specified voltage.

[0026] In addition, if the regulation circuit determines that the voltage on the voltage supply node is too high above the specified voltage, the regulation circuit adjusts the capacitance of the adjustable capacitor downward. Reducing the capacitance of the adjustable capacitor reduces the amount of charge that the adjustable capacitor pumps to the voltage supply node in one cycle. Therefore, by reducing the capacitance of the adjustable capacitor, the voltage generated on the voltage supply node can be reduced to be closer to the specified voltage.

[0027] Thus, by adjusting the capacitance of the adjustable capacitor upward or downward depending on whether the sampled voltage on the voltage supply node is less than or greater than the specified voltage, respectively, the voltage supply circuit is able to accurately generate the specified voltage on the voltage supply node (or carefully control the voltage). In addition, frequent automatic capacitance adjustments allow the voltage supply circuit to continue to accurately generate the specified voltage on the voltage supply node, continuously compensating for changes such as aging of components in the voltage supply circuit, operating temperature changes, or other sudden or gradual environmental changes. In addition, because the capacitance will be adjusted during normal operation, fine-tuning the capacitance of the adjustable capacitor to account for device-to-device manufacturing deviations or defects can be avoided.

[0028] Figure 1 A voltage supply circuit 100 in which the principles described herein may be practiced is illustrated, and is merely one example of a voltage supply circuit consistent with the principles described herein. The voltage supply circuit 100 is configured to supply a voltage to a voltage supply node 101. The voltage on the voltage supply node 101 may be used to provide power to a component (not shown) that may be coupled to the voltage supply circuit 100 (e.g., a power transistor (not shown)). However, the principles described herein are not limited to the type of component that receives power from the voltage supply node 101, and / or the reason for generating the voltage on the voltage supply node 101.

[0029] Voltage supply circuit 100 includes adjustable capacitor 110, AC voltage source 120, and charge source 130. In one embodiment, charge source 130 may be powered by voltage supply node 101. However, the principles described herein are not limited to how charge source 130 receives power.

[0030] The adjustable capacitor 110 is "adjustable" because the adjustable capacitor 110 has a capacitance that can be adjusted. The adjustability of the capacitance is used to control the voltage present on the voltage supply node 101, which will be described below. The adjustable capacitor has two terminals. One terminal 111 (hereinafter referred to as "first terminal 111") is coupled to both the voltage supply node 101 and the charge source 130. The other terminal 112 (hereinafter referred to as "second terminal 112", only for distinguishing from the first terminal 111) is connected to the AC voltage source 120.

[0031] In this specification and claims, circuit elements are "connected" to each other if they are directly connected without any explicit intermediate circuit elements connected between them. For example, the AC voltage source 120 and the second capacitor terminal 112 are "connected" because there are no explicit intermediate circuit elements between the AC voltage source 120 and the second capacitor terminal 112. All real circuit parts have some non-ideal electrical characteristics, such as "parasitic" resistance, inductance, or capacitance. Therefore, two circuit elements are "connected" to each other even if a conductor with some resistance can connect the two circuit elements.

[0032] On the other hand, circuit elements are "coupled" to each other if charge can be transferred from one of these circuit elements to another circuit element, either because the circuit elements are connected or because charge can be transferred via some intermediate circuit element if certain conditions are met. For example, ellipsis 102 indicates that the charge source 130 and the first capacitor terminal 111 are "coupled" together, directly or via some intermediate circuit element, so that charge flows from the charge source 130 to the first capacitor terminal 111 if a condition is met. The condition may be that the voltage present at the first capacitor terminal 111 is a threshold voltage lower than the voltage present at the charge source 130. Ellipsis 103 indicates that the first capacitor terminal 111 and the voltage supply node 101 are "coupled" together so that charge can be transferred from the first capacitor terminal 111 to the voltage supply node 101 when a condition is met. The condition may be that the voltage present at the first capacitor terminal 111 is a threshold voltage higher than the voltage present at the voltage supply node 101.

[0033] The AC voltage source 120 provides an AC voltage to the second capacitor terminal 112. The AC voltage alternates between two voltage levels within a repeating cycle. For example, when the AC voltage transitions to low, the AC voltage decreases from a higher voltage (also referred to herein as the "second voltage") to a lower voltage (also referred to herein as the "first voltage"). Also, when the AC voltage transitions to high, the AC voltage increases from the first voltage back to the second voltage. Thus, each cycle of the repeating cycle includes a transition to low and a transition to high.

[0034] In addition, when the AC voltage transitions to low or transitions to high, the transition can be instantaneous in nature, such as if the AC voltage substantially takes the form of a square wave. Alternatively, when the AC voltage transitions to low or transitions to high, the transition can be gradual, such as if the AC voltage substantially takes the form of a sine wave. In addition, each cycle of the AC voltage can include approximately equal amounts of time that the AC voltage is at its lower voltage and the AC voltage is at its higher voltage. Alternatively, each cycle of the AC voltage can include unequal amounts of time that the AC voltage is at its lower voltage and the AC voltage is at its higher voltage. However, the principles described herein are not limited to how the AC voltage transitions to low and to high immediately or gradually, and are not limited to the ratio of the higher voltage to the lower voltage of the AC voltage that exists in each cycle of the AC voltage.

[0035] When the AC voltage on the second capacitor terminal 112 turns low, the first capacitor terminal 111 is connected to the charge source 130, which provides charge to the first capacitor terminal 111 of the adjustable capacitor 110. On the other hand, when the AC voltage on the second capacitor terminal 112 turns high, the first capacitor terminal 111 can be decoupled from the charge source 130 and coupled to the voltage supply node 101, and thereby charge is pumped from the first capacitor terminal 111 to the voltage supply node 101. Therefore, the adjustable capacitor 110, the AC voltage source 120, and the charge source 130 can be used to supplement the voltage generated on the voltage supply node 101 in each cycle by 1) supplying charge from the charge source 130 to the first capacitor terminal 111 when the AC voltage is low, and 2) pumping charge from the first capacitor terminal 111 to the voltage supply node 101 when the AC voltage is high.

[0036] In order to supplement the voltage supply node 101 with the correct amount of voltage, the voltage supply circuit 100 further includes a regulating circuit 140. The regulating circuit 140 periodically (e.g., once per AC voltage cycle) samples the voltage on the voltage supply node 101 and determines whether the voltage on the voltage supply node 101 is too low below a specified voltage or too high above a specified voltage. For example, the regulating circuit 140 is connected (as shown by line 141) to the voltage supply node 101 so as to sample the voltage on the voltage supply node 101.

[0037] If the regulation circuit 140 determines that the voltage on the voltage supply node 101 is too low below the specified voltage, the regulation circuit 140 adjusts the capacitance of the adjustable capacitor 110 upward. The control involved in the regulation circuit 140 making this adjustment is represented by the dashed arrow 142. Increasing the capacitance of the adjustable capacitor 110 increases the amount of charge that the adjustable capacitor 110 can pump to the voltage supply node 101 in one cycle. Therefore, by increasing the capacitance of the adjustable capacitor 110, the voltage generated on the voltage supply node 101 can be increased.

[0038] Furthermore, if the regulation circuit 140 determines that the voltage on the voltage supply node 101 is too high above the specified voltage, the regulation circuit 140 adjusts downward the capacitance of the adjustable capacitor 110. Reducing the capacitance of the adjustable capacitor 110 reduces the amount of charge that the adjustable capacitor 110 can pump to the voltage supply node 101 in one cycle. Therefore, by reducing the capacitance of the adjustable capacitor 110, the voltage generated on the voltage supply node 101 can be reduced.

[0039] In one embodiment, as will be referred to Figure 2 As described, if the regulating circuit 140 determines that the voltage on the voltage supply node 101 is not too low below a specified voltage and is not too high above another specified voltage, the regulating circuit 140 will not adjust the capacitance of the adjustable capacitor 110 .

[0040] Thus, by adjusting the capacitance of the adjustable capacitor 110 upward or downward depending on whether the sampled voltage on the voltage supply node 101 is less than or greater than the specified voltage, respectively, the voltage supply circuit 100 is able to accurately generate a specified voltage (or carefully control the voltage) on the voltage supply node 101. Furthermore, frequent automatic capacitance adjustments allow the voltage supply circuit 100 to continue to accurately generate a specified voltage on the voltage supply node 101, continuously compensating for changes, such as aging of components in the voltage supply circuit 100, operating temperature changes, or other sudden or gradual environmental changes. Furthermore, because the adjustable capacitor 110 will be adjusted during normal operation, fine-tuning the capacitance of the adjustable capacitor 110 to account for device-to-device manufacturing variations or defects can be avoided.

[0041] Figure 2 Description Figure 1 Flowchart of an example method 200 of operation of the voltage supply circuit 100 during a single cycle of the AC voltage; for example, when the AC voltage transitions to low, the cycle of the AC voltage begins ( Figure 2 When the AC voltage changes to low, the voltage on the first capacitor terminal 111 also changes to low, and the charge source 130 provides charge to the first capacitor terminal 111 of the adjustable capacitor (also action 201). Thereafter, the AC voltage changes to high, and thus the voltage on the first capacitor terminal 111 also changes to high, and thereby charge is pumped from the first capacitor terminal 111 to the voltage supply node 101 (action 202). Figure 2 In the present invention, for the sake of brevity, the voltage supply node 101 may be referred to as “VSN”.

[0042] As previously mentioned, the regulation circuit 140 periodically samples the voltage on the voltage supply node 101. Figure 2In method 200, regulation circuit 140 samples the voltage on voltage supply node 101 a single time during each cycle of the AC voltage after the AC voltage transitions to high (act 203). However, the principles described herein are not limited to the frequency at which regulation circuit 140 samples the voltage on voltage supply node 101, and are not limited to the specific moments during the cycle at which regulation circuit 140 samples the AC voltage on voltage supply node 101. That is, for the purpose of explanation, it is assumed that regulation circuit 140 samples the voltage on voltage supply node 101 a single time during each cycle of the AC voltage, and that the sampling occurs after the AC voltage transitions to high.

[0043] If the voltage on the voltage supply node 101 is below the first threshold voltage when the regulation circuit 140 samples the voltage supply node 101, the regulation circuit 140 increases the adjustable capacitance of the adjustable capacitor 110 (action 204A). For example, the voltage supply circuit 100 may be calibrated so that the specified voltage to be generated on the voltage supply node is 8 volts, and the first threshold voltage is 7.8 volts. In this case, if the regulation circuit 140 samples the voltage on the voltage supply node 101 less than 7.8 volts, the regulation circuit 140 will increase the adjustable capacitance of the adjustable capacitor 110 so that during the next cycle of the AC voltage, slightly more charge will be pumped from the first capacitor terminal 111 to the voltage supply node 101.

[0044] On the other hand, if the voltage on the voltage supply node 101 is above the second threshold voltage when the regulation circuit 140 samples the voltage supply node, the regulation circuit 140 reduces the adjustable capacitance of the adjustable capacitor 110 (action 204B). For example, if the voltage supply circuit 100 is calibrated so that the specified voltage to be generated on the voltage supply node is 8 volts, then the second threshold voltage may be 8.2 volts. In this case, if the regulation circuit 140 samples the voltage on the voltage supply node 101 to be greater than 8.2 volts, the regulation circuit 140 will reduce the adjustable capacitance of the adjustable capacitor 110 so that during the next cycle of the AC voltage, slightly less charge will be pumped from the first capacitor terminal 111 to the voltage supply node 101.

[0045] Finally, if the voltage on the voltage supply node 101 is higher than the first threshold voltage but lower than the second threshold voltage when the adjustment circuit 140 samples the voltage supply node 101, the adjustment circuit 140 may not change the adjustable capacitance of the adjustable capacitor 110 (action 204C). For example, if the voltage supply circuit 100 is calibrated so that the specified voltage to be generated on the voltage supply node 101 is 8 volts, then the first threshold voltage may be 7.8 volts and the second threshold voltage may be 8.2 volts. In this case, if the voltage sampled by the adjustment circuit 140 on the voltage supply node 101 is greater than 7.8 volts but less than 8.2 volts, the adjustment circuit 140 will not change the adjustable capacitance of the adjustable capacitor 110.

[0046] Therefore, the actual voltage generated on the voltage supply node 101 can be maintained approximately at the specified voltage within the range between the first threshold voltage and the second threshold voltage. In order to make the actual voltage generated on the voltage supply node 101 closer to the specified voltage, the values ​​of the first threshold voltage and the second threshold voltage that are closer to the specified voltage can be selected. For example, if the specified voltage is 8 volts, the first threshold voltage can be 7.95 volts and the second threshold voltage can be 8.05 volts. To further advance this concept, the first and second threshold voltages can actually even be the same as each other and equal to the specified voltage. For example, if the specified voltage is 8 volts, if the adjustment circuit 140 detects a voltage higher than 8 volts, the adjustable capacitor is adjusted downward; if the adjustment circuit 140 detects a voltage lower than 8 volts, the adjustable capacitor is adjusted upward.

[0047] The adjustable capacitance of the adjustable capacitor 110 can be increased and / or decreased in small increments. By way of example only, this can be achieved by having the adjustable capacitor 110 comprise a capacitor bank of capacitors of various sizes. Figure 3 Such an example is described.

[0048] Figure 3 Explained as Figure 1 1. The adjustable capacitor bank 300 of the example of the adjustable capacitor 110 of FIG. 1 is shown. Specifically, the adjustable capacitor bank 300 includes four fixed capacitors connected in parallel to each other - capacitors 310A, 310B, 310C, and 310D. However, the principles described herein are not limited to the number of capacitors included in the capacitor bank 300, and are not limited to the capacitors included in the capacitor bank 300 being fixed capacitors themselves.

[0049] Capacitors 310A to 310D include respective upper terminals 311A ​​to 311D that can be selectively coupled to first capacitor bank terminal 301 via switches 320A to 320D. First capacitor bank terminal 301 is Figure 1The capacitors 310A to 310D also include respective lower terminals 312A to 312D, which can be selectively coupled to the second capacitor bank terminal 302 via switches 330A to 330D. The second capacitor bank terminal 302 is Figure 1 An example of a second capacitor terminal 112 .

[0050] like Figure 3 As shown, capacitors 310A to 310D can have different sizes and therefore can have different capacitance values ​​from each other. As an example, assume that each subsequent capacitor of capacitors 310A to 310D is sized in a binary scale. For example, if the largest capacitor 310A has a capacitance of 8×Z (8 times Z) farads, then capacitor 310B will have a capacitance of 4×Z farads, capacitor 310C will have a capacitance of 2×Z farads, and the smallest capacitor 310D will have a capacitance of only Z farads. The total capacitance of the adjustable capacitor bank 300 will be the sum of the capacitances of any one of the capacitors 310A to 310D that is actually coupled to the first capacitor bank terminal 301 and the second capacitor bank terminal 302.

[0051] In the case where the sizes of capacitors 310A to 310D are in binary proportions, a binary sequence can be used to drive the adjustable capacitor bank 300, such that each bit of the binary sequence defines whether the corresponding switch of the capacitor is open or closed. In practice, the binary sequence can be viewed as a binary value, wherein the most significant bit is used to drive switches 320A and 330A of the largest capacitor 310A, the next most significant bit is used to drive switches 320B and 330B of the next largest capacitor 310B, the next most significant bit is used to drive switches 320C and 330C of the next largest capacitor 310C, and the least significant bit is used to drive switches 320D and 330D of the smallest capacitor 310D. Thus, a binary value of 1111 (15 in decimal) is used to adjust the adjustable capacitor bank 300 to have a capacitance of 15×Z farads, while a binary value of 0001 (1 in decimal) is used to adjust the adjustable capacitor bank 300 to have a capacitance of only Z farads.

[0052] More generally, the binary value will cause the adjustable capacitor bank 300 to have a capacitance of S×Z farads, where S is the binary value of the binary sequence in base 10 (and, recall, Z represents the capacitance of the smallest capacitor 310D in farads). However, the principles described herein are not limited to a particular language or protocol used by the adjustment circuit 140 to send instructions to the adjustable capacitor bank 300. Furthermore, there may be more than (or less than) four binary-sized capacitors that receive instructions in the form of a binary sequence having more than (or less than) four bits. Of course, the principles described herein are not limited to how the adjustable capacitor bank 300 is constructed. Figure 1 The adjustable capacitor 110 is provided.

[0053] Furthermore, the adjustable capacitor bank 300 may optionally include one or more additional fixed capacitors that may be directly connected to the first and second capacitor bank terminals 301 and 302, such that these particular fixed capacitors may provide at least some minimum amount of capacitance "Y" of the adjustable capacitor bank 300. Thus, a binary sequence (with a value of S in base 10) may be used such that the adjustable capacitor has a total capacitance of Y+S×Z.

[0054] In an example where the adjustable capacitor 110 includes an adjustable capacitor bank 300, if the sampled voltage of the voltage supply node 101 is below the first threshold voltage, the adjustment circuit 140 may increment the binary sequence by one to increase the capacitance of the adjustable capacitor bank 300, thereby increasing the voltage on the voltage supply node 101. For example, if the binary sequence is 0101 (to provide a capacitance of 5×Z farads), the binary sequence will increase to 0110 (to provide an increased capacitance of 6×Z farads). On the other hand, if the sampled voltage of the voltage supply node 101 is above the second threshold voltage, the adjustment circuit 140 may decrement the binary sequence by one to decrease the capacitance of the adjustable capacitor bank 300, thereby decreasing the voltage on the voltage supply node 101. For example, if the binary sequence is 0110 (to provide a capacitance of 6×Z farads), the binary sequence will decrease to 0101 (to provide a decreased capacitance of 5×Z farads).

[0055] In one embodiment, if the voltage on the voltage supply node 101 is significantly lower than the first threshold voltage, or significantly higher than the second threshold voltage, the adjustment circuit 140 may respectively increment (or decrement) the binary sequence by more than one, so as to more quickly increase (or decrease) the adjustable capacitance of the adjustable capacitor bank 300, and thus more quickly correct the voltage on the voltage supply node 101. In the case of using a binary sequence to adjust capacitance, the principles described herein are not limited to the adjustment circuit 140 incrementing and / or decrementing a particular number of binary sequences.

[0056] Figure 4 A voltage supply circuit 400 is illustrated, which is Figure 1 Specifically, Figure 4 The voltage supply node 401, the adjustable capacitor 410, the first capacitor terminal 411, the second capacitor terminal 412, the AC voltage supply 420 and the regulating circuit 440 are Figure 1 1 , a voltage supply node 101, an adjustable capacitor 110, a first capacitor terminal 111, a second capacitor terminal 112, an AC voltage source 120, and a regulating circuit 140. Figure 1, line 441 indicates that the regulating circuit 440 samples the voltage on the voltage supply node 401 , and the dashed arrow 442 indicates that the regulating circuit 440 controls the adjustable capacitance of the adjustable capacitor 410 . However, the voltage supply circuit 400 further includes diodes 450 and 460 , a resistor 470 , and a load 480 .

[0057] exist Figure 4 , the voltage supply node 401 acts as Figure 1 The voltage supply node 101 and Figure 1 The diode 450 and the resistor 470 connected in series act as a voltage supply node 401 (which is Figure 1 130) and the first capacitor terminal 411 (which is Figure 1 An example of an intermediate circuit element between the first capacitor terminal 111 and the Figure 4 In the embodiment, the voltage supply node 401 is coupled to the first capacitor terminal 411, and the intermediate circuit element allows current to flow from the voltage supply node 401 to the first capacitor terminal 411 as long as the voltage on the voltage supply node 401 is greater than the threshold voltage of the diode 450 and higher than the voltage on the first capacitor terminal 411. Therefore, when the AC voltage provided by the AC voltage source 420 decreases from a high voltage to a low voltage, a corresponding decrease in the voltage on the first capacitor terminal 411 is induced (i.e., at least the diode threshold voltage of the diode 450 is lower than the voltage on the voltage supply node 401), and the charge from the voltage supply node 401 is forced to reach the first capacitor terminal 411 through the diode 450 and the resistor 470.

[0058] In addition, a diode 460 is provided between the first capacitor terminal 411 (which is Figure 1 1) and the voltage supply node 401 (now acting as Figure 1 101) between the voltage supply nodes 102 and 103. Figure 4 In the embodiment, the first capacitor terminal 411 is coupled to the voltage supply node 401, and the middle diode 460 allows current to flow from the first capacitor terminal 411 to the voltage supply node 401 as long as the voltage on the first capacitor terminal 411 is greater than the threshold voltage of the diode 460 and higher than the voltage on the voltage supply node 401. Therefore, when the AC voltage provided by the AC voltage source 420 increases from a low voltage to a high voltage, a corresponding increase in the voltage on the first capacitor terminal 411 is induced (i.e., at least the diode threshold voltage of the diode 460 is higher than the voltage on the voltage supply node 401), and the charge from the first capacitor terminal 411 is forced to reach the voltage supply node 401 through the diode 460.

[0059] In one embodiment, load 480 is a switching load (e.g., a load using AC power) that alternates between a fast draw state in which load 480 quickly draws charge from voltage supply node 401 and a slow draw state in which load 480 draws charge more slowly from voltage supply node 401. Load 480 alternates between the fast draw state and the slow draw at a certain frequency. In one embodiment, the AC voltage provided by AC voltage source 420 may also alternate between its higher voltage and its lower voltage at the same frequency as load 480, and cause the AC voltage to transition to high at about the time that load 480 enters its fast draw state. This allows charge to be pushed to voltage supply node 401 only when load 480 uses charge, thereby matching the needs of switching load 480. This prevents the voltage on voltage supply node 401 from being depleted while providing charge to the switching load.

[0060] As previously described, the regulating circuit 440 periodically samples the voltage on the voltage supply node 401, and can increase or decrease the adjustable capacitance of the adjustable capacitor 410 to increase or decrease the voltage on the voltage supply node 401, respectively. Therefore, by adjusting the capacitance of the adjustable capacitor 410 upward or downward according to whether the sampled voltage on the voltage supply node 401 is less than the specified voltage or greater than the specified voltage, respectively, the voltage supply circuit 400 is able to accurately generate a specified voltage (or carefully control the voltage) on the voltage supply node 401. This further allows the voltage supply circuit 400 to continuously compensate for changes in the amount of charge drawn by the load 480 per cycle of the AC voltage. In addition, in the case of a switching load, the fast draw state can be more closely aligned with the period when the AC voltage is high, so that charge is provided to the voltage supply node 401, while the highest rate of charge is drawn from the voltage supply node 401.

[0061] Figure 5 A voltage supply circuit 500 is illustrated, which is Figure 1 Specifically, Figure 5 The voltage supply node 501, the adjustable capacitor 510, the first capacitor terminal 511, the second capacitor terminal 512 and the regulating circuit 540 are Figure 1 1 , a voltage supply node 101, an adjustable capacitor 110, a first capacitor terminal 111, a second capacitor terminal 112, and a corresponding example of a regulating circuit 140. In addition, similar to Figure 1 , line 541 indicates that the regulating circuit 540 samples the voltage on the voltage supply node 501 , and the dashed arrow 542 indicates that the regulating circuit 540 controls the adjustable capacitance of the adjustable capacitor 510 .

[0062] exist Figure 5In the embodiment, the voltage on the control node 501 can be used to turn the power transistor (not shown) on and off. For example, assuming that the power transistor is an enhancement mode field effect transistor (in this case, the control node 501 is connected to the gate terminal of the field effect transistor). In this case, the power transistor can be turned off by applying 0 volts to the control node 501, and the power transistor can be turned on by applying 6 volts to the control node 501. In one embodiment, a voltage is generated on the voltage supply node 501 so that the power transistor is turned on even more than normally by applying a higher overdrive voltage to the control node 501. For example, when entering the overdrive mode, an overdrive voltage of 8 volts can be provided on the voltage supply node 501.

[0063] The voltage supply circuit 500 further includes a voltage source 520, a voltage source 521 and two switches 522 and 523, which together serve as Figure 1 1. An example of an AC voltage source 120. For example, when switch 522 is closed and switch 523 is open, a higher voltage (e.g., 6 volts) is applied to the second capacitor terminal 512. On the other hand, when switch 523 is closed and switch 522 is open, a lower voltage (e.g., ground) is applied to the second capacitor terminal 512. Therefore, for each cycle, an AC voltage can be applied to the second capacitor terminal 512 by controlling switches 522 and 523 to apply a high voltage and then controlling switches 522 and 523 again to apply a low voltage.

[0064] The voltage supply circuit 500 further includes a field effect transistor 530 having a gate terminal 531 that controls whether current flows between a drain terminal 532 and a source terminal 533. The drain terminal 532 is connected to a high voltage source 534 that provides a much higher voltage (e.g., several hundred volts) to the drain terminal 532. The field effect transistor 530 and the high voltage source 534 together serve as Figure 1 The source terminal 533 is switchably connected to the voltage supply node 501 via the switch 562 .

[0065] For example, assume that the voltage supply circuit 500 is configured to generate an internal voltage source of 8 volts on the voltage supply node 501. For example, this may help to generate an overdrive voltage internally for a power transistor (not shown). In this case, when the voltage at the gate terminal 531 is at least 8 volts plus a certain threshold voltage (e.g., the gate-to-source threshold voltage of the field effect transistor 530), the field effect transistor 530 is turned on. Therefore, for the purpose of explanation, it is assumed that 8 volts plus the threshold voltage is always supplied to the gate terminal 531, so that when the voltage on the voltage supply node 501 becomes less than 8 volts (and the switch 562 is closed), the field effect transistor 530 is turned on, and thus charge is supplied from the high voltage source 534 to the voltage supply node 501 via the field effect transistor 530 and the switch 562.

[0066] The voltage supply circuit 500 further includes a voltage source 550, a voltage source 570, and a small fixed capacitor 580. For example, the voltage source 550 may provide 6 volts, and the voltage source 570 may be ground. The control node 502 may be selectively coupled to the voltage source 570 via a switch 560, may be selectively coupled to the voltage source 550 via a switch 561, and may be selectively coupled to the voltage supply node 501 via a switch 562.

[0067] In order to provide zero volts to the control node 501 (e.g., to turn off the power transistor), switches 561 and 562 will be opened, and switch 560 will be closed, thereby connecting the control node 502 to the ground provided by the voltage source 570. The voltage source 570 is also referred to as the "off voltage source". In order to provide 6 volts to the control node 501 (e.g., to normally turn on the power transistor), switches 560 and 562 will be opened, and switch 561 will be closed, thereby connecting the control node 501 to the voltage source 550 providing 6 volts. The voltage source 550 is also referred to as the "normal on voltage source". When the power transistor is disconnected or normally on, the second capacitor terminal 512 is connected to zero volts via switch 523. In addition, in these states, due to the reasons previously described, the capacitor 510 has been charged to a voltage difference of 6 volts. Both the voltage source 550 and the voltage source 520 can be provided by external pins, etc., and the charge is easily obtained from the external pins. Therefore, the power transistor can be easily turned on and off.

[0068] Once the power transistor is normally turned on (e.g., by applying 6 volts to the control node 502), the power transistor can be turned on more by overdriving the transistor. Overdriving the power transistor is achieved by providing an overdrive voltage (such as 8 volts) to the control node 502 by opening switch 561 and closing switch 562. However, the collective capacitance of the voltage supply node 501 is more limited. Therefore, when overdriving of the power transistor is to occur, in order to ensure that sufficient charge is provided from the capacitor 510 to the voltage supply node, overdriving is started by opening switch 523 and closing switch 522. This causes the voltage at the second capacitor terminal 512 to increase from ground to 6 volts, thereby causing charge to flow into the control node 501 to help quickly equalize the voltage at the node 502 to the desired overdrive voltage.

[0069] However, the equalization voltage will depend on the relative sizes of the capacitance of capacitor 510 and the capacitance of the gate terminal of the power transistor connected to control node 501. The principles described herein adjust the capacitance of adjustable capacitor 510 so that the equalization voltage is a suitable voltage for overdriving the power transistor.

[0070] The regulating circuit 540 can periodically and / or continuously sample the control node 501. If the regulating circuit 540 samples the gate voltage V on the control node 501 when the control node 501 is g If the voltage is not fully boosted to 8 volts, the regulating circuit 540 can increase the capacitance of the adjustable capacitor 510 so that more charge will be provided to the voltage supply node 501. On the other hand, if the regulating circuit 540 samples the gate voltage V on the control node 501 g If the gate voltage V provided to the control node 501 is being boosted to slightly above 8 volts (which could damage the power transistor), the regulation circuit 540 can reduce the capacitance of the adjustable capacitor 510 so that less charge will be provided from the first capacitor terminal 511 to the voltage supply node 501. Thus, the voltage supply circuit 500 allows precise control of the gate voltage V provided to the control node 501. g , particularly when the control node 501 is being provided with a voltage from the voltage supply node 501 .

[0071] As an example of sampling and capacitance adjustment performed by adjustment circuit 540, Figure 6 A signal graph 600 is illustrated, which shows an example simulation of the voltage supply circuit 500 repeatedly alternating by connecting the control node 502 to the ground voltage source 570, the 6 volt voltage source 550 and the 8 volt voltage supply node 501. In addition, the signal graph 600 shows an exemplary timeline 602 (dashed line) of the adjustable capacitance value of the sampled adjustable capacitor 510 superimposed on the sampled gate voltage V g601 (solid line), each provided by way of example only. The horizontal axis represents the time elapsed from left to right in microseconds, where the same horizontal position in each timeline 601 and 602 represents the same time. The vertical axis of timeline 601 represents the sampled gate voltage V on the control node 502 in volts. g The vertical axis of the timeline 602 represents the adjustable capacitance value of the adjustable capacitor 510 in farads in decimal.

[0072] Gate voltage V g The time line 601 is divided into periods T1 to T17. Each of the periods T1 to T17 is when the gate voltage V g The time starts at the beginning of the rising edge of and ends just before the beginning of the next rising edge. Figure 6 As shown, in each cycle T1 to T17, the gate voltage V g First, it increases sharply from ground to 6 volts. Then the gate voltage V g From 6V to a certain sampling voltage V C (For simplicity, only the time period T4 is marked). C is referred to as a “sampled voltage” because it is sampled by the adjustment circuit 540. By increasing the adjustable capacitance of the adjustable capacitor 510, the voltage on the voltage supply node 501 is boosted higher, thereby increasing the sampled voltage V C On the other hand, by reducing the adjustable capacitance of the adjustable capacitor 510, the voltage on the voltage supply node 501 is not boosted in the same manner, so the sampling voltage V C In the time period T1 to T7, the sampling voltage V C is higher than 6 V but lower than 8 V. On the other hand, during the time period T8 to T17, the sampled voltage V C Alternate between above and below 8 volts.

[0073] In any case, when the regulating circuit 540 samples the voltage V C When sampling (for example, Figure 6 In each cycle T1 to T17), if the sampling voltage V C If the voltage V is less than 8V, the regulating circuit 540 increases the value of the adjustable capacitor 510 by one in the next cycle. For example, for cycle T4, the regulating circuit 540 samples the sampling voltage V C is less than 8V, so the regulating circuit 540 increases the adjustable capacitance of the adjustable capacitor 510 from 7×Z farads to 8×Z farads in the subsequent period T5. On the other hand, when the regulating circuit 540 adjusts the sampling voltage V C When sampling, if the sampling voltage V CIf the sampling voltage V is greater than 8V, the regulating circuit 540 decreases the value of the adjustable capacitor 510 by one in the next cycle. For example, for cycle T8, the regulating circuit 540 adjusts the sampling voltage V C The voltage is greater than 8V, so the adjustment circuit 540 reduces the adjustable capacitance of the adjustable capacitor 510 from 11×Z farads to 10×Z farads in the subsequent period T9.

[0074] exist Figure 6 , the first threshold voltage and the second threshold voltage are each equal to a specified voltage (which is 8 volts). Therefore, from time period T8 to T17, the adjustment circuit 540 alternately increases and decreases the adjustable capacitance of the adjustable capacitor 510 so that the sampling voltage V C Maintain approximately (just above and just below) the specified voltage.

[0075] Therefore, by adjusting the capacitance of the adjustable capacitor 510 upward or downward according to whether the sampled voltage on the voltage supply node 501 is less than the specified voltage or greater than the specified voltage, respectively, the voltage supply circuit 600 is able to accurately generate a specified voltage (or carefully control the voltage) on the voltage supply node 501. Therefore, the voltage supply circuit 600 is further able to provide a precise overdrive sampled voltage V on the control node 501. C In addition, frequent automatic capacitance adjustments allow the voltage supply circuit 600 to continue to accurately generate a specified voltage on the voltage supply node 501 (thereby providing an accurate overdrive sampling voltage V on the control node 502). C ), continuously compensating for changes, such as aging of components in the voltage supply circuit 600, operating temperature changes, or other sudden or gradual environmental changes. In addition, since the capacitance will be adjusted during normal operation, fine-tuning the capacitance of the adjustable capacitor 510 to account for device-to-device manufacturing variations or defects can be avoided.

[0076] Text support part

[0077] Item 1. A voltage supply circuit configured to generate a voltage on a voltage supply node, the voltage supply circuit comprising: a charge source; an AC voltage source configured to provide an AC voltage alternating between a first voltage and a second voltage; and an adjustable capacitor having an adjustable capacitance and comprising a first capacitor terminal, and having a second capacitor terminal, the first capacitor terminal being coupled to the voltage supply node and the charge source, and the second capacitor terminal being connected to the AC voltage source so as to receive the AC voltage from the AC voltage source; wherein when the AC voltage on the second capacitor terminal turns to low, the voltage on the first capacitor terminal also turns to low, and the charge source provides charge to the first capacitor terminal of the adjustable capacitor; and when the AC voltage on the second capacitor terminal turns to high, the voltage on the first capacitor terminal also turns to high, and thereby charge is pumped from the first capacitor terminal to the voltage supply node.

[0078] Item 2. The voltage supply circuit of Item 1, further comprising a regulation circuit configured to periodically adjust the adjustable capacitance in response to periodically sampling the voltage on the voltage supply node, wherein when the regulation circuit determines that the voltage on the voltage supply node is below a first threshold voltage, the regulation circuit upwardly adjusts the adjustable capacitance of the adjustable capacitor, and when the regulation circuit determines that the voltage on the voltage supply node is above a second threshold voltage, the regulation circuit downwardly adjusts the adjustable capacitance of the adjustable capacitor.

[0079] Clause 3. The voltage supply circuit of clause 2, wherein the first threshold voltage and the second threshold voltage are the same threshold voltage.

[0080] Item 4. The voltage supply circuit of Item 2, wherein the second threshold voltage is higher than the first threshold voltage.

[0081] Clause 5. The voltage supply circuit of clause 4, wherein the regulation circuit does not change the adjustable capacitance of the adjustable capacitor when the regulation circuit determines that the voltage on the voltage supply node is above the first threshold voltage and below the second threshold voltage.

[0082] Item 6. The voltage supply circuit according to Item 1 further comprises: a group of binary capacitors having sizes in binary proportion; and a group of switches, each switch connecting or disconnecting a corresponding binary capacitor in the group of binary capacitors, so that a group of connected binary capacitors forms an adjustable capacitor, and so that adjustment of the adjustable capacitance of the adjustable capacitor is performed by selecting a binary capacitor to be connected and connecting the selected binary capacitor.

[0083] Clause 7. The voltage supply circuit of clause 6, the regulating circuit being configured to regulate the adjustable capacitance by generating a binary code and providing a corresponding bit of the binary code to each switch in a set of switches.

[0084] Clause 8. The voltage supply circuit of clause 1, the charge source being a voltage supply node connected to the switched load.

[0085] Clause 9. The voltage supply circuit of clause 8, the charge source being configured to provide charge to the first capacitor terminal of the adjustable capacitor through a series connection of a diode and a resistor.

[0086] Clause 10. The voltage supply circuit of clause 9, wherein when the AC voltage decreases from the second voltage to the first voltage at the second capacitor terminal of the adjustable capacitor, a corresponding voltage decrease at the voltage supply node is induced by forcing charge from the voltage supply node through the diode and the resistor and to the first capacitor terminal.

[0087] Item 11. A voltage supply circuit according to Item 10, the diode being a first diode, wherein when the AC voltage increases from a first voltage to a second voltage at a second capacitor terminal of the adjustable capacitor, a corresponding voltage increase at the voltage supply node is induced by forcing charge from the first capacitor terminal through the second diode to the voltage supply node.

[0088] Item 12. A voltage supply circuit according to Item 9, the diode being a first diode, wherein when the AC voltage increases from a first voltage to a second voltage at a second capacitor terminal of the adjustable capacitor, a corresponding voltage increase at the voltage supply node is induced by forcing charge from the first capacitor terminal through the second diode to the voltage supply node.

[0089] Clause 13. The voltage supply circuit of clause 1, the charge source being configured to supply charge to the first capacitor terminal when the voltage of the first capacitor terminal drops below a reference voltage, but being configured not to supply charge to the first capacitor terminal when the voltage is above the reference voltage.

[0090] Item 14. According to the voltage supply circuit of Item 13, the charge source includes: a field effect transistor having a gate-source threshold voltage; a source terminal of the field effect transistor, which is connected to the first capacitor terminal; a drain terminal, which is connected to a voltage source providing a voltage greater than a reference voltage; and a gate terminal, which is biased to the reference voltage plus the gate-source threshold voltage.

[0091] Item 15. The voltage supply circuit of Item 13, wherein when the AC voltage increases from a first voltage to a second voltage at the second capacitor terminal of the adjustable capacitor, a corresponding voltage increase is induced at a voltage supply node, and the voltage supply node is connected to the gate terminal of the power transistor.

[0092] Clause 16. The voltage supply circuit of clause 15, wherein when the AC voltage increases from a first voltage to a second voltage at the second capacitor terminal of the adjustable capacitor, a corresponding voltage increase is induced at a voltage supply node, and the voltage supply node is connected to the gate terminal of the power transistor.

[0093] Clause 17. The voltage supply circuit of clause 1, further comprising: a fixed capacitance capacitor connected between the fixed voltage source and the voltage supply node.

[0094] Although the subject matter has been described in language specific to structural features and / or methodological acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the above features or acts, or the order of the above acts. Instead, the above features and acts are disclosed as example forms of implementing the claims.

[0095] The present disclosure may be implemented in other specific forms without departing from its essential features. The described embodiments are considered in all respects to be illustrative and non-restrictive. All changes within the equivalent meaning and range of the claims are included within their scope.

[0096] When introducing elements in the appended claims, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements. The terms "comprising", "including", and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Claims

1. A voltage supply circuit configured to generate a voltage on a voltage supply node, the voltage supply circuit comprising: Charge source; an AC voltage source configured to provide an AC voltage alternating between a first voltage and a second voltage; as well as an adjustable capacitor having an adjustable capacitance and including a first capacitor terminal coupled to the voltage supply node and the charge source, and having a second capacitor terminal connected to the AC voltage source to receive the AC voltage from the AC voltage source; in When the AC voltage on the second capacitor terminal changes to low, the voltage on the first capacitor terminal also changes to low, and the charge source provides charge to the first capacitor terminal of the adjustable capacitor; as well as When the AC voltage on the second capacitor terminal transitions to high, the voltage on the first capacitor terminal also transitions to high, and thereby charge is pumped from the first capacitor terminal to the voltage supply node.

2. The voltage supply circuit of claim 1 , further comprising a regulating circuit configured to periodically regulate the adjustable capacitance in response to periodically sampling the voltage on the voltage supply node, wherein When the regulation circuit determines that the voltage on the voltage supply node is lower than a first threshold voltage, the regulation circuit adjusts the adjustable capacitance of the adjustable capacitor upward, and When the regulation circuit determines that the voltage on the voltage supply node is above a second threshold voltage, the regulation circuit adjusts the adjustable capacitance of the adjustable capacitor downward. 3 . The voltage supply circuit according to claim 2 , wherein the first threshold voltage and the second threshold voltage are the same threshold voltage. The voltage supply circuit according to claim 2 , wherein the second threshold voltage is higher than the first threshold voltage.

5. The voltage supply circuit according to claim 4, wherein When the regulation circuit determines that the voltage on the voltage supply node is above the first threshold voltage and below the second threshold voltage, the regulation circuit does not change the adjustable capacitance of the adjustable capacitor.

6. The voltage supply circuit according to claim 1, further comprising: a set of binary capacitors having sizes in binary proportions; and A set of switches, each switch connecting or disconnecting a corresponding binary capacitor in the set of binary capacitors, so that a set of connected binary capacitors forms the adjustable capacitor, and so that adjustment of the adjustable capacitance of the adjustable capacitor is performed by selecting a binary capacitor to be connected and connecting the selected binary capacitor. 7 . The voltage supply circuit of claim 6 , the regulating circuit being configured to regulate the adjustable capacitance by generating a binary code and providing a corresponding bit of the binary code to each switch in the set of switches.

8. The voltage supply circuit of claim 1, the charge source being a voltage supply node connected to a switching load. 9 . The voltage supply circuit of claim 8 , the charge source being configured to provide charge to the first capacitor terminal of the adjustable capacitor through a series connection of a diode and a resistor.

10. The voltage supply circuit of claim 9, wherein when the AC voltage decreases from the second voltage to the first voltage at the second capacitor terminal of the adjustable capacitor, a corresponding voltage decrease on the voltage supply node is induced by forcing charge from the voltage supply node through the diode and resistor and to the first capacitor terminal.

11. The voltage supply circuit of claim 10 , wherein the diode is a first diode, wherein when the AC voltage increases from the first voltage to the second voltage at the second capacitor terminal of the adjustable capacitor, a corresponding voltage increase on the voltage supply node is induced by forcing charge from the first capacitor terminal through the second diode to the voltage supply node.

12. The voltage supply circuit of claim 9 , wherein the diode is a first diode, wherein when the AC voltage increases from the first voltage to the second voltage at the second capacitor terminal of the adjustable capacitor, a corresponding voltage increase on the voltage supply node is induced by forcing charge from the first capacitor terminal through the second diode to the voltage supply node.

13. The voltage supply circuit according to claim 1, the charge source is configured to supply charge to the first capacitor terminal when the voltage of the first capacitor terminal drops below a reference voltage, but is configured not to supply charge to the first capacitor terminal when the voltage is higher than the reference voltage.

14. The voltage supply circuit of claim 13, the charge source comprising: a field effect transistor having a gate-source threshold voltage; a source terminal of the field effect transistor connected to the first capacitor terminal; a drain terminal connected to a voltage source providing a voltage greater than the reference voltage; and a gate terminal biased at the reference voltage plus the gate-source threshold voltage.

15. The voltage supply circuit of claim 13, wherein when the AC voltage increases from the first voltage to the second voltage at the second capacitor terminal of the adjustable capacitor, a corresponding voltage increase is induced at the voltage supply node, and the voltage supply node is connected to the gate terminal of a power transistor.

16. The voltage supply circuit of claim 15, wherein when the AC voltage increases from the first voltage to the second voltage at the second capacitor terminal of the adjustable capacitor, a corresponding voltage increase is induced at the voltage supply node, and the voltage supply node is connected to the gate terminal of a power transistor.

17. The voltage supply circuit according to claim 1, further comprising: A fixed capacitance capacitor is connected between a fixed voltage source and the voltage supply node.

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