Patent Publication Number: US-11646657-B2

Title: DC-DC transformer with inductor for the facilitation of adiabatic inter-capacitor charge transport

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 15/557,970, filed on Sep. 13, 2017, which is the national phase under 35 USC 371 of international application no. PCT/US2016/021920 filed Mar. 11, 2016 which claims the benefit of the priority date of U.S. Provisional Application No.: 62/132,934, filed Mar. 13, 2015. The contents of which are incorporated herein in their entirety. 
    
    
     FIELD OF DISCLOSURE 
     This disclosure relates to power conversion, and in particular, to DC power conversion. 
     BACKGROUND 
     A known power converter is obtained by placing a regulator in series with a charge pump. An example of such a regulator operates by switching an inductor into one state and into a second state according to some switch duty cycle. The inductor in this regulator performs two functions. One is to control the output voltage of the converter. The other is to promote adiabatic charge transfer among the capacitors within the charge pump. 
     Known power converters operating according to the above principles are described in U.S. Pat. Nos. 8,860,396, 8,743,553, 8,503,203, 8,693,224, 8,339,184, 8,619,445, 8,723,491, and 8,817,501, the contents of which are all herein incorporated by reference in their entirety. 
     SUMMARY 
     The invention is based on the recognition that the regulator&#39;s dual function of regulation and promoting adiabatic charge transfer can be carried out by different components. 
     The invention includes reducing the functionality of a component that has always been used to carry out two functions and relocating it so that it can no longer carry out one of those functions. A new circuit component is added to carry out the function that used to be carried out by the existing component. The invention thus achieves a more complex circuit with an additional component that was not needed in the prior art. 
     The invention also reduces the die area required for the circuit by increasing the number of components that have to be placed on the die. 
     In addition to reducing chip area, the invention described herein also fills in certain holes in the performance of the overall power converter and makes it possible to carry out more of the voltage transformation within the charge pump, where it can be done most efficiently. 
     In a general aspect, one or more arrangements of a power converter are made up of a combination of an interconnection of sections, including at least a “voltage transformer,” a “magnetic filter,” and a “current regulator,” wherein these denotations have no further implicit connotations. 
     The power converter has terminals that include a first pair of terminals and a second pair of terminals, also referred to as the “controller” pair of terminals. In at least some embodiments, an operating power converter controls a voltage measured between the controlled pair of terminals. Typically, the power converter accepts power at the first pair of terminals from a power source (e.g., an unregulated voltage source), referred to as the “powered” pair of terminals, and provides power at a controlled voltage at the second pair of terminals (e.g., to a substantially resistive load), referred to as the “load” pair of terminals. It should be understood, however, that other arrangements can be used. 
     The voltage transformer, which is not to be confused with a conventional magnetic core alternating current “transformer,” has a least three terminals and comprises a switched arrangement of capacitors. Generally, sequential operation of switches in the voltage transformer causes a voltage transformation, generally by a rational multiple, between a first pair of terminals of the voltage transformer and a second pair of terminals of the voltage transformer. In general, one pair of terminals is associated with a higher voltage than the other pair. These pairs of terminals are hereinafter referred to as the “high voltage” pair of terminals and the “low voltage” pair of terminals, respectively. 
     The sequential operation of the switches causes charge to transfer between capacitors of the voltage transformer. The rate of charge transfer is constrained by a current through at least one of the terminals of the voltage transformer. This terminal will be referred to as a “charge transfer rate constraint” terminal. 
     When the rate of charge transfer between capacitors in at least one capacitor of the voltage transformer is constrained for at least some of the time, for example, by the current at the charge transfer rate constraint terminals, the voltage transformer is deemed to be “adiabatic.” If at least some but not necessarily all of the charge transfers are controlled, the voltage transformer is termed “partially adiabatic.” Otherwise the voltage transformer is “fully adiabatic.” 
     The magnetic filter comprises two terminals coupled in a circuit path without any switching activity. The magnetic filter opposes changes in the current flowing through at least one of the terminals, hereinafter referred to as the “filtered terminal(s)” of the magnetic filter, and generally maintains a substantially constant current through the filtered terminal(s) during steady state operation of the power converter. In some examples, the circuit path joining the terminals includes a passive inductor. In any case, because the path between the two terminals does not require a switch, there is no switch on the path that must be sized or selected to accommodate the maximum voltage or current that may be present on the path during operation. 
     The current regulator has at least two terminals and comprises a switched arrangement of at least one inductor. Generally, controlled sequential operation of one or more switches of the current regulator controls current flow through a least one of the terminals, hereinafter referred to as a “controlled terminal,” of the current regulator. In general, although the current regulator may regulate current flow, the regulation of current flow may be based on the output voltage (e.g., a time average voltage), which may be measured between a pair of terminals of the current regulator, or between other terminals within or at the interface of the power converter. 
     A common feature of a number of embodiments is that the arrangement of the voltage transformer, magnetic filter, and current regulator of the power converter is that a filtered terminal of the magnetic filter is directly coupled (i.e., without intervening switches) to a first terminal of the voltage transformer, with this first terminal being a charge transfer control terminal. Preferably, the magnetic filter is so coupled to a low voltage pair of terminals, recognizing that generally, the magnitude of current flow is higher at the low voltage terminals that at the high voltage terminals of the voltage transformer. 
     Another common feature is that the controlled terminal of the current regulator is directly coupled (i.e., without intervening switches) to a second terminal (different than the first terminal) of the voltage transformer. The second terminal may be, but is not necessarily, a charge transfer rate control terminal of the voltage transformer. 
     In some examples, the current regulator is coupled to multiple terminals of the voltage transformer, or to multiple separate voltage transformer sections of the power converter. In other examples, multiple current regulators, or current regulators having multiple separate controlled terminals, are coupled to multiple terminals of the voltage transformer or to multiple separate voltage transformers. 
     In operation of the power converter, the current regulator is controlled to achieve a controlled voltage at the controlled terminals of the power converter. 
     A number of configurations of the voltage transformer, magnetic filter, and current regulator can be grouped into (possibly overlapping) classes referred to as “series,” “sigma,” and “pseudo series,” without connoting any particular attributes by these names. 
     The series class of configurations includes configurations in which the current regulator, the voltage transformer, and the magnetic filter are connected in series between the first pair and the second pair of terminals of the power converter. In at least some of these configurations, the magnetic filter is coupled to a controlled/load terminals of the power converter, and the current regulator is coupled to a powered terminal of the regulator. In at least other of these configurations, the magnetic filter is coupled to a powered terminal of the power converter and the current regulator is coupled to a controlled terminal of the power converter. 
     The sigma class and the pseudo series class of configurations include configurations in which one controlled terminal of the current regulator is coupled to a controlled terminal of the power converter. The voltage transformer is also coupled to the same (or potentially a different) controlled terminal of the power converter via the magnetic filter such that the magnetic filter provides a path from a charge transfer rate control terminal of the voltage transformer to the controlled terminal. In at least some configurations of the sigma class, another terminal of the current regulator is coupled to the voltage transformer, such that in operation, control of the current regulator affects a voltage on the first pair or the second pair of terminals of the voltage transformer. For example, if a terminal of the first pair of terminals of the voltage transformer is coupled via the magnetic filter to a controlled terminal of the power converter to which a controlled terminal of the current regulator is also coupled, then another terminal of the current regulator is coupled to a terminal of the second pair of terminals of the voltage transformer. 
     The sigma class of configurations includes configurations in which there exists a path from a terminal of the first pair of terminals of the power converter to a terminal of the second pair of terminals of the power converter that passes through the current regulator without passing through the voltage transformer. 
     The pseudo series class of configurations includes configurations in which the voltage transformer is coupled to a controlled terminal of the power converter through a first path that passes via the magnetic filter but not the current regulator, as well as via a second path that that passes via the current regulator but not the magnetic filter. 
     An advantage of at least some configurations of the sigma and the pseudo parallel classes is that some of the power flow through the power converter passes through the magnetic filter but not the current regulator. Because the magnetic filter does not introduce a switch on power flow path though the magnetic filter, power losses (e.g., resistive and capacitive losses in a switch) are reduced and overall efficiency of the power converter is improved. 
     An advantage of at least some configurations of any of the classes are that the number or range of combinations of terminal voltages supported by the power converted can be increases as compared to other configurations that are affected by limitations on voltage differences between pair of its terminals of the current regulator that differ by less than a threshold voltage. 
     Another advantage of at least some configurations is that voltage or current handling requirements of switches of the voltage transformed and/or the current regulator can be reduced as compared to other configurations. These reduced requirements can result in physically smaller semiconductor devices, which can reduce the size of an integrated circuit implementation of some or all of the power converter. 
     In one aspect, the invention features a power converter that transforms a first voltage at a first power-converter terminal into a second voltage at a second power-converter terminal. The power converter includes a switching network in which switches that operate at a common frequency and duty cycle interconnect certain circuit elements. These circuit elements include a magnetic filter and capacitors. The magnetic filter includes first and second magnetic-filter terminals, with the second magnetic-filter terminal being maintained at the second voltage. When connected to the capacitors by a switch from the switching network, the magnetic filter imposes a constraint upon inter-capacitor charge transfer between the capacitors. 
     During the course of its operation, the switching network transitions between states. These states include at least first, second, and third states. In both the first state and the third state, the first magnetic-filter terminal couples to the capacitor network. In the second state, which occurs between the first and third states, the switches ground the first magnetic-filter terminal is grounded 
     Embodiments include those in which the capacitors and the switching network cooperate to define a single-phase charge pump and those in which they cooperate to define a multi-phase charge pump. 
     In some embodiments, in the first state, the first magnetic-filter terminal couples to a node, a cathode of a first capacitor connects to the node, and an anode of a second capacitor connects to the node. In the second state, cathodes of the first and second capacitors connect to each other and the first magnetic-filter terminal connects to an anode of one of the first and second capacitors. 
     In some embodiments, there exists a fourth state, with the fourth state being either the first state, the second state, or the third state. In these embodiments, the switching network executes a cycle that begins with a transition out of the fourth state and ends with a transition into the fourth state. Among these are embodiments in which the cycle consists of four transitions between states and those in which the cycle consists of only three transitions between states. 
     Also among the embodiments are those in which the second state occurs twice. 
     In some embodiments, the switching network comprises a stabilizing switch that connects a stabilizing capacitor to the first magnetic-filter terminal and disconnects the stabilizing capacitor from the first magnetic-filter terminal. Among these are embodiments in which, during a cycle, each switch in the switching network sustains a current therethrough and the stabilizing switch sustains less current than any other switch in the switching network. 
     In some embodiments, the second magnetic-filter terminal connects to capacitor. 
     In other embodiments, the switching network comprises a first switch. This first switch connects the first magnetic-filter terminal to the capacitor network and disconnects the first magnetic-filter terminal from the capacitor network. Among these are embodiments that also include a second switch. This second switch connects the first magnetic-filter terminal to ground when the first switch has disconnected the first magnetic-filter terminal from the capacitor network. The second switch is open otherwise. 
     In some embodiments, the switching network comprises a first switch. The first switch transitions between first and second states. The first state connects the first magnetic-filter terminal to ground. The second state disconnects the first magnetic-filter terminal from ground. 
     In some embodiments, the magnetic filter is a constituent of an LC circuit connected to the capacitor network. Among these are embodiments in which the capacitor network and the switching network cooperate to define a two-phase charge pump. 
     Some embodiments include a controller for controlling operation of the regulator based on an output of the power converter. Others include a clock configured to provide a clock signal to either the regulator or the charge pump. 
     Also among the embodiments are those that have a control system configured to control operation of the power converter based on a measured output of the power converter. Among these are those that have a controller to control the regulator, those that have a controller to control the charge pump, those that have both, those that have a clock signal input that can receive a clock signal, those in which the controller has digital inputs, those in which the controller has analog inputs, and any combination of the foregoing. 
     In another aspect, the invention features an apparatus that includes switches that interconnect capacitors of a charge pump that connects to a first terminal of a power converter that comprises the charge pump and a regulator. A first power path connects the power converter to a first terminal of a magnetic filter and a second power path connects the power converter to a second terminal of the magnetic filter and to a second terminal of the power converter. 
     In some embodiments are those in which the first power path couples the charge pump to the magnetic filter and the magnetic filter imposes a constraint in inter-capacitor charge transport within the charge pump and wherein a third power path connects the charge pump to the regulator. 
     In other embodiments, the first power path couples the regulator to the magnetic filter and a third power path connects the charge pump to the regulator. 
     Embodiments include those in which the charge pump and the regulator share a common ground and those in which the charge pump has a fixed reference potential and the regulator has a floating reference potential or vice versa. 
     A variety of charge pumps and regulators can be used. For example, among the embodiments are those that have a multi-phase charge pump, those that have a single-phase charge pump, those that have a multi-stage charge pump, those have a two-phase charge pump, those that have a resonant power converter, those that have a switch mode power converter, those that have a buck converter, those that have a bidirectional regulator, and those that a multi-phase regulator. 
     In some embodiments, the charge pump comprises capacitors interconnected by sets of switches. During operation, switches in the first set are opposite in state to switches in the second set. 
     In some embodiments, the charge pump is a reconfigurable charge pump. Among these are embodiments in which the regulator is configured to transition from providing a first voltage to providing a second voltage during reconfiguration of the charge pump. 
     In another aspect, the invention features an apparatus for power transformation. Such an apparatus includes a power converter having a charge pump, a first regulator that regulates the power provided by the power converter, and a magnetic filter connected to a terminal of the charge pump. The particular terminal to which the magnetic filter is connected is selected to facilitate causing a constraint in inter-capacitor charge transport within the charge pump. 
     In another aspect, the invention features a power converter that has switches that cause it to carry out cycles of operation. Each cycle of operation comprises connecting a first capacitor network to a first terminal of a magnetic filter, disconnecting the first capacitor network from said first terminal, connecting a second capacitor network to the first terminal, and disconnecting the second capacitor network from said first terminal to end said cycle, wherein disconnecting the first terminal comprises grounding the first terminal. 
     Among these are embodiments in which connecting the first capacitor network comprises connecting a cathode of a first capacitor to an anode of a second capacitor, connecting the cathode to the first terminal, and connecting the anode to the first terminal. 
     In another aspect, the invention features a non-transitory computer-readable medium that stores a data structure that is to be operated upon by a program executable on a computer system, wherein, when operated upon by such a program, the data structure causes at least a portion of a process for fabricating an integrated circuit that includes circuitry described by the data structure, wherein the circuitry described by the data structure includes a switching network that has been configured to be used with a power converter that comprises the components described above. 
     These and other features of the invention will be apparent from the following detailed description, and the accompanying figures, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows one embodiment of a power converter; 
         FIG.  2    shows a switched-capacitor charge pump for use with a power converter such as that shown in  FIG.  1   ; 
         FIG.  3 A  shows terminals that connect to the various capacitor networks that will be formed and unformed as the charge pump of  FIG.  2    transitions through its various states; 
         FIG.  3 B  shows a first capacitor network corresponding to a first configuration of switches for the charge pump of  FIG.  2   ; 
         FIG.  3 C  shows a second capacitor network corresponding to a second configuration of switches for the charge pump of  FIG.  2   ; 
         FIG.  4    shows a block diagram of the 4-terminal charge pump of  FIG.  2   ; 
         FIG.  5    shows a block diagram of the 3-terminal charge pump of  FIG.  3 A ; 
         FIG.  6 A  shows the components of a typical regulator that can be used in a power converter such as that shown in  FIG.  1   ; 
         FIGS.  6 B- 6 D  show alternative regulators for use with a power converter such as that shown in  FIG.  1   ; 
         FIGS.  7 A- 7 B  show magnetic filters that can be used in the embodiment of  FIG.  1   ; 
         FIG.  8    shows an embodiment in which a diode is used to conduct current in a magnetic filter that has no place to go during the dead time of the charge pump; 
         FIG.  9    shows the power converter of  FIG.  1    but with parallel charge pumps and parallel magnetic filters. 
         FIG.  10    shows the power converter of  FIG.  9    but with the magnetic filters sharing a common inductor; 
         FIG.  11    shows the power converter of  FIG.  1    but with the regulator having switches that share a common inductor; 
         FIG.  12    shown an embodiment similar to that shown in  FIG.  1    but with a four-terminal charge pump; 
         FIG.  13    shows an embodiment having a bifurcated power path through the power converter; 
         FIG.  14 A  shows a circuit that implements the bifurcated power path of  FIG.  13   , with the input voltage split so that the voltage presented to the regulator is twice that presented to the charge pump; 
         FIG.  14 B  shows a circuit that implements the bifurcated power path of  FIG.  13   , with the input voltage split so that the voltage presented to the regulator is half that presented to the charge pump; 
         FIG.  15 A , shows another embodiment having a bifurcated power path through a power converter; 
         FIG.  15 B  shows a circuit that implements the bifurcated power path of  FIG.  15 A ; 
         FIG.  16 A  shows an isolated charge pump that is suitable for use with the architecture shown in  FIG.  15 A ; 
         FIG.  16 B  shows a single-phase implementation of the isolated charge pump shown in  FIG.  16 A ; 
         FIG.  16 C  shows a two-phase implementation of the isolated charge pump shown in  FIG.  16 A ; 
         FIGS.  17 A- 17 D  show variants of the architecture shown in  FIG.  15 A ; 
         FIGS.  18 A- 18 C  show circuit topologies having bifurcated power paths with grounded charge pumps. 
         FIGS.  19 A- 19 C  show circuit topologies similar to those in  FIGS.  18 A- 18 C  except with grounded regulators instead of charge pumps. 
         FIG.  20    shows a power converter that shows features common to the embodiments of  FIGS.  1 ,  12 ,  13 , and  15 A ; 
         FIG.  21 A  shows a regulated charge pump; 
         FIGS.  21 B- 21 C  show the switch configurations and network states for the regulated charge pump of  FIG.  21 A ; 
         FIG.  22 A  shows a regulated charge pump of  FIG.  21 A  with a switch having been eliminated; 
         FIG.  22 B  shows the switch configurations for the regulated charge pump of  FIG.  22 A ; 
         FIG.  23 A  shows the regulated charge pump of  FIG.  22 A  with a stabilizing capacitor; 
         FIGS.  23 B- 23 C  show the switch configurations and network states for the regulated charge pump of  FIG.  23 A ; 
         FIG.  24 A  shows a regulated charge pump in which both switches of the regulator have been removed; 
         FIG.  24 B  shows the switch configurations for the regulated charge pump of  FIG.  24 A ; 
         FIGS.  25 A- 26 B  show, for the regulated charge pump of  FIG.  24 A , additional switch configurations and network states in which there are only three states and configurations needed to operate the charge pump; 
         FIG.  27 A  is a two-phase implementation of the regulated charge pump of  FIG.  24 A ; and 
         FIG.  27 B  shows the network states for the regulated charge pump of  FIG.  27 A . 
     
    
    
     DETAILED DESCRIPTION 
     A charge pump has a high-voltage terminal and a low-voltage terminal. Because of conservation of energy, the high-voltage terminal is associated with a lower current, whereas the low-voltage terminal is associated with a higher current. The regulator can, in principle, be placed at either end. 
     However, in order to allow the inductor in the regulator to participate in the adiabatic charging of all capacitors in the charge pump, it is important that the regulator be connected to the low-voltage side. There are two disadvantages to this configuration: one physical and the other operational. 
     The physical disadvantage arises from the fact that the low-voltage terminal of the charge pump has a great deal of current coming out of it. This means that the switch within the regulator must be able to accommodate very high currents. This is most often achieved by making the transistor that implements the switch physically larger, so that the current density at any point within the transistor will be smaller. Unfortunately, with this switch consuming so much of the die area, it can become necessary to use a larger die. This increases cost of manufacture, as well as size of the power converter as a whole. 
     The operational disadvantage arises from the fact that charge pumps are generally more efficient at executing a voltage transformation than regulators. Although the regulator can also transform voltage, it is not particularly efficient at doing so. Where it excels is in providing fine control over voltage and suppressing current ripple. Thus, when a power converter is asked to transform a first voltage into a second voltage, it is preferable that the charge pump carry out as much of the voltage transformation as possible, and that the regulator do as little of the voltage transformation as possible. 
     There are two constraints that militate against achieving this. The first constraint is that charge pumps are designed around a particular integer ratio, n/m. Thus, for a given input voltage V in , the output voltage V out  of a charge pump is V in *(n/m). This ratio is fixed for a particular configuration of the charge pump. Among the regulator&#39;s functions is to bridge the gap between the overall factor required to reach a target value of voltage and the factor (n/m) that the charge pump contributes. 
     The second constraint that arises in known designs is that a minimum voltage margin must exist between the input and output of the regulator. If the regulator is placed at the low-voltage terminal of the charge pump, it is quite possible that the voltage at the output of the charge pump and the target voltage will differ by less than this minimum voltage margin. 
     For example, if the desired power converter output is 1.0 volt, and V in  is 4.2 volts, one can use a charge pump designed with m/n=3 to maintain 1.4 volts at the low voltage output. Although this slightly exceeds the target voltage, the regulator is intended to bridge the gap between the 1.4 volts and the desired 1.0 volts. This is desirable because a large fraction of the required voltage transformation will have been carried out by the more efficient charge pump. 
     However, if this output is provided to a regulator that requires, for example, a 0.6 volt minimum voltage margin, then it will not be possible to output 1.0 volts. This creates what amounts to a gap in the performance of the power converter. 
     Of course, this problem can easily be solved by using a charge pump designed with m/n=2 instead. If this is done, the output of the charge pump will be 2.1 volts, which will be enough to provide the 0.6 voltage margin. However, the job of transforming the 2.1 volts into the desired 1.0 volt must now be carried out by the regulator, which is not particularly efficient at doing so. 
     In a first embodiment, shown in  FIG.  1   , a power converter  10  transforms a first voltage V 1  into a second voltage V 2 . The power converter  10  includes a regulator  12  and a 3-terminal charge pump  14  in series. The 3-terminal charge pump  14  has a first CP-terminal  16 , a second CP-terminal  18 , and a third CP-terminal  17 . 
     A regulator controller  13  connected to a regulator-control output  132  controls the switching activity of the regulator  12  based at least in part on feedback from a feedback line  144  connected to the second voltage V 2 . The regulator controller  13  can, however, rely on other inputs such as a feed-forward line  141 , a first intermediate feedback line  142 , and a second intermediate feedback line  143 . A regulator-control input  131 , which can be a digital input or an analog input, enables one to enter a set point for operation of the regulator  12 . 
     Meanwhile, a charge-pump controller  15  that is connected to a charge-pump-control output  152  controls the switching activity of the 3-terminal charge pump  14 . A charge-pump-control input  151 , which can be a digital input or an analog input, enables one to enter a set point for operation of the 3-terminal charge pump  14 . 
     The power converter  10  further includes a clock  145  connected to both the charge-pump controller  15  and the regulator controller  13  to ensure that switches open and close at the correct time and in synchrony. 
     For the sake of clarity, the regulator controller  13 , the charge-pump controller  15 , and the clock  145  have been omitted from certain figures. However, it is understood that they are always implicitly present. 
     During operation of the 3-terminal charge pump  14 , the regulator  12  maintains the first CP-terminal  16  at a high voltage, but has a low current passing through it. The second CP-terminal  18  is maintained at a relatively low voltage by the action of the 3-terminal charge pump  14 . Both the first and second CP-terminals  16 ,  18  share a common ground reference at the third CP-terminal  17 . 
     In particular, for an input voltage V h , at the first CP-terminal  16 , the voltage at the second CP-terminal  18  is V h *(m/n) where m/n is the defining voltage transformation ratio of the particular charge pump. The second CP-terminal  18  will, however, also have a higher current passing through it. In the ideal case, with no loss, the power entering the 3-terminal charge pump  14  should be equal to the power leaving the 3-terminal charge pump  14 . This means that the product of high current and low voltage at the second CP-terminal  18  should be equal to the product of high voltage and low current at the first CP-terminal  16 . 
     The 3-terminal charge pump  14  can be implemented using many different charge pump topologies such as Ladder, Dickson, Series-Parallel, Fibonacci, and Doubler. Some of these topologies can be configured such that the ground reference associated with the first CP-terminal  16  and the ground reference associated with the second CP-terminal  18  are different, resulting in a 4-terminal charge pump  74  with four terminals. 
       FIG.  2    illustrates a 4-terminal charge pump  74  that is a two-phase variant of the Dickson charge pump, also known as a cascade multiplier. In addition to the first and second CP-terminals  16 ,  18 , the 4-terminal charge pump  74  also includes fourth and fifth CP-terminals  116 ,  118 . Unlike in the 3-terminal charge pump  14 , the first and second CP-terminals  16 ,  18  in the 4-terminal charge pump  74  do not share a common ground reference. Instead, the first CP-terminal  16  has its own ground reference at the fourth CP-terminal  116  and the second CP-terminal  18  has its own ground reference at the fifth CP-terminal  118 . 
     The 4-terminal charge pump  74  features a switching network that causes transitions between first and second states. A switched-capacitor network  21  inside of the 4-terminal charge pump  74  alternates between first and second states depending on which of these switches are open and which ones are closed. A first switch configuration causes the switched-capacitor network  21  to transition from the first state to the second state. A second switch configuration causes the switched-capacitor network  21  to transition from the second state to the first state. Charge pumping action arises as a result of the switches causing the switched-capacitor network  21  to switch between these states. 
     In operation, different amounts of current will flow through different switches. It is therefore useful to size the switches in a manner appropriate to the currents that will be flowing through them. For example, the switches connected to the second and fifth CP-terminals  18 ,  118  carry more current then the other switches in  FIG.  2   . By making these switches larger than the other switches one avoids the need to have unnecessarily large switches and thus results in a smaller circuit footprint. This also avoids unnecessary additional capacitive losses, which are proportional to the size of the switch. 
       FIG.  3 A  shows the terminals that will connect to a switched-capacitor network  21  of the 4-terminal charge pump  74 . The 4-terminal charge pump  74  is constantly transitioning between states, each of which is a different capacitor network. In the discussion that follows, the switched-capacitor network  21  shown in  FIG.  2    will only be shown in one state or the other. As a result, the proliferation of switches shown in  FIG.  2    will no longer need to be shown. 
     Of course, no one state can be said to actually define the 4-terminal charge pump  74  any more than it is possible to identify one frame that defines a movie. In recognition of this, the switched-capacitor network  21  is shown as a blank screen in  FIG.  3 A . Either a first state  21 A or a second state  21 B will be projected into this blank screen. The actual switched capacitor network that exists in  FIG.  3 A  will depend on exactly when one looks at it. Sometimes, the switched-capacitor network  21  will be in its first state  21 A, as shown in  FIG.  3 B , and sometimes it will be in its second state  21 B, as shown in  FIG.  3 C . 
     The first and second states  21 A,  21 B are essentially symmetric. Although the topology appears the same, a close examination of  FIGS.  3 B and  3 C  will reveal that the capacitors have switched places. This switching places is what the switches shown in  FIG.  2    accomplish. 
     In the 4-terminal charge pump  74  shown in  FIG.  4   , there are three internal charge-transport paths. A first charge-transport path, between the fifth CP-terminal  118  and the second CP-terminal  18  carries a first current, i P . This first charge-transport path carries the highest current. A second charge-transport path between the first CP-terminal  16  and the second CP-terminal  18  carries a second current, i H . A third charge-transport path between the fifth CP-terminal  118  and the fourth CP-terminal  116  carries a third current, i L . The current present at the second CP-terminal  18  is thus the sum (i P +i H ). This is approximately equal to N*i H , where N depends on the topology of the switched-capacitor network  21 . In this embodiment, the grounds are not completely isolated because there is a charge-transport path between them. 
     The 3-terminal charge pump  14  can be created from the 4-terminal charge pump  74  by shorting the fourth CP-terminal  116  to the second CP-terminal  18  and by shorting the fifth CP-terminal  118  to the third CP-terminal  17  of the 3-terminal charge pump  14 . A block diagram of the resulting charge pump is shown in  FIG.  5   . 
     It is apparent from  FIG.  5    that there are two internal charge-transport paths within the 3-terminal charge pump  14 . A first charge-transport path, between the third CP-terminal  17  and the second CP-terminal  18  carries a first current, i P +i L . This first charge-transport path carries the highest current. A second charge-transport path between the first CP-terminal  16  and the second CP-terminal  18  carries a second current, i H . The current present at the second CP-terminal  18  is thus the sum (i P +i H +i L ). This is approximately equal to (N+1)i H , wherein N depends on the topology of the switched-capacitor network  21 . 
     In the embodiment shown in  FIG.  1   , the regulator  12  is placed between the first voltage V 1  to be transformed and the first CP-terminal  16  of the 3-terminal charge pump  14 . This hinders the regulator&#39;s ability to promote adiabatic inter-capacitor charge transport among the capacitors in the 3-terminal charge pump  14 . To improve this ability, it is preferable to connect the regulator  12  to the second CP-terminal  18 . 
     The desirability of placing the regulator  12  at the second CP-terminal  18  is apparent from  FIGS.  3 B- 3 C . An examination of the network topology reveals that an inductor coupled to the second CP-terminal  18  would be coupled to all capacitors in the switched-capacitor network  21 . Therefore, it will be able to influence all three charge-transport paths simultaneously. In contrast, an inductor coupled to the first CP-terminal  16  will only be able to affect the second charge-transport path between the first CP-terminal  16  and the second CP-terminal  18 . To make matters worse, the second charge-transport path does not carry nearly as much current as the first charge-transport path between the fifth CP-terminal  118  and the second CP-terminal  18 . Thus, to reduce loss, it is more important to influence the first charge transport path. 
     In the configuration shown in  FIG.  1   , the regulator  12  has been partially side-lined. It can still regulate the current at the second CP-terminal  18 . But it has lost its ability to promote adiabatic inter-capacitor charge transport. 
     However, having the regulator  12  connected to the first CP-terminal  16  instead of the second CP-terminal  18  is not without its advantages. In particular, at the first CP-terminal  16 , only a small current, i H , flows through regulator  12 . This means that the various components in the regulator  12  no longer have to be sized to accommodate the larger current, (i H +i P ), present at the second CP-terminal  18 . 
     In particular, in a common embodiment of a regulator  12 , such as that shown in  FIG.  6 A , a switch  20  periodically connects an inductor  22  into a first state and into a second state according to a duty cycle. This switch  20  ultimately bears the full brunt of the current passing through the regulator  12 . Since practical switches  20  are implemented with semiconductor materials, there is some risk that the switch  20  will overheat. Since the heat produced in a bulk material is the product of resistivity and current density, one way to reduce excessive heating of a semiconductor switch  20  so that it can accommodate large amounts of current is to simply spread the current over a larger area of semiconductor material, thus lowering the current density. However, this results in a switch  20  that consumes a great deal of area on a semiconductor die. 
     Many other regulator configurations have such a switch  20  that periodically connects an inductor into a first state and into a second state to regulate. Other examples are shown in  FIGS.  6 B- 6 D , which features a boost converter in  FIG.  6 B , a boost-buck converter in  FIG.  6 C , and a Flyback converter in  FIG.  6 D . Although these regulators are somewhat different in topology, they all feature a switch  20  that modulates an inductor  22  (or transformer). Other suitable regulators not shown, include Flyback converters, quasi-resonant Flyback converters, active-clamp Flyback converters, interleaved Flyback converters, Cuk converters, SEPIC converters, resonant converters, multi-level converters, Forward converters, two-switch Forward converters, active-clamp Forward converters, interleaved Forward converters, multi-Resonant Forward converters, Half-Bridge converters, asymmetric Half-Bridge converters, multi-resonant Half-Bridge converters, LLC resonant Half-Bridge converters, and Full-Bridge converters. 
     As a result of having connected the regulator  12  to the first CP-terminal  16  as shown in  FIG.  1   , the switch  20  needs only to accommodate a smaller current than it would have had to accommodate had it been connected to the second CP-terminal  18 . Of course, the switch  20  may need to be designed to accommodate the high voltage at the first CP-terminal  16 . However, this trade-off is usually favorable in most designs. 
     Another advantage of connecting the regulator  12  to the first CP-terminal  16  is that the inductor  22  does not need as large of an inductance as it would have had it been connected to the second CP-terminal  18 . This reduces the dc resistance of the inductor  22  and thus reduces energy losses associated with the current through the inductor  22 . 
     Adiabatic inter-capacitor charge transport remains desirable no matter where the regulator  12  is placed. With the inductor  22  within the regulator  12  no longer available for this purpose, it is necessary to add another component to the power converter  10 . This results in an increase in the component count and a resultant increase in circuit complexity. 
     To promote adiabatic intra-capacitor charge transport within the 3-terminal charge pump  14 , the illustrated embodiment in  FIG.  1    features a magnetic filter  24  that is connected to the second CP-terminal  18 . The magnetic filter  24  includes an inductor that tends to promote adiabatic inter-capacitor charge transport within the 3-terminal charge pump  14 . 
     The switches shown in  FIG.  2    will transition between states at some switching frequency. It is desirable that, in order to reduce loss, the charge pump  14  operate adiabatically at that switching frequency. One way to ensure that this is the case is to choose the resistances of the switches such that they are so large that the RC time constant of the charge transfer between the capacitors is similar if not longer than the switching frequency. Unfortunately, this increases the resistive losses. The magnetic filter  24 , allows us to reduce the resistance of the switches without incurring substantial redistribution loss and thereby operate adiabatically. Therefore, the switches can be optimally sized for the highest efficiency without worrying about redistribution loss. The optimal size for each switch is chosen by balancing the resistive and capacitive losses in each switch at a given switching frequency and at a given current. 
     Yet another advantage of connecting the regulator  12  to the first CP-terminal  16  arises with certain dynamically reconfigurable charge pumps. 
     In some cases, it is possible for the first voltage V 1  shown in  FIG.  1    to fluctuate considerably. There may be times, for example, where the voltage drops enough so that the voltage across the regulator  12  is insufficient for proper operation. This requires reducing the voltage transformation ratio of the 3-terminal charge pump  14 , thus providing enough slack voltage for the regulator  12  to work with. Such dynamic reconfiguration can be carried out using charge pumps, such as those described in U.S. Pat. No. 8,817,501. 
     When a charge pump is in a new configuration, the voltages across the capacitors in the charge pump may have to change to be appropriate to the new configuration. This change often has to occur rapidly. A rapid change in capacitor voltage requires a very large current. 
     For some charge pumps, the capacitor voltages are set by whatever is present at the second CP-terminal  18 . An example of such a configuration is the one shown in  FIGS.  3 A- 3 C , where it is apparent that the voltage across the capacitors is a function of the voltage between the second CP-terminal  18  and the third CP-terminal  17 . For these charge pump configurations, a dynamic reconfiguration may draw considerable current through the first CP-terminal  16  as the charge pump begins to operate in its new configuration. 
     Placing the regulator  12  before the 3-terminal charge pump  14  as illustrated in  FIG.  1   , and carefully synchronizing the operation of the regulator  12  with the dynamic reconfiguration of the 3-terminal charge pump  14 , can avoid this disturbance. In particular, while the 3-terminal charge pump  14  is in the old configuration, the regulator  12  supplies a first intermediate voltage to the 3-terminal charge pump  14  via the first CP-terminal  16 . Then, during the brief interval that reconfiguration is actually taking place, the regulator  12  is quickly adjusted so that instead of providing the first intermediate voltage, it provides a second intermediate voltage that is more appropriate for the charge pump&#39;s new configuration. Once dynamic reconfiguration is complete, the 3-terminal charge pump  14  resumes operation. However, by this time, the regulator  12  is already ready and waiting to supply it with the correct second intermediate voltage at the first CP-terminal  16 . 
     The magnetic filter  24  can be created in many different ways.  FIG.  7 A  shows one implementation of the magnetic filter  24  that features a first inductor  26  and, optionally, a capacitor  28 . 
       FIG.  7 B  shows an alternative magnetic filter  24  that features an a second inductor  27  in addition to the first inductor  26  and the capacitor  28 . This embodiment of the magnetic filter  24  is a third order low pass filter and therefore, more effective than the magnetic filter  24  in  FIG.  7 A  at attenuating high frequencies. 
     A charge pump is constantly opening and closing one or more switches. It is important, particularly when an inductor is present in a circuit, that whenever a switch is opened, current flowing in the circuit have someplace to go. Otherwise it may damage the switch. 
     Between the first state and the second state of a charge pump (e.g., the 3-terminal charge pump  14 ), there is a dead-time interval during which all of the switches in the switched-capacitor network  21  are open. Although not, in principle, required, this dead-time interval is a practical necessity because switches do not transition instantaneously. Thus, it is necessary to provide a margin to avoid the undesirable result of having switches closed at the same time. 
     In a preferred embodiment, a magnetic filter  24  connected to the second CP-terminal  18  in a power converter  10  is modified to include a circuit element to safely shunt current that would otherwise have no place during the dead-time of the 3-terminal charge pump  14 . In one such embodiment shown in  FIG.  8   , a shunt diode  29  is used to direct such current. Alternatively, if the dead-time interval in the switched-capacitor network  21  does not last too long, a shunt capacitor can be connected to ground to temporarily store excess charge during that interval and to release it once the switches have been properly reconnected. In some cases, a switch is placed in series with the shunt capacitor so that the shunt capacitor can be disconnected from the circuit when it is not needed. This avoids having the shunt capacitor interfere with circuit operation. 
       FIG.  9    shows a variant of the power converter  10  in  FIG.  1    in which the output of a regulating circuit  12  connects to multiple 3-terminal charge pumps  14  in parallel. Each 3-terminal charge pump  14  has a corresponding magnetic filter  24  at its second CP-terminal  18 . The outputs of each magnetic filter  24  are then combined at a common node, which is a second voltage V 2  of a power converter  10 . 
       FIG.  10    shows a variant of the embodiment in  FIG.  9    in which the magnetic filters  24  are constructed using a coupled inductor  26 . The coupled inductor  26  is constructed by having two windings sharing a common core. 
     The idea of a coupled inductor as shown in  FIG.  10    can also be used in the regulator  12 . This is shown in  FIG.  11   , in which a regulator  12  such as that shown in  FIG.  6 A  is opened up to reveal a coupled inductor  22  shared by two switches  20 . 
       FIG.  12    illustrates yet another embodiment in which a regulator  12 , a 4-terminal charge pump  74 , and a magnetic filter  24  are connected in series. However, unlike the embodiment in  FIG.  1   , the 4-terminal charge pump  74  is used instead of the 3-terminal charge pump  14 . This 4-terminal charge pump  74  is a four-terminal charge pump, rather than a three-terminal charge pump  14  as shown in  FIG.  1   . Since there are more terminals, there are more options for interconnection. For example, in the particular example shown, as a result of the orientation of the grounds, the first and second voltages V 1 , V 2  are of opposite polarity. This provides a simple way to change the polarity of an input voltage without having any additional stages (e.g, a polarity inverting stage). 
     In the embodiments discussed thus far, all power that passes through the power converter  10  flows through both the regulator  12  and the 3-terminal charge pump  14 . However, in certain embodiments, the power path is bifurcated within the power converter so that some of the power bypasses the regulator  12  altogether. 
       FIG.  13    shows one embodiment that achieves a bifurcated power path, one of which carries more power than the other. In  FIG.  13   , a first power path  30  and a second power path  32  traverse the power converter  10 . The heavier line on the second power path  32  indicates that it carries the higher of the two powers. Conversely, the lighter line on the first power path  30  indicates that this path carries the lower of the two powers. 
     The second power path  32  carries power that goes through the 3-terminal charge pump  14 . Meanwhile, the first power path  30  passes through the regulator  12 , bypassing the 3-terminal charge pump  14  in the process. Because the 3-terminal charge pump  14  is more efficient at executing a voltage transformation, it is desirable for most of the power to use the second power path  32 . 
     An additional advantage to a bifurcated power path is that the regulator  12  can be used to provide an additive offset to the voltage difference across the first CP-terminal  16  and third CP-terminal  17  of the 3-terminal charge pump  14 . As a result, there is an extra degree of freedom available for controlling the voltage at the output of the power converter  10 . This provides greater flexibility and thus fewer voltage ranges at which the power converter  10  will not be able to provide a desired output voltage. 
     In the embodiment shown in  FIG.  13   , the voltage at an output  83  of the regulator  12  is the same as that at the output  38  of the magnetic filter  24 . This is achieved by connecting the ground terminal  86  of the regulator  12  to the first CP-terminal  16  of the 3-terminal charge pump  14 . The output  83  of the regulator  12  that was connected to the first CP-terminal  16  in  FIG.  1    is then connected to the output  38  of the magnetic filter  24  instead. 
       FIG.  14 A  shows an exemplary circuit that uses the configuration of  FIG.  13    to transform a 12-volt input voltage into a 1-volt output at a load  40 . A 4-volt input is provided at the first CP-terminal  16  of the 3-terminal charge pump  14 . The 3-terminal charge pump  14 , being a 4:1 charge pump, outputs 1 volt at its second CP-terminal  18 . 
     Meanwhile, the remaining 8 volts is presented across the input terminal  81  and ground terminal  86  of the regulator  12 , which presents −3 volts at the output  83  of regulator  12 . However, this −3 volts is measured relative to the ground of the regulator  12 , which is not the same as that of the 3-terminal charge pump  14 . Because the ground terminal  86  of the regulator  12  is connected to the first CP-terminal  16  of the 3-terminal charge pump  14 , it too must be at 4 volts. Therefore, the voltage measured at the output  83  of the regulator  12  would actually be 1 volt (i.e. 4−3) when measured relative to the ground of the 3-terminal charge pump  14 . As a result, the voltage at the output  83  of the regulator  12  and the output  38  of the magnetic filter  24  will be the same at the load  40 , as they should be. 
       FIG.  14 B  shows the circuit of  FIG.  14 A  being used to transform a 12-volt input voltage into a 2-volt output at a load  40 . Unlike the circuit in  FIG.  14 A , the voltage presented to the regulator  12  is half that presented to the 3-terminal charge pump  14  instead of the other way around. 
     In operation, an 8-volt input is provided at the first CP-terminal  16  of the 3-terminal charge pump  14 . The 3-terminal charge pump  14 , being a 4:1 charge pump, outputs 2 volts at its second CP-terminal  18  as required. 
     Meanwhile, the remaining 4 volts is presented across the input terminal  81  and ground terminal  86  of the regulator  12 , which presents −6 volts at the output  83  of the regulator  12 . However, this −6 volts is measured relative to the ground of the regulator  12 , which is not the same as that of the 3-terminal charge pump  14 . Because the ground terminal  86  of the regulator  12  is connected to the first CP-terminal  16  of the 3-terminal charge pump  14 , it too must be at 8 volts. Therefore, the voltage measured at the output  83  of the regulator  12  would actually be 2 volts (i.e. 8−6) when measured relative to the ground of the 3-terminal charge pump  14 . As a result, the voltages at the output  83  of the regulator  12  and the output  38  of the magnetic filter  24  at the load  40  will be the same, as they should be. 
     With isolated charge pumps, such as a 4-terminal charge pump  74 , it becomes possible to create alternative architectures for bifurcating the power path where only a portion of the total power passes through the regulator  12 .  FIG.  15    shows such an architecture. 
     Referring to  FIG.  15 A , the first power path  30  starts at the fourth CP-terminal  116  and leads to the input terminal  81  of the regulator  12  while the second power path  32  starts at the second CP-terminal  18  and leads to a magnetic filter  24 . The bulk of the power goes through the second power path  32 . This configuration is advantageous because the regulator  12  no longer has to bear the brunt of carrying all the power that goes through the power converter  10 . As was the case in  FIG.  13   , the output  83  of the regulator  12  and the output  38  of the magnetic filter  24  meet at a common node, a second voltage V 2  of the power converter  10 , to which a load  40  will be connected. 
       FIG.  15 B  is an implementation of the embodiment shown in  FIG.  15 A . The configuration shown is analogous to that shown in  FIG.  14 B  except that in  FIG.  15 B , it is the regulator that is grounded and the charge pump that floats. 
     Embodiments of the type shown in  FIG.  15 A  require that the regulator  12  and 4-terminal charge pump  74  have separate grounds. This requires a fully-isolated version of the 4-terminal charge pump  74 , an example of which is shown in  FIG.  16 A . 
     In operation, the fully-isolated version of the 4-terminal charge pump  74  shown in  FIG.  16 A  transitions between a first state and a second state. During the first state, switches in a first switch-set  1  open and switches in a second switch-set  2  close. During the second state, switches in the second switch-set  2  open and switches in the first switch-set  1  close. 
     While the 4-terminal charge pump  74  is in its first state, a coupling capacitor C C  that stores charge sufficient for maintaining the voltage across the first CP-terminal  16  and the fourth CP-terminal  116 . Then, when the charge pump  74  transitions into its second state, the coupling capacitor C c  presents its maintained voltage to the 3-terminal charge pump  14  contained within the 4-terminal charge pump  74 . 
     This method will work for any type of charge pump topology, two examples of which are shown in  FIGS.  16 B and  16 C . 
     In particular,  FIG.  16 B  shows the architecture of the charge pump  74  in  FIG.  16 A  in use with a cascade multiplier type similar to the charge pump in  FIGS.  3 A- 3 C , the difference being that the voltage transformation ratio is different and the number of phases is different. 
       FIG.  16 C  is a two-phase version of the 4-terminal charge pump  74  in  FIG.  16 B . In contrast to the implementation shown in  FIG.  16 B , this implementation can draw continuous input current. This results in the ability to reduce the size of first and second DC capacitors C DC1 , C DC2  in  FIG.  15 B . 
     The particular implementations shown in  FIGS.  16 B and  16 C  have switch pairs with switches that belong to the same switch set and that are in series. For example, the embodiment in  FIG.  16 B  has one such switch pair between the coupling capacitor C c  and pump capacitor C 1 . Since the switches in each of these switch pairs belong to the first switch-set  1 , they always open and close together. Thus, it is possible to eliminate additional switches by merging the switches in each switch pair. The embodiment in  FIG.  16 C  has two such switch pairs in a similar location, but were merged in the figure. 
       FIGS.  17 A- 17 D  show four possible variants of configurations for the architecture of  FIG.  15   . These differ in whether or not they use a magnetic filter  24  at all, and if so, which charge-pump terminal is connected to it. 
     In a first configuration  42 , shown in  FIG.  17 A , the regulator  12  is connected to the second CP-terminal  18  of the 4-terminal charge pump  74 , while the magnetic filter  24  is connected to the fourth CP-terminal  116  of the 4-terminal charge pump  74 . A suitable regulator for this configuration is a boost converter. 
     A second configuration  44 , shown in  FIG.  17 B , is the converse of the first configuration  42 . This second configuration  44  is particularly advantageous because most of the current flows through the second CP-terminal  18 . Thus, the regulator  12  is placed at the lower current terminal, and therefore accrues all the advantages associated with such placement as already discussed. 
     A third configuration  46 , shown in  FIG.  17 C , dispenses with a magnetic filter  24  altogether and just has a regulator  12  connected to the second and fourth CP-terminals  18 ,  116  of the 4-terminal charge pump  74 . 
     A fourth configuration  48 , shown in  FIG.  17 D , also dispenses with the magnetic filter  24  but uses a separate regulator  12  at the second and fourth CP-terminals  18 ,  116 . This fourth configuration offers considerable flexibility since the duty cycles of each regulator  12  can be controlled independently of each other. 
     In the third configuration  46 , shown in  FIG.  17 C , there is only multiplicative control over a second voltage V 2 . In particular, the second voltage V 2  is given by the product of the first voltage V 1  and ((N+1)/(D+1)), where N is the number of stages in the 4-terminal charge pump  74  and D is the duty cycle of the regulator  12 , with D=1 corresponding to a permanently closed switch. 
     On the other hand, the first and second configurations  42 ,  44 , shown in  FIGS.  17 A and  17 B , offer a combination of additive and multiplicative control over the second voltage V 2 . 
     In particular, in the first configuration  42 , shown in  FIG.  17 A , the second voltage V 2  is given by the product of the first voltage V 1  and (1+N/(1−D)). 
     In the second configuration  44 , shown in  FIG.  17 B , the second voltage V 2  is given by the product of the first voltage V 1  and (N+1/(1−D)). This provides greater flexibility because the additive and multiplicative control is decoupled. 
     The fourth configuration  48 , shown in  FIG.  17 D , provides greater flexibility in control because of the presence of another degree of freedom. In the fourth configuration  48 , the second voltage V 2  is given by the product of the first voltage V 1  and ((1/(1−D 2 ))+(N/(1−D 1 ))), where D 1  and D 2  are duty cycles for the two regulators shown in the  FIG.  17 D . 
     The circuits described above are representative of a variety of topologies that provide parallel power paths. However, many others are shown in  FIGS.  18 A- 18 C  and  FIGS.  19 A- 19 C . 
       FIGS.  18 A- 18 C  show three topologies in which the 4-terminal charge pump  74  has a ground that is separate from that of the regulator  12 . The terms “down” and “up” indicate the direction of voltage transformation. Thus, a circuit element identified by “down” will have its output be at a lower voltage than its input. In contrast, a circuit element identified by “up” will have its output be at a higher voltage than its input. 
       FIGS.  19 A- 19 C  show topologies in which the regulator  12 , rather than the 3-terminal charge pump  14 , has been isolated. These topologies require a regulator that incorporates a transformer, such as a flyback converter. As was the case with  FIGS.  18 A- 18 C , the regulator and charge pump can work in tandem or in opposite directions. 
       FIG.  20    consolidates and summarizes the embodiments shown in  FIGS.  1 ,  12 ,  13   , and  15 A, and in particular, draws attention to the fundamental modularity of the concepts described herein. The three general classes of components described herein, namely the regulator  12  (either isolated or non-isolated versions are applicable), the 4-terminal charge pump  74  (either isolated or non-isolated versions are applicable), and the magnetic filter  24 , can be mixed and matched in various ways to achieve a variety of technical goals. What the embodiments have in common however is the ability to split the task of regulation from the task of promoting adiabatic charge transfer within the 3-terminal charge pump  14 . 
     The circuit topologies described herein thus enable one to eliminate the large switch associated with having a regulator connected to a terminal of a charge pump that has a low voltage and a high current. Instead, an inductor replaces the regulator. The inductor is able to carry out one of the regulator&#39;s functions in the prior art, namely that of facilitating adiabatic inter-capacitor charge transport within the charge pump. However, it was precisely this function that pinned the regulator to the low-voltage second CP-terminal  18  of the charge pump. The fact that the regulator was pinned to the second CP-terminal  18  resulted in a great many technical problems, including the introduction of dead zones that may be inconveniently located, and the need to allocate a great deal of die space to the oversized switches that were necessary at that location. Having been liberated from its location at the second CP-terminal  18  of the charge pump, the regulator can now be placed in a variety of other locations. This, in turn, enables the circuit designer to adjust the locations of the dead zones of operation based on the requirements of the power converter. It also results in the ability to use a more modestly sized switch in the regulator, and to thereby save considerable die space. 
     In some embodiments described thus far, the regulator  12  connects to the first CP-terminal  16  of the 3-terminal charge pump  14 . This means that less current will flow through the switch  20  in the regulator  12 . As a result, it is possible to reduce the size of the switch  20 . However, these embodiments have the disadvantage of still having a switch size greater than zero. 
     In other embodiments described thus far, the power path is bifurcated so that the majority of the current bypasses the regulator  12 , and hence the switch  20 , altogether. This approach also permits making the switch  20  smaller. However, this approach suffers from the disadvantage that some current still goes through the switch  20 . 
     In another embodiment, the switch size is reduced to zero, effectively eliminating the problem altogether, but without giving up the regulating function of the regulator  12 . The resulting circuit, which is referred to as a “regulated charge pump,” minimizes loss due to the switch  20  by causing the 3-terminal charge pump  14  and regulator  12  to share a common switch set, none of which will carry the full brunt of all the current that passes through the power converter  10 . 
     As a first example,  FIG.  21 A  shows a buck converter  12  and a 3-terminal charge pump  14  that have been merged to create a first regulated charge pump  41 . The first regulated charge pump  41  still has the switch  20  that was originally in the regulator  12 . This switch  20  carries considerable current. Operation of the first regulated charge pump  41  includes cycling the circuit through a first set of network states  51  using a first set of switch configurations  61 , as shown in  FIGS.  21 B- 21 C . A disadvantage of the first regulated charge pump  41  is therefore that the switch  20  is still present. 
     A second regulated charge pump  42 , shown in  FIG.  22 A , eliminates the switch  20 . In effect, the functionality of the switch  20  has been incorporated into the 3-terminal charge pump  14 . Operation of this second regulated charge pump  42  includes attaining the same first set of network states  51  but using a different, second set of switch configurations  62 , shown in  FIG.  22 B . 
     A disadvantage of the second regulated charge pump  42  is that all switches must run at the same frequency. This can be inconvenient because the capacitors and the inductor tend to have different energy densities. However, for cases in which the current is quite high, the advantage associated with eliminating the switch  20  can outweigh this disadvantage. 
     Another disadvantage of the second regulated charge pump  42  is that the overall circuit can potentially become an unstable oscillator. To reduce the likelihood of this occurring, a third regulated charge pump  43 , shown in  FIG.  23 A , introduces a stabilizing capacitor  94  and a stabilizing switch  96 . The loss arising from the stabilizing switch  96  is minimal because only a small amount of current has to flow into the stabilizing capacitor  94 . Operation of this third regulated charge pump  43  involves cycling through a second set of network states  53  using a third set of switch configurations  63 , as shown in  FIGS.  23 B- 23 C . 
     In the regulated charge pumps thus far, although a first switch  20  of the regulator  12  has been eliminated, a second switch remains. In a fourth regulated charge pump  44 , shown in  FIG.  24 A , even this switch is eliminated. The resulting circuit is essentially a 3-terminal charge pump  14  with an LC circuit  98  at its output end. Operation of this fourth regulated charge pump  44  involves cycling through the first set of network states  51  using a fourth set of switch configurations  64 , as shown in  FIG.  21 B  and  FIG.  24 B , respectively. 
     The fourth regulated charge pump  44  can also be operated by cycling through three network states instead of four. This reduces switching loss associated with each switch transition because there are fewer switch transitions per cycle. The two alternatives are represented by third and fourth sets of network states  58 ,  59 , each of which consists of three rather than four states, and corresponding fifth and sixth sets of three switch configurations  68 ,  69 , as shown in  FIGS.  25 A- 26 B . 
     The technique used to eliminate both switches from the regulator  12  that was used in connection with the fourth regulated charge pump  44 , shown in  FIG.  24 A , can be used to implement a two-phase version, which is the fifth regulated charge pump  45  shown in  FIG.  27 A . 
     Operation of this fifth regulated charge pump  45  involves cycling through a fifth set of network states  55  using the fourth set of switch configurations  64 , as shown in  FIG.  27 B  and  FIG.  24 B , respectively. 
     In some implementations, a computer accessible storage medium includes a database representative of one or more components of the converter. For example, the database may include data representative of a switching network that has been optimized to promote low-loss operation of a charge pump. 
     Generally speaking, a computer accessible storage medium may include any non-transitory storage media accessible by a computer during use to provide instructions and/or data to the computer. For example, a computer accessible storage medium may include storage media such as magnetic or optical disks and semiconductor memories. 
     Generally, a database representative of the system may be a database or other data structure that can be read by a program and used, directly or indirectly, to fabricate the hardware comprising the system. For example, the database may be a behavioral-level description or register-transfer level (RTL) description of the hardware functionality in a high level design language (HDL) such as Verilog or VHDL. The description may be read by a synthesis tool that may synthesize the description to produce a netlist comprising a list of gates from a synthesis library. The netlist comprises a set of gates that also represent the functionality of the hardware comprising the system. The netlist may then be placed and routed to produce a data set describing geometric shapes to be applied to masks. The masks may then be used in various semiconductor fabrication steps to produce a semiconductor circuit or circuits corresponding to the system. In other examples, Alternatively, the database may itself be the netlist (with or without the synthesis library) or the data set.