Isolated switched capacitor converter

An isolated switched capacitor converter can include: first switches coupled in series between terminals of an input port, and being configured to selectively connect a first terminal of a first capacitor to a first or second terminal of the input port; second switches coupled in series between terminals of an output port, and being configured to selectively connect a second terminal of the first capacitor to a first or second terminal of the output port; third switches coupled in series between terminals of the input port, and being configured to selectively connect a first terminal of a second capacitor to the first or second terminal of the input port; and fourth switches coupled in series between terminals of the output port, and being configured to selectively connect a second terminal of the second capacitor to the first or second terminal of the output port.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No. 201710364680.9, filed on May 22, 2017, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of power electronics, and more particularly to isolated switched capacitor converters.

BACKGROUND

A switched-mode power supply (SMPS), or a “switching” power supply, can include a power stage circuit and a control circuit. When there is an input voltage, the control circuit can consider internal parameters and external load changes, and may regulate the on/off times of the switch system in the power stage circuit. Switching power supplies have a wide variety of applications in modern electronics. For example, switching power supplies can be used to drive light-emitting diode (LED) loads.

DETAILED DESCRIPTION

Referring now toFIG. 1, shown is a schematic block diagram of an example switched capacitor converter. Referring also toFIG. 2, shown is a waveform diagram of example operation of the switched capacitor converter ofFIG. 1. A switched capacitor converter may realize voltage or current conversion by controlling the charge and discharge of capacitors through switches. Here, an input port can receive input voltage Vin. Switch Q1can connect between terminal “a” of capacitor C and a first terminal of a voltage input port, and may be turned on and off under the control of control signal G1. Switch Q2can connect between terminal “a” of capacitor C and a first terminal of an output port, and can be turned on and off under the control of control signal G2. Also control signals G1and G2may be complementary, such that when control signal G1is high, control signal G2is low, and vice versa.

Terminal “b” of capacitor C can connect to a second terminal of the input port and a second terminal of the output port. The second terminal of the input port and the second terminal of the output port may be a reference terminal (e.g., a ground terminal). Output capacitor Co can also be configured in the output port to smooth output voltage Vout. Thus, capacitor C May intermittently discharge to the output port by alternately turning switches Q1and Q2on and off, thereby realizing power transmission and voltage/current conversion. However, in this structure, the input port and the output port share a common ground, and capacitor C intermittently outputs an output current to the output port, which can lead to larger undesirable current pulsation on an input source and the output capacitor. Further, this example isolated converter may utilize coils with a larger volume that is not conducive to a miniaturized system.

In one embodiment, an isolated switched capacitor converter can include: (i) a first capacitor; (ii) a first set of switches coupled in series between two terminals of an input port, and being configured to selectively connect a first terminal of the first capacitor to a first or second terminal of the input port; (iii) a second set of switches coupled in series between two terminals of an output port, and being configured to selectively connect a second terminal of the first capacitor to a first or second terminal of the output port; (iv) a second capacitor; (v) a third set of switches coupled in series between two terminals of the input port, and being configured to selectively connect a first terminal of the second capacitor to the first or second terminal of the input port; and (vi) a fourth set of switches coupled in series between two terminals of the output port, and being configured to selectively connect a second terminal of the second capacitor to the first or second terminal of the output port, wherein at least portions of the first, second, third, and fourth sets of switches are controlled to perform state switching such that a voltage conversion ratio of the isolated switched capacitor converter is adjustable.

Referring now toFIG. 3, shown is a schematic block diagram of an example isolated switched capacitor converter, in accordance with embodiments of the present invention. In this particular example, isolated switched capacitor converter1can include capacitor C1, capacitor C2, first set of switches Q1and Q2, second set of switches Q3and Q4, third set of switches Q5and Q6, and fourth set of switches Q7and Q8. The first set of switches Q1and Q2can connect in series between two terminals of an input port (e.g., terminals “i” and “g1”). For example, terminal “g1” of the input port is a reference terminal or a ground terminal of the input port. The common terminal of switches Q1and Q2can connect to terminal “a” of capacitor C1.

The first set of switches Q1and Q2can selectively connect terminal “a” of capacitor C1to terminal “i” or terminal “g1” of the input port under the control of control signals G1and G2. Also, switch Q1can connect between terminal “i” of the input port and terminal “a” of capacitor C1. Switch Q2can connect between terminal “g1” of the input port and terminal “a” of capacitor C1. Switches Q1and Q2may be controlled to be alternately turned on and off, thereby connecting terminal “a” of capacitor C1to terminal “i” or terminal “g1” of the input port.

The second set of switches Q3and Q4can connect in series between two terminals of an output port (e.g., terminals “o” and “g2”). In this particular example, terminal “g2” of the output port is as a reference terminal or a ground terminal of the output port. The common terminal of switches Q3and Q4can connect to terminal “b” of capacitor C1. The second set of switches Q3and Q4may selectively connect terminal “b” of capacitor C1to terminal “o” or terminal “g2” of the output port under the control of control signals G3and G4. Also, switch Q3can connect between terminal “o” of the output port and terminal “b” of capacitor C1. Switch Q4can connect between terminal “g2” of the output port and terminal “b” of capacitor C1. Switches Q3and Q4may be controlled to be alternately turned on and off, thereby connecting terminal “b” of capacitor C1to terminal “o” or terminal “g2” of the output port.

The third set of switches Q5and Q6can connect in series between two terminals of the input port. The common terminal of switches Q5and Q6can connect to terminal “c” of capacitor C2. The third set of switches Q5and Q6may selectively connect terminal “c” of capacitor C2to terminal “i” or terminal “g1” of the input port under the control of control signals G5and G6. Also, switch Q5can connect between terminal “i” of the input port and terminal “c” of capacitor C2. Switch Q6can connect between terminal “g1” of the input port and terminal “c” of capacitor C2. Switches Q5and Q6may be controlled to be alternately turned on and off, thereby connecting terminal “c” of capacitor C2to terminal “i” or terminal “g1” of the input port.

The fourth set of switches Q7and Q8can connect in series between two terminals of the output port. The common terminal of switches Q7and Q8can connect to terminal “d” of capacitor C2. The fourth set of switches Q7and Q8can selectively connect terminal “d” of the capacitor C2to terminal “o” or terminal “g2” of the output port under the control of control signals G7and G8. Also, switch Q7can connect between terminal “o” of the output port and terminal “d” of capacitor C2. Switch Q8can connect between terminal “g2” of the output port and terminal “d” of capacitor C2. Switches Q7and Q8may be controlled to be alternately turned on and off, thereby connecting terminal “d” of capacitor C2to terminal “o” or terminal “g2” of the output port.

When the switches change the connection relationship between the terminals of the capacitor and the input port or the output port by changing states, this can be referred to as the corresponding switch set performing state switching. The control signals that respectively control corresponding switches in a switch set may be referred to as a set of control signals. In this example, switches Q1-Q8can be implemented by any suitable electrical controlled switching devices, such as metal oxide semiconductor field effect transistors (MOSFET), bipolar junction transistors (BJT), or insulated gate bipolar transistors (IGBT). Though each set of switches includes two switches in the example ofFIG. 3, more switches can alternatively be configured therein in particular embodiments.

InFIG. 3, the first set of switches Q1and Q2, the second set of switches Q3and Q4, and capacitor C1may form an H-bridge. The third set of switches Q5and Q6, the fourth set of switches Q7and Q8, and capacitor C2may form another H-bridge. In this example, the two H-bridges are parallel and share the input port and the output port. At least portions of the first set of switches Q1and Q2, the second set of switches Q3and Q4, the third set of switches Q5and Q6, and the fourth set of switches Q7and Q8may be controlled to perform state switching in order to make the voltage conversion ratio of isolated switched capacitor converter1adjustable. For example, the voltage conversion ratio can be adjusted by controlling portions of switch sets to remain in a constant state or to perform state switching. Here, the voltage conversion ratio may refer to a ratio of the output voltage to the input voltage.

In particular embodiments, the circuit may operate in the following 3 different modes. In a first mode, there may be isolated buck conversion, switch Q1can remain turned off, and switch Q2may remain turned on, making terminal “a” of capacitor C1connected to terminal “g1” of the input port. Or, switch Q5may remain turned off, and switch Q6can remain turned on, making terminal “c” of capacitor C2connected to terminal “g1” of the input port. Other sets of the switches can perform state switching.

In a second mode, there may be isolated boost conversion, switch Q3can remain turned off, and switch Q4may remain turned on, making terminal “b” of capacitor C1connected to terminal “g2” of the output port. Or, switch Q7can remain turned off, and switch Q8may remain turned on, making terminal “d” of capacitor C2connected to terminal “g2” of the output port. Other sets of the switches perform may state switching.

In a third mode, there may be isolated isobaric conversion, and all the switches can be controlled to perform state switching. The following further describes the three modes of control signals and equivalent circuits with reference to the drawings. The following description illustrates an example case whereby the duty cycle of the control signal is 50%. The time of the isolated switched capacitor converter in the first and second states is thus the same, in order to better reflect the characteristics of the circuit in different modes. However, those skilled in the art will recognize that by adjusting the duty cycle of control signals, operation of the converter can be optimized for a given application.

The two sets of control signals can also have a certain dead time. The dead time may be configured as a protection period in order to prevent the upper and lower switches of the H-bridge or half-H-bridge from being turned on simultaneously due to the switching speed problem during the pulse-width modulation (PWM) output or the PWM response time.

Referring now toFIG. 4, shown is a waveform diagram of example operation of the isolated switched capacitor converter in a first mode, in accordance with embodiments of the present invention. Referring also toFIG. 5, shown is an equivalent circuit diagram of the isolated switched capacitor converter in a first state of the first mode, in accordance with embodiments of the present invention. Referring also toFIG. 6, shown is an equivalent circuit diagram of the isolated switched capacitor converter in a second state of the first mode, in accordance with embodiments of the present invention.

In the example ofFIGS. 4-6, the third set of switches Q5and Q6may remain in a constant state. Here, control signals G1and G2can control the first set of switches Q1and Q2. For example, control signals G1and G2may respectively control switches Q1and Q2. Control signals G1and G2may be inverted and changed alternately to make switches Q1and Q2alternately turn on. In addition, control signals G3and G4may be inverted and changed alternately. That is, the first and second sets of switches may perform state switching in the same way.

Thus, control signals G1and G2can be seen as a first set of control signals, and since control signals G3and G4are the same as control signals G1and G2respectively, control signals G3and G4can also be seen as the first set of control signals. Control signal G5may remain low while control signal G6remains high in order to make switch Q5remain off and switch Q6remain on. Control signals G7and G8can be inverted and changed alternately to make switches Q7and Q8turn on alternately. Control signals G7and G8can control the fourth set of switches Q7and Q8to perform state switching in the opposite way to the first and second sets of switches. Control signals G7and G8may form a second set of control signals which are in opposite phase with the first set of control signals.

In this example, the circuit can operate through multiple cycles before entering the steady state. When output capacitor Co or a capacitive load connected to the output port is charged to a predetermined output voltage, the circuit may enter the steady state. In the first state, switches Q2, Q4, Q6, and Q7can be turned on, and switches Q1, Q3, Q5, and Q8may be turned off. At this time, capacitors C1and C2may form a loop with the output port and discharge to the output port. The current path corresponding to the equivalent circuit can include capacitor C1, switch Q2, switch Q6, capacitor C2, switch Q7, the output port, and switch Q4. Thus, output voltage Vout may be equal to Vc1+Vc2, where Vc1is the voltage across capacitor C1, and Vc2is the voltage across capacitor C2.

In the second state, the first set of switches, the second set of switches, and the fourth set of switches may all perform state switching, where switches Q1, Q3, and Q8are turned on and switches Q2, Q4, and Q7are turned off. In addition, the third set of switches may remain in a constant state; that is, switch Q6is still on and switch Q5is still off. At this time, terminal “i” of the input port can connect the circuit forming a current path via switch Q1, capacitor C1, switch Q3, the output port, switch Q8, capacitor C2, and switch Q6. The input port may discharge the output port through capacitors C1and C2. In the second state, output voltage Vout may satisfy: Vout+Vc1+Vc2=Vin. Since the time period of the first and second states is relatively short, and the capacitive load or output capacitor Co may obstruct the change of voltage, voltages Vc1and Vc2in the second state may remain unchanged with respect to the first state. Therefore, the following formula (1) may be applied.
Vout+Vc1+Vc2=2Vout=Vin  (1)

As described above, since output voltage Vout may not change significantly in the two states, output voltage Vout can be maintained around ½ of input voltage Vin, thereby achieving buck isolated conversion. Simultaneously, the input port and the output port can be isolated by capacitors C1and C2regardless of the state, such that there may be no need to use a transformer in order to realize isolation. Similarly, since the H-bridge formed by the first set of switches Q1and Q2, the second set of switches Q3and Q4, and capacitor C1is symmetrical to the H-bridge formed by the third set of switches Q5and Q6, the fourth set of switches Q7and Q8, and capacitor C2, the first set of switches Q1and Q2can be controlled to remain in a constant state by the control signals, and other sets of switches can be controlled to perform state switching periodically at the same time, thereby reaching the same effect.

Referring now toFIG. 7, shown is a waveform diagram of example operation of the isolated switched capacitor converter in a second mode, in accordance with embodiments of the present invention. Referring also toFIG. 8, shown is an equivalent circuit diagram of the isolated switched capacitor converter in a first state of the second mode, in accordance with embodiments of the present invention. Referring also toFIG. 9, shown is an equivalent circuit diagram of the isolated switched capacitor converter in a second state of the second mode, in accordance with embodiments of the present invention.

In the example ofFIGS. 7-9, the fourth set of switches Q7and Q8may remain in a constant state. Here, control signals G1and G2can respectively control switches Q1and Q2. Control signals G1and G2may be inverted and changed alternately to make switches Q1and Q2alternately turn on. Moreover, control signals G3and G4can be alternately inverted and changed. Control signals G1and G3may be in phase, and control signals G2and G4may be in phase. That is, the first and second sets of switches can be controlled to perform state switching in the same way under the control of the first set of control signals. Control signal G7can remain low while control signal G8remains high to make switch Q7remain off and switch Q8remain on, such that that terminal “d” of capacitor C2can be connected to terminal “g2” of the output port whether in the first or the second state.

Control signals G5and G6may be inverted and changed to make switches Q5and Q6turn on alternately. In addition, control signals G5and G2may be in phase, and control signals G6and G1may be in phase. That is, the third set of control signals G5and G6can control the third set of switches Q5and Q6to perform state switching in the opposite way to the first and second sets of switches. The first and second sets of control signals may be inverted. In this example, the circuit can operate through multiple cycles before entering the steady state, and when output capacitor Co or the capacitive load connected to the output port is charged to a predetermined output voltage, the circuit may enter the steady state.

In the first state, switches Q2, Q4, Q5and Q8can be turned on, and switches Q1, Q3, Q6and Q7turned off. Isolated switched capacitor converter1may form a current loop from terminal “i” of the input port via switch Q5, capacitor C2, switch Q8, terminal “g2” of the output port, switch Q4, capacitor C1, and switch Q2to terminal “g1” of the input port. Thus, input voltage Vin may be equal to Vc1′+Vc2′, where Vc1′ is the voltage across capacitor C1, and Vc2′ is the voltage across capacitor C2. In the second mode, voltage Vc1′ across capacitor C1and voltage Vc2′ across capacitor C2can be inverted relative to voltage sVc1and Vc2inFIGS. 5 and 6. In the first state, the output port may not be connected to the circuit such that output voltage Vout can be maintained according to the capacitance of the capacitive load itself or output capacitor Co of the output port.

In the second state, the first, second, and third sets of switches may all perform state switching, where switches Q1, Q3, and Q6are turned on and switches Q2, Q4, and Q5are turned off. In addition, the fourth set of switches may remain in a constant state; that is, switch Q8is still on and switch Q7is still off. At this time, terminal “o” of the output port can connect the circuit forming a current path via switch Q1, capacitor C1, switch Q3, the output port, switch Q8, capacitor C2, and switch Q6to terminal “g1” of the input port. The input port can discharge the output port through capacitors C1and C2. In the second state, output voltage Vout may satisfy: Vout=Vin+Vc1′+Vc2′. Since the time period of the first and second states is relatively short, and the capacitive load or output capacitor Co may obstruct the change of voltage, voltages Vc1′ and Vc2′ in the second state may be unchanged with respect to the first state. Therefore, the following formula (2) may be applied.
Vin+Vc1′+Vc2′=2Vin=Vout  (2)

As described above, since output voltage Vout may not change significantly in the two states, output voltage Vout can be maintained at 2 times input voltage Vin, thereby achieving boost isolated conversion. In addition, the input port and the output port can be isolated by capacitors C1and C2regardless of the state, such that there may be no need to utilize a transformer in order to realize isolation. Since the H-bridge formed by the first set of switches Q1and Q2, the second set of switches Q3and Q4, and capacitor C1is symmetrical to the H-bridge formed by the third set of switches Q5and Q6, the fourth set of switches Q7and Q8, and capacitor C2, the second set of switches Q3and Q4can be controlled to remain in a constant state through control signals, and other sets of switches can be controlled to perform state switching periodically at the same time, thereby reaching the same effect.

Referring now toFIG. 10is a waveform diagram of example operation of the isolated switched capacitor converter in a third mode, in accordance with embodiments of the present invention. Referring also toFIG. 11, shown is an equivalent circuit diagram of the isolated switched capacitor converter in a first state of the third mode, in accordance with embodiments of the present invention. Referring also toFIG. 12, shown is an equivalent circuit diagram of the isolated switched capacitor converter in a second state of the third mode, in accordance with embodiments of the present invention.

In the third mode, all switches perform state switching periodically to make the output voltage the same as the input voltage. Control signals G1-G4can respectively control switches Q1-Q4. Control signals G1and G2may be inverted and changed alternately to make switches Q1and Q2turn on alternately. Simultaneously, control signals G3and G4can be inverted and changed alternately. Control signals G1and G3may be in phase, and control signals G2and G4can be in phase. That is, the first and second sets of switches may perform state switching in the same way.

Correspondingly, control signals G5-G8can respectively control switches Q5-Q8. Control signals G5and G6may be inverted and changed alternately to make switches Q5and Q6turn on alternately. Simultaneously, control signals G7and G8can be inverted and changed alternately. Control signals G5and G7may be in phase, and control signals G6and G8are in phase. Control signals G5and G7, and control signals G1and G3may be inverted. That is, the third and fourth sets of switches may perform state switching in the same way, which is opposite to that of the first and second sets of switches.

Thus, in the first state, switches Q2, Q4, Q5and Q7can be turned on, and switches Q1, Q3, Q6and Q8may be turned off. Therefore, a current path can be formed from terminal “i” of the input port via switch Q5, capacitor C2, switch Q7, the output port, switch Q4, capacitor C1, and switch Q2, to terminal “g1” of the input port. The input port can charge the output port through capacitors C1and C2, and output voltage Vout may satisfy: Vout−Vc1−Vc2=Vin.

In the second state, switches Q1, Q3, Q6, and Q8can be turned on, and switches Q2, Q4, Q5, and Q7may be turned off. Thus, a current path may be formed from terminal “i” of the input port via switch Q1, capacitor C1, switch Q3, the output port, switch Q8, capacitor C2, and switch Q6, to terminal “g1” of the input port. It can be seen that the currents flowing through capacitors C1and C2in the first and second states may be inverted. The input port can charge the output port through capacitors C1and C2, and the output voltage may satisfy: Vout+Vc1+Vc2=Vin. In both states, the currents flowing through capacitors C1and C2can be counterbalanced by each other, such that that Vc1+Vc2=0, and Vout=Vin. That is, the output voltage is equal to the input voltage in this case, reaching isobaric conversion. Further, the input port and the output port can be isolated by capacitors C1and C2regardless of the state, such that there may be no need to utilize inductors in order to realize isolation.

Two parallel H-bridge switched capacitor networks may be respectively built by the first and second sets of switches and capacitor C1, and the third and fourth sets of switches and capacitor C2, in order to effectively isolate the input port and the output port. In addition, power conversion can be realized by controlling each set of switches to remain in a constant state or to perform state switching, and then controlling capacitors C1and C2to charge and discharge. The voltage conversion ratio can be adjusted by applying different control methods. Therefore, the input port and the output port can be isolated without the transformer, which can reduce the volume of the isolated converter and further realize buck and boost operation. The isolated switched capacitor converter in particular embodiments has a simple structure and improved flexibility, as compared to other approaches, and the voltage conversion ratio can be adjusted while the input and output ports are isolated.