JP7698491B2 - Three-level converter, controller circuit and control method thereof, and electronic device using the same - Google Patents

Description

This disclosure relates to a resonant switched capacitor converter.

DC/DC converters and charge pumps are used to generate voltages higher or lower than the power supply voltage. DC/DC converters that use inductors as an element to store energy can control the output voltage by using the inductor, but they have the problem of reduced efficiency due to switching operations.

In applications that require high efficiency, switched capacitor converters (charge pumps) are used, which do not require an inductor as an energy storage element. One type of switched capacitor converter is known to operate in resonance by adding a resonant inductor in series with the flying capacitor (called a resonant switched capacitor converter). A resonant switched capacitor converter enables zero current switching (soft switching), making it possible to operate with high efficiency.

Also, hybrid DC/DC converters, three-level converters, series capacitor DC/DC converters, etc. have been proposed. A general DC/DC converter generates a switching signal having an amplitude according to the input voltage V _IN and stores energy in an inductor, whereas a hybrid DC/DC converter, a three-level converter, and a series capacitor DC/DC converter use a capacitor to generate a switching signal having an amplitude V _IN /2, which is half the input voltage V _IN , and store energy in an inductor. This can improve efficiency.

U.S. Patent No. 9,917,517

This disclosure has been made in this context, and one of its exemplary objectives is to provide a novel switched capacitor converter and a controller for the same.

An aspect of the present disclosure relates to a controller circuit for a three-level converter. The three-level converter includes a first switch, a second switch, a third switch, and a fourth switch connected in series between an input line and a ground line, a capacitor connected between both ends of the second switch and the third switch, and an inductor connected between a connection node of the second switch and the third switch and an output line. The controller circuit can switch between a first state in which the first switch and the second switch are on, a second state in which the first switch and the third switch are on, a third state in which the third switch and the fourth switch are on, and a fourth state in which the second switch and the fourth switch are on, and repeats the first state, the second state, the third state, the first state, the fourth state, and the third state in this order.

In addition, any combination of the above components, or mutual substitution of components or expressions between methods, devices, systems, etc., are also valid aspects of the present invention.

According to certain aspects of the present disclosure, a three-level converter can be operated in zero voltage switching mode, improving efficiency.

FIG. 1 is a circuit diagram of a resonant switched capacitor converter according to an embodiment. FIG. 2 is an equivalent circuit diagram of the resonant switched capacitor converter of FIG. 1 in a first state. FIG. 3 is an equivalent circuit diagram of the resonant switched capacitor converter of FIG. 1 in a second state. FIG. 4 is an equivalent circuit diagram of the resonant switched capacitor converter of FIG. 1 in a third state. FIG. 5 is an equivalent circuit diagram of the resonant switched capacitor converter of FIG. 1 in a fourth state. FIG. 6 is a waveform diagram illustrating the operation of the resonant switched capacitor converter. FIG. 7 is a diagram for explaining the operation of a three-level converter according to a comparative technique. FIG. 8 is a circuit diagram of a resonant switched capacitor converter including a controller IC with feedback function. FIG. 9 is a circuit diagram showing a configuration example of the feedback controller and the state control unit. FIG. 10 is a diagram showing an example of an electronic device including a resonant switched capacitor converter.

(Overview of the embodiment)
A summary of some exemplary embodiments of the present disclosure will be described. This summary is intended to provide a simplified overview of some concepts of one or more embodiments for a basic understanding of the embodiments as a prelude to the detailed description that follows, and is not intended to limit the scope of the invention or disclosure. This summary is not an exhaustive overview of all possible embodiments, and is not intended to identify key elements of all embodiments or to delineate the scope of some or all aspects. For convenience, the term "one embodiment" may be used to refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed in this specification.

A controller circuit according to one embodiment controls a three-level converter. The three-level converter to be controlled includes a first switch, a second switch, a third switch, and a fourth switch connected in series between an input line and a ground line, a capacitor connected between both ends of the second switch and the third switch, and an inductor connected between a connection node of the second switch and the third switch and an output line. The controller circuit can switch between a first state in which the first switch and the second switch are on, a second state in which the first switch and the third switch are on, a third state in which the third switch and the fourth switch are on, and a fourth state in which the second switch and the fourth switch are on, and repeats the first state, the second state, the third state, the first state, the fourth state, and the third state in this order.

This control sequence allows for zero voltage switching, improving efficiency.

In one embodiment, the time of the first state may be equal to the time of the third state, and the time of the second state may be equal to the time of the fourth state. This simplifies the control and simplifies the configuration of the controller circuit.

In one embodiment, the controller circuit may be capable of controlling the time of the first state and the time of the third state depending on the state of the load. By controlling the length of the first state and the third state, the average value of the coil current flowing through the inductor can be controlled.

In one embodiment, the controller circuit may include a feedback controller that feedback controls the lengths of at least the first and third states so that the error between the output voltage generated on the output line and the target level is reduced. This allows the output voltage to be stabilized at the target level.

In one embodiment, the feedback controller may include an error amplifier that amplifies the error between the output voltage generated on the output line and a target level, a pulse modulator that generates a pulse signal according to the output of the error amplifier, and a state control unit that switches from a first state to a fourth state according to the pulse signal.

In one embodiment, the controller circuit may be monolithically integrated on a single semiconductor substrate. "Monolithic integration" includes cases where all of the circuit components are formed on a semiconductor substrate, and cases where the main components of the circuit are monolithically integrated, and some resistors, capacitors, etc. may be provided outside the semiconductor substrate for adjusting the circuit constants. By integrating the circuit on a single chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

(Embodiment)
The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, the embodiments are not intended to limit the invention, but are merely examples, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, "a state in which component A is connected to component B" includes not only cases in which component A and component B are directly physically connected, but also cases in which component A and component B are indirectly connected via other components that do not substantially affect their electrical connection state or impair the function or effect achieved by their combination.

Similarly, "a state in which component C is provided between components A and B" includes not only cases in which components A and C, or components B and C, are directly connected, but also cases in which they are indirectly connected via other components that do not substantially affect their electrical connection state or impair the function or effect achieved by their combination.

Furthermore, "signal A (voltage, current) corresponds to signal B (voltage, current)" means that signal A has a correlation with signal B, specifically meaning (i) when signal A is signal B, (ii) when signal A is proportional to signal B, (iii) when signal A is obtained by level-shifting signal B, (iv) when signal A is obtained by amplifying signal B, (v) when signal A is obtained by inverting signal B, (vi) or any combination thereof. Those skilled in the art will understand that the scope of "corresponding" is determined according to the type and application of signals A and B.

The vertical and horizontal axes of the waveform diagrams and time charts referred to in this specification have been appropriately enlarged or reduced to facilitate understanding, and the waveforms shown have been simplified, exaggerated, or emphasized to facilitate understanding.

(Embodiment)
1 is a circuit diagram of a resonant switched capacitor converter 100 according to an embodiment. The resonant switched capacitor converter 100 is a three-level converter and includes a controller IC (Integrated Circuit) 200 and its peripheral circuit 110. The resonant switched capacitor converter 100 steps down an input voltage V _IN supplied to an input line 102, and generates an output voltage V _OUT on an output line 104.

Specifically, the peripheral circuit 110 includes a first switch SW1 to a fourth switch SW4, capacitors C1 and C2, and an inductor L1. The first switch SW1 to the fourth switch SW4 are connected in series between the input line 102 and the ground line 106. One end of the capacitor C1 is connected to the first switching node _n1 , and the other end of the capacitor C1 is connected to the third switching node _n3 . In other words, the capacitor C1 is connected between both ends of the second switch SW2 and the third switch SW3.

The inductor L1 is connected between a connection node (second switching node) _n2 between the second switch SW2 and the third switch SW3 and the output line 104. The output capacitor C2 is connected to the output line 104. In this embodiment, the first switch SW1 to the fourth switch SW4 are N-channel MOSFETs, but this is not limited thereto, and some of them may be replaced with P-channel MOSFETs. Also, instead of the MOSFETs, bipolar transistors or IGBTs (Insulated Gate Bipolar Transistors) may be used.

The controller IC 200 drives multiple switches SW1 to SW4. The controller IC 200 is a functional IC that includes a drive circuit 210 and a state control unit 220 and is integrated into a single semiconductor chip. The first switch SW1 to the fourth switch SW4 may be integrated into the controller IC 200.

The controller IC 200 is configured to be switchable among four states φ1 to φ4.
First state φ1
First switch SW1 and second switch SW2: ON
Third switch SW3 and fourth switch SW4: OFF
Second state φ2
First switch SW1 and third switch SW3: ON
Second switch SW2 and fourth switch SW4: OFF
Third state φ3
Third switch SW3 and fourth switch SW4: ON
First switch SW1 and second switch SW2: OFF
Fourth state φ4
Second switch SW2 and fourth switch SW4: ON
First switch SW1 and third switch SW3: OFF

The controller IC 200 repeats the sequence of the first state φ1, the second state φ2, the third state φ3, the first state φ1, the fourth state φ4, and the third state φ3. The state transitions are controlled by the state control unit 220. Note that in the state transitions, each switch is switched from the on state to the off state first, and then switched from the off state to the on state.

The state control unit 220 generates control signals S1 to S4 that instruct the switches SW1 to SW4 to be on or off in each of the states φ1 to φ4. The drive circuit 210 drives the corresponding switches SW1 to SW4 based on the control signals S1 to S4.

The above is the configuration of the resonant switched capacitor converter 100 and the controller IC 200. Next, we will explain their operation.

Fig. 2 is an equivalent circuit diagram of the first state φ1 of the resonant switched capacitor converter 100 in Fig. 1. In the first state φ1, the first switch SW1 and the second switch SW2 are on. Since _Vn1 = _Vn2 = _VIN , the voltage across the inductor L1 is _VIN - _VOUT , and in the first state φ1, the coil current I _L of the inductor L1 increases at a slope of ( _VIN - _VOUT )/L.

3 is an equivalent circuit diagram of the resonant switched capacitor converter 100 in the second state φ2 of FIG. 1. In the second state φ2, the first switch SW1 and the third switch SW3 are on. If the voltage across the capacitor C1 is Vc, then in the second state φ2, V _n3 =V _n2 =V _IN -Vc. At this time, the voltage across the inductor L1 is V _n2 -V _OUT =(V _IN -Vc)-V _OUT , and in the second state φ2, the coil current I _L of the inductor L1 changes with a slope of (V _IN -Vc-V _OUT )/L. In addition, in the steady state, Vc≈V _IN /2, so the coil current I _L is substantially constant.

4 is an equivalent circuit diagram of the resonant switched capacitor converter 100 in FIG 1 in the third state φ3. In the third state φ3, the third switch SW3 and the fourth switch SW4 are on. The voltage across the inductor L1 is −V _OUT , and in the third state φ3, the coil current I _L of the inductor L1 increases with a slope of −V _OUT /L (and decreases with a slope of V _OUT /L).

5 is an equivalent circuit diagram of the resonant switched capacitor converter 100 in FIG. 1 in the fourth state φ4. In the fourth state φ4, the second switch SW2 and the fourth switch SW4 are on. If the voltage across the capacitor C1 is Vc, then in the fourth state φ4, V _n2 =Vc. At this time, the voltage across the inductor L1 is V _n2 -V _OUT =Vc-V _OUT , and in the fourth state φ4, the coil current I _L of the inductor L1 changes with a slope of (Vc-V _OUT )/L. In addition, in the steady state, Vc≈V _IN /2, so the coil current I _L is substantially constant.

Fig. 6 is a waveform diagram illustrating the operation of the resonant switched capacitor converter 100. Fig. 6 shows the coil current I _L flowing through the inductor L1. When the time length of the first state φ1 is t _on1 and the time length of the third state φ3 is t _on3 , the amount of change ΔI _L1 of the coil current I _L in the first state φ1 and the amount of change ΔI L3 of the coil current I _L in the third state _φ3 are expressed by the following equations.
ΔI _L1 = (V _IN - V _OUT )/L×t _on1
ΔI _L3 =-V _OUT /L×t _on3
In a steady state, when the coil current _IL is stabilized, the absolute values of _ΔIL1 and _ΔIL3 are equal.
(V _IN - V _OUT )/L x t _on1 = V _OUT /L x t _on3
If we impose the constraint t _on1 =t _on3 ,
(V _IN - V _OUT ) = V _OUT
That is, in the steady state,
_VOUT = _VIN /2
can be obtained.

This resonant switched capacitor converter 100 enables zero voltage switching, which allows for low-loss, highly efficient operation. The reason for this will be explained below.

Transition from the first state φ1 to the second state φ2 In the steady state, Vc=V _IN /2 and V _OUT =V _IN /2 are established. In the first state φ1, V _n1 =V _n2 =V _IN , V _n3 =V _IN /2. When the second switch SW2 is turned off during the transition from the first state φ1 to the second state φ2, the current flows through the body diode of the MOSFET that is the third switch SW3, forming the same current path as in the second state. The switching voltage V _n2 drops to V _IN /2, and the drain-source voltage of the MOSFET that is the third switch SW3 becomes zero. When the third switch SW3 is turned on in this state, zero-voltage switching occurs and no loss occurs.

Transition from the second state φ2 to the third state φ3 In the second state φ2, V _n1 =V _IN , V _n2 =V _n3 =V _IN /2. When the first switch SW1 is turned off during the transition from the second state φ2 to the third state φ3, the current flows through the body diode of the MOSFET which is the fourth switch SW4, forming the same current path as in the third state φ3. The switching voltage V _n3 drops to 0 V, and the drain-source voltage of the MOSFET which is the fourth switch SW4 becomes zero. When the fourth switch SW4 is turned on in this state, zero-voltage switching occurs, and no loss occurs.

Transition from the third state φ3 to the first state φ1 In the third state φ3, V _n1 =V _n2 =V _IN /2, V _n3 =0V (GND). In the third state φ3, as shown in FIG. 6, the coil current I _L decreases over time and becomes a negative current (current in the reverse direction). When the third switch SW3 and the fourth switch SW4 are turned off during the transition from the third state φ3 to the first state φ1, the current flows into the input line 102 via the body current of the MOSFETs that are the first switch SW1 and the second switch SW2, and the current path is the same as that of the first state φ1. At this time, the voltage V _n1 of the first switching node n1 becomes equal to the input voltage V _IN , so that the drain-source voltage of the MOSFETs that are the first switch SW1 and the second switch SW2 becomes zero. When the first switch SW1 and the second switch SW2 are turned on in this state, zero voltage switching occurs and no loss occurs.

The above is the reason for zero voltage switching. The advantages of the resonant switched capacitor converter 100 become clear when compared with comparative technologies.

In the comparative technique, a three-level converter is switched in the following three states.
Condition I
First switch SW1, third switch SW3: ON
Second switch SW2, fourth switch SW4: OFF

Condition II
Third switch SW3, fourth switch SW4: ON
First switch SW1, second switch SW2: OFF

Condition III
Second switch SW2, fourth switch SW4: ON
First switch SW1, third switch SW3: OFF

States I to III correspond to states φ2, φ3, and φ4 in the embodiment, respectively. In the comparative technology, one cycle is repeated, consisting of states I, II, III, and II. In state I, capacitor C1 is charged, and in state III, the energy stored in capacitor C1 is supplied to inductor L1.

Fig. 7 is a diagram for explaining the operation of a three-level converter according to a comparative technique. Fig. 7 shows a coil current I _L. In state I, the voltage across the inductor L1 is (V _IN -Vc)-V _OUT , and the coil current I _L changes with a slope {(V _IN -Vc)-V _OUT }/L. In state II, the voltage across the inductor L1 is -V _OUT , and the coil current I _L changes with a slope -V _OUT /L.

In state III, the voltage across inductor L1 is Vc- _VOUT , and coil current I _L changes with a slope of {Vc- _VOUT }/L.

If the time in state I and state III is t _on and the time in state II is t _off , the amounts of change ΔI _L1 to ΔI _L3 in the coil current I _L in each state are as follows:
ΔI _L1 = {(V _IN - Vc) - V _OUT }/L×t _on ...(1)
ΔI _L2 =-V _OUT /L×t _off …(2)
ΔI _L3 = {Vc-V _OUT }/L×t _on …(3)
In a steady state, when the average value of the coil current I _L is constant, ΔI _L1 = |ΔI _L2 | = ΔI _L3 holds. Since equation (1) and equation (3) are equal,
Vc=V _IN /2
Substituting this into equation (1), we get
ΔI _L1 = (V _IN /2-V _OUT )/L×t _on ...(1')
Since the absolute values of equation (1') and equation (2) are equal, we obtain equation (4).
V _OUT = V _IN /2×t _on /(t _on +t _off )=V _IN /2×d…(4)
Here, d=t _on /(t _on +t _off ) represents the duty cycle. When d=0.5, V _OUT =V _IN /4.

The above is the operation of the three-level converter according to the comparative technology. In the comparative technology, when transitioning from state II to III, switch SW3 turns off first. After switch SW3 turns off, current flows through the body diode of switch SW3, so the current path remains in state II. At this time, the drain-source voltage of second switch SW2 is non-zero, so turning on second switch SW2 in this state results in hard switching, resulting in power loss.

When transitioning from state II to state I, switch SW4 turns off first. After switch SW4 turns off, current flows through the body diode of switch SW4, so the current path remains in state II. At this time, the drain-source voltage of first switch SW1 is non-zero, so turning on first switch SW1 in this state results in hard switching, which causes power loss.

As such, hard switching occurs in the comparison technology.

In contrast, the controller IC 200 according to the embodiment can achieve soft switching, improving efficiency.

The controller IC 200 according to the embodiment operates as a converter with a gain of 1/2 when operated in an open loop, but by incorporating feedback control, it becomes possible to set the gain, that is, the output voltage V _OUT .

8 is a circuit diagram of a resonant switched capacitor converter 100A including a controller IC 200A with a feedback function. The controller IC 200A can control the lengths of the first state φ1 and the third state φ3 according to the load state. The control method may be PWM (pulse width modulation) or PFM (pulse frequency modulation). In the case of PWM, when the length of the first state φ1 and the third state φ3 is t _on and the pulse period is Tp, the length t _off of the second state φ2 and the fourth state φ4 is Tp-t _on . In the case of PFM control, the length t _off of the second state φ2 and the fourth state φ4 may be constant.

The controller IC 200A includes a feedback controller 230 in addition to a drive circuit 210 and a state control unit 220. A feedback signal VFB corresponding to an output voltage _VOUT generated on an output line 104 is input to a feedback pin _FB of the controller IC 200A. The feedback signal _VFB may be a voltage obtained by dividing the output voltage _VOUT by resistors R11 and R12, or may be the output voltage _VOUT itself.

The feedback controller 230 feedback controls at least the lengths t on of the first and third states so that the error between the feedback signal V _FB and the reference voltage V _REF becomes _zero , in other words, so that the error between the output voltage V _OUT and the target level V _OUT(REF) becomes small.

The feedback controller 230 can be configured similarly to a modulator used in a DC/DC converter.

9 is a circuit diagram showing a configuration example of the feedback controller 230 and the state control unit 220. The feedback controller 230 includes an error amplifier 232 and a pulse modulator 234. The error amplifier 232 amplifies the error between the feedback signal _VFB and the reference voltage _VREF to generate an error signal _VERR . The pulse modulator 234 generates a pulse signal Sp according to the error signal _VERR . In this example, the pulse modulator 234 is a pulse width modulator, and generates the pulse signal Sp in synchronization with an oscillator 236. The pulse width of the pulse signal Sp is controlled according to the error signal _VERR .

The state control unit 220 receives the pulse signal Sp and the clock CLK generated by the oscillator 236. The state control unit 220 switches between the first state φ1, the second state φ2, the third state φ3, the first state φ1, the fourth state φ4, and the third state φ3 in sequence according to the pulse signal Sp and the clock CLK. The lengths of the first state φ1 and the third state φ3 change according to the pulse width of the pulse signal Sp.

(Modification)
The above-described embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each processing step. Such modifications will be described below.

In FIG. 9, the feedback controller 230 is configured as an analog circuit, but it may be configured as a digital circuit. In this case, the error amplifier 232 is replaced with a subtractor and a compensator (controller). The compensator may be a PID (proportional integral differential) compensator or a PI (proportional integral) compensator.

8, the constant current output controller IC 200A that stabilizes the output voltage _VOUT has been described, but the present invention can also be applied to a constant current output converter. In this case, a signal indicating the output current _IOUT may be used as the feedback signal _VFB .

(Application)
10 is a diagram showing an example of an electronic device 700 including a resonant switched capacitor converter 100. A suitable example of the electronic device 700 is a server. Originally, a 12V power line was drawn into the server, so the internal circuit 710 is designed to operate at 12V. The internal circuit 710 may include a CPU (Central Processing Unit), a memory, a LAN (Local Area Network) interface circuit, a DC/DC converter that steps down the 12V voltage, and the like.

In recent years, there has been a movement to replace the bus voltage from 12V to 48V in order to reduce the current flowing through the electric wires. In this case, a power supply circuit 720 is required to step down the 48V power supply voltage to 12V or 24V. The resonant switched capacitor converter 100 can be suitably used for such a power supply circuit 720.

The electronic device 700 is not limited to a server, but may be an in-vehicle device. Conventional automobile batteries are mainly 12V or 24V, but hybrid vehicles may use 48V systems, and in this case too, a power supply circuit is required to convert the 48V battery voltage to 12V or 24V. In such cases, the 1/2 resonant switched capacitor converter 100 can be suitably used.

In addition, the electronic device 700 may be industrial equipment, office automation equipment, or consumer equipment such as audio equipment.

The embodiments are merely examples, and those skilled in the art will understand that there are various variations in the combination of each component and each processing process, and that such variations are also included in this disclosure and may constitute the scope of the present invention.

REFERENCE SIGNS LIST 100 Resonant switched capacitor converter 102 Input line 104 Output line 106 Ground line 110 Peripheral circuit SW1 First switch SW2 Second switch SW3 Third switch SW4 Fourth switch C1 Capacitor L1 Inductor C2 Capacitor 200 Controller IC
210 Drive circuit 220 State control unit 230 Feedback controller 232 Error amplifier 234 Pulse modulator 236 Oscillator

Claims (10)

A controller circuit for a three-level converter, comprising:
The three-level converter comprises:
a first switch, a second switch, a third switch, and a fourth switch connected in series between an input line and a ground line;
a capacitor connected across the second switch and the third switch;
an inductor connected between a connection node of the second switch and the third switch and an output line;
Equipped with
The controller circuit includes:
a first state in which the first switch and the second switch are on;
a second state in which the first switch and the third switch are on;
a third state in which the third switch and the fourth switch are on;
a fourth state in which the second switch and the fourth switch are on;
a controller circuit that repeats the first state, the second state, the third state, the first state, the fourth state, and the third state in this order. The controller circuit of claim 1, wherein the time of the first state is equal to the time of the third state, and the time of the second state is equal to the time of the fourth state. The controller circuit according to claim 1 or 2, wherein the controller circuit is capable of controlling the lengths of the first state and the third state depending on the load state. The controller circuit includes:
4. The controller circuit according to claim 1, further comprising a feedback controller that feedback controls the lengths of at least the first state and the third state so as to reduce an error between the output voltage generated on the output line and a target level. The feedback controller:
an error amplifier that amplifies an error between an output voltage generated on the output line and a target level;
a pulse modulator that generates a pulse signal according to an output of the error amplifier;
a state control unit that switches from the first state to the fourth state in response to the pulse signal;
5. The controller circuit of claim 4, comprising: A controller circuit according to any one of claims 1 to 5, which is integrated on a single semiconductor substrate. A three-level converter comprising a controller circuit according to any one of claims 1 to 6. An electronic device comprising the three-level converter according to claim 7. A control method for a three-level converter, comprising the steps of:
The three-level converter comprises:
a first switch, a second switch, a third switch, and a fourth switch connected in series between an input line and a ground line;
a capacitor connected across the second switch and the third switch;
an inductor connected between a connection node of the second switch and the third switch and an output line;
Equipped with
The control method includes:
a first state in which the first switch and the second switch are on;
a second state in which the first switch and the third switch are on;
a third state in which the third switch and the fourth switch are on;
The first state,
a fourth state in which the second switch and the fourth switch are on;
The third state,
A control method in which the above steps are repeated in sequence. The control method according to claim 9, further comprising a step of feedback-controlling the lengths of at least the first state and the third state so as to reduce an error between the output voltage generated on the output line and a target level.

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