# US 2018/0026518 A1 · Multi-Stage Multilevel DC-DC Step-Down Converter

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- Number: US 2018/0026518 A1
- Document ID: US20180026518A1
- Status: Published application
- Kind: A1
- Application number: 15/643,023
- Filed: 2017-07-06
- Published: 2018-01-25
- Earliest claimed: 2016-07-07
- Assignees: Queen's University at Kingston
- Inventors: Tianshu Liu; Yan-Fei Liu
- Web page: https://patentgrep.com/patent/US20180026518A1

## CPC

- H02M 1/088: for the simultaneous control of series or parallel connected semiconductor devices
- H02M 3/158: including plural semiconductor devices as final control devices for a single load
- H02M 3/1584: {with a plurality of power processing stages connected in parallel}
- H02M 1/0054: {Transistor switching losses (periodically suspending operation of switching converter in low power mode H02M1/0035)}
- Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

Disclosed are multi-stage multilevel DC-DC step-down converters. Stages may include three or four switches, and switches of each stage are operated at selected duty cycles such that each stage reduces an input voltage by one-half and voltage stress on switches is reduced. In some embodiments only a single output inductor is used in an LC filter, and the inductor may be very small as compared with a conventional Buck converter. Thus, embodiments provide DC-DC step-down converters with high power density and efficiency.

## Claims

### Claim 1

A method for controlling a DC-DC converter, wherein the DC-DC converter comprises at least one stage, wherein the at least one stage is a first stage comprising:
first and second input terminals and first and second output terminals, wherein the second input terminal and the second output terminal are connected together as a common terminal;
first, second, third, and fourth switches connected together in series across the first and second input terminals;
a first capacitor connected in parallel with the second and third switches;
a first inductor having a first terminal connected between the second and third switches and a second terminal connected to a first output terminal; and
a second capacitor connected across the first and second output terminals;
wherein the method comprises:
turning on the first and third switches for a first selected portion of a first switching cycle;
turning on the second and fourth switches for a second selected portion of the first switching cycle;
wherein the first and second selected portions of the first switching cycle are each 50%;
wherein an output DC voltage of the DC-DC converter is 0.5 times an input DC voltage of the DC-DC converter; and
wherein a voltage across the first inductor is substantially zero volts.

### Claim 2 (depends on 1)

The method of claim 1, wherein the DC-DC converter comprises a second stage;
wherein the second stage comprises fifth, sixth, seventh, and eighth switches connected together in series, a second stage first input terminal connected to an input terminal of the fifth switch, a second stage first output terminal connected to a point between the sixth and seventh switches, and a third capacitor connected in parallel with the sixth and seventh switches;
wherein the second stage first input terminal is connected between the second and third switches and the second stage first output terminal is connected to the first terminal of the first inductor;
wherein the method comprises:
turning on the first and third switches for a first 25% of a first switching cycle at a first switching frequency;
turning on the second and fourth switches for a second 25% of the first switching cycle at the first switching frequency;
turning on the fifth and seventh switches for a first 50% of a first switching cycle at a second switching frequency;
turning on the sixth and eighth switches for a second 50% of the first switching cycle at the second switching frequency;
wherein an output DC voltage of the DC-DC converter is 0.25 times an input DC voltage of the DC-DC converter; and
wherein a voltage across the first inductor is substantially zero volts and a voltage across the second inductor is substantially zero volts.

### Claim 3 (depends on 1)

The method of claim 1, wherein the DC-DC converter comprises a second stage connected between the second capacitor of the first stage and the output terminals;
wherein the second stage comprises fifth, sixth, seventh, and eighth switches connected together in series across the second capacitor;
a third capacitor connected in parallel with the sixth and seventh switches;
a second inductor having a first terminal connected between the sixth and seventh switches and a second terminal connected to the first output terminal; and
a fourth capacitor connected across the first and second output terminals;
wherein the method comprises:
turning on the first and third switches for a first 50% of a first switching cycle at a first switching frequency;
turning on the second and fourth switches for a second 50% of the first switching cycle at the first switching frequency;
turning on the fifth and seventh switches for a first 50% of a first switching cycle at a second switching frequency;
turning on the sixth and eighth switches for a second 50% of the first switching cycle at the second switching frequency;
wherein an output DC voltage of the DC-DC converter is 0.25 times an input DC voltage of the DC-DC converter; and
wherein a voltage across the first inductor is substantially zero volts and a voltage across the second inductor is substantially zero volts.

### Claim 4 (depends on 2)

The method of claim 2, wherein:
the first switching frequency and the second switching frequency are different; or
the first switching frequency and the second switching frequency are the same and a phase of the first stage and a phase of the second stage are different, or
the first switching frequency and the second switching frequency are the same and a phase of the first stage and a phase of the second stage are the same.

### Claim 5 (depends on 3)

The method of claim 3, wherein:
the first switching frequency and the second switching frequency are different; or
the first switching frequency and the second switching frequency are the same and a phase of the first stage and a phase of the second stage are different, or
the first switching frequency and the second switching frequency are the same and a phase of the first stage and a phase of the second stage are the same.

### Claim 6 (depends on 1)

The method of claim 1, further comprising controlling a dead time of the first, second, third, and fourth switches;
wherein controlling the dead time minimizes a volt-second produced across the first inductor for a duration of the dead time.

### Claim 7 (depends on 6)

The method of claim 6, wherein the duration of the dead time is less than 200 nanoseconds.

### Claim 8 (depends on 2)

The method of claim 2, further comprising controlling a dead time of the first to eighth switches;
wherein a duration of the dead time is less than 200 nanoseconds.

### Claim 9 (depends on 3)

The method of claim 3, further comprising controlling a dead time of the first to eighth switches;
wherein a duration of the dead time is less than 200 nanoseconds.

### Claim 10 (depends on 1)

The method of claim 1, wherein the DC-DC converter comprises a second stage connected between the third and fourth switches of the first stage and the first inductor;
wherein the second stage comprises fifth, sixth, and seventh switches connected together in series across the third and fourth switches;
a third capacitor connected in parallel with the fifth and sixth switches;
wherein the first terminal of the first inductor is connected between the fifth and sixth switches and the second terminal of the first inductor is connected to the first output terminal; and
the second capacitor is connected across the first and second output terminals;
wherein the method comprises:
turning on the first and third switches for a first 25% of a switching cycle;
turning on the second and fourth switches for a second 25% of the switching cycle;
turning on the fifth and seventh switches for a first 50% of the switching cycle;
turning on the sixth switch for a second 50% of the switching cycle;
wherein an output DC voltage of the DC-DC converter is 0.25 times an input DC voltage of the DC-DC converter; and
wherein a voltage across the first inductor is substantially zero volts.

### Claim 11 (depends on 10)

The method of claim 10, further comprising controlling a dead time of the first to seventh switches;
wherein a duration of the dead time is less than 200 nanoseconds.

### Claim 12 (depends on 10)

The method of claim 10, wherein the DC-DC converter comprises a third stage connected between the sixth and seventh switches of the second stage and the first inductor;
wherein the third stage comprises eighth, ninth, and tenth switches connected together in series across the sixth and seventh switches;
a fourth capacitor connected in parallel with the eighth and ninth switches;
wherein the first terminal of the first inductor is connected between the eighth and ninth switches and the second terminal of the first inductor is connected to the first output terminal; and
the second capacitor is connected across the first and second output terminals;
wherein the method comprises:
turning on the first and third switches for a first 12.5% of a switching cycle;
turning on the second and fourth switches for a second 12.5% of the switching cycle;
turning on the fifth and seventh switches for a first 25% of the switching cycle;
turning on the sixth switch for a second 25% of the switching cycle;
turning on the eighth and ninth switches for a first 50% of the switching cycle;
turning on the tenth switch for a second 50% of the switching cycle;
wherein an output DC voltage of the DC-DC converter is 0.125 times an input DC voltage of the DC-DC converter; and
wherein a voltage across the first inductor is substantially zero volts.

### Claim 13 (depends on 12)

The method of claim 12, further comprising controlling a dead time of the first to tenth switches.

### Claim 14 (depends on 13)

The method of claim 13, wherein the duration of the dead time is less than 200 nanoseconds.

### Claim 15

A DC-DC converter, comprising:
a first input terminal adapted to receive an input DC voltage;
a common terminal;
a first four switch (4S) stage comprising:
first, second, third, and fourth switches connected together in series across the first input terminal and the common terminal;
a first capacitor connected in parallel with the series-connected second and third switches;
a 4S input point connected to an input terminal of the first switch;
a 4S output point at a first node between the second and third switches;
a common terminal connected to an output terminal of the fourth switch;
an output circuit comprising a series inductor, a parallel capacitor, and a first output terminal adapted to output a DC voltage; and
a controller that controls the 4S switches such that the first and third switches are switched on and off together, the second and fourth switches are switched on and off together, the first and third switches are not on when the second and fourth switches are on, and the duty cycle of the switches is 50% or less;
wherein an output DC voltage is one-half of the input DC voltage.

### Claim 16 (depends on 15)

The DC-DC converter of claim 15, wherein the DC-DC converter comprises a second 4S stage;
wherein the second 4S stage comprises fifth, sixth, seventh, and eighth switches connected together in series, a second 4S stage first input point connected to an input terminal of the fifth switch, a second 4S stage first output point connected between the sixth and seventh switches, and a third capacitor connected in parallel with the sixth and seventh switches;
wherein the second 4S stage first input point is connected between the second and third switches and the second 4S stage first output point is connected to a first terminal of the series inductor;
a controller that controls the first 4S stage switches and the second 4S stage switches such that:
the first and third switches are switched on and off together for a first 25% of a first switching cycle at a first switching frequency;
the second and fourth switches are switched on and off together for a second 25% of the first switching cycle at the first switching frequency;
the fifth and seventh switches are switched on and off together for a first 50% of a first switching cycle at a second switching frequency; and
the sixth and eighth switches are switched on and off together for a second 50% of the first switching cycle at the second switching frequency;
wherein an output DC voltage of the DC-DC converter is 0.25 times an input DC voltage of the DC-DC converter; and
wherein a voltage across the series inductor is substantially zero volts.

### Claim 17 (depends on 15)

The DC-DC converter of claim 15, further comprising a three switch (3S) stage, wherein the 3S stage comprises:
fifth, sixth, and seventh switches connected together in series;
a 3S input point connected to an input terminal of the fifth switch;
a 3S output point connected to an output terminal of the fifth switch;
a second capacitor connected in parallel with the series-connected fifth and sixth switches; and
a common terminal connected to an output terminal of the seventh switch;
wherein the 3S input point is connected to the 4S output point of the 4S stage, and the 3S output point is connected to the output circuit;
wherein the controller controls the 4S switches such that the duty cycle is 25%; and
wherein the controller controls the 3S switches such that the fifth and seventh switches are switched on and off together, the sixth switch is switched on and off, the fifth and seventh switches are not on when the sixth switch is on, and the duty cycle of the 3S switches is 50%;
wherein an output DC voltage is one-quarter of the input DC voltage.

### Claim 18 (depends on 17)

The DC-DC converter of claim 17, comprising first and second 3S stages;
wherein the first and second 3S stages are cascaded by connecting the first 3S stage output point to the second 3S stage input point;
wherein the first 3S stage input point is connected to the 4S output point of the 4S stage, and the second 3S stage output point is connected to the output circuit;
wherein the controller controls the 4S switches such that the duty cycle is 12.5%; and
wherein the controller controls the first 3S stage such that the duty cycle is 25%;
wherein the controller controls the second 3S stage such that the duty cycle is 50%;
wherein an output DC voltage is one-eighth of the input DC voltage.

### Claim 19 (depends on 17)

The DC-DC converter of claim 17, comprising three or more 3S stages;
wherein the three or more 3S stages are cascadable by connecting a first 3S stage output point to a second 3S stage input point, connecting a second 3S stage output point to a third 3S stage input point, and continuing to a final 3S stage;
wherein the first 3S stage input point is connected to the 4S output point of the 4S stage, and the final 3S stage output point is connected to the output circuit;
wherein a total number of stages is N;
wherein the controller controls switches of the Nth stage such that the duty cycle is 50%, and controls the switches of each preceding stage such that the duty cycle decreases by half for each preceding stage;
wherein the output DC voltage is equal to the input DC voltage divided by 2N.

### Claim 20 (depends on 15)

The DC-DC converter of claim 15, wherein the controller further comprises a dead time control circuit, wherein the controller controls duration of the dead time to be less than 200 nanoseconds.