Efficient single-mode Buck-Boost DC-DC converter

Abstract

The invention provides a high-efficiency single-mode Buck-Boost DC-DC converter, and the converter comprises a power switch group which is used for controlling the duty ratio outputted in each period through controlling the conduction time of the power switch group; the flying capacitor is used for alternately bearing multiplied input voltage and storing energy of the input voltage in different phases of the power switch group; and the output filtering unit is used for filtering the multiplied input voltage according to the duty ratio and then taking the multiplied input voltage as an output voltage, or releasing energy stored in each period and outputting the voltage. According to the invention, in a mode of supporting continuous conduction, continuous transmission of inductive current is realized by alternately switching energy paths, and in a non-continuous conduction mode, reverse current is blocked during light load, and light load efficiency is improved. The method has the advantages that the inductive current is continuous, mode switching is not needed, the inductive current is reduced in the Boost mode, the inductive conduction loss can be remarkably reduced, and the efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of converters, and in particular relates to a high-efficiency single-mode Buck-Boost DC-DC converter. Background Art

[0002] A buck-boost converter is a device that converts a DC input voltage into an adjustable DC output voltage. The output voltage can be higher, equal to, or lower than the input voltage. Due to its wide input voltage adaptability, this type of converter is widely used in the power supply systems of various electronic devices.

[0003] Figure 1 shows a prior art buck-boost converter circuit diagram, Figure 2 The converter consists of four switches (S1-S4), an inductor (L) and an output capacitor (C L When the input voltage (V IN ) is higher than the output voltage (V O ), the converter operates in buck mode. When the input voltage is lower than the output voltage, it operates in boost mode. Conventional buck-boost converters typically use a four-switch topology (e.g. Figure 1 As shown in FIG), the operating mode is switched by controlling the switch state. However, the prior art has the following defects: 1. There is a zero point on the right side of the plane: In the boost and buck-boost modes, the inductor current is discontinuous due to the periodic shutdown of the switch, resulting in unstable output.

[0004] 2. Mode switching transient discontinuity: There is a voltage jump in the transition between different operating modes, which affects the system stability.

[0005] 3. Slow dynamic response: When the duty cycle of the control signal changes, there is a delay in the regulation of the output current.

[0006] 4. Inductor current is greater than load current: In boost mode, the average inductor current is greater than the load current, resulting in increased DC conduction losses in the inductor and reduced efficiency. Summary of the Invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a high-efficiency single-mode Buck-Boost DC-DC converter. The technical problem to be solved by the present invention is achieved through the following technical solutions: A high-efficiency single-mode Buck-Boost DC-DC converter includes: The power switch group is used to control the duty cycle of the output in each cycle by controlling its own conduction time; A flying capacitor, used to alternately bear the multiplied input voltage and store energy of the input voltage in different phases of the power switch group; The output filtering unit is used to filter the multiplied input voltage according to the duty cycle and use it as the output voltage, or release the energy stored in each cycle and convert the energy into the output voltage.

[0008] Beneficial effects: The present invention provides a high-efficiency single-mode Buck-Boost DC-DC converter comprising: a power switch group for controlling the duty cycle of the output in each cycle by controlling its own conduction time; a flying capacitor for alternately bearing the multiplied input voltage and storing the energy of the input voltage in different phases of the power switch group; an output filter unit for filtering the multiplied input voltage according to the duty cycle and then using it as the output voltage, or releasing the energy stored in each cycle and outputting the voltage. In the continuous conduction mode supported by the present invention, the continuous transmission of the inductor current is achieved by alternately switching the energy path, and in the discontinuous conduction mode, the reverse current is blocked under light load to improve the light load efficiency. The present invention has the characteristics of continuous inductor current, no need for mode switching, and reduced inductor current in Boost mode, which can significantly reduce the inductor conduction loss and improve efficiency.

[0009] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is the circuit diagram of a traditional four-switch Buck-Boost converter.

[0011] Figure 2 It is the working waveform when the load changes suddenly in boost mode.

[0012] Figure 3 This is a topological diagram of the Buck-Boost converter provided by the present invention.

[0013] Figure 4 This is the working mode of the Buck-Boost converter provided by the present invention and the voltage waveforms of each node.

[0014] Figure 5 Schematic diagram of the specific power level of the Buck-Boost converter provided by the present invention.

[0015] Figure 6a This is a CCM steady-state simulation diagram of the Buck-Boost converter provided by the present invention.

[0016] Figure 6b This is a DCM steady-state simulation diagram of the Buck-Boost converter provided by the present invention.

[0017] Figure 7 This is a load switching simulation diagram of the Buck-Boost converter provided by the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0019] refer to Figure 3 As shown, the present invention provides a high-efficiency single-mode Buck-Boost DC-DC converter comprising: The power switch group is used to control the duty cycle of the output in each cycle by controlling its own conduction time; A flying capacitor, used to alternately bear the multiplied input voltage and store energy of the input voltage in different phases of the power switch group; The output filtering unit is used to filter the multiplied input voltage according to the duty cycle and use it as the output voltage, or release the energy stored in each cycle and convert the energy into the output voltage.

[0020] refer to Figure 3 , the power switch group includes power switches S1-S5; The first terminal of the power switch S1 is connected to the first terminal of the power switch S2, the input voltage V IN and voltage source VCC, the second end of the power switch S1 is respectively connected to the first end of the power switch S3, the second end of the power switch S3 is grounded GND, the middle node of the power switches S1 and S3 is A, the second end of the power switch S2 is connected to the first end of the power switch S5, the first end of the power switch S5 serves as node B, the second end of the power switch S5 serves as node C and is connected to the first end of the power switch S4, the second end of the power switch S4 is grounded GND; the flying capacitor C F The upper plate is connected to the second end of the power switch S1, and the lower plate is connected to the second end of the power switch S2; the output filter unit includes an inductor L, an output capacitor C L and the load resistor R L Wherein, the first end of the inductor L is connected to the first end of the power switch S4, and the second end of the inductor L is connected to the output capacitor C L and the load resistor R L The first end of the output capacitor C L and the load resistor R L The second end is grounded GND.

[0021] The high efficiency single mode Buck-Boost DC-DC converter of the present invention is realized by changing the load resistance R LThe resistance value enables the high-efficiency single-mode Buck-Boost DC-DC converter to operate in continuous conduction mode or discontinuous conduction mode.

[0022] Figure 4 The CCM and DCM operation of the Buck-Boost converter are illustrated accordingly. IN and V O are the input and output voltages. V CF It is C F The voltage. V A It is S1, S2 and C F The node voltage at the intersection of the lower plate, V B It is C F The node voltage at the intersection of the positive plate and switches S2 and S5, V C is the node voltage at the intersection of S4, S5 and the inductor. CF and I L , are the flying capacitor current and the load current, respectively. Figure 4 shows the Buck-Boost converter's I L , V A , V B and V C The corresponding operating waveforms are shown in Figure 2. (a) supports continuous conduction mode (CCM) and (b) supports discontinuous conduction mode (DCM).

[0023] When the converter inductor current I L <100mA, the converter enters DCM mode, for example: V O =3.3V, R L <33Ω, the converter enters DCM mode; when the converter inductor current I L >100mA, the converter enters CCM mode, for example: V O =3.3V, R L When the resistor is >33Ω, the converter enters CCM mode.

[0024] The continuous conduction mode is divided into phase 1 and phase 2; In the continuous conduction mode supporting phase 1: the power switches S1 and S5 are turned on, the power switches S2, S3, and S4 are turned off; the node V A The voltage is V IN , node V B With V C The voltage is 2V IN ; Current I of the inductor (L) L With slope The energy increases linearly, and is transferred to the load through the flying capacitor path (C-PATH) and the inductor path (L-PATH) at the same time. is the input voltage, is the output voltage; In the continuous conduction mode supporting phase 2: power switches S1 and S5 are turned off, S2, S3, and S4 are turned on; node V A Ground, node V B The voltage is V IN , node V C Ground; current I in inductor (L) L With slope The inductor energy decreases linearly, and the energy stored in the inductor is released to the load through S4. The volt-second balance equation is expressed as:

[0025] The steady-state conversion ratio is solved as:

[0026] The discontinuous conduction mode is divided into stage 1, stage 2 and stage 3; In the phase 1 of the discontinuous conduction mode, the power switches S1 and S5 are turned on, and the power switches S2, S3, and S4 are turned off; the node V A The voltage is V IN , node V B With V C The voltage is 2V IN ; Current I of the inductor (L) L With slope linear increase; In the discontinuous conduction mode, in phase 2, power switches S1 and S5 are turned off, while switches S2, S3, and S4 are turned on. A Ground, node V B The voltage is V IN , node V C Ground; current I in inductor (L) L With slope Linear decline; In phase 3 of the discontinuous conduction mode: the current I L When the voltage drops to zero, the power switches S1, S4, and S5 are turned off, and S2 and S3 are turned on; the node V A Ground, node V B The voltage is V IN , node V C The voltage is V O ; Inductor current I L Keep it at zero, the flying capacitance (C F ) is maintained at V IN The Buck-Boost converter enters a light-load state, avoiding reverse current loss and improving light-load efficiency.

[0027] Compared with CCM operation, Phase 3 adopts DCM phase to prevent the inductor from reverse current under light load conditions. In Phase 2, P2, I L V O / L decreases. When I L When it reaches 0, the ZCD circuit forces the Buck-Boost converter to operate in P3. In P3, S1, S4, and S5 are closed, and S2 and S3 are opened. F The upper voltage is maintained at V IN , the inductor current is equal to 0, in this stage V A =GND, V B =V IN , V C =V O In this stage, the inductor current is equal to 0, which is similar to the DCM stage of the buck converter, thereby improving the light-load efficiency.

[0028] Among them, switches S1, S2 and S5 are PMOS tubes or NMOS tubes, and power switches S3 and S4 are NMOS tubes.

[0029] based on Figure 4 The switching operation mode of the Buck-Boost converter in phase 1 (P1) and phase 2 (P2) is given by the inductor volt-second rule:

[0030] It can be obtained that the conversion ratio of the Buck-Boost converter is:

[0031] According to the capacitance charge balance: C F The amount of charge discharged at P1. C F Charge amount at P2. Under equilibrium conditions , verify V CF Stable at V IN .

[0032] In order to verify the beneficial effects of the present invention, the capacitance charge balance of a conventional four-switch Buck-Boost converter is compared with that of the converter of the present invention.

[0033] For a traditional four-switch Buck-Boost converter in Boost mode, the average inductor current is:

[0034] Where, is the load resistance (R L ) current, is the duty cycle.

[0035] The average inductor current of the converter of the present invention is Reduce to ,Right now .

[0036] Figure 5 The specific power stage diagram of the Buck-Boost converter is shown in Figure 1, where the switches S1, S2, and S5 are PMOS and the switches S3 and S4 are NMOS. The driver power supply and ground of S2 and S5 are respectively V B and V A Provided, the switch tube S1, S3 and S4 drive stage power supply and ground are respectively V IN and GND, which can save the bootstrap circuit and additional off-chip bootstrap capacitors, which is beneficial to the control of the power stage and simplifies the complex logic of startup.

[0037] Figure 6a This is the CCM steady-state simulation diagram of the Buck-Boost converter in Boost mode. IN =2.8V, output voltage V O =3.3V, load current 1A, inductor current I L =1A.

[0038] Figure 6b This is the DCM steady-state simulation diagram of the Buck-Boost converter in Boost mode. IN =2.8V, output voltage V O =3.3V, load current 10mA, inductor current I L =10mA.

[0039] Figure 7 This is the Buck-Boost converter load switching simulation diagram. IN =2.8V, output voltage V O =3.3V, the load current jumps from 1mA to 1A and then jumps back to 10mA, the recovery time is 11.87μs and 10.23μs respectively. The undershoot recovery time is faster because in stage 1, the inductor current I L With slope Increase, compared with the traditional BUCK stage , the inductor current slope is larger, which is conducive to energy transfer. Therefore, the undershoot recovery time is also improved to a certain extent.

[0040] Compared with the two, the Buck-Boost converter proposed in the present invention has a lower average inductor current, which is conducive to improving efficiency. The DCR conduction loss and core loss of the present invention are reduced, and the efficiency of the converter in Boost mode is improved.

[0041] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A high-efficiency single-mode Buck-Boost DC-DC converter, characterized in that: include: The power switch group is used to control the duty cycle of the output in each cycle by controlling its own conduction time; A flying capacitor, used to alternately bear the multiplied input voltage and store energy of the input voltage in different phases of the power switch group; The output filtering unit is used to filter the multiplied input voltage according to the duty cycle and use it as the output voltage, or release the energy stored in each cycle and convert the energy into the output voltage.

2. The high-efficiency single-mode Buck-Boost DC-DC converter according to claim 1, characterized in that: The power switch group includes power switches S1-S5; The first terminal of the power switch S1 is connected to the first terminal of the power switch S2, the input voltage (V IN ) and a voltage source (VCC), the second end of the power switch S1 is connected to the first end of the power switch S3 respectively, the second end of the power switch S3 is grounded (GND), the middle node between the power switches S1 and S3 is A, the second end of the power switch S2 is connected to the first end of the power switch S5, the first end of the power switch S5 serves as a node B, the second end of the power switch S5 serves as a node C and is connected to the first end of the power switch S4, the second end of the power switch S4 is grounded (GND); the flying capacitor (C F ) is connected to the second end of the power switch S1, and the lower plate is connected to the second end of the power switch S2.

3. The high-efficiency single-mode Buck-Boost DC-DC converter according to claim 2, characterized in that: The output filter unit includes an inductor (L), an output capacitor (C L ) and the load resistance (R L ); wherein the first end of the inductor (L) is connected to the first end of the power switch S4, and the second end of the inductor (L) is connected to the output capacitor (C L ) and the load resistance (R L ) first terminal; output capacitor (C L ) and the load resistance (R L ) is connected to ground (GND).

4. The high-efficiency single-mode Buck-Boost DC-DC converter according to claim 3, characterized in that: The high efficiency single mode Buck-Boost DC-DC converter is realized by changing the load resistance (R L ) resistance value, which enables the high-efficiency single-mode Buck-Boost DC-DC converter to operate in continuous conduction mode or discontinuous conduction mode.

5. The high-efficiency single-mode Buck-Boost DC-DC converter according to claim 4, characterized in that: The continuous conduction mode is divided into phase 1 and phase 2; In the continuous conduction mode supporting phase 1: the power switches S1 and S5 are turned on, the power switches S2, S3, and S4 are turned off; the node V A The voltage is V IN , node V B With V C The voltage is 2V IN ; Current I of the inductor (L) L With slope linearly increase; is the input voltage, is the output voltage; In the continuous conduction mode supporting phase 2: power switches S1 and S5 are turned off, S2, S3, and S4 are turned on; node V A Ground, node V B The voltage is V IN , node V C Ground; current I in inductor (L) L With slope Linear decrease.

6. The high-efficiency single-mode Buck-Boost DC-DC converter according to claim 4, characterized in that: The discontinuous conduction mode is divided into stage 1, stage 2 and stage 3; In the phase 1 of the discontinuous conduction mode, the power switches S1 and S5 are turned on, and the power switches S2, S3, and S4 are turned off; the node V A The voltage is V IN , node V B With V C The voltage is 2V IN ; Current I of the inductor (L) L With slope linear increase; In the discontinuous conduction mode, in phase 2, power switches S1 and S5 are turned off, while switches S2, S3, and S4 are turned on. A Ground, node V B The voltage is V IN , node V C Ground; current I in inductor (L) L With slope Linear decline; In the phase 2 of the discontinuous conduction mode: the current I L When the voltage drops to zero, the power switches S1, S4, and S5 are turned off, and S2 and S3 are turned on; the node V A Ground, node V B The voltage is V IN , node V C The voltage is V O ; Inductor current I L Keep it at zero, the flying capacitance (C F ) is maintained at V IN .

7. The high-efficiency single-mode Buck-Boost DC-DC converter according to claim 3, characterized in that: The power switches S1, S2 and S5 are PMOS tubes or NMOS tubes, and the power switches S3 and S4 are NMOS tubes.

8. The high-efficiency single-mode Buck-Boost DC-DC converter according to claim 3, wherein: The current of the inductor (L) , where is the load resistance (R L ) current, is the duty cycle.

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