US-12620899-B2 - Buck-boost switching regulator and control method thereof

US12620899B2US 12620899 B2US12620899 B2US 12620899B2US-12620899-B2

Abstract

A buck-boost switching power circuit comprises a bypass control circuit which configured to determine whether the buck-boost switching power circuit operates in a bypass mode according to a bypass enable signal. When the conversion voltage difference between the input voltage and the output voltage is less than a reference voltage, the bypass control circuit controls to electrically connect the input power source with the output power source, and operates the buck-boost switching power circuit in the bypass phase of the bypass mode. Before and/or after the bypass phase, the bypass control circuit respectively controls the buck-boost switching power circuit to operate in a first transition phase and/or a second transition phase. During the first transition phase or the second transition phase, the bypass control circuit controls the output voltage to gradually change towards the input voltage or target voltage, until the conversion voltage difference is less than the first reference voltage or the output voltage equals the target voltage.

Inventors

Tung-Hang Liu
Chi-Jen Yang
Chun-Jen Yu
Tsung-Han Yu

Assignees

RICHTEK TECHNOLOGY CORPORATION

Dates

Publication Date: 20260505
Application Date: 20240403
Priority Date: 20231018

Claims (20)

1 . A buck-boost switching power circuit for converting an input power source into an output power source, comprising: a power switch circuit, including an input switch unit and an output switch unit, wherein the input switch unit is configured to switch a first end of an inductor between the input power source or a ground potential, and the output switch unit is configured to switch a second end of the inductor between the output power source or the ground potential, to convert the input power source into the output power source; and a bypass control circuit, configured to determine whether the buck-boost switching power circuit operates in a bypass mode according to a bypass enable signal; wherein, when the bypass enable signal is at an enable level, the buck-boost switching power circuit operates in the bypass mode, and when an absolute value of a conversion voltage difference between an input voltage of the input power source and an output voltage of the output power source is less than a first reference voltage, the bypass control circuit controls the power switch circuit to electrically connect the input power source with the output power source in bypass, and causes the buck-boost switching power circuit to operate in a bypass phase of the bypass mode; wherein, in the bypass mode, before the bypass phase, the bypass control circuit controls the buck-boost switching power circuit to operate in a first transition phase, and/or after the bypass mode, the bypass control circuit controls the buck-boost switching power circuit to operate in a second transition phase; wherein, during the first transition phase, the bypass control circuit controls the output voltage to gradually change towards the input voltage in a feedback regulation manner, until the conversion voltage difference is less than the first reference voltage, ending the first transition phase; wherein, during the second transition phase, the bypass control circuit controls the output voltage to gradually change towards a target voltage, until the output voltage equals the target voltage.
2 . The buck-boost switching power circuit of claim 1 , wherein, when not in the bypass mode, the bypass control circuit enables the bypass enable signal according to a conversion voltage difference between the input voltage and an output-related voltage being less than a second reference voltage, or according to an external command, where the second reference voltage is greater than the first reference voltage; wherein the output-related voltage is the output voltage or the target voltage.
3 . The buck-boost switching power circuit of claim 1 , wherein, during the bypass phase, when a regulation voltage difference between the input voltage and the target voltage exceeds a third reference voltage, the bypass control circuit disables the bypass enable signal, to control the buck-boost switching power circuit to end the bypass phase of the bypass mode, and commence the second transition phase.
4 . The buck-boost switching power circuit of claim 1 , wherein, during the first transition phase of the bypass mode, the bypass control circuit gradually changes a fourth reference voltage according to the input voltage and the target voltage, and according fourth reference voltage in a feedback regulation manner, gradually adjusts the output voltage, thereby making the output voltage gradually change towards the input voltage until the absolute value of the conversion voltage difference is less than the first reference voltage, wherein an initial value of the fourth reference voltage is related to the target voltage.
5 . The buck-boost switching power circuit of claim 1 , wherein, during the second transition phase, the bypass control circuit gradually changes a fourth reference voltage according to the input voltage and the target voltage, and gradually adjusts the output voltage according to the fourth reference voltage in a feedback regulation manner, thereby making the output voltage gradually change towards the target voltage until the output voltage equals the target voltage, wherein an initial value of the fourth reference voltage is related to the target voltage.
6 . The buck-boost switching power circuit of claim 1 , wherein, during the bypass phase, an output high-side switch within the output switch unit and an input high-side switch within the input switch unit are both conducted to electrically connect the input power source with the output power source through the inductor.
7 . The buck-boost switching power circuit of claim 1 , further comprising a bypass switch, which is directly electrically connected between the input power source and the output power source, wherein the bypass control circuit, during the bypass phase, controls the bypass switch to conduct to directly electrically connect the input power source with the output power source.
8 . The buck-boost switching power circuit of claim 1 , wherein the bypass control circuit, during the first transition phase and/or the second transition phase, controls the output voltage in a feedback regulation manner, thereby preventing overshoot or undershoot of the output voltage.
9 . The buck-boost switching power circuit of claim 1 , wherein the input switch unit includes: an input high-side switch, coupled between the input power source and the first end of the inductor; and an input low-side switch or an input low-side diode, coupled between the ground potential and the first end of the inductor; wherein the input high-side switch, and the input low-side switch or the input low-side diode, are configured to switch the first end of the inductor between the input power source or the ground potential.
10 . The buck-boost switching power circuit of claim 1 , wherein the output switch unit includes: an output low-side switch, coupled between the ground potential and the second end of the inductor; and an output high-side switch, coupled between the output power source and the second end of the inductor; wherein the output low-side switch and the output high-side switch are configured to switch the second end of the inductor between the output power source or the ground potential.
11 . The buck-boost switching power circuit of claim 1 , wherein during the first transition phase, the bypass control circuit controls the buck-boost switching power circuit to enter a forced continuous conduction mode (FCCM).
12 . The buck-boost switching power circuit of claim 1 , wherein during the second transition phase, the bypass control circuit controls the buck-boost switching power circuit to enter or not enter a forced continuous conduction mode.
13 . The buck-boost switching power circuit of claim 1 , wherein the target voltage is the initial output voltage or a set voltage updated during the bypass phase.
14 . The buck-boost switching power circuit of claim 6 , wherein the buck-boost switching power circuit enters the bypass phase of the bypass mode only after the absolute value of the conversion voltage difference is less than the first reference voltage and both the output high-side switch and the input high-side switch are conducted.
15 . The buck-boost switching power circuit of claim 4 , further comprising an error amplification circuit, wherein the bypass control circuit includes a reference voltage generation circuit, and the error amplification circuit generates an error amplification signal according to the fourth reference voltage and an output voltage-related signal related to the output voltage, wherein the error amplification signal is configured to generate multiple switching signals for controlling the power switch circuit; wherein the bypass control circuit, during the bypass phase, further controls the buck-boost switching power circuit to stop powering at least one of the reference voltage generation circuit and the error amplification circuit, wherein the fourth reference voltage is generated by the reference voltage generation circuit according to the target voltage and the input voltage.
16 . A control method for controlling a buck-boost switching power circuit for converting an input power source into an output power source, comprising: operating a buck-boost switching power circuit in a bypass mode when a bypass enable signal is at an enable level; controlling to electrically connect, by bypassing, the input power source with the output power source and to operate the buck-boost switching power circuit in a bypass phase of the bypass mode when an absolute value of a conversion voltage difference between an input voltage of the input power source and an output voltage of the output power source is less than a first reference voltage; controlling the buck-boost switching power circuit to operate in a first transition phase before the bypass phase in the bypass mode, and/or controlling the buck-boost switching power circuit to operate in a second transition phase after the bypass mode; controlling the output voltage to gradually change towards the input voltage in a feedback regulation manner until the conversion voltage difference is less than the first reference voltage to end the first transition phase; and controlling the output voltage to gradually change towards a target voltage in a feedback regulation manner until the output voltage equals the target voltage during the second transition phase.
17 . The control method for controlling a buck-boost switching power circuit of claim 16 , further comprising: enabling the bypass enable signal according to a conversion voltage difference between the input voltage and an output-related voltage being less than a second reference voltage, or according to an external command, wherein the second reference voltage is greater than the first reference voltage; wherein the output-related voltage is the output voltage or the target voltage.
18 . The control method for controlling a buck-boost switching power circuit of claim 16 , further comprising: disabling the bypass enable signal during the bypass phase when a regulation voltage difference between the input voltage and the target voltage exceeds a third reference voltage, to control the buck-boost switching power circuit to end the bypass phase of the bypass mode and commence the second transition phase.
19 . The control method for controlling a buck-boost switching power circuit of claim 16 , wherein the step of controlling the output voltage to gradually change towards the input voltage until the conversion voltage difference is less than the first reference voltage during the first transition phase includes: gradually changing a fourth reference voltage according to the input voltage and the target voltage during the first transition phase of the bypass mode; and gradually adjusting the output voltage in a feedback regulation manner according to the fourth reference voltage, thereby making the output voltage gradually change towards the input voltage until the absolute value of the conversion voltage difference is less than the first reference voltage; wherein an initial value of the fourth reference voltage is related to the target voltage.
20 . The control method for controlling a buck-boost switching power circuit of claim 16 , wherein the step of controlling the output voltage to gradually change towards the target voltage until the output voltage equals the target voltage during the second transition phase includes: gradually changing a fourth reference voltage according to the input voltage and the target voltage during the second transition phase; and gradually adjusting the output voltage in a feedback regulation manner according to the fourth reference voltage, thereby making the output voltage gradually change towards the target voltage until the output voltage equals the target voltage, wherein an initial value of the fourth reference voltage is related to the target voltage.

Description

CROSS REFERENCE The present invention priority to TW patent application No. 112139728, filed on Oct. 18, 2023. BACKGROUND OF THE INVENTION Field of Invention The present invention pertains to a buck-boost switching regulator and its control method; more specifically, it concerns a buck-boost switching regulator designed to smoothly transition into bypass mode irrespective of the load current level, along with its associated control method. Description of Related Art It is well-known that buck-boost switching power converters are often required to operate in a low-power, energy-saving mode when applied in battery charging systems. In this mode, due to the continued switching of the power switches within the buck-boost converter, there are switching losses, which reduce conversion efficiency. Therefore, in the energy-saving mode, further maintaining an electrical connection between the input and output without switching the power switches (i.e., transitioning into bypass mode) can enhance conversion efficiency. However, in typical applications, transitioning into and out of bypass mode necessitates an additional switch to serve as the bypass path, thereby electrically connecting the input and output. In practical applications, situations may arise where there is a significant voltage difference between the input and output voltages. At the moment of short-circuiting in the bypass path, a relatively large current can occur. This sudden change in current can cause excessive output fluctuation, leading to the destruction of the aforementioned switch, its inductors, or the circuits connected downstream. Please refer to FIG. 1, which shows a schematic diagram of the signal waveforms of a prior art buck-boost switching power converter. The upper panel of FIG. 1 illustrates the input voltage VIN (dashed line), two scenarios of output voltage VOUT1 and VOUT2, and the bypass control signals SBYPS1 and SBYPS2 that enable the bypass mode in the respective scenarios. When the bypass control signals SBYPS1 and SBYPS2 are high, it indicates that the buck-boost switching power converter has transitioned into the bypass mode Bypass. As previously mentioned, this known buck-boost switching power converter, when applied in battery charging system applications, enters bypass mode Bypass when the voltage difference between the input voltage VIN and either of the output voltages VOUT1 or VOUT2 is less than a reference voltage, and the input voltage VIN is greater than or equal to a first threshold. As shown in FIG. 1, when this prior art buck-boost switching power converter transitions from buck-boost mode Buck-Boost into bypass mode Bypass, the sudden change in inductor current IL, as illustrated in the lower part of FIG. 1, causes the output voltage VOUT1 to experience ringing. Not only does the excessive amplitude of the ringing in output voltage VOUT1 generate significant stress on the components, but it can also cause the buck-boost switching power converter to mistakenly trigger an overvoltage protection mechanism and exit bypass mode when the output voltage VOUT1 exceeds a second threshold. Although increasing the preset second threshold of the overvoltage protection mechanism to a third threshold could prevent the erroneous trigger, this would also increase the opportunity of overvoltage damage to the system. In light of this, the present invention addresses the aforementioned shortcomings of the prior art by proposing a buck-boost switching power circuit that can smoothly transition into bypass mode regardless of the magnitude of the load current. SUMMARY OF THE INVENTION From one perspective, the present invention provides a buck-boost switching power circuit for converting an input power source into an output power source, including: a power switch circuit, including an input switch unit and an output switch unit, wherein the input switch unit is configured to switch a first end of an inductor between the input power source or a ground potential, and the output switch unit is configured to switch a second end of the inductor between the output power source or the ground potential, to convert the input power source into the output power source; and a bypass control circuit, configured to determine whether the buck-boost switching power circuit operates in a bypass mode according to a bypass enable signal; wherein, when the bypass enable signal is at an enable level, the buck-boost switching power circuit operates in the bypass mode, and when the absolute value of a conversion voltage difference between an input voltage of the input power source and an output voltage of the output power source is less than a first reference voltage, the bypass control circuit controls the power switch circuit to electrically connect the input power source with the output power source in bypass, and causes the buck-boost switching power circuit to operate in a bypass phase of the bypass mode; wherein, in the bypass mode, before the bypass