阅读说明：本技术 基于acot控制模式的功率变换器及其控制电路 (Power converter based on ACOT control mode and control circuit thereof ) 是由 张炜华 顾雁鸣 黄太毅 于 2021-08-20 设计创作，主要内容包括：本公开提供了一种基于ACOT控制模式的功率变换器及其控制电路,其中,该控制电路利用导通时间控制单元响应于开关控制信号,根据该功率变换器输入端接入的输入电压生成导通控制信号,并根据该开关控制信号的占空比调节该导通控制信号的导通时间；以及通过逻辑控制单元根据导通控制信号的导通时间调节其生成的开关控制信号的占空比,而该导通时间控制单元利用获得与输入电压成正比的充电电流,以维持该开关控制信号的频率不变。由此可通过控制电路实现自适应跟随开关控制信号占空比的变化调整导通控制信号的导通时间,而且保持开关控制信号的频率恒定不变,从而增强系统的稳定性。(The utility model provides a power converter based on ACOT control mode and control circuit thereof, wherein, the control circuit utilizes the on-time control unit to respond to the switch control signal, generates the on-control signal according to the input voltage that the input end of the power converter is accessed, and adjusts the on-time of the on-control signal according to the duty ratio of the switch control signal; and adjusting the duty ratio of the generated switch control signal according to the on-time of the on-control signal through a logic control unit, wherein the on-time control unit obtains a charging current in proportion to the input voltage so as to keep the frequency of the switch control signal unchanged. Therefore, the control circuit can realize that the self-adaption follows the change of the duty ratio of the switch control signal to adjust the conduction time of the conduction control signal, and the frequency of the switch control signal is kept constant, thereby enhancing the stability of the system.)

1. A control circuit of a power converter based on an ACOT control mode, the power converter including a first switch tube, a second switch tube and an inductor connected between an input end and an output end of the power converter, the control circuit respectively controlling conduction states of the first switch tube and the second switch tube through switch control signals to provide an output voltage through the inductor, wherein the control circuit includes:

the conduction time control unit responds to the switch control signal, generates a conduction control signal according to input voltage accessed by the input end of the power converter, and adjusts the conduction time of the conduction control signal according to the duty ratio of the switch control signal;

a logic control unit for adjusting the duty ratio of the switch control signal generated by the logic control unit according to the on-time of the on-control signal,

the on-time control unit includes:

a first input stage generating a first voltage according to the input voltage in response to the first and second switch control signals;

a control stage for generating a second voltage from the input voltage;

the second input stage is used for adjusting the communication state of the second input stage according to the second voltage and the second switch control signal and generating a third voltage;

a first comparator, wherein the non-inverting input terminal of the first comparator is connected to the output terminal of the second input stage and is connected to the third voltage, the inverting input terminal of the first comparator is connected to the output terminal of the first input stage and is connected to the first voltage, and the output terminal of the first comparator is used for providing the conduction control signal,

the conduction time control unit repeatedly etches the conduction states of the first switching tube and the second switching tube by using the first input stage to obtain a charging current which is in direct proportion to the input voltage so as to maintain the frequency of the switch control signal unchanged.

2. The control circuit of claim 1, wherein the switch control signal comprises a first switch control signal and a second switch control signal, the first switch control signal is provided to the control terminal of the first switch tube for driving and controlling the conducting state of the first switch tube, the second switch control signal is provided to the control terminal of the second switch tube for driving and controlling the conducting state of the second switch tube, and the second switch tube is turned off when the first switch tube is turned on, and the second switch tube is turned on when the first switch tube is turned off.

3. The control circuit of claim 2, wherein the first input stage comprises:

the third switching tube and the fourth switching tube are connected between the input end of the power converter and the ground in series, the control end of the third switching tube is connected to the first switching control signal, and the control end of the fourth switching tube is connected to the second switching control signal; and

and a first end of the first capacitor is connected to a connection node of the third switching tube and the fourth switching tube, a second end of the first capacitor is grounded, and the first end of the first capacitor is used as an output end of the first input stage and is used for providing the first voltage.

4. The control circuit of claim 3, wherein the control stage comprises:

a first resistor and a second resistor connected in series between an input of the power converter and ground;

a non-inverting input terminal of the second comparator is connected to a connection node of the first resistor and the second resistor, and an output terminal of the second comparator is used for providing the second voltage;

the power converter comprises a power converter, a first switch tube, a second switch tube, a third resistor, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube and a third resistor, wherein the fifth switch tube, the sixth switch tube and the third resistor are sequentially connected in series between the input end of the power converter and the ground, the control end of the fifth switch tube is connected with the second end of the fifth switch tube, the first end of the sixth switch tube is connected with the second end of the fifth switch tube, the control end of the sixth switch tube is connected with the output end of a second comparator, and the inverting input end of the second comparator is connected with the second end of the sixth switch tube.

5. The control circuit of claim 4, wherein the second input stage comprises:

a seventh switching tube and a second capacitor, wherein the seventh switching tube and the second capacitor are connected in series between the output end of the power converter and the ground, the seventh switching tube is connected with the fifth switching tube in a cascode mode, and a connection node of the seventh switching tube and the second capacitor is used as the output end of the second input stage and is used for providing the third voltage;

an eighth switching tube, connected in parallel to two ends of the second capacitor, having a control end connected to a control end of the third switching tube, and commonly connected to the first switch control signal,

and when the seventh switching tube is conducted, the seventh switching tube is used as a control current source to charge the second capacitor so as to obtain a charging current which is in direct proportion to the input voltage.

6. The control circuit of claim 5, wherein any one of the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube is a metal oxide semiconductor field effect transistor.

7. The control circuit of claim 6, wherein the first switching tube and the third switching tube have the same channel type, and the second switching tube and the fourth switching tube have the same channel type.

8. The control circuit of claim 7, wherein the first, third, fifth and seventh switching tubes are P-channel MOSFETs, and the second, fourth, sixth and eighth switching tubes are N-channel MOSFETs.

9. A power converter based on an ACOT control mode, the power converter comprising:

the main circuit comprises a first switching tube, a second switching tube and an inductor, the first switching tube and the second switching tube are connected between the input end of the power converter and the ground in series, and the inductor is connected between the connection node of the first switching tube and the second switching tube and the output end of the power converter; and

the control circuit according to any one of claims 1 to 8, wherein the control circuit controls the conduction states of the first switch tube and the second switch tube respectively through switch control signals to provide an output voltage through the inductor,

the control circuit utilizes the conduction time control unit to repeatedly carve the conduction states of the first switch tube and the second switch tube, and obtains a charging current in direct proportion to the input voltage so as to maintain the frequency of the switch control signal unchanged.

Technical Field

The disclosure relates to the technical field of integrated circuits, in particular to a power converter based on an ACOT control mode and a control circuit thereof.

Background

The switching power supply is a device which controls the on and off of a power tube through an IC control circuit, thereby stabilizing an output voltage. The most common switching power supply is a DC-DC converter, which includes three basic architectures, i.e., buck, boost, and buck-boost. The modulation modes comprise a Pulse Width Modulation (PWM) mode, a Pulse Frequency Modulation (PFM) mode and a cycle-crossing modulation (PSM) mode, and the control modes mainly comprise a voltage mode and a current mode. At present, the transient response speed of the DC-DC converter has become a focus of increasing attention, and a Constant On Time (COT) control mode is widely applied due to its faster response speed.

A conventional COT control mode buck converter samples the output voltage through a feedback resistor (see fig. 1), and then compares the output voltage ripple valley directly with a reference voltage to generate a fixed on-time pulse to turn on the top-tube MOSFET. When the on-time pulse expires, the upper tube MOSFET is turned off (and the lower tube is turned on). As shown in fig. 1, the conventional COT control mode buck converter 100 includes: a main circuit and a control circuit 110, wherein the main circuit comprises an upper tube Q1 and a lower tube Q2 connected in series between the converter input and ground, an inductor L connected between the connection node SW of the two and the converter output, and an output capacitor Co and an output resistor Ro connected in parallel between the converter output and ground, the feedback network being connected in parallel across the output resistor Ro and comprising resistors Ra and Rb, for generating a feedback voltage Vfb, the control circuit 110 includes a loop comparator 113, a timer unit 111, and a logic control unit 112, the feedback network inputs the generated feedback voltage Vfb into the loop comparator 113, the output of the loop comparator 113, compared to the reference voltage Vref, controls the switching on and off of the timer unit 111, thereby controlling the logic control unit 112, the control signals HSON and LSON are generated to control the conduction of the upper tube Q1 and the lower tube Q2, respectively, to regulate the output voltage Vout.

From volt-second equilibrium law:

an expression for duty cycle D may be obtained:

thus, the frequency equation for the buck converter 100 is:

wherein Ton is an on-time generated by the timer unit, D is a duty cycle, Vout is an output voltage, Vin is an input voltage, Io is a load current, and RD1 and RD2 are on-resistances of the first switching tube Q1 and the second switching tube Q2, respectively.

In the timer unit 111 of the conventional COT mode, the on-time Ton generated is a fixed value, and the switching frequency varies with the input voltage, the output voltage, and the load current, so that the instability of the switching frequency makes the design of the system filter difficult. For a voltage mode Buck converter, although the design is simple, the circuit cost is low and the size is small, the output regulation response speed of the voltage mode is slow, and the stability problem of a system is brought by an output filter capacitor; compared with a voltage mode, a current mode has higher stability and better voltage regulation rate, but on the other hand, the current mode is very sensitive to noise, particularly subharmonic oscillation can occur when the duty ratio is more than 50%, and moreover, the current mode adopts double-loop control, so that the system design is complex, the cost and the volume are large, and the accuracy and the portability requirements of the system requirements cannot be met; although the hysteresis mode and the conventional constant conduction mode have faster transient response, a simple control loop and low cost and volume, the problems of system operating frequency drift and ripple under a steady state exist, and the high-precision design requirement is difficult to achieve.

Disclosure of Invention

In order to solve the above technical problem, the present disclosure provides a power converter based on an ACOT control mode and a control circuit thereof, which can obtain a charging current proportional to an input voltage, and finally fix a switching frequency of a system, thereby enhancing stability of the system.

In one aspect, the present disclosure provides a control circuit of a power converter based on an ACOT control mode, the power converter including a first switching tube, a second switching tube and an inductor connected between an input end and an output end of the power converter, the control circuit respectively controlling conduction states of the first switching tube and the second switching tube through switch control signals to provide an output voltage through the inductor, wherein the control circuit includes:

the on-time control unit responds to the switch control signal, generates an on-control signal according to the input voltage accessed by the input end of the power converter, and adjusts the on-time of the on-control signal according to the duty ratio of the switch control signal;

a logic control unit for adjusting the duty ratio of the switch control signal generated by the logic control unit according to the on-time of the on-control signal,

the on-time control unit obtains a charging current proportional to the input voltage to maintain the frequency of the switch control signal constant.

Preferably, the switch control signal includes a first switch control signal and a second switch control signal, the first switch control signal is provided to the control terminal of the first switch tube for driving and controlling the on-state of the first switch tube, the second switch control signal is provided to the control terminal of the second switch tube for driving and controlling the on-state of the second switch tube, and the second switch tube is turned off when the first switch tube is turned on, and the second switch tube is turned on when the first switch tube is turned off.

Preferably, the aforementioned on-time control unit includes:

a first input stage that generates a first voltage from the input voltage in response to the first and second switch control signals;

a control stage for generating a second voltage from the aforementioned input voltage;

the second input stage is used for adjusting the communication state of the second input stage according to the second voltage and the second switch control signal and generating a third voltage;

and a non-inverting input terminal of the first comparator is connected to the output terminal of the second input stage and is connected to the third voltage, an inverting input terminal of the first comparator is connected to the output terminal of the first input stage and is connected to the first voltage, and an output terminal of the first comparator is used for providing the conduction control signal.

Preferably, the aforementioned first input stage comprises:

the third switching tube and the fourth switching tube are connected between the input end of the power converter and the ground in series, the control end of the third switching tube is connected to the first switching control signal, and the control end of the fourth switching tube is connected to the second switching control signal; and

and a first end of the first capacitor is connected with a connection node of the third switching tube and the fourth switching tube, a second end of the first capacitor is grounded, and the first end of the first capacitor is used as an output end of the first input stage and is used for providing the first voltage.

Preferably, the aforementioned control stage comprises:

a first resistor and a second resistor connected in series between the input of the power converter and ground;

a second comparator, a non-inverting input terminal of which is connected to a connection node of the first resistor and the second resistor, and an output terminal of which is used for providing the second voltage;

the fifth switching tube, the sixth switching tube and the third resistor are sequentially connected between the input end of the power converter and the ground in series, the control end of the fifth switching tube is connected with the second end of the fifth switching tube, the first end of the sixth switching tube is connected with the second end of the fifth switching tube, the control end is connected with the output end of the second comparator, and the inverting input end of the second comparator is connected with the second end of the sixth switching tube.

Preferably, the aforementioned second input stage comprises:

a seventh switching tube and a second capacitor, wherein the seventh switching tube and the second capacitor are connected in series between the output end of the power converter and the ground, the seventh switching tube is connected with the fifth switching tube in a cascode manner, and a connection node of the seventh switching tube and the second capacitor is used as the output end of the second input stage and is used for providing the third voltage;

an eighth switch tube connected in parallel to both ends of the second capacitor, having a control end connected to a control end of the third switch tube, and commonly connected to the first switch control signal,

when the seventh switch tube is conducted, the seventh switch tube is used as a control current source to charge the second capacitor, so as to obtain a charging current which is in direct proportion to the input voltage.

Preferably, any one of the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube is a metal oxide semiconductor field effect transistor.

Preferably, the channel types of the first switching tube and the third switching tube are the same, and the channel types of the second switching tube and the fourth switching tube are the same.

Preferably, the first switch tube, the third switch tube, the fifth switch tube and the seventh switch tube are P-channel type metal oxide semiconductor field effect transistors, and the second switch tube, the fourth switch tube, the sixth switch tube and the eighth switch tube are N-channel type metal oxide semiconductor field effect transistors.

In another aspect, the present disclosure also provides a power converter based on an ACOT control mode, the power converter including:

the main circuit comprises a first switching tube, a second switching tube and an inductor, wherein the first switching tube and the second switching tube are connected between the input end of the power converter and the ground in series, and the inductor is connected between the connection node of the first switching tube and the second switching tube and the output end of the power converter; and

the control circuit controls the conducting states of the first switch tube and the second switch tube respectively through the switch control signal to provide the output voltage through the inductor,

the control circuit obtains a charging current proportional to the input voltage to maintain the frequency of the switch control signal unchanged.

The beneficial effects of this disclosure are: the power converter comprises a first switch tube, a second switch tube and an inductor which are connected between an input end and an output end of the power converter, the control circuit respectively controls the conduction states of the first switch tube and the second switch tube through switch control signals so as to provide output voltage through the inductor, wherein the control circuit utilizes a conduction time control unit to respond to the switch control signals, generates conduction control signals according to input voltage accessed at the input end of the power converter, and adjusts the conduction time of the conduction control signals according to the duty ratio of the switch control signals; and adjusting the duty ratio of the generated switch control signal according to the on-time of the on-control signal through a logic control unit, wherein the on-time control unit obtains a charging current in proportion to the input voltage so as to keep the frequency of the switch control signal unchanged. Therefore, the conducting state of the first switching tube and the second switching tube in the main circuit can be repeatedly etched through the control circuit, the feedback control scheme of sampling the voltage of the SW node in the prior art is effectively avoided, the influence of reduction of the load capacity caused by the increase of the frequency due to the change of the on-resistance of the upper tube (the first switching tube) and the lower tube (the second switching tube) after the load is carried is avoided, the charging current in direct proportion to the input voltage is obtained through the control circuit, the self-adaption following the change of the duty ratio (of the switch control signal) to adjust the conducting time of the conducting control signal is realized, the frequency (of the switch control signal) is kept constant, and the stability of the system is enhanced.

Drawings

The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of the embodiments of the present disclosure with reference to the accompanying drawings.

Fig. 1 is a schematic diagram illustrating a structure of a COT mode based buck converter in the prior art;

fig. 2 is a schematic diagram illustrating a buck converter based on an ACOT control mode according to an embodiment of the disclosure;

fig. 3 is a schematic diagram of a structure of an on-time control unit in the control circuit of the buck converter shown in fig. 2.

Detailed Description

To facilitate an understanding of the present disclosure, the present disclosure will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present disclosure are set forth in the accompanying drawings. However, the present disclosure may be embodied in different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description of the disclosure herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure.

The present disclosure is described in detail below with reference to the accompanying drawings.

Fig. 2 shows a schematic diagram of a buck converter based on an ACOT control mode according to an embodiment of the present disclosure, and fig. 3 shows a schematic diagram of a structure of an on-time control unit in a control circuit of the buck converter shown in fig. 2.

Referring to fig. 2, taking a Buck (Buck) type topology power converter as an example, an embodiment of the present disclosure provides a Buck converter 200 based On an Adaptive Constant On Time (ACOT) control mode, which includes: the main circuit comprises a first switch tube Q1 and a second switch tube Q2 connected in series between the input end of the buck converter 200 and the ground, an inductor L connected between the connection node SW of the first switch tube Q1 and the second switch tube Q2 and the output end of the buck converter 200, and a filter network consisting of an output capacitor Co and an output resistor Ro connected in parallel between the output end of the buck converter 200 and the ground, and the control circuit 210 controls the conduction states of the first switch tube Q1 and the second switch tube Q2 respectively through switch control signals (HSON and LSON) to provide the output voltage Vout through the inductor L.

Referring to fig. 2 and 3, in the present embodiment, the control circuit 210 includes: an on-time control unit 21 and a logic control unit 22, wherein the on-time control unit 21 responds to the aforementioned switch control signals (HSON and LSON), generates an on-control signal TON according to an input voltage Vin inputted at an input terminal of the buck converter 200, and adjusts an on-time TON of the on-control signal TON according to a duty ratio of the switch control signals (HSON and LSON); the logic control unit 22 is configured to adjust the duty ratio D of the aforementioned switching control signals (HSON and LSON) generated by the logic control unit 22 according to the on-time TON of the on-control signal TON, and the control circuit 210 obtains the charging current I proportional to the input voltage Vin to maintain the frequency of the switching control signals (HSON and LSON) constant.

In this embodiment, the aforementioned switch control signals include a first switch control signal HSON provided to the control terminal of the first switch Q1 for driving and controlling the on-state of the first switch Q1, and a second switch control signal LSON provided to the control terminal of the second switch Q2 for driving and controlling the on-state of the second switch Q2, wherein the second switch Q2 is turned off when the first switch Q1 is turned on, and the second switch Q2 is turned on when the first switch Q1 is turned off.

Further, referring to fig. 3, in the present embodiment, the aforementioned on-time control unit 21 includes: a first input stage 211, a control stage 212, a second input stage 213 and a first comparator 202,

wherein the first input stage 211 generates a first voltage V1 according to the input voltage Vin in response to a first switching control signal HSON and a second switching control signal LSON; the control stage 212 is configured to generate a second voltage V2 according to the input voltage Vin; the second input stage 213 is configured to adjust its own connection state according to the second voltage V2 and the second switch control signal LSON, and generate a third voltage V3; the non-inverting input terminal of the first comparator 202 is connected to the output terminal of the second input stage 213 and is connected to the third voltage V3, the inverting input terminal of the first comparator 202 is connected to the output terminal of the first input stage 211 and is connected to the first voltage V1, and the output terminal of the first comparator 202 is used for providing the on control signal TON.

Further, in this embodiment, the first input stage 211 includes: a third switching tube M1, a fourth switching tube M2 and a first capacitor C1, wherein the third switching tube M1 and the fourth switching tube M2 are connected in series between the input end of the buck converter 200 and the ground, a control end of the third switching tube M1 is connected to the first switching control signal HSON, and a control end of the fourth switching tube M2 is connected to the second switching control signal LSON; the first end of the first capacitor C1 is connected to the connection node of the third switching transistor M1 and the fourth switching transistor M2, the second end is grounded, and the first end of the first capacitor C1 is used as the output end of the first input stage 211 for providing the first voltage V1.

Further, in this embodiment, the aforementioned control stage 212 includes: a first resistor R1, a second resistor R2, a third resistor R3, a second comparator 201, a fifth switching tube M3 and a sixth switching tube M4, wherein the first resistor R1 and the second resistor R2 are connected in series between the input end of the buck converter 200 and the ground; the non-inverting input terminal of the second comparator 201 is connected to the connection node between the first resistor R1 and the second resistor R2, and the output terminal of the second comparator 201 is used for providing the second voltage V2; the fifth switch tube M3, the sixth switch tube M4 and the third resistor R3 are sequentially connected in series between the input end of the power converter 200 and the ground, the control end of the fifth switch tube M3 is connected with the second end of the fifth switch tube M3, the first end of the sixth switch tube M4 is connected with the second end of the fifth switch tube M3, the control end is connected with the output end of the second comparator 201, and the inverting input end of the second comparator 201 is connected with the second end of the sixth switch tube M4.

Further, in this embodiment, the second input stage 213 includes: a seventh switching tube M5, an eighth switching tube M6 and a second capacitor C2, wherein the seventh switching tube M5 and the second capacitor C2 are connected in series between the output end of the buck converter 200 and ground, the seventh switching tube M5 is cascode-connected to the fifth switching tube M3 to form a current mirror structure, and a connection node of the seventh switching tube M5 and the second capacitor C2 is used as the output end of the second input stage 213 for providing the third voltage V3; the eighth switch transistor M6 is connected in parallel to two ends of the second capacitor C2, a control end of the eighth switch transistor M6 is connected to a control end of the third switch transistor M1, and is commonly connected to the first switch control signal HSON, and the seventh switch transistor M5 is used as a control current source to charge the second capacitor C2 when turned on, so as to obtain a charging current I proportional to the input voltage Vin.

Further, in this embodiment, any one of the first switch tube Q1, the second switch tube Q2, the third switch tube M1, the fourth switch tube M2, the fifth switch tube M3, the sixth switch tube M4, the seventh switch tube M5 and the eighth switch tube M6 is a Metal Oxide Semiconductor Field Effect Transistor (MOSFET, hereinafter, abbreviated as MOS Transistor).

Further, in this embodiment, the channel types of the first transistor Q1 and the third transistor M1 are the same, and the channel types of the second transistor Q2 and the fourth transistor M2 are the same.

Preferably, the first switching transistor Q1, the third switching transistor M1, the fifth switching transistor M3 and the seventh switching transistor M5 are all P-channel MOS transistors, and the second switching transistor Q2, the fourth switching transistor M2, the sixth switching transistor M4 and the eighth switching transistor M6 are all N-channel MOS transistors.

In the present embodiment, the first input stage 211 in the on-time control unit 21 of the control circuit 210 repeatedly switches on states of the first switch Q1 and the second switch Q2 in the main circuit, so as to effectively avoid the prior art feedback control scheme of sampling the voltage of the SW node, because of the on-resistance of the upper tube (the first switch tube Q1) and the lower tube (the second switch tube Q2) after loading, the variation of the load-side inductive current IL is caused, and the charging current I proportional to the input voltage Vin is obtained through the control circuit 210, so as to adaptively adjust the on-time TON of the on-control signal TON following the change of the duty ratio D (of the on-off control signal), but also keeps the frequency f (of the switch control signal) constant, thereby enhancing the stability of the buck converter system.

Specifically, in the present embodiment, the operation principle of the buck converter 200 can be understood by referring to the operation principle of the conventional buck converter 100, which is expressed by the volt-second equilibrium law:

where D is the duty cycle of the switching control signals (HSON and LSON), Vout is the output voltage, Vin is the input voltage, Io is the load current, and RD1 and RD2 are the on-resistances of the first switching transistor Q1 and the second switching transistor Q2, respectively.

An expression for duty cycle D may be obtained:

therefore, the duty ratio D is proportional to the load current Io, and the duty ratio D becomes larger as the load current Io becomes larger. Further, the frequency formula of the buck converter 200 can be obtained as follows:

where Ton is the on-time of the on-control signal Ton, T is the period of the switch control signals (HSON and LSON), and f is the frequency of the switch control signals (HSON and LSON).

In the first input stage 211 of the on-time control unit 21, a signal related to the output voltage Vout is generated by the third switch M1 and the fourth switch M2:

in the control stage 212, when the first switch Q1 is turned on by the first resistor R1 and the second resistor R2, the current I charged in the second capacitor C2 is:

r2 in the formula (8) represents the set resistance value of the second resistor R2, and similarly, R1 and R3 are represented as the set resistance values of the first resistor R1 and the third resistor R3, respectively, and I is the current value of the charging current of the second capacitor C2.

In the second input stage 213, under the control of the second voltage V2, when the sixth switching tube M4 is turned on, the seventh switching tube M5 mirrors the current flowing through the third resistor R3 on the current path of the fifth switching tube M3 as a control current source to charge the second capacitor C2 when the first switching tube Q1 is in the on state, and the eighth switching tube M6 is controlled by the first control signal HSON to be turned on when the first switching tube is turned off to provide a bleeding path of the second capacitor C2, thereby clamp-controlling the third voltage V3 to become the zero level. Thus, according to the volt-second balance principle, in combination with equations (7) and (8) above, the on-time of the on-control signal TON output by the first comparator 202 can be expressed as:

c2 in equation (9) is represented as a set capacitance value of the second capacitance C2.

As can be seen, the on time TON of the on control signal TON is only related to the duty ratio of the switching control signals (HSON and LSON).

Further, combining the above equations (6), (7) and (9), the frequency of the buck converter 200 is:

therefore, the buck converter 200 based on the ACOT control mode according to the embodiment of the present disclosure obtains the charging current I proportional to the input voltage Vin through the control circuit 210, so that not only can the on-time TON of the on-control signal TON be adjusted adaptively to follow the change of the duty ratio D (of the switch control signal), but also the frequency f (of the switch control signal) can be kept constant, thereby enhancing the stability of the buck converter system.

It should be noted that in the description of the present disclosure, it is to be understood that the terms "upper", "lower", "inner", and the like, indicate orientation or positional relationship, are only for convenience in describing the present disclosure and simplifying the description, but do not indicate or imply that the referenced components or elements must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present disclosure.

Further, in this document, the contained terms "include", "contain" or any other variation thereof are intended to cover a non-exclusive inclusion, so that a process, a method, an article or an apparatus including a series of elements includes not only those elements but also other elements not explicitly listed or inherent to such process, method, article or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

Finally, it should be noted that: it should be understood that the above examples are only for clearly illustrating the present disclosure, and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention as herein taught are within the scope of the present disclosure.