阅读说明：本技术 电压差分采样电路及开关变换器的控制电路 (Voltage differential sampling circuit and control circuit of switch converter ) 是由 钱钦松 邵宸晟 郭守誉 张琥 许胜有 孙伟锋 时龙兴 于 2018-12-24 设计创作，主要内容包括：本发明涉及一种电压差分采样电路及开关变换器的控制电路,所述电压差分采样电路包括：双路差分采样电路,每路采样走线的输入端连接电压采样点,以对电压采样点进行差分采样；频率补偿模块,包括第一频率补偿电路和第二频率补偿电路,第一频率补偿电路连接第一采样走线,第二频率补偿电路连接第二采样走线,用于消除两路采样走线采集到的电压信号中的高频振荡信号；第一电压跟随器,输入端连接第一采样走线；第二电压跟随器,输入端连接第二采样走线；差分运算电路,用于对两个电压跟随器输出的电压信号进行减法运算后将运算结果输出。本发明设置频率补偿模块以衰减高频分量,并通过电压跟随器进行缓冲和隔离,最终得到消除了共模噪声的电压信号。(The invention relates to a voltage differential sampling circuit and a control circuit of a switch converter, wherein the voltage differential sampling circuit comprises: the input end of each path of sampling wiring is connected with a voltage sampling point so as to perform differential sampling on the voltage sampling point; the frequency compensation module comprises a first frequency compensation circuit and a second frequency compensation circuit, the first frequency compensation circuit is connected with the first sampling wiring, the second frequency compensation circuit is connected with the second sampling wiring, and the frequency compensation module is used for eliminating high-frequency oscillation signals in the voltage signals collected by the two paths of sampling wirings; the input end of the first voltage follower is connected with the first sampling wire; the input end of the second voltage follower is connected with the second sampling wire; and the differential operation circuit is used for performing subtraction operation on the voltage signals output by the two voltage followers and then outputting an operation result. The invention sets a frequency compensation module to attenuate high-frequency components, and performs buffering and isolation through the voltage follower, thereby finally obtaining the voltage signal with common-mode noise eliminated.)

1. A voltage differential sampling circuit, comprising:

the double-path differential sampling circuit comprises two paths of sampling wires, wherein the input end of each path of sampling wire is used for connecting a voltage sampling point so as to perform differential sampling on the voltage sampling point;

the frequency compensation module comprises a first frequency compensation circuit and a second frequency compensation circuit, the first frequency compensation circuit is connected with a first sampling wire in the two sampling wires, the second frequency compensation circuit is connected with a second sampling wire in the two sampling wires and is used for eliminating a high-frequency oscillation signal in the voltage signals collected by the two sampling wires;

the input end of the first voltage follower is connected with the first sampling wire to obtain a sampled voltage signal;

the input end of the second voltage follower is connected with the second sampling wire to obtain a sampled voltage signal;

and a first input end of the differential operation circuit is connected with the output end of the first voltage follower, a second input end of the differential operation circuit is connected with the output end of the second voltage follower, and the differential operation circuit is used for performing subtraction operation on voltage signals output by the two voltage followers and then outputting an operation result.

2. The voltage differential sampling circuit according to claim 1, wherein the first sampling trace comprises a first resistor and a second resistor connected in series, an input end of the first voltage follower is connected to a connection point of the first resistor and the second resistor, the other end of the first resistor is used for connecting the voltage sampling point, and the other end of the second resistor is used for connecting a first potential point; the second sampling routing comprises a third resistor and a fourth resistor which are connected in series, the input end of the second voltage follower is connected with the connection point of the third resistor and the fourth resistor, the other end of the third resistor is used for connecting the voltage sampling point, and the other end of the fourth resistor is used for connecting the first potential point; the resistance value satisfies the formula R2R3 ≠ R1R 4; wherein R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, R3 is the resistance of the third resistor, and R4 is the resistance of the fourth resistor.

3. The voltage differential sampling circuit of claim 2, wherein the first frequency compensation circuit comprises a first capacitor in parallel with the second resistor, and wherein the second frequency compensation circuit comprises a second capacitor in parallel with the fourth resistor.

4. The voltage differential sampling circuit of claim 3, wherein the product of the resistance value of the third resistor and the capacitance value of the second capacitor is consistent with the product of the resistance value of the first resistor and the capacitance value of the first capacitor.

5. The voltage differential sampling circuit of claim 4, wherein the impedance of the second resistor is greater than the impedance of the first capacitor, and the impedance of the fourth resistor is greater than the impedance of the second capacitor.

6. The voltage differential sampling circuit of claim 5, wherein a product of an inductance value of the parasitic inductance on the first sampling trace and a resistance value of the third resistance and a product of an inductance value of the parasitic inductance on the second sampling trace and a resistance value of the first resistance tend to coincide.

7. A control circuit of a switching converter, comprising a voltage differential sampling circuit and a PWM module, wherein the PWM module is configured to perform loop compensation control on the switching converter according to an output of the voltage differential sampling circuit, and the voltage differential sampling circuit comprises:

the two-way differential sampling circuit comprises two sampling wires, wherein the input end of each sampling wire is used for being connected with the output end of the switch converter so as to perform differential sampling on the output voltage of the switch converter;

the frequency compensation module comprises a first frequency compensation circuit and a second frequency compensation circuit, the first frequency compensation circuit is connected with a first sampling wire in the two sampling wires, the second frequency compensation circuit is connected with a second sampling wire in the two sampling wires and is used for eliminating a high-frequency oscillation signal in the voltage signals collected by the two sampling wires;

the input end of the first voltage follower is connected with the first sampling wire to obtain a sampled voltage signal;

the input end of the second voltage follower is connected with the second sampling wire to obtain a sampled voltage signal;

and a first input end of the differential operation circuit is connected with the output end of the first voltage follower, a second input end of the differential operation circuit is connected with the output end of the second voltage follower, and the differential operation circuit is used for performing subtraction operation on voltage signals output by the two voltage followers and then outputting an operation result through the output end of the differential operation circuit.

8. The control circuit of the switching converter according to claim 7, wherein the first sampling trace includes a first resistor and a second resistor connected in series, an input terminal of the first voltage follower is connected to a connection point of the first resistor and the second resistor, the other terminal of the first resistor is used for connecting an output positive terminal of the switching converter, and the other terminal of the second resistor is used for connecting an output ground terminal of the switching converter; the second sampling wire comprises a third resistor and a fourth resistor which are connected in series, the input end of the second voltage follower is connected with the connection point of the third resistor and the fourth resistor, the other end of the third resistor is used for connecting the positive output terminal, and the other end of the fourth resistor is used for connecting the negative output terminal; the resistance value satisfies the formula R2R3 ≠ R1R 4; wherein R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, R3 is the resistance of the third resistor, and R4 is the resistance of the fourth resistor;

the first frequency compensation circuit comprises a first capacitor connected in parallel with the second resistor, and the second frequency compensation circuit comprises a second capacitor connected in parallel with the fourth resistor.

9. The control circuit of the switching converter according to claim 8, wherein a product of a resistance value of the third resistor and a capacitance value of the second capacitor is approximately equal to a product of a resistance value of the first resistor and a capacitance value of the first capacitor, an impedance of the second resistor is greater than an impedance of the first capacitor, and an impedance of the fourth resistor is greater than an impedance of the second capacitor.

10. The control circuit of the switching converter according to claim 8 or 9, wherein the product of the inductance value of the parasitic inductance on the first sampling trace and the resistance value of the third resistor and the product of the inductance value of the parasitic inductance on the second sampling trace and the resistance value of the first resistor tend to coincide.

Technical Field

The present invention relates to voltage sampling, and more particularly, to a voltage differential sampling circuit and a control circuit of a switching converter.

Background

The sampling circuit is an essential link when a feedback loop is involved in an analog circuit, and is particularly important in the design of a switching power supply. With the rapid development of the power electronic field, high reliability and high power density become important indexes for measuring the switching converter. The sampled voltage needs to be input into an error amplifier, and a stable output result is obtained through an error signal regulating loop output by the error amplifier.

A common sampling method in the design of the switching power supply is to divide the voltage by two sampling resistors to obtain a sampling voltage. However, this method has very limited stability and poor accuracy, and is liable to affect the loop control.

Disclosure of Invention

In view of the above, there is a need for a voltage differential sampling circuit and a control circuit of a switching converter with better stability and accuracy.

A voltage differential sampling circuit, comprising: the double-path differential sampling circuit comprises two paths of sampling wires, wherein the input end of each path of sampling wire is used for connecting a voltage sampling point so as to perform differential sampling on the voltage sampling point; the frequency compensation module comprises a first frequency compensation circuit and a second frequency compensation circuit, the first frequency compensation circuit is connected with a first sampling wire in the two sampling wires, the second frequency compensation circuit is connected with a second sampling wire in the two sampling wires and is used for eliminating a high-frequency oscillation signal in the voltage signals collected by the two sampling wires; the input end of the first voltage follower is connected with the first sampling wire to obtain a sampled voltage signal; the input end of the second voltage follower is connected with the second sampling wire to obtain a sampled voltage signal; and a first input end of the differential operation circuit is connected with the output end of the first voltage follower, a second input end of the differential operation circuit is connected with the output end of the second voltage follower, and the differential operation circuit is used for performing subtraction operation on voltage signals output by the two voltage followers and then outputting an operation result.

In one embodiment, the first sampling trace comprises a first resistor and a second resistor which are connected in series with each other, the input end of the first voltage follower is connected with the connection point of the first resistor and the second resistor, the other end of the first resistor is used for connecting the voltage sampling point, and the other end of the second resistor is used for connecting a first potential point; the second sampling routing comprises a third resistor and a fourth resistor which are connected in series, the input end of the second voltage follower is connected with the connection point of the third resistor and the fourth resistor, the other end of the third resistor is used for connecting the voltage sampling point, and the other end of the fourth resistor is used for connecting the first potential point; the resistance value satisfies the formula R2R3 ≠ R1R 4; wherein R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, R3 is the resistance of the third resistor, and R4 is the resistance of the fourth resistor.

In one embodiment, the first frequency compensation circuit includes a first capacitor connected in parallel with the second resistor, and the second frequency compensation circuit includes a second capacitor connected in parallel with the fourth resistor.

In one embodiment, the product of the resistance value of the third resistor and the capacitance value of the second capacitor and the product of the resistance value of the first resistor and the capacitance value of the first capacitor tend to be consistent.

In one embodiment, the impedance of the second resistor is greater than the impedance of the first capacitor, and the impedance of the fourth resistor is greater than the impedance of the second capacitor.

In one embodiment, the product of the inductance value of the parasitic inductance on the first sampling trace and the resistance value of the third resistor and the product of the inductance value of the parasitic inductance on the second sampling trace and the resistance value of the first resistor tend to be consistent.

According to the voltage differential sampling circuit, the frequency compensation module is arranged to attenuate high-frequency components greatly so as to realize compensation frequency, buffering and isolation are carried out through the voltage follower, and finally a voltage signal with common-mode noise eliminated is obtained and can reflect the voltage of a voltage sampling point.

A control circuit of a switching converter, comprising a voltage differential sampling circuit and a PWM module for loop compensation control of the switching converter according to an output of the voltage differential sampling circuit, the voltage differential sampling circuit comprising: the two-way differential sampling circuit comprises two sampling wires, wherein the input end of each sampling wire is used for being connected with the output end of the switch converter so as to perform differential sampling on the output voltage of the switch converter; the frequency compensation module comprises a first frequency compensation circuit and a second frequency compensation circuit, the first frequency compensation circuit is connected with a first sampling wire in the two sampling wires, the second frequency compensation circuit is connected with a second sampling wire in the two sampling wires and is used for eliminating a high-frequency oscillation signal in the voltage signals collected by the two sampling wires; the input end of the first voltage follower is connected with the first sampling wire to obtain a sampled voltage signal; the input end of the second voltage follower is connected with the second sampling wire to obtain a sampled voltage signal; and a first input end of the differential operation circuit is connected with the output end of the first voltage follower, a second input end of the differential operation circuit is connected with the output end of the second voltage follower, and the differential operation circuit is used for performing subtraction operation on voltage signals output by the two voltage followers and then outputting an operation result through the output end of the differential operation circuit.

In one embodiment, the first sampling trace includes a first resistor and a second resistor connected in series, an input terminal of the first voltage follower is connected to a connection point of the first resistor and the second resistor, the other terminal of the first resistor is used for connecting an output positive terminal of the switching converter, and the other terminal of the second resistor is used for connecting an output ground terminal of the switching converter; the second sampling wire comprises a third resistor and a fourth resistor which are connected in series, the input end of the second voltage follower is connected with the connection point of the third resistor and the fourth resistor, the other end of the third resistor is used for connecting the positive output terminal, and the other end of the fourth resistor is used for connecting the negative output terminal; the resistance value satisfies the formula R2R3 ≠ R1R 4; wherein R1 is the resistance of the first resistor, R2 is the resistance of the second resistor, R3 is the resistance of the third resistor, and R4 is the resistance of the fourth resistor; the first frequency compensation circuit comprises a first capacitor connected in parallel with the second resistor, and the second frequency compensation circuit comprises a second capacitor connected in parallel with the fourth resistor.

In one embodiment, the product of the resistance value of the third resistor and the capacitance value of the second capacitor and the product of the resistance value of the first resistor and the capacitance value of the first capacitor tend to be consistent, the impedance of the second resistor is greater than that of the first capacitor, and the impedance of the fourth resistor is greater than that of the second capacitor.

In one embodiment, the product of the inductance value of the parasitic inductance on the first sampling trace and the resistance value of the third resistor and the product of the inductance value of the parasitic inductance on the second sampling trace and the resistance value of the first resistor tend to be consistent.

According to the control circuit of the switch converter, the frequency compensation module is arranged to attenuate high-frequency components greatly so as to realize compensation frequency, buffering and isolation are performed through the voltage follower, the influence of different on-load of the switch converter on sampling precision can be reduced, and finally voltage signals with common-mode noise eliminated are output to the PWM module, so that accurate control over the switch converter is realized.

Drawings

FIG. 1 is a circuit schematic diagram of a control circuit of a switching converter for loop compensation control of the switching converter;

FIG. 2 is a block diagram of a control circuit of the switching converter in one embodiment;

FIG. 3 is a circuit schematic of a control circuit of the switching converter in one embodiment;

fig. 4 is an equivalent circuit schematic diagram of the embodiment shown in fig. 3 with consideration of the parasitic inductance of the sampling trace;

FIG. 5 is a simulation result of sampling a DC voltage signal doped with high frequency noise using the sampling circuit shown in FIG. 1;

fig. 6 is a simulation result of the voltage differential sampling circuit according to the embodiment sampling the same voltage signal.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth 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 invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element or layer is referred to as being "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it can be directly on, adjacent to, connected or coupled to the other elements or layers or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly adjacent to," "directly connected to" or "directly coupled to" other elements or layers, there are no intervening elements or layers present. It will be understood that, although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term "and/or" includes any and all combinations of the associated listed items.

Fig. 1 is a circuit diagram of a control circuit of a switching converter for loop compensation control of the switching converter. The input voltage of the switching converter is subjected to power transmission and voltage conversion through the power conversion circuit to form the output voltage Vo, the power conversion circuit is mainly formed by connecting a power switching device, a diode, an inductor, a capacitor and a transformer, and the power conversion circuit in fig. 1 only illustrates the representative components and does not show the connection relationship of the components and the components. In order to stabilize the output voltage of the switching converter, the converter needs to be closed-loop controlled using a control circuit or a control IC (integrated circuit). For example, the control circuit or the control IC may sample the output voltage Vo through two sampling resistors R1 and R2 to obtain a feedback voltage, the feedback voltage is input to an inverting input terminal of an Error Amplifier EA (also referred to as an Error comparison Amplifier) inside the control circuit or the control IC, and is compared with a reference voltage Vref connected to a non-inverting input terminal of the Error Amplifier, and then the compared Error voltage is amplified and output from an output terminal of the Error Amplifier to form a voltage signal Vc, and then the Vc is input to a PWM (pulse width modulation) module. The PWM module may be composed of a comparator, and outputs a PWM signal after comparing the received voltage signal Vc with the ramp voltage Vcs to drive the switching tube in the power conversion circuit to be turned on and off, and adjust the driving duty ratio of the switching tube, thereby maintaining the stability of the output voltage of the switching converter, enabling the switching converter to respond to various disturbances quickly, and thus being capable of working efficiently, stably, and reliably.

Fig. 2 is a block diagram of a control circuit of the switching converter in one embodiment. The control circuit of the switching converter includes a voltage differential sampling circuit 100 and a PWM module 50. The input end of the PWM module 50 is connected to the output end of the voltage differential sampling circuit 100, the output end of the PWM module 50 is connected to the switching tube of the switching converter, and the PWM module 50 is configured to perform loop compensation control on the switching converter according to the output of the voltage differential sampling circuit 100. The voltage differential sampling circuit 100 includes:

the two-way differential sampling circuit 10 includes two sampling traces (one is a first sampling trace, the other is a second sampling trace, which is not shown in fig. 2), and an input end of each sampling trace is used for connecting an output end of the switch converter to perform differential sampling on an output voltage of the switch converter.

And a frequency compensation module including a first frequency compensation circuit 22 and a second frequency compensation circuit 24. The first frequency compensation circuit 22 is connected to the first sampling trace, and the second frequency compensation circuit 24 is connected to the second sampling trace, so as to eliminate the high-frequency oscillation signal in the voltage signals collected by the two sampling traces.

A follower module including a first voltage follower and a second voltage follower (not shown in fig. 2). The input end of the first voltage follower is connected with the first sampling wire so as to obtain a voltage signal sampled by the first sampling wire; the input end of the second voltage follower is connected with the second sampling wire so as to obtain a voltage signal sampled by the second sampling wire.

And a differential operation circuit 40, wherein a first input end of the differential operation circuit 40 is connected with an output end of the first voltage follower, and a second input end of the differential operation circuit 40 is connected with an output end of the second voltage follower. The difference operation circuit 40 is configured to perform subtraction on the voltage signals output by the two voltage followers, and then output an operation result through an output terminal of the difference operation circuit 40.

The control circuit of the switching converter is provided with the frequency compensation module, the compensation frequency is realized by greatly attenuating the high-frequency component, and the voltage follower is used for buffering and isolating, so that the influence of different on-load of the switching converter on the sampling precision can be reduced, and finally, the voltage signal which eliminates the common-mode noise is output to the PWM module, thereby realizing the accurate control of the switching converter.

Fig. 3 is a circuit schematic of a control circuit of the switching converter in one embodiment. In this embodiment, the first sampling trace includes a first resistor R1 and a second resistor R2 in series with each other. The input end of the first voltage follower A1 is connected with the connection point A of the first resistor R1 and the second resistor R2, the other end (the end not connected with A) of the first resistor R1 is connected with the positive output end of the switching converter, and the other end (the end not connected with A) of the second resistor R2 is connected with the output ground end of the switching converter. The second sampling trace comprises a third resistor R3 and a fourth resistor R4 which are connected in series, the input end of the second voltage follower A2 is connected with a connection point B of the third resistor R3 and the fourth resistor R4, the other end (i.e. the end not connected with B) of the third resistor R3 is used for connecting the output positive end of the switching converter, and the other end (i.e. the end not connected with B) of the fourth resistor R4 is used for connecting the output ground end of the switching converter. Because differential sampling is adopted, the voltage between the two points AB is not 0, and therefore the resistance value should satisfy the formula: R2R3 ≠ R1R 4.

The frequency compensation module is mainly composed of capacitors meeting a certain relation, and high-frequency signals, particularly high-frequency oscillation signals of a sampling object, can be eliminated through the capacitor branch circuits, so that the influence of high-frequency noise on sampling can be effectively eliminated. In the embodiment shown in fig. 3, the first frequency compensation circuit includes a first capacitor C2 connected in parallel with a second resistor R2, and the second frequency compensation circuit includes a second capacitor C4 connected in parallel with a fourth resistor R4.

Two points of voltage are analyzed A, B using complex frequency domain:

the voltage at the point A is:the voltage at the point B is:

where Vout is the voltage value of the output voltage Vo of the switching converter, S is the complex frequency of laplace variation, i.e., S ═ σ + j ω, ω is the angular frequency, and S ═ j ω is 0 for the capacitance and inductance σ.

The differential sampling signal, i.e. the voltage between two points AB, is:

from this, it is found that, in order to attenuate the high frequency component in the sampling signal and to prevent the sampling voltage from being affected by the frequency domain, the following conditions should be satisfied: for this reason, the product of the resistance value of the third resistor and the capacitance value of the second capacitor and the product of the resistance value of the first resistor and the capacitance value of the first capacitor tend to be consistent, and a good effect of eliminating high-frequency components can be obtained.

When the influence of high-frequency components on the sampling effect is eliminated, the high-frequency signals are expected to be transmitted through the first capacitor C2 and the second capacitor C4, so that the influence of the high-frequency signals on the voltage division sampling can be effectively reduced. The general requirements are as follows:

for example, the impedance of the second resistor R2 is ten times or more the impedance of the first capacitor C2 (capacitive reactance for capacitance), and the impedance of the fourth resistor R4 is ten times or more the impedance of the second capacitor C4.

When the above conditions are satisfied, the sampled voltage between the two points AB is:

referring to fig. 4, the parasitic inductance L2 on the first sampling trace may be equivalently connected in series between the second resistor R2 and the output ground, and the parasitic inductance L4 on the first sampling trace may be equivalently connected in series between the fourth resistor R4 and the output ground, the specific value of the parasitic inductance may be obtained by simulation of actual test or simulation software (for example, ANSYS Q3D), and the voltages at two points A, B in fig. 4 are:

the differential sampling signal, i.e. the voltage between two points AB, is:

the simplified expression yields the voltage Vab between two points AB as:

the influence of the parasitic inductances L2, L4 on the sampling result can be eliminated, and the following requirements are met:

L2R 3 is L4R 1, the product of the inductance of the parasitic inductance on the first sampling trace and the resistance of the third resistor is set to be consistent with the product of the inductance of the parasitic inductance on the second sampling trace and the resistance of the first resistor.

In the embodiment shown in fig. 3 and 4, the differential operation circuit includes an operational amplifier a 3. The voltage signal at the connection point a is connected to the positive input terminal of the operational amplifier A3 through the first voltage follower a1, and the voltage signal at the connection point B is connected to the negative input terminal of the operational amplifier A3 through the second voltage follower a 2. The voltage follower has the remarkable characteristics of high input impedance and low output impedance, wherein the input impedance can generally reach several mega ohms, and the output impedance is usually only a few ohms or even lower.

For the control circuit of the switching converter, if the input impedance of the rear stage is small, a considerable part of the signal is lost in the output resistor of the front stage. The inventor uses the voltage follower as a buffer stage and an isolation stage between the double-path differential sampling circuit and the feedback loop, can improve the input impedance, greatly reduces the input capacitance, provides a precondition guarantee for applying high-quality capacitance, and can reduce the influence of different loading of the switching converter on the sampling precision.

In the embodiment shown in fig. 3 and 4, the first voltage follower a1 and the second voltage follower a2 are followed by a subtraction circuit made up of an operational amplifier A3. The fifth resistor R5 is connected in series between the output terminal of the first voltage follower A1 and the non-inverting input terminal of the operational amplifier A3, and the non-inverting input terminal of the operational amplifier A3 is grounded through the sixth resistor R6. A seventh resistor R7 is connected in series between the output end of the second voltage follower A2 and the inverting input end of the operational amplifier A3, and an eighth resistor R8 is connected between the output end and the inverting input end of the operational amplifier A3. When R5 is R7 and R6 is R8, Vout is (R6/R5) (Vb-Va). When R5 ═ R6 ═ R7 ═ R8, Vout ═ Vb-Va.

In the above example, the voltage differential sampling circuit adopts a differential mode, two different voltage sampling wires are arranged between the output voltage and the ground wire, each sampling wire samples the output voltage of the switching converter through a sampling resistor, and the sampled voltage is input to the input end of the voltage follower. The frequency compensation module is mainly composed of capacitors meeting a certain relation, and because high-frequency signals, particularly high-frequency oscillation signals of a sampling object, can be eliminated through the capacitor branches, the influence of high-frequency noise on sampling can be effectively eliminated, the sampling resistance ratios of the two branches cannot be the same, otherwise, differential signals are zero. The two differential signals respectively pass through the corresponding voltage followers, the followers play roles of buffering and isolating and reduce the influence of different loading on sampling precision, and then are respectively connected with operational amplifiers playing a role of subtraction operation, and the influence of common-mode noise in the sampling circuit on sampling can be effectively eliminated by adopting a differential mode.

It will be appreciated that the voltage differential sampling circuit may also be applied in environments other than the control circuit of a switching converter. Namely, the voltage differential sampling circuit includes:

the double-path differential sampling circuit comprises two paths of sampling wires, wherein the input end of each path of sampling wire is used for connecting a voltage sampling point so as to perform differential sampling on the voltage sampling point;

the frequency compensation module comprises a first frequency compensation circuit and a second frequency compensation circuit, the first frequency compensation circuit is connected with a first sampling wire in the two sampling wires, the second frequency compensation circuit is connected with a second sampling wire in the two sampling wires and is used for eliminating a high-frequency oscillation signal in the voltage signals collected by the two sampling wires;

the input end of the first voltage follower is connected with the first sampling wire to obtain a sampled voltage signal;

the input end of the second voltage follower is connected with the second sampling wire to obtain a sampled voltage signal;

and a first input end of the differential operation circuit is connected with the output end of the first voltage follower, a second input end of the differential operation circuit is connected with the output end of the second voltage follower, and the differential operation circuit is used for performing subtraction operation on voltage signals output by the two voltage followers and then outputting an operation result.

The specific structure of the voltage differential sampling circuit can be seen in any one of the embodiments of the control circuit of the switching converter described above.

Fig. 5 is a simulation result of sampling a dc voltage signal doped with high-frequency noise by using the sampling circuit shown in fig. 1, fig. 6 is a simulation result of sampling the same voltage signal by using a voltage differential sampling circuit according to an embodiment of the present invention, and the abscissa of fig. 5 and fig. 6 is time and the ordinate is voltage. It can be clearly seen that the present invention can effectively perform frequency compensation and suppress high frequency oscillation, thereby enhancing the stability of the sampling signal.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.