Slope compensation circuit of switching power supply

Abstract

The invention discloses a slope compensation circuit of a switching power supply. The slope compensation circuit comprises a control signal generation unit, a first switching tube, a first capacitor, a first current source, a buffer amplifier, a second switching tube, a first resistor, a third switching tube, a fourth switching tube, a second current source and a second resistor, the control signal generation unit generates a PWM (Pulse Width Modulation) control signal with a duty ratio less than or equal to 50%, and controls the slope compensation voltage by using the PWM control signal; and generating a slope compensation current based on the slope compensation voltage, generating a slope compensation control signal by using the slope compensation current, and comparing the slope compensation control signal with a reference voltage to generate a peak current of the switching power supply.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and in particular to a slope compensation circuit of a switching power supply. Background Art

[0002] The current-controlled switching power supply introduces current feedback on the basis of the traditional PWM voltage control method, and improves the original single voltage closed-loop control to voltage and current dual closed-loop control to improve the performance of the power supply. There are two types of current control: peak current control and average current control. The peak current control method is simple, but in the Buck series circuit of peak current control, since the change of feedback current cannot fully reflect the change of load current, when the duty cycle D>50%, the power supply cannot work stably, which limits the application of the peak current control method and must be improved by slope compensation.

[0003] The main function of the slope compensation circuit in the switching power supply is to generate a slope compensation signal to suppress the open-loop instability and subharmonic oscillation phenomenon that occurs when the duty cycle is greater than 50%. Figure 1 As shown, a slope compensation signal V_ is generated from the beginning of each cycle. SLOPE , and the slope compensation signal V_ SLOPE Superimposed on the reference level V_ C On the current sampling signal V_ SNS Compared with the superimposed signal, a peak current signal I_ is generated when the reversal point is reached. PEAK , and control the PWM to be turned off. In the actual circuit, in order to simplify the design, there is also a slope compensation signal V_ SLOPE And the current sampling signal V_ SNS Superimposed with the reference level V_ C Compare to generate peak current signal I_ PEAK implementation method.

[0004] However, the slope compensation method in the above-mentioned prior art has obvious defects, that is, when the slope slope and the reference level remain unchanged, the longer the PWM cycle or the larger the amplitude of the slope, the smaller the amplitude of the sampling signal, and finally the smaller the peak current in the corresponding switch tube, which in turn leads to a smaller maximum energy that can be transmitted.

[0005] It can be seen that a new slope compensation circuit of a switching power supply is needed in the prior art to solve the problem of too small peak current when the switching power supply performs slope compensation. Summary of the invention

[0006] The technical purpose to be achieved by the present invention is to provide a slope compensation circuit for a switching power supply. The slope compensation circuit can suppress subharmonic oscillation when the duty cycle is greater than 50%, while reducing the amplitude of the ramp signal as much as possible, so that the sampling signal can reach a larger amplitude, thereby increasing the maximum power that the switching power supply can transmit.

[0007] Based on the above technical purpose, the present invention provides a slope compensation circuit of a switching power supply, the slope compensation circuit comprising: a control signal generating unit, a first switch tube, a first capacitor, a first current source, a buffer amplifier, a second switch tube, a first resistor, a third switch tube, a fourth switch tube, a second current source and a second resistor;

[0008] The control signal generating unit generates a PWM control signal with a duty cycle less than or equal to 50%, and uses the PWM control signal to control the conduction of the first switch tube;

[0009] The first switch tube, the first capacitor, the first current source and the buffer amplifier output a slope compensation voltage under the control of the PWM control signal;

[0010] The second switch tube is controlled by the output end of the buffer amplifier, and the on-current of the second switch tube is controlled by using the voltage of the inverting input end of the buffer amplifier and the first resistor, wherein the on-current of the second switch tube is a slope compensation current;

[0011] The third switch tube and the fourth switch tube form a current mirror, and the three switch tubes mirror the slope compensation current generated by the second switch tube to the fourth switch tube;

[0012] The current of the second current source is the sampling current of the switching power supply. The fourth switch tube, the second current source and the second resistor are used to generate a slope compensation control signal, and the slope compensation control signal is compared with a reference voltage to generate a peak current of the switching power supply.

[0013] In one embodiment, the slope of the slope compensation voltage is controlled by parameters of the first capacitor and the first current source.

[0014] In one embodiment, the duty cycle of the PWM control signal is set to 45%.

[0015] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 It is a signal waveform and timing diagram of a slope compensation circuit in the prior art;

[0018] Figure 2 is a schematic diagram of the structure of the slope compensation circuit of the present invention;

[0019] Figure 3 It is a schematic diagram of the signal waveform and timing of the slope compensation circuit of the present invention;

[0020] Figure 4 It is a schematic diagram comparing the slope compensation signal of the present invention and the slope compensation signal in the prior art. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings.

[0022] It should be understood that when an element or layer is referred to as "on ...", "adjacent to ...", "connected to" or "coupled to" other elements or layers, it can be directly on, adjacent to, connected to or coupled to other elements or layers, or there can be intervening elements or layers. On the contrary, when an element is referred to as "directly on ...", "directly adjacent to ...", "directly connected to" or "directly coupled to" other elements or layers, there is no intervening element or layer. It should be understood that although the terms first, second, third, etc. can be used to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, without departing from the teachings of the present invention, the first element, component, region, layer or part discussed below can be represented as the second element, component, region, layer or part. And when the second element, component, region, layer or part is discussed, it does not indicate that the present invention necessarily has the first element, component, region, layer or part.

[0023] Spatially relative terms such as "under", "beneath", "below", "under", "above", "above", etc., may be used here for convenience of description to describe the relationship between an element or feature shown in the figure and other elements or features. It should be understood that in addition to the orientation shown in the figure, the spatial relationship terms are intended to also include different orientations of the device in use and operation. For example, if the device in the accompanying drawings is turned over, then the elements or features described as "under other elements" or "under it" or "under it" will be oriented as "on" other elements or features. Therefore, the exemplary terms "under" and "under" may include both upper and lower orientations. The device can be oriented otherwise (rotated 90 degrees or other orientations) and the spatial descriptors used herein are interpreted accordingly.

[0024] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0025] Example 1

[0026] like Figure 2-3 As shown, the slope compensation circuit of the present invention includes: a control signal generating unit 1, a first switch tube 2, a first capacitor 3, a first current source 4, a buffer amplifier 5, a second switch tube 6, a first resistor 7, a third switch tube 8, a fourth switch tube 9, a second current source 10 and a second resistor 11.

[0027] The control signal generating unit 1 generates a PWM control signal V_ with a duty cycle less than or equal to 50%. CTRL , and inputs the PWM control signal to the gate of the first switch tube 2, the first switch tube 2 is an NMOS tube, the drain of the first switch tube 2, the first end of the first capacitor 3 and the first end of the first current source 4 are all connected to the in-phase input end of the buffer amplifier 5, and the source of the first switch tube 2 and the second end of the first capacitor 3 are grounded.

[0028] In this embodiment, the PWM control signal V_ CTRL The starting time of the slope compensation can be determined. In order to ensure sufficient slope compensation, the duty cycle is set to be less than or equal to 50%. In this embodiment, the PWM control signal V_CTRL The duty cycle is set to 45%. When the PWM control signal V_ CTRL When the first switch tube 2 is turned on, the slope compensation voltage V_ SLOPE Quickly discharge to ground level; when PWM control signal V_ CTRL When the first switch tube 2 is turned off, the charging current I_ CHG The first capacitor 3 is charged at a predetermined slope, and a slope compensation voltage V_ is generated at the non-inverting input terminal of the buffer amplifier 5. SLOPE .

[0029] The output end of the buffer amplifier 5 is connected to the gate of the second switch tube 6, which is an NMOS tube. The source of the second switch tube 6 is connected to the first end of the first resistor 7. The inverting input end of the buffer amplifier 5 is also connected to the first end of the first resistor 7. The second end of the first resistor 7 is grounded. Through the action of the buffer amplifier 5 and the second switch tube 6, the voltage at the first end of the first resistor 7 is equal to the slope compensation voltage V_ SLOPE , so the current on the first resistor 7 is equal to V_ SLOPE / R1, where R1 is the resistance value of the first resistor 7.

[0030] The third switch tube 8 and the fourth switch tube 9 form a current mirror, that is, the gates of the third switch tube 8 and the fourth switch tube 9 are interconnected, the drain of the third switch tube 8 is connected to the drain of the second switch tube 6, and the sources of the third switch tube 8 and the fourth switch tube 9 are connected to the power supply Vcc. The third switch tube 8 and the fourth switch tube 9 are both PMOS tubes. And the conduction current of the third switch tube 8, that is, the slope compensation current I_ SLOPE The on-state current of the fourth switch tube 9 is mirrored.

[0031] The drain of the fourth switch tube 9 is connected to the first end of the second resistor 11, and the second end of the second resistor 11 is grounded. At the same time, the second current source 10 is connected between the power supply and the drain of the fourth switch tube 9, and the current of the second current source 10 is the sampling current I_ SNS The voltage at the first end of the second resistor is used as the slope compensation control signal V_ SIGMA , the slope compensation control signal V_ SIGMA is the slope compensation voltage V_ SLOPE And the current sampling signal voltage V_ SNS The slope compensation control signal V_ SIGMA With reference level V_ C Compare to generate peak current signal I_ PEAK .

[0032] As shown in Figures 3-4, it is a schematic diagram of the signal waveform and timing of this embodiment. It can be seen that according to the slope compensation current of the present invention, the PWM control signal V_ CTRL The peak current signal I_ PEAK The amplitude of the peak current is higher than the amplitude of the peak current generated in the slope compensation circuit in the prior art.

[0033] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A slope compensation circuit for a switching power supply, characterized in that: The slope compensation circuit includes: a control signal generating unit, a first switch tube, a first capacitor, a first current source, a buffer amplifier, a second switch tube, a first resistor, a third switch tube, a fourth switch tube, a second current source and a second resistor; The control signal generating unit generates a PWM control signal with a duty cycle less than or equal to 50%, and uses the PWM control signal to control the conduction of the first switch tube; The first switch tube, the first capacitor, the first current source and the buffer amplifier output a slope compensation voltage under the control of the PWM control signal; The second switch tube is controlled by the output end of the buffer amplifier, and the on-current of the second switch tube is controlled by using the voltage of the inverting input end of the buffer amplifier and the first resistor, wherein the on-current of the second switch tube is a slope compensation current; The third switch tube and the fourth switch tube form a current mirror, and the three switch tubes mirror the slope compensation current generated by the second switch tube to the fourth switch tube; The current of the second current source is the sampling current of the switching power supply. The fourth switch tube, the second current source and the second resistor are used to generate a slope compensation control signal, and the slope compensation control signal is compared with a reference voltage to generate a peak current of the switching power supply.

2. The slope compensation circuit of the switching power supply according to claim 1, characterized in that: The slope of the slope compensation voltage is controlled by parameters of the first capacitor and the first current source.

3. The slope compensation circuit of the switching power supply according to claim 1, characterized in that: The duty cycle of the PWM control signal is set to 45%.

4. A switching power supply, characterized in that: The switching power supply comprises the slope compensation circuit as claimed in any one of claims 1 to 3.

5. An integrated circuit structure, characterized in that: The integrated circuit structure comprises the slope compensation circuit as claimed in any one of claims 1-3.

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