Switching Converter, Its Control Circuit, and Control Method

Abstract

The present application discloses a switching converter, its control circuit and control method. The control circuit includes an adaptive on-time control circuit, an adaptive on-frequency control circuit, a PWM signal generation circuit, a logic circuit and a driving circuit. The logic circuit compares the off-time determined by the pulse width modulation signal with a first off-time, and controls the switching converter to operate in an adaptive on-time control mode or an adaptive on-frequency control mode according to the comparison result. When the DC input voltage and the DC output voltage are close, the on-time of the switching converter can be extended, so that the switching converter can linearly transition to 100% duty cycle, improving the light-load efficiency and stability of the switching converter.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies, and more particularly, to a switching converter, its control circuit, and a control method thereof. Background Art

[0002] With the demand for power electronic products and the development of semiconductor technology, power management chips are more widely used in portable computers, mobile phones, personal digital assistants, and other portable or non-portable electronic devices. The switching converter uses a power switch tube to control the power transmission from the input end to the output end, and thus can provide a constant output voltage and / or output current at the output end. In the switching converter, the ripple-based constant on-time control method evolved from the hysteresis mode has the advantages of a constant system frequency, good light-load efficiency, fast transient response, and easy implementation, and thus has been widely used in recent years.

[0003] Figure 1 A schematic circuit diagram of a switching converter according to the prior art is shown. The switching converter 100 includes a main circuit and a control circuit. The main circuit includes a main switch tube MD1 and a synchronous switch tube MD2 connected in series between the input end and the ground end. An inductor Lx is connected between the intermediate node of the main switch tube MD1 and the synchronous switch tube MD2 and the output end. An output capacitor Cout is connected between the output end and the ground end. The input end of the switching converter 100 receives a DC input voltage Vin, and the output end provides a DC output voltage Vout. The control circuit of the switching converter 100 is used to provide switching drive signals to the main switch tube MD1 and the synchronous switch tube MD2.

[0004] In the control circuit of the switching converter 100, the on-time control circuit 110 sets a fixed on-time Ton of the switching period Tsw, thereby generating a reset signal. The minimum off-time control circuit 120 sets a minimum off-time Toff_min (or maximum switching frequency) corresponding to a predetermined output voltage and a predetermined load. The error amplifier 131 obtains an error signal Vcomp based on the feedback signal FB of the DC output voltage Vout and the reference voltage Vref. The PWM comparator 132 compares the error signal Vcomp with the feedback signal FB to obtain an intermediate signal. Two input terminals of the NAND gate 133 respectively receive the intermediate signal output by the comparator and the minimum off-time Toff_min, and the output terminal provides a set signal. The RS flip-flop 140 generates a switching signal SW according to the reset signal and the set signal. The drive circuit 150 converts the switching signal SW into a switching drive signal to control the conduction states of the main switch tube MD1 and the synchronous switch tube MD2.

[0005] When the feedback signal FB is less than or equal to the error signal Vcomp, the on-time control circuit 110 sets a fixed on-time such that the on-time of the switch drive signal is a fixed value. When the feedback signal FB is greater than the error signal Vcomp, the off-signal of the switch drive signal is valid, thereby dynamically adjusting the off-time according to the DC output voltage Vout, and the off-time is greater than the minimum off-time Toff_min.

[0006] However, in some applications, it is necessary to use a low-ESR (Equivalent Series Resistance) capacitor (such as a ceramic capacitor) as the output capacitor at the output end of the switch converter 100. Since this type of output filter generates very small output ripple even in the presence of a large amount of noise, and there is a phase delay of the capacitor ripple compared to the inductor ripple, subharmonic oscillations will occur in the system, so it may cause problems of unstable control systems. Using a capacitor with a larger ESR (such as an electrolytic capacitor) as the output capacitor at the output end of the switch converter 100 will not only increase the circuit area and cost, but also cause a large increase in the ripple of the output voltage, resulting in large fluctuations and affecting the normal operation of the subsequent circuit.

[0007] In addition, the transient response of the existing switch converter 100 is slow. When a large voltage drop event occurs at the load end, it will cause a change in the output voltage, limiting the application of this control model in fields that require fast transient response. And due to the limitation of the on-time of the switch drive signal, the switch converter 100 cannot provide stable power supply when the input voltage Vin and the output voltage Vout are close, reducing the overall efficiency of the switch converter. Summary of the Invention

[0008] In view of the above problems, an object of the present invention is to provide a switch converter, its control circuit and control method, which can extend the on-time of the switch converter when the DC input voltage and the DC output voltage are close, and improve the light-load efficiency and stability of the switch converter.

[0009] According to a first aspect of the present invention, there is provided a control circuit for a switching converter. The switching converter uses a main switching transistor to control the power transfer from the input terminal to the output terminal, so as to generate a DC output voltage according to a DC input voltage. Wherein, the control circuit includes: an adaptive on-time control circuit for generating a first on-time of the main switching transistor in an adaptive on-time control mode; an adaptive on-frequency control circuit for generating a first off-time of the main switching transistor in an adaptive on-frequency control mode; a PWM signal generation circuit for generating a pulse width modulation signal according to a feedback signal of the DC output voltage; a logic circuit for generating a switching signal based on the pulse width modulation signal, the first off-time, and the first on-time; and a drive circuit for converting the switching signal into a switching drive signal to control the conduction state of the main switching transistor. Wherein, the logic circuit is further configured to control the switching converter to operate in an adaptive on-time control mode or an adaptive on-frequency control mode according to a comparison result between an off-time of the pulse width modulation signal and the first off-time.

[0010] Optionally, the logic circuit is configured to: control the switching converter to operate in the adaptive on-time control mode when the off-time of the pulse width modulation signal is greater than the first off-time, and control the switching converter to operate in the adaptive on-frequency control mode when the off-time of the pulse width modulation signal is less than the first off-time.

[0011] Optionally, the logic circuit is configured to: in the adaptive on-time control mode, the on-time of the main switching transistor is determined by the first on-time, and the off-time of the main switching transistor is determined by the pulse width modulation signal; and in the adaptive on-frequency control mode, the on-time of the main switching transistor is determined by the pulse width modulation signal, and the off-time of the main switching transistor is determined by the first off-time.

[0012] Optionally, the logic circuit includes: a NAND gate, the first input terminal receives the first on-time, the second input terminal receives a minimum on-time, the third input terminal receives the pulse width modulation signal, and the output terminal provides a reset signal; an OR gate, the first input terminal receives the pulse width modulation signal, the second input terminal receives the first off-time, the third input terminal receives a minimum off-time, and the output terminal provides a set signal; and an RS flip-flop for generating the switching signal according to the set signal and the reset signal respectively.

[0013] Optionally, the control circuit further includes: a minimum off-time control circuit for generating the minimum off-time, where the off-time of the main switch tube is greater than the minimum off-time; and a minimum on-time control circuit for generating the minimum on-time, where the on-time of the main switch tube is greater than the minimum on-time.

[0014] Optionally, the PWM signal generation circuit includes: an error amplifier, with its inverting input terminal and non-inverting input terminal receiving the feedback signal and the reference voltage respectively, and its output terminal for providing the error signal; and a PWM comparator, with its inverting input terminal and non-inverting input terminal receiving the feedback signal and the superimposed signal of the error signal and the ripple injection signal respectively, and its output terminal for providing the pulse width modulation signal.

[0015] Optionally, the PWM signal generation circuit further includes: a first capacitor, with its first terminal connected to the output terminal of the error amplifier and its second terminal grounded; and a compensation resistor and a compensation capacitor connected in series between the output terminal of the error amplifier and the ground.

[0016] Optionally, the PWM signal generation circuit further includes: a ripple injection circuit for generating the ripple injection signal during the inductor current drop phase of the switch converter.

[0017] Optionally, the first on-time is equal to the product of the ratio of the DC output voltage to the DC input voltage and the switching period of the switch converter.

[0018] Optionally, the first off-time is equal to the ratio of a constant to the DC output voltage.

[0019] According to a second aspect of the present invention, there is provided a switch converter, including: a main power circuit that uses a main switch tube to control the power transmission from the input terminal to the output terminal, so as to generate a DC output voltage according to the DC input voltage; and the above-mentioned control circuit for generating a switch drive signal to control the on-state of the main switch tube.

[0020] Optionally, the main power circuit adopts any one of the following topological structures: a floating-ground Buck power circuit, a grounded Buck power circuit, a flyback power circuit, a Buck-boost power circuit, a Boost power circuit.

[0021] According to a third aspect of the present invention, there is provided a control method for a switching converter, where the switching converter uses a main switch tube to control the power transmission from the input end to the output end, so as to generate a DC output voltage according to a DC input voltage. Wherein, the control method includes: generating a first conduction time of the main switch tube in an adaptive conduction time control mode; generating a first turn-off time of the main switch tube in an adaptive conduction frequency control mode; generating a pulse width modulation signal according to a feedback signal of the DC output voltage; generating a switching signal based on the pulse width modulation signal, the first turn-off time, and the first conduction time; and converting the switching signal into a switching drive signal to control the conduction state of the main switch tube. Wherein, the control method further includes: controlling the switching converter to operate in an adaptive conduction time control mode or an adaptive conduction frequency control mode according to a comparison result between the turn-off time of the pulse width modulation signal and the first turn-off time.

[0022] Optionally, the controlling the switching converter to operate in an adaptive conduction time control mode or an adaptive conduction frequency control mode according to a comparison result between the turn-off time of the pulse width modulation signal and the first turn-off time includes: controlling the switching converter to operate in the adaptive conduction time control mode when the turn-off time of the pulse width modulation signal is greater than the first turn-off time, and controlling the switching converter to operate in the adaptive conduction frequency control mode when the turn-off time of the pulse width modulation signal is less than the first turn-off time.

[0023] Optionally, the controlling the switching converter to operate in an adaptive conduction time control mode or an adaptive conduction frequency control mode according to a comparison result between the turn-off time of the pulse width modulation signal and the first turn-off time further includes: in the adaptive conduction time control mode, the conduction time of the main switch tube is determined by the first conduction time, and the turn-off time of the main switch tube is determined by the pulse width modulation signal; and in the adaptive conduction frequency control mode, the conduction time of the main switch tube is determined by the pulse width modulation signal, and the turn-off time of the main switch tube is determined by the first turn-off time.

[0024] Optionally, the generating a switching signal based on the pulse width modulation signal, the first turn-off time, and the first conduction time includes: generating a set signal based on the pulse width modulation signal and the first turn-off time; generating a reset signal based on the pulse width modulation signal and the first conduction time; and generating the switching signal according to the set signal and the reset signal.

[0025] Optionally, generating the set signal based on the pulse width modulation signal and the first turn-off time includes: respectively providing the pulse width modulation signal, the first turn-off time, and a minimum turn-off time to the input terminals of an OR gate to generate the set signal, where the minimum turn-off time is a fixed time period, and the turn-off time of the main switch tube is greater than the minimum turn-off time.

[0026] Optionally, generating the reset signal based on the pulse width modulation signal and the first turn-on time includes: respectively providing the pulse width modulation signal, the first turn-on time, and a minimum turn-on time to the input terminals of a NAND gate to generate the reset signal, where the minimum turn-on time is a fixed time period, and the turn-on time of the main switch tube is greater than the minimum turn-on time.

[0027] Optionally, generating the pulse width modulation signal according to the feedback signal of the DC output voltage includes: comparing the feedback signal with a reference voltage to generate an error signal; and comparing a superimposed signal of the error signal and a ripple injection signal with the feedback signal to generate the pulse width modulation signal.

[0028] Optionally, the first turn-on time is equal to the product of the ratio of the DC output voltage to the DC input voltage and the switching period of the switching converter.

[0029] Optionally, the first turn-off time is equal to the ratio of a constant to the DC output voltage.

[0030] In the switching converter, its control circuit, and control method according to the embodiments of the present invention, a logic circuit compares the turn-off time determined by the pulse width modulation signal with the first turn-off time, and controls the switching converter to operate in an adaptive turn-on time control mode or an adaptive turn-on frequency control mode according to the comparison result. When the DC input voltage and the DC output voltage are close, the turn-on time of the switching converter can be extended so that the switching converter can linearly transition to 100% duty cycle, improving the light load efficiency and stability of the switching converter. The control circuit can also improve the transient response problem of the switching converter and introduce an additional ripple injection signal using a ripple injection circuit. The ripple injection signal can be adaptively adjusted according to the DC output voltage, so that a ceramic capacitor with low ESR can be used as the output capacitor in the switching converter to maintain system stability and suppress output ripple. Description of the Drawings

[0031] Through the following description of the embodiments of the present invention with reference to the drawings, the above and other objects, features, and advantages of the present invention will become clearer. In the drawings:

[0032] Figure 1 A schematic circuit diagram of a switching converter according to the prior art is shown;

[0033] Figure 2 Schematic circuit diagram showing a switching converter according to an embodiment of the present invention;

[0034] Figure 3 Schematic circuit diagram showing a PWM signal generation circuit in a switching converter according to an embodiment of the present invention;

[0035] Figure 4 Flowchart showing a control method of a switching converter according to an embodiment of the present invention. Detailed implementation manners

[0036] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In the respective drawings, the same elements are denoted by the same or similar reference numerals. For the sake of clarity, the various parts in the drawings are not drawn to scale. In addition, some well-known parts may not be shown.

[0037] It should be understood that in the following description, a "circuit" refers to a conductive loop formed by at least one element or sub-circuit through electrical connection or electromagnetic connection. When an element or circuit is said to be "connected to" another element or when an element / circuit is said to be "connected between" two nodes, it can be directly coupled or connected to another element or there may be intermediate elements, and the connection between the elements can be physical, logical, or a combination thereof. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there are no intermediate elements between the two.

[0038] In the present application, a switching transistor is a transistor that operates in a switching mode to provide a current path and includes one selected from a bipolar transistor or a field effect transistor. The first end and the second end of the switching transistor are respectively the high-potential end and the low-potential end on the current path, and the control end is used to receive a driving signal to control the conduction and turn-off of the switching transistor.

[0039] The present invention can be presented in various forms, and some examples will be described below.

[0040] Figure 2 Schematic circuit diagram showing a switching converter according to an embodiment of the present invention. The switching converter 200 adopts a Buck topology and operates in a floating ground mode, and includes a main power circuit and a control circuit. The main power circuit includes a main switching transistor MD1 and a synchronous switching transistor MD2 connected in series between the input end and the ground end, an inductor Lx connected between the intermediate node of the main switching transistor MD1 and the synchronous switching transistor MD2 and the output end, and an output capacitor Cout connected between the output end and the ground end. The input end of the switching converter 200 receives a DC input voltage Vin, and the output end provides a DC output voltage Vout. A voltage dividing network composed of resistors R1 and R2 is used to obtain a feedback signal FB of the DC output voltage Vout.

[0041] The control circuit of the switching converter 200 is used to provide switching drive signals to the main switching transistor MD1 and the synchronous switching transistor MD2. Among them, the control circuit of the switching converter 200 includes an adaptive conduction time control circuit 210, an adaptive conduction frequency control circuit 220, a PWM signal generation circuit 230, a minimum conduction time control circuit 240, a minimum turn-off time control circuit 250, a logic circuit 260, and a drive circuit 270.

[0042] The adaptive conduction time control circuit 210 receives the DC input voltage Vin and the DC output voltage Vout, and is used to set the first conduction time Ton1 of the main switching transistor MD1 in the adaptive conduction time control mode. Further, the adaptive conduction time control circuit 210 sets the first conduction time Ton1 as:

[0043] Ton1 = Tsw * Vout / Vin

[0044] Wherein, Vout represents the voltage value of the DC output voltage, Vin represents the voltage value of the DC input voltage, and Tsw represents the switching period of the switching converter, which can ensure the consistency of the operating frequency of the switching converter.

[0045] The adaptive conduction frequency control circuit 220 receives the DC output voltage Vout and is used to set the first turn-off time Toff1 of the main switching transistor MD1 in the adaptive conduction frequency control mode. Further, the adaptive conduction frequency control circuit 220 sets the first turn-off time Toff1 as:

[0046] Toff1 = M / Vout

[0047] Wherein, Vout represents the voltage value of the DC output voltage, and M is a set constant.

[0048] The PWM signal generation circuit 230 receives the feedback signal FB of the DC output voltage Vout and is used to generate a pulse width modulation signal PWM according to the feedback signal FB.

[0049] The minimum conduction time control circuit 240 and the minimum turn-off time control circuit 250 are respectively used to set the minimum conduction time Ton_min and the minimum turn-off time Toff_min corresponding to the preset output voltage and the predetermined load.

[0050] The logic circuit 260 is used to implement the logic control function of the system and is used to generate a switching signal SW according to the pulse width modulation signal PWM, the first conduction time Ton1, the first turn-off time Toff1, the minimum conduction time Ton_min, and the minimum turn-off time Toff_min.

[0051] Further, the logic circuit 260 includes a NAND gate 261, an OR gate 262, and an RS flip-flop 263. The first input terminal of the NAND gate 261 receives the first conduction time Ton1, the second input terminal of the NAND gate 261 receives the minimum conduction time Ton_min, the third input terminal of the NAND gate 261 receives the pulse width modulation signal PWM of the PWM signal generation circuit 230, and the output terminal of the NAND gate 261 provides a set signal. The first input terminal of the OR gate 262 receives the pulse width modulation signal PWM of the PWM signal generation circuit 230, the second input terminal of the OR gate 262 receives the first turn-off time Toff1, the third input terminal of the OR gate 262 receives the minimum turn-off time Toff_min, and the output terminal of the OR gate 262 provides a reset signal. The RS flip-flop 263 generates a switching signal SW according to the set signal and the reset signal.

[0052] The drive circuit 270 is used to convert the switching signal SW into a switching drive signal to control the conduction states of the main switching transistor MD1 and the synchronous switching transistor MD2. For example, the switching drive signal of the main switching transistor MD1 is the in-phase signal of the switching signal SW, and the switching drive signal of the synchronous switching transistor MD2 is the anti-phase signal of the switching signal SW.

[0053] Further, the logic circuit 260 controls the operating mode of the switching converter (operating in the adaptive conduction time control mode or the adaptive conduction frequency control mode) according to the comparison result between the turn-off time determined by the pulse width modulation signal PWM and the first turn-off time Toff1. When the turn-off time Toff determined by the pulse width modulation signal PWM is greater than the first turn-off time Toff1, the switching converter 200 operates in the adaptive conduction time control mode. The conduction time of the main switching transistor MD1 is determined by the first conduction time Ton1, and the turn-off time of the main switching transistor MD1 is determined by the pulse width modulation signal PWM. At this time, the turn-off time Toff determined by the pulse width modulation signal PWM is:

[0054] Toff = Tsw * (Vin - Vout) / Vin

[0055] As the DC input voltage Vin decreases, when the turn-off time determined by the pulse width modulation signal PWM is less than the first turn-off time Toff1, the switching converter 200 operates in the adaptive conduction frequency control mode. The turn-off time of the main switching transistor MD1 is determined by the first turn-off time Toff1, and the conduction time of the main switching transistor MD1 is determined by the pulse width modulation signal PWM. At this time, the conduction time Ton determined by the pulse width modulation signal PWM is:

[0056] Ton = M / (Vin - Vout)

[0057] Wherein, M represents a preset constant, Vout represents the voltage value of the DC output voltage, and Vin represents the voltage value of the DC input voltage. In this state, since the conduction time Ton determined by the pulse width modulation signal PWM is greater than the first conduction time Ton1, the system completes the switching from the adaptive conduction time control mode to the adaptive conduction frequency control mode, and the PWM signal generation circuit 230 also completes the transition from valley detection to peak detection. After entering the adaptive conduction frequency control mode, when the DC input voltage Vin and the DC output voltage Vout are close, the conduction time of the switching converter can be extended so that the switching converter can linearly transition to a 100% duty cycle.

[0058] Figure 3 FIG. shows a schematic circuit diagram of a PWM signal generation circuit in a switching converter according to an embodiment of the present invention. As Figure 3 shown, the PWM signal generation circuit 230 includes an error amplifier 231, a PWM comparator 232, and a ripple injection circuit 233.

[0059] The inverting input terminal of the error amplifier 231 receives the feedback signal FB, and the non-inverting input terminal receives the reference voltage Vref. The error amplifier 231 is configured to compare the feedback signal FB of the DC output voltage Vout with the reference voltage Vref to generate an error signal Vcomp. The ripple injection circuit 233 is configured to generate a ripple injection signal Ripple during the inductor current drop stage of the switching converter 200, and compensate the error signal Vcomp according to the ripple injection signal Ripple, so that the switching converter can use a ceramic capacitor with low ESR as the output capacitor, reduce the circuit area, and reduce the ripple of the output voltage. The PWM comparator 232 is configured to compare the superimposed signal of the ripple injection signal Ripple and the error signal Vcomp with the feedback signal FB to generate the pulse width modulation signal PWM.

[0060] Furthermore, the slope of the ripple injection signal Ripple generated by the ripple injection circuit 233 in the switching converter 200 of the embodiment of the present invention is not fixed, and its slope is related to the DC output voltage Vout, so that the ripple injection circuit 233 has the function of adaptive ramp modulation.

[0061] Furthermore, the PWM signal generation circuit 230 further includes a capacitor Cc, a compensation resistor Rea, and a compensation capacitor Cea. The first end of the capacitor Cc is connected to the output terminal of the error amplifier 231, and the second end is grounded. The compensation resistor Rea and the compensation capacitor Cea are connected in series between the output terminal of the error amplifier 231 and the ground.

[0062] In the control circuit of the switching converter 200, the logic circuit 260 compares the turn-off time Toff determined by the pulse-width modulation signal PWM with the first turn-off time Toff1, and controls the switching converter to operate in the adaptive conduction time control mode or the adaptive conduction frequency control mode according to the comparison result. When the DC input voltage Vin and the DC output voltage Vout are close, the conduction time of the switching converter can be extended so that the switching converter can linearly transition to a 100% duty cycle. This control circuit can also improve the transient response problem of the switching converter and introduce an additional ripple injection signal Ripple using a ripple injection circuit. The ripple injection signal Ripple can be adaptively adjusted according to the DC output voltage Vout, so that a ceramic capacitor with a low ESR can be used as the output capacitor in the switching converter to maintain system stability and suppress output ripple.

[0063] Figure 4 The flowchart showing the control method of the switching converter according to an embodiment of the present invention. The switching converter is, for example, Figure 2 the switching converter shown, which operates in the adaptive conduction time control mode or the adaptive conduction frequency control mode.

[0064] In step S01, a first conduction time and a first turn-off time are generated. Among them, the first conduction time is used to control the conduction time of the main switch tube MD1 in the adaptive conduction time control mode, and the first turn-off time is used to control the turn-off time of the main switch tube MD1 in the adaptive conduction frequency control mode.

[0065] In step S02, a pulse-width modulation signal is generated according to the feedback signal of the DC output voltage. Further, in this step, first, the feedback signal FB of the DC output voltage Vout is compared with a reference voltage to generate an error signal Vcomp, then a ripple injection signal Ripple is generated during the inductor current drop phase of the switching converter, and the error signal Vcomp is compensated according to the ripple injection signal Ripple. Finally, the superimposed signal of the ripple injection signal Ripple and the error signal Vcomp is compared with the feedback signal FB to generate the pulse-width modulation signal PWM.

[0066] In step S03, a switching signal is generated based on the pulse-width modulation signal, the first conduction time, and the first turn-off time.

[0067] In step S04, the switching signal is converted into a switching drive signal, and the switching drive signal is used to control the conduction states of the main switch tube MD1 and the synchronous switch tube MD2 in the switching converter.

[0068] Further, in the above step S03, it also includes controlling the switching converter to operate in an adaptive conduction time control mode or an adaptive conduction frequency control mode according to the comparison result between the turn-off time of the pulse width modulation signal and the first turn-off time. When the turn-off time of the pulse width modulation signal is greater than the first turn-off time, control the switching converter to operate in the adaptive conduction time control mode. At this time, the conduction time of the main switch tube is determined by the first conduction time, and the turn-off time of the main switch tube is determined by the pulse width modulation signal. When the turn-off time of the pulse width modulation signal is less than the first turn-off time, control the switching converter to operate in the adaptive conduction frequency control mode. At this time, the conduction time of the main switch tube is determined by the pulse width modulation signal, and the turn-off time of the main switch tube is determined by the first turn-off time.

[0069] Further, set the first conduction time as:

[0070] Ton1 = Vout / Vin * Tsw

[0071] Wherein, Vout represents the voltage value of the DC output voltage, Vin represents the voltage value of the DC input voltage, and Tsw represents the switching period of the switching converter, which can ensure the consistency of the operating frequency of the switching converter.

[0072] Further, set the first turn-off time as:

[0073] Toff1 = M / Vout

[0074] Wherein, Vout represents the voltage value of the DC output voltage, and M is a set constant.

[0075] Further, the above step S03 also includes respectively providing the pulse width modulation signal, the first turn-off time and the minimum turn-off time to the input terminals of an OR gate to generate a set signal. The minimum turn-off time is a fixed time period, and the turn-off time of the main switch tube is greater than the minimum turn-off time. Respectively provide the pulse width modulation signal, the first conduction time and the minimum conduction time to the input terminals of a NAND gate to generate the reset signal. The minimum conduction time is a fixed time period, and the conduction time of the main switch tube is greater than the minimum conduction time. Then generate the switching signal according to the set signal and the reset signal.

[0076] In summary, in the switching converter, its control circuit, and the control method according to the embodiments of the present invention, the logic circuit compares the off-time determined by the pulse-width modulation signal with the first off-time, and controls the switching converter to operate in the adaptive conduction time control mode or the adaptive conduction frequency control mode according to the comparison result. When the DC input voltage and the DC output voltage are close, the conduction time of the switching converter can be extended, so that the switching converter can linearly transition to a 100% duty cycle, improving the light-load efficiency and stability of the switching converter. The control circuit can also improve the transient response problem of the switching converter and introduce an additional ripple injection signal by using a ripple injection circuit. The ripple injection signal can be adaptively adjusted according to the DC output voltage, so that a ceramic capacitor with a low ESR can be used as the output capacitor in the switching converter to maintain system stability and suppress output ripple.

[0077] In the above embodiments, although the switching converter with a buck topology structure is described in combination with Figure 2 However, it can be understood that the control circuit according to the embodiments of the present invention can also be used in switching converters with other topology structures. The structure of the main power circuit includes, but is not limited to, topology structures such as a floating-ground Buck power circuit, a grounded Buck power circuit, a flyback power circuit, a Buck-boost power circuit, and a Boost power circuit.

[0078] In the above description, no detailed description is made of the well-known structural elements and steps. However, those skilled in the art should understand that corresponding structural elements and steps can be implemented by various technical means. In addition, in order to form the same structural elements, those skilled in the art can also design methods that are not exactly the same as the methods described above. In addition, although the above embodiments are described separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination.

[0079] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to only the specific embodiments. Obviously, many modifications and variations can be made according to the above description. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can make good use of the present invention and its modifications based on the present invention. The protection scope of the present invention should be defined by the scope of the claims of the present invention.

Claims

1. A control circuit for a switching converter, where the switching converter uses a main switching transistor to control the power transfer from the input terminal to the output terminal, so as to generate a DC output voltage according to the DC input voltage. Wherein, the control circuit includes: An adaptive on-time control circuit for generating a first on-time of the main switching transistor in the adaptive on-time control mode; An adaptive on-frequency control circuit for generating a first off-time of the main switching transistor in the adaptive on-frequency control mode; A PWM signal generation circuit for generating a pulse width modulation signal according to the feedback signal of the DC output voltage; A logic circuit for generating a switching signal based on the pulse width modulation signal, the first off-time, and the first on-time; and A driving circuit for converting the switching signal into a switching drive signal to control the on-state of the main switching transistor, wherein the logic circuit is further configured to control the switching converter to operate in the adaptive on-time control mode or the adaptive on-frequency control mode according to the comparison result between the off-time of the pulse width modulation signal and the first off-time, wherein the logic circuit is configured to: control the switching converter to operate in the adaptive on-time control mode when the off-time of the pulse width modulation signal is greater than the first off-time, determine the on-time of the main switching transistor by the first on-time, determine the off-time of the main switching transistor by the pulse width modulation signal, and control the switching converter to operate in the adaptive on-frequency control mode when the off-time of the pulse width modulation signal is less than the first off-time, determine the on-time of the main switching transistor by the pulse width modulation signal, and determine the off-time of the main switching transistor by the first off-time.

2. The control circuit according to claim 1, wherein the logic circuit includes: A NAND gate, with the first input terminal receiving the first on-time, the second input terminal receiving the minimum on-time, the third input terminal receiving the pulse width modulation signal, and the output terminal providing a reset signal; An OR gate, with the first input terminal receiving the pulse width modulation signal, the second input terminal receiving the first off-time, the third input terminal receiving the minimum off-time, and the output terminal providing a set signal; and an RS flip-flop for generating the switching signal according to the set signal and the reset signal respectively.

3. The control circuit according to claim 2, further includes: A minimum off-time control circuit for generating the minimum off-time, and the off-time of the main switching transistor is greater than the minimum off-time; and A minimum on-time control circuit for generating the minimum on-time, and the on-time of the main switching transistor is greater than the minimum on-time.

4. The control circuit according to claim 1, wherein, the PWM signal generation circuit includes: An error amplifier, with the inverting input terminal and the non-inverting input terminal receiving the feedback signal and the reference voltage respectively, and the output terminal for providing an error signal; and A PWM comparator, whose inverting input terminal and non-inverting input terminal respectively receive the feedback signal and the superimposed signal of the error signal and the ripple injection signal, and the output terminal is used to provide the pulse width modulation signal.

5. The control circuit according to claim 4, wherein, the PWM signal generation circuit further includes: a first capacitor, whose first terminal is connected to the output terminal of the error amplifier and the second terminal is grounded; and a compensation resistor and a compensation capacitor connected in sequence between the output terminal of the error amplifier and the ground.

6. The control circuit according to claim 4, wherein, the PWM signal generation circuit further includes: a ripple injection circuit, which is used to generate the ripple injection signal during the inductor current drop phase of the switching converter.

7. For the control circuit according to claim 1, the first conduction time is equal to the product of the ratio of the DC output voltage to the DC input voltage and the switching period of the switching converter.

8. For the control circuit according to claim 1, the first turn-off time is equal to the ratio of a constant to the DC output voltage.

9. A switching converter, comprising: a main power circuit, which uses a main switch tube to control the power transmission from the input terminal to the output terminal, so as to generate a DC output voltage according to the DC input voltage; and the control circuit according to any one of claims 1-8, which is used to generate a switch drive signal to control the conduction state of the main switch tube.

10. For the switching converter according to claim 9, the main power circuit adopts any one of the following topological structures: floating ground type Buck power circuit, grounded type Buck power circuit, flyback power circuit, Buck-boost type power circuit, Boost type power circuit.

11. A control method for a switching converter, the switching converter uses a main switch tube to control the power transmission from the input terminal to the output terminal, so as to generate a DC output voltage according to the DC input voltage, wherein, the control method includes: generating a first conduction time of the main switch tube in the adaptive conduction time control mode; generating a first turn-off time of the main switch tube in the adaptive conduction frequency control mode; generating a pulse width modulation signal according to the feedback signal of the DC output voltage; generating a switch signal based on the pulse width modulation signal, the first turn-off time, and the first conduction time; and converting the switch signal into a switch drive signal to control the conduction state of the main switch tube, wherein, the control method further includes: controlling the switching converter to operate in the adaptive conduction time control mode or the adaptive conduction frequency control mode according to the comparison result between the turn-off time of the pulse width modulation signal and the first turn-off time, wherein, the controlling the switching converter to operate in the adaptive conduction time control mode or the adaptive conduction frequency control mode according to the comparison result between the turn-off time of the pulse width modulation signal and the first turn-off time includes: When the off - time of the pulse - width modulation signal is greater than the first off - time, control the switching converter to operate in the adaptive conduction - time control mode. The conduction time of the main switching transistor is determined by the first conduction time, and the off - time of the main switching transistor is determined by the pulse - width modulation signal. And When the off - time of the pulse - width modulation signal is less than the first off - time, control the switching converter to operate in the adaptive conduction - frequency control mode. The conduction time of the main switching transistor is determined by the pulse - width modulation signal, and the off - time of the main switching transistor is determined by the first off - time.

12. The control method according to claim 11, wherein, generating a switching signal based on the pulse - width modulation signal, the first off - time, and the first conduction time includes: generating a set signal based on the pulse - width modulation signal and the first off - time; generating a reset signal based on the pulse - width modulation signal and the first conduction time; and generating the switching signal according to the set signal and the reset signal.

13. The control method according to claim 12, the generating a set signal based on the pulse - width modulation signal and the first off - time includes: respectively providing the pulse - width modulation signal, the first off - time, and a minimum off - time to the input terminals of an OR gate to generate the set signal. The minimum off - time is a fixed time period, and the off - time of the main switching transistor is greater than the minimum off - time.

14. The control method according to claim 12, the generating a reset signal based on the pulse - width modulation signal and the first conduction time includes: respectively providing the pulse - width modulation signal, the first conduction time, and a minimum conduction time to the input terminals of a NAND gate to generate the reset signal. The minimum conduction time is a fixed time period, and the conduction time of the main switching transistor is greater than the minimum conduction time.

15. The control method according to claim 11, wherein, generating a pulse - width modulation signal according to the feedback signal of the DC output voltage includes: comparing the feedback signal with a reference voltage to generate an error signal; and comparing a superimposed signal of the error signal and a ripple injection signal with the feedback signal to generate the pulse - width modulation signal.

16. The control method according to claim 11, wherein, the first conduction time is equal to the product of the ratio of the DC output voltage to the DC input voltage and the switching period of the switching converter.

17. The control method according to claim 11, wherein, the first off - time is equal to the ratio of a constant to the DC output voltage.

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