Switching converter and control circuit therefor

Abstract

The application discloses a switching converter and a control circuit thereof. The control circuit comprises a ripple generation circuit, a capacitor-resistor structure, a switching network and a voltage-current converter. The switching network is coupled with a first node of the capacitor-resistor structure and is used for switching a charging or discharging path of the capacitor-resistor structure according to a control signal with a fixed conduction time. The voltage-current converter is coupled with a second node of the capacitor-resistor structure and is used for converting a voltage of the second node into a ripple signal which is synchronous and in phase with an inductor current. Therefore, a ceramic capacitor with low ESR can be used as an output capacitor in the switching converter, the system stability is maintained, the output ripple is suppressed, the number of devices of a power module is not increased, the application difficulty of the switching converter is greatly reduced, and the application flexibility is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of switching power supply technology, and more particularly, to a switching converter and a control circuit thereof. BACKGROUND

[0002] Switching converters have been widely used in electronic systems to generate operating voltages and currents required by internal circuit modules or loads. A switching converter controls the power transfer from an input terminal to an output terminal by using power switches, and thus can provide a constant output voltage and / or output current at the output terminal. In a switching converter, a constant on-time control method based on ripple has the advantages of 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 switching transistors M1 and M2 connected in series between an input terminal and a ground terminal, an inductor Lx connected between a switching node SW between the switching transistors M1 and M2 and an output terminal, an input capacitor Cin connected between the input terminal and the ground terminal, and an output capacitor Cout connected between the output terminal and the ground terminal. The input terminal of the switching converter 100 receives an input voltage Vin, and the output terminal provides an output voltage Vout. A voltage dividing network composed of resistors R1 and R2 is used to obtain a feedback signal FB of the output voltage Vout, and a resistor R3 is an equivalent series resistance (ESR) of the output capacitor Cout. The switching transistors M1 and M2 are referred to as high-side and low-side switching transistors, respectively, and the control circuit of the switching converter 100 is used to provide switching signals to the switching transistors M1 and M2.

[0004] In the control circuit of the switching converter 100, an error amplifier 130 obtains an error signal Vc from a feedback signal FB of the output voltage Vout and a reference voltage Vref, an on-time control circuit 120 generates a control signal Pluse with a fixed on-time according to the error signal Vc, and a drive circuit 110 converts the control signal Pluse into switching signals to control the on-off states of the switching transistors M1 and M2. During a high level of the control signal Pluse, the switching transistor M1 is on and the switching transistor M2 is off; during a low level of the control signal Pluse, the switching transistor M1 is off and the switching transistor M2 is on.

[0005] The constant on-time controller (COT) and constant off-time controller (CFT) in the existing switching converter 100 need to use the ESR of the output capacitor to generate a ripple signal on the output voltage Vout, which is fed back to the input of the internal comparator of the controller through the feedback end for the controller to obtain the inductor current information to determine the opening timing of the switch tube. If a low ESR capacitor (such as a ceramic capacitor) is used as the output capacitor, because its equivalent series resistance is small, the ripple of the output voltage Vout and the feedback signal FB is also small, and even regarded as a direct current signal, thus sub-harmonic oscillation occurs in the system, which may cause the problem of unstable control system. Therefore, the output end of the existing switching converter 100 can only use a capacitor with a large ESR (such as an electrolytic capacitor) as the output capacitor, which not only increases the circuit area and cost, but also increases the ripple of the output voltage, affecting the normal work of the subsequent circuit.

[0006] To solve the above problems, the prior art provides another switching converter, as shown in Figure 2 The switching converter 200 uses an external ripple injection method to reduce the ESR of the output capacitor, that is, a set of resistor-capacitor devices Rr and Cr are connected in series between the switching node SW and the output end, and then the potential Vrc of the resistor-capacitor connection point is coupled to the feedback end of the chip through the capacitor Cj. The principle is to use the periodic change of the switching node SW to make the voltage Vrc generate an alternating ripple signal with the same period, and the ripple signal is coupled to the feedback signal FB through the capacitor Cj, so that the feedback signal FB appears an alternating ripple signal, achieving a similar effect when using a large ESR output capacitor.

[0007] Although the external ripple injection scheme solves the dependence of the system on the ESR of the output capacitor, it also increases the number of devices in the power module. More importantly, due to the influence of the resolution and noise of the internal comparator of the chip, the peak-to-peak amplitude of the ripple usually needs to be greater than 20mV, so the user needs to calculate the device parameters of the external ripple injection circuit according to the actual application conditions, increasing the application difficulty and flexibility of the switching converter. SUMMARY

[0008] In view of the above problems, the purpose of the present application is to provide a switching converter and a control circuit thereof, which solves the problem of sub-harmonic oscillation in the system when a low ESR ceramic capacitor is used as the output capacitor in the switching converter.

[0009] According to an aspect of an embodiment of the present application, there is provided a control circuit of a switching converter, the switching converter controlling transmission of electric energy from an input terminal to an output terminal by at least one switch, so as to generate an output voltage according to an input voltage, wherein the control circuit comprises: a ripple generation circuit configured to generate a ripple signal in synchronization with and in phase with an inductor current of the switching converter; an error amplifier configured to generate an error signal according to a feedback signal of the output voltage, the ripple signal and a reference voltage; a conduction time control circuit configured to generate a control signal with a fixed conduction time according to the error signal; and a drive circuit configured to convert the control signal into a switching signal to control a conduction state of the at least one switch, wherein the ripple generation circuit comprises: a resistor-capacitor structure; a switch network coupled to a first node of the resistor-capacitor structure, the switch network being configured to switch a charging or discharging path of the resistor-capacitor structure according to the control signal and a zero-crossing detection signal; and a current-voltage converter coupled to a second node of the resistor-capacitor structure, the current-voltage converter being configured to convert a voltage of the second node into the ripple signal in the form of a current.

[0010] Optionally, the switch network is configured to charge the second node during a high level of the control signal, discharge the second node during a low level of the control signal, and position a voltage of the second node at the output voltage during a high level of the zero-crossing detection signal.

[0011] Optionally, the switch network comprises: a first switch and a second switch connected in series between the input voltage and a ground, a middle node of the first switch and the second switch being coupled to the first node of the resistor-capacitor structure; and a third switch coupled between the output voltage and the second node.

[0012] Optionally, the first switch is controlled by the control signal, the third switch is controlled by the zero-crossing detection signal, and the switch network further comprises an NOR gate, a first input end of the NOR gate receiving the control signal, a second input end of the NOR gate receiving the zero-crossing detection signal, and an output end of the NOR gate being connected to a control terminal of the second switch.

[0013] Optionally, the resistor-capacitor structure comprises: a first resistor, a first end of the first resistor being connected to the first node and a second end of the first resistor being connected to the second node; and a first capacitor, a first end of the first capacitor being connected to the second node and a second end of the first capacitor being grounded.

[0014] Optionally, the control circuit further comprises a zero-crossing detection circuit configured to generate the zero-crossing detection signal by detecting a switching node voltage of the switching converter.

[0015] Optionally, the inverting input terminal of the error amplifier receives a superimposed signal of the ripple signal and the feedback signal, the non-inverting input terminal of the error amplifier receives the reference voltage, and the output terminal is used for outputting the error signal.

[0016] Optionally, the control circuit further comprises a second resistor, a first terminal of the second resistor being connected with the feedback signal, and a second terminal of the second resistor being connected with the ripple signal and the inverting input terminal of the error amplifier, and the second resistor is used for superimposing the ripple signal on the feedback signal.

[0017] According to another aspect of the embodiments of the present application, a switching converter is provided, comprising: a main circuit for controlling the transmission of electric energy from an input terminal to an output terminal by using at least one switching tube, so as to generate an output voltage according to an input voltage; and the above-mentioned control circuit for generating a switching signal to control the conduction state of the at least one switching tube.

[0018] Optionally, the main circuit adopts a topology selected from any one of the following: a buck type, a boost type, a buck-boost type, a non-inverted buck-boost type, a forward type, and a flyback type.

[0019] In the switching converter and the control circuit thereof according to the embodiments of the present application, an additional ripple compensation is introduced by using the ripple generation circuit built in the chip. The ripple signal is synchronous and in phase with the inductor current in the switching converter, so that a low-ESR ceramic capacitor can be used as the output capacitor in the switching converter, thereby maintaining the system stability and suppressing the output ripple. In addition, the ripple generation circuit according to the embodiments of the present application does not increase the number of devices of the power module, and the device parameters of the ripple injection circuit do not need to be calculated according to the actual application conditions, so that the application difficulty of the switching converter is greatly reduced, and the flexibility of the application is improved. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0021] Figure 1 a schematic circuit diagram of a switching converter according to the prior art is shown;

[0022] Figure 2 a schematic circuit diagram of another switching converter according to the prior art is shown;

[0023] Figure 3 a schematic circuit diagram of a switching converter according to the embodiments of the present application is shown;

[0024] Figure 4 a schematic circuit diagram of a ripple generation circuit in a switching converter according to the embodiments of the present application is shown;

[0025] Figure 5 A schematic waveform diagram of a switching converter operating in continuous current mode (CCM) according to an embodiment of the present invention is shown.

[0026] Figure 6 A schematic waveform diagram is shown for a switching converter operating in discontinuous current mode (DCM) according to an embodiment of the present invention. Detailed Implementation

[0027] Various embodiments of the invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements are indicated by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale. Furthermore, some well-known parts may not be shown.

[0028] It should be understood that, in the following description, "circuit" refers to a conductive loop consisting of at least one element or sub-circuit connected by an electrical or electromagnetic link. When an element or circuit is said to be "connected" to another element or "connected" between two nodes, it can be directly coupled or connected to the other element, or there may be intermediate elements. The connection between elements can be physical, logical, or a combination thereof. Conversely, 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 them.

[0029] In this application, the switching transistor is a transistor that operates in switching mode to provide a current path, including a bipolar transistor or a field-effect transistor. The first and second terminals of the switching transistor are respectively a high-potential terminal and a low-potential terminal on the current path, and the control terminal is used to receive a drive signal to control the switching transistor's on and off states. This invention can be presented in various forms, some of which are described below.

[0030] Figure 3 A schematic circuit diagram of a switching converter according to an embodiment of the present invention is shown. Figure 3 As shown, the switching converter 300 includes a main circuit and a control circuit. The main circuit of the switching converter 300 includes switching transistors M1 and M2 connected in series between the input terminal and the ground terminal. An inductor Lx is connected between the switching node SW between the switching transistors M1 and M2 and the output terminal. An input capacitor Cin is connected between the input terminal and the ground terminal, and an output capacitor Cout is connected between the output terminal and the ground terminal. The input terminal of the switching converter 300 receives the input voltage Vin, and the output terminal provides the output voltage Vout. A voltage divider network composed of resistors R1 and R2 is used to obtain the feedback signal FB of the output voltage Vout.

[0031] The switch tube M1 and the switch tube M2 are, for example, respectively referred to as a high side switch tube and a low side switch tube. The control circuit of the switch converter 200 is used to provide a switching signal to the switch tubes M1 and M2. The switching signal is a driving signal generated according to a control signal Pluse. For example, the switching signal of the switch tube M1 is an in-phase signal of the control signal Pluse, and the switching signal of the switch tube M2 is an anti-phase signal of the control signal Pluse.

[0032] Further, the control circuit of the switch converter 300 includes a driving circuit 310, a conduction time control circuit 320, an error amplifier 330, a ripple generating circuit 340, and a zero-crossing detection circuit 350.

[0033] The zero-crossing detection circuit 350 is connected with a switching node SW between the switch tubes M1 and M2, and is used to obtain a zero-crossing detection signal ZCD by detecting a voltage of the switching node SW.

[0034] The ripple generating circuit 340 is used to generate a ripple signal Iripple which is synchronous and in-phase with the inductor current of the switch converter, and the error amplifier 330 compares a superimposed signal of the feedback signal FB and the ripple signal Iripple with a reference voltage Vref to generate an error signal Vc. In an example, the switch converter 300 further includes a resistor Ra connected between the intermediate node of the resistor R1 and the resistor R2 and the inverting input terminal of the error amplifier 330, so that the ripple signal Iripple can be superimposed on the feedback signal FB.

[0035] In other embodiments, the ripple signal Iripple can also be superimposed on the reference voltage Vref, so that the error amplifier 330 compares the feedback signal FB with a superimposed signal of the ripple signal Iripple and the reference voltage Vref to generate the error signal.

[0036] The switch converter 300 of the embodiment of the present application generates the ripple signal Iripple which is synchronous and in-phase with the inductor current through the ripple generating circuit 340, and superimposes the ripple signal Iripple on the feedback signal FB to generate a superimposed signal with large ripple, thereby solving the problem of loop instability caused by too small equivalent series resistance R3, so that the switch 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.

[0037] Furthermore, the conduction time control circuit 320 generates a control signal Pluse with a fixed conduction time based on the error signal Vc. The drive circuit 310 converts the control signal Pluse into a switching signal to control the conduction state of switches M1 and M2. During the high level of the control signal Pluse, switch M1 is turned on and switch M2 is turned off; during the low level of the control signal Pluse, switch M1 is turned off and switch M2 is turned on.

[0038] Figure 4 A schematic circuit diagram of a ripple generation circuit in a switching converter according to an embodiment of the present invention is shown. Figure 4 As shown, the ripple generation circuit 340 includes a switching network consisting of switches K1 to K3 and a NOR gate NOR1, a resistor-capacitor structure consisting of a resistor Rr and a capacitor Cr, and a voltage-to-current converter VCCS. Switches K1 and K2 are connected sequentially between the input voltage Vin and ground. The first end of resistor Rr is connected to node A between switches K1 and K2, and the second end of resistor Rr is connected to the first end of capacitor Cr at node B. The second end of capacitor Cr is grounded. The first input terminal of the voltage-to-current converter VCCS is connected to the output voltage Vout, and the second input terminal is connected to node B. The voltage-to-current converter VCCS is used to convert the voltage at node B into a current-form ripple signal Iripple. Switch K3 is connected between the first and second input terminals of the voltage-to-current converter VCCS. The first input terminal of the NOR gate NOR1 receives the control signal Plus, the second input terminal receives the zero-crossing detection signal ZCD, and the output terminal is connected to the control terminal of switch K2.

[0039] In this circuit, switch K1 is controlled by the control signal Plus, switch K2 is controlled by the output signal of the NOR gate NOR1, and switch K3 is controlled by the zero-crossing detection signal ZCD. The ripple generation circuit 340 typically operates in the following states:

[0040] 1. During the high level period of the control signal Puse (i.e., when switch M1 is on and switch M2 is off), switch K1 is on, and switches K2 and K3 are off. Since node A is connected to the input voltage Vin, the potential of node A is higher than that of node B. Therefore, the input voltage Vin charges capacitor Cr, and the voltage of node B increases. The amount of voltage increase at node B is:

[0041] ΔVrise=(VA-VB)×Ton / (Rr×Cr) (1)

[0042] Wherein, Ton represents the on-time of the switch signal.

[0043] 2. During the inductor freewheeling period when the control signal Puse is low (i.e., when switch M1 is off and switch M2 is on), switch K2 is on, and switches K1 and K3 are off. Since node A is connected to ground, the potential of node A is lower than the potential of node B. Therefore, capacitor Cr discharges to ground, and the voltage of node B decreases. The amount of voltage decrease at node B is:

[0044] ΔVfall=VB×Toff / (Rr×Cr) (2)

[0045] 3. During the stage when the control signal Pluse is at a low level and the inductor freewheeling has ended, the zero-crossing detection signal ZCD is triggered, switch K3 is turned on, switches K1 and K2 are turned off, and the potential of node B is set to the output voltage Vout.

[0046] Generally, when the system operates in continuous current mode (CCM), the inductor current never crosses zero during the turn-off period of switch M1, therefore the ripple generation circuit 340 alternates between states 1 and 2. When the system operates in discontinuous current mode (DCM), the inductor current crosses zero during the turn-off period of switch M1, therefore the ripple generation circuit 340 cycles sequentially between states 1 to 3. In state 1, the voltage at node B rises; in state 2, the voltage at node B falls; and in state 3, the voltage at node B remains constant. Therefore, as the system's ON / OFF states alternate, a gradually rising or falling, continuous voltage ripple signal will be generated at node B. The amplitude of this voltage ripple signal depends on the input voltage Vin, the output voltage Vout, and the system's turn-on and turn-off times.

[0047] Furthermore, due to the setting effect of switch K3, the DC component of the voltage at node B can be considered equal to the output voltage Vout. Therefore, the DC component of the voltage at node B is usually much larger than its change ΔV. Thus, the nonlinear effect of the RC structure on the voltage change at node B can be ignored in the above equations. Therefore, the above equations (1) and (2) can be replaced with:

[0048] ΔVrise=(Vin-Vout)×Ton / (Rr×Cr) (3)

[0049] ΔVfall=Vout×Toff / (Rr×Cr) (4)

[0050] Since the positive and negative volt-seconds across the inductor in a steady-state switching converter are equal (i.e., volt-second balance), the relationship between the inductor current IL and the input voltage Vin, output voltage Vout, on-time Ton, and off-time Toff in a steady-state switching converter is as follows:

[0051] ΔIL_ON = (Vin - Vout) x Ton / L (5)

[0052] ΔIL_OFF = Vout x Toff / L (6)

[0053] From the above equations, it can be seen that the voltage variation of node B in the on-time and off-time of the switching signal has a strong correlation with the variation of the inductor current of the switching converter, so the variation of the inductor current can be simulated by the voltage ripple variation of node B, thereby realizing the synchronization of the inductor current.

[0054] Further, in order to introduce the ripple voltage of node B into the voltage converter system, the present embodiment proposes an adding mode. First, the voltage of node B is converted into a current form ripple signal Iripple by the current-voltage converter VCCS, and then the ripple signal Iripple is superimposed on the feedback signal FB through the resistance Ra in the equation. Figure 3 It should be noted that the present application is not limited thereto, and those skilled in the art can also use other adding modes to introduce the ripple voltage into the voltage converter system.

[0055] Figure 5 A schematic waveform diagram showing the operation of the ripple generation circuit of the switching converter according to the embodiment of the present application in the continuous current mode CCM is shown. In the figure, the curves Pluse, IL, ZCD, VB and Iripple respectively represent the waveform diagrams of the control signal, the inductor current, the zero-crossing detection signal, the voltage variation of node B and the ripple signal related to the switching tube M1.

[0056] In this embodiment, the switching converter 300 operates in the continuous current mode CCM, and in the switching period of the switching converter 300, the inductor current IL is always not zero during the on-time of the switching tube M2.

[0057] As Figure 5As shown, in the first time period T1 starting from the rising edge of the control signal Pluse, the switch tube M1 is turned on, the switch tube M2 is turned off, the inductor current IL gradually increases, at the same time, the switch K1 in the ripple generating circuit 340 is turned on, the switches K2 and K3 are turned off, the input voltage Vin charges the capacitor Cr, the voltage VB of the node B gradually increases, and the ripple signal Iripple gradually increases; in the second time period T2 starting from the falling edge of the control signal Pluse, the switch tube M1 is turned off, the switch tube M2 is turned on, the inductor current IL gradually decreases, at the same time, the switches K1 and K3 in the ripple generating circuit 340 are turned off, the switch K2 is turned on, the capacitor Cr is discharged to the ground, the voltage VB of the node B gradually decreases, and the ripple signal Iripple gradually decreases, so that the ripple signal Iripple generated in the ripple generating circuit 340 of the embodiment of the present application changes synchronously with the inductor current IL. In addition, it can be known from the above formula that, in the steady state operation of the switching converter, the change slope of the voltage VB of the node B is the same as the change slope of the inductor current IL, therefore, the ripple generating circuit 340 of the embodiment of the present application can generate the ripple signal synchronous and in-phase with the inductor current of the switching converter when working in the continuous current mode CCM.

[0058] Figure 6 A schematic waveform diagram showing the ripple generating circuit of the switching converter according to the embodiment of the present application working in the discontinuous current mode DCM is shown. In the diagram, the curves Pluse, IL, ZCD, VB and Iripple respectively represent the waveform diagrams of the control signal related to the switch tube M1, the inductor current, the zero-crossing detection signal, the voltage change of the node B and the ripple signal.

[0059] In this embodiment, the switching converter 300 works in the discontinuous current mode DCM, and in the switching period of the switching converter 300, the inductor current IL crosses zero during the conduction period of the switch tube M2.

[0060] As Figure 6As shown, in the third time period T3 starting from the rising edge of the control signal Plus, switch M1 is turned on and switch M2 is turned off, the inductor current IL gradually increases, and at the same time, switch K1 in the ripple generation circuit 340 is turned on, while switches K2 and K3 are turned off. The input voltage Vin charges capacitor Cr, the voltage VB at node B gradually increases, and the ripple signal Iripple gradually increases. In the fourth time period T4 starting from the falling edge of the control signal Plus, switch M1 is turned off and switch M2 is turned on, the inductor current IL gradually decreases, and at the same time, the ripple is generated. In circuit 340, switches K1 and K3 are open, switch K2 is open, capacitor Cr discharges to ground, the voltage VB at node B gradually decreases, and the ripple signal Iripple gradually decreases. During the fifth time period T5 when the control signal Plus is low, the inductor current IL crosses zero, the zero-crossing detection signal ZCD flips to high, and switches M1 and M2 are open. At this time, the inductor current IL no longer changes. Simultaneously, switches K1 and K2 in the ripple generation circuit 340 are open, switch K3 is open, and the potential of node B is set to the output voltage Vout. Therefore, the ripple signal Iripple generated in the ripple generation circuit 340 of this embodiment changes synchronously with the inductor current IL. Furthermore, based on the above formula, it can be seen that under the steady-state operation of the switching converter, the slope of the voltage VB at node B is the same as the slope of the inductor current IL. Therefore, the ripple generation circuit 340 of this embodiment can also generate a ripple signal that is synchronous and in phase with the inductor current of the switching converter when operating in discontinuous current mode (DCM).

[0061] In summary, the switching converter and its control circuit of this invention introduce additional ripple compensation by employing a built-in ripple generation circuit in the chip. This ripple signal is synchronized and in phase with the inductor current in the switching converter, thereby allowing the use of low-ESR ceramic capacitors as output capacitors in the switching converter, maintaining system stability and suppressing output ripple. Furthermore, the ripple generation circuit of this invention does not increase the number of components in the power module, and there is no need to calculate the component parameters of the ripple injection circuit based on actual application conditions. Therefore, it greatly reduces the application difficulty of the switching converter and facilitates greater application flexibility.

[0062] In the above embodiments, although combined Figure 3 A buck converter topology has been described. However, it is understood that the control circuit of the present invention can also be used in other topologies of switching converters, including but not limited to buck, boost, buck-boost, non-inverter buck-boost, forward, and flyback topologies.

[0063] In the above description, well-known structures and steps have not been described in detail. However, it should be appreciated that the corresponding structures and steps can be implemented by various means. In addition, those skilled in the art can also design methods that are not exactly the same as the above description to form the same structures. In addition, although each embodiment is described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination.

[0064] In accordance with the embodiments of the present application as described above, these embodiments do not describe all the details and are not limited to the specific embodiments. Obviously, many modifications and changes can be made according to the above description. The present description selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well utilize the present application and make modifications and uses on the basis of the present application. The scope of protection of the present application should be defined by the scope of the claims of the present application.

Claims

1. A control circuit for a switching converter, wherein the switching converter uses at least one switching transistor to control the transfer of electrical energy from the input terminal to the output terminal, thereby generating an output voltage based on the input voltage, wherein, The control circuit includes: A ripple generation circuit is used to generate a ripple signal that is synchronized with and in phase with the inductor current of the switching converter. The zero-crossing detection circuit generates a zero-crossing detection signal by detecting the switching node voltage of the switching converter. An error amplifier is used to generate an error signal based on the feedback signal of the output voltage, the ripple signal, and the reference voltage; On-time control circuitry, configured to generate a control signal with a fixed on-time based on the error signal; and A driving circuit is used to convert the control signal into a switching signal to control the conduction state of at least one switching transistor. The ripple generation circuit includes: RC structure; A switching network, coupled to a first node of the resistor-capacitor structure, is used to switch the charging or discharging path of the resistor-capacitor structure according to the control signal and the zero-crossing detection signal; and A voltage-to-current converter, wherein the first input terminal of the voltage-to-current converter is connected to the output voltage, and the second input terminal is coupled to the second node of the RC structure, for converting the voltage of the second node into a ripple signal in the form of current. The RC structure includes: a first resistor, with its first end connected to the first node and its second end connected to the second node; and a first capacitor, with its first end connected to the second node and its second end grounded. The switching network is used to charge the second node when the control signal is high, discharge the second node when the control signal is low, and position the electrical position of the second node at the output voltage when the zero-crossing detection signal is high.

2. The control circuit according to claim 1, wherein, The switching network includes: A first switch and a second switch are connected in series between the input voltage and ground, and the intermediate node of the first switch and the second switch is coupled to the first node of the resistor-capacitor structure; and A third switch is coupled between the output voltage and the second node.

3. The control circuit according to claim 2, wherein, The first switch is controlled by the control signal, and the third switch is controlled by the zero-crossing detection signal. The switch network also includes a NOR gate, the first input of which receives the control signal, the second input of which receives the zero-crossing detection signal, and the output of which is connected to the control terminal of the second switch.

4. The control circuit according to claim 1, wherein, The inverting input of the error amplifier receives the superposition of the ripple signal and the feedback signal, the non-inverting input of the error amplifier receives the reference voltage, and the output is used to output the error signal.

5. The control circuit according to claim 4, wherein, Also includes: The second resistor has a first end connected to the feedback signal and a second end connected to the ripple signal and the inverting input of the error amplifier, and is used to superimpose the ripple signal onto the feedback signal.

6. A switching converter, comprising: The main circuit uses at least one switching transistor to control the transfer of electrical energy from the input terminal to the output terminal, thereby generating the output voltage according to the input voltage. as well as The control circuit according to any one of claims 1-5 is used to generate a switching signal to control the conduction state of the at least one switching transistor.

7. The switching converter according to claim 6, wherein the main circuit adopts a topology selected from any of the following: buck converter, boost converter, buck-boost converter, forward converter, and flyback converter.

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