Multi-modulation-mode power converter and switch control circuit thereof

Abstract

The invention discloses a multi-modulation-mode power converter and a switching control circuit thereof. The switch control circuit comprises a reset circuit used for generating a reset signal according to a current detection signal representing an inductive current of the power converter and an error signal of a feedback loop of the power converter; the setting circuit is used for generating a setting signal according to the error signal; the RS trigger is used for generating a switch control signal of a switch tube in the power converter according to the reset signal and the set signal; the mode selection circuit is used for comparing the error signal with a switching reference voltage to generate a mode selection signal, and the reset circuit and the setting circuit respond to the mode selection signal to switch internal signal paths respectively, so that the power converter selectively works in one of a PFM mode and a COFT mode. The switch control circuit can adaptively work in one of a PFM mode and a COFT mode according to load conditions, and smooth mode switching can be realized when the COFT mode is switched to the PFM mode.

Description

Technical Field

[0001] The present invention relates to the technical field of power management, and in particular to a multi-modulation mode power converter and a switch control circuit thereof. Background Art

[0002] In power converters, PWM (pulse width modulation) and PFM (pulse frequency modulation) are two common modulation methods, and the choice usually depends on the load conditions. The PWM mode controls the power output by adjusting the pulse width, which is suitable for working under medium and high load conditions. Its advantages are small output ripple and fast dynamic response; however, under light load conditions, the efficiency of the PWM mode is low because frequent switching losses will lead to energy waste.

[0003] In contrast, PFM mode adjusts the power output by adjusting the pulse frequency and is usually used under light load conditions to improve efficiency. At light load, the power demand is low, and PFM mode can reduce energy loss by reducing the switching frequency, but this mode will bring larger output ripple, especially when the loop response is slow or the sampling circuit bandwidth is limited. In addition, in order to take into account different load conditions, modern power converters may also adopt multiple modulation modes to achieve a balance between efficiency and performance by automatically switching between PWM and PFM modes.

[0004] The power converter compares the error signal of the feedback loop with a preset threshold to determine whether to switch from one modulation mode to another. When the error signal is less than the preset threshold, the power converter switches from COFT (constant off time) mode to PFM mode. In COFT mode, a timer is used to set a roughly constant switching period, and the error signal is used to limit the peak value of the inductor current. In PFM mode, the switching period varies with the fluctuation of the error signal. When entering PFM mode, the output pulse signal is paused. After exiting this mode, the error signal returns to normal and the output pulse signal resumes. However, due to the slow loop response speed, precise control of a single pulse is usually not achieved in this mode, and multiple pulses are often output continuously, resulting in large output ripple. This disadvantage is more obvious in large loop systems, especially when the sampling circuit bandwidth is limited.

[0005] Therefore, it is expected to achieve smooth mode switching in a multi-modulation mode power converter to reduce output ripple and improve the overall system performance and stability. Summary of the invention

[0006] In view of the above problems, the object of the present invention is to provide a multi-modulation mode power converter and a switching control circuit thereof, wherein the switching control circuit can adaptively operate in one of the PFM mode and the COFT mode according to the load conditions, and can achieve smooth mode switching when switching from the COFT mode to the PFM mode.

[0007] According to one aspect of the present invention, there is provided a switch control circuit for a power converter, comprising: a reset circuit for generating a reset signal according to a current detection signal characterizing an inductor current of the power converter, wherein the reset signal is used to control a conduction time period of a switch tube in the power converter; a set circuit for generating a set signal according to an error signal of a feedback loop of the power converter, wherein the set signal is used to control a switching cycle of the switch tube in the power converter; an RS trigger for generating a switch control signal of the switch tube in the power converter according to the reset signal and the set signal; and a mode selection circuit for comparing the error signal with a switching reference voltage to generate a mode selection signal, wherein the reset circuit and the set circuit respectively switch internal signal paths in response to the mode selection signal so that the power converter selectively operates in one of a PFM mode and a COFT mode.

[0008] Optionally, in the PFM mode, the reset circuit compares the current detection signal with the inductor current reference voltage so that the on-time period corresponds to a fixed value of the inductor current peak value, and the switching period is dynamically adjusted according to the error signal. In the COFT mode, the switching period is fixed to a predetermined value, and the reset circuit compares the current detection signal with the error signal so that the on-time period corresponds to the inductor current peak value dynamically adjusted according to the error signal.

[0009] The above switch control circuit, wherein, in the PFM mode, the setting circuit adjusts the switching period according to the difference between the error signal and the spread spectrum reference voltage to achieve smooth mode switching.

[0010] Optionally, the set circuit includes: a first timer, used to generate a first timing signal; a transconductance amplifier, used to amplify the difference between the error signal and the spread spectrum reference voltage to generate a first adjustment signal; and a first switch, used to provide the first adjustment signal to the first timer in the PFM mode, and disconnect the first adjustment signal from the first timer in the COFT mode, wherein the first timer dynamically adjusts the time length of the first timing signal according to the first adjustment signal in the PFM mode, and sets the time length of the first timing signal to the predetermined value in the COFT mode.

[0011] Optionally, the reset circuit includes: a second switch for selecting one of the error signal and the inductor current reference voltage according to the selection signal; and a comparator for comparing one of the error signal and the inductor current reference voltage with the current detection signal to generate the set signal.

[0012] Optionally, it further includes: an error amplifier, used to generate the error signal according to a voltage feedback signal representing the DC output voltage of the power converter and / or a current feedback signal representing the DC output current of the power converter.

[0013] Optionally, the method further includes: a gate driver configured to convert the switch control signal into a first non-overlapping gate drive signal and a second non-overlapping gate drive signal.

[0014] According to another aspect of the present invention, a power converter is provided, comprising: a main circuit; and the above-mentioned switch control circuit, wherein the main circuit comprises at least one switch tube, and the switch control signal generated by the switch control signal is used to adjust the conduction state of the at least one switch tube, so that the power converter selectively operates in one of the PFM mode and the COFT mode to obtain a stable DC output voltage.

[0015] Optionally, the main circuit includes: a first switch tube and a second switch tube connected in series between an input end and ground; and an inductor connected between an intermediate node of the first switch tube and the second switch tube and an output end, wherein the switch control circuit is used to generate a first gate drive signal for the first switch tube and a second gate drive signal for the second switch tube.

[0016] According to the switch control circuit of the embodiment of the present invention, the reset signal generated by the reset circuit and the set signal generated by the set circuit are respectively used to adjust the conduction time period and the switching cycle of the switch control signal. The reset circuit and the set circuit respectively switch the internal signal path in response to the mode selection signal so that the power converter selectively operates in one of the PFM mode and the COFT mode. In the PFM mode and the COFT mode, the conduction time period corresponds to the fixed value of the inductor current peak value and the inductor current peak value dynamically adjusted according to the error signal, so as to limit the excessive fluctuation of the inductor current, thereby improving the circuit stability during the mode switching process. The switch control circuit shares at least a part of the modulator circuit in the PFM mode and the COFT mode, thereby reducing the number of electronic components, circuit cost and power consumption.

[0017] In a preferred embodiment, in the PFM mode, the switch control circuit adjusts the switching period of the switch control signal according to the difference between the error signal of the feedback loop and the spread spectrum reference voltage. When switching from one modulation mode to another, the jump amount of the switching period is related to the change amount of the error signal, so that adaptive spread spectrum corresponding to the degree of change of the load condition can be achieved. In the process of switching the modulation mode, the use of adaptive spread spectrum can maintain the output of a single pulse per switching period, avoid the ripple degradation of the DC output voltage, and thus improve the overall performance and stability of the system.

[0018] In a preferred embodiment, the switch control circuit generates a mode selection signal according to a comparison result between the error signal of the feedback loop and the switching reference voltage, and generates a switching cycle adjustment signal according to a difference between the error signal of the feedback loop and the spread spectrum reference voltage. Since the switching control and the spread spectrum control are based on the same error signal, the switch control circuit can simultaneously realize automatic mode switching and adaptive spread spectrum according to the error signal of the feedback loop, thereby realizing smooth mode switching.

[0019] In a preferred embodiment, the setting circuit in the switch control circuit includes a transconductance amplifier for amplifying the difference between the error signal of the feedback loop and the spread spectrum reference voltage to generate a regulation signal for the switching cycle. The adaptive spread spectrum of the setting circuit is equivalent to generating a regulation signal after integrating the error signal, and the requirement for the sampling loop bandwidth is greatly reduced. Therefore, the switch control circuit is not only applicable to a fast voltage feedback loop, but also to a slow current feedback loop. For example, in the voltage feedback loop, the error amplifier compares the voltage feedback signal representing the DC output voltage of the power converter with the reference voltage to generate the above-mentioned error signal, and in the current feedback loop, the error amplifier compares the current feedback signal representing the DC output current of the power converter with the reference current to generate the above-mentioned error signal. The switch control circuit can be applied to different types of feedback loops to achieve automatic mode switching and adaptive spread spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0021] Figure 1 A schematic circuit diagram of a multi-modulation mode power converter according to the prior art is shown;

[0022] Figure 2 A schematic circuit diagram of a multi-modulation mode power converter according to an embodiment of the present invention is shown;

[0023] Figure 3 Schematic waveform diagrams of two modulation modes of the power converter shown;

[0024] Figure 4 Show Figure 2 A schematic circuit diagram of a reset circuit in the power converter shown;

[0025] Figure 5 Show Figure 2 A schematic circuit diagram of a set circuit in the power converter shown;

[0026] Figure 6 Show Figure 2 A schematic circuit diagram of a mode switching circuit in a power converter is shown. DETAILED DESCRIPTION

[0027] The present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements are represented by similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale. In addition, some well-known parts may not be shown in the drawings.

[0028] Many specific details of the present invention are described below, such as component structures, materials, dimensions, processing techniques and technologies, in order to more clearly understand the present invention. However, as those skilled in the art will appreciate, the present invention may be implemented without following these specific details.

[0029] It should be understood that in the following description, a "circuit" may include a single or multiple combined hardware circuit, a programmable circuit, a state machine circuit and / or an element that can store instructions executed by a programmable circuit. When an element or circuit is said to be "connected to" another element or an element / circuit is said to be "connected between" two nodes, it can be directly coupled or connected to another element or there can be an intermediate element, 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 is no intermediate element between the two.

[0030] In the present application, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) includes a first terminal, a second terminal and a control terminal. When the MOSFET is in the on state, current flows from the first terminal to the second terminal. The first terminal, the second terminal and the control terminal of a P-type field effect transistor are the source, the drain and the gate, respectively, and the first terminal, the second terminal and the control terminal of an N-type field effect transistor are the drain, the source and the gate, respectively.

[0031] The present invention first provides a switch control circuit with an analog multiplier, which is used for PWM control and PFM control of a power converter. Various exemplary examples are illustrated and described below in conjunction with a buck converter type system, but the present invention is not limited thereto, and the various concepts disclosed in the present invention can be used in association with any type of power converter architecture, such as a buck converter, a boost converter, a flyback converter, and a buck-boost converter, etc., according to the topology classification of the power circuit.

[0032] Figure 1 A schematic circuit diagram of a multi-modulation mode power converter according to the prior art is shown.

[0033] In this example, the main circuit of the power converter 100 has a Buck type topology, including a high-side switch tube M1 and a low-side switch tube M2 located between the input terminal and the ground, and an inductor L connected between the intermediate node of the high-side switch tube M1 and the low-side switch tube M2 and the output terminal. The power converter 100 also includes an input capacitor Cin connected between the input terminal and the ground, and an output capacitor Co connected between the output terminal and the ground. However, as described above, the present invention is not limited to a specific type of topology.

[0034] The power converter 100 further includes resistors R11 and R12 connected in series between the output terminal and the ground. The resistors R11 and R12 form a resistor network for obtaining a proportional signal of the DC output voltage Vo as the voltage feedback signal Vfb. The power converter 100 may further include a detection element for obtaining a proportional signal of the inductor current IL as the current detection signal Isen.

[0035] Furthermore, the switch control circuit 110 of the power converter 100 generates gate drive signals Vg1 and Vg2 of the high-side switch tube M1 and the low-side switch tube M2 according to the voltage feedback signal Vfg and the current detection signal Isen.

[0036] In this example, the switch control circuit 110 includes an error amplifier 111 , a PFM modulator (ie, pulse frequency modulator) 112 , a PWM modulator (ie, pulse width frequency modulator) 113 , a multiplexer 114 , a driver 115 , and a mode switching circuit 101 .

[0037] The error amplifier 111 compares the voltage feedback signal Vfb with the reference voltage Vref to obtain the error signal EAO between the two. The PWM modulator 112 generates a switch control signal according to the clock signal CLK, so that the switch cycle of the switch control signal is the same as the clock cycle of the clock signal CLK. Further, the moment when the on state switches to the off state in the switch cycle is determined according to the comparison result of the error signal EAO and the current detection signal Isen, thereby adjusting the duty cycle of the gate drive signals Vg1 and Vg2. The PFM modulator 114 uses an internal timer to set a fixed on time for each switch cycle, and dynamically adjusts the length of each switch cycle according to the error signal EAO, thereby adjusting the duty cycle of the gate drive signals Vg1 and Vg2.

[0038] The mode switching circuit 101 generates a corresponding selection signal SEL according to the load condition, which is used to select the modulation mode of the switch control circuit 110. The multiplexer 114 selectively transmits the PFM signal generated by the PFM modulator 112 and the PWM signal generated by the PWM modulator 113 to the driver 115 according to the selection signal SEL. The driver 115 generates a gate drive signal Vg1 of the high-side switch tube M1 and a gate drive signal Vg2 of the low-side switch tube M2 according to the PFM signal or the PWM signal.

[0039] In each switching cycle, the high-side switch tube M1 and the low-side switch tube M2 are turned on alternately. During the conduction phase of the high-side switch tube M1, the low-side switch tube M2 is turned off. During the conduction phase of the low-side switch tube M2, the high-side switch tube M1 is turned off. The inductor L is charged during the conduction phase of the high-side switch tube M1 and discharged during the conduction phase of the low-side switch tube M2. By adjusting the duty cycle of the gate drive signals Vg1 and Vg2, the energy stored and released by the inductor L in each switching cycle can be changed, thereby adjusting the energy ratio transferred from the input end to the output end of the power converter 100, and finally achieving precise control of the DC output voltage Vo.

[0040] Furthermore, the switch control circuit 110 switches the modulation mode according to the load conditions, thereby operating in one of the PFM mode and the COFT mode. Under light load conditions, the switch control circuit 110 can switch to the PFM mode to reduce power loss by reducing the switching frequency, thereby improving the light load efficiency of the system. Under heavy load conditions, the switch control circuit 110 can switch to the COFT mode, in which the switching period remains constant and the output voltage is maintained stable by adjusting the duty cycle of the pulse. The COFT mode can provide lower output ripple and higher dynamic response performance under heavy load conditions, and is therefore suitable for scenarios with high power output or high voltage accuracy requirements. By dynamically switching the modulation mode, the switch control circuit 110 can take into account the energy efficiency and performance of the power converter, ensuring optimized circuit operation under different operating conditions.

[0041] Figure 2 A schematic circuit diagram of a multi-modulation mode power converter according to an embodiment of the present invention is shown.

[0042] The main circuit of the power converter 200 according to the embodiment of the present invention is Figure 1 The main circuit structure of the power converter 100 of the prior art shown is the same and will not be described in detail here.

[0043] Furthermore, the switch control circuit 210 of the power converter 200 generates gate drive signals Vg1 and Vg2 of the high-side switch tube M1 and the low-side switch tube M2 according to the voltage feedback signal Vfg and the current detection signal Isen.

[0044] In this example, the switch control circuit 210 includes the error amplifier 111 , a reset circuit 201 , a set circuit 202 , a mode switching circuit 203 , an RS flip-flop 205 , and a driver 115 .

[0045] The error amplifier 111 compares the voltage feedback signal Vfb with the reference voltage Vref to obtain the error signal EAO of the two. In the present embodiment, the error amplifier generates the error signal EAO according to the voltage feedback signal on the voltage feedback loop. However, the present invention is not limited thereto. Due to the characteristics of the setting circuit 202 in the switch control circuit 210, the error amplifier 111 is not only applicable to a fast voltage feedback loop, but also to a slow current feedback loop. In the case of being applied to the current feedback loop, the error amplifier 111 generates the error signal EAO, for example, according to the current feedback signal of the DC output current of the power converter 200.

[0046] The reset circuit 201 receives the error signal EAO and the current detection signal Isen for characterizing the inductor current IL of the power converter 200, and generates a reset signal Ton according to the current detection signal Isen and the error signal EAO. In the switching cycle, the reset signal Ton is used to control the turn-off moment of the high-side switch tube M1 of the power converter 200, thereby controlling the on-time period of the switching cycle. Therefore, the reset circuit 201 can also be called an on-time control circuit.

[0047] The setting circuit 202 receives the error signal EAO and generates a setting signal Tsw according to the error signal. In the switching cycle, the setting signal Tsw is used to control the turn-on time of the high-side switch tube M1 of the power converter 200. Since the time period between consecutive turn-on times is the switching cycle, the setting signal Tsw is used to control the length of the switching cycle. The setting circuit 201 can also be called a turn-off time control circuit.

[0048] The mode switching circuit 203 receives the error signal EAO, and compares the error signal EAO with the switching reference voltage Vref_pfm to generate a corresponding selection signal SEL for selecting the modulation mode of the switch control circuit 210 according to the load condition. The reset circuit 201 and the set circuit 202 respectively switch the internal signal path in response to the mode selection signal SEL, so that the power converter 200 selectively operates in one of the PFM mode and the COFT mode.

[0049] The reset terminal of the RS flip-flop 204 is connected to the reset circuit 201 to receive the reset signal Ton, and the set terminal is connected to the set circuit 202 to receive the set signal Tsw. The RS flip-flop 204 generates a switch control signal according to the reset signal Ton and the set signal Tsw.

[0050] The input end of the driver 115 is connected to the output end of the RS trigger 204 , and generates a gate driving signal Vg1 of the high-side switch tube M1 and a gate driving signal Vg2 of the low-side switch tube M2 according to the switch control signal.

[0051] In each switching cycle, the high-side switch tube M1 and the low-side switch tube M2 are turned on alternately. During the conduction phase of the high-side switch tube M1, the low-side switch tube M2 is turned off. During the conduction phase of the low-side switch tube M2, the high-side switch tube M1 is turned off. The inductor L is charged during the conduction phase of the high-side switch tube M1 and discharged during the conduction phase of the low-side switch tube M2. By adjusting the duty cycle of the gate drive signals Vg1 and Vg2, the energy stored and released by the inductor L in each switching cycle can be changed, thereby adjusting the energy ratio from the input end to the output end of the power converter 200, and ultimately achieving precise control of the DC output voltage Vo.

[0052] Further, the switch control circuit 210 switches the modulation mode according to the load condition, thereby operating in one of the PFM mode and the COFT mode. Under light load conditions, the switch control circuit 210 can switch to the PFM mode, wherein the switching cycle is dynamically adjusted according to the error signal EAO, and the on-time period in the switching cycle corresponds to the fixed inductor current peak value. Compared with the COFT mode, the PFM mode reduces power loss by reducing the switching frequency, thereby improving the light load efficiency of the system. Under heavy load conditions, the switch control circuit 210 can switch to the COFT mode, wherein the switching cycle is kept at a fixed value, and the on-time period in the switching cycle is dynamically adjusted according to the error signal EAO. Compared with the PFM mode, the COFT mode provides lower output ripple and higher dynamic response performance under heavy load conditions, and is therefore suitable for scenarios with high power output or high voltage accuracy requirements.

[0053] The switch control circuit 210 can take into account both the energy efficiency and performance of the power converter by dynamically switching the modulation mode, thereby ensuring optimized circuit operation under different working conditions.

[0054] According to the switch control circuit of the embodiment of the present invention, the reset signal generated by the reset circuit and the set signal generated by the set circuit are respectively used to adjust the conduction time period and the switching cycle of the switch control signal. The reset circuit and the set circuit respectively switch the internal signal path in response to the mode selection signal so that the power converter selectively operates in one of the PFM mode and the COFT mode. The switch control circuit shares at least a part of the modulator circuit in the PFM mode and the COFT mode, thereby reducing the number of electronic components, circuit cost and power consumption.

[0055] Furthermore, in the PFM mode, the switch control circuit adjusts the switching period of the switch control signal according to the difference between the error signal of the feedback loop and the spread spectrum reference voltage. When switching from one modulation mode to another, the jump amount of the switching period is related to the change amount of the error signal, so that adaptive spread spectrum corresponding to the degree of change of the load condition can be achieved. In the process of switching the modulation mode, the use of adaptive spread spectrum can maintain the output of a single pulse per switching cycle, avoid the ripple degradation of the DC output voltage, and thus improve the overall performance and stability of the system.

[0056] Figure 3 Schematic waveform diagram of two modulation modes of the power converter shown.

[0057] Before time t0, under heavy load conditions, the power converter operates in COFT mode, wherein the switch control circuit maintains a constant switching period T1, and adjusts the duty cycle of the switch control signal according to the error signal EAO to change the charging and discharging time of the inductor L, thereby adjusting the DC output voltage Vo. In this example, in COFT mode, the current is continuously conducted (i.e., continuous conduction mode, abbreviated as CCM) to provide high power output, reduce current ripple and improve power efficiency.

[0058] At time t0 , the load current Iload decreases from I1 to I2 , and the load condition of the power converter changes from heavy load to light load.

[0059] After time t1, under light load conditions, the power converter operates in PFM mode, wherein the switch control circuit maintains a constant on-time Ton and a dynamically adjusted off-time Toff, thereby adjusting the duty cycle of the switch control signal according to the error signal EAO to change the charging and discharging time of the inductor L, thereby adjusting the DC output voltage Vo. In this example, in the PFM mode, the current is intermittently conducted (i.e., discontinuous conduction mode, abbreviated as DCM) to reduce the switching frequency to reduce power loss, thereby improving the light load efficiency of the system.

[0060] When switching from the COFT mode to the PFM, the setting circuit 202 in the switch control circuit 200 dynamically adjusts the switching cycle jump amount T1-T2 according to the error signal EAO. That is, the switching cycle T1 of the COFT mode has a fixed value, and the switching cycle T2 of the PFM mode adopts the EAO control method. The greater the load fluctuation, the smaller the error signal EAO in the PFM mode after the mode switching, the longer the switching cycle T2 of the PFM mode, and the greater the value of the switching cycle jump amount T2-T1. The switching cycle jump amount T2-T1 is related to the change amount of the error signal EAO, so that an adaptive spread spectrum corresponding to the degree of change of the load condition can be achieved.

[0061] Figure 4 Show Figure 2 A schematic circuit diagram of a reset circuit in a power converter is shown.

[0062] The reset circuit 201 includes a comparator 1 and a switch S1 . The switch S1 is, for example, a single-pole double-throw switch, with two input terminals receiving the error signal EAO and the inductor current reference voltage Vref_sen respectively, and an output terminal connected to the inverting input terminal of the comparator 1 .

[0063] The non-inverting input terminal of the comparator 1 receives a current detection signal Isen representing the inductor current IL of the power converter 200. The comparator 1 compares the current detection signal Isen with one of the error signal EAO and the inductor current reference voltage Vref_sen to generate a reset signal.

[0064] In the working state of the switch control circuit 210, the switch S1 switches the switch state according to the mode selection signal SEL. In the COFT mode, the switch S1 provides the error signal EAO to the inverting input terminal of the comparator 1, so the switch control circuit 200 dynamically adjusts the on-time period in each switching cycle according to the error signal EAO. In the PFM mode, the switch S1 provides the inductor current reference voltage Vref_sen to the inverting input terminal of the comparator 1, so the switch control circuit 200 maintains the inductor current peak value in each switching cycle as a fixed value.

[0065] Figure 5 Show Figure 2 A schematic circuit diagram of a set circuit in a power converter is shown.

[0066] The setting circuit 202 includes a transconductance amplifier 3 , a timer 4 , and a switch S2 . The switch S2 is, for example, a single-pole single-throw switch, connected between the transconductance amplifier 3 and the timer 4 .

[0067] The inverting input terminal of the transconductance amplifier 3 receives the error signal EAO of the voltage feedback loop, and the non-inverting input terminal receives the spread spectrum reference voltage Vref_stretch. The transconductance amplifier 3 amplifies the difference between the error signal EAO and the spread spectrum reference voltage Vref_stretch to generate a regulation signal. The output signal of the transconductance amplifier 3 is a current signal. Although not shown in the figure, the current signal can be converted into a voltage signal and an integral characteristic can be achieved by using the capacitive load of the transconductance amplifier 3. Therefore, the regulation signal is not limited to the current signal.

[0068] Timer 3 generates a timing signal related to the regulation signal. The timing signal is used to set a fixed switching period in the COFT mode.

[0069] In the working state of the switch control circuit 210, the switch S2 switches the switch state according to the mode selection signal SEL. In the COFT mode, the switch S2 disconnects the output end of the transconductance amplifier 3 from the timer 3, so the set signal output by the set circuit 202 is a fixed-period timing signal that is independent of the adjustment signal. In the PFM mode, the switch S2 connects the output end of the transconductance amplifier 3 to the timer 3, so the set signal output by the set circuit 202 is a timing signal that dynamically adjusts the time length according to the adjustment signal.

[0070] Figure 6 Show Figure 2 A schematic circuit diagram of a mode switching circuit in a power converter is shown.

[0071] The mode switching circuit 203 includes a comparator 5 .

[0072] The comparator 5 has a non-inverting input terminal receiving a switching reference voltage Vref_pfm, and an inverting input terminal receiving an error signal EAO of a voltage feedback loop. The comparator 5 compares the error signal EAO with the switching reference voltage Vref_pfm to generate a switching selection signal SEL.

[0073] In this embodiment, the spread spectrum reference voltage Vref_stretch is greater than or equal to the switching reference voltage Vref_pfm. Therefore, when the switching selection signal SEL indicates switching from the COFT mode to the PFM mode according to the comparison result of the error signal EAO and the switching reference voltage Vref_pfm, the transconductance amplifier 202 in the setting circuit 202 outputs a positive current to generate an appropriate adjustment signal, thereby achieving adaptive spread spectrum corresponding to the degree of change of the load condition.

[0074] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0075] 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 the specific embodiments described. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A switch control circuit for a power converter, comprising: A reset circuit, used to generate a reset signal according to a current detection signal representing the inductor current of the power converter, wherein the reset signal is used to control the conduction time period of the switch tube in the power converter; A setting circuit, used for generating a setting signal according to an error signal of a feedback loop of the power converter, wherein the setting signal is used for controlling a switching cycle of a switch tube in the power converter; An RS trigger, used for generating a switch control signal of a switch tube in the power converter according to the reset signal and the set signal; as well as a mode selection circuit, configured to compare the error signal with a switching reference voltage to generate a mode selection signal, The reset circuit and the set circuit respectively switch internal signal paths in response to the mode selection signal, so that the power converter selectively operates in one of the PFM mode and the COFT mode.

2. The switch control circuit according to claim 1, wherein: In the PFM mode, the reset circuit compares the current detection signal with the inductor current reference voltage so that the on-time period corresponds to a fixed value of the inductor current peak value, and the switching period is dynamically adjusted according to the error signal. In the COFT mode, the switching period is fixed to a predetermined value, and the reset circuit compares the current detection signal with the error signal so that the on-time period corresponds to the inductor current peak value dynamically adjusted according to the error signal.

3. The switch control circuit according to claim 2, wherein: In the PFM mode, the setting circuit adjusts the switching period according to the difference between the error signal and the spread spectrum reference voltage to achieve smooth mode switching.

4. The switch control circuit according to claim 3, wherein: The setting circuit comprises: A first timer, used to generate a first timing signal; a transconductance amplifier, configured to amplify a difference between the error signal and the spread spectrum reference voltage to generate a first adjustment signal; and a first switch, configured to provide the first regulating signal to the first timer in the PFM mode, and disconnect the first regulating signal from the first timer in the COFT mode; The first timer dynamically adjusts the time length of the first timing signal according to the first adjustment signal in the PFM mode, and sets the time length of the first timing signal to the predetermined value in the COFT mode.

5. The switch control circuit according to claim 3, wherein: The reset circuit comprises: a second switch, configured to select one of the error signal and the inductor current reference voltage according to the selection signal; and A comparator is used for comparing one of the error signal and the inductor current reference voltage with the current detection signal to generate the set signal.

6. The switch control circuit according to claim 1, further comprising: The error amplifier is used to generate the error signal according to a voltage feedback signal representing the DC output voltage of the power converter and / or a current feedback signal representing the DC output current of the power converter.

7. The switch control circuit according to claim 1, further comprising: The gate driver is used to convert the switch control signal into a first gate drive signal and a second gate drive signal that are non-overlapping.

8. A power converter comprising: Main circuit; as well as The switch control circuit according to any one of claims 1 to 7, Wherein, the main circuit includes at least one switching tube, and the switching control signal generated by the switching control signal is used to adjust the conduction state of the at least one switching tube, so that the power converter selectively operates in one of the PFM mode and the COFT mode to obtain a stable DC output voltage.

9. The power converter according to claim 8, wherein: The main circuit comprises: a first switch tube and a second switch tube connected in series between the input terminal and the ground; and An inductor connected between the intermediate node of the first switch tube and the second switch tube and the output end The switch control circuit is used to generate a first gate drive signal for the first switch tube and a second gate drive signal for the second switch tube.

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