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 reference voltage calculation circuit used for calculating a switching reference voltage according to at least one of a signal parameter and a circuit parameter of the power converter; the mode switching circuit is used for generating a selection signal according to the error signal and a switching reference voltage, and the modulation circuit changes an internal modulation mode according to the selection signal, so that the power converter selectively works in one of a PFM mode and a COFT mode, and a current conduction mode is switched while the PFM mode and the COFT mode are switched. The switch control circuit can adaptively work in one of a PFM mode and a COFT mode according to a load condition, and the power converter can synchronously switch a modulation mode and a current conduction mode by accurately calculating a switching reference voltage related to a critical condition of a continuous conduction mode so as to optimize system efficiency.

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 in correlation with the fluctuation of the error signal.

[0005] However, due to the improper setting of the preset threshold, it is difficult for the existing power converter to switch the modulation mode and the current conduction mode synchronously. Before switching from the COFT mode to the PFM mode, the current conduction mode of the power converter has been switched from the continuous conduction mode (abbreviated as CCM) to the discontinuous conduction mode (abbreviated as DCM). Therefore, the power converter operates in the COFT+DCM mode. Compared with COFT+CCM, the system switching frequency is increased, which is not conducive to the improvement of EMI performance and system efficiency.

[0006] Therefore, it is expected to achieve synchronous switching of the modulation mode and the current conduction mode in a multi-modulation mode power converter to improve the overall performance and stability of the system. Summary of the invention

[0007] 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, by accurately calculating the switching reference voltage related to the critical conditions of the continuous conduction mode, the power converter can synchronously switch the modulation mode and the current conduction mode to optimize the system efficiency.

[0008] According to one aspect of the present invention, there is provided a switching control circuit for a power converter, comprising: an error amplifier for obtaining an error signal of a feedback loop of the power converter; a modulation circuit for generating a switching control signal of a switch tube in the power converter based on a current detection signal of an inductor current of the power converter and the error signal; a reference voltage calculation circuit for calculating a switching reference voltage based on at least one of a signal parameter and a circuit parameter of the power converter; and a mode switching circuit for generating a selection signal based on the error signal and the switching reference voltage, wherein the modulation circuit changes an internal modulation mode based on the selection signal so that the power converter selectively operates in one of a PFM mode and a COFT mode, and switches a current conduction mode while switching between the PFM mode and the COFT mode.

[0009] Optionally, the reference voltage calculation circuit includes a multiplier, and the multiplier performs multiplication calculation on a signal parameter and a circuit parameter to obtain the switching reference voltage.

[0010] Optionally, the multiplier performs the following calculation:

[0011] Vref_pfm=K*(Vin-Vo)*Vo*Tcoft

[0012] Wherein, Vin and Vo represent the DC input voltage and DC output voltage of the power converter respectively, K represents the circuit parameters of the power converter, and Tcoft represents the switching period of the COFT mode.

[0013] Optionally, the circuit parameter K of the power converter is:

[0014] K=R / (L*K1)

[0015] Wherein, L represents the inductance value of the power converter, K1 represents the current sampling ratio, and R represents the sampling output resistance.

[0016] Optionally, the reference voltage calculation circuit further includes an adder for performing a DC offset correction on the switching reference voltage.

[0017] Optionally, the modulation circuit includes: a PFM modulator, used to generate a PFM signal according to the error signal; a PWM modulator, used to generate a PWM signal according to the error signal and the current detection signal; and a multiplexer, which selects one of the PFM signal and the PWM signal as a switch control signal according to the selection signal.

[0018] Optionally, the modulation circuit includes: a reset circuit, used to generate a reset signal according to the current detection signal and the error signal, and the reset signal is used to control the conduction time period of the switch tube in the power converter; a set circuit, used to generate a set signal according to the error signal, and the set signal is used to control the switching cycle of the switch tube in the power converter; and an RS trigger, used to generate a switching control signal of the switch tube in the power converter according to the reset signal and the set signal, wherein the reset circuit and the set circuit respectively switch the internal signal path in response to the selection signal so that the power converter selectively operates in one of the PFM mode and the COFT mode.

[0019] Optionally, in the PFM mode, the on-time period is fixed to a first predetermined value, and the switching period is dynamically adjusted according to the error signal; in the COFT mode, the switching period is fixed to a second predetermined value, and the on-time period is dynamically adjusted according to the error signal and the current detection signal.

[0020] Optionally, 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] According to the switch control circuit of the embodiment of the present invention, the reference voltage calculation circuit calculates the switching reference voltage according to at least one of the signal parameters and circuit parameters of the power converter, and the mode switching circuit generates a selection signal according to the error signal of the feedback loop and the switching reference voltage. By accurately calculating the switching reference voltage related to the critical condition of the continuous conduction mode, the power converter can synchronously switch the modulation mode and the current conduction mode. When the load condition of the power converter changes from a heavy load state to a light load state, the power converter switches from the COFT+CCM mode to the PFM+DCM mode. Due to the synchronous switching of the modulation mode and the current conduction mode, the switching frequency can be timely reduced under light load conditions, which is conducive to improving EMI performance and system efficiency.

[0025] In a preferred embodiment, the reference voltage calculation circuit includes a multiplier for multiplying the signal parameters of the power converter. The signal parameters include the DC input voltage, the DC output voltage, and the switching period of the COFT mode of the power converter. The load condition of the power converter can be determined according to the signal parameters of the power converter, thereby achieving accurate mode switching control to eliminate the COFT+DCM working area.

[0026] In a preferred embodiment, the multiplier in the reference voltage calculation circuit also performs multiplication on the circuit parameters of the power converter. The circuit parameters include the inductance value, current sampling ratio and sampling output resistance of the power converter. Correcting the circuit parameters when calculating the switching reference voltage can further improve the accuracy of the mode switching control and further optimize the EMI performance and system efficiency.

[0027] In a preferred embodiment, the reference voltage calculation circuit further includes an adder for performing DC offset correction on the switching reference voltage to further improve the accuracy of the mode switching control and further optimize the EMI performance and system efficiency.

[0028] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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:

[0030] Figure 1 A schematic circuit diagram of a multi-modulation mode power converter according to a first embodiment of the present invention is shown;

[0031] Figure 2 A schematic circuit diagram of a multi-modulation mode power converter according to a second embodiment of the present invention is shown;

[0032] Figure 3 Show Figure 2 Schematic waveform diagrams of two modulation modes of the power converter shown;

[0033] Figure 4 Show Figure 2 A schematic circuit diagram of a reset circuit in the power converter shown;

[0034] Figure 5 Show Figure 2 A schematic circuit diagram of a set circuit in the power converter shown;

[0035] Figure 6 Show Figure 2 A schematic circuit diagram of a mode switching circuit in a power converter is shown.

[0036] Figure 7 Show Figure 2 A schematic circuit diagram of a reference voltage calculation circuit in a power converter shown in FIG. DETAILED DESCRIPTION

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Figure 1 A schematic circuit diagram of a multi-modulation mode power converter according to a first embodiment of the present invention is shown.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The switch control circuit 110 includes an error amplifier 101 , a modulation circuit 102 , a mode switching circuit 103 , and a reference voltage calculation circuit 104 .

[0047] The error amplifier 101 compares the voltage feedback signal Vfb with the reference voltage Vref to obtain an error signal EAO therebetween.

[0048] The modulation circuit 102 includes a PFM modulator (i.e., a pulse frequency modulator) 111, a PWM modulator (i.e., a pulse width frequency modulator) 112, a multiplexer 113, and a driver 114. The PWM modulator 112 generates a PWM signal according to the error signal EAO and the current detection signal Isen. The timer inside the PWM modulator 112 samples the DC input voltage Vin and the DC output voltage Vo to obtain a timing signal that is approximately constant at different DC input voltages Vin and DC output voltages Vo. Therefore, in the PWM modulator 112, a timer is used to set an approximately constant switching cycle, and the switching cycle of the switch control signal is the same as the time length of the timing signal. Further, the moment when the on state switches to the off state in the switching cycle is determined according to the comparison result of the error signal EAO and the current detection signal Isen. The PFM modulator 111 uses an internal timer to set a fixed on time for each switching cycle, and dynamically adjusts the length of each switching cycle according to the error signal EAO, thereby generating a PFM signal. The multiplexer 113 selectively transmits the PFM signal generated by the PFM modulator 111 and the PWM signal generated by the PWM modulator 112 to the driver 114 according to the selection signal SEL. The driver 114 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.

[0049] The mode switching circuit 103 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 reference voltage calculation circuit 104 calculates the switching reference voltage Vref_pfm according to at least one of the signal parameters and circuit parameters of the power converter 100. The mode switching circuit 103 compares the error signal EAO with the switching reference voltage Vref_pfm to generate the selection signal SEL.

[0050] 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.

[0051] 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.

[0052] Further, the mode switching circuit 103 in the switch control circuit 110 generates a selection signal according to the error signal of the feedback loop and the switching reference voltage. By accurately calculating the switching reference voltage related to the critical condition of the continuous conduction mode, the power converter can synchronously switch the modulation mode and the current conduction mode. When the load condition of the power converter changes from a heavy load state to a light load state, the power converter switches from the COFT+CCM mode to the PFM+DCM mode. Due to the synchronous switching of the modulation mode and the current conduction mode, the switching frequency can be reduced in time under light load conditions, which is conducive to improving EMI performance and system efficiency.

[0053] Figure 2 A schematic circuit diagram of a multi-modulation mode power converter according to a second embodiment of the present invention is shown.

[0054] The main circuit of the power converter 200 according to the second embodiment of the present invention is Figure 1 The main circuit structure of the power converter 100 of the first embodiment shown is the same and will not be described in detail here.

[0055] 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.

[0056] In this example, the switch control circuit 210 includes an error amplifier 101 , a modulation circuit 202 , a mode switching circuit 103 , and a reference voltage calculation circuit 104 .

[0057] The error amplifier 101 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 212 in the switch control circuit 210, the error amplifier 101 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 101 generates the error signal EAO, for example, according to the current feedback signal of the DC output current of the power converter 200.

[0058] The modulation circuit 202 includes a reset circuit 211 , a set circuit 212 , an RS flip-flop 213 , and a driver 114 .

[0059] The reset circuit 211 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 211 can also be called an on-time control circuit.

[0060] The setting circuit 212 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 conduction time of the high-side switch tube M1 of the power converter 200. Since the time period between consecutive conduction 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.

[0061] The reset terminal of the RS flip-flop 204 is connected to the reset circuit 211 to receive the reset signal Ton, and the set terminal is connected to the set circuit 212 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.

[0062] The input terminal of the driver 114 is connected to the output terminal 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.

[0063] The mode switching circuit 103 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 reference voltage calculation circuit 104 calculates the switching reference voltage Vref_pfm according to at least one of the signal parameters and circuit parameters of the power converter 100. The mode switching circuit 103 compares the error signal EAO with the switching reference voltage Vref_pfm to generate the selection signal SEL.

[0064] The reset circuit 211 and the set circuit 212 respectively switch internal signal paths in response to the selection signal SEL, so that the power converter 200 selectively operates in one of the PFM mode and the COFT mode.

[0065] 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.

[0066] 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 is kept fixed. 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 fixed, 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.

[0067] Further, the mode switching circuit 103 in the switch control circuit 110 generates a selection signal according to the error signal of the feedback loop and the switching reference voltage. By accurately calculating the switching reference voltage related to the critical condition of the continuous conduction mode, the power converter can synchronously switch the modulation mode and the current conduction mode. When the load condition of the power converter changes from a heavy load state to a light load state, the power converter switches from the COFT+CCM mode to the PFM+DCM mode. Due to the synchronous switching of the modulation mode and the current conduction mode, the switching frequency can be reduced in time under light load conditions, which is conducive to improving EMI performance and system efficiency.

[0068] 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.

[0069] 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 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.

[0070] 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.

[0071] Figure 3 Show Figure 2 Schematic waveform diagram of two modulation modes of the power converter shown.

[0072] 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 determines the moment of switching from the on state to the off state in the switching period according to the comparison result of the error signal EAO and the current detection signal Isen, so as 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.

[0073] 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.

[0074] 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.

[0075] When switching from the COFT mode to the PFM, the setting circuit 212 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 in the error signal EAO, so that an adaptive spread spectrum corresponding to the degree of change in the load conditions can be achieved.

[0076] Figure 4 Show Figure 2 A schematic circuit diagram of a reset circuit in a power converter is shown.

[0077] The reset circuit 211 includes a comparator 1, a timer 2, and a switch S1. The switch S1 is, for example, a single-pole double-throw switch, with two input terminals connected to the comparator 1 and the timer 2 respectively, and one output terminal for providing a reset signal Ton.

[0078] The comparator 1 has a non-inverting input terminal receiving a current detection signal Isen representing the inductor current IL of the power converter 200, and an inverting input terminal receiving an error signal EAO of a voltage feedback loop. The comparator 1 compares the current detection signal Isen with the error signal EAO to generate a comparison signal.

[0079] Timer 2 generates a timing signal of a fixed value. The timing signal is used to set a fixed on-time period in the PFM mode, and thus corresponds to the peak value of the inductor current IL in the PFM mode.

[0080] In the working state of the switch control circuit 210, the switch S1 switches the switch state according to the selection signal SEL. In the COFT mode, the switch S1 connects the output end of the comparator 1 with the output end of the reset circuit 211, so the reset signal output by the reset circuit 211 is the comparison signal generated by the comparator 1, and the conduction time period in each switching cycle is dynamically adjusted according to the error signal EAO. In the PFM mode, the switch S1 connects the output end of the timer 2 with the output end of the reset circuit 211, so the reset signal output by the reset circuit 211 is the timing signal generated by the timer 2, and the conduction time period in the switching cycle is maintained as a fixed value in each switching cycle.

[0081] Figure 5 Show Figure 2 A schematic circuit diagram of a set circuit in a power converter is shown.

[0082] The setting circuit 212 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 .

[0083] 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.

[0084] The timer 3 samples the DC input voltage Vin and the DC output voltage Vo to obtain a timing signal that is substantially constant at different DC input voltages Vin and DC output voltages Vo. The timer sets a substantially constant switching cycle.

[0085] In the working state of the switch control circuit 210, the switch S2 switches the switch state according to the 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 212 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 212 is a timing signal that dynamically adjusts the time length according to the adjustment signal.

[0086] Figure 6 Show Figure 2 A schematic circuit diagram of a mode switching circuit in a power converter is shown.

[0087] The mode switching circuit 103 includes a comparator 5 .

[0088] 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.

[0089] Figure 7 Show Figure 2 A schematic circuit diagram of a reference voltage calculation circuit in a power converter shown in FIG.

[0090] The reference voltage calculation circuit 104 includes at least a multiplier 6 .

[0091] The multiplier 6 performs multiplication calculation on the signal parameters and circuit parameters of the power converter 200 to obtain a switching reference voltage Vref_pfm related to the critical condition of the continuous conduction mode, as shown in the following formula:

[0092] Vref_pfm=K*(Vin-Vo)*Vo*Tcoft (1)

[0093] Wherein, Vin and Vo represent the DC input voltage and DC output voltage of the power converter respectively, K represents the circuit parameters of the power converter, and Tcoft represents the switching period of the COFT mode.

[0094] Furthermore, the circuit parameter K of the above-mentioned power converter is a parameter related to the inductance of the main circuit, as shown in the following formula:

[0095] K=R / (L*K1)(2)

[0096] Wherein, L represents the inductance value of the main circuit inductor of the power converter, K1 represents the current sampling ratio, and R represents the sampling output resistance.

[0097] Preferably, the reference voltage calculation circuit 104 further includes an adder 7 for performing a DC offset correction on the switching reference voltage Vref_pfm, as shown in the following formula:

[0098] Vref_pfm' = Vref_pfm + Vdc (3)

[0099] Wherein, Vdc represents the correction amount of DC offset.

[0100] The reference voltage calculation circuit 104 uses formulas (1)-(3) to accurately calculate the switching reference voltage related to the critical condition of the continuous conduction mode. The power converter can synchronously switch the modulation mode and the current conduction mode to optimize the system efficiency.

[0101] 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.

[0102] 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: an error amplifier, used to obtain an error signal of a feedback loop of the power converter; A modulation circuit, used for generating a switch control signal of a switch tube in the power converter according to a current detection signal of the inductor current of the power converter and the error signal; A reference voltage calculation circuit, used for calculating a switching reference voltage according to at least one of a signal parameter and a circuit parameter of the power converter; as well as a mode switching circuit, configured to generate a selection signal according to the error signal and the switching reference voltage, The modulation circuit changes the internal modulation mode according to the selection signal, so that the power converter selectively operates in one of the PFM mode and the COFT mode, and switches the current conduction mode while switching between the PFM mode and the COFT mode.

2. The switch control circuit according to claim 1, wherein: The reference voltage calculation circuit includes a multiplier, which performs multiplication calculation on a signal parameter and a circuit parameter to obtain the switching reference voltage.

3. The switch control circuit according to claim 2, wherein: The multiplier performs the following calculation: Vref_pfm=K*(Vin-Vo)*Vo*Tcoft Wherein, Vin and Vo represent the DC input voltage and DC output voltage of the power converter respectively, K represents the circuit parameters of the power converter, and Tcoft represents the switching period of the COFT mode.

4. The switch control circuit according to claim 3, wherein: The circuit parameter K of the power converter is: K=R / (L*K1) Wherein, L represents the inductance value of the main circuit inductor of the power converter, K1 represents the current sampling ratio, and R represents the sampling output resistance.

5. The switch control circuit according to claim 2, wherein: The reference voltage calculation circuit also includes an adder for performing a DC offset correction on the switching reference voltage.

6. The switch control circuit according to claim 1, wherein: The modulation circuit comprises: A PFM modulator, used for generating a PFM signal according to the error signal; A PWM modulator, used for generating a PWM signal according to the error signal and the current detection signal; The multiplexer selects one of the PFM signal and the PWM signal as a switch control signal according to the selection signal.

7. The switch control circuit according to claim 1, wherein: The modulation circuit comprises: A reset circuit, used for generating a reset signal according to the current detection signal and the error signal, wherein the reset signal is used for controlling the conduction time period of the switch tube in the power converter; a setting circuit, used for generating a setting signal according to the error signal, wherein the setting signal is used for controlling a switching cycle of a switch tube in the power converter; and 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, The reset circuit and the set circuit respectively switch internal signal paths in response to the selection signal, so that the power converter selectively operates in one of the PFM mode and the COFT mode.

8. The switch control circuit according to claim 7, wherein: In the PFM mode, the on-time period is fixed to a first predetermined value, and the switching period is dynamically adjusted according to the error signal. In the COFT mode, the switching period is fixed to a second predetermined value, and the on-time period is dynamically adjusted according to the error signal and the current detection signal.

9. The switch control circuit according to claim 8, 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.

10. The switch control circuit according to claim 6 or 7, 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.

11. A power converter comprising: Main circuit; as well as The switch control circuit according to any one of claims 1 to 10, 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.

12. The power converter according to claim 11, 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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