Switching power supply and control method thereof

Abstract

The invention discloses a switching type power supply and a control method thereof. The switching type power supply comprises a power level circuit which is used for controlling a power switch according to a pulse width modulation signal and switching an inductor coupled to a phase node so as to convert an input voltage into an output voltage; and a control circuit for, in a discontinuous conduction mode, determining an equivalent capacitance adjustment program in an enabled state according to a phase node voltage on the phase node at the starting point of an inductance excitation, and further adjusting an equivalent capacitance on the phase node, and reducing a cross voltage of the power switch at another inductance excitation starting time point after the equivalent capacitance adjustment program.

Description

Technical Field

[0001] The present invention relates to a switching power supply and a control method thereof, and particularly to a switching power supply and a control method thereof that can have a fixed frequency and better light load efficiency. Background Art

[0002] Figure 1 FIG. is a schematic diagram showing the light load efficiency of a known switching power supply with respect to the phase node voltage when the lower bridge switch is turned on. As Figure 1 shown, since this known switching power supply uses a single fixed switching frequency and does not have a zero voltage switching (ZVS) function, the switching loss is lower when the phase node voltage when the lower bridge switch is turned on is lower (i.e., when the lower bridge switch is turned on, it is close to the trough of the resonant signal), and the light load efficiency is relatively high; when the phase node voltage when the lower bridge switch is turned on is higher (i.e., when the lower bridge switch is turned on, it is close to the peak of the resonant signal), the switching loss is higher, and the light load efficiency is relatively low, resulting in unstable light load efficiency. Only when it is close to the trough of the phase node voltage, the light load efficiency is high.

[0003] Another known technique is to use the switching function of zero voltage switching to adjust the turn-on time point of the lower bridge switch so that the turn-on time point of the lower bridge switch is at the time point when the phase node voltage is zero voltage, so as to achieve zero voltage switching and make the power conversion efficiency better. However, this will exceed the allowable operating frequency range of the circuit of the load device that requires a fixed frequency for the switching frequency (operating frequency). That is to say, when the circuit of the load device, such as a light-emitting diode driver, is applied to a stylus touch screen and requires the operating frequency to be limited to a specific frequency range, the zero voltage switching method is not applicable. Related prior art is shown in US Patent No. US8629660B2.

[0004] In view of this, the present invention aims at the deficiencies of the above-mentioned prior art and provides a switching power supply and a control method thereof that can have a certain fixed frequency and better light load efficiency. Summary of the Invention

[0005] In one aspect, the present invention provides a switching power supply, comprising: a power stage circuit for controlling one of the power switches according to a pulse width modulation signal, and switching and coupling an inductor coupled to a phase node to convert an input voltage into an output voltage; and a control circuit for determining an equivalent capacitance adjustment procedure in an enabled state according to a phase node voltage on the phase node at a start point of inductor magnetization in a discontinuous conduction mode (DCM), and then adjusting an equivalent capacitance on the phase node to reduce a voltage across the power switch at another start point of inductor magnetization after the equivalent capacitance adjustment procedure.

[0006] In one embodiment, when the phase node voltage exceeds a preset threshold voltage at the start point of inductor magnetization, the control circuit determines the equivalent capacitance adjustment procedure in the enabled state and adjusts the equivalent capacitance on the phase node.

[0007] In one embodiment, after the equivalent capacitance adjustment procedure is turned to the enabled state and maintained for a duration, the control circuit adjusts the equivalent capacitance.

[0008] In one embodiment, when the equivalent capacitance adjustment procedure is in the enabled state, the control circuit counts the pulses of the pulse width modulation signal, and when the pulse count of the pulse width modulation signal exceeds a preset number of pulses, it indicates that the equivalent capacitance adjustment procedure has maintained the duration.

[0009] In one embodiment, the control circuit includes: a comparison circuit for comparing the phase node voltage with the preset threshold voltage to generate a comparison signal; a judgment circuit for judging, according to the comparison signal and the pulse width modulation signal, that when the phase node voltage on the phase node exceeds the preset threshold voltage at the start point of inductor magnetization, to generate an enable and hold signal; a capacitance adjustment procedure circuit for performing the equivalent capacitance adjustment procedure according to the enable and hold signal and the pulse width modulation signal to generate a procedure signal; and an equivalent capacitance adjustment circuit for generating an equivalent capacitance adjustment signal according to the procedure signal.

[0010] In one embodiment, the switching power supply further includes a resonant regulator, wherein the resonant regulator is coupled to the phase node and includes a capacitor array having a plurality of capacitors. During the equivalent capacitance adjustment procedure, the resonant regulator determines the number of capacitors coupled to the phase node according to the equivalent capacitance adjustment signal to adjust the equivalent capacitance on the phase node.

[0011] In one embodiment, a maximum total capacitance value and / or a capacitance resolution of the plurality of capacitors in the capacitor array are related to the preset threshold voltage.

[0012] In one embodiment, the capacitance adjustment program circuit includes a first counting circuit for counting the pulses of the pulse width modulation signal according to the enable and hold signals to generate the program signal.

[0013] In one embodiment, the capacitance adjustment program circuit further includes a logic circuit for generating an adjustment enable signal to enable the equivalent capacitance adjustment circuit to generate the equivalent capacitance adjustment signal when the program signal indicates that the pulse count of the pulse width modulation signal exceeds the preset pulse count.

[0014] In one embodiment, the equivalent capacitance adjustment circuit includes a second counter for cumulatively counting and adjusting the equivalent capacitance adjustment signal by a preset unit when the adjustment enable signal switches to an enable bit time to adjust the number of the plurality of capacitors coupled to the phase node.

[0015] In one embodiment, the first counting circuit includes a first unidirectional counter for unidirectionally counting the pulses of the pulse width modulation signal according to the enable and hold signals, and when the program signal indicates that the pulse count of the pulse width modulation signal exceeds the preset pulse count, the logic circuit generates the adjustment enable signal.

[0016] In one embodiment, when the first unidirectional counter counts to the point where the program signal indicates that the pulse count of the pulse width modulation signal exceeds the preset pulse count, the first unidirectional counter overflows and cycles the count.

[0017] In one embodiment, the second counter includes a second unidirectional counter for unidirectionally cumulatively counting the equivalent capacitance adjustment signal when the adjustment enable signal switches to the enable bit time to correspondingly adjust the number of the plurality of capacitors coupled to the phase node.

[0018] In one embodiment, when the second unidirectional counter unidirectionally cumulatively counts to a preset count limit, the second unidirectional counter overflows and cycles the count.

[0019] In one embodiment, the duration is related to a control loop bandwidth of the switching power supply and / or a stability of the equivalent capacitance adjustment program.

[0020] In one embodiment, the control circuit adjusts the equivalent capacitance on the phase node to adjust the phase node voltage to not exceed the preset threshold voltage at the starting point of the inductor magnetization in a stable state.

[0021] In another aspect, the present invention provides a control method for controlling a switching power supply. The switching power supply includes a power stage circuit for controlling a power switch according to a pulse width modulation signal, and switching an inductor coupled to a phase node to convert an input voltage into an output voltage. The control method includes: in a discontinuous conduction mode (DCM), determining an equivalent capacitance adjustment procedure in an enabled state according to a phase node voltage at a magnetic excitation start point of the inductor; and adjusting an equivalent capacitance at the phase node according to the equivalent capacitance adjustment procedure to reduce a voltage across the power switch at another magnetic excitation start point after the equivalent capacitance adjustment procedure.

[0022] In an embodiment, the step of determining an equivalent capacitance adjustment procedure in an enabled state according to a phase node voltage at a magnetic excitation start point of the inductor in a discontinuous conduction mode (DCM) includes: at the magnetic excitation start point, when the phase node voltage exceeds a preset threshold voltage, determining the equivalent capacitance adjustment procedure in the enabled state.

[0023] In an embodiment, the step of adjusting an equivalent capacitance at the phase node according to the equivalent capacitance adjustment procedure to reduce a voltage across the power switch at another magnetic excitation start point after the equivalent capacitance adjustment procedure further includes: after the equivalent capacitance adjustment procedure is turned to the enabled state and maintained for a duration, adjusting the equivalent capacitance.

[0024] In an embodiment, when the equivalent capacitance adjustment procedure is in the enabled state, counting pulses of the pulse width modulation signal, and when the pulse count of the pulse width modulation signal exceeds a preset pulse number, indicating that the equivalent capacitance adjustment procedure has been maintained for the duration.

[0025] In an embodiment, the step of counting pulses of the pulse width modulation signal and when the pulse count of the pulse width modulation signal exceeds a preset pulse number, indicating that the equivalent capacitance adjustment procedure has been maintained for the duration includes: unidirectionally counting pulses of the pulse width modulation signal, and when the count reaches that the pulse count of the pulse width modulation signal exceeds the preset pulse number, overflowing and cycling the count.

[0026] In one embodiment, in a discontinuous conduction mode (DCM), the steps of determining an equivalent capacitance adjustment procedure in an enabled state according to a phase node voltage at a phase node at an initial point of inductor magnetization include: comparing the phase node voltage with a preset threshold voltage to generate a comparison signal; according to the comparison signal and the pulse width modulation signal, at the initial point of inductor magnetization, determining that when the phase node voltage at the phase node exceeds the preset threshold voltage, generating an enable and hold signal; according to the enable and hold signal and the pulse width modulation signal, performing the equivalent capacitance adjustment procedure to generate a procedure signal; and generating an equivalent capacitance adjustment signal according to the procedure signal.

[0027] In one embodiment, the control method further includes: in the equivalent capacitance adjustment procedure, determining the number of capacitors coupled to the phase node according to the equivalent capacitance adjustment signal to adjust the equivalent capacitance at the phase node.

[0028] In one embodiment, a maximum total capacitance value and / or a capacitance resolution of the capacitor are related to the preset threshold voltage.

[0029] In one embodiment, the duration is related to a control loop bandwidth of the switching power supply and / or a stability of the equivalent capacitance adjustment procedure.

[0030] In one embodiment, the step of adjusting an equivalent capacitance at the phase node according to the equivalent capacitance adjustment procedure to reduce a breakdown voltage of a power switch at another initial point of inductor magnetization after the equivalent capacitance adjustment procedure further includes: adjusting the equivalent capacitance at the phase node to adjust the phase node voltage to not exceed the preset threshold voltage at the initial point of inductor magnetization in a stable state.

[0031] In one embodiment, the step of generating an equivalent capacitance adjustment signal according to the procedure signal includes: unidirectionally accumulating and counting the equivalent capacitance adjustment signal to correspondingly adjust the number of capacitors coupled to the phase node, and overflowing and cycling counting when unidirectionally accumulating and counting reaches a preset counting limit.

[0032] The advantages of the present invention are that the present invention can achieve fixed frequency and at the same time have better light load efficiency.

[0033] The following will be described in detail through specific embodiments to more easily understand the purpose, technical content, features and achieved effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1It is a schematic diagram showing the light load efficiency of a known switched-mode power supply with respect to the phase node voltage when the lower bridge switch conducts.

[0035] Figure 2A It is a circuit block diagram showing a switched-mode power supply according to an embodiment of the present invention.

[0036] Figure 2B It is a circuit block diagram showing a switched-mode power supply according to an embodiment of the present invention.

[0037] Figure 2C It is a circuit schematic diagram showing a resonant regulator of a switched-mode power supply according to an embodiment of the present invention.

[0038] Figure 2D It is a circuit schematic diagram showing a comparison circuit and a judgment circuit in a control circuit of a switched-mode power supply according to an embodiment of the present invention.

[0039] Figure 2E It is a circuit schematic diagram showing a capacitor adjustment program circuit in a control circuit of a switched-mode power supply according to an embodiment of the present invention.

[0040] Figure 2F It is a circuit schematic diagram showing an equivalent capacitor adjustment circuit in a control circuit of a switched-mode power supply according to an embodiment of the present invention.

[0041] Figure 2G It is a circuit block diagram showing a counting circuit of a capacitor adjustment program circuit in a control circuit of a switched-mode power supply according to an embodiment of the present invention.

[0042] Figure 2H It is a circuit block diagram showing a counter of an equivalent capacitor adjustment circuit in a control circuit of a switched-mode power supply according to an embodiment of the present invention.

[0043] Figures 3A to 3K It shows various embodiments of the present invention applicable to a switched-mode power supply.

[0044] Figure 4 And Figure 5 It is shown according to an embodiment of the present invention Figure 2A A signal waveform schematic diagram of relevant signals of a switched-mode power supply.

[0045] Figure 6 It is a relationship diagram showing the light load efficiency of the switched-mode power supply of the present invention with respect to the phase node voltage when the lower bridge switch conducts and the light load efficiency of a known switched-mode power supply with respect to the phase node voltage when the lower bridge switch conducts.

[0046] Figure 7It is a list showing the light load efficiency of the switching power supply of the present invention and the phase node voltage when the lower bridge switch is turned on, and the light load efficiency of a known switching power supply and the phase node voltage when the lower bridge switch is turned on, according to an embodiment of the present invention.

[0047] Symbol Explanation in the Figure

[0048] 20: Switching power supply

[0049] 201: Power stage circuit

[0050] 202: Control circuit

[0051] 2021: Comparison circuit

[0052] 2022: Judgment circuit

[0053] 2023: Capacitance adjustment program circuit

[0054] 20231: Counting circuit

[0055] 202311, 202411: Unidirectional counter

[0056] 20232: Logic circuit

[0057] 2024: Equivalent capacitance adjustment circuit

[0058] 20241: Counter

[0059] 203: Resonant regulator

[0060] C1, C2, C3, C4: Capacitor

[0061] Ceq: Equivalent capacitance

[0062] FF: Flip-flop

[0063] fsw: Frequency

[0064] INV: Inverter

[0065] L: Inductor

[0066] LX: Phase node

[0067] Lx_lo: Comparison signal

[0068] Lx_lolb: Enable and hold signal

[0069] NGATE, NGATEi: Pulse width modulation signal

[0070] PG: Pulse generator

[0071] Ploss: Switching loss

[0072] POR: Power-On Reset

[0073] QCOUNT<3:0>, QCOUNT<0>, QCOUNT<1>, QCOUNT<2>, QCOUNT<3>: Program signals

[0074] QGATE<3:0>, QGATE<0>, QGATE<1>, QGATE<2>, QGATE<3>: Equivalent capacitance adjustment signals

[0075] QH, QL: Power switches

[0076] Sen: Adjust enable signal

[0077] t1, t2: Time points

[0078] Tc: Duration

[0079] VCC: Power supply

[0080] Vin: Input voltage

[0081] Vlx: Phase node voltage

[0082] Vlx_ref: Preset threshold voltage

[0083] Vout, Vout(-), Vout1, Vout2: Output voltages Detailed implementation manners

[0084] The attached drawings in the present invention are all schematic, mainly intended to show the coupling relationships between circuits and the relationships between signal waveforms. As for circuits, signal waveforms and frequencies, they are not drawn according to scale. For the sake of clear explanation, many practical details will be described together in the following description, but this is not intended to limit the scope of the patent application of the present invention.

[0085] Figure 2A is a circuit block diagram showing a switching power supply according to an embodiment of the present invention. Figure 2B is a circuit block diagram showing a switching power supply according to an embodiment of the present invention. As Figure 2A shown, the switching power supply 20 of the present invention includes a power stage circuit 201 and a control circuit 202. Please refer to Figure 2A and Figure 2B, the power stage circuit 201 is used to control the power switches QL and QH therein according to the pulse width modulation signal NGATE, and switch the inductor L coupled to the phase node LX to convert the input voltage Vin into the output voltage Vout. The control circuit 202 is used to determine the equivalent capacitance adjustment procedure in the enabled state according to the phase node voltage Vlx on the phase node LX at the start point of inductor magnetization in the discontinuous conduction mode (DCM), and then adjust the equivalent capacitance Ceq on the phase node LX to reduce the voltage across the power switch QL at another inductor magnetization start point after the equivalent capacitance adjustment procedure. The power stage circuit 201 is, for example but not limited to, Figure 2B the boost power stage circuit shown.

[0086] Please refer to Figure 2A and Figure 5 simultaneously. In this embodiment, for example, after the equivalent capacitance adjustment procedure is turned on and maintained for a duration Tc, the control circuit 202 adjusts the equivalent capacitance Ceq. When the equivalent capacitance adjustment procedure is in the enabled state, the control circuit 202 counts the pulses of the pulse width modulation signal NGATE. When the pulse count of the pulse width modulation signal NGATE exceeds the preset number of pulses and during the counting period, the equivalent capacitance adjustment procedure remains in the enabled state, indicating that the equivalent capacitance adjustment procedure has been maintained for the duration Tc in the enabled state. As Figure 2A shown, the switching power supply 20 further includes a resonant regulator 203, where the resonant regulator 203 is coupled to the phase node LX. In one embodiment, the control circuit 202 can also adjust the equivalent capacitance Ceq immediately after the equivalent capacitance adjustment procedure is turned on, as long as the control circuit 202 adjusts the equivalent capacitance Ceq according to the enabled state of the equivalent capacitance adjustment procedure to achieve, after the equivalent capacitance adjustment procedure, and at another inductor magnetization start point in the DCM when the power switches QL and QH are in the off state, reducing the phase node voltage Vlx. The control circuit 202 can also time the time that the equivalent capacitance adjustment procedure remains in the enabled state in other ways to determine to adjust the equivalent capacitance Ceq. In a preferred embodiment, the control circuit 202 continuously adjusts the equivalent capacitance Ceq according to the time that the equivalent capacitance adjustment procedure remains in the enabled state, so that the phase node voltage Vlx reaches zero potential at another inductor magnetization start point after the equivalent capacitance adjustment procedure, enabling zero voltage switching of the power switches QL and / or QH in the power stage circuit 201 to reduce the switching loss.

[0087] It should be noted that when the pulse width modulation signal NGATE of the switching power supply 20 has a single fixed frequency, and when the switching power supply 20 operates in DCM and the power switches QL and QH are in the off state, the phase node voltage Vlx on the phase node LX is a quasi-resonance signal. Taking the power stage circuit 201 as a boost power stage circuit as an example, in DCM, at the start point of another inductor excitation after the off state of the power switches QL and QH ends, the power switch QL switches to the on state, and the switching loss Ploss formula of the power switch QL is as follows:

[0088]

[0089] Among them, fsw is the single fixed frequency of the pulse width modulation signal NGATE. It can be seen from the above formula that the switching loss Ploss of the power switch QL is proportional to the square of the phase node voltage Vlx on the phase node LX. If the phase node voltage Vlx can be reduced at the start point of another inductor excitation after the off state of the power switches QL and QH ends (that is, the on point of the power switch QL), the switching loss Ploss can be reduced, and the conversion efficiency of the switching power supply 20 under light load and operating in DCM (that is, the aforementioned light load efficiency) can be improved. As mentioned above, when the power switches QL and QH are in the off state, the equivalent capacitor Ceq and the inductor L form a resonant circuit and resonate, so that the phase node voltage Vlx on the phase node LX is a quasi-resonant signal, and the frequency of this quasi-resonant signal is related to the equivalent capacitor Ceq and the inductor L. Therefore, according to the present invention, the purpose of adjusting the equivalent capacitor Ceq is to adjust the frequency of this resonant signal, so that after the equivalent capacitor adjustment process, at the start point of another inductor excitation (that is, the on point of the power switch QL), it is as close as possible to the trough of this quasi-resonant signal, thereby reducing the switching loss Ploss of the power switch QL.

[0090] In one embodiment, the duration Tc is related to the control loop bandwidth of the switching power supply 20 and / or the stability of the equivalent capacitor adjustment process. As Figure 2B shown, the control circuit 202 adjusts the equivalent capacitor Ceq on the phase node LX to adjust the phase node voltage Vlx not to exceed the preset threshold voltage Vlx_ref at the start point of inductor excitation in the steady state.

[0091] Please refer to Figure 2B, at the starting point of the inductor excitation, when the phase node voltage Vlx exceeds the preset threshold voltage Vlx_ref, the control circuit 202 determines that the equivalent capacitance adjustment program is in the enabled state, and then adjusts the equivalent capacitance Ceq on the phase node LX according to the enabled state of the equivalent capacitance adjustment program. The control circuit 202 includes a comparison circuit 2021, a judgment circuit 2022, a capacitance adjustment program circuit 2023, and an equivalent capacitance adjustment circuit 2024. The comparison circuit 2021 is used to compare the phase node voltage Vlx with the preset threshold voltage Vlx_ref to generate a comparison signal Lx_lo. The judgment circuit 2022 is used to judge, according to the pulse width modulation signal NGATE, whether the phase node voltage Vlx on the phase node LX exceeds the preset threshold voltage Vlx_ref at each starting point of the inductor excitation based on the comparison signal Lx_lo, and generates an enable and hold signal Lx_lolb when the phase node voltage Vlx exceeds the preset threshold voltage Vlx_ref.

[0092] The capacitance adjustment program circuit 2023 is used to perform the equivalent capacitance adjustment program according to the enable and hold signal Lx_lolb and the pulse width modulation signal NGATEi to generate a program signal QCOUNT<3:0>. The equivalent capacitance adjustment circuit 2024 is used to generate an equivalent capacitance adjustment signal QGATE<3:0> according to the program signal QCOUNT<3:0>.

[0093] Figure 2C is a circuit schematic diagram showing the resonant regulator of a switching power supply according to an embodiment of the present invention. As Figure 2C shown, the resonant regulator 203 includes a capacitor array, and the capacitor array has a plurality of capacitors C1, C2, C3, C4, corresponding to capacitance values of 1C, 2C, 4C, and 8C respectively. In the equivalent capacitance adjustment program, the resonant regulator 203 determines the number of capacitors coupled to the phase node LX according to the equivalent capacitance adjustment signal QGATE<3:0> to adjust the equivalent capacitance Ceq on the phase node LX. In this embodiment, the number of capacitors coupled to the phase node LX can be determined according to the equivalent capacitance adjustment signal QGATE<3:0>, and the capacitance value coupled to the phase node LX is determined to be between 0 and 15C. In an embodiment, the maximum total capacitance value (in this embodiment, 15C) and / or capacitance resolution (in this embodiment, 1C) of the plurality of capacitors C1, C2, C3, C4 in the capacitor array are related to the preset threshold voltage Vlx_ref.

[0094] Figure 2D is a circuit schematic diagram showing the comparison circuit and the judgment circuit in the control circuit of a switching power supply according to an embodiment of the present invention. This embodiment is Figure 2BAn exemplary embodiment of the comparison circuit 2021 and the determination circuit 2022. As Figure 2D shown, the comparison circuit 2021 can be a comparator, for example, used to compare the phase node voltage Vlx with the preset threshold voltage Vlx_ref. The determination circuit 2022 includes, for example, a pulse generator PG, a flip-flop FF, and an inverter INV.

[0095] Figure 2E is a circuit schematic diagram showing a capacitance adjustment program circuit in a control circuit of a switching power supply according to an embodiment of the present invention. As Figure 2E shown, the capacitance adjustment program circuit 2023 includes a counting circuit 20231, which is used to count the pulses of the pulse width modulation signal NGATEi according to the enable and hold signals Lx_lolb to generate a program signal QCOUNT<3:0>. The capacitance adjustment program circuit 20231 also includes a logic circuit 20232, which is used to generate an adjustment enable signal Sen when the pulse count of the pulse width modulation signal NGATEi indicated by the program signal QCOUNT<3:0> exceeds a preset number of pulses, so as to enable the equivalent capacitance adjustment circuit 2024, and further generate an equivalent capacitance adjustment signal QGATE<3:0>.

[0096] Figure 2G is a circuit block diagram showing a counting circuit of a capacitance adjustment program circuit in a control circuit of a switching power supply according to an embodiment of the present invention. As Figure 2G shown, in one embodiment, the counting circuit 20231 includes a unidirectional counter 202311, which is used to unidirectionally count the pulses of the pulse width modulation signal NGATEi according to the enable and hold signals Lx_lolb. When the pulse count of the pulse width modulation signal NGATEi indicated by the program signal QCOUNT<3:0> exceeds a preset number of pulses, the logic circuit 20232 generates an adjustment enable signal Sen. When the unidirectional counter 202311 counts up to the pulse count of the pulse width modulation signal NGATEi indicated by the program signal QCOUNT<3:0> exceeding a preset number of pulses, the unidirectional counter 202311 overflows and counts cyclically.

[0097] Figure 2F is a circuit schematic diagram showing an equivalent capacitance adjustment circuit in a control circuit of a switching power supply according to an embodiment of the present invention. As Figure 2F shown, the equivalent capacitance adjustment circuit 2024 includes a counter 20241, which is used to accumulate the count and adjust the equivalent capacitance adjustment signal QGATE<3:0> by a preset unit when the adjustment enable signal Sen switches to the enable level, so as to adjust the number of a plurality of capacitors coupled to the phase node LX. Figure 2H is a circuit block diagram showing a counter of an equivalent capacitance adjustment circuit in a control circuit of a switching power supply according to an embodiment of the present invention. AsFigure 2H As shown, in one embodiment, the counter 20241 includes a unidirectional counter 202411 for unidirectionally accumulating and counting the equivalent capacitor adjustment signal QGATE<3:0> when the adjustment enable signal Sen switches to the enable level, so as to correspondingly adjust the number of a plurality of capacitors coupled to the phase node LX. When the unidirectional counter 202411 unidirectionally accumulates and counts to a preset count limit, the unidirectional counter 202411 overflows and cycles through the count.

[0098] Figures 3A to 3K Multiple embodiments showing that the present invention can be applied to a switching power supply are presented. Figure 2A The power stage circuit 201 can be configured as Figures 3A to 3K any one of the power stage circuit topologies shown, such as a buck power stage circuit, a boost power stage circuit, a buck-boost power stage circuit, a buck-boost inverting power stage circuit, and a flyback power stage circuit.

[0099] Figure 4 is a schematic diagram of signal waveforms of relevant signals of a switching power supply according to an embodiment of the present invention. The phase node voltage Vlx, the preset threshold voltage Vlx_ref, the comparison signal Lx_lo, the pulse width modulation signal NGATE, and the enable and hold signal Lx_lolb are shown in Figure 2A Please also refer to Figure 4 In Figure 4 , Figure 2D and Figure 2E , at time point t1, when both the comparison signal Lx_lo and the pulse width modulation signal NGATE are at the enable level, it indicates that the phase node voltage Vlx is lower than the preset threshold voltage Vlx_ref at the start of the inductor magnetization time point. Therefore, the enable and hold signal Lx_lolb switches to the disable level, causing the capacitor adjustment program circuit 2023 not to perform the capacitor adjustment program.

[0100] It should be noted that after time point t1 and when the pulse width modulation signal NGATE is at the enable level, it indicates that the power switch QL is conducting and the inductor L is in the magnetization state. The control circuit 202 does not perform the capacitor adjustment program and does not determine whether the equivalent capacitor adjustment program is in the enabled state. At this time, the equivalent capacitor Ceq and the inductor L do not form a resonant circuit and do not resonate; therefore, the phase node voltage Vlx on the phase node LX is not a quasi-resonant signal as shown in Figure 4 the schematic diagram of the signal waveform of the phase node voltage Vlx.

[0101] Continuing to refer to Figure 4, at time point t2, when the comparison signal Lx_lo is at the disabled level and the pulse width modulation signal NGATE is at the enabled level, it indicates that the phase node voltage Vlx at the electromagnetic starting point of the inductor exceeds, for example, is higher than the preset threshold voltage Vlx_ref. Therefore, the enable and hold signal Lx_lolb is changed to the enabled level, causing the capacitance adjustment program circuit 2023 to perform the capacitance adjustment program.

[0102] It should be noted that in this embodiment, performing the capacitance adjustment program means that the capacitance adjustment program circuit 2023 continuously accumulates the number of pulses of the pulse width modulation signal NGATE. When the number of pulses of the pulse width modulation signal NGATE accumulated by the capacitance adjustment program circuit 2023 exceeds the preset number of pulses, the equivalent capacitance adjustment circuit 2024 is enabled, and then an equivalent capacitance adjustment signal QGATE<3:0> is generated for the resonant regulator 203, so that the resonant regulator 203 changes the number of capacitors C1 - C4 coupled to the phase node LX, thereby changing the equivalent capacitance Ceq of the phase node LX, causing the phase node voltage Vlx to decrease at another electromagnetic starting point of the inductor after the equivalent capacitance adjustment program, and reducing the switching loss Ploss when the power switch QL is turned on.

[0103] Figure 5 is a schematic diagram of the signal waveforms of the relevant signals of the Figure 2A switching power supply according to an embodiment of the present invention. The enable and hold signal Lx_lolb, the pulse width modulation signal NGATE, the program signal QCOUNT<3:0>, and the equivalent capacitance adjustment signal QGATE<3:0> are shown in Figure 5 . Please also refer to Figure 5 and Figure 2E , when Lx_lolb is at the enabled level, the counting circuit 20231 starts counting the pulses of the pulse width modulation signal NGATEi. When the program signal QCOUNT<3:0> counts from 0 and exceeds the preset number of pulses, for example, 15, the counter 20241 will accumulate and count, for example, Figure 5 as shown, the equivalent capacitance adjustment signal QGATE<3:0> accumulates from 5 to 6, thereby correspondingly adjusting the number of a plurality of capacitors coupled to the phase node LX to, for example, 6 capacitors.

[0104] It should be noted that the program signal QCOUNT<3:0> and the equivalent capacitance adjustment signal QGATE<3:0> are represented by binary numbers, for example, but not limited to. In this embodiment, the program signal QCOUNT<3:0> and the equivalent capacitance adjustment signal QGATE<3:0> are, for example, 4 - bit binary numbers. The program signal QCOUNT<3:0> counts the number of pulses of the pulse width modulation signal NGATEi, while the equivalent capacitance adjustment signal QGATE<3:0> accumulates and counts the number of a plurality of capacitors coupled to the phase node LX.

[0105] Figure 6 It is a graph showing the relationship between the light load efficiency of the switching power supply of the present invention and the phase node voltage when the lower bridge switch is turned on, and the relationship between the light load efficiency of a known switching power supply and the phase node voltage when the lower bridge switch is turned on, according to an embodiment of the present invention. Figure 7 It is a list showing the light load efficiency of the switching power supply of the present invention and the phase node voltage when the lower bridge switch is turned on, and the light load efficiency of a known switching power supply and the phase node voltage when the lower bridge switch is turned on, at different load currents, according to an embodiment of the present invention. Refer to Figure 6 and Figure 7 It can be seen that at the same load current, the light load efficiency of the present invention is relatively higher than that of the known technology, and the phase node voltage Vlx when the lower bridge switch of the present invention is turned on is relatively lower than the phase node voltage Vlx when the lower bridge switch of the known technology is turned on.

[0106] In summary, the present invention can adjust the equivalent capacitance by determining whether the phase node voltage exceeds a preset threshold voltage and adjusting the equivalent capacitance when the phase node voltage exceeds the preset threshold voltage, so as to adjust the resonance frequency during the quasi-resonant period and make the phase node voltage lower than the preset threshold voltage, thereby keeping the switching frequency at a fixed frequency and achieving better light load efficiency, so as to achieve a fixed frequency and at the same time have better light load efficiency.

[0107] The above has described the present invention with respect to the preferred embodiments. However, the above description is only for making those skilled in the art easily understand the content of the present invention, and is not used to limit the scope of the rights of the present invention. Each of the described embodiments is not limited to being applied alone, and can also be combined. For example, two or more embodiments can be combined, and some components in one embodiment can also be used to replace the corresponding components in another embodiment. In addition, under the same spirit of the present invention, those skilled in the art can think of various equivalent changes and various combinations. For example, the so-called "processing or operating or generating a certain output result according to a certain signal" in the present invention is not limited to the signal itself, and also includes, when necessary, converting the signal between voltage and current, current and voltage, and / or ratio conversion, etc., and then processing or operating according to the converted signal to generate a certain output result. It can be seen that under the same spirit of the present invention, those skilled in the art can think of various equivalent changes and various combinations, and there are many combination methods, which are not listed one by one here. Therefore, the scope of the present invention should cover the above and all other equivalent changes.

Claims

1. A switching power supply, comprising: A power stage circuit for controlling a power switch according to a pulse width modulation signal, and switching and coupling an inductor coupled to a phase node to convert an input voltage into an output voltage; and A control circuit for determining an equivalent capacitor adjustment procedure in an enabled state according to a phase node voltage on the phase node at a starting point of inductor magnetization in a discontinuous conduction mode, and then adjusting an equivalent capacitor on the phase node to reduce a breakdown voltage of the power switch at another starting point of inductor magnetization after the equivalent capacitor adjustment procedure.

2. The switching power supply according to claim 1, wherein, At the initial point of excitation of the inductor, when the voltage of the phase node exceeds a preset threshold voltage, the control circuit determines that the equivalent capacitance adjustment program is in the enabled state and adjusts the equivalent capacitance on the phase node.

3. The switching power supply according to claim 1, wherein, After the equivalent capacitance adjustment program is turned to the enabled state and maintained for a duration, the control circuit adjusts the equivalent capacitance.

4. The switching power supply according to claim 3, wherein, When the equivalent capacitance adjustment program is in the enabled state, the control circuit counts the pulses of the pulse width modulation signal. When the pulse count of the pulse width modulation signal exceeds a preset number of pulses, it indicates that the equivalent capacitance adjustment program has maintained the duration.

5. The switching power supply according to claim 2, wherein, The control circuit includes: A comparison circuit for comparing the voltage of the phase node with the preset threshold voltage and generating a comparison signal; A judgment circuit for judging, according to the comparison signal and the pulse width modulation signal, at the initial point of excitation of the inductor, when the voltage of the phase node on the phase node exceeds the preset threshold voltage, to generate an enable and hold signal; A capacitance adjustment program circuit for performing the equivalent capacitance adjustment program according to the enable and hold signal and the pulse width modulation signal and generating a program signal; and An equivalent capacitance adjustment circuit for generating an equivalent capacitance adjustment signal according to the program signal.

6. The switching power supply according to claim 5, wherein, It further includes a resonance regulator, wherein the resonance regulator is coupled to the phase node and includes a capacitor array having a plurality of capacitors. In the equivalent capacitance adjustment program, the resonance regulator determines the number of capacitors coupled to the phase node according to the equivalent capacitance adjustment signal to adjust the equivalent capacitance on the phase node.

7. The switching power supply according to claim 6, wherein, A maximum total capacitance value and / or a capacitance resolution of the plurality of capacitors in the capacitor array are related to the preset threshold voltage.

8. The switching power supply according to claim 6, wherein, The capacitance adjustment program circuit includes a first counting circuit for counting the pulses of the pulse width modulation signal according to the enable and hold signal to generate the program signal.

9. The switching power supply according to claim 8, wherein, The capacitance adjustment program circuit further includes a logic circuit for generating an adjustment enable signal when the program signal indicates that the pulse count of the pulse width modulation signal exceeds the preset number of pulses, to enable the equivalent capacitance adjustment circuit to generate the equivalent capacitance adjustment signal.

10. The switching power supply according to claim 9, wherein, The equivalent capacitance adjustment circuit includes a second counter for accumulating and adjusting the equivalent capacitance adjustment signal by a preset unit when the adjustment enable signal switches to an enable bit time to adjust the number of the plurality of capacitors coupled to the phase node.

11. The switching power supply according to claim 9, wherein, The first counting circuit includes a first unidirectional counter for unidirectionally counting the pulses of the pulse width modulation signal according to the enable and hold signal. When the program signal indicates that the pulse count of the pulse width modulation signal exceeds the preset number of pulses, the logic circuit generates the adjustment enable signal.

12. The switching power supply according to claim 11, wherein, When the first unidirectional counter counts up to the point where the program signal indicates that the pulse count of the pulse width modulation signal exceeds the preset number of pulses, the first unidirectional counter overflows and counts cyclically.

13. The switching power supply according to claim 10, wherein, The second counter includes a second unidirectional counter for unidirectionally accumulating and counting the equivalent capacitance adjustment signal when the adjustment enable signal switches to the enable bit, so as to correspondingly adjust the number of the plurality of capacitors coupled to the phase node.

14. The switching power supply according to claim 13, wherein, When the second unidirectional counter unidirectionally accumulates and counts up to a preset count limit, the second unidirectional counter overflows and cycles the count.

15. The switching power supply according to claim 3, wherein, This duration is related to a control loop bandwidth of the switching power supply and / or a stability of the equivalent capacitance adjustment process.

16. The switching power supply according to claim 2, wherein, The control circuit adjusts the equivalent capacitance on the phase node to adjust the phase node voltage to not exceed the preset threshold voltage at the starting point of the inductor magnetization in a steady state.

17. A control method for controlling a switching power supply, the switching power supply including a power stage circuit for controlling a power switch according to a pulse width modulation signal to switch an inductor coupled to a phase node so as to convert an input voltage into an output voltage, the control method comprising: In a discontinuous conduction mode, determining an equivalent capacitance adjustment procedure in an enabled state according to a phase node voltage at a phase node at an inductor magnetization start point; and Adjusting an equivalent capacitance at the phase node according to the equivalent capacitance adjustment procedure to reduce a voltage across the power switch at another inductor magnetization start point after the equivalent capacitance adjustment procedure.

18. The control method according to claim 17, wherein, The step of determining an equivalent capacitance adjustment process in an enabled state according to a phase node voltage on the phase node at an inductor magnetization starting point in a discontinuous conduction mode includes: At the inductor magnetization starting point, when the phase node voltage exceeds a preset threshold voltage, determining that the equivalent capacitance adjustment process is in the enabled state.

19. The control method according to claim 17, wherein, The step of adjusting an equivalent capacitance on the phase node according to the equivalent capacitance adjustment process to reduce a breakdown voltage of a power switch at another inductor magnetization starting point after the equivalent capacitance adjustment process further includes: After the equivalent capacitance adjustment process switches to the enabled state and maintains a duration, adjusting the equivalent capacitance.

20. The control method according to claim 19, wherein, When the equivalent capacitance adjustment process is in the enabled state, counting the pulses of the pulse width modulation signal, and when the pulse count of the pulse width modulation signal exceeds a preset number of pulses, indicating that the equivalent capacitance adjustment process has maintained the duration.

21. The control method according to claim 20, wherein, The step of counting the pulses of the pulse width modulation signal and when the pulse count of the pulse width modulation signal exceeds a preset number of pulses, indicating that the equivalent capacitance adjustment process has maintained the duration includes: unidirectionally counting the pulses of the pulse width modulation signal, and when the count reaches that the pulse count of the pulse width modulation signal exceeds the preset number of pulses, overflowing and cycling the count.

22. The control method according to claim 18, wherein, The step of determining an equivalent capacitance adjustment process in an enabled state according to a phase node voltage on the phase node at an inductor magnetization starting point in a discontinuous conduction mode includes: Comparing the phase node voltage with the preset threshold voltage to generate a comparison signal; According to the comparison signal and the pulse width modulation signal, at the inductor magnetization starting point, when it is determined that the phase node voltage on the phase node exceeds the preset threshold voltage, generating an enable and hold signal; According to the enable and hold signal and the pulse width modulation signal, performing the equivalent capacitance adjustment process to generate a program signal; and Generating an equivalent capacitance adjustment signal according to the program signal.

23. The control method according to claim 22, wherein, It further includes: in the equivalent capacitance adjustment process, determining the number of a capacitor coupled to the phase node according to the equivalent capacitance adjustment signal to adjust the equivalent capacitance on the phase node.

24. The control method according to claim 23, wherein, A maximum total capacitance value and / or a capacitance resolution of the capacitor are related to the preset threshold voltage.

25. The control method according to claim 19, wherein, This duration is related to a control loop bandwidth of the switching power supply and / or a stability of the equivalent capacitance adjustment process.

26. The control method according to claim 18, wherein, The step of adjusting an equivalent capacitance on the phase node according to the equivalent capacitance adjustment program to reduce a turn-on voltage of the power switch at another electromagnetic excitation start point after the equivalent capacitance adjustment program further includes: adjusting the equivalent capacitance on the phase node to adjust the phase node voltage to not exceed the preset threshold voltage at the electromagnetic excitation start point in a steady state.

27. The control method according to claim 22, wherein, The step of generating an equivalent capacitance adjustment signal according to the program signal includes: unidirectionally cumulatively counting the equivalent capacitance adjustment signal to correspondingly adjust the number of capacitors coupled to the phase node, and overflowing and circularly counting when the unidirectional cumulative count reaches a preset count limit.

Images