A switching power supply and audio noise suppression method thereof

Abstract

The present invention discloses a switching power supply and an audio noise suppression method thereof. The switching power supply includes an audio noise suppression circuit, which is used to start timing at the charging cycle of each switching cycle when the switching power supply is operated in DCM, and detect whether the output voltage is lower than the trigger threshold voltage when the timing reaches the threshold cycle indicating the lowest frequency of the switching power supply. If the output voltage is still higher than the trigger threshold voltage, the switching power supply is controlled to switch from DCM to super audio mode to limit the switching frequency to above the audio range, thereby solving the audio noise generated when the switching power supply is under light load, and will not cause energy loss, and the efficiency is higher.

Description

Technical Field

[0001] The present invention relates to the field of power supply design, and more particularly to a switching power supply and an audio noise suppression method thereof. Background Art

[0002] A switching power converter is a power supply that uses modern power electronics technology to control the on-off time ratio of the switch tube to maintain a stable output voltage. A switching power converter is generally composed of a pulse width modulation (PWM) control circuit, an energy storage element (such as an inductor) and a switch tube. A large number of switching power converters are used in mobile terminals to provide stable power to various modules inside them, such as the central processing unit (CPU), subscriber identification module (S1M) card, and radio frequency power amplifier.

[0003] When the load current is relatively large, the switching power converter (hereinafter referred to as the switching power supply) generally operates in continuous conduction mode (CCM). At this time, the switching frequency of the switching power supply is relatively high, usually several hundred kHz to several MHz. However, when the load current is relatively small or there is no load current, in order to reduce losses and improve efficiency, the switching power supply generally reduces the operating frequency and enters discontinuous conduction mode (DCM). Under DCM, the smaller the load current, the lower the operating frequency. When the operating frequency falls into the audio range (20Hz-20kHz), audio noise will be generated. This noise affects the customer experience and also interferes with the communication of the mobile terminal, which is unacceptable.

[0004] Figure 1 and Figure 2 The structure diagram and waveform diagram of a switching power supply with audio noise suppression in the prior art are shown respectively. Figure 1As shown, the switching power supply 100 of the prior art includes a comparator 110 and a negative current control circuit 120. The comparator 110 is used to detect whether the switching frequency enters a range close to the audio frequency. The negative current control circuit 120 is used to extend the discharge time before approaching the audio frequency to allow the inductor L to have a negative current, thereby using an analog method to lock the switching frequency after the load is less than a critical value at a frequency higher than the audio frequency. Although this solution is highly efficient, it has a great correlation with peripheral devices and input and output voltages. In order to meet the application scenarios of various peripheral devices and voltage ranges, the required compensation is relatively complex, resulting in a large hardware overhead. At the same time, due to the existence of loop gain in the analog circuit, the control loop will generate an overshoot voltage (such as Vsw) at the switch node Vsw at the end of discharge. Figure 2 This can cause the output voltage to rise and generate electromagnetic interference, which is unacceptable for some applications, such as battery charging. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a switching power supply and an audio noise suppression method thereof, which solves the audio noise generated when the switching power supply is under light load, does not cause energy loss, and is more efficient.

[0006] According to one aspect of an embodiment of the present invention, a method for suppressing audio noise of a switching power supply is provided, wherein the switching power supply comprises a main switch, a synchronous switch and an inductor, wherein the main switch and the synchronous switch are controlled to be turned on or off so that the switching power supply provides an output voltage at an output terminal, and the switching power supply has a switching cycle, wherein the switching cycle comprises a charging cycle for charging the inductor and a discharging cycle for discharging the output terminal, wherein the method for suppressing audio noise comprises: when the switching power supply operates in a discontinuous conduction mode, timing is started during a charging cycle of the switching cycle; when the timing reaches a threshold cycle, detecting whether the output voltage is lower than a trigger threshold voltage, and if the output voltage is higher than the trigger threshold voltage, switching the switching power supply from the discontinuous conduction mode to a super-audio mode, and inserting an active discharge interval before the start of the next switching cycle to turn on the synchronous switch.

[0007] Optionally, the threshold period is used to indicate the lowest frequency of the switching power supply, and the frequency is above the audio range.

[0008] Optionally, the active discharge interval is of fixed duration.

[0009] Optionally, the audio noise suppression method further includes: when the switching power supply is switched from the discontinuous conduction mode to the super-audio mode, synchronously reducing the duration of the threshold period to introduce feedforward.

[0010] Optionally, the audio noise suppression method further includes: obtaining a reduction amount of the threshold period in the super audio mode relative to the threshold period in the discontinuous conduction mode according to the input voltage and the output voltage of the switching power supply.

[0011] Optionally, the audio noise suppression method also includes: when the switching power supply operates in the ultrasonic audio mode, obtaining the interval time during which the output voltage is lower than the trigger threshold voltage, and when the interval time is less than the threshold period in the ultrasonic audio mode, switching the switching power supply from the ultrasonic audio mode to the discontinuous conduction mode.

[0012] According to another aspect of an embodiment of the present invention, a switching power supply is provided, comprising: a main switch, a synchronous switch and an inductor, wherein the main switch and the synchronous switch are controlled to be turned on or off so that the switching power supply provides an output voltage at an output terminal; a switching power supply controller, which is used to provide a switching control signal to the main switch and the synchronous switch, wherein the switching power supply has a switching cycle, wherein the switching cycle includes a charging cycle for charging the inductor and a discharging cycle for discharging the output terminal; and an audio noise suppression circuit, which is configured to start timing during a charging cycle of the switching cycle when the switching power supply operates in a discontinuous conduction mode, and detect whether the output voltage is lower than a trigger threshold voltage when the timing reaches a threshold cycle, wherein the audio noise suppression circuit is used to provide a mode switching signal to the switching power supply controller when the output voltage is higher than the trigger threshold voltage, so as to switch the switching power supply from the discontinuous conduction mode to the super audio mode, and the switching power supply controller is used to insert an active discharge interval before the start of the next switching cycle to turn on the synchronous switch.

[0013] Optionally, the audio noise suppression circuit includes: a comparator configured to compare the output voltage with the trigger threshold voltage and output a comparison result; a timing circuit configured to start timing at a charging period of the switching period and stop timing when the timing reaches the threshold period, thereby generating a timing signal; and a mode switching circuit configured to receive the timing signal and the comparison result, wherein the mode switching circuit is used to provide the mode switching signal to the switching power supply controller when the timing signal is received and the comparison result indicates that the output voltage is higher than the trigger threshold voltage.

[0014] Optionally, the threshold period is used to indicate the lowest frequency of the switching power supply, and the frequency is above the audio range.

[0015] Optionally, the active discharge interval is of fixed duration.

[0016] Optionally, the timing circuit is configured to synchronously reduce the duration of the threshold period to introduce feedforward when the switching power supply switches from the discontinuous conduction mode to the supersonic frequency mode.

[0017] Optionally, the timing circuit includes: a first current source configured to provide a first current to a first node; a second current source configured to provide a second current to the first node; a first capacitor, a first end of which is coupled to the first node and a second end is grounded; a first switch, connected across the two ends of the first capacitor and having a current terminal coupled between the first node and ground; a first comparator, a positive input of which is coupled to the first node, a negative input for receiving a reference voltage, and an output for outputting the timing signal; and a monostable trigger for controlling the on and off of the first switch based on the comparison result, wherein the first current source is started only when the switching power supply is in supersonic mode, and the second current source is started when the switching power supply is in both modes.

[0018] Optionally, the current value of the first current is Proportional to, wherein Vin is the input voltage of the switching power supply, and Vout is the output voltage of the switching power supply.

[0019] Optionally, the first current source includes: a first resistor, whose first end is coupled to the input voltage; a diode, whose anode is coupled to the second end of the first resistor; a first operational amplifier, whose positive input is coupled to the intermediate node between the first resistor and the diode, whose negative input is coupled to the output voltage, and whose output is coupled to the cathode of the diode; a second resistor, whose first end is coupled to the output voltage; a first transistor, whose source is coupled to the second end of the second resistor, and whose drain is coupled to the output end of the first current; a second operational amplifier, whose positive input is coupled to the intermediate node between the second resistor and the first transistor, whose negative input is coupled to the output end of the first operational amplifier, and whose output is coupled to the gate of the first transistor; a third resistor, whose first end is grounded; a second transistor, whose source is coupled to the second end of the third resistor, and whose drain is coupled to the output end of the first current; and a third operational amplifier, whose positive input is coupled to the output voltage, whose auxiliary terminal is coupled to the intermediate node between the third resistor and the second transistor, and whose output is coupled to the gate of the second transistor.

[0020] Optionally, the switching power supply also includes: a voltage-dividing resistor network for obtaining a voltage-dividing value of the output voltage; and an error amplifier configured to perform error amplification between the voltage-dividing value of the output voltage and a reference voltage, and the switching power supply controller drives the main switch and the synchronous switch according to the output control of the error amplifier.

[0021] In summary, the switching power supply of the embodiment of the present invention includes an audio noise suppression circuit, which is used to start timing at the charging cycle of each switching cycle when the switching power supply operates in DCM, and detect whether the output voltage is lower than the trigger threshold voltage when the timing reaches the threshold cycle indicating the lowest frequency of the switching power supply. If the output voltage is still higher than the trigger threshold voltage, the switching power supply is controlled to switch from DCM to super-audio mode to limit the switching frequency to above the audio range, thereby solving the audio noise generated when the switching power supply is under light load, and will not cause energy loss, and the efficiency is higher. In addition, compared with conventional circuits, the switching power supply of the present invention only needs to add a timing circuit for timing the threshold cycle, and does not need to make excessive changes to the existing switching power supply, and the engineering cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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.

[0023] Figure 1 It is a structural schematic diagram of a switching power supply 100 with audio noise suppression in the prior art;

[0024] Figure 2 for Figure 1 The waveform diagram of the switching power supply 100 in the super audio frequency light load mode is shown;

[0025] Figure 3 is a schematic structural diagram of a switching power supply 200 according to an embodiment of the present invention;

[0026] Figure 4 A timing diagram of the switching power supply 200 in the ultrasonic audio mode according to an embodiment of the present invention;

[0027] Figure 5 Shows Figure 3 A circuit diagram of the timing circuit 212;

[0028] Figure 6 Shows Figure 5 A circuit diagram of the current source 2121 in FIG.

[0029] Figure 7 The figure is a schematic diagram of the structure of a computing system having a switching power supply including an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not have to be used to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, materials or methods are not specifically described.

[0031] Throughout the specification, reference to "one embodiment", "an embodiment", "an example" or "an example" means that a particular feature, structure or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment", "in an embodiment", "an example" or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. In addition, specific features, structures or characteristics can be combined in one or more embodiments or examples in any appropriate combination and / or sub-combination. In addition, it should be understood by those of ordinary skill in the art that the drawings provided herein are for illustrative purposes, and the drawings are not necessarily drawn to scale. It should be understood that when an "element" is said to be "connected to" or "coupled" to another element, it can be directly connected or coupled to another element or there can be an intermediate element. On the contrary, when an element is said to be "directly connected to" or "directly coupled to" another element, there is no intermediate element. The same reference numerals indicate the same element. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0032] Figure 3 2 is a schematic diagram of the structure of a switching power supply 200 according to an embodiment of the present invention. In this embodiment, a buck switching power supply is used as an example for description, but the application scope of the present invention is not limited to the buck switching power supply, and can also be applied to a boost switching power supply, a buck-boost switching power supply, etc. Figure 3As shown, the switching power supply 200 includes a main switch Q1 (also known as a high-side switch) and a synchronous switch Q2 (also known as a low-side switch), an inductor L, a voltage-dividing resistor network 201, a reference voltage, an error amplifier 202, a switching power supply controller 203, and an output capacitor Cout. The first end of the main switch Q1 is coupled to the input voltage Vin, the second end is coupled to the first end of the synchronous switch Q2 at the switch node SW, the second end of the synchronous switch Q2 is grounded GND, the first end of the inductor L is coupled to the switch node SW, and the second end is coupled to the output voltage Vout of the switching power supply. The voltage-dividing resistor network 201 is used to divide the output voltage Vout and perform error amplification with the reference voltage and is used for the switching power supply controller 203 to control and drive the main switch Q1 and the synchronous switch Q2. The main switch Q1 and the synchronous switch Q2 can be any controllable semiconductor switch device, such as a metal oxide semiconductor field effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), etc.

[0033] In this embodiment, the switching power supply controller 203 is illustrated in a general form, but the controller can be implemented according to voltage mode control, current mode control, constant on-time (or constant frequency), etc., and the controller can be configured as an analog controller or a digital controller.

[0034] The switching power supply controller 203 provides an upper switch driving signal HSG to the main switch Q1 and a lower switch driving signal LSG to the synchronous switch Q2. The HSG and LSG signals are otherwise referred to as switch control signals, which are used to control the excitation of the electronic switches Q1 and Q2, respectively.

[0035] The switching power supply 200 has a switching cycle, and the switching cycle includes a charging cycle for charging the inductor L and a discharging cycle for discharging the output terminal. When the load is large, the switching power supply 200 operates in a continuous conduction mode (CCM). In each of the switching cycles, at least one of the main switch Q1 and the synchronous switch Q2 is turned on for the entire portion of each switching cycle (ignoring the dead time between switching to ensure that only one switch is turned on at any given time), and the current IL flowing through the inductor L is never zero, or the inductor L is never "reset", which means that during the switching cycle, the magnetic flux of the inductor never returns to zero, and when the synchronous switch Q2 is turned off, the current IL flowing through the inductor L always remains greater than zero.

[0036] When the load is small, the switching power supply 200 operates in a discontinuous conduction mode (DCM). When the switching power supply 200 operates in DCM, the size of each switching cycle is equal to t1+t2. Wherein, t1 defines the following process: under the control of the control signals LSG and HSG, the main switch Q1 is turned on, the synchronous switch Q2 is turned off, the input voltage Vin forms a path to the ground through the inductor L, the inductor L stores energy, and the current IL flowing through it increases. Then, while the main switch Q1 is controlled to be turned off, the synchronous switch Q2 is controlled to be turned on, and the inductor L transmits the stored electric energy to the output end of the switching power supply 200 to charge it, and the output voltage increases until the current IL flowing through the inductor L drops to zero, which means that the inductor L is properly "reset". When the synchronous switch Q2 is turned off, the current IL flowing through the inductor L is zero. The time t2 defines the following process: the current IL flowing through the inductor L is kept at zero, and the current flowing through the load discharges the load capacitor until the output voltage Vout drops to the lower threshold, and the switching power supply 200 starts a new switching cycle under the control of the switching power supply controller 203, and the cycle repeats.

[0037] Secondly, in response to the existing technical problems, the switching power supply 200 of the embodiment of the present invention also includes an audio noise suppression circuit 204. The audio noise suppression circuit 204 is used to time each switching cycle when the switching power supply operates in the discontinuous conduction mode. When the switching cycle exceeds the set threshold, it is considered that the switching frequency will enter the audio range at this time, and at the same time provide the mode switching signal Mode to the switching power supply controller 203 to switch the switching power supply from the discontinuous conduction mode to the super-audio mode. Further, the switching power supply controller 203 is used to perform the following operations in the super-audio mode: briefly turn on the synchronous switch Q2 to accelerate the DCM operation. By turning on the synchronous switch Q2 in advance, the output voltage Vout is pulled down faster than in the normal DCM situation. After that, by setting the control signal HSG to the effective state, the switching power supply controller 203 starts a new switching cycle to increase the output voltage Vout, thereby shortening the switching cycle to achieve the purpose of suppressing audio noise.

[0038] In one embodiment, the audio noise suppression circuit 204 includes a comparator 211, a timing circuit 212, and a mode switching control circuit 213. The comparator 211 is used to compare the output voltage Vout with the trigger threshold voltage Vo_low and output the comparison result. The timing circuit 212 is used to perform timing before the start of the charging cycle of each switching cycle, and generate a timing signal Tani when the timing is completed. The mode switching control circuit 213 receives the comparison result and the timing signal Tani, and determines whether the switching frequency of the switching power supply is within the audio range according to the comparison result and the timing signal Tani.

[0039] In one embodiment, a threshold period Tani0 for indicating the minimum frequency of the switching power supply is generated by the timing circuit 212. The frequency corresponding to the threshold period Tani0 needs to be designed to be above the audio frequency range. When the timing reaches the threshold period Tani0, the timing is completed, and the timing circuit 212 generates a timing signal Tani0. When the mode switching control circuit 213 receives the timing signal Tani0, it determines whether the output voltage Vout is lower than the trigger threshold voltage Vo_low according to the comparison result of the comparator 211. If the output voltage Vout is still higher than the trigger threshold voltage Vo_low (that is, the output of the comparator 211 has not yet flipped to a high level), the switching is triggered to switch the switching power supply from the discontinuous conduction mode to the super-audio frequency mode. Among them, the mode switching control circuit 213 can be configured as an analog circuit or a digital circuit.

[0040] It can be understood that the continuous conduction mode, discontinuous conduction mode and super audio mode of the switching power supply 200 of the embodiment of the present invention are compatible with each other and these modes can be smoothly transformed. When the inductor current reaches zero, the switching power supply 200 switches to the discontinuous conduction mode by terminating the LSG pulse earlier. When the switching frequency is reduced to the audio range, the switching power supply 200 discharges the output terminal by inserting an active discharge interval before the start of the next switching cycle, thereby limiting the switching frequency to switch to the super audio mode.

[0041] Figure 4 FIG. 2 is a timing diagram of the switching power supply 200 in the super audio mode according to an embodiment of the present invention, which respectively shows the timing diagrams of the switch control signals HSG and LSG, the switch node voltage VSW, the output voltage Vout and the inductor current IL. Figure 3 and Figure 4 The working principle of the switching power supply 200 according to the embodiment of the present invention is described in detail.

[0042] Between time t0 and t3, the switching power supply 200 operates in DCM, which is started by a HSG pulse starting between time t0 and t1, followed by a LSG pulse lasting between time t1 and t2. The inductor current IL gradually increases during the charging period between time t0 and t1, reaches a peak value at time t1, and then discharges to the output terminal during the discharge period between time t1 and t2, and drops to zero at time t2. Between time t2 and t3, the current IL flowing through the inductor L remains zero, and the current flowing through the load discharges the load capacitor. At the same time, the timing circuit 212 starts timing at time t0 when the charging period starts. When the timing reaches the threshold period Tani0, the mode switching control circuit 213 detects that the output voltage Vout is still higher than the trigger threshold voltage Vo_low according to the comparison result of the comparator 211, and provides the mode signal Mode to the switching power supply controller 203, triggering the switch, and switching the switching power supply from DCM to the super audio mode.

[0043] Between time t3 and t6, the switching power supply 200 operates in the super audio mode. The super audio mode starts with the LSG pulse between time t3 and t4. The switching power supply 200 terminates the normal DCM operation in advance by inserting an active discharge interval before the next switching cycle. The duration of the active discharge interval is Tn, which makes the inductor current IL enter the negative current earlier. Then, between time t4 and t5 of the next switching cycle, the LSG pulse is terminated and the HSG pulse is started, so that the inductor current IL increases to the peak level. Then, between time t5 and t6, the HSG pulse is terminated and the LSG pulse is started, so that the inductor current IL decreases to 0. When the inductor current IL reaches 0, the LSG pulse is terminated and the control signals HSG and LSG are both low level for the rest of the switching cycle.

[0044] Furthermore, since the super audio mode inserts an active discharge interval before the start of the switching cycle, the discharge amount at the output end increases, which causes a slight drop in the output voltage Vout. This drop needs to be corrected by the negative feedback of the stabilization loop. In order to reduce the impact of the sudden change injected into the feedback stabilization system, the present invention also includes reducing the threshold period in the super audio mode to introduce feedforward. That is, the timing circuit 212 starts timing again at the time t4 when the charging cycle of this switching cycle begins. When the timing reaches the threshold period Tani1 (the threshold period Tani1 is less than the threshold period Tani0), the mode switching control circuit 213 cooperates with the comparison result of the comparator 211 to determine whether the output voltage Vout is reduced to the trigger threshold voltage Vo_low, thereby determining whether to repeat the operation between time t3 and t6 in the next switching cycle to continue in the super audio mode or return to DCM.

[0045] In one embodiment, the mode switching control circuit 213 is further configured to time the two output intervals Tvo_low of the comparator 211 in the ultrasonic mode. If the two output intervals Tvo_low of the comparator 211 are less than the threshold period Tani1, the mode switching control circuit 213 triggers the switch again to control the switching power supply to switch from the ultrasonic mode back to DCM in the next switching cycle.

[0046] Figure 5 Shows Figure 3 An implementation of the timing circuit 212 in FIG. Figure 5 As shown, the timing circuit 212 includes current sources 2121 and 2122, a capacitor C1, a switch Q3, a comparator 2123 and a monostable trigger 2125. Among them, one end of the current sources 2121 and 2122 is coupled to the power supply end, and the other end is coupled to the node 2124. The current source 2121 is used to provide a current Id to the node 2124, and the current source 2122 is used to provide a current It to the node 2124. The first end of the capacitor C1 is coupled to the node 2124, and the second end is grounded. The switch Q3 is connected across the two ends of the capacitor C1 and has a current terminal coupled between the node 2124 and the ground. The node 2124 is coupled to the positive input end of the comparator 2123, and the negative input end of the comparator 2124 is used to receive the reference voltage VT, and the output end is used to output the signal Tani. The monostable trigger 2125 is used to generate a reference voltage based on the reference voltage VT. Figure 3 The comparison signal output by the comparator 211 controls the on and off of the switch Q3. The switch Q3 may be a transistor device, such as a FET or MOS transistor, having a drain, a source and a gate, or any other type of switch, including various other types of transistors.

[0047] In this embodiment, the current source 2121 is a controlled current source, which is started only when the switching power supply is in the super audio mode, while the current source 2122 is started regardless of the mode the switching power supply is in. The operation of the timing circuit 212 in DCM is as follows: when the output voltage Vout is lower than the trigger threshold voltage Vo_low, the switch Q3 triggers a charging process, which is briefly turned on by the leading edge of the output of the comparator 211 for a period of time, so that the charge on the capacitor C1 is discharged to the ground, and then the switch Q3 is turned off, and the capacitor C1 is charged by the current It to increase the voltage of the node 2124, that is, the timing of the next switching cycle is restarted. When the voltage of the node 2124 becomes higher than the reference voltage VT, the output of the comparator 2123 flips to a high level, indicating that the timing is over. When the output of the comparator 2123 flips to a high level, the voltage increment of the current It on the capacitor C1 is: (It*Tani0) / C1=VT, so according to the above formula, the threshold period Tani0=(VT*C1) / It under DCM can be obtained. The operation of the timing circuit 212 in the super audio mode is as follows: the switch Q3 triggers a charging process when the output voltage Vout is lower than the trigger threshold voltage Vo_low. It is briefly turned on by the leading edge of the output of the comparator 211 for a period of time, so that the charge on the capacitor C1 is discharged to the ground. After that, the switch Q3 is turned off, and the capacitor C1 is charged by the current It and Id to increase the voltage of the node 2124, that is, the timing of the next switching cycle is restarted. When the voltage of the node 2124 becomes higher than the reference voltage VT, the output of the comparator 2123 flips to a high level, indicating that the timing is over. The voltage increment of the current It and Id on the capacitor C1 is: [(It+Id)*Tani1] / C1=VT, so according to the above formula, the threshold period Tani1=(VT*C1) / (It+Id) in the super audio mode can be obtained. For a fixed reference voltage VT, the voltage increment caused by the current Id can make the capacitor voltage quickly reach the reference voltage VT, thereby shortening the threshold period that limits the switching frequency in the super audio mode.

[0048] Furthermore, the current Id provided by the current source 2121 has a certain proportional relationship with the current input voltage Vin and the output voltage Vout. Assume that the duration of the threshold period Tani0 under DCM is T, and the duration of the threshold period Tani1 under the super audio mode is (Td), where d is the change in the threshold period of the super audio mode relative to the threshold period of DCM. When the average charging current in the next switching cycle of DCM is consistent with the average charging and discharging current in the previous switching cycle of the super audio mode, the impact of this change on the circuit is minimal. According to the volt-second balance, it can be deduced that: Wherein, Tn is the active discharge interval inserted before the switching cycle in the super audio mode, Tm is the charging period within a switching cycle in the super audio mode, T is the duration of the threshold period Tani0 in the normal DCM, and T, Tn and Tm are constants selected for a specific design. Further, refer to Figure 5 , the currents It and Id each generate a voltage increment on the capacitor C1. For a fixed reference voltage VT, the voltage increment caused by the current Id can accelerate the capacitor voltage to reach the reference voltage VT. Therefore, the voltage increment caused by the current Id corresponds to the portion of the charging timing reduction in the super audio mode, that is: Where VT and C1 are also constants for a particular design. Compared with the volt-second balance derivation, the current Id and That is, the current source 2121 only needs to generate a current Id having the above relationship to obtain the threshold period variation related to the input voltage Vin and the output voltage Vout of the circuit in the super audio mode, thereby reducing the impact of mode switching on the output voltage.

[0049] Figure 6 Shows Figure 5 A way to realize the current source 2121 in FIG. Figure 6As shown, the current source 2121 includes resistors R1 to R3, operational amplifiers A1 to A3, transistors M1 and M2, and a diode D1. The first end of the resistor R1 is coupled to the input voltage Vin, the second end is coupled to the anode of the diode D1, and the cathode of the diode D1 is coupled to the output end of the operational amplifier A1. The positive input end of the operational amplifier A1 is coupled to the middle node of the resistor R1 and the diode D1, and the negative input end is coupled to the output voltage Vout. The first end of the resistor R2 is coupled to the output voltage Vout, the second end is coupled to the source of the transistor M1, the gate of the transistor M1 is coupled to the output end of the operational amplifier A2, and the drain is used to output the current Id. The positive input end of the operational amplifier A2 is coupled to the middle node of the resistor R2 and the transistor M1, and the negative input end is coupled to the output end of the operational amplifier A1 and the cathode of the diode D1. One end of the resistor R3 is grounded, and the other end is coupled to the source of the transistor M2. The gate of the transistor M2 is coupled to the output end of the operational amplifier A3, and the drain is coupled to the output end of the current Id. The positive input end of the operational amplifier A3 is coupled to the output voltage Vout, and the negative input end is coupled to the middle node of the resistor R3 and the transistor M2. Among them, the resistor R1, the diode D1 and the operational amplifier A1 are used to convert the difference between the input voltage and the output voltage Vin-Vout into a logarithmic voltage through the diode D1. This logarithmic voltage outputs Vout when there is no voltage difference between the input voltage Vin and the output voltage Vout. The resistor R2, the transistor M1 and the operational amplifier A2 form a current injection, and the resistor R3, the transistor M2 and the operational amplifier A3 form a current drain. The current injection and the current drain together complete the subtraction relationship calculation in the above formula, and the resistor R2, the transistor M1 and the operational amplifier A2 convert the logarithmic voltage into the current injection of the transistor M1 for output.

[0050] Figure 7 FIG. 3 is a schematic diagram of a computing system 300 having a switching power supply according to an embodiment of the present invention. Figure 7As shown, the power supply 301 generates one or more supply voltages for providing power to other system devices of the computer system 300 via the connection network 305, wherein the regulator 303 is implemented, for example, by the switching power supply of the above embodiment, for regulating and stabilizing the supply voltage. The connection network 305 can be a bus system or a switch system or a group of conductors, etc. In the embodiment shown, the computer system 300 includes a processor 307 and a peripheral system 309, both of which are coupled to the connection network 305 to receive the supply voltage from the power supply 301. In the embodiment shown, the peripheral system 309 may include any combination of a system memory 311 (for example, including any combination of RAM and ROM type devices and memory controllers, etc.) and an input / output (I / O) system 313, which may include a system controller, such as a graphics controller, an interrupt controller, a keyboard and mouse controller, a system storage device controller (for example, a controller for a hard disk drive, etc.), etc. The system shown is only exemplary, as it can be understood by those skilled in the art that many processor systems and supporting devices can be integrated into the processor chip.

[0051] As described in the above embodiment, the regulator 303 has three modes: CCM, DCM and super audio mode. The regulator 303 operates in CCM at higher loads, switches to DCM when the load decreases while the switching frequency is maintained above the audio range, and then switches to super audio mode at lighter loads (otherwise, the switching frequency will enter the audio range). At lighter loads, DCM can provide maximum efficiency. Although the super audio mode is more efficient than CCM at lighter loads, it is not as efficient as DCM, but the super audio mode can prevent the generation of audio noise. Therefore, at very light loads, the super audio mode is actually a compromise between efficiency and consumer annoyance.

[0052] The switching power supply of the embodiment of the present invention includes an audio noise suppression circuit, which is used to start timing at the charging cycle of each switching cycle when the switching power supply is operated in DCM, and detect whether the output voltage is lower than the trigger threshold voltage when the timing reaches the threshold cycle indicating the lowest frequency of the switching power supply. If the output voltage is still higher than the trigger threshold voltage, the switching power supply is controlled to switch from DCM to super audio mode to limit the switching frequency to above the audio range, thereby solving the audio noise generated when the switching power supply is under light load, and will not cause energy loss, and the efficiency is higher. In addition, compared with conventional circuits, the switching power supply of the present invention only needs to add a timing circuit for timing the threshold cycle, and does not need to make excessive changes to the existing switching power supply, and the engineering cost is low.

[0053] Furthermore, the switching power supply of the present invention performs the following operations in the super-audio mode: an active discharge interval is inserted before each switching cycle to pull the inductor current to a negative current so as to pull down the output voltage more quickly, thereby shortening the switching cycle. Since the active discharge interval is followed by the charging interval of the switching cycle, the output voltage surge caused by the reverse current when the synchronous switch is disconnected is well avoided, and the circuit stability is better.

[0054] Furthermore, the audio noise suppression circuit of the present invention is also used to reduce the threshold period in the super-audio mode to introduce feedforward, thereby correcting the output voltage drop caused by the inserted active discharge interval through negative feedback of the stable loop, further improving the stability of the circuit.

[0055] 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 statement "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0056] 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 method for suppressing audio noise of a switching power supply, the switching power supply comprising a main switch, a synchronous switch and an inductor, the main switch and the synchronous switch being controlled to be turned on or off so that the switching power supply provides an output voltage at an output terminal, the switching power supply having a switching cycle, the switching cycle comprising a charging cycle for charging the inductor and a discharging cycle for discharging the output terminal, wherein: The audio noise suppression method comprises: When the switching power supply operates in a discontinuous conduction mode, timing starts during a charging period of the switching period; When the timing reaches the threshold period, detecting whether the output voltage is lower than the trigger threshold voltage, If the output voltage is higher than the trigger threshold voltage, the switching power supply is switched from the discontinuous conduction mode to the super-audio mode, and an active discharge interval is inserted before the start of the next switching cycle to turn on the synchronous switch to limit the switching frequency to above the audio range. Wherein, the audio noise suppression method further includes: When the switching power supply is switched from the discontinuous conduction mode to the super audio mode, the duration of the threshold period is synchronously reduced to introduce feedforward.

2. The audio noise suppression method according to claim 1, wherein: The threshold period is used to indicate the lowest frequency of the switching power supply, and the frequency is above the audio range.

3. The audio noise suppression method according to claim 1, wherein: The active discharge interval is of fixed duration.

4. The audio noise suppression method according to claim 1, wherein: Also includes: The reduction amount of the threshold period in the super audio mode relative to the threshold period in the discontinuous conduction mode is obtained according to the input voltage and the output voltage of the switching power supply.

5. The audio noise suppression method according to claim 1, wherein: Also includes: When the switching power supply operates in the ultrasonic audio mode, the interval time during which the output voltage is lower than the trigger threshold voltage is obtained, and when the interval time is less than the threshold period in the ultrasonic audio mode, the switching power supply is switched from the ultrasonic audio mode to the discontinuous conduction mode.

6. A switching power supply comprising: A main switch, a synchronous switch and an inductor, wherein the main switch and the synchronous switch are controlled to be turned on or off so that the switching power supply provides an output voltage at an output end; A switching power supply controller, configured to provide a switching control signal to the main switch and the synchronous switch, wherein the switching power supply has a switching cycle, and the switching cycle includes a charging cycle for charging the inductor and a discharging cycle for discharging the output terminal; as well as The audio noise suppression circuit is configured to start timing at a charging period of the switching period when the switching power supply operates in a discontinuous conduction mode, and detect whether the output voltage is lower than a trigger threshold voltage when the timing reaches a threshold period, The audio noise suppression circuit is used to provide a mode switching signal to the switching power supply controller when the output voltage is higher than the trigger threshold voltage, so as to switch the switching power supply from the discontinuous conduction mode to the super-audio mode, and the switching power supply controller is used to insert an active discharge interval before the start of the next switching cycle to turn on the synchronous switch, so as to limit the switching frequency to above the audio range. The audio noise suppression circuit is further used to synchronously reduce the duration of the threshold period to introduce feedforward when the switching power supply switches from the discontinuous conduction mode to the super-audio mode.

7. The switching power supply according to claim 6, wherein: The audio noise suppression circuit comprises: a comparator, configured to compare the output voltage with the trigger threshold voltage and output a comparison result; a timing circuit configured to start timing at a charging period of the switching period, and stop timing when the timing reaches the threshold period, thereby generating a timing signal; and The mode switching circuit is configured to receive the timing signal and the comparison result, wherein the mode switching circuit is used to provide the mode switching signal to the switching power supply controller when the timing signal is received and the comparison result indicates that the output voltage is higher than the trigger threshold voltage.

8. The switching power supply according to claim 6, wherein: The threshold period is used to indicate the lowest frequency of the switching power supply, and the frequency is above the audio range.

9. The switching power supply according to claim 6, wherein: The active discharge interval is of fixed duration.

10. The switching power supply according to claim 7, wherein: The timing circuit is configured to synchronously reduce the duration of the threshold period to introduce feed-forward when the switching power supply switches from the discontinuous conduction mode to the super-audio mode.

11. The switching power supply according to claim 10, wherein: The timing circuit comprises: a first current source configured to provide a first current to the first node; a second current source configured to provide a second current to the first node; A first capacitor, a first end of which is coupled to the first node and a second end of which is grounded; a first switch connected across the first capacitor and having a current terminal coupled between the first node and ground; A first comparator, having a positive input terminal coupled to the first node, a negative input terminal for receiving a reference voltage, and an output terminal for outputting the timing signal; and a monostable trigger, used for controlling the on and off of the first switch based on the comparison result, The first current source is started only when the switching power supply is in the super audio mode, and the second current source is started when the switching power supply is in both modes.

12. The switching power supply according to claim 11, wherein: The current value of the first current is Proportional to, wherein Vin is the input voltage of the switching power supply, and Vout is the output voltage of the switching power supply.

13. The switching power supply according to claim 12, wherein: The first current source comprises: A first resistor, a first end of which is coupled to the input voltage; a diode, an anode of which is coupled to the second end of the first resistor; a first operational amplifier, having a positive input terminal coupled to an intermediate node between the first resistor and the diode, a negative input terminal coupled to the output voltage, and an output terminal coupled to a cathode of the diode; A second resistor, a first end of which is coupled to the output voltage; a first transistor, a source of which is coupled to the second end of the second resistor, and a drain of which is coupled to the output end of the first current; a second operational amplifier, having a positive input terminal coupled to an intermediate node between the second resistor and the first transistor, a negative input terminal coupled to an output terminal of the first operational amplifier, and an output terminal coupled to a gate of the first transistor; a third resistor, a first end of which is grounded; a second transistor, a source of which is coupled to the second end of the third resistor, and a drain of which is coupled to the output end of the first current; and The third operational amplifier has a positive input terminal coupled to the output voltage, an auxiliary terminal coupled to an intermediate node between the third resistor and the second transistor, and an output terminal coupled to the gate of the second transistor.

14. The switching power supply according to claim 6, wherein: Also includes: A voltage-dividing resistor network, used to obtain a voltage-dividing value of the output voltage; as well as The error amplifier is configured to perform error amplification on the voltage division value of the output voltage and the reference voltage, and the switching power supply controller drives the main switch and the synchronous switch according to the output control of the error amplifier.

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