Zero-crossing detection circuit, zero-crossing detection method and switching power supply circuit

Abstract

The present application discloses a zero-crossing detection circuit, a zero-crossing detection method, and a switching power supply circuit. The zero-crossing detection circuit is used to provide a zero-crossing indication signal according to a signal to be detected. The signal to be detected responds to an inductor current provided by an inductor. The inductor is charged when a power switch tube is turned on and discharges to achieve freewheeling when the power switch tube is turned off. The zero-crossing detection circuit includes: a detection unit that determines whether the inductor current has dropped to zero according to a zero-crossing reference value and the signal to be detected, and provides a zero-crossing indication signal representing the determination result; and an adjustment signal generation unit that is used to detect the freewheeling time of the inductor and adjust the zero-crossing reference value according to the freewheeling time. The present application can optimize the zero-crossing detection function under different output voltages of the switching power supply circuit to prevent abnormalities such as interference and detection failure.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and more particularly, to a zero-crossing detection circuit, a zero-crossing detection method, and a switching power supply circuit. Background Art

[0002] In some circuits, the characteristic that an inductor impedes current change is often utilized to achieve some functions. For example, in a switching power supply circuit, the inductor can be charged during the conduction stage of the power driving transistor to make the current flowing through the inductor reach the peak value, and during the turn-off stage of the power driving transistor, the inductor discharges the load capacitor, so that the output voltage across the load capacitor can be maintained within an allowable range. Therefore, by detecting whether the current flowing through the inductor crosses zero during the turn-off stage of the power driving transistor, combining the circuit topology to estimate the output voltage across the load capacitor and the current flowing through the inductor, the inductor current zero-crossing detection can also be used to indicate whether it is necessary to turn on the power driving transistor to recharge the inductor again, and / or to indicate the overvoltage condition of the output voltage to achieve overvoltage protection.

[0003] Traditional inductor current zero-crossing detection schemes usually obtain a signal to be detected responsive to the inductor current by using an auxiliary winding, capacitive coupling, or a voltage division network, and use a zero-crossing comparator to compare the signal to be detected with a fixed zero-crossing reference value to obtain a detection result for characterizing whether the inductor current crosses zero.

[0004] The problems existing in the above traditional scheme are as follows: If the sensitivity of the zero-crossing detection is set relatively high, when the output voltage across the load capacitor is relatively high, the change amplitude of the inductor current is relatively large, resulting in the signal to be detected being prone to glitches. The glitches on the signal to be detected will cause the output signal of the zero-crossing comparator to flip erroneously under the condition of relatively high sensitivity of the zero-crossing detection, resulting in an incorrect zero-crossing detection result and easily triggering overvoltage protection, that is, the anti-interference ability of the zero-crossing detection is weak; if the sensitivity of the zero-crossing detection is set relatively low, then the output signal of the zero-crossing comparator will flip only when the signal to be detected differs greatly from the zero-crossing reference value. However, when the output voltage across the load capacitor is very low, the change amplitude of the inductor current is relatively small, and it is difficult for the signal to be detected to have a large difference from the zero-crossing reference value. Therefore, it may lead to the inability to detect whether the inductor current crosses zero, that is, the zero-crossing detection function is abnormal. Summary of the Invention

[0005] In view of the above problems, an object of the present invention is to provide a zero-crossing detection circuit, a zero-crossing detection method, and a switching power supply circuit, which can adjust the zero-crossing reference value according to the freewheeling time of the inductor current to realize the adjustment of the sensitivity of the zero-crossing detection circuit. Since the freewheeling time of the inductor current is related to the amplitude of the output voltage, the technical solution provided by the present invention can adaptively adjust the sensitivity of the zero-crossing detection circuit under different output voltages to prevent glitch interference and avoid abnormal operation caused by the failure to detect the zero-crossing.

[0006] According to a first aspect of the present invention, there is provided a zero-crossing detection circuit for providing a zero-crossing indication signal according to a signal to be detected, the signal to be detected responding to an inductor current provided by an inductor, the inductor being charged when a power switch is turned on and discharging to realize freewheeling when the power switch is turned off, the power switch being used to convert an input voltage into an output voltage, characterized in that the zero-crossing detection circuit includes: a detection unit for judging whether the inductor current has dropped to zero according to a zero-crossing reference value and the signal to be detected, and providing the zero-crossing indication signal representing the judgment result; and an adjustment signal generation unit for detecting the freewheeling time of the inductor and adjusting the zero-crossing reference value according to the freewheeling time.

[0007] Optionally, when the freewheeling time detected by the adjustment signal generation unit is short, the output voltage is high, and the adjustment signal generation unit adjusts the zero-crossing reference value to lower the sensitivity of the zero-crossing detection circuit; when the freewheeling time detected by the adjustment signal generation unit is long, the output voltage is low, and the adjustment signal generation unit adjusts the zero-crossing reference value to increase the sensitivity of the zero-crossing detection circuit.

[0008] Optionally, as the freewheeling time increases, the adjustment signal generation unit continuously or stepwise lowers the zero-crossing reference value.

[0009] Optionally, as the freewheeling time increases, the adjustment signal generation unit stepwise lowers the zero-crossing reference value. When the freewheeling times at different moments are in the same time interval among a plurality of preset time intervals, the corresponding zero-crossing reference values are the same. The length of each time interval is a fixed value, or is positively correlated with the peak current of the inductor current corresponding to this time interval, or is negatively correlated with the amplitude of the output voltage corresponding to this time interval.

[0010] Optionally, when the power switch tube is turned off, the regulation signal generation unit starts timing from an initial value to obtain a timing signal, and adjusts the zero-crossing reference value according to the timing signal. When the zero-crossing indication signal indicates that the inductor current has dropped to zero, the regulation signal generation unit stops timing, and the timing signal represents the freewheeling time experienced by the inductor since the power switch tube was turned off.

[0011] Optionally, the regulation signal generation unit adjusts the zero-crossing reference value according to the comparison result between the timing signal and at least one reference time value, so that the zero-crossing reference value decreases step by step as the freewheeling time increases.

[0012] Optionally, the detection unit includes: a conversion module that converts the signal to be detected into a resonant sampling voltage according to a conversion coefficient; a reference voltage generation module for generating a first reference voltage; and a comparison module that provides the zero-crossing indication signal according to the comparison result between the resonant sampling voltage and the first reference voltage, where the zero-crossing reference value is positively correlated with the first reference voltage and negatively correlated with the conversion coefficient.

[0013] Optionally, the regulation signal generation unit includes: a first current source that provides a charging current; a first capacitor, the first end of which starts to receive the charging current when the power driving tube is turned off to provide a timing voltage for characterizing the freewheeling time, and is reset to an initial potential characterizing the initial value when the zero-crossing indication signal indicates that the inductor current has dropped to zero. The regulation unit adjusts the first reference voltage and / or the conversion coefficient according to the timing voltage or the digital signal corresponding to the timing voltage to adjust the zero-crossing reference value.

[0014] Optionally, the conversion module is coupled to the second end of the power driving tube to be coupled to the current output end of the inductor to obtain the signal to be detected.

[0015] Optionally, the conversion module includes a second capacitor and a first resistor connected in series between the second end of the power driving tube and the reference ground. The node where the second capacitor and the first resistor are connected provides the resonant sampling voltage, and the conversion coefficient is positively correlated with the product of the capacitance value of the second capacitor and the resistance value of the first resistor.

[0016] Optionally, the regulation signal generation unit provides a corresponding first regulation signal according to the freewheeling time, where the capacitance value of the second capacitor and / or the resistance value of the first resistor continuously increases or increases step by step under the control of the first regulation signal as the freewheeling time increases.

[0017] Optionally, the conversion module includes a second resistor and a third resistor connected in series between the second end of the power driving transistor and the reference ground in sequence, a node where the second resistor and the third resistor are connected provides the resonant sampling voltage, and the conversion coefficient is negatively correlated with the resistance ratio of the second resistor to the third resistor.

[0018] Optionally, the adjustment signal generation unit provides a corresponding second adjustment signal according to the freewheeling time, and the resistance value of the second resistor and / or the third resistor is controlled by the second adjustment signal. Wherein, under the action of the second adjustment signal, the resistance ratio of the second resistor to the third resistor continuously decreases or decreases step by step as the freewheeling time increases.

[0019] Optionally, the adjustment signal generation unit provides a corresponding third adjustment signal according to the freewheeling time, and the reference voltage generation module is controlled by the third adjustment signal to provide the variable first reference voltage. Wherein, the first reference voltage continuously decreases or decreases step by step as the freewheeling time increases.

[0020] Optionally, the conversion module is connected to the control end of the power driving transistor to be coupled with the current output end of the inductor and obtain the signal to be detected.

[0021] Optionally, the conversion module includes: an enable switch that conducts alternately with the power driving transistor; a detection resistor unit connected in series with the enable switch between the control end of the power driving transistor and the reference ground, and the conversion coefficient is positively correlated with the resistance value of the detection resistor unit. Wherein, when the enable switch conducts, under the coupling action of the control end of the power driving transistor and the current output end of the inductor, the control end of the power driving transistor provides the resonant sampling voltage according to the signal to be detected.

[0022] Optionally, the conversion module further includes a clamping element connected in parallel with the detection resistor unit. When the power driving transistor is turned off, the clamping element clamps the resonant sampling voltage so that the resonant sampling voltage does not exceed a set threshold and the power driving transistor cannot be turned on.

[0023] Optionally, the adjustment signal generation unit provides a corresponding fourth adjustment signal according to the freewheeling time, and the resistance value of the detection resistor unit is controlled by the fourth adjustment signal. Wherein, the total resistance value of the detection resistor unit continuously increases or increases step by step as the freewheeling time increases.

[0024] Optionally, the detection resistor unit includes a plurality of first detection resistors and a plurality of first detection switches. The first end of each first detection resistor is connected to the reference ground through a corresponding one of the first detection switches. The second ends of the plurality of first detection resistors are interconnected. The enable switch is connected in series between the first end of each first detection resistor and the reference ground, or in series between the common connection point of the second ends of the plurality of first detection resistors and the control end of the power driving transistor. A plurality of sub-signals of the fourth adjustment signal respectively control the conduction and cutoff of each first detection switch to adjust the total resistance value of the detection resistor unit.

[0025] Optionally, at the initial conduction moment of the enable switch, the plurality of first detection switches are all turned on under the control of the fourth adjustment signal. As the freewheeling time increases, the plurality of first detection switches are sequentially turned off by the corresponding sub-signals of the fourth adjustment signal.

[0026] Optionally, the detection resistor includes a plurality of second detection resistors and a plurality of second detection switches. The plurality of second detection resistors are sequentially connected in series between the control end of the power driving transistor and the reference ground. The connection nodes between every two second detection resistors are respectively connected to the reference ground through a corresponding one of the second detection switches. The enable switch is connected in series between the plurality of second detection resistors and the control end of the power driving transistor or in series between the plurality of second detection resistors and the reference ground. A plurality of sub-signals of the fourth adjustment signal respectively control the conduction and cutoff of each second detection switch to adjust the resistance value of the detection resistor.

[0027] Optionally, at the initial conduction moment of the enable switch, the plurality of second detection switches are all turned on under the control of the fourth adjustment signal. As the freewheeling time increases, the plurality of second detection switches are sequentially turned off by the corresponding sub-signals of the fourth adjustment signal.

[0028] Optionally, the comparison module includes: a first comparator, the positive-phase input terminal receives the first reference voltage, the negative-phase input terminal receives the resonant sampling voltage, and the output terminal provides the zero-crossing indication signal.

[0029] Optionally, it further includes a delay unit, which is connected to the output terminal of the first comparator to filter out the narrow pulses with a pulse width less than a preset pulse width in the zero-crossing indication signal.

[0030] Optionally, the adjustment unit provides a fifth adjustment signal to the delay unit according to the freewheeling time to adjust the preset pulse width, so that the preset pulse width is negatively correlated with the freewheeling time.

[0031] According to a second aspect of the present invention, there is provided a switching power supply circuit, comprising: a zero-crossing detection circuit as described in any one of the above; a load capacitor for providing the output voltage; the power driving transistor, the control end of which is controlled by a switching control signal; the inductor for providing an inductor current, and the inductor current flows from the current input end of the inductor to the current output end of the inductor; a driving circuit for providing the switching control signal according to the zero-crossing indication signal.

[0032] Optionally, it further comprises an auxiliary driving transistor, which is connected in series between the current output end of the inductor and the second end of the power driving transistor, and the control end of the auxiliary driving transistor receives a conduction voltage level for turning on the auxiliary driving transistor.

[0033] Optionally, the switching power supply circuit further comprises: a sampling resistor connected in series between the first end of the power driving transistor and the reference ground; and a current detection circuit coupled to the first end of the power driving transistor to obtain a current sampling voltage, and determining whether the inductor current has reached the current peak according to the current sampling voltage, and providing a peak indication signal representing the determination result, wherein the driving circuit provides the switching control signal according to the zero-crossing indication signal and the peak indication signal.

[0034] Optionally, the switching power supply circuit further comprises an overvoltage detection circuit for determining whether the output voltage exceeds an expected value according to the freewheeling time and an overvoltage reference value, and providing an overvoltage indication signal according to the determination result, and the overvoltage indication signal controls the driving circuit to adjust the duty cycle of the switching control signal, and / or controls the zero-crossing detection circuit to enable the zero-crossing detection circuit to adjust the zero-crossing reference value according to the overvoltage indication signal.

[0035] Optionally, when the overvoltage indication signal represents that the output voltage is less than the expected value, the zero-crossing reference value is equal to a first preset value, and when the overvoltage indication signal represents that the output voltage is greater than or equal to the expected value, the zero-crossing reference value is equal to a second preset value, and the first preset value is greater than the second preset value.

[0036] According to a third aspect of the present invention, there is also provided a zero-crossing detection method for providing a zero-crossing indication signal according to a signal to be detected, the signal to be detected responding to an inductor current provided by an inductor, the inductor being charged when a power switching transistor is turned on and discharging to achieve freewheeling when the power switching transistor is turned off, and the power switching transistor being used to convert an input voltage into an output voltage, characterized in that the zero-crossing detection method comprises: determining whether the inductor current has dropped to zero according to a zero-crossing reference value and the signal to be detected, and providing the zero-crossing indication signal representing the determination result; detecting the freewheeling time of the inductor; and adjusting the zero-crossing reference value according to the freewheeling time.

[0037] Optionally, when the detected freewheeling time is short, the output voltage is high, and the zero-crossing reference value is adjusted to reduce the sensitivity of zero-crossing detection. When the detected freewheeling time is long, the output voltage is low, and the zero-crossing reference value is adjusted to increase the sensitivity of zero-crossing detection.

[0038] Optionally, the step of adjusting the zero-crossing reference value includes: continuously reducing or stepwise adjusting the zero-crossing reference value as the freewheeling time increases.

[0039] Optionally, as the freewheeling time increases, the zero-crossing reference value is stepwise reduced. When the freewheeling time at different moments is in the same one of a plurality of preset time intervals, the corresponding zero-crossing reference values are the same. The length of each time interval is a fixed value, or is positively correlated with the peak current of the inductor current corresponding to this time interval, or is negatively correlated with the amplitude of the output voltage corresponding to this time interval. The output voltage is provided by the switching power supply circuit where the power switch tube and the inductor are located.

[0040] Optionally, the step of detecting the freewheeling time includes: when the power switch tube is turned off, starting timing from an initial value to obtain a timing signal, where the timing signal represents the freewheeling time experienced by the inductor since the power switch tube was turned off; and stopping timing when the zero-crossing indication signal indicates that the inductor current has dropped to zero.

[0041] Optionally, the step of adjusting the zero-crossing reference value includes: adjusting the zero-crossing reference value according to the comparison result between the timing signal and at least one reference time value, such that the zero-crossing reference value decreases stepwise as the freewheeling time increases.

[0042] Optionally, the step of providing the zero-crossing indication signal includes: converting the signal to be detected into a resonant sampling voltage according to a conversion coefficient; and providing the zero-crossing indication signal according to the comparison result between the resonant sampling voltage and a first reference voltage, where the zero-crossing reference value is positively correlated with the first reference voltage and negatively correlated with the conversion coefficient.

[0043] Optionally, the conversion coefficient continuously increases or stepwise increases as the freewheeling time increases.

[0044] Optionally, the first reference voltage continuously decreases or stepwise decreases as the freewheeling time increases.

[0045] Optionally, the step of adjusting the zero-crossing reference value includes: when the power driving transistor is turned off, starting to charge a first capacitor with a charging current so that a first end of the first capacitor provides a timing voltage for characterizing the freewheeling time; when the zero-crossing indication signal characterizes that the inductor current has dropped to zero, the first end of the first capacitor is reset to an initial potential characterizing the initial value; and adjusting the first reference voltage and / or the conversion coefficient according to the timing voltage or a digital signal corresponding to the timing voltage to adjust the zero-crossing reference value.

[0046] Optionally, a second end of the power driving transistor is coupled to a current output end of the inductor to provide the signal to be detected.

[0047] Optionally, the conversion coefficient is positively correlated with a time constant of a filter, an input end of the filter is coupled to the second end of the power driving transistor, and an output end of the filter provides the resonant sampling voltage.

[0048] Optionally, the conversion coefficient is a voltage division coefficient of a voltage division resistor network, an input end of the voltage division resistor network is coupled to the second end of the power driving transistor, and an output end of the voltage division resistor network provides the resonant sampling voltage.

[0049] Optionally, a control end of the power driving transistor is coupled to a current output end of the inductor to provide the signal to be detected.

[0050] Optionally, the conversion coefficient is a total resistance value of a detection resistor unit, the detection resistor unit is coupled between the current output end and a reference ground, and provides the resonant sampling voltage related to the total resistance value under the action of the signal to be detected.

[0051] Optionally, the step of providing the zero-crossing indication signal includes: delaying the zero-crossing indication signal to filter out narrow pulses with a pulse width less than a preset pulse width in the zero-crossing indication signal.

[0052] Optionally, the step of providing the zero-crossing indication signal further includes: adjusting the preset pulse width according to the freewheeling time so that the preset pulse width is negatively correlated with the freewheeling time.

[0053] According to the zero-crossing detection circuit, zero-crossing detection method, and switching power supply circuit provided by the embodiments of the present invention, the sensitivity of zero-crossing detection can be adjusted according to the freewheeling time of the inductor current, so as to be applicable to applications with relatively high and low output voltages of the switching power supply circuit. That is, when the detected freewheeling time is short, it indicates that the output voltage is high. At this time, the zero-crossing detection function can be adjusted to have a lower sensitivity, and the lower sensitivity can improve the anti-interference ability, thereby weakening or eliminating the influence of interference such as glitches. When the detected freewheeling time increases, it indicates that the output voltage is low. At this time, the sensitivity of the zero-crossing detection function can be increased, and the higher sensitivity can ensure that the zero-crossing moment of the inductor current can be detected, avoiding the occurrence of the failure of the zero-crossing detection function.

[0054] Therefore, the zero-crossing detection circuit, zero-crossing detection method, and switching power supply circuit provided by the embodiments of the present invention can adaptively complete zero-crossing detection at different output voltage amplitudes, enabling the switching power supply circuit to have strong anti-interference ability and stable zero-crossing detection function, and having a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Through the following description of the embodiments of the present invention with reference to the drawings, the above and other objects, features, and advantages of the present invention will become more apparent.

[0056] Figure 1 The circuit schematic diagram of the switching power supply circuit showing the embodiments of the present invention.

[0057] Figure 2 The circuit schematic diagram of the switching power supply circuit showing another embodiment of the present invention.

[0058] Figure 3 The schematic block diagram showing an implementation manner of the controller in the first embodiment of the present invention.

[0059] Figure 4 The waveform schematic diagram of some signals in the main circuit showing the embodiments of the present invention.

[0060] Figure 5 The relationship schematic diagram between the zero-crossing reference value and the freewheeling time showing the embodiments of the present invention.

[0061] Figure 6a The schematic circuit diagram showing an implementation manner of the zero-crossing detection circuit showing the embodiments of the present invention.

[0062] Figure 6b The schematic circuit diagram showing another implementation manner of the zero-crossing detection circuit showing the embodiments of the present invention.

[0063] Figures 7a to 7d The circuit schematic diagram showing various implementation manners of the conversion module showing the embodiments of the present invention.

[0064] Figure 8 shows Figure 7d a waveform schematic diagram of some signals in

[0065] Figure 9 shows Figure 6b a schematic circuit diagram of one implementation manner of the delay unit shown Detailed implementation manners

[0066] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the drawings, the same elements are denoted by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0067] The present invention can be presented in various forms, and some examples will be described below.

[0068] Figure 1 A circuit schematic diagram of the switching power supply circuit showing the first embodiment of the present invention.

[0069] As Figure 1 shown, the switching power supply circuit 1000 includes a main circuit 1100 and a controller 1200. Taking a buck structure as an example, the switching power supply circuit 1000 of this embodiment will be described below. However, the embodiments of the present invention are not limited thereto, and the basic concept of the present invention is equally applicable to switching power supply circuits of other structures, such as flyback structures, boost structures, etc.

[0070] 1. Main circuit

[0071] As Figure 1 shown, the main circuit 1100 of the switching power supply circuit may include a power driving transistor M1, a diode D1, an inductor L1, a load capacitor Cout, and a sampling resistor Rcs.

[0072] The first end of the power driving transistor M1 is connected to the first end of the sampling resistor Rcs, and the second end of the sampling resistor Rcs is grounded. The sampling resistor Rcs is in series with the power driving transistor M1, so the sampling voltage Vcs provided at the first end of the sampling resistor Rcs can represent the current flowing through the power driving transistor M1.

[0073] The second end of the power driving transistor M1 is connected to the anode of the diode D1 and the first end (current output end) of the inductor L1 at the switching node LX. The cathode of the diode D1 is connected to the positive input terminal of the input voltage (receiving the input voltage Vin) and the first end of the load capacitor Cout. The second end of the inductor L1 is connected to the second end of the load capacitor Cout, so that the voltage difference across the load capacitor Cout is equal to the output voltage Vout. Among them, the load capacitor Cout may be an equivalent capacitor provided by the subsequent circuit or an independently provided capacitor.

[0074] The power driving transistor M1 is, for example, an N-channel or P-channel field effect transistor. In this embodiment, an N-channel field effect transistor will be taken as an example for illustration, where: the first end of the power driving transistor M1 is the source electrode, the second end is the drain electrode, and the control end is the gate electrode.

[0075] As an alternative embodiment, as Figure 2 shown, the main circuit 1100 may further include an auxiliary driving transistor M2 connected in series between the first end of the power driving transistor M1 and the current output end of the inductor L1 (for example, connected to the switching node LX). The control end of the auxiliary driving transistor M2 receives a conduction level. The auxiliary driving transistor M2 is, for example, an N-channel field effect transistor, and the conduction level is, for example, the supply voltage VCC. Figure 2 The main circuit 1100 shown is Figure 1 basically the same as the main circuit shown except for the auxiliary driving transistor M2, and the same parts will not be described again.

[0076] Furthermore, Figure 4 a waveform schematic diagram of some signals in the main circuit of the embodiment of the present invention is shown. As Figure 4 shown, during the conduction stage of the power driving transistor M1 (for example, corresponding to the high level stage of the switching control signal GT), the inductor L1 stores energy so that the current flowing through the inductor L1 reaches the current peak value at the turn-off moment of the power driving transistor M1; during the turn-off stage of the power driving transistor (for example, corresponding to the low level stage of the switching control signal GT), the inductor L1 in the freewheeling state releases electrical energy to charge the load capacitor, and the inductor current flowing through the inductor L1 continuously decreases; when the inductor current drops to 0, the inductor L1 ends the freewheeling state and enters the resonance state. At this time, the residual energy in the inductor L1 will cause the inductor current to resonate, and the drain voltage VD and the gate voltage GT of the power driving transistor M1 will also resonate due to capacitive coupling; when the power driving transistor M1 conducts again (for example, conducts at the resonance valley), the inductor current rises again until it reaches the current peak value.

[0077] As Figure 1 and Figure 2 shown, if the voltage drop of the diode D1 is ignored, during the turn-off stage of the power driving transistor M1, the time Tdis experienced by the inductor current flowing through the inductor L1 from the peak value to 0 is approximately:

[0078] Tdis = L * Ipk / Vout

[0079] where, L represents the inductance of the inductor L1, Ipk represents the current peak value of the current flowing through the inductor L1, and Vout represents the output voltage. It can be seen that the higher the output voltage Vout, the shorter the freewheeling state duration (hereinafter referred to as the freewheeling time) Tdis of the inductor that can be detected. Therefore, the amplitude of the output voltage Vout can be estimated according to the freewheeling time Tdis of the inductor.

[0080] At the end of the freewheeling state of the inductor, that is, when the drain voltage of the power driving transistor M1 starts to resonate, the initial resonance amplitude corresponds to the output voltage Vout. Therefore, when the inductance L of the inductor L1 and the peak current Ipk flowing through the inductor L1 are fixed, the higher the output voltage Vout provided by the switching power supply circuit, the larger the initial resonance amplitude corresponding to the end of the freewheeling state, and the shorter the detectable freewheeling time Tdis; at the same time, when performing zero-crossing detection, the larger the resonance amplitude (for example, the change in the drain voltage VD of the power driving transistor M1), the easier it is to detect the change in the current signal / voltage signal, and thus the more accurately it can be detected whether the inductor current has reached 0.

[0081] 2. Controller

[0082] As Figure 1 shown, the controller 1200 of the switching power supply circuit is used to provide a switching control signal GT to the control terminal of the power driving transistor M1. The controller 1200 may include: a zero-crossing detection circuit 1210, a current detection circuit 1220, and a switching drive circuit 1230.

[0083] In the embodiment of the present invention, the controller 1200 can operate in the discontinuous conduction mode or the critical conduction mode. The discontinuous conduction mode means that after detecting that the inductor current provided by the inductor L1 drops to 0, a period of time is delayed and then the power driving transistor M1 is switched from the off state to the on state; the critical conduction mode means that when detecting that the current provided by the inductor L1 has dropped to 0, the power driving transistor M1 is immediately switched from the off state to the on state. Both of these operating modes need to use the zero-crossing detection circuit 1210 to know whether the inductor current flowing through the inductor L1 passes through zero.

[0084] 2.1 Current detection circuit

[0085] The current detection circuit 1220 is connected to the first end of the sampling resistor Rcs to receive the sampling voltage Vcs, and detects the sampling voltage Vcs to generate a peak indication signal Vpkd. The current detection circuit 1220 determines whether the current flowing through the power driving transistor M1 reaches the set peak value by detecting the amplitude of the sampling voltage Vcs, and provides a peak indication signal Vpkd according to the detection result. As an optional embodiment, the current detection circuit 1220 may include a voltage comparator for comparing the sampling voltage Vcs with the voltage representing the set peak value, so as to output a peak indication signal Vpkd in response to the comparison result.

[0086] 2.2 Zero-crossing detection circuit

[0087] The zero-crossing detection circuit 1210 is coupled to the inductor L1 (for example, connected to the drain or gate of the power driving transistor M1 to be coupled to the current output terminal / switching node LX of the inductor L1), so as to obtain a signal to be detected Vts that can characterize the inductor current flowing through the inductor L1, and is used to provide a zero-crossing indication signal Vzcd according to the signal to be detected Vts and a zero-crossing reference value ZRef. The zero-crossing indication signal Vzcd is used to characterize whether the inductor current flowing through the inductor L1 has dropped to 0.

[0088] The working principle of the zero-crossing detection circuit 1210 can be equivalently described as the following process, for example: when the signal to be detected Vts is less than the zero-crossing reference value ZRef, the zero-crossing detection circuit 1210 provides a valid zero-crossing indication signal Vzcd to indicate that the inductor current is detected to cross zero; when the signal to be detected Vts is greater than or equal to the zero-crossing reference value ZRef, the zero-crossing detection circuit 1210 provides an invalid zero-crossing indication signal Vzcd to indicate that the inductor current has not crossed zero. However, the embodiments of the present invention are not limited thereto.

[0089] When the zero-crossing indication signal Vzcd characterizes that the current flowing through the inductor L1 has dropped to 0 (crossed zero), it means that the inductor L1 can no longer provide sufficient energy, and the power driving transistor M1 needs to be turned on to increase the inductor current flowing through the inductor L1. Therefore, the zero-crossing indication signal Vzcd can be used to determine whether the power driving transistor M1 needs to start conducting.

[0090] In some embodiments, as Figure 1 shown, the zero-crossing detection circuit 1210 can be coupled to the gate of the power driving transistor M1, that is, the signal to be detected Vts can be the signal provided by the gate of the power driving transistor M1. Thus, the zero-crossing detection circuit 1210 can determine whether the inductor current flowing through the inductor L1 has dropped to 0 by detecting the voltage change occurring at the gate of the power driving transistor M1 under the coupling action of the gate-drain parasitic capacitance during the turn-off stage of the power driving transistor M1, and provide a corresponding zero-crossing indication signal Vzcd; in other embodiments, the zero-crossing detection circuit 1210 can be coupled to the drain of the power driving transistor M1, that is, the signal to be detected Vts can be the drain voltage VD provided by the power driving transistor M1. Thus, the zero-crossing detection circuit 1210 can determine whether the inductor current flowing through the inductor L1 has reached 0 according to the drain voltage VD, and provide a corresponding zero-crossing indication signal Vzcd.

[0091] In some embodiments, the output current and / or output voltage Vout of the switching power supply circuit 1000 can also be calculated according to the actual circuit topology and the zero-crossing indication signal Vzcd.

[0092] When the power driving transistor M1 is turned off (or when it is detected that the inductor current reaches the current peak), the zero-crossing detection circuit 1210 provided in the embodiment of the present invention starts timing from the initial value to detect the freewheeling time Tdis of the current inductor, and adjusts the zero-crossing reference value ZRef according to the detected freewheeling time Tdis.

[0093] According to the above analysis, the higher the output voltage Vout, the shorter the freewheeling time Tdis of the inductor, the larger the resonance amplitude of the inductor current, and the larger the change amplitude of the signal Vts to be detected representing the inductor current at the time of zero-crossing. Therefore, the change of the signal Vts to be detected is easier to detect. At this time, the zero-crossing reference value ZRef can be appropriately set to a larger value to improve the anti-interference ability; when the output voltage Vout is lower, the corresponding freewheeling time Tdis is longer, the resonance amplitude of the inductor current is smaller, and the change amplitude of the signal Vts to be detected at the time of zero-crossing is smaller. Therefore, the change of the signal to be detected is not easy to detect. At this time, the zero-crossing reference value ZRef can be appropriately set to a smaller value to improve the sensitivity.

[0094] The zero-crossing detection circuit 1210 provided in the embodiment of the present invention can detect the duration of the freewheeling state of the inductor to obtain the freewheeling time Tdis, and continuously lower the zero-crossing reference value ZRef as the detected freewheeling time Tdis gradually increases (such as Figure 5 The continuous adjustment method shown can be a linear adjustment method), or lower the zero-crossing reference value ZRef in segments (or called stepwise) (such as Figure 5 The segmented adjustment method shown or other non-linear adjustment methods), or lower the zero-crossing reference value ZRef in a linear-nonlinear hybrid adjustment manner, so as to continuously improve the sensitivity of the zero-crossing detection circuit 1210 to the change of the signal to be detected, making the zero-crossing of the inductor current easier to be detected by the zero-crossing detection circuit 1210.

[0095] In some embodiments of segmentally adjusting the zero-crossing reference value ZRef, referring to Figure 5For the curve corresponding to the segmented adjustment method, the interval of the freewheeling time Tdis corresponding to the same zero-crossing reference value ZRef can be a fixed time interval. However, the embodiments of the present invention are not limited thereto. In some other embodiments of segmentally adjusting the zero-crossing reference value ZRef, the interval of the freewheeling time Tdis corresponding to a zero-crossing reference value ZRef can be set according to the peak current of the inductor current. The duration of this interval is, for example, positively correlated with the peak current, that is, the larger the peak current, the wider the range of the freewheeling time Tdis corresponding to the corresponding zero-crossing reference value ZRef; in some other embodiments, the interval of the freewheeling time Tdis corresponding to a zero-crossing reference value ZRef can be set according to the amplitude of the output voltage. The duration of this interval is, for example, negatively correlated with the amplitude of the output voltage, that is, the higher the output voltage, the smaller the range of the freewheeling time Tdis corresponding to the corresponding zero-crossing reference value ZRef.

[0096] It should be noted that the embodiments of the present invention are not limited to directly comparing the signal representing the zero-crossing reference value ZRef with the signal to be detected. The zero-crossing reference value can be a value equivalent under the cooperative action of multiple signals.

[0097] 2.3 Switch driving circuit

[0098] The switch driving circuit 1230 is respectively connected to the current detection circuit 1220 and the zero-crossing detection circuit 1210, and is used to generate a switch control signal GT according to the peak indication signal Vpkd and the zero-crossing indication signal Vzcd. The turn-off control of the switch control signal GT for the power driving transistor M1 can respond to the peak indication signal Vpkd provided by the current detection circuit 1220, and the turn-on control of the switch control signal GT for the power driving transistor M1 can respond to the zero-crossing indication signal Vzcd provided by the zero-crossing detection circuit 1210. As an alternative embodiment, the edge of the level change (rising edge or falling edge) of the peak indication signal Vpkd is used to determine the falling edge of the switch control signal GT, and the edge of the level change of the zero-crossing indication signal Vzcd is used to determine the rising edge of the switch control signal GT, so that the power driving transistor M1 can be turned on and off at an appropriate moment under the control of the switch control signal GT.

[0099] As an alternative embodiment, as Figure 3 shown, the switch driving circuit 1230 may include a logic control unit 1231 and a driving output unit 1232. The logic control unit 1231 is used to generate a logic control signal Vgt_pre according to the logic levels of the peak indication signal Vpkd and the zero-crossing indication signal Vzcd, and the driving output unit 1232 is used to drive the logic control signal Vgt_pre to provide the corresponding switch control signal GT to the control end of the power driving transistor M1.

[0100] As a non - restrictive embodiment, the logic control unit 1231 can be implemented by an RS flip - flop. Among them, the set input terminal of the RS flip - flop can be connected to the zero - crossing detection circuit 1210 to receive the zero - crossing indication signal Vzcd, and the reset input terminal of the RS flip - flop can be connected to the current detection circuit 1220 to receive the peak indication signal Vpkd. The RS flip - flop provides a corresponding logic control signal Vgt_pre according to the peak indication signal Vpkd and the zero - crossing indication signal Vzcd.

[0101] As a non - restrictive embodiment, the drive output unit 1232 can include at least one cascaded buffer. The input terminal of the first - stage buffer receives the logic control signal Vgt_pre provided by the logic control unit 1231, and the output terminal of the last - stage buffer provides a corresponding switch control signal GT.

[0102] 2.4 Over - voltage detection circuit

[0103] As Figure 3 shown, in order to implement the functions of over - voltage detection and over - voltage protection, the controller 1200 can further include an over - voltage detection circuit 1240.

[0104] The over - voltage detection circuit 1240 can judge whether the output voltage provided by the switching power supply circuit 1000 exceeds the expected value according to the free - wheeling time Tdis of the inductor current provided by the zero - crossing detection circuit 1210 and a preset over - voltage reference value, and provide an over - voltage indication signal Vovd according to the judgment result. The over - voltage indication signal Vovd can be used to control the switch drive circuit 1230 (for example, control the logic control unit 1231) to adjust the duty cycle of the switch control signal GT, and / or control the zero - crossing detection circuit 1210 to enable the zero - crossing detection circuit to adjust the zero - crossing reference value ZRef according to the over - voltage indication signal Vovd.

[0105] According to the above analysis, since the amplitude of the output voltage Vout is negatively correlated with the free - wheeling time Tdis of the inductor current, and even in a proportional relationship, in some embodiments, the over - voltage detection circuit 1240 can compare the free - wheeling time Tdis provided by the zero - crossing detection circuit 1210 with the over - voltage reference value. When the free - wheeling time Tdis exceeds the maximum free - wheeling time Tdis_max characterized by the over - voltage reference value, it indicates that an over - voltage phenomenon has occurred in the switching power supply circuit 1000, that is, the output voltage Vout exceeds the expected value.

[0106] Further, in some embodiments, when the overvoltage indication signal indicates that no overvoltage phenomenon has occurred, that is, when the output voltage is less than the expected value, the zero-crossing detection circuit 1210 can set the zero-crossing reference value ZRef to a first preset value (the initial default value of the zero-crossing reference value) under the control of the overvoltage indication signal; when the overvoltage indication signal indicates that an overvoltage phenomenon has occurred, that is, when the output voltage is greater than or equal to the expected value, the zero-crossing detection circuit can set the zero-crossing reference value ZRef to a second preset value under the control of the overvoltage indication signal, and the second preset value is less than the first preset value, thereby realizing the switching of the two zero-crossing reference values and simply realizing the segmented adjustment of the zero-crossing reference value ZRef.

[0107] The working process of the switching power supply circuit of this embodiment will be described below based on Figure 4 the above.

[0108] The first stage: When the switch control signal GT is in the effective level state (in this embodiment, the switch control signal GT is at a logic high level in the effective level state), the power driving transistor M1 is turned on, and the positive input voltage terminal forms a current path to ground through the load, the inductor L1, the power driving transistor M1, and the sampling resistor Rcs. The inductor current flowing through the inductor L1 continuously increases, and the inductor L1 stores energy. The sampling resistor Rcs provides a sampling voltage CS representing the inductor current.

[0109] The second stage: When the sampling voltage CS across the sampling resistor Rcs reaches the voltage value corresponding to the set peak value of the inductor current, the switch control signal GT output by the controller 1200 changes from the effective level state to the ineffective level state (in this embodiment, the switch control signal GT is at a logic low level in the ineffective level state), causing the power driving transistor M1 to turn off. The inductor current flowing through the inductor L1 continues to flow through the diode D1, and the zero-crossing detection circuit 1210 starts timing to detect the freewheeling time Tdis of the inductor. At this time, the inductor L1, the diode D1, and the output capacitor Cout form a freewheeling loop, and the inductor L1 releases energy to the output capacitor Cout, and the inductor current flowing through the inductor L1 gradually decreases; as the detected freewheeling time Tdis continuously increases, the zero-crossing detection circuit 1210 adjusts the zero-crossing reference value ZRef to adjust the sensitivity of the zero-crossing detection.

[0110] The third stage: After the inductor current flowing through the inductor L1 drops to zero, resonance will occur at the second terminal (drain) of the power driving transistor M1. Therefore, the zero-crossing detection circuit 1210 can determine whether the inductor current flowing through the inductor L1 reaches 0 by detecting the signal to be detected Vts (for example, the drain voltage of the power driving transistor M1); when the zero-crossing detection circuit 1210 detects that the inductor current reaches 0 (critical conduction mode) or later (discontinuous conduction mode), the drive circuit 1230 can output a switch control signal GT in the effective level state to turn on the power driving transistor M1.

[0111] The switching power supply circuit operates in a cycle according to the order of the above first to third stages, so as to be able to adaptively maintain the output voltage Vout at a constant voltage value.

[0112] Figure 6a A schematic circuit diagram showing an implementation manner of the zero-crossing detection circuit according to an embodiment of the present invention. Figure 6b A schematic circuit diagram showing another implementation manner of the zero-crossing detection circuit according to an embodiment of the present invention.

[0113] As Figure 6a and Figure 6b shown, the zero-crossing detection circuit according to an embodiment of the present invention may include a detection unit and an adjustment signal generation unit 1214. The detection unit may include a conversion module 1211, a reference voltage generation module 1212, and a comparator 1213. In some embodiments (as Figure 6b shown), the zero-crossing detection circuit 1210 may further include a delay unit 1215 for filtering narrow pulses.

[0114] The reference voltage generation module 1212 is used to generate a first reference voltage Vref1.

[0115] The conversion module 1211 is coupled to the current output terminal of the inductor L1 (as Figure 1 and Figure 2 shown) to obtain a signal to be detected Vts (for example, the drain voltage VD of the power driving transistor M1 or the signal GT provided to the gate), and convert the signal to be detected according to a conversion coefficient k to convert the signal to be detected into a resonant sampling voltage Vtr, where k is a positive number.

[0116] Hereinafter, the embodiments of the present invention will be described based on Vtr = k * Vts. However, the embodiments of the present invention are not limited thereto, and the resonant sampling voltage Vtr may also be positively correlated with the ratio Vts / k between the signal to be detected and the conversion coefficient.

[0117] The adjustment signal generation unit 1214 is used to start timing from an initial value when the power driving transistor M1 is turned off to detect the freewheeling time Tdis of the inductor L1, and generate an adjustment signal according to the detected freewheeling time Tdis (for example, Figure 6a and Figure 6b the adjustment signals ST1 to ST3 shown). The adjustment signal acts on the reference voltage generation module 1212 to adjust the first reference voltage Vref1, and / or acts on the conversion module 1211 to adjust the conversion coefficient k, so as to realize the adjustment of the zero-crossing reference value ZRef.

[0118] For example, the regulation signal generation unit 1214 may provide a regulation signal ST2 according to the freewheeling time Tdis, and the reference voltage generation module 1212 is controlled by the regulation signal ST2 to provide a variable first reference voltage Vref1, where the first reference voltage Vref1 continuously decreases or decreases stepwise as the freewheeling time Tdis increases.

[0119] As an alternative embodiment, the regulation signal generation unit 1214 may include: a first current source for providing a first charging current and a first capacitor. The first end of the first capacitor starts to receive the first charging current when the power driving transistor M1 is turned off to provide a timing voltage for characterizing the freewheeling time Tdis, and is reset to an initial potential characterizing the initial value when the zero-crossing indication signal Vzcd characterizes that the inductor current has dropped to zero. In the regulation signal generation unit 1214, a timing control signal may be generated according to the drain voltage VD of the power driving transistor or other signals capable of characterizing whether the inductor is in the freewheeling stage, and the charging and resetting of the first capacitor are controlled according to the timing control signal. The regulation signal generation unit 1214 may adjust the zero-crossing reference value Vref according to the timing voltage or the digital signal corresponding to the timing voltage.

[0120] The comparator 1213 is used to provide a zero-crossing indication signal Vzcd according to the comparison result of the resonant sampling voltage Vtr and the first reference voltage Vref1.

[0121] As one embodiment, as Figure 6a shown, the positive input terminal of the comparator 1213 receives the first reference voltage Vref1, the negative input terminal receives the resonant sampling voltage Vtr, and the output terminal directly provides the zero-crossing indication signal Vzcd.

[0122] As another embodiment, as Figure 6b shown, the positive input terminal of the comparator 1213 receives the first reference voltage Vref1, the negative input terminal receives the resonant sampling voltage Vtr, and the output terminal provides the zero-crossing indication signal Vzcd through the delay unit 1215. The delay unit 1215 is used to filter out the narrow pulses (pulse width less than the preset pulse width) in the zero-crossing indication signal Vzcd to avoid erroneously indicating zero-crossing.

[0123] The regulation signal generation unit 1214 may also provide a regulation signal ST3 according to the freewheeling time Tdis, and the regulation signal ST3 acts on the delay unit 1215 to adjust the preset pulse width. The preset pulse width is, for example, negatively correlated with the freewheeling time Tdis, that is, the shorter the freewheeling time Tdis, the more the zero-crossing detection circuit needs to improve the anti-interference ability against interference such as glitches, so the preset pulse width can be longer.

[0124] The zero-crossing reference value ZRef in this embodiment is defined exemplarily below. As can be analyzed from the above, the condition for the zero-crossing detection circuit 1210 to output a valid zero-crossing indication signal Vzcd is:

[0125] Vts < ZRef (1)

[0126] In the zero-crossing detection circuit of the embodiment of the present invention, the condition for the comparator 1213 to output a valid zero-crossing indication signal Vzcd is:

[0127] Vtr < Vref1 (2)

[0128] According to the function of the conversion module 1211 in this embodiment, it can be known that:

[0129] Vtr = Vts * k (3)

[0130] Substituting equation (3) into inequality (2), we get:

[0131]

[0132] Combining inequalities (1) and (4), it can be known that the zero-crossing reference value ZRef for determining whether zero-crossing occurs in this embodiment is ZRef = Vref1 / k, that is, the zero-crossing reference value ZRef is a design parameter limited by the first reference voltage Vref1 and the conversion coefficient k. When adjusting the zero-crossing reference value ZRef, only the first reference voltage Vref1 and / or the conversion coefficient k need to be adjusted, and there is no need to generate the zero-crossing reference value ZRef by using a circuit structure.

[0133] Figure 9 shows Figure 6b A schematic circuit diagram of an implementation manner of the shown delay unit.

[0134] As Figure 9 shown, the delay unit 1215 may include: a current source CS2, a capacitor C10, a reset switch M10, a comparator U0, and an inverter INV0. The current source CS2 is used to provide a constant or charging current Ics2 that changes according to a preset trend; the capacitor C10 is connected in series between the current output terminal of the second current source CS2 and the reference ground; the reset switch M10 is connected in parallel with the capacitor C10, and the control end of the reset switch is connected to the output end of the comparator U0; the positive input terminal of the comparator U0 receives the second reference voltage Vref2 representing the preset pulse width, the negative input terminal is connected to the non-ground terminal of the capacitor C10, and the output terminal provides the zero-crossing indication signal Vzcd.

[0135] The output terminal of the comparator 1213 outputs the zero-crossing indication signal Vzcd through the delay unit 1215. The input terminal of the inverter INV0 is connected to the output terminal of the comparator 1213, and the output terminal of the inverter INV0 is connected to the control end of the reset switch M10.

[0136] Taking the reset switch M10 as an N-channel transistor as an example for illustration, however, the embodiments of the present invention are not limited thereto. The reset switch M10 may also be a P-channel transistor. Those skilled in the art can add the inverter INV0 or omit the inverter INV0 according to different types of transistors, or other structures with switching functions can also be used to implement the reset switch M10 and its corresponding functions.

[0137] When the first reference voltage Vref1 is less than or equal to the resonant sampling voltage Vtr, the comparator 1213 outputs a low-level logic, and the inverter INV0 outputs a high-level logic to turn on the reset switch M10, so that the voltage Vc at the non-ground end of the capacitor C10 is reset to the reference ground.

[0138] When the first reference voltage Vref1 is greater than the resonant sampling voltage Vtr, the comparator 1213 outputs a high-level logic, and the inverter INV0 outputs a low-level logic to turn off the reset switch M10. The current source CS2 starts to charge the capacitor C10, so that the voltage Vc at the non-ground end of the capacitor C10 starts to rise from the reference ground. And when the voltage Vc rises to be greater than the second reference voltage Vref2, it indicates that the pulse width output by the comparator 1213 is greater than the preset pulse width characterized by the second reference voltage Vref2, and the comparator U0 outputs a high-level logic zero-crossing indication signal Vzcd.

[0139] Figure 9 The above-mentioned delay unit 1215 shown delays the output signal of the comparator 1213 to provide a delayed zero-crossing indication signal Vzcd, thereby filtering out the narrow pulses with a pulse width less than the preset pulse width in the zero-crossing indication signal Vzcd.

[0140] It should be noted that Figure 9 The circuit structure shown is only one implementation manner of the delay unit 1215, and the delay unit can still be implemented by other circuit structures. For example, in some other embodiments, the positive input terminal and the negative input terminal of the comparator U0 can be interchanged and the corresponding circuit structure can be adjusted accordingly. The inverter INV0 can be omitted or replaced with a buffer, etc.

[0141] As an optional embodiment, the adjustment signal generation unit 1214 can provide an adjustment signal ST3 to the delay unit 1215 according to the freewheeling time Tdis, so that at least one of the amplitude of the charging current Ics2, the capacitance value of the capacitor C10, and the second reference voltage Vref2 changes to adjust the preset pulse width for filtering out narrow pulses. The preset pulse width, for example, decreases as the freewheeling time Tdis increases, that is, the preset pulse width is negatively correlated with the freewheeling time.

[0142] Figures 7a to 7dA circuit schematic diagram showing various implementation manners of the conversion module according to an embodiment of the present invention.

[0143] As Figure 7a and 7b shown, the conversion module 1211 can be connected to the drain of the power driving transistor M1 (the conversion module can also be connected to the drain of the power driving transistor M1 through other resistors or capacitors) to be coupled to the current output terminal of the inductor L1 and obtain the signal to be detected (drain voltage VD).

[0144] Implementation manner 1 of the conversion module 1211

[0145] In Figure 7a the shown implementation manner, the conversion module 1211 can be a filter (for example, a high-pass filter). The conversion coefficient k of the conversion module 1211 is positively correlated with the RC time constant of the filter. The filter can filter the signal to be detected Vts to reduce the resonance amplitude of the signal to be detected; when the first reference voltage Vref1 remains unchanged, by increasing the RC time constant, the zero-crossing reference value ZRef can be reduced.

[0146] As a specific embodiment, as Figure 7a shown, the conversion module 1211 includes a capacitor Ca and a resistor Ra connected in series between the drain of the power driving transistor M1 and the reference ground in sequence. The node where the capacitor Ca and the resistor Ra are connected provides the resonance sampling voltage Vtr. Since the RC time constant of the filter is equal to the product of the capacitance value of the capacitor Ca and the resistance value of the resistor Ra, the conversion coefficient k is positively correlated with the capacitance value of the capacitor Ca and the resistance value of the resistor Ra.

[0147] The adjustment signal generation unit 1214 provides a corresponding adjustment signal ST1 according to the freewheeling time Tdis. The capacitance value of the capacitor Ca and / or the resistance value of the resistor Ra is controlled by the adjustment signal ST1, so that the capacitance value of the capacitor Ca and / or the resistance value of the resistor Ra continuously increases or increases step by step as the freewheeling time Tdis increases.

[0148] Implementation manner 2 of the conversion module 1211

[0149] In Figure 7b the shown implementation manner, the conversion module 1211 can be a voltage division network (for example, implemented by multiple resistors). The conversion coefficient k of the conversion module 1211 is related to the voltage division coefficient of the voltage division network.

[0150] As a specific embodiment, as Figure 7b shown, the conversion module 1211 includes a resistor Rb1 and a resistor Rb2 connected in series between the drain of the power driving transistor M1 and the reference ground in sequence. The node where the resistor Rb1 and the resistor Rb2 are connected provides the resonance sampling voltage Vtr. The conversion coefficient k is negatively correlated with the ratio of the resistance values of the resistor Rb1 and the resistor Rb2.

[0151] The regulation signal generation unit 1214 provides a corresponding regulation signal ST1 according to the freewheeling time Tdis, and the resistance values of the resistor Rb1 and / or the resistor Rb2 are controlled by the regulation signal ST1, so that the resistance ratio of the resistor Rb1 to the resistor Rb2 continuously decreases or decreases stepwise as the freewheeling time Tdis increases.

[0152] In some other embodiments, such as Figure 7c and 7d shown, the conversion module 1211 may be connected to the gate of the power driving transistor M1 (the conversion module may also be connected to the gate of the power driving transistor M1 through other resistors or capacitors) to be coupled to the current output terminal of the inductor L1 and obtain a signal to be detected.

[0153] The third implementation manner of the conversion module 1211

[0154] In Figure 7c the implementation manner shown, the conversion module 1211 includes an enable switch Mc1 and a detection resistor unit, and may further include a clamping element Mc2.

[0155] The enable switch Mc1 conducts alternately with the power driving transistor M1, and the control terminal of the enable switch Mc1 is controlled by, for example, the inverted signal of the switch control signal GT. The enable switch Mc1 may be implemented by a transistor such as a field effect transistor.

[0156] The detection resistor unit is connected in series with the enable switch Mc1 between the gate of the power driving transistor M1 and the reference ground, and the conversion coefficient k of the conversion module 1211 is related to the total resistance value of the detection resistor unit. Among them, when the enable switch Mc1 conducts, under the coupling effect (for example, generated by the gate-drain parasitic capacitance of the power driving transistor M1) between the gate of the power driving transistor M1 and the current output terminal of the inductor L1, the gate of the power driving transistor M1 provides a signal to be detected, so that the gate voltage of the power driving transistor M1 can be detected as the resonant sampling voltage Vtr.

[0157] The clamping element Mc2 is connected in parallel with the detection resistor unit. When the switch control signal GT turns off the power driving transistor M1, the clamping element Mc2 limits the gate voltage of the power driving transistor M1 (i.e., the resonance sampling voltage Vtr), so that the gate voltage does not exceed the set threshold and cannot cause the power driving transistor M1 to be mis-conducted. The clamping element Mc2 can be implemented by a PNP-type triode or an NPN-type triode. For example, when a PNP-type triode is used as the clamping element Mc2, the emitter is connected to the first end of the detection resistor unit, and the base and collector are connected to the second end of the detection resistor unit. In some embodiments, the first end of the detection resistor unit can be coupled to the gate of the power driving transistor M1 through an enable switch Mc1, and the second end of the detection resistor unit is connected to the reference ground; in other embodiments, the first end of the detection resistor unit can be directly coupled to the gate of the power driving transistor M1, and the second end of the detection resistor unit is connected to the reference ground through an enable switch Mc1.

[0158] The regulation signal generation unit 1214 provides a corresponding regulation signal ST1 according to the freewheeling time Tdis, and the total resistance value of the detection resistor unit is controlled by the regulation signal ST1, so that the total resistance value of the detection resistor unit continuously increases or increases step by step as the freewheeling time Tdis increases.

[0159] As an alternative embodiment, as Figure 7c shown, the detection resistor unit may include a plurality of first detection resistors Rc_1 to Rc_n, and may also include a plurality of first detection switches Sc_1 to Sc_n, where n is a natural number greater than 1. In an alternative embodiment, the number of the first detection switches may be different from the number of the first detection resistors.

[0160] The first end of each first detection resistor is respectively connected to the reference ground through a corresponding first detection switch, and the second ends of the respective first detection resistors are interconnected. The enable switch Mc1 is connected in series between the first end of each first detection resistor and the reference ground, or in series between the common connection point of the second ends of the plurality of first detection resistors and the control end of the power driving transistor M1.

[0161] The regulation signal generation unit 1214 provides a signal for controlling the plurality of first detection switches. The signal includes a plurality of regulation signals ST1 (which can also be referred to as a plurality of sub-signals, and the plurality of sub-signals can be a plurality of analog signals or multi-bit data of digital signals). The plurality of regulation signals ST1 respectively control the conduction and turn-off of the corresponding first detection switches to adjust the total resistance value of the detection resistor unit.

[0162] As a preferred embodiment, at the initial conduction moment of the enabling switch Mc1, each first detection switch is turned on under the control of the corresponding adjustment signal ST1. As the freewheeling time Tdis increases, each first detection switch is turned off by a corresponding adjustment signal ST1 in sequence, so that the total resistance value of the detection resistance unit can increase step by step as the freewheeling time Tdis increases.

[0163] As another alternative embodiment, as Figure 7d shown, the detection resistance unit may include a plurality of second detection resistors Rd_1 to Rd_m, and may also include a plurality of second detection switches Sd_1 to Sd_m, where m is a natural number greater than 1. In an alternative embodiment, the number of second detection switches may be different from the number of first detection resistors.

[0164] The plurality of second detection resistors Rd_1 to Rd_m are connected in series between the control terminal of the power driving transistor M1 and the reference ground in sequence. The connection nodes between every two adjacent second detection resistors are respectively connected to the reference ground through a corresponding second detection switch. The enabling switch Mc1 is connected in series between the first second detection resistor Rd_1 and the control terminal of the power driving transistor M1 or in series between the last second detection resistor Rd_n and the reference ground.

[0165] The adjustment signal generation unit 1214 provides a plurality of adjustment signals ST1 (which may be a plurality of analog signals or multi-bit data of digital signals). The plurality of adjustment signals ST1 respectively control the conduction and cutoff of the corresponding second detection switches to adjust the total resistance value of the detection resistance unit.

[0166] As a preferred embodiment, as Figure 8 shown, when the enabling switch Mc1 is turned on, as the freewheeling time Tdis increases, the plurality of second detection switches are turned on and off in sequence under the control of the corresponding adjustment signals ST1[1:m], so that the total resistance value of the detection resistance unit can increase step by step as the freewheeling time Tdis increases.

[0167] The embodiment of the present invention also provides the above zero-crossing detection circuit and zero-crossing detection method.

[0168] According to the zero-crossing detection circuit, zero-crossing detection method, and switching power supply circuit provided by the embodiments of the present invention, the sensitivity of zero-crossing detection can be adjusted according to the freewheeling time of the inductor current, so as to be applicable to applications with relatively high and low output voltages of the switching power supply circuit. That is, when the detected freewheeling time is short, it indicates that the output voltage is high. At this time, the zero-crossing detection function can be adjusted to have a lower sensitivity, and the lower sensitivity can improve the anti-interference ability, thus weakening or eliminating the influence brought by interference such as glitches. When the detected freewheeling time increases, it indicates that the output voltage is low. At this time, the sensitivity of the zero-crossing detection function can be increased, and the higher sensitivity can ensure that the zero-crossing moment of the inductor current can be detected, avoiding the occurrence of the failure of the zero-crossing detection function.

[0169] Therefore, the zero-crossing detection circuit, zero-crossing detection method, and switching power supply circuit provided by the embodiments of the present invention can adaptively complete zero-crossing detection under different output voltage amplitudes, enabling the switching power supply circuit to have strong anti-interference ability and stable zero-crossing detection function, and having a wide range of applications.

[0170] As described above in accordance with the embodiments of the present invention, these embodiments do not elaborate on all details and do not limit the invention to only the specific embodiments. Obviously, according to the above description, many modifications and variations can be made. These embodiments are selected and specifically described in this specification 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 its modified use based on the present invention. The protection scope of the present invention should be defined by the scope of the claims of the present invention.

Claims

1. A zero-crossing detection circuit for providing a zero-crossing indication signal according to a signal to be detected, where the signal to be detected responds to an inductor current provided by an inductor. The inductor is charged when a power driving transistor is turned on and discharges to achieve freewheeling when the power driving transistor is turned off. The power driving transistor is used to convert an input voltage into an output voltage. Characterized in that, the zero-crossing detection circuit includes: a detection unit for judging whether the inductor current has dropped to zero according to a zero-crossing reference value and the signal to be detected, and providing the zero-crossing indication signal characterizing the judgment result; and an adjustment signal generation unit for detecting the freewheeling time of the inductor, adjusting the zero-crossing reference value according to the freewheeling time, and continuously or stepwise lowering the zero-crossing reference value as the freewheeling time increases.

2. The zero-crossing detection circuit according to claim 1, Characterized in that, when the freewheeling time detected by the adjustment signal generation unit is short, the output voltage is high, and the adjustment signal generation unit adjusts the zero-crossing reference value to lower the sensitivity of the zero-crossing detection circuit, when the freewheeling time detected by the adjustment signal generation unit is long, the output voltage is low, and the adjustment signal generation unit adjusts the zero-crossing reference value to increase the sensitivity of the zero-crossing detection circuit.

3. The zero-crossing detection circuit according to claim 1, Characterized in that, when the freewheeling times at different moments are in the same time interval among a preset plurality of time intervals, the corresponding zero-crossing reference values are the same, the length of each time interval is a fixed value, or is positively correlated with the peak current of the inductor current corresponding to this time interval, or is negatively correlated with the amplitude of the output voltage corresponding to this time interval.

4. The zero-crossing detection circuit according to claim 1, Characterized in that, the adjustment signal generation unit starts timing from an initial value when the power driving transistor is turned off to obtain a timing signal, and adjusts the zero-crossing reference value according to the timing signal, wherein, when the zero-crossing indication signal characterizes that the inductor current has dropped to zero, the adjustment signal generation unit stops timing, and the timing signal characterizes the freewheeling time experienced by the inductor since the power driving transistor was turned off.

5. The zero-crossing detection circuit according to claim 4, Characterized in that, the adjustment signal generation unit adjusts the zero-crossing reference value according to the comparison result of the timing signal and at least one reference time value, so that the zero-crossing reference value decreases stepwise as the freewheeling time increases.

6. The zero-crossing detection circuit according to claim 4, Characterized in that, the detection unit includes: a conversion module for converting the signal to be detected into a resonant sampling voltage according to a conversion coefficient; a reference voltage generation module for generating a first reference voltage; and a comparison module for providing the zero-crossing indication signal according to the comparison result of the resonant sampling voltage and the first reference voltage, wherein, the zero-crossing reference value is positively correlated with the first reference voltage and negatively correlated with the conversion coefficient.

7. The zero-crossing detection circuit according to claim 6, Characterized in that, The regulation signal generation unit includes: A first current source for providing a charging current; A first capacitor, whose first terminal starts to receive the charging current when the power driving transistor is turned off to provide a timing voltage for characterizing the freewheeling time, and is reset to an initial potential characterizing the initial value when the zero-crossing indication signal characterizes that the inductor current has dropped to zero; The regulation unit adjusts the first reference voltage and / or the conversion coefficient according to the timing voltage or the digital signal corresponding to the timing voltage to adjust the zero-crossing reference value.

8. The zero-crossing detection circuit according to claim 6, wherein, The conversion module is coupled to the second terminal of the power driving transistor to be coupled to the current output terminal of the inductor and obtain the signal to be detected.

9. The zero-crossing detection circuit according to claim 8, wherein, The conversion module includes a second capacitor and a first resistor connected in series between the second terminal of the power driving transistor and the reference ground in sequence. The node where the second capacitor and the first resistor are connected provides the resonant sampling voltage, and the conversion coefficient is positively correlated with the product of the capacitance value of the second capacitor and the resistance value of the first resistor.

10. The zero-crossing detection circuit according to claim 9, wherein, The regulation signal generation unit provides a corresponding first regulation signal according to the freewheeling time, wherein, the capacitance value of the second capacitor and / or the resistance value of the first resistor continuously increases or increases step by step with the increase of the freewheeling time under the control of the first regulation signal.

11. The zero-crossing detection circuit according to claim 8, wherein, The conversion module includes a second resistor and a third resistor connected in series between the second terminal of the power driving transistor and the reference ground in sequence. The node where the second resistor and the third resistor are connected provides the resonant sampling voltage, and the conversion coefficient is negatively correlated with the ratio of the resistance values of the second resistor and the third resistor.

12. The zero-crossing detection circuit according to claim 11, wherein, The regulation signal generation unit provides a corresponding second regulation signal according to the freewheeling time, and the resistance values of the second resistor and / or the third resistor are controlled by the second regulation signal, wherein, under the action of the second regulation signal, the ratio of the resistance values of the second resistor and the third resistor continuously decreases or decreases step by step with the increase of the freewheeling time.

13. The zero-crossing detection circuit according to claim 6, wherein, The regulation signal generation unit provides a corresponding third regulation signal according to the freewheeling time, and the reference voltage generation module is controlled by the third regulation signal to provide a variable first reference voltage, wherein, the first reference voltage continuously decreases or decreases step by step with the increase of the freewheeling time.

14. The zero-crossing detection circuit according to claim 6, wherein, The conversion module is connected to the control terminal of the power driving transistor to be coupled to the current output terminal of the inductor and obtain the signal to be detected.

15. The zero-crossing detection circuit according to claim 14, wherein, The conversion module includes: An enable switch, which conducts alternately with the power driving transistor; A detection resistance unit, which is connected in series with the enable switch between the control terminal of the power driving transistor and the reference ground. The conversion coefficient is positively correlated with the resistance value of the detection resistance unit. Wherein, when the enable switch conducts, under the coupling action between the control terminal of the power driving transistor and the current output terminal of the inductor, the control terminal of the power driving transistor provides the resonant sampling voltage according to the signal to be detected.

16. The zero-crossing detection circuit according to claim 15, characterized in that, The conversion module further includes a clamping element connected in parallel with the detection resistance unit. When the power driving transistor is turned off, the clamping element clamps the resonant sampling voltage so that the resonant sampling voltage does not exceed a set threshold and cannot turn on the power driving transistor.

17. The zero-crossing detection circuit according to claim 15, characterized in that, The adjustment signal generation unit provides a corresponding fourth adjustment signal according to the freewheeling time, and the resistance value of the detection resistance unit is controlled by the fourth adjustment signal. Wherein, the total resistance value of the detection resistance unit continuously increases or increases step by step as the freewheeling time increases.

18. The zero-crossing detection circuit according to claim 17, characterized in that, The detection resistance unit includes a plurality of first detection resistors and a plurality of first detection switches. The first end of each of the first detection resistors is respectively connected to the reference ground through a corresponding one of the first detection switches. The second ends of the plurality of first detection resistors are interconnected. The enable switch is connected in series between the first end of each of the first detection resistors and the reference ground, or in series between the common connection point of the second ends of the plurality of first detection resistors and the control terminal of the power driving transistor. A plurality of sub-signals of the fourth adjustment signal respectively control the conduction and turn-off of each of the first detection switches to adjust the total resistance value of the detection resistance unit.

19. The zero-crossing detection circuit according to claim 18, characterized in that, At the starting conduction moment of the enable switch, the plurality of first detection switches are all turned on under the control of the fourth adjustment signal. As the freewheeling time increases, the plurality of first detection switches are sequentially turned off by the corresponding sub-signals of the fourth adjustment signal.

20. The zero-crossing detection circuit according to claim 17, characterized in that, The detection resistor includes a plurality of second detection resistors and a plurality of second detection switches. The plurality of second detection resistors are sequentially connected in series between the control terminal of the power driving transistor and the reference ground. The connection nodes between every two of the second detection resistors are respectively connected to the reference ground through a corresponding one of the second detection switches. The enable switch is connected in series between the plurality of second detection resistors and the control terminal of the power driving transistor or in series between the plurality of second detection resistors and the reference ground. A plurality of sub-signals of the fourth adjustment signal respectively control the conduction and turn-off of each of the second detection switches to adjust the resistance value of the detection resistor.

21. The zero-crossing detection circuit according to claim 20, characterized in that, At the initial conduction moment of the enabling switch, the plurality of second detection switches are all turned on under the control of the fourth adjustment signal. As the freewheeling time increases, the plurality of second detection switches are sequentially turned off by corresponding sub-signals of the fourth adjustment signal.

22. The zero-crossing detection circuit according to claim 6, wherein, the comparison module includes: a first comparator, having its non-inverting input terminal receiving the first reference voltage, its inverting input terminal receiving the resonant sampling voltage, and its output terminal providing the zero-crossing indication signal.

23. The zero-crossing detection circuit according to claim 22, wherein, it further includes a delay unit connected to the output terminal of the first comparator to filter out narrow pulses in the zero-crossing indication signal having a pulse width less than a preset pulse width.

24. The zero-crossing detection circuit according to claim 23, wherein, the adjustment unit provides a fifth adjustment signal to the delay unit according to the freewheeling time to adjust the preset pulse width such that the preset pulse width is negatively correlated with the freewheeling time.

25. A switching power supply circuit, wherein, it includes: the zero-crossing detection circuit according to any one of claims 1 to 24; the power driving transistor, whose control terminal is controlled by a switching control signal; the inductor for providing an inductor current, and the inductor current flows from the current input terminal of the inductor to the current output terminal of the inductor; a driving circuit for providing the switching control signal according to the zero-crossing indication signal.

26. The switching power supply circuit according to claim 25, wherein, it further includes an auxiliary driving transistor, which is connected in series between the current output terminal of the inductor and the second terminal of the power driving transistor, and the control terminal of the auxiliary driving transistor receives a conduction level for turning on the auxiliary driving transistor.

27. The switching power supply circuit according to claim 25, wherein, it further includes: a sampling resistor connected in series between the first terminal of the power driving transistor and the reference ground; and a current detection circuit coupled to the first terminal of the power driving transistor to obtain a current sampling voltage, and judging whether the inductor current has reached the current peak value according to the current sampling voltage, and providing a peak indication signal representing the judgment result, wherein, the driving circuit provides the switching control signal according to the zero-crossing indication signal and the peak indication signal.

28. The switching power supply circuit according to claim 25, wherein, it further includes an overvoltage detection circuit for judging whether the output voltage exceeds an expected value according to the freewheeling time and an overvoltage reference value, and providing an overvoltage indication signal according to the judgment result, the overvoltage indication signal controls the driving circuit to adjust the duty ratio of the switching control signal, and / or controls the zero-crossing detection circuit to enable the zero-crossing detection circuit to adjust the zero-crossing reference value according to the overvoltage indication signal.

29. The switching power supply circuit according to claim 28, wherein, when the overvoltage indication signal represents that the output voltage is less than the expected value, the zero-crossing reference value is equal to a first preset value. When the overvoltage indication signal indicates that the output voltage is greater than or equal to the expected value, the zero-crossing reference value is equal to a second preset value, wherein the first preset value is greater than the second preset value.

30. A zero-crossing detection method for providing a zero-crossing indication signal according to a signal to be detected, the signal to be detected responding to an inductor current provided by an inductor, the inductor being charged when a power driving transistor is turned on and discharging to achieve freewheeling when the power driving transistor is turned off, the power driving transistor being used to convert an input voltage into an output voltage, characterized in that, the zero-crossing detection method includes: judging whether the inductor current has dropped to zero according to a zero-crossing reference value and the signal to be detected, and providing the zero-crossing indication signal representing the judgment result; detecting the freewheeling time of the inductor; and adjusting the zero-crossing reference value according to the freewheeling time, this step includes: continuously or stepwise decreasing the zero-crossing reference value as the freewheeling time increases.

31. The zero-crossing detection method according to claim 30, characterized in that, when the detected freewheeling time is short, the output voltage is high, and the zero-crossing reference value is adjusted to lower the sensitivity of zero-crossing detection, when the detected freewheeling time is long, the output voltage is low, and the zero-crossing reference value is adjusted to increase the sensitivity of zero-crossing detection.

32. The zero-crossing detection method according to claim 30, characterized in that, as the freewheeling time increases, the zero-crossing reference value is stepwise decreased, when the freewheeling times at different moments are in the same time interval among a plurality of preset time intervals, the corresponding zero-crossing reference values are the same, the length of each time interval is a fixed value, or is positively correlated with the peak current of the inductor current corresponding to this time interval, or is negatively correlated with the amplitude of the output voltage corresponding to this time interval, and the output voltage is provided by a switching power supply circuit where the power driving transistor and the inductor are located.

33. The zero-crossing detection method according to claim 30, characterized in that, the step of detecting the freewheeling time includes: when the power driving transistor is turned off, starting timing from an initial value to obtain a timing signal, the timing signal representing the freewheeling time experienced by the inductor since the power driving transistor was turned off; and stopping timing when the zero-crossing indication signal indicates that the inductor current has dropped to zero.

34. The zero-crossing detection method according to claim 33, characterized in that, the step of adjusting the zero-crossing reference value includes: adjusting the zero-crossing reference value according to the comparison result between the timing signal and at least one reference time value, so that the zero-crossing reference value decreases stepwise as the freewheeling time increases.

35. The zero-crossing detection method according to claim 33, characterized in that, the step of providing the zero-crossing indication signal includes: converting the signal to be detected into a resonant sampling voltage according to a conversion coefficient; and providing the zero-crossing indication signal according to the comparison result between the resonant sampling voltage and a first reference voltage, wherein, the zero-crossing reference value is positively correlated with the first reference voltage and negatively correlated with the conversion coefficient.

36. The zero-crossing detection method according to claim 35, characterized in that, the conversion coefficient continuously increases or increases stepwise as the freewheeling time increases.

37. The zero-crossing detection method according to claim 35, characterized in that, the first reference voltage continuously decreases or decreases stepwise as the freewheeling time increases.

38. The zero-crossing detection method according to claim 35, characterized in that, the step of adjusting the zero-crossing reference value includes: when the power driving transistor is turned off, starting to charge a first capacitor with a charging current, so that a first end of the first capacitor provides a timing voltage for characterizing the freewheeling time; when the zero-crossing indication signal indicates that the inductor current has dropped to zero, the first end of the first capacitor is reset to an initial potential for characterizing the initial value; and adjusting the first reference voltage and / or the conversion coefficient according to the timing voltage or a digital signal corresponding to the timing voltage to adjust the zero-crossing reference value.

39. The zero-crossing detection method according to claim 35, characterized in that, a second end of the power driving transistor is coupled to a current output end of the inductor to provide the signal to be detected.

40. The zero-crossing detection method according to claim 39, characterized in that, the conversion coefficient is positively correlated with the time constant of a filter, an input end of the filter is coupled to the second end of the power driving transistor, and an output end of the filter provides the resonant sampling voltage.

41. The zero-crossing detection method according to claim 39, characterized in that, the conversion coefficient is a voltage division coefficient of a voltage division resistor network, an input end of the voltage division resistor network is coupled to the second end of the power driving transistor, and an output end of the voltage division resistor network provides the resonant sampling voltage.

42. The zero-crossing detection method according to claim 35, characterized in that, a control end of the power driving transistor is coupled to a current output end of the inductor to provide the signal to be detected.

43. The zero-crossing detection method according to claim 39, characterized in that, the conversion coefficient is the total resistance value of a detection resistor unit, the detection resistor unit is coupled between the current output end and the reference ground, and provides the resonant sampling voltage related to the total resistance value under the action of the signal to be detected.

44. The zero-crossing detection method according to claim 30, characterized in that, the step of providing the zero-crossing indication signal includes: delaying the zero-crossing indication signal to filter out narrow pulses with a pulse width less than a preset pulse width in the zero-crossing indication signal.

45. The zero-crossing detection method according to claim 44, characterized in that, the step of providing the zero-crossing indication signal further includes: adjusting the preset pulse width according to the freewheeling time, so that the preset pulse width is negatively correlated with the freewheeling time.

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