Load current detection method and circuit for inductive switching power converter

Abstract

The load current detection method of the inductor switching power supply converter comprises the following steps: obtaining the inductor current rising or falling period time T in the Ath and Bth switching cycles respectively; A and T B The starting point of the inductor current rising or falling period in the Bth switching cycle is 0.5T A The first midpoint time T MB Sample the load current; at the first midpoint time T MB To the second midpoint time T MC During this period, according to the type and working mode of the switching power converter, a corresponding method is used to sample and hold the load current sampling value, and used as the load current of the switching power converter in one switching cycle; the second midpoint time T MC The starting point of the inductor current rising or falling period of the Cth switching cycle is 0.5T B The inductor current changes linearly during the conduction period of the power tube, and the sampled and held current signal can be converted into a load current signal according to the circuit type and working mode, which greatly simplifies the detection circuit and improves the detection accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power converter circuits, and in particular to a load current detection method and circuit for an inductive switching power converter, which reduces the complexity of the load current detection circuit and improves the accuracy of load current detection. Background Art

[0002] The switching power converter circuit is one of the most important types of power voltage converters, and is mainly applicable to voltage conversion situations. The circuit forms of DC / DC switching power converters include charge pump circuits implemented with capacitors, and also include step-down Buck switch circuits, step-up Boost circuits, and negative voltage circuits Buck-Boost circuits implemented with inductors. In order to accurately control the current in the switching power converter circuit, it is necessary to accurately detect the load current.

[0003] In the prior art, one of the commonly used load current detection methods is as follows Figure 2 In the technical solution shown, a current sensing resistor is connected in series in the current path of the inductor, and the voltage on the current sensing resistor is amplified by an operational amplifier to realize load current detection. In the solution with an external current sensing resistor, the operational amplifier needs to detect the voltage across the resistor at all times, which places extremely high requirements on the speed and accuracy of the operational amplifier.

[0004] In the attached Figure 2 In the technical solution shown, it is assumed that the circuit terminal V1 is the input terminal of the external power supply, and V2 is the power output terminal of the switching power converter. In this case, the switching power converter is a switching power converter based on a Buck type circuit. On the contrary, if the circuit terminal V1 is the power output terminal of the switching power converter, and V2 is the input terminal of the external power supply, in this case, the switching power converter is a switching power converter based on a Boost type circuit.

[0005] When the switching power converter works in the Buck circuit mode, the current flowing through the load detection resistor Rsen also flows through the inductor, so the amplifier can indirectly detect the current flowing through the current detection resistor Rsen and the inductor by detecting the voltage on the load detection resistor Rsen. This structure of the circuit requires a load detection resistor Rsen to be connected in series to the inductor. This switching power converter has some efficiency loss, requires an additional pin to detect the voltage across the resistor, and the high-precision current detection resistor is relatively expensive.

[0006] In the prior art, the second commonly used load current detection method is as follows Figure 3The technical solution of detecting the load current through the power tube current mirror shown in the figure requires a mirror tube Q3 in the method of detecting the load current through the power tube current mirror. The ratio of the mirror tube Q3 to the power tube Q1 is 1:K. For a switching power converter based on a Buck type circuit, the sum of the currents flowing through the power tube Q1 and the power tube Q2 is the load current. If both the power tube Q1 and the power tube Q2 need to be detected, the circuit will be very complicated. Although the current of the Buck type switching power converter circuit is continuous, if the currents of the two power tubes, i.e., the switch tube and the freewheeling tube, need to be detected, two sets of load current detection circuits are required, the detection cost is relatively high, and the implementation is complicated.

[0007] In some load detection circuits in the prior art, the peak current of any one of the power tubes Q1 or Q2 is detected, and the peak current is sampled and held as the load current of a switching cycle. Figure 4 and 5 As shown in the figure, it is obvious that there is an error in the shaded part between the current sampled and held according to the peak current of the power tube Q1 and the actual load current. When the Buck-type circuit-based switching power converter works in CCM mode, its error is already relatively large, such as Figure 4 As shown in the shaded part in the figure; when the load current becomes smaller and smaller, or even enters the DCM mode, as shown in the figure Figure 5 As shown, the greater the error, that is, the proportion of the shadow area to the area of ​​the entire figure, the greater the error of the detection circuit.

[0008] In summary, in a Buck-type switching power converter circuit, if only the peak current of one of the power tubes, such as the switch tube, is detected during the conduction period, and the current of the freewheeling tube during the conduction period is simulated and calculated, the simulation error will be large, and the operational amplifier is also required to have good response capabilities throughout the entire load detection cycle to ensure the accuracy of the current detection; if a general operational amplifier is used, the error of the above method will be even greater.

[0009] Detecting the load current by mirroring the switch tube current also has limitations in the Boost type switching power converter circuit; Figure 6 As shown in the figure, the shaded part is the error of the load current. Due to the limited bandwidth of the operational amplifier, there will be an error at the beginning of the detection. In the Boost type switching power converter circuit, since the load current is discontinuous, the operational amplifier is required to have a fast response and high accuracy. The load current detected by the ordinary operational amplifier has a large error. Furthermore, in Figure 3 In the technical solution shown, if the freewheeling tube is replaced by a diode, the circuit of the current mirror architecture cannot be used for detecting the load current of the asynchronous rectification.

[0010] Glossary:

[0011] Buck type switching power converter in this application means a step-down DC / DC conversion system using Buck REGULATOR mode; its input voltage is greater than the output voltage;

[0012] The meaning of the boost type switching power converter in this application is a boost DC / DC conversion system using the boost REGULATOR method; its output voltage is greater than the input voltage;

[0013] Buck-Boost type switching power converter in this application means a negative voltage DC / DC conversion system using Buck-Boost REGULATOR mode;

[0014] PWM is the abbreviation of Pulse Width Modulation, which means pulse width modulation in Chinese. The pulse width modulation (PWM) switching power converter achieves the purpose of stabilizing the output voltage by adjusting the duty cycle of the control circuit while keeping the output frequency unchanged.

[0015] PFM is the abbreviation of Pulse Frequency Modulation, which means pulse frequency modulation in Chinese. The pulse frequency modulated (PFM) switching type voltage regulator circuit is a "equal width frequency modulation" method, that is, the chopping frequency of the circuit is adjusted to achieve the purpose of stabilizing the output voltage.

[0016] CCM is the abbreviation of Continuous Conduction Mode in English. It means continuous conduction mode in Chinese. It means that in the boost circuit, the power tube is alternately turned on continuously so that the current in the inductor changes continuously.

[0017] DCM: It is the abbreviation of Discontinuous Conduction Mode in English. Its Chinese meaning is discontinuous conduction mode. It means that in the Boost circuit, one of the power tubes is alternately turned off, so that the current in the inductor changes discontinuously. Summary of the invention

[0018] The technical problem to be solved by the present invention is to avoid the shortcomings of the above-mentioned existing technical solutions, and propose a load current detection method and circuit for an inductive switching power supply converter, which greatly reduces the requirements for the transient step response of the operational amplifier in load current detection, reduces the complexity of the load current detection circuit, and improves the accuracy of load current detection.

[0019] The technical solution adopted by the present invention to solve the technical problem is a load current detection method for an inductive switching power converter, comprising the following steps: obtaining the time of the inductor current rising period or falling period in the Ath switching cycle of the switching power converter and recording it as TA; obtaining the time of the inductor current rising period or falling period in the Bth switching cycle of the switching power converter and recording it as TB, where B is equal to A+N; obtaining the first midpoint time TMB of the inductor current rising period or falling period in the Bth switching cycle; the first midpoint time TMB is the time after 0.5TA from the starting time of the inductor current rising period or falling period in the Bth switching cycle; obtaining the second midpoint time TMC of the inductor current rising period or falling period in the Cth switching cycle, where C is equal to B+M; the second midpoint time TMC is the time after 0.5TB from the starting time of the inductor current rising period or falling period in the Cth switching cycle; wherein A, B, C, N and M are all natural numbers greater than or equal to 1; at the first midpoint time TMB The load current is sampled, and the sampled value of the load current is maintained through a sample-and-hold circuit until a second midpoint time T MC ; during the period from the first midpoint time T MB to the second midpoint time T MC , if the switching power converter is a Buck-type switching power converter, a load current sampling signal is output during both the rising and falling time periods of the inductor current; if the switching power converter is a Boost-type or Buck-Boost-type switching power converter, a load current sampling signal is output during the falling time period of the inductor current.

[0020] In the load current detection method for the inductive switching power converter, the load current sampling signal output by the sampling and holding circuit is filtered by a low-pass filter and used as the load current signal of the switching power converter; or the load current sampling signal output by the sampling and holding circuit is integrated by an integration circuit and used as the load current signal of the switching power converter.

[0021] In the load current detection method for an inductive switching power converter, when the switching power converter is a Buck switching power converter and the Buck switching power converter operates in CCM mode; the sampling moment of the load current, i.e., the first midpoint moment T MB, is the moment 0.5TA after the starting moment of the inductive current rising period or falling period of the Bth switching cycle, where B=A+1, i.e., N=1; the updating moment of the load current, i.e., the second midpoint moment T MC, is the moment 0.5TB after the starting moment of the inductive current rising period or falling period of the Cth switching cycle, where C=B+1, i.e., M=1.

[0022] The load current detection method for the inductive switching power converter is as follows: when the switching power converter is a Buck switching power converter and the Buck switching power converter operates in the DCM mode; the sampling moment of the load current, i.e., the first midpoint moment TMB, is the moment after 0.5TA from the starting moment of the inductive current rising period or falling period of the Bth switching cycle, where B=A+1, i.e., N=1; the updating moment of the load current, i.e., the second midpoint moment TMC, is the moment after 0.5TB from the starting moment of the inductive current rising period or falling period of the Cth switching cycle, where C=B+1, i.e., M=1; when the inductive current is zero, the load current output is turned off by the switching circuit, that is, in the time period when the inductive current is zero, the sampled and held load current value is not output externally.

[0023] The load current detection method for the inductive switching power converter, when the switching power converter is a Boost switching power converter or a Buck-Boost switching power converter, and the switching power converter operates in CCM mode; the sampling moment of the load current, i.e., the first midpoint moment TMB, is the moment after 0.5TA from the starting moment of the inductive current rising period or falling period of the Bth switching cycle, where B=A+1, i.e., N=1; the updating moment of the load current, i.e., the second midpoint moment TMC, is the moment after 0.5TB from the starting moment of the inductive current rising period or falling period of the Cth switching cycle, where C=B+1, i.e., M=1; in the period of inductive current rising, the load current output is turned off by the switching circuit, that is, in the period of inductive current rising, the sampled and held load current value is not output externally.

[0024] The load current detection method for the inductive switching power converter is as follows: when the switching power converter is a Boost switching power converter or a Buck-Boost switching power converter, and the switching power converter operates in a DCM mode; the sampling moment of the load current, i.e., the first midpoint moment TMB, is the moment after 0.5TA from the starting moment of the inductive current rising period or falling period of the Bth switching cycle, wherein B=A+1, i.e., N=1; the updating moment of the load current, i.e., the second midpoint moment TMC, is the moment after 0.5TB from the starting moment of the inductive current rising period or falling period of the Cth switching cycle, wherein C=B+1, i.e., M=1; in the period when the inductive current rises, the load current output is turned off by the switching circuit, and the sampled and held load current value is not outputted externally; and when the inductive current is zero, the load current output is turned off by the switching circuit, and the sampled and held load current value is not outputted externally.

[0025] The load current detection method of the inductive switching power converter includes the step of obtaining the midpoint time of the inductive current falling period or rising period in the switching signal cycle by using the switching signal of the switching power converter, and the step includes the following sub-steps: the step of generating a first midpoint detection control signal and a second midpoint detection control signal according to the switching signal of the switching power converter: the switching signal is divided into odd cycles and even cycles, the first midpoint detection control signal is high only when the switching signal in the odd switching cycle is high, and is low at other times; the second midpoint detection control signal is high only when the switching signal in the even switching cycle is high, and is low at other times The invention relates to a method for controlling the charging and discharging of the first midpoint detection capacitor and the second midpoint detection capacitor. The method comprises the steps of: setting a midpoint detection operational amplifier, connecting a first midpoint detection capacitor and a second midpoint detection capacitor to a non-inverting input terminal and an inverting input terminal of the midpoint detection operational amplifier, respectively, wherein the capacitance values ​​of the first midpoint detection capacitor and the second midpoint detection capacitor are the same, and the other terminals of the two capacitors are grounded; using the first midpoint detection control signal and the second midpoint detection control signal to control the charging and discharging process of the first midpoint detection capacitor and the second midpoint detection capacitor respectively; and outputting a midpoint time signal according to the voltage inputted from the non-inverting input terminal and the inverting input terminal of the midpoint detection operational amplifier, wherein the midpoint time signal includes information of a first midpoint time TMB and a second midpoint time TMC.

[0026] The technical solution adopted by the present invention to solve the technical problem can also be a load current detection circuit of an inductive switching power supply converter, including a midpoint detection circuit of an inductive current rising period or falling period and a sampling and holding circuit for sampling and holding the load current; the midpoint detection circuit of the inductive current rising period or falling period is used to obtain the inductive current rising period or falling period in the Ath switching cycle, recorded as TA, and also used to obtain the inductive current rising period or falling period in the Bth switching cycle, recorded as TB, B equals A+N; the midpoint detection circuit of the inductive current rising period or falling period is also used to obtain the first midpoint moment T MB in the Bth switching cycle and the second midpoint moment T MC in the Cth switching cycle; the first midpoint moment T MB is the moment after 0.5TA from the starting moment of the inductive current rising period or falling period in the Bth switching cycle; the second midpoint moment T MC is the moment after 0.5TB from the starting moment of the inductive current rising period or falling period in the Cth switching cycle. the moment after the inductor current rises or falls; wherein C is equal to B+M; A, B, C, N and M are all natural numbers greater than or equal to 1; the midpoint detection circuit of the inductor current rise period or fall period is electrically connected to the sampling and holding circuit, and the midpoint detection circuit of the inductor current rise period or fall period outputs a midpoint time signal to the sampling and holding circuit; the midpoint time signal includes information of a first midpoint time T MB and a second midpoint time T MC; the sampling and holding circuit samples the load current at the first midpoint time T MB and keeps the sampled load current until the update moment, i.e., the second midpoint time T MC; during the period from the first midpoint time T MB to the second midpoint time T MC, if the switching power converter is a Buck type switching power converter, the load current sampling signal is output in both the inductor current rise and fall time periods; if the switching power converter is a Boost type or Buck-Boost type switching power converter, the load current sampling signal is output in the time period when the inductor current falls.

[0027] The load current detection circuit of the inductive switching power supply converter also includes a low-pass filter; the low-pass filter is electrically connected to the sampling and holding circuit; the load current sampling signal input from the sampling and holding circuit to the low-pass filter is output after low-pass filtering by the low-pass filter.

[0028] The midpoint detection circuit during the rising period or the falling period of the inductor current comprises a first midpoint detection switch, a second midpoint detection switch, a third midpoint detection switch, a fourth midpoint detection switch, a first midpoint detection capacitor, a second midpoint detection capacitor, a midpoint detection operational amplifier, and two current sources of the same size, namely a first current source and a second current source, wherein the first current source is used to inject current, and the second current source is used to output current; the output terminal of the first current source is electrically connected to the inverting input terminal of the midpoint detection operational amplifier through the first midpoint detection switch, and the output terminal of the first current source is also electrically connected to the inverting input terminal of the midpoint detection operational amplifier through the second midpoint detection switch. The input terminal of the second current source is electrically connected to the inverting input terminal of the midpoint detection operational amplifier through the third midpoint detection switch, and the input terminal of the second current source is also electrically connected to the non-inverting input terminal of the midpoint detection operational amplifier through the fourth midpoint detection switch; the non-inverting input terminal of the midpoint detection operational amplifier is electrically connected to one end of the second midpoint detection capacitor, and the other end of the second midpoint detection capacitor is grounded; the inverting input terminal of the midpoint detection operational amplifier is electrically connected to one end of the first midpoint detection capacitor, and the other end of the first midpoint detection capacitor is grounded; the capacitance of the first midpoint detection capacitor and the second midpoint detection capacitor are the same; the first midpoint detection switch The first midpoint detection switch and the fourth midpoint detection switch are controlled by the first midpoint detection control signal; when the first midpoint detection control signal is at a high level, the first midpoint detection switch and the fourth midpoint detection switch are both closed, so that the two ends of the switch are connected; when the first midpoint detection control signal is at a low level, the first midpoint detection switch and the fourth midpoint detection switch are both opened, so that the two ends of the switch are disconnected; the second midpoint detection switch and the third midpoint detection switch are controlled by the second midpoint detection control signal; when the second midpoint detection control signal is at a high level, the second midpoint detection switch and the third midpoint detection switch are both closed, so that the two ends of the switch are connected; when the second midpoint detection control signal is at a low level , the second midpoint detection switch and the third midpoint detection switch are both turned on, so that the two ends of the switch are disconnected; the first midpoint detection control signal or the second midpoint detection control signal is equal to the switching signal of the inductive switching power supply converter; when the switching signal is in an odd number of cycles, the high level of the first midpoint detection control signal is the same as the high level of the switching signal; when the switching signal is in an even number of cycles, the high level of the second midpoint detection control signal is the same as the high level of the switching signal; the output terminal of the midpoint detection operational amplifier outputs a first midpoint time signal, and the first midpoint time signal is transmitted to the sampling and holding circuit to control the sampling time of the sampling circuit.

[0029] The midpoint detection circuit during the rising or falling period of the inductor current also includes a D trigger and an XOR gate; the clock signal of the D trigger is an externally input switching signal for controlling an inductor switching power converter; the first input terminal of the D trigger is electrically connected to the second output terminal of the D trigger, and the first output terminal of the D trigger outputs a signal to an input terminal of the XOR gate; the output terminal of the midpoint detection operational amplifier outputs a first midpoint time signal to the other input terminal of the XOR gate, and the output terminal of the XOR gate outputs a second midpoint time signal, and the second midpoint time signal is transmitted to the sample and hold circuit to control the sampling time of the sampling circuit.

[0030] The first output terminal of the D flip-flop outputs a signal to a first AND gate, performs an AND operation with the switch signal controlled by the inductive switching power converter, and outputs a first midpoint detection control signal; the second output terminal of the D flip-flop outputs a signal to a second AND gate, performs an AND operation with the switch signal controlled by the inductive switching power converter, and outputs a second midpoint detection control signal.

[0031] The sampling and holding circuit includes a second sampling and holding switch, a second sampling and holding capacitor, a third sampling and holding switch, a third sampling and holding capacitor and a sampling and holding operational amplifier; one end of the second sampling and holding switch is used to connect to an external inductor current detection circuit to obtain a load current sampling signal, the other end of the second sampling and holding switch is electrically connected to one end of the second sampling and holding capacitor and one end of the third sampling and holding switch, and the other end of the second sampling and holding capacitor is grounded; the other end of the third sampling and holding switch is electrically connected to the non-inverting input terminal of the sampling and holding operational amplifier and one end of the third sampling and holding capacitor, and the other end of the third sampling and holding capacitor is grounded; the sampling and holding The inverting input terminal of the operational amplifier is electrically connected to the output terminal of the sampling and holding operational amplifier; the second sampling and holding switch is controlled by the non-signal of the second midpoint time signal, when the non-signal of the second midpoint time signal is at a high level, the second sampling and holding switch is closed to connect the two ends of the switch, when the non-signal of the second midpoint time signal is at a low level, the second sampling and holding switch is opened to disconnect the two ends of the switch; the third sampling and holding switch is controlled by the second midpoint time signal, when the second midpoint time signal is at a high level, the third sampling and holding switch is closed to connect the two ends of the switch, when the second midpoint time signal is at a low level, the third sampling and holding switch is opened to disconnect the two ends of the switch.

[0032] The load current detection circuit of the inductive switching power supply converter also includes an inductive current zero-crossing point detection circuit for obtaining a low-pass filter switch control signal.

[0033] The low-pass filter and the sample-holding circuit are electrically connected via a low-pass filter switch; the low-pass filter switch is controlled by a low-pass filter switch control signal output from an inductor current zero-crossing detection circuit; when the inductor current is zero, the low-pass filter switch control signal controls the low-pass filter switch to open, disconnecting the two ends of the switch, thereby disconnecting the low-pass filter and the sample-holding circuit, and grounding the input of the low-pass filter; when the inductor current is non-zero, the low-pass filter switch control signal controls the low-pass filter switch to close, connecting the two ends of the switch, thereby electrically connecting the low-pass filter and the sample-holding circuit.

[0034] The load current detection circuit of the inductive switching power supply converter also includes a low-pass filter input pull-down MOS tube, which is used to pull down the input of the low-pass filter after the connection between the low-pass filter and the sampling and holding circuit is disconnected, so that the low-pass filter input is zero.

[0035] The low-pass filter includes one or more stages of low-pass filters.

[0036] When the low-pass filter is a first-level RC low-pass filter, the first-level RC low-pass filter includes a low-pass filter resistor and a low-pass filter capacitor; one end of the low-pass filter resistor is electrically connected to one end of the low-pass filter switch, and at the same time, one end of the low-pass filter resistor is electrically connected to the source of the low-pass filter input pull-down MOS tube, the gate of the low-pass filter input pull-down MOS tube is connected to the non-signal of the low-pass filter switch control signal, and the drain of the low-pass filter input pull-down MOS tube is grounded; the other end of the low-pass filter resistor is used as the output terminal of the low-pass filter, and at the same time, the other end of the low-pass filter resistor is also electrically connected to one end of the low-pass filter capacitor, and the other end of the low-pass filter capacitor is grounded.

[0037] The load current detection circuit of the inductive switching power supply converter also includes an inductive current detection circuit for sampling and obtaining the load current; the inductive current detection circuit is electrically connected to the sample and hold circuit; and the inductive current detection circuit outputs a load current signal to the sample and hold circuit.

[0038] The technical solution adopted by the present invention to solve the technical problem can also be an inductive switching power converter, comprising any one of the switching power converter load current detection circuits described above.

[0039] The inductive switching power converter also includes a logic control circuit; the logic control circuit is used to generate a basic switching signal for timing control of the inductive switching power converter; the logic control circuit generates a first control signal GP and a second control signal GN for controlling two power switch tubes according to the basic switching signal; when the first control signal GP is at a high level, one of the power tubes is turned on; when the first control signal GP is at a low level, the other power tube is turned on; the first control signal GP and the second control signal GN are synchronous conversion signals of the basic switching signal; the inductive current rising time period and the inductive current falling time period are synchronized with the first control signal GP and the second control signal GN; thereby, the inductive current rising time period and the inductive current falling time period are also synchronized with the basic switching signal.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Through clever timing control, the midpoint of the inductor rising period or falling period of the current switching cycle is simulated and obtained according to the time of the inductor current rising period or falling period of the past switching cycle, and the sampling and holding at this moment are cleverly performed, making full use of the linear change characteristic of the inductor current in the rising or falling cycle. At the same time, when the load current is constant, the midpoint of the inductor current rising is equal to the midpoint of the inductor current falling, so the load detection circuit can be greatly simplified; 2. At the same time, because the sampling moment is close to or approximately the midpoint of the switch tube conduction period or the freewheeling tube conduction period, the sampling current size is usually at the working time of the operational amplifier. : Within the optimal response range, the overall load current detection accuracy is also improved, which not only avoids complex circuit design, but also improves the detection accuracy of the load current, reducing the complexity and design difficulty of the circuit; 3. The circuit structure is simple and ingenious, and has strong applicability. It can be used with various DC / DC switching power converters such as Buck, Boost and Buck-Boost; whether it is a switching tube or a freewheeling tube, this method can be used to restore the size of the load current, and it has strong flexibility; it is also suitable for synchronous and non-synchronous rectification circuits, and is commonly used for power tube proportional current detection and series resistance current detection circuits; in integrated circuit applications, it is easy to deploy and save chip area. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic block diagram of a preferred embodiment of a load current detection circuit of the present invention;

[0042] Figure 2 It is one of the principle schematic block diagrams of the prior art load current detection circuit in the application of the DC / DC switching power converter circuit;

[0043] Figure 3 This is the second schematic diagram of the principle of the prior art load current detection circuit in the application of the DC / DC switching power converter circuit;

[0044] Figure 4 yes Figure 3 The circuit in FIG. 1 is a schematic diagram showing the corresponding timing and error description of the inductor current and load current detection when the circuit works in Buck CCM mode;

[0045] Figure 5 yes Figure 3 The circuit in the figure works in Buck type DCM mode, and the corresponding timing and error description diagram of the inductor current and load current detection;

[0046] Figure 6 yes Figure 3 The circuit in FIG. 1 is a schematic diagram showing the corresponding timing and error description of the inductor current and load current detection when the circuit works in the Boost CCM mode;

[0047] Figure 7 It is the inductor current characteristic analysis diagram of the inductor switching power converter;

[0048] Figure 8 It is a schematic diagram of the inductor current timing of an inductor switching power converter;

[0049] Fig. 9 It is a schematic block diagram of a preferred embodiment of the load current detection circuit of the present invention in the application of a DC / DC switching power converter circuit;

[0050] Fig.10 yes Figure 1 A schematic diagram of the circuit principle of a preferred embodiment of a circuit for detecting the midpoint of a rising or falling inductor current;

[0051] Fig.11 yes Fig.10 The timing relationship diagram of each signal in the Buck type switching power converter application example;

[0052] Fig.12 1 is a schematic block diagram of the circuit principle of a preferred embodiment of the load current detection circuit of the present invention; the figure shows a sampling and holding circuit 34 and a low-pass filter 35;

[0053] Fig.13 is a schematic diagram of the circuit structure of a preferred embodiment of the low-pass filter 35;

[0054] Fig.14 It is a schematic diagram of the relationship between the transient response curve of the sampling current signal of the operational amplifier and the load current in the prior art;

[0055] Fig.15 and 16 It is a signal timing relationship diagram of the present invention when the switching power converter is a Buck type switching power converter and the Buck type switching power converter operates in a CCM mode; Fig.15 In the example, the current sampling time is in the period when the inductor current rises; Fig.16 In the example, the current sampling time is in the period when the inductor current decreases;

[0056] Fig.17 and 18 It is a signal timing relationship diagram of the present invention when the switching power converter is a Buck type switching power converter and the Buck type switching power converter works in a DCM mode; Fig.17 In the example, the current sampling time is in the period when the inductor current rises; Fig.18 In the example, the current sampling time is in the period when the inductor current decreases;

[0057] Fig.19 and 20 It is a signal timing relationship diagram of the present invention when the switching power converter is a Boost type or Buck-Boost type switching power converter and the switching power converter operates in a CCM mode; Fig.18 In the example, the current sampling time is in the period when the inductor current decreases; Fig.19 In the example, the current sampling time is in the period when the inductor current rises;

[0058] Fig.21 and 22 It is a signal timing relationship diagram of the present invention when the switching power converter is a Boost type or Buck-Boost type switching power converter and the switching power converter operates in a DCM mode; Fig.21 In the example, the current sampling time is in the period when the inductor current decreases; Fig. 22 In the example, the current sampling time is in the period when the inductor current rises. DETAILED DESCRIPTION

[0059] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0060] The basic principle of the inductive switching power converter is to use the energy storage characteristics of the inductor to achieve voltage changes. The rate of change of the inductor current is equal to the voltage across the inductor divided by the Henry value of the inductor, which can be expressed by the equation: the change of the inductor current is a linear process. The speed of change of the inductor current, that is, the slope of the linear change of the inductor current, is related to the voltage across the inductor and the inductance value. When the external voltage across the inductor is constant and the inductance value is also determined, the rising and falling slopes of the inductor current are also fixed.

[0061] The basic features of the switching power converter referred to in the present invention include: in the CCM working mode, the switching power converter controls the two power switches to be turned on alternately through a logic control circuit, and one switching cycle includes an inductor current rising time period and an inductor current falling time period; in the DCM working mode, the switching power converter controls the two power switches to be turned on alternately and turned off at intervals through a logic control circuit, that is, in one switching cycle, it includes an inductor current rising time period, an inductor current falling time period and a time period when the inductor current is zero.

[0062] The logic control circuit in the switching power converter not only generates the basic switching signal of the switching power converter, such as the PWM switching signal, but also generates the first control signal GP and the second control signal GN for controlling the two power switch tubes; when the first control signal GP is at a high level, one of the power tubes is turned on; when the second control signal GN is at a low level, the other power tube is turned on; the first control signal GP for controlling the switch tube and the second control signal GN for controlling the freewheeling tube are both generated based on the PWM switching signal, so the first control signal GP and the second control signal GN are conversion signals of the PWM signal, and the signals are synchronized. The inductor current rising time period and the inductor current falling time period are synchronized with the first control signal GP and the second control signal GN; and the first control signal GP and the second control signal GN are synchronized with the PWM switching signal, so the high and low level periods of the PWM switching signal can be used to obtain the inductor current rising time period and the inductor current falling time period.

[0063] like Figure 7 As shown in the figure, the inductor current of the inductor switching power converter is a triangular wave. It can be seen from the figure that the inductor current climbs from T0 to T1, and 0.5T1 is the midpoint of the inductor current climb; from T1 to T3, the inductor current drops, and T2 is the midpoint of its drop. When the load current is constant, in each switching cycle, the starting point of the inductor current rise is equal to the end point of the drop. If not, if the end point of each drop is higher than the starting point of the rise, the inductor current will continue to increase, otherwise it will continue to decrease. Therefore, at T0 and T3, the inductor current is the same. If the midpoint of the rising edge of the inductor is connected to the midpoint of the drop, this line segment is parallel to the X-axis, that is, the midpoint of the inductor current rise is equal to the midpoint of the inductor current drop, so the midpoint of the sampling inductor current rise period and the midpoint of the sampling inductor current drop period are equivalent changes.

[0064] like Figure 7 As shown in FIG. 1 , if the starting current magnitude of the inductor current rising period is equal to the ending current magnitude of the inductor current falling period and has a peak current, then Figure 7In the figure, the area of ​​the first triangle 1 is equal to the area of ​​the second triangle 2, and the area of ​​the third triangle 3 is equal to the area of ​​the fourth triangle 4. For any type of inductive switching power converter using an inductor, according to the characteristic that the inductor current changes linearly in this interval, as long as the magnitude of the inductor current at the moment of 0.5T1 or T2 is found, and the current at the sampling moment is sampled and held, it can be converted into the magnitude of the load current through simple calculation. If the midpoint moment of the rising edge of the inductor current 0.5T1 or the falling midpoint moment of the inductor current T2, that is, the inductor current at the midpoint moment of the inductor current triangular wave is obtained, the load current of the entire switching cycle can be calculated and obtained, so the above two moments are the key points of the sampling current. To obtain the midpoint of the rising period or the falling period of the inductor current of the current switching cycle, the real-time characteristics of the circuit are often very high; in the present invention, the total time T of the rising period or the falling period of the inductor current in the past switching cycle is first obtained, and then the midpoint moment of the current cycle is replaced by the moment from the beginning of the cycle to 0.5T, and the load current of the full switching cycle is obtained through the corresponding sampling and holding strategy.

[0065] like Figure 7 As shown in , for the Buck type switching power converter circuit, the midpoint current sampled is I h . Since the inductor current outputs energy to the outside during both the rising and falling processes, . Figure 7 As shown, for a Boost or Buck-Boost converter, the output is discharged only when the inductor current decreases.

[0066] like Figure 8 As shown in the figure, when n is 1, the total time for the inductor current to rise in the first cycle is Ta, the total time for the inductor current to rise in the second cycle is Tb, and the total time for the inductor current to rise in the third cycle is Tc. At the midpoint of the second cycle: T MB = T1 + 0.5Ta, and at the midpoint of the third cycle: T MC = T2 + 0.5Tb. Similarly, the same method can be used to collect the midpoint of the falling period. When the load current remains unchanged, the peak and valley values ​​of the inductor current also remain unchanged, so the midpoint of the rising period and the midpoint of the falling period of the inductor current are the same, and can be flexibly selected according to the actual application.

[0067] like Fig. 9 The figure is a schematic block diagram showing the principle of a load current detection circuit for realizing a load current detection method according to the present invention in an application of a DC / DC switching power supply converter circuit.

[0068] exist Fig. 9In the figure, if the circuit terminal V1 is the external power input terminal of the switching power converter, and the circuit terminal V2 is connected to the capacitor as the output terminal of the switching power converter, the switching power converter is a Buck type switching power converter, and the transistor Q1 in the figure is a PMOS tube used as a switching tube, and the transistor Q2 in the figure is an NMOS tube used as a freewheeling tube.

[0069] exist Fig. 9 In the figure, if the circuit terminal V2 is the external power input terminal of the switching power converter, and the circuit terminal V1 is used as the output terminal of the switching power converter, then the switching power converter is a Boost type switching power converter, and the transistor Q2 in the figure is an NMOS tube used as a switching tube, and the transistor Q1 in the figure is a PMOS tube used as a freewheeling tube.

[0070] Fig. 9 The current midpoint sampling and holding circuit indicated by the reference numeral 41 is the load current detection circuit of the switching power supply converter referred to in the present invention.

[0071] exist Fig. 9 In the embodiment, the inductor current is input to the current midpoint sampling and holding circuit 41, the current midpoint sampling and holding circuit 41 outputs the load current signal, namely the IFB signal, the output voltage sampling circuit 40 outputs the voltage feedback signal, namely the VFB signal, the load current signal, namely the IFB signal, the output voltage feedback signal, namely the VFB signal, and the reference voltage VBG signal are transmitted to the internal CC / CV error amplifier 42 together, the CC / CV error amplifier 42 outputs the signal to the PWM comparator 44; the output signal of the CC / CV error amplifier 42 and the output signal of the slope compensation circuit 43 are input to the control PWM comparator 44 together, the PWM comparator 44 outputs the PWM control signal to the logic control module 45, and the output of the PWM comparator 44 is controlled to control the output of the logic control module 45, so that the PWM signal of each cycle is controlled by the feedback load current signal, thereby controlling the power output stage to control the maximum output load current, thereby achieving the purpose of constant maximum output current. Fig. 9 Only an embodiment of a PWM switching power converter is provided. In fact, the technical solution of the present invention is also applicable to a PFM switching power converter circuit.

[0072] like Figure 1 As shown, it is a circuit block diagram of one of the preferred embodiments of the present invention, including a midpoint detection circuit 32 of the inductor current rising period or falling period, an inductor current detection circuit 30, an inductor current zero-crossing detection circuit 31, a sampling and holding circuit 34 and a low-pass filter 35.

[0073] like Figure 1The midpoint detection circuit 32 of the inductor current rising period or falling period shown in the figure obtains the total time of the inductor current rising period or falling period in the Ath switching cycle of the switching power converter, which is recorded as TA, and the total time of the inductor current rising period or falling period in the Bth switching cycle is recorded as TB. The load current is sampled at the first midpoint time TMB after 0.5TA from the starting point of the Bth inductor current rising period or falling period, and the load current sampling value is maintained by the sampling and holding circuit to the second midpoint time TMC; the second midpoint time TMC is the Cth switching cycle, the starting point of the inductor current rising period or falling period after 0.5TB; during the period from the first midpoint time TMB to the second midpoint time TMC, the sampled current value at the first midpoint time TMB is sampled and maintained. Wherein A, B and C are all natural numbers greater than or equal to 1, B=A+1, C=B+1;

[0074] The application of the present invention in the Buck type switching power converter is described in detail below. Assume that the Buck type switching power converter operates in CCM mode, i.e., continuous operation mode, and the output load current is equal to the mean value of the inductor current. In the absence of a load current sampling resistor, it is difficult to directly sample the current on the inductor, but the inductor current is divided into two parts, one of which is when the switch tube is turned on, the current flowing through the switch tube is equal to the current of the inductor, and the current flowing through the freewheeling tube is 0 at this time, and the other part of the inductor current is when the freewheeling tube is turned on, the current flowing through the freewheeling tube is equal to the current of the inductor, and the current flowing through the switch tube is 0, so the load current is the mean value of the sum of the current flowing through the switch tube and the freewheeling tube current. When the load current is constant, the current flowing through the switch tube in each switching cycle is a linearly increasing current; accordingly, in the present invention, first obtain the time T when the switch tube is turned on in the previous cycle, and when the switch tube is turned on for T / 2 in the current cycle, sample the inductor current, i.e., the load current, and keep the load current sampling value at this moment until the switch tube conduction time of the next cycle reaches half of the switch tube conduction time of the previous cycle. Assuming that the Buck type switching power supply converter works in DCM mode, that is, discontinuous working mode, it only needs to keep the sampled value until the freewheeling tube is turned off. When the switch tube and the freewheeling tube are not turned on, no current flows to the load, and the output voltage is maintained only by the output capacitor; when the switch tube and the freewheeling tube are not turned on, the sampled and held value of the sample and hold circuit is not output to the outside.

[0075] For Boost or Buck-Boost switching power converters, the same method can also be used to sample the load current at the midpoint of the freewheeling tube conduction period, and the load current sampling value is sampled and maintained; during the time period when the freewheeling tube is turned on in the current switching cycle, the load current sampling value sampled and maintained in the previous cycle is output, until the moment from the start of the freewheeling tube conduction in the current switching cycle to half of the conduction period of the previous cycle, the load current sampling value of the current cycle is refreshed. Finally, the sampled and maintained load current signal is output after passing through a low-pass filter as the load current of the switching power converter in this period. The present invention does not require accurate sampling of the inductor current of the entire switching cycle for the entire cycle, but only needs to sample the load current from the starting moment of the current switching cycle to half of the conduction period of the previous cycle in the current switching cycle, and the load current sampling value is sampled and maintained until the next update moment, so as to accurately obtain the load current of the entire cycle. In this way, the requirements for the load current detection circuit and the sampling circuit are greatly reduced, the circuit complexity is reduced, and the accuracy of load detection is improved. Especially in the full cycle when the switch tube and the freewheeling tube are alternately turned on, the current changes of the switch tube and the freewheeling tube usually need to go through a process of linearly increasing from zero or from the base current to the peak current. To accurately obtain the current size of the switch tube and the freewheeling tube, the operational amplifier in the current detection circuit is required to have high requirements. The operational amplifier is required to have full-band response capabilities, otherwise the current sampling error in the full cycle is inevitable.

[0076] In the PWM switching power converter circuit, the rising period or falling period of the inductor current corresponds to the on period and off period of the switch tube; and the pulse width of the PWM switch signal is equal to the on time of the switch tube or the freewheeling tube. The first control signal GP and the second control signal GN for controlling the switch tube and the freewheeling tube are generated based on the PWM switch signal. Therefore, the first control signal GP and the second control signal GN are conversion signals of the PWM signal, and the signals are synchronized. In addition, when the switch tube or the freewheeling tube is turned on and off, the inductor current rises linearly during this period, so the midpoint of the rise or fall of the inductor current is the position of half the pulse width of the PWM, GP or GN switch signal. Therefore, it is only necessary to detect the midpoint moment of the pulse width of the PWM switch signal to find the midpoint moment of the inductor current. When the sampling and holding circuit obtains the information of the above midpoint moment, it can sample the current at the midpoint moment, and sample and hold the output until the midpoint moment of the switch tube conduction time of the next PWM switch signal cycle.

[0077] In the present invention, the time of half of the switch tube conduction period in the previous PWM switch signal cycle is used to replace the time of half of the switch tube conduction period in the current PWM switch signal cycle. When the PWM switch signal cycle is stable, a very clever and simple circuit can be used to complete the control of the sampling time. Even in the process of PWM switch signal cycle change, because the conduction period information in two adjacent cycles is used, PWM only lags behind the inductor current change by one or several switch cycles, and basically achieves real-time detection. The load current can only be obtained after being averaged by the subsequent low-pass filter, which has no effect on the accuracy of inductor current detection.

[0078] like Fig.10 As shown, in a specific embodiment of the midpoint detection circuit 32 of the inductor current rising period or falling period of the present invention, it includes two first current sources I1 and second current sources I2 of the same size, a midpoint detection operational amplifier OP1, four midpoint detection switches, namely a first midpoint detection switch, a second midpoint detection switch, a third midpoint detection switch and a fourth midpoint detection switch, and two first midpoint detection capacitors CA and second midpoint detection capacitors CB with the same capacitance. Fig.11 yes Fig.10 Timing relationship diagram of each signal in .

[0079] like Fig.10 and 11 As shown, the first midpoint detection control signal Φ1 and the second midpoint detection control signal Φ1B are signals generated after the PWM switching signal of the switching power converter is transformed; Fig.10 As shown, the first midpoint detection control signal Φ1 and the second midpoint detection control signal Φ1B are respectively signals obtained after the first control signal GP or the second control signal GN passes through the cloud. When the PWM switch signal is in an odd number of cycles, the high level of the first midpoint detection control signal Φ1 is the same as the high level of the PWM switch signal; when the PWM switch signal is in an even number of cycles, the high level of the second midpoint detection control signal Φ1B is the same as the high level of the PWM switch signal. The relationship between the first midpoint detection control signal Φ1 and the second midpoint detection control signal Φ1B is: the first midpoint detection control signal Φ1 or the second midpoint detection control signal Φ1B is equal to the PWM switch signal.

[0080] like Fig.10 and 11As shown, the first current source I1 and the second current source I2 are current sources of the same size, wherein the first current source I1 is used to inject current, and the second current source I2 is used to output current; assuming that the capacitance of the first midpoint detection capacitor CA and the second midpoint detection capacitor CB are equal, and the initial values ​​of the non-grounded terminals are both 0 with respect to the ground potential, that is, the voltages VC1=VC2=0 on the positive input terminal and the negative input terminal of the midpoint detection operational amplifier OP1, in the pulse width period of the first PWM switch signal, the first midpoint detection control signal Φ1 is high level Φ1=1, the second midpoint detection control signal Φ1B is low level, that is, Φ1B=0, and the first midpoint detection capacitor CA starts to charge to VC1=Vch, the second midpoint detection capacitor CB is discharged to VC2=0; when the first midpoint detection control signal Φ1 and the second midpoint detection control signal Φ1B are both low level, that is, Φ1=Φ1B=0, the voltage VC1 on the first midpoint detection capacitor CA and the voltage VC2 on the second midpoint detection capacitor CB are maintained; in the pulse width period of the second cycle PWM switch signal, the first midpoint detection control signal Φ1 is high level φ1=1, the second midpoint detection control signal Φ1B is low level φ1B=0, the voltage VC1 on the first midpoint detection capacitor CA starts to discharge from Vch, and the voltage VC2 on the second midpoint detection capacitor CB starts to charge from 0. Since CA=CB and I1=I2, when VC1=VC2, the level of the MID signal output by the midpoint detection operational amplifier flips, and the flipping moment is the PWM pulse width midpoint of the previous cycle of the PWM switch signal.

[0081] like Fig.12 , which is a schematic diagram of the circuit principle of one of the preferred embodiments of the load current detection circuit of the present invention, shows a midpoint detection circuit 32 during the rising period or the falling period of the inductor current, an inductor current detection circuit 30, an inductor current zero-crossing detection circuit 31, a sampling and holding circuit 34 and a low-pass filter 35.

[0082] like Fig.12As shown, the sampling and holding circuit 34 includes a second sampling and holding switch, a second sampling and holding capacitor C2, a third sampling and holding switch, a third sampling and holding capacitor C3, and a sampling and holding operational amplifier; one end of the second sampling and holding switch is used to connect to the external inductor current detection circuit 30 to obtain a load current sampling signal, the other end of the second sampling and holding switch is electrically connected to one end of the second sampling and holding capacitor and one end of the third sampling and holding switch, and the other end of the second sampling and holding capacitor is grounded; the other end of the third sampling and holding switch is electrically connected to the non-inverting input terminal of the sampling and holding operational amplifier and one end of the third sampling and holding capacitor, and the other end of the third sampling and holding capacitor is grounded; the sampling and holding The inverting input terminal of the operational amplifier is electrically connected to the output terminal of the sampling and holding operational amplifier; the second sampling and holding switch is controlled by the non-signal of the second midpoint time signal, when the non-signal of the second midpoint time signal is at a high level, the second sampling and holding switch is closed to connect the two ends of the switch, when the non-signal of the second midpoint time signal is at a low level, the second sampling and holding switch is opened to disconnect the two ends of the switch; the third sampling and holding switch is controlled by the second midpoint time signal D50C, when the second midpoint time signal D50C is at a high level, the third sampling and holding switch is closed to connect the two ends of the switch, when the second midpoint time signal D50C is at a low level, the third sampling and holding switch is opened to disconnect the two ends of the switch.

[0083] like Fig.12 As shown, the low-pass filter 35 and the sampling and holding circuit 34 are electrically connected via a low-pass filter switch; the low-pass filter switch is controlled by the negation signal of the low-pass filter switch control signal ZC output from the inductor current zero-crossing detection circuit 31. At this time, the load current detection circuit of the switching power supply converter also includes the inductor current zero-crossing detection circuit 31, which is used to obtain the low-pass filter switch control signal ZC and its negation signal, which is the logical negation signal of ZC.

[0084] For a Buck type switching power supply circuit, when the inductor current is zero, the low-pass filter switch control signal ZC controls the low-pass filter switch to open, disconnecting the two ends of the switch, thereby disconnecting the low-pass filter 35 and the sampling and holding circuit 34; when the inductor current is non-zero, the low-pass filter switch control signal controls the low-pass filter switch to close, connecting the two ends of the switch, thereby electrically connecting the low-pass filter 35 and the sampling and holding circuit 34.

[0085] For a Boost or Buck-Boost type switching power supply circuit, the low-pass filter switch control signal ZC is high when the inductor current is zero or the switch tube is turned on. The low-pass filter switch control signal ZC controls the low-pass filter switch to open, so that the connection between the low-pass filter 35 and the sampling and holding circuit 34 is disconnected, and the low-pass filter input is pulled to ground; when the inductor current is non-zero and the freewheeling tube is turned on, the low-pass filter switch control signal controls the low-pass filter switch to close, so that the low-pass filter 35 and the sampling and holding circuit 34 are electrically connected.

[0086] like Fig.12 As shown, the low-pass filter 35 includes a low-pass filter resistor and a low-pass filter capacitor; the sampling and holding circuit 34 also includes a low-pass filter input pull-down MOS tube for controlling the low-pass filter input when the inductor current is zero; one end of the low-pass filter resistor is electrically connected to one end of the low-pass filter switch, and at the same time, one end of the low-pass filter resistor is electrically connected to the source of the low-pass filter input pull-down MOS tube, the gate of the low-pass filter input pull-down MOS tube is connected to the low-pass filter switch control signal ZC, and the drain of the low-pass filter input pull-down MOS tube is grounded; the other end of the low-pass filter resistor is used as the output terminal of the low-pass filter 35, and at the same time, the other end of the low-pass filter resistor is also electrically connected to one end of the low-pass filter capacitor, and the other end of the low-pass filter capacitor is grounded.

[0087] like Fig.13 As shown, another embodiment of the low-pass filter includes two stages of RC low-pass filters with the same circuit parameters, and the resistors and capacitors in each two-stage filter are 1MΩ and 4pF respectively, which is suitable for the case where the switching signal frequency is 500MHz. The parameters of the low-pass filter can be selected according to actual conditions, such as selecting appropriate low-pass filter parameters according to different maximum load currents, current sampling ratios, switching signal frequencies and loop gains of corresponding circuits.

[0088] Combined with Fig.12The sample-and-hold circuit 34 shown in the figure assumes that the switching power converter is a Buck type switching power converter and the Buck type switching power converter operates in CCM mode. After the sample-and-hold circuit 34 detects the inductor current signal, the second midpoint time signal D50C is obtained through the midpoint detection circuit. In the first half cycle of the PWM switching signal, the second sample-and-hold capacitor C2 samples the inductor current. When the time given by the midpoint detection circuit is reached, that is, after the first sampling time given by the second midpoint time signal D50C is reached, the second sample-and-hold capacitor C2 and the third sample-and-hold capacitor C3 are short-circuited by the switch, wherein C2>>C3, so that the upper voltage of the third sample-and-hold capacitor C3 is consistent with the voltage of the second sample-and-hold capacitor C2 at the sampling time. The sampling operation amplifier is used to hold the sampling time of the next PWM switching signal cycle, and the electrical connection between the third sample-and-hold capacitor C3 and the second sample-and-hold capacitor C2 is disconnected, and the second sample-and-hold capacitor C2 samples the inductor current of a new PWM switching signal cycle.

[0089] Combined with Fig.12 The sample-and-hold circuit 34 shown in the figure assumes that the switching power converter is a Buck-type switching power converter and the Buck-type switching power converter operates in DCM mode. The other working timings are the same as those of the Buck-type switching power converter operating in CCM mode. The difference is that when the inductor current becomes zero, that is, when the signal of the low-pass filter switch control signal is high, ZC=1, the low-pass filter switch is controlled to open, so that the electrical connection between the sample-and-hold circuit 34 and the low-pass filter 35 is disconnected, and the input of the low-pass filter is pulled to ground through the low-pass filter input pull-down MOS tube, so that the current output by the low-pass filter 35 can truly represent the magnitude of the load current of the switching power converter.

[0090] Combined with Fig.12 The sample-and-hold circuit 34 shown assumes that the switching power converter is a Boost or Buck-Boost switching power converter and that the switching power converter operates in CCM mode. The other working timings are the same as those of the Buck switching power converter operating in CCM mode, except that the load current is sampled and held only during the conduction period of the freewheeling tube. During the period when the switch tube is on, the low-pass filter switch control signal will be at a high level, i.e., ZC=1, thereby disconnecting the sample-and-hold circuit and the low-pass filter 35. In this way, the sampled and held current is only the current of the freewheeling tube, and the averaged current through the low-pass filter is the load current of the Boost or Buck-Boost switching power converter in CCM mode.

[0091] Combined with Fig.12The sampling and holding circuit 34 shown in the figure assumes that the switching power converter is a Boost or Buck-Boost switching power converter and the switching power converter operates in DCM mode. The other working timings of the Boost or Buck-Boost switching power converter operating in CCM mode are the same. The difference is that when the inductance becomes zero, the signal of the low-pass filter switch control signal will also be high, that is, ZC=1, and the low-pass filter switch will be controlled to open, disconnect the sampling and holding circuit and the low-pass filter 35, and pull the output of the low-pass filter 35 to the ground, without waiting until the switch tube is turned on to set the signal of the low-pass filter switch control signal to a high level. In this way, the output of the low-pass filter 35 is the actual load current of the Boost or Buck-Boost switching power converter in DCM mode.

[0092] like Fig.14 Schematic diagram of the relationship between the operational amplifier response curve and the load current in the prior art; the dotted line in the figure represents the actual transient response curve of the operational amplifier. During the process of the load current rising from near the zero point, the operational amplifier of the prior art needs to track and detect the inductor current size during the entire rising time period of the output. The limited gain and response time of the operational amplifier require a certain response time. The inductor current detection error in the initial stage is large, which will also affect the accuracy of the load current detection in the entire cycle. Since the present invention only needs to sample at the midpoint, there is enough time to establish the operational amplifier response during the period from the inductor current climbing from the low point to the midpoint. The operational amplifier response error in the initial stage does not affect the accuracy of the sampled current. Therefore, the design difficulty and requirements of the operational amplifier are greatly reduced.

[0093] Fig.15This is a signal timing relationship diagram when the switching power converter of the present invention is a Buck type switching power converter working in CCM mode, and the Buck type switching power converter performs load current sampling during the inductor current rising period; it can be seen in the figure that after the first inductor current rising period T1 starts, the midpoint current sampling value Vsen1 of the previous cycle is output first, and the input signal Vsen2 of the low-pass filter is equal to Vsen1. When the time reaches half of the previous inductor current rising period T0, the inductor current sampling value Vsen1 is updated, and this signal is output to the low-pass filter at the same time, and the low-pass filter input voltage Vsen2 is equal to Vsen1, until the next inductor current rising period T2 reaches the moment of 0.5T1. When the T2 period reaches the moment of 0.5T1, the current is sampled again, and the updated midpoint current sampling value Vsen1 is maintained until the T3 period reaches the moment of 0.5T2; it repeats itself and is not repeated. Because when the switch tube and the freewheeling tube are turned on, the switching power converter outputs current to the load, so the load current I load should be the sum of the switch tube and freewheeling tube currents. The current feedback signal IFB in the figure is the sampled and held load current value, which is filtered by a low-pass filter and then output as a load current signal representing the load current size.

[0094] Fig.16 The present invention is a signal timing relationship diagram when the switching power converter is a Buck type switching power converter operating in CCM mode and the Buck type switching power converter performs load current sampling during the inductor current drop period. Fig.15 The difference is that the sampling and holding circuit samples and updates the current sampling value Vsen1 at the midpoint of the inductor current decreasing period, and samples and updates the current sampling value again at the midpoint of the next inductor current decreasing period.

[0095] Fig.17This is a signal timing relationship diagram when the switching power converter of the present invention is a Buck-type switching power converter operating in DCM mode, and the Buck-type switching power converter performs load current sampling during the inductor current rising period; after the start of the first inductor current rising period T1, the midpoint sampling signal Vsen1 of the previous cycle is first output, and the input Vsen2 of the low-pass filter is equal to Vsen1. When the time reaches half of the previous inductor current rising period T0, the midpoint current sampling value Vsen1 is sampled and updated. When the inductor current zero detection circuit detects that the inductor current drops to zero, the low-pass filter input signal Vsen2=0. When the next inductor current rising period T2 arrives, the midpoint sampling current sampling value Vsen1 of the T1 period is output first, and when it reaches 0.5T1, the midpoint current sampling value Vsen1 is sampled and updated again, and maintained until the freewheeling tube is turned off, and then the input signal Vsen2 of the low-pass filter is pulled to the ground. Repeatedly, no further elaboration is given. In a single switching cycle, the output load current size I load should be Fig.17 The area of ​​the rectangle with the same hatching in one switching cycle is the integral value of the load current divided by the time of the integration period. In DCM mode, the inductor current will drop to zero, the inductor current is discontinuous, so the inductor current sampling is also discontinuous, and the load current is the average value of this discontinuous current. Therefore, in this mode, the load current I load will be smaller than the midpoint sampling current.

[0096] Fig.18 The present invention is a signal timing relationship diagram when the switching power converter is a Buck type switching power converter working in DCM mode, and the Buck type switching power converter performs load current sampling during the inductor current falling period. Fig.17 The difference is that the sampling and holding circuit samples and updates the sampled current at the midpoint of the inductor current falling period.

[0097] Fig.19The present invention is a signal timing relationship diagram of the switching power converter of the Boost type or Buck-Boost type working in the CCM mode, and the switching power converter samples the load current in the falling period of the inductor current; after the first falling period of the inductor current T1 begins, the current sampling value Vsen1 at the midpoint of the previous cycle is output first, and the input signal Vsen2 of the low-pass filter is Vsen1. When it reaches 0.5T0, the inductor current sampling value Vsen1 is updated, and at the same time, this current is output to the low-pass filter, and the low-pass filter input signal Vsen2 is Vsen1, until the end of the falling period of the inductor current. When the second falling period of the inductor current T2 arrives, the sampling current value at the moment of the previous falling period of the inductor current T1+0.5T0 is output first, and when the falling period of the inductor current reaches 0.5T1, the current sampling value Vsen1 is sampled and updated again, and maintained until the end of the falling period of the inductor current. Repeatedly, no further description is given. Because the Boost type switching power converter circuit outputs current to the output capacitor only when the freewheeling tube is turned on, the load current is equal to the magnitude of the current flowing through the freewheeling tube. Therefore, the output sampling current is output only when the freewheeling tube is turned on, and the magnitude of I load is the area of ​​the rectangle with the same hatching in one switching cycle, that is, the integral value of the load current divided by the time of the integral period.

[0098] Fig. 20 The present invention is a signal timing relationship diagram when the switching power converter is a Boost type or Buck-Boost type switching power converter working in CCM mode and sampling the load current during the inductor current rising period. After the inductor current rising period T1 of this cycle begins, the input Vsen2 of the low-pass filter is pulled down to 0, and the sampling current value Vsen1 is proportional to the inductor current; when the expected midpoint 0.5T0 is reached, the sampling current value Vsen1 is obtained and maintained at Vsen1, and the input signal Vsen2 of the low-pass filter is still equal to 0; until the moment when the inductor current starts to decrease, the switch is turned on to make the low-pass filter input signal Vsen2=Vsen1, until the end of the switching cycle, this Vsen1 is the inductor current sampling value sampled at 0.5T0 of the inductor current rising period T1 in this period. When the next switching cycle's inductor current rising period T2 arrives, the input signal Vsen2 of the low-pass filter is pulled low during the entire time period of the inductor current rising. When the inductor current rising period 0.5T1 is reached, the inductor current is sampled and the current sampling value Vsen1 is updated and maintained, but not output to the low-pass filter. When the inductor current starts to decrease, the input signal Vsen2 of the low-pass filter is made to be Vsen1, until the end of the switching cycle, this Vsen1 is the inductor current sampling value sampled at 0.5T1 of the inductor current rising period T2. This cycle repeats itself and is not repeated here.

[0099] Fig.21 The present invention is a signal timing relationship diagram of the switching power converter of the Boost type or Buck-Boost type working in the DCM mode and sampling the load current at the falling edge of the inductor current. After the first inductor current falling period T1 begins, the current sampling value Vsen1 of the previous switching cycle is output first, and the current is sampled at the moment T1+0.5T0, and the current sampling value Vsen1 is updated and output to the low-pass filter, and the input signal Vsen2 of the low-pass filter is Vsen1. At the same time, this current sampling value is maintained until the inductor current drops to 0, and the electrical connection between the sampling and holding circuit and the low-pass filter is disconnected, and the input signal Vsen2 of the low-pass filter is pulled low.

[0100] Fig. 22 The present invention is a signal timing relationship diagram of the load current sampled at the rising edge of the inductor current when the switching power converter is a Boost type or Buck-Boost type switching power converter working in the DCM mode. After the inductor current rising period T1 of the current switching cycle begins, the sampled current is not output externally first; when the expected midpoint 0.5T0 is reached, the current is sampled to obtain the rising edge midpoint current sampling value Vsen1 and maintain it, but the sampling current signal is not output, and the input signal Vsen2 of the low-pass filter is still 0 during the inductor rising period; until the moment when the inductor current starts to drop, the input Vsen2 of the low-pass filter is made to be Vsen1, and Vsen1 is the inductor current signal value sampled at 0.5T0 of the inductor current rising period T1; the sampling and holding circuit outputs the current sampling value Vsen1 to the low-pass filter until the inductor current drops to 0, the electrical connection between the sampling and holding circuit and the low-pass filter is disconnected, and the input signal Vsen2 of the low-pass filter is pulled down. A load current detection method for a switching power converter comprises the following steps: obtaining the total time TA and TB of the switching power converter in the Ath and Bth inductor current rising or falling periods, where B is equal to A+1; sampling the load current at the moment 0.5TA after the starting moment of the Bth inductor current rising or falling period, that is, the first midpoint moment TMB, and holding the load current sampling value through a sampling and holding circuit to the second midpoint moment TMC; the second midpoint moment TMC is the moment 0.5TB after the starting moment of the Cth inductor current rising or falling period; during the period from the first midpoint moment TMB to the second midpoint moment TMC, using the sampled and held current sampling signal, according to different types of circuits and different working modes, to transform into a load current signal. The load current sampling signal is smoothed by a low-pass filter to obtain the load current signal of the switching power converter. Regardless of the type of circuit, the load current sampling value is not output when the inductor current is zero.

[0101] Through clever timing control, the total time of the inductor current rising period or falling period in the past switching signal cycle is used to simulate the midpoint of the inductor current rising period or falling period in the current cycle, and the sampling and holding is cleverly performed at this moment, making full use of the linear characteristics of the inductor current in the switch tube conduction period or the freewheeling tube conduction period, simplifying the load detection circuit; at the same time, because the sampling moment is close to or approximately the midpoint of the switch tube conduction period or the freewheeling tube conduction period, the sampling current size is usually within the optimal response range of the operational amplifier, so the overall load current detection accuracy is also improved, not only avoiding complex circuit design, but also improving the detection accuracy of the load current, reducing the complexity and difficulty of the circuit; the circuit structure is simple and clever, and has strong applicability. It can be used with various DCDC switching power converters such as Buck, Boost and Buck-Boost; whether it is a switch tube or a freewheeling tube, the load current size can be restored by this method, and it has strong flexibility; it is also commonly used in power tube proportional current detection, series resistance current detection circuit, synchronous or asynchronous rectification circuit; in integrated circuit applications, it is easy to deploy and save chip area.

[0102] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for detecting load current of an inductive switching power supply converter, comprising the following steps: The time of the inductor current rising period or falling period in the Ath switching cycle of the switching power converter is obtained and recorded as TA; The time of the inductor current rising period or falling period in the Bth switching cycle of the switching power converter is obtained and recorded as TB, where B is equal to A+N; Obtaining a first midpoint time T MB of a rising period or a falling period of the inductor current in the Bth switching cycle; The first midpoint time T MB is a time after 0.5TA from the starting time of the rising period or the falling period of the inductor current in the Bth switching cycle; Obtaining a second midpoint time T MC of the inductor current rising period or falling period in the Cth switching cycle, where C is equal to B+M; the second midpoint time T MC is a time after 0.5TB from the starting time of the inductor current rising period or falling period in the Cth switching cycle; wherein A, B, C, N and M are all natural numbers greater than or equal to 1; The load current is sampled at a first midpoint time T MB , and the sampled value of the load current is held until a second midpoint time T MC by a sample-and-hold circuit; during the period from the first midpoint time T MB to the second midpoint time T MC , if the switching power converter is a Buck-type switching power converter, a load current sampling signal is output during both the rising and falling time periods of the inductor current; if the switching power converter is a Boost-type or Buck-Boost-type switching power converter, a load current sampling signal is output during the falling time period of the inductor current.

2. The load current detection method of the inductive switching power supply converter according to claim 1, wherein: The load current sampling signal output by the sample-and-hold circuit is filtered by a low-pass filter and then used as the load current signal of the switching power converter; Or the load current sampling signal output by the sample-and-hold circuit is integrated by the integration circuit and used as the load current signal of the switching power converter.

3. The load current detection method of the inductive switching power supply converter according to claim 1, wherein: When the switching power converter is a Buck type switching power converter, and the Buck type switching power converter operates in CCM mode; The sampling time of the load current, i.e., the first midpoint time T MB , is the time after 0.5TA from the starting time of the rising period or falling period of the inductor current of the Bth switching cycle, where B=A+1, i.e., N=1; The update time of the load current, ie, the second midpoint time T MC , is the time after 0.5TB from the starting time of the rising period or the falling period of the inductor current in the Cth switching cycle, where C=B+1, ie, M=1.

4. The load current detection method of the inductive switching power converter according to claim 1, wherein: When the switching power converter is a Buck type switching power converter, and the Buck type switching power converter operates in a DCM mode; The update time of the load current, i.e., the second midpoint time T MC , is the time after 0.5TB from the starting time of the rising period or falling period of the inductor current in the Cth switching cycle, where C=B+1, i.e., M=1; When the inductor current is zero, the load current output is turned off through the switch circuit, that is, during the time period when the inductor current is zero, the sampled and held load current value is not output externally.

5. The load current detection method of the inductive switching power converter according to claim 1, wherein: When the switching power converter is a Boost switching power converter or a Buck-Boost switching power converter, and the switching power converter operates in a CCM mode; The sampling time of the load current, i.e., the first midpoint time T MB , is the time after 0.5TA from the starting time of the rising period or falling period of the inductor current of the Bth switching cycle, where B=A+1, i.e., N=1; During the period when the inductor current rises, the load current output is turned off by the switch circuit, that is, during the period when the inductor current rises, the sampled and held load current value is not output externally.

6. The load current detection method of the inductive switching power converter according to claim 1, wherein: When the switching power converter is a Boost switching power converter or a Buck-Boost switching power converter, and the switching power converter operates in a DCM mode; During the period when the inductor current rises, the load current output is turned off through the switch circuit, and the sampled and held load current value is not output externally; And when the inductor current is zero, the load current output is turned off through the switch circuit, and the sampled and held load current value is not output externally.

7. The load current detection method of the inductive switching power supply converter according to claim 1, wherein: The method comprises the steps of using a switching signal of a switching power converter to obtain a midpoint time of a falling period or a rising period of an inductor current within a switching signal cycle, wherein the step comprises the following sub-steps: The step of generating a first midpoint detection control signal (Φ1) and a second midpoint detection control signal (Φ1B) according to a switching signal of a switching power converter: dividing the switching signal into odd cycles and even cycles, the first midpoint detection control signal (Φ1) is at a high level only when the switching signal is at a high level in an odd switching cycle, and is at a low level at other times; the second midpoint detection control signal (Φ1B) is at a high level only when the switching signal is at a high level in an even switching cycle, and is at a low level at other times; that is, the first midpoint detection control signal (Φ1) or the second midpoint detection control signal (Φ1B) is equal to the switching signal; A midpoint detection operational amplifier is provided, and a first midpoint detection capacitor and a second midpoint detection capacitor are connected to the non-inverting input terminal and the inverting input terminal of the midpoint detection operational amplifier respectively, the capacitance values ​​of the first midpoint detection capacitor and the second midpoint detection capacitor are the same, and the other terminals of the two capacitors are grounded; A first midpoint detection control signal (Φ1) and a second midpoint detection control signal (Φ1B) are used to control the charging and discharging processes of the first midpoint detection capacitor and the second midpoint detection capacitor respectively; a midpoint detection operational amplifier outputs a midpoint time signal according to the voltage inputted by the non-inverting input terminal and the inverting input terminal, and the midpoint time signal includes information of the first midpoint time T MB and the second midpoint time T MC .

8. A load current detection circuit for an inductive switching power supply converter, characterized in that: It includes a midpoint detection circuit (32) for the inductor current rising period or falling period and a sampling and holding circuit (34) for sampling and holding the load current; The inductor current rising period or falling period midpoint detection circuit (32) is used to obtain the inductor current rising period or falling period in the Ath switching cycle, recorded as TA, and is also used to obtain the inductor current rising period or falling period in the Bth switching cycle, recorded as TB, where B is equal to A+N; The midpoint detection circuit (32) of the inductor current rising period or falling period is further used to obtain a first midpoint moment TMB in the Bth switching cycle and a second midpoint moment TMC in the Cth switching cycle; the first midpoint moment TMB is the moment after 0.5TA from the starting moment of the inductor current rising period or falling period in the Bth switching cycle; the second midpoint moment TMC is the moment after 0.5TB from the starting moment of the inductor current rising period or falling period in the Cth switching cycle; wherein C is equal to B+M; A, B, C, N and M are all natural numbers greater than or equal to 1; The midpoint detection circuit (32) of the inductor current rising period or falling period is electrically connected to the sampling and holding circuit (34); the midpoint detection circuit (32) of the inductor current rising period or falling period outputs a midpoint time signal to the sampling and holding circuit (34); the midpoint time signal includes information of a first midpoint time TMB and a second midpoint time TMC; the sampling and holding circuit (34) samples the load current at the first midpoint time TMB, and holds the sampled load current until an update time, i.e., a second midpoint time TMC; during the period from the first midpoint time TMB to the second midpoint time TMC, If the switching power converter is a Buck type switching power converter, the load current sampling signal is output during both the rising and falling time periods of the inductor current; if the switching power converter is a Boost type or Buck-Boost type switching power converter, the load current sampling signal is output during the falling time period of the inductor current.

9. The load current detection circuit of the inductive switching power converter as claimed in claim 8, wherein: Also included is a low pass filter (35); The low-pass filter (35) is electrically connected to the sample-and-hold circuit (34); The load current sampling signal input from the sample-and-hold circuit (34) to the low-pass filter (35) is low-pass filtered by the low-pass filter (35) and then output.

10. The load current detection circuit of the inductive switching power supply converter as claimed in claim 8, characterized in that: The midpoint detection circuit (32) during the rising period or the falling period of the inductor current comprises a first midpoint detection switch, a second midpoint detection switch, a third midpoint detection switch, a fourth midpoint detection switch, a first midpoint detection capacitor, a second midpoint detection capacitor, a midpoint detection operational amplifier, and two current sources of the same size, namely a first current source and a second current source, wherein the first current source is used to inject current, and the second current source is used to output current; The output terminal of the first current source is electrically connected to the inverting input terminal of the midpoint detection operational amplifier through the first midpoint detection switch, and the output terminal of the first current source is also electrically connected to the non-inverting input terminal of the midpoint detection operational amplifier through the second midpoint detection switch; the input terminal of the second current source is electrically connected to the inverting input terminal of the midpoint detection operational amplifier through the third midpoint detection switch, and the input terminal of the second current source is also electrically connected to the non-inverting input terminal of the midpoint detection operational amplifier through the fourth midpoint detection switch; The non-inverting input terminal of the midpoint detection operational amplifier is electrically connected to one end of the second midpoint detection capacitor, and the other end of the second midpoint detection capacitor is grounded; the inverting input terminal of the midpoint detection operational amplifier is electrically connected to one end of the first midpoint detection capacitor, and the other end of the first midpoint detection capacitor is grounded; the capacitance of the first midpoint detection capacitor and the second midpoint detection capacitor are the same; The first midpoint detection switch and the fourth midpoint detection switch are controlled by a first midpoint detection control signal (Φ1); when the first midpoint detection control signal is at a high level, the first midpoint detection switch and the fourth midpoint detection switch are both closed, so that both ends of the switch are connected; when the first midpoint detection control signal is at a low level, the first midpoint detection switch and the fourth midpoint detection switch are both opened, so that both ends of the switch are disconnected; The second midpoint detection switch and the third midpoint detection switch are controlled by a second midpoint detection control signal (Φ1B); when the second midpoint detection control signal is at a high level, the second midpoint detection switch and the third midpoint detection switch are both closed, so that both ends of the switch are connected; when the second midpoint detection control signal is at a low level, the second midpoint detection switch and the third midpoint detection switch are both opened, so that both ends of the switch are disconnected; The first midpoint detection control signal (Φ1) or the second midpoint detection control signal (Φ1B) is equal to the switching signal of the inductive switching power converter; when the switching signal is in an odd number of cycles, the high level of the first midpoint detection control signal (Φ1) is the same as the high level of the switching signal; when the switching signal is in an even number of cycles, the high level of the second midpoint detection control signal (Φ1B) is the same as the high level of the switching signal; The output terminal of the midpoint detection operational amplifier outputs a first midpoint time signal, and the first midpoint time signal is transmitted to the sampling and holding circuit (34) to control the sampling time of the sampling circuit.

11. The load current detection circuit of the inductive switching power supply converter according to claim 10, wherein: The midpoint detection circuit (32) for the inductor current rising period or falling period also includes a D trigger and an XOR gate; The clock signal of the D flip-flop is an externally input switching signal for controlling an inductive switching power converter; the first input terminal (D) of the D flip-flop and the second output terminal (Qn) of the D flip-flop are electrically connected, and the first output terminal (Q) of the D flip-flop outputs a signal to an input terminal of an XOR gate; The output terminal of the midpoint detection operational amplifier outputs a first midpoint time signal to another input terminal of the XOR gate, and the output terminal of the XOR gate outputs a second midpoint time signal, which is transmitted to the sampling and holding circuit (34) to control the sampling time of the sampling circuit.

12. The load current detection circuit of the inductive switching power converter according to claim 11, wherein: The first output terminal (Q) of the D flip-flop outputs a signal to the first AND gate, performs an AND operation with the switch signal controlled by the inductive switching power converter, and outputs a first midpoint detection control signal (Φ1); The second output terminal (Qn) of the D flip-flop outputs a signal to the second AND gate, performs an AND operation with the switch signal controlled by the inductive switching power converter, and outputs a second midpoint detection control signal (Φ1B).

13. The load current detection circuit of the inductive switching power supply converter according to claim 11, wherein: The sample-hold circuit (34) comprises a second sample-hold switch, a second sample-hold capacitor, a third sample-hold switch, a third sample-hold capacitor and a sample-hold operational amplifier; One end of the second sampling and holding switch is used to connect to an external inductor current detection circuit to obtain a load current sampling signal, the other end of the second sampling and holding switch is electrically connected to one end of the second sampling and holding capacitor and one end of the third sampling and holding switch, and the other end of the second sampling and holding capacitor is grounded; the other end of the third sampling and holding switch is electrically connected to the non-inverting input terminal of the sampling and holding operational amplifier and one end of the third sampling and holding capacitor, and the other end of the third sampling and holding capacitor is grounded; the inverting input terminal of the sampling and holding operational amplifier is electrically connected to the output terminal of the sampling and holding operational amplifier; The second sampling and holding switch is controlled by the negative signal of the second midpoint signal. When the negative signal of the second midpoint signal is at a high level, the second sampling and holding switch is closed to connect the two ends of the switch. When the negative signal of the second midpoint signal is at a low level, the second sampling and holding switch is opened to disconnect the two ends of the switch. The third sampling and holding switch is controlled by the second midpoint time signal. When the second midpoint time signal is at a high level, the third sampling and holding switch is closed to connect the two ends of the switch. When the second midpoint time signal is at a low level, the third sampling and holding switch is opened to disconnect the two ends of the switch.

14. The load current detection circuit of the inductive switching power converter as claimed in claim 9, wherein: It also includes an inductor current zero-crossing point detection circuit (31) for obtaining a low-pass filter switch control signal.

15. The load current detection circuit of the inductive switching power converter as claimed in claim 14, wherein: The low-pass filter (35) and the sample-and-hold circuit (34) are electrically connected via a low-pass filter switch; the low-pass filter switch is controlled by a low-pass filter switch control signal output from the inductor current zero-crossing point detection circuit (31); When the inductor current is zero, the low-pass filter switch control signal controls the low-pass filter switch to open, disconnecting the two ends of the switch, thereby disconnecting the low-pass filter (35) and the sampling and holding circuit (34), and grounding the input of the low-pass filter (35); when the inductor current is non-zero, the low-pass filter switch control signal controls the low-pass filter switch to close, connecting the two ends of the switch, thereby electrically connecting the low-pass filter (35) and the sampling and holding circuit (34).

16. The load current detection circuit of the inductive switching power supply converter according to claim 15, wherein: It also includes a low-pass filter input pull-down MOS tube, which is used to pull down the input of the low-pass filter (35) after the connection between the low-pass filter (35) and the sampling and holding circuit (34) is disconnected, so that the input of the low-pass filter (35) is zero.

17. The load current detection circuit of the inductive switching power supply converter according to claim 16, wherein: The low-pass filter (35) comprises one or more stages of low-pass filters.

18. The load current detection circuit of the inductive switching power supply converter according to claim 17, wherein: When the low-pass filter (35) is a first-stage RC low-pass filter, the first-stage RC low-pass filter comprises a low-pass filter resistor and a low-pass filter capacitor; One end of the low-pass filter resistor is electrically connected to one end of the low-pass filter switch, and at the same time, one end of the low-pass filter resistor is electrically connected to the source of the low-pass filter input pull-down MOS tube, the gate of the low-pass filter input pull-down MOS tube is connected to the non-signal of the low-pass filter switch control signal, and the drain of the low-pass filter input pull-down MOS tube is grounded; The other end of the low-pass filter resistor is used as an output terminal of the low-pass filter (35), and the other end of the low-pass filter resistor is also electrically connected to one end of a low-pass filter capacitor, and the other end of the low-pass filter capacitor is grounded.

19. The load current detection circuit of the inductive switching power converter as claimed in claim 8, wherein: It also includes an inductor current detection circuit (30) for sampling and obtaining load current; The inductor current detection circuit (30) and the sample-and-hold circuit (34) are electrically connected; The inductor current detection circuit (30) outputs a load current signal to the sample and hold circuit (34).

20. An inductive switching power converter, characterized in that: A load current detection circuit for a switching power supply converter comprising any one of claims 8 to 19.

21. The inductive switching power converter according to claim 20, wherein: It also includes a logic control circuit; the logic control circuit is used to generate a basic switching signal for timing control of an inductive switching power converter; The logic control circuit generates a first control signal GP and a second control signal GN for controlling two power switch tubes according to the basic switch signal; when the first control signal GP is at a high level, one of the power tubes is turned on; when the first control signal GP is at a low level, the other power tube is turned on; the first control signal GP and the second control signal GN are synchronous conversion signals of the basic switch signal; the inductor current rising time period and the inductor current falling time period are synchronized with the first control signal GP and the second control signal GN; thus, the inductor current rising time period and the inductor current falling time period are also synchronized with the basic switch signal.

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