Switching power supply converter load current detection circuit and method

Abstract

Switching power supply converter load current detection circuit and method, only need to set a switching transistor peak current sampling circuit, a sample and hold circuit, an inductor current compensation circuit and a low-pass filter circuit; the detection method includes the following steps: sampling to obtain the peak current during the inductor current rising period, i.e., the switching transistor conduction period, of a Boost-type or Buck-Boost type switching power supply converter in the current switching cycle; sampling and holding the peak current sampling value during the inductor current rising period, i.e., the switching transistor conduction period, through the sample and hold circuit; during the freewheeling diode conduction period, compensating the peak current sampling value during the switching transistor conduction period through the inductor current compensation circuit, and the compensated inductor current signal is output to the low-pass filter after being held by the sample and hold circuit, and the load current signal of the switching power supply converter is obtained after being smoothed by the low-pass filter. The above method simplifies the circuit, improves the detection accuracy and reliability, and reduces the cost and power consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power converter circuits, and particularly relates to a method and circuit for detecting load current of a switching power converter, which reduces the complexity of the load current detection circuit while improving 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, mainly applicable to voltage conversion situations. The circuit forms of DC / DC switching power converters include charge pump circuits implemented by capacitors, as well as buck-type Buck switching circuits, boost-type Boost circuits, and buck-boost circuits for negative voltage implemented by inductors. In order to precisely 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 the technical solution shown in the attached Figure 2 figure. A external current sensing resistor Rsen is connected in series on the current path of the inductor outside the switching power converter chip. When the current of the inductor flows through the current sensing resistor Rsen, a voltage drop will be generated, and it is returned to the operational amplifier inside the chip through two pins on the chip. The load current detection is achieved by amplifying the voltage on the current sensing resistor through the operational amplifier. In the solution with an external current sensing resistor, the operational amplifier needs to constantly detect the voltage across the resistor, which requires extremely high speed and accuracy of the operational amplifier; and this circuit structure needs to connect a load detection resistor Rsen in series to the inductor in the loop. In each switching cycle, the current flowing through the load detection resistor Rsen will cause efficiency loss of the switching power converter; due to the power loss heating on the off-chip load detection resistor Rsen, the resistance value of the load detection resistor Rsen will change, not only resulting in efficiency loss, but also reducing the detection accuracy, and high-precision current sensing resistors are relatively expensive; in addition, two pins need to be set on the chip for the current sensing resistor, so the complexity of the chip increases, the integration degree decreases, and the cost of the system rises. In boost-type and buck-boost-type switching power converter circuits, since the load current is discontinuous, it is required that the operational amplifier has a fast response and high precision, and the error of the load current detected by using a common operational amplifier is large.

[0004] In the prior art solutions, some switching power converter chips require an external freewheeling diode design, and such solutions cannot adopt in-chip load current sampling.

[0005] In the switching power supply converter chips of the prior art, if the on-chip load current sampling technology is adopted, the detection of the output load current is achieved by sampling the current of the freewheeling diode. This method is relatively complex and consumes a large amount of power when the output voltage and the input voltage of Boost or Buck-Boost have a large difference. In addition, in the switching power supply converter chips of the prior art, it is also necessary to limit the peak value of the inductor current, so the sampling of the switch tube current is essential. In addition, if the load current is to be detected, the current of the freewheeling diode needs to be sampled, which is equivalent to adding a set of circuits.

[0006] Glossary:

[0007] The meaning of the Buck-type switching power supply converter in this application is a step-down DC / DC conversion system adopting the Buck REGULATOR method; its input voltage is greater than the output voltage;

[0008] The meaning of the Boost-type switching power supply converter in this application is a boost DC / DC conversion system adopting the Boost REGULATOR method; its output voltage is greater than the input voltage;

[0009] The meaning of the Buck-Boost-type switching power supply converter in this application is a negative voltage DC / DC conversion system adopting the Buck-Boost REGULATOR method;

[0010] PWM is the abbreviation of Pulse Width Modulation in English, and its Chinese meaning is Pulse Width Modulation; the pulse width modulation (PWM) switching power supply converter adjusts its duty cycle under the condition that the output frequency of the control circuit remains unchanged, so as to achieve the purpose of stabilizing the output voltage;

[0011] CCM is the abbreviation of Continuous Conduction Mode in English, and its Chinese meaning is Continuous Conduction Mode, which refers to the working mode in the Boost boost circuit where the power tubes are alternately and continuously conducting, making the current in the inductor continuously change;

[0012] DCM: is the abbreviation of Discontinuous Conduction Mode in English, and its Chinese meaning is Discontinuous Conduction Mode, which refers to the working mode in the Boost boost circuit where one of the power tubes is alternately turned off, making the current in the inductor change discontinuously. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to avoid the deficiencies of the above-mentioned prior art solutions, and a method and circuit for detecting the load current of a switching power converter suitable for sampling the load current inside the switching power converter chip are proposed, which reduces the complexity of the load current detection circuit and improves the accuracy of the load current detection.

[0014] The technical solution adopted by the present invention to solve the above technical problem is a load current detection circuit for a switching power converter, which includes a switching transistor peak current sampling circuit for obtaining the peak current signal of the switching transistor of a Boost-type or Buck-Boost type switching power converter, a sample and hold circuit for holding the sampling signal of the switching transistor peak current, an inductive current compensation circuit for compensating the sampling signal of the switching transistor peak current, and a low-pass filter circuit; the switching transistor peak current sampling circuit is electrically connected to the sample and hold circuit, and the sample and hold circuit obtains the peak current signal of the switching transistor from the switching transistor peak current sampling circuit; the inductive current compensation circuit is electrically connected to the sample and hold circuit, and during the conduction period of the freewheeling diode of the switching power converter, the peak current signal of the switching transistor is compensated to obtain a compensated inductive current signal; the low-pass filter circuit is electrically connected to the sample and hold circuit, and the compensated inductive current signal is output after low-pass filtering and used as the load current signal.

[0015] The sample and hold circuit includes a first switch, a sampling capacitor, and a sampling operational amplifier; one end of the first switch is electrically connected to the switching transistor peak current sampling circuit, the other end of the first switch is electrically connected to one end of the sampling capacitor and the positive input terminal of the sampling operational amplifier; the other end of the sampling capacitor is grounded; the negative input terminal of the sampling operational amplifier is electrically connected to the output terminal of the sampling operational amplifier; the inductive current compensation circuit is electrically connected to one end of the sampling capacitor and the positive input terminal of the sampling operational amplifier; the first switch is controlled by a second control signal obtained from the switching power converter; when the second control signal is at a high level, the first switch is closed to electrically connect the sample and hold circuit to the switching transistor peak current sampling circuit; when the second control signal is at a low level, the first switch is opened to disconnect the connection between the sample and hold circuit and the switching transistor peak current sampling circuit.

[0016] A third switch is provided between the inductive current compensation circuit and the sample and hold circuit; the third switch is controlled by a first control signal obtained from the switching power converter; when the first control signal is at a high level, the third switch is closed to electrically connect the sample and hold circuit to the inductive current compensation circuit; when the first control signal DRN is at a low level, the third switch is opened to disconnect the connection between the sample and hold circuit and the inductive current compensation circuit; or the third switch is a diode, and the electrical connection or disconnection between the sample and hold circuit and the inductive current compensation circuit is controlled by the voltage signal across the two ends of the diode.

[0017] The inductive current compensation circuit is a current source.

[0018] During the inductor current decline period, i.e., the freewheeling diode conduction period, the compensation current provided by the inductor current compensation circuit is equal to the peak current value of the switching transistor minus the inductor current value during the freewheeling diode conduction period.

[0019] When the switching power supply converter is a Boost type switching power supply converter, the inductor current compensation circuit includes a first current mirror, a first operational amplifier, a first resistor, a first transistor, a third resistor, and a fourth resistor; one end of the third resistor is used to be electrically connected to the voltage output terminal of the switching power supply converter, the other end of the third resistor, one end of the fourth resistor, and the positive input terminal of the first operational amplifier are electrically connected; the other end of the fourth resistor is grounded; the negative output terminal of the first operational amplifier, the drain of the first transistor, and one end of the first resistor are electrically connected; the other end of the first resistor is grounded; the output terminal of the first operational amplifier and the gate of the first transistor are electrically connected, and the source of the first transistor is electrically connected to one end of the first current mirror; the inductor current compensation circuit further includes a third current mirror, a second current mirror, a second operational amplifier, a second resistor, a second transistor, a fifth resistor, and a sixth resistor; one end of the fifth resistor is used to be electrically connected to the voltage input terminal of the switching power supply converter; the other end of the fifth resistor, one end of the sixth resistor, and the positive input terminal of the second operational amplifier are electrically connected; the other end of the sixth resistor is grounded; the negative output terminal of the second operational amplifier, the drain of the second transistor, and one end of the second resistor are electrically connected; the other end of the second resistor is grounded; the output terminal of the second operational amplifier and the gate of the second transistor are electrically connected, and the source of the second transistor is electrically connected to one end of the second current mirror; one end of the third current mirror is electrically connected to one end of the first current mirror, and the other end of the third current mirror is electrically connected to one end of the second current mirror; in the third current mirror, the end connected to the second current mirror is simultaneously used as the inductor current compensation signal output terminal.

[0020] When the switching power supply converter is a Buck - Boost type switching power supply converter, the inductor current compensation circuit includes a fourth current mirror, a seventh resistor, an eighth resistor, a third operational amplifier, a fourth transistor, and a fifth transistor; one end of the eighth resistor is used to be electrically connected to the voltage output terminal of the switching power supply converter; the other end of the eighth resistor, one end of the seventh resistor, and the negative input terminal of the third operational amplifier are electrically connected; the positive output terminal of the second operational amplifier is grounded; the other end of the seventh resistor is electrically connected to the drain of the fourth transistor; the output terminal of the third operational amplifier is electrically connected to the gate of the fourth transistor and the gate of the fifth transistor, the source of the fourth transistor and the source of the fifth transistor are connected to the power supply; the fourth current mirror includes a forty - first transistor and a forty - second transistor, the gate of the forty - first transistor is electrically connected to the gate of the forty - second transistor, the drains of the forty - first transistor and the forty - second transistor are both grounded, the gate of the forty - first transistor is electrically connected to the source of the forty - first transistor to be used as the first terminal of the fourth current mirror, the source of the forty - second transistor is used as the second terminal of the fourth current mirror; the first terminal of the fourth current mirror is electrically connected to the drain of the fifth transistor, and the second terminal of the fourth current mirror is used as the inductor current compensation signal output terminal.

[0021] The sample - and - hold circuit further includes a low - pass filter input control transistor; the input terminal of the low - pass filter circuit is electrically connected to the source of the low - pass filter input control transistor, the gate of the low - pass filter input control transistor receives a second control signal obtained from the switching power supply converter, and the drain of the low - pass filter input control transistor is grounded; the low - pass filter input control transistor is controlled by the second control signal. When the second control signal is at a low level, the low - pass filter input control transistor is turned on, and the input signal at the input terminal of the low - pass filter circuit is pulled low; the sample - and - hold circuit further includes a second switch, one end of the second switch is electrically connected to the input terminal of the low - pass filter circuit, and the other end of the second switch is electrically connected to the output terminal of the sampling operational amplifier; the second switch is controlled by the inverted signal of the second control signal obtained from the switching power supply converter; when the inverted signal of the second control signal is at a high level, the second switch is closed, and the sample - and - hold circuit is connected to the low - pass filter circuit; when the inverted signal of the second control signal is at a high level, the second switch is opened, and the sample - and - hold circuit is disconnected from the low - pass filter circuit.

[0022] The technical solution adopted by the present invention to solve the above - mentioned technical problem may also be a switching power supply converter, including the above - mentioned switching power supply converter load current detection circuit;

[0023] The described switching power converter circuit further includes a logic control circuit; the logic control circuit is used to generate a basic switching signal for the timing control of the inductive switching power converter; the logic control circuit generates a first control signal for controlling the switching transistor and a second control signal for controlling the freewheeling diode according to the basic switching signal; when the first control signal is at a high level, the switching transistor is turned on; when the second control signal is at a high level, the freewheeling diode is turned on; the first control signal and the second control signal are synchronous transformation signals of the basic switching signal; the inductor current rising period is synchronous with the first control signal; the inductor current falling period is synchronous with the second control signal.

[0024] The technical solution adopted by the present invention to solve the above technical problem may also be a method for detecting the load current of a switching power converter, including the following steps: sampling and obtaining the peak current during the inductor current rising period, i.e., the switching transistor conduction period, in the current switching cycle of a Boost-type or Buck-Boost type switching power converter; maintaining the peak current sampling value during the inductor current rising period, i.e., the switching transistor conduction period, through a sample and hold circuit; during the inductor current falling period, i.e., the freewheeling diode conduction period, in the current switching cycle, using an inductor current compensation circuit to compensate for the inductor current drop during the freewheeling diode conduction period, compensating the peak current sampling value during the switching transistor conduction period through the inductor current compensation circuit, and the compensated inductor current signal is output after being held by the sample and hold circuit, and the signal output by the sample and hold circuit is smoothed by a low-pass filter to obtain the load current signal of the switching power converter.

[0025] In the method for detecting the load current of the described switching power converter, during the inductor current falling period, i.e., the freewheeling diode conduction period, the compensation current provided by the inductor current compensation circuit is equal to the switching transistor peak current value minus the inductor current value during the freewheeling diode conduction period.

[0026] The inductor current compensation circuit is a current source.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The number of pins of the chip is reduced. The current of the switching transistor is detected during the conduction period of the switching transistor, and the current sampling value is sampled and held at the peak of the switching transistor. The sampled current is maintained during the conduction period of the freewheeling diode, and the current is compensated, saving the circuit for detecting the freewheeling diode current, simplifying the design of the switching transistor drive, greatly reducing the complexity of the load current detection circuit, and simplifying the load current detection circuit; 2. The number of external components is reduced, that is, the external current sensing resistor is omitted, reducing a part of the heat dissipation power consumption, improving the efficiency of the circuit; and improving the integration of the circuit, simplifying the electronic circuit, the circuit board has a small volume, and the circuit reliability is also greatly improved; 3. Due to the introduction of compensation, and the compensation process is due to precise timing control, the compensation can be closer to the real load current to a greater extent, not only avoiding complex circuit design, but also improving the accuracy of load current detection, greatly reducing the complexity and design difficulty of the circuit; 4. The circuit structure is simple and ingenious, with strong applicability, and can be used in Boost-type and Buck-Boost-type DC / DC switching power converters; it is also applicable to synchronous and asynchronous rectifier circuits. In integrated circuit applications, it is easy to deploy and apply, saving chip area and pins, and reducing the complexity and power consumption of load current detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic block diagram of the principle of a preferred embodiment of the load current detection circuit of the present invention;

[0029] Figure 2 is one of the schematic diagrams of the principle of the prior art load current detection circuit in the application of the DC / DC switching power converter circuit;

[0030] Figure 3 is a schematic diagram of the corresponding timing and error description of the inductor current and load current detection when the prior art load current detection circuit operates in the Boost-type CCM mode;

[0031] Figure 4 is a schematic diagram of the circuit principle of a preferred embodiment of the load current detection circuit of the present invention;

[0032] Figure 5 is Figure 4 a schematic diagram of the circuit principle of one of the specific embodiments of the inductor current compensation circuit 32 in

[0033] Figure 6 is a schematic diagram of the circuit principle of a second preferred embodiment of the load current detection circuit of the present invention;

[0034] Figure 7 is Figure 6 a schematic diagram of the circuit principle of one of the specific embodiments of the inductor current compensation circuit 32 in

[0035] As Figure 8 shown is a schematic diagram of the working waveform timing of the load current detection circuit of the present invention when the Boost or Buck - boost type switching power supply converter operates in the CCM (Continuous Conduction Mode).

[0036] As Figure 9 shown is a schematic diagram of the working waveform timing of the load current detection circuit of the present invention when the Boost or Buck - boost type switching power supply converter operates in the DCM (Discontinuous Conduction Mode). Figure 8 and Figure 9 the IFB signal in is the load current signal output by the load current detection circuit for the control of the switching power supply converter system. Specific Embodiments

[0037] The following further details the embodiments of the present invention in conjunction with the accompanying drawings.

[0038] For inductive switching power supply converters, their basic principle is to utilize the energy storage characteristic of the inductor to achieve voltage variation. The rate of change of the inductor current is equal to the voltage across the inductor divided by the inductance value in henries, 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 applied voltage across the inductor is constant and the inductance value is determined, the slopes of the rise and fall of the inductor current are also fixed.

[0039] In the existing boost - type Boost switching power supply converter circuit and negative - voltage Buck - Boost switching power supply converter circuit, the two power transistors are respectively called the switching transistor and the free - wheeling transistor. The basic characteristics of the switching power supply converter referred to in the present invention include: in the CCM operating mode, the switching power supply converter controls the alternating conduction of the switching transistor and the free - wheeling transistor through a logic control circuit. One switching cycle includes a period of rising inductor current and a period of falling inductor current; in the DCM operating mode, the switching power supply converter controls the alternating conduction and intermittent shutdown of the two switching transistors and the free - wheeling transistor through a logic control circuit, that is, in one switching cycle, it includes a period of rising inductor current, a period of falling inductor current, and a period when the inductor current is zero.

[0040] As Figure 3 shown in the typical waveform of the inductor current of the switching power supply converter, after the switching transistor conducts, the inductor current starts to rise until the switching transistor turns off and the inductor current reaches the peak; the free - wheeling transistor starts to conduct and the inductor current starts to fall until the end of the cycle. Therefore, only by obtaining the area of the slanted shaded part during the conduction time of the free - wheeling transistor, that is, the total output charge amount. Dividing the sum of the shaded areas of N consecutive cycles by the total cycle time can obtain the magnitude of the load current.

[0041] As Figure 3 shown, if the peak current of the freewheeling diode is maintained as the load current throughout the entire switching cycle, there is an extra triangular shaded area as shown by the shaded line in the figure compared to the actual load current. There is an error in the shaded part between the current sampled and held using the peak current of the freewheeling diode and the actual load current. Further, in the technical solutions for sampling the peak current of the freewheeling diode, there are various circuit implementation forms. If the freewheeling diode is replaced by a diode, the load current detection circuit with a current mirror architecture cannot be used for load current detection in asynchronous rectification.

[0042] In Boost and Buck - Boost switching power converters, energy is stored in the inductor during the conduction period of the switching transistor and output to the load during the conduction period of the freewheeling diode. During the conduction period of the switch, only the inductor is charged and no energy is output to the load. Therefore, in the prior art, the inductor current during the conduction period of the freewheeling diode is usually sampled as the load current. From Figure 3 It can be seen that only by obtaining the area of the slanted shaded part during the conduction time of the freewheeling diode and dividing the sum of the shaded areas of N consecutive cycles by the total cycle time can the magnitude of the load current be obtained.

[0043] In the prior art, there are also some technical solutions that detect the peak current of the freewheeling diode and sample and hold this peak current as the load current for one switching cycle. From Figure 3 It can be seen that if the peak current is maintained throughout the switching cycle, there is an extra triangular shaded area, which is the sampling error.

[0044] In this patent, instead of sampling the peak current of the freewheeling diode, the peak value of the inductor current during the conduction period of the switching transistor is sampled and held starting from when the freewheeling diode begins to conduct until the end of the current switching cycle or the inductor current drops to zero. For conventional switching power converters, it is usually necessary to detect the inductor current value during the conduction period of the control switching transistor to prevent damage due to inductor current saturation. Therefore, the inductor current peak sampling circuit can be shared, and there is no need to separately set up a special inductor current sampling circuit for the conduction period of the freewheeling diode.

[0045] Further, in this patent, an inductor current compensation circuit is designed to perform current compensation during the conduction period of the freewheeling diode to eliminate the error caused by current peak sampling. The current of the switching transistor is detected during the conduction period of the switching transistor, and the magnitude of this current is sampled and held at the moment before the switching transistor turns off, which is the peak value of the inductor current. When the freewheeling diode conducts, the sampled peak current is held, and at the same time, the sampling signal is output to the low - pass filter, and a compensation current is also added to simulate the decrease process of the inductor current of the freewheeling diode, greatly improving the detection accuracy.

[0046] As Figure 4As shown, it is a preferred example of the load current detection circuit of the present invention applied to a Boost-type switching power supply converter. When the second control signal DRN is at a high level and the switching transistor, i.e., transistor M1, is turned on, transistor M2 in the switching transistor peak current sampling circuit 30 is a mirror transistor of transistor M1. Due to the virtual short characteristic of the operational amplifier, the drain voltages of transistor M2 and transistor M1 are kept the same. The current magnitude of transistor M2 is 1 / K of the current of transistor M1, where K is the magnification ratio of the current mirror formed by transistor M1 and transistor M2. The relationship between the current IM2 of transistor M2 and the current IM1 of transistor M1 is: . The voltage on the sampling capacitor C1 becomes higher as the current of transistor M1 increases.

[0047] As Figure 4 shown, when the second control signal DRN becomes low, at the moment before turning off the switching transistor, i.e., transistor M1, the voltage stored on the sampling capacitor C1 is the peak inductor current. After the second control signal DRN becomes low, the inductor current compensation circuit 32 will slowly discharge the sampling capacitor C1 to simulate the process of the inductor current decreasing. The voltage signal on the internal current sensing resistor Rs is the simulated inductor current signal of the freewheeling diode, and this inductor current signal is the switching transistor peak current minus the current compensation signal output by the inductor current compensation circuit 32. Thus, the load current detection of the Boost-type voltage converter is achieved. Figure 4 Transistor M3 in

[0048] As Figure 5 shown is a preferred example of the inductor current compensation circuit 32 in the load current detection circuit of the Boost-type switching power supply converter.

[0049] As Figure 5As shown, when the switching power supply converter is a Boost-type switching power supply converter, the inductor current compensation circuit 32 includes a first current mirror, a first operational amplifier OA1, a first resistor R1, a first transistor MA1, a third resistor R3, and a fourth resistor R4; one end of the third resistor R3 is used to be electrically connected to the voltage output terminal of the switching power supply converter, the other end of the third resistor R3, one end of the fourth resistor R4, and the positive input terminal of the first operational amplifier OA1 are electrically connected; the other end of the fourth resistor R4 is grounded; the negative output terminal of the first operational amplifier OA1, the drain of the first transistor MA1, and one end of the first resistor R1 are electrically connected; the other end of the first resistor R1 is grounded; the output terminal of the first operational amplifier OA1 and the gate of the first transistor MA1 are electrically connected, and the source of the first transistor MA1 and one end of the first current mirror are electrically connected; the inductor current compensation circuit 32 further includes a third current mirror, a second current mirror, a second operational amplifier OA2, a second resistor R2, a second transistor MA2, a fifth resistor R5, and a sixth resistor R6; one end of the fifth resistor R5 is used to be electrically connected to the voltage input terminal of the switching power supply converter; the other end of the fifth resistor R5, one end of the sixth resistor R6, and the positive input terminal of the second operational amplifier OA2 are electrically connected; the other end of the sixth resistor R6 is grounded; the negative output terminal of the second operational amplifier OA2, the drain of the second transistor MA2, and one end of the second resistor R2 are electrically connected; the other end of the second resistor R2 is grounded; the output terminal of the second operational amplifier OA2 and the gate of the second transistor MA2 are electrically connected, and the source of the second transistor MA2 and one end of the second current mirror are electrically connected; one end of the third current mirror and one end of the first current mirror are electrically connected, and the other end of the third current mirror and one end of the second current mirror are electrically connected; in the third current mirror, the end connected to the second current mirror is simultaneously used as the inductor current compensation signal output terminal.

[0050] As Figure 5 shown, the first current mirror includes an eleventh transistor MA11 and a twelfth transistor MA12. The gate of the eleventh transistor MA11 and the gate of the twelfth transistor MA12 are electrically connected, the drain of the eleventh transistor MA11 and the drain of the twelfth transistor MA12 are electrically connected, the gate of the eleventh transistor MA11 and the source of the eleventh transistor MA11 are electrically connected and used as the first terminal of the first current mirror, and the source of the twelfth transistor MA12 is used as the second terminal of the first current mirror.

[0051] As Figure 5As shown, the second current mirror includes a twenty-first transistor MA21 and a twenty-second transistor MA22. The gates of the twenty-first transistor MA21 and the twenty-second transistor MA22 are electrically connected. The drains of the twenty-first transistor MA21 and the twenty-second transistor MA22 are electrically connected. The gate and the source of the twenty-second transistor MA22 are electrically connected and used as the first terminal of the second current mirror. The source of the twenty-first transistor MA21 is used as the second terminal of the second current mirror.

[0052] As Figure 5 shown, the third current mirror includes a thirty-first transistor MA31 and a thirty-second transistor MA32. The gates of the thirty-first transistor MA31 and the thirty-second transistor MA32 are electrically connected. The drains of the thirty-first transistor MA31 and the thirty-second transistor MA32 are grounded. The gate and the source of the thirty-first transistor MA31 are electrically connected and used as the first terminal of the third current mirror. The source of the thirty-second transistor MA32 is used as the second terminal of the third current mirror.

[0053] As Figure 5 shown, for a Boost-type switching power supply converter, the sum of the conduction times of the switching transistor and the freewheeling diode is defined as T. Among them, the duty cycle of the conduction time of the switching transistor is D. Then there is: (Equation 1); where V O is the output potential of the switching power supply converter with respect to ground, and V IN is the input potential of the switching power supply converter with respect to ground. Then in the Boost-type switching power supply converter, the peak-to-peak value of the inductor current is: (Equation 2), where L is the Henry value of the externally connected inductor.

[0054] If Boost is in continuous operation mode, the voltage change of the peak-to-peak value of the inductor current reflected on the sampling capacitor C1 is , where Rs is the on-chip sampling resistor.

[0055] If it is required that the compensation current output by the inductor current compensation circuit can exactly compensate for the current change trend during the conduction period of the freewheeling diode, the compensation current I1 should satisfy: ;

[0056] Substituting Equation 3 into Equation 4, we can get: ,

[0057] And according to Equation 1, it can be known that ;

[0058] Therefore, the magnitude of the compensation current I1 can be obtained as: .

[0059] As Figure 5In an embodiment of the designed inductor current compensation circuit, the resistance values of the first resistor R1 and the second resistor R2 are equal, i.e., R1 = R2, and the compensation current I1 is equal to ; By appropriately selecting the relationship between the sampling capacitor C1, the resistor R1 in the compensation circuit, the on-chip sampling resistor Rs of the peak current sampling circuit, the amplification factor K of the sampling current in the peak current sampling circuit 30, and the external inductor L, the detection of the conduction period of the freewheeling diode can be made consistent with the inductor current. When the difference range between V o and V IN is relatively small, the inductor current compensation circuit can be designed as a constant current source to output a constant compensation current I1, but the compensation accuracy will be reduced in this way.

[0060] As Figure 6 shown is a preferred example of the application of the load current detection circuit in a Buck-Boost type switching power supply converter. When the second control signal DRH is at a low level to turn on the M11 transistor, i.e., the switching transistor, the M12 transistor is the mirror transistor of the M11 transistor. Due to the virtual short characteristic of the operational amplifier, the drain voltages of the M12 and M11 transistors remain the same. The current magnitude of the M12 transistor is 1 / K of the current of the M11 transistor, where K is the magnification ratio of the current mirror formed by the M11 and M12 transistors. After the sampling capacitor C11 samples the peak value of the inductor current, a part of the current is compensated through the inductor current compensation circuit.

[0061] As Figure 7 shown is a preferred design of the inductor current compensation circuit 32 adopted in the load current detection circuit of a Buck-Boost type switching power supply converter.

[0062] As Figure 7 shown, when the switching power supply converter is a Buck-Boost type switching power supply converter, the inductor current compensation circuit 32 includes a fourth current mirror, a seventh resistor R7, an eighth resistor R8, a third operational amplifier OA3, a fourth transistor MA4, and a fifth transistor MA5; One end of the eighth resistor R8 is used to be electrically connected to the voltage output terminal of the switching power supply converter; The other end of the eighth resistor R8 is electrically connected to one end of the seventh resistor R7 and the negative input terminal of the third operational amplifier OA3; The positive output terminal of the third operational amplifier OA3 is grounded; The other end of the seventh resistor R7 is electrically connected to the drain of the fourth transistor MA4; The output terminal of the third operational amplifier OA3 is electrically connected to the gate of the fourth transistor MA4 and the gate of the fifth transistor MA5. The source of the fourth transistor MA4 and the source of the fifth transistor MA5 are connected to the external input power supply V IN of the switching power supply converter.

[0063] As Figure 7As shown, the fourth current mirror includes a forty-first transistor MA41 and a forty-second transistor MA42. The gates of the forty-first transistor MA41 and the forty-second transistor MA42 are electrically connected. The drains of the forty-first transistor MA41 and the forty-second transistor MA42 are both grounded. The gate of the forty-first transistor MA41 is electrically connected to the source of the forty-first transistor MA41 and serves as the first terminal of the fourth current mirror. The source of the forty-second transistor MA42 serves as the second terminal of the fourth current mirror. The first terminal of the fourth current mirror is electrically connected to the drain of the fifth transistor MA5. The second terminal of the fourth current mirror serves as the inductor current compensation signal output terminal.

[0064] As Figure 7 shown, for a Buck-Boost type switching power supply converter, the sum of the conduction times of its switching transistor and freewheeling diode is defined as T. Among them, the duty cycle of the switching transistor conduction time is D, then there is: ; The peak-to-peak value of its inductor current is .

[0065] If the Buck-Boost type switching power supply converter is in continuous operation mode, the peak-to-peak value of the inductor current is reflected in the voltage change of the sampling capacitor as: , where Rs is the on-chip sampling resistor.

[0066] If it is required that the compensation current output by the inductor current compensation circuit can exactly compensate for the current change trend during the conduction period of the freewheeling diode, the compensation current I1 should satisfy: ; Substituting equations 5, 6, and 7 into equation 8, we can get: ; The magnitude of the compensation current I1 can be obtained as .

[0067] As Figure 7 designed circuit, due to the virtual short characteristic of the operational amplifier, the voltage across the R8 resistor is equal to 0 - V o , so the generated mirror compensation current I1 is equal to ; Appropriately select the sampling capacitor C 11 , the seventh resistor R7 in the compensation circuit, and the on-chip sampling resistor Rs of the peak current sampling circuit, as well as the amplification factor K of the sampling current of the peak current sampling circuit and the relationship with the external inductor L, so that the detection of the freewheeling diode conduction period is consistent with the inductor current. When the change range of V o is relatively small, the inductor current compensation circuit can be designed as a constant current source to make its output a constant compensation current I1, but only in this way, the compensation accuracy is reduced.

[0068] As Figure 8The following is a schematic diagram of the working waveform timing of the load current detection circuit of the present invention when the Boost or Buck - boost type switching power supply converter operates in the CCM (Continuous Conduction Mode). When the second control signal DRN or DRH is equal to the high level, the inductor current starts to rise, and the inductor current peak sampling circuit starts to work. The inductor current sampling signal V SEN1 increases as the inductor current increases. After the inductor current reaches the peak, the first switch K1 / K11 is turned off, and what is maintained on the sampling capacitors C1 / C11 is the peak value of the inductor current. If there is no compensation current circuit, during the inductor current decline period, the inductor current sampling signal V SEN1 would be an approximately constant value parallel to the X - axis. Such a sampling and holding method would have a relatively large error. In the present invention, the added compensation current I1 simulates the slope of the inductor current decline during the inductor current decline period, reducing the error. During the inductor current decline period, the second switch K2 / K12 is turned on, and the current sampling and holding signal V SEN2 output by the sampling and holding circuit is output to the input end of the low - pass filter. After low - pass filtering, the accurate magnitude of the inductor current is obtained.

[0069] As Figure 9 shown is a schematic diagram of the waveform timing of the load current detection circuit of the present invention when the Boost or Buck - boost type switching power supply converter operates in the DCM (Discontinuous Conduction Mode), i.e., the discontinuous working mode. Its working principle is the same as Figure 8 that in the CCM mode. Only when operating in the DCM mode, the peak value of Vsen2 is relatively small, and the compensation current can discharge the charge of the sampling capacitor in one cycle, representing the time period when the inductor current is 0.

[0070] In embodiments not shown in some of the drawings, the logic control circuit in the switching power supply converter not only generates the basic switching signals of the switching power supply converter, such as the PWM switching signal, but also generates the first control signal DRP and the second control signal DRN for controlling two power switching transistors. When the first control signal DRP is at the high level, one of the power transistors is turned on; when the second control signal DRN is at the high level, the other power transistor is turned on. The first control signal DRP for controlling the switching transistor and the second control signal DRN for controlling the free - wheeling diode are both generated based on the PWM switching signal. Therefore, the first control signal DRP and the second control signal DRN are transformed signals of the PWM signal, and the signals are synchronous with each other. The inductor current rising time period and the inductor current falling time period are synchronous with the first control signal DRP and the second control signal DRN.

[0071] A method for detecting the load current of a switching power supply converter includes the following steps: sampling and obtaining the peak current during the rising period of the inductor current, i.e., the on-period of the switching transistor, in the current switching cycle of a Boost-type or Buck-Boost type switching power supply converter; maintaining the sampled value of the peak current during the rising period of the inductor current, i.e., the on-period of the switching transistor, through a sample-and-hold circuit; during the falling period of the inductor current in the current switching cycle, i.e., the on-period of the freewheeling diode, using an inductor current compensation circuit to compensate for the falling process of the inductor current during the on-period of the freewheeling diode, compensating the sampled value of the peak current during the on-period of the switching transistor through the inductor current compensation circuit, and the compensated inductor current signal is output after being held by the sample-and-hold circuit, and the signal output by the sample-and-hold circuit is smoothed by a low-pass filter to obtain the load current signal of the switching power supply converter.

[0072] During the falling period of the inductor current, i.e., the on-period of the freewheeling diode, the compensation current provided by the inductor current compensation circuit is equal to the peak current value of the switching transistor minus the inductor current value during the on-period of the freewheeling diode. The inductor current compensation circuit 32 is a current source.

[0073] The load current detection circuit of the switching power supply converter includes a switching transistor peak current sampling circuit for obtaining the peak current signal of the switching transistor of a Boost-type or Buck-Boost type switching power supply converter, a sample-and-hold circuit, an inductor current compensation circuit, and a low-pass filter circuit; the sample-and-hold circuit obtains the peak current signal of the switching transistor from the switching transistor peak current sampling circuit; during the on-period of the freewheeling diode of the switching power supply converter, current compensation is performed on the peak current signal of the switching transistor to obtain a compensated inductor current signal; the low-pass filter circuit is electrically connected to the sample-and-hold circuit, and the compensated inductor current signal is low-pass filtered and output as the load current signal. The circuit is simplified, the detection accuracy and reliability are improved, and the cost and power consumption are reduced.

[0074] In the above load current detection method, first, the current of the switching transistor is detected during the on-period of the switching transistor, and the magnitude of this current is sampled and held at the peak of the switching transistor current. During this period, the electrical connection between the sample-and-hold circuit and the input end of the low-pass filter is disconnected, and the input of the low-pass filter is pulled to ground; when the freewheeling diode is on, the sampled current is held, a sampling signal is output to the low-pass filter, and at the same time, a compensation current is added to simulate the falling process of the inductor current of the freewheeling diode, greatly improving the detection accuracy.

[0075] The above are only embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any equivalent structural or equivalent process transformation made using the content of the invention specification and drawings, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A load current detection circuit for a switching power supply converter, characterized in that: It includes a switching transistor peak current sampling circuit (30) for obtaining the peak current signal of the switching transistor of a Boost-type or Buck-Boost-type switching power supply converter, a sample and hold circuit (34) for holding the switching transistor peak current sampling signal, an inductor current compensation circuit (32) for compensating the switching transistor peak current sampling signal, and a low-pass filter circuit (35); The switching transistor peak current sampling circuit (30) is electrically connected to the sample and hold circuit (34), and the sample and hold circuit (34) obtains the switching transistor peak current signal from the switching transistor peak current sampling circuit (30); The inductor current compensation circuit (32) is electrically connected to the sample and hold circuit (34), and during the conduction period of the freewheeling diode of the switching power supply converter, it compensates the switching transistor peak current signal to obtain a compensated inductor current signal; The low-pass filter circuit (35) is electrically connected to the sample and hold circuit (34), and after low-pass filtering the compensated inductor current signal, it outputs it as the load current signal; The sample and hold circuit (34) further includes a low-pass filter input control transistor; The input end of the low-pass filter circuit (35) is electrically connected to the source of the low-pass filter input control transistor. The gate of the low-pass filter input control transistor is connected to the second control signal (DRN / DRH) obtained from the switching power supply converter, and the drain of the low-pass filter input control transistor is grounded. The low-pass filter input control transistor is controlled by the second control signal (DRN / DRH). When the second control signal (DRN / DRH) is at a low level, the low-pass filter input control transistor conducts, and the input signal at the input end of the low-pass filter circuit (35) is pulled low; The sample and hold circuit (34) further includes a second switch (K2 / K12). One end of the second switch (K2 / K12) is electrically connected to the input terminal of the low-pass filter circuit (35), and the other end of the second switch (K2 / K12) is electrically connected to the output end of the sampling operational amplifier; The second switch (K2 / K12) is controlled by the non-signal of the second control signal obtained from the switched-mode power supply converter ; when the non-signal of the second control signal is at a high level, the second switch (K2 / K12) closes, and the sample-and-hold circuit (34) and the low-pass filter circuit (35) are turned on; when the non-signal of the second control signal is at a high level, the second switch (K2 / K12) opens, and the sample-and-hold circuit (34) and the low-pass filter circuit (35) are disconnected.

2. The load current detection circuit for a switching power supply converter according to claim 1, characterized in that: The sample and hold circuit (34) includes a first switch (K1 / K11), a sampling capacitor (C1 / C11), and a sampling operational amplifier (OAS1 / OAS2); one end of the first switch (K1 / K11) is electrically connected to the switching transistor peak current sampling circuit (30), the other end of the first switch (K1 / K11) is electrically connected to one end of the sampling capacitor (C1 / C11) and the positive input terminal of the sampling operational amplifier (OAS1 / OAS2); the other end of the sampling capacitor (C1 / C11) is grounded; the negative input terminal of the sampling operational amplifier (OAS1 / OAS2) is electrically connected to the output end of the sampling operational amplifier (OAS1 / OAS2); the inductor current compensation circuit (32) is electrically connected to one end of the sampling capacitor (C1 / C11) and the positive input terminal of the sampling operational amplifier (OAS1 / OAS2); The first switch (K1 / K11) is controlled by a second control signal (DRN / DRH) obtained from a switching power supply converter; when the second control signal (DRN / DRH) is at a high level, the first switch (K1 / K11) is closed, electrically connecting the sample and hold circuit (34) and the switching transistor peak current sampling circuit (30); when the second control signal (DRN / DRH) is at a low level, the first switch (K1 / K11) is opened, disconnecting the connection between the sample and hold circuit (34) and the switching transistor peak current sampling circuit (30).

3. The load current detection circuit of the switching power supply converter according to claim 1, wherein: The inductance current compensation circuit (32) is a current source.

4. The load current detection circuit of the switching power supply converter according to claim 1, wherein: During the inductor current decreasing period, i.e., the freewheeling diode conduction period, the compensation current provided by the inductance current compensation circuit is equal to the switching transistor peak current value minus the inductor current value during the freewheeling diode conduction period.

5. The load current detection circuit of the switching power supply converter according to claim 1, wherein: When the switching power supply converter is a Boost type switching power supply converter, The inductance current compensation circuit (32) includes a first current mirror, a first operational amplifier (OA1), a first resistor (R1), a first transistor (MA1), a third resistor (R3) and a fourth resistor (R4); one end of the third resistor (R3) is used to be electrically connected to the voltage output terminal of the switching power supply converter, the other end of the third resistor (R3) is electrically connected to one end of the fourth resistor (R4) and the positive input terminal of the first operational amplifier (OA1); the other end of the fourth resistor (R4) is grounded; the negative output terminal of the first operational amplifier (OA1) is electrically connected to the drain of the first transistor (MA1) and one end of the first resistor (R1); the other end of the first resistor (R1) is grounded; the output terminal of the first operational amplifier (OA1) is electrically connected to the gate of the first transistor (MA1), and the source of the first transistor (MA1) is electrically connected to one end of the first current mirror; The inductance current compensation circuit (32) further includes a third current mirror, a second current mirror, a second operational amplifier (OA2), a second resistor (R2), a second transistor (MA2), a fifth resistor (R5) and a sixth resistor (R6); one end of the fifth resistor (R5) is used to be electrically connected to the voltage input terminal of the switching power supply converter; the other end of the fifth resistor (R5) is electrically connected to one end of the sixth resistor (R6) and the positive input terminal of the second operational amplifier (OA2); the other end of the sixth resistor (R6) is grounded; the negative output terminal of the second operational amplifier (OA2) is electrically connected to the drain of the second transistor (MA2) and one end of the second resistor (R2); the other end of the second resistor (R2) is grounded; the output terminal of the second operational amplifier (OA2) is electrically connected to the gate of the second transistor (MA2), and the source of the second transistor (MA2) is electrically connected to one end of the second current mirror; One end of the third current mirror is electrically connected to one end of the first current mirror, and the other end of the third current mirror is electrically connected to one end of the second current mirror; in the third current mirror, the end connected to the second current mirror is simultaneously used as the inductor current compensation signal output terminal.

6. The switching power converter load current detection circuit according to claim 1, characterized in that: When the switching power converter is a Buck-Boost type switching power converter, the inductor current compensation circuit (32) includes a fourth current mirror, a seventh resistor (R7), an eighth resistor (R8), a third operational amplifier (OA3), a fourth transistor (MA4), and a fifth transistor (MA5); One end of the eighth resistor (R8) is used to be electrically connected to the voltage output terminal of the switching power converter; the other end of the eighth resistor (R8) is electrically connected to one end of the seventh resistor (R7) and the negative input terminal of the third operational amplifier (OA3); the positive output terminal of the second operational amplifier is grounded; the other end of the seventh resistor (R7) is electrically connected to the drain of the fourth transistor (MA4); The output terminal of the third operational amplifier (OA3) is electrically connected to the gate of the fourth transistor (MA4) and the gate of the fifth transistor (MA5), and the source of the fourth transistor (MA4) and the source of the fifth transistor (MA5) are connected to the power supply; The fourth current mirror includes a forty-first transistor (MA41) and a forty-second transistor (MA42), the gate of the forty-first transistor (MA41) is electrically connected to the gate of the forty-second transistor (MA42), the drains of the forty-first transistor (MA41) and the forty-second transistor (MA42) are both grounded, the gate of the forty-first transistor (MA41) is electrically connected to the source of the forty-first transistor (MA41) and used as the first terminal of the fourth current mirror, and the source of the forty-second transistor (MA42) is used as the second terminal of the fourth current mirror; The first terminal of the fourth current mirror is electrically connected to the drain of the fifth transistor (MA5), and the second terminal of the fourth current mirror is used as the inductor current compensation signal output terminal.

7. A switching power converter circuit, characterized in that: It includes the switching power converter load current detection circuit described in any one of claims 1 to 6 above.

8. The switching power converter circuit according to claim 7, characterized in that: It further includes a logic control circuit; the logic control circuit is used to generate a basic switching signal for the timing control of the inductor type switching power converter. The logic control circuit generates a first control signal (DRP / DRL) for controlling the switching transistor and a second control signal (DRN / DRH) for controlling the freewheeling diode according to the basic switching signal; when the first control signal (DRP / DRL) is at a high level, the switching transistor is turned on; when the second control signal (DRN / DRH) is at a high level, the freewheeling diode is turned on; the first control signal (DRP / DRL) and the second control signal (DRN / DRH) are synchronous transformation signals of the basic switching signal; the inductor current rising period is synchronous with the first control signal (DRP / DRL); the inductor current falling period is synchronous with the second control signal (DRN / DRH).

9. A method for detecting the load current of a switching power supply converter, comprising the following steps: Based on the switching power supply converter circuit according to any one of claims 7 to 8; Sampling to obtain the peak current during the inductor current rising period, i.e., the switching transistor conduction period, of a Boost or Buck - Boost type switching power supply converter in the current switching cycle; maintaining the peak current sampling value during the inductor current rising period, i.e., the switching transistor conduction period, through a sample - and - hold circuit; During the inductor current falling period, i.e., the freewheeling diode conduction period, in the current switching cycle, an inductor current compensation circuit is used to compensate for the inductor current decrease process during the freewheeling diode conduction period, compensating the peak current sampling value during the switching transistor conduction period. The compensated inductor current signal is maintained by a sample - and - hold circuit and then output, and the signal output by the sample - and - hold circuit is smoothed by a low - pass filter to obtain the load current signal of the switching power supply converter.

10. The method for detecting the load current of a switching power supply converter according to claim 9, wherein: During the inductor current falling period, i.e., the freewheeling diode conduction period, the compensation current provided by the inductor current compensation circuit is equal to the switching transistor peak current value minus the inductor current value during the freewheeling diode conduction period.

11. The method for detecting the load current of a switching power supply converter according to claim 9, wherein: The inductor current compensation circuit (32) is a current source.

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