Electronic load control circuit, electronic load and power supply test system

Abstract

The present application discloses a control circuit of an electronic load, an electronic load and a power supply test system, wherein the circuit includes an MCU; a DAC module, wherein the signal output end of the MCU is connected to the input end of the DAC module; a closed-loop control circuit, wherein the closed-loop control circuit includes a first error amplifier, a mutual inductor, a MOS tube, a current sampling resistor and a power supply end VBUS; a mutual inductor is arranged between the first error amplifier and the MOS tube of the closed-loop control circuit, the power supply end VBUS is connected to the drain of the MOS tube through the primary side of the mutual inductor, the first secondary side of the mutual inductor is fed back to the input signal of the first error amplifier, and the second secondary side of the mutual inductor is fed back to the driving signal of the first error amplifier to the MOS tube. The present application can improve the dynamic response speed of the electronic load when pulling high-frequency current, and meet the test requirements of high precision and high dynamic response.

Description

Technical Field

[0001] The present application relates to the field of power supply testing, and in particular to a control circuit of an electronic load, an electronic load and a power supply testing system. Background Art

[0002] Electronic load is a device used to test the performance of power supply, with constant current, constant voltage, constant resistance, constant power and combined load test functions. Electronic load can simulate the characteristics of different loads. Since different devices under test have different response speeds to load requirements, the response time is a very important performance parameter for products such as GPU chip power supply, Hall current sensor, high-speed switching power supply, etc.

[0003] The disadvantage of current electronic loads is that the dynamic response speed is insufficient when drawing high-frequency current, making it difficult to meet the testing requirements of high precision and high dynamic response. Summary of the invention

[0004] The present application proposes a control circuit of an electronic load, an electronic load and a power supply testing system, which can improve the dynamic response speed of the electronic load when drawing a high-frequency current, and meet the testing requirements of high precision and high dynamic response.

[0005] According to the control circuit of the electronic load of the embodiment of the first aspect of the present application, the control circuit includes: an MCU; a DAC module, the signal output end of the MCU is connected to the input end of the DAC module; and a closed-loop control circuit, the closed-loop control circuit including a first error amplifier, a mutual inductor, a MOS tube, a current sampling resistor and a power supply terminal VBUS, the output end of the DAC module is connected to the inverting end of the first error amplifier, one end of the first secondary side of the mutual inductor is connected to the non-inverting end of the first error amplifier, the other end of the first secondary side of the mutual inductor is connected to the inverting end of the first error amplifier, the output end of the first error amplifier is connected to one end of the second secondary side of the mutual inductor, the other end of the second secondary side of the mutual inductor is connected to the gate of the MOS tube, the drain of the MOS tube is connected to one end of the primary side of the mutual inductor, the other end of the primary side of the mutual inductor is connected to the power supply terminal VBUS, the source of the MOS tube is grounded through the current sampling resistor, the non-inverting end of the first error amplifier is grounded, the inverting end of the first error amplifier is connected to the common end of the current sampling resistor and the MOS tube, and the output end of the first error amplifier is connected to the inverting end of the first error amplifier through a first capacitor.

[0006] According to some embodiments of the present application, the closed-loop control circuit also includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a second capacitor and a third capacitor. The output end of the DAC module is connected to the inverting end of the first error amplifier, the non-inverting end of the first error amplifier is grounded through the second resistor, the inverting end of the first error amplifier is connected to the common end of the current sampling resistor and the MOS tube through the third resistor, the non-inverting end of the first error amplifier is connected to the ground end of the current sampling resistor through the fourth resistor, the other end of the first secondary side of the mutual inductor is connected to the inverting end of the first error amplifier through the fifth resistor, one end of the first secondary side of the mutual inductor is connected to the non-inverting end of the first error amplifier through the sixth resistor, the second capacitor is connected in parallel with the second resistor, and the third capacitor is connected in parallel with the first resistor.

[0007] According to some embodiments of the present application, the first resistor and the second resistor have the same resistance value, and the third resistor and the fourth resistor have the same resistance value; the first resistor and the second resistor, and the third resistor and the fourth resistor satisfy the following relationship:

[0008] Ra / Rb=GBP / f;

[0009] Wherein, Ra is the resistance value of the first resistor and the second resistor, Rb is the resistance value of the third resistor and the fourth resistor, GBP is the gain-bandwidth product of the first error amplifier, and f is the signal frequency.

[0010] According to some embodiments of the present application, there are multiple closed-loop control circuits, and the output end of the DAC module is respectively connected to the inverting ends of multiple first error amplifiers.

[0011] According to some embodiments of the present application, the closed-loop control circuit also includes a second error amplifier, a differential amplifier and a multiplier, the output end of the DAC module is connected to the in-phase end of the second error amplifier, the output end of the second error amplifier is connected to the inverting end of the first error amplifier, the input end of the differential amplifier is respectively connected to the two ends of the current sampling resistor, the output end of the differential amplifier is connected to the first input end of the multiplier, the power supply end VBUS is connected to the second input end of the multiplier, and the output end of the multiplier is connected to the inverting end of the second error amplifier.

[0012] According to some embodiments of the present application, the closed-loop control circuit also includes a dual-way switch and a reference power supply, the first input end of the dual-way switch is connected to the power supply end VBUS, the second input end of the dual-way switch is connected to the reference power supply, and the output end of the dual-way switch is connected to the reference voltage end of the DAC module.

[0013] The electronic load according to the second aspect of the present application includes the control circuit of the electronic load described above.

[0014] According to the third aspect of the present application, a power supply testing system includes a device under test and the above-mentioned electronic load, wherein the electronic load is connected to the device under test.

[0015] The control circuit of the electronic load, the electronic load and the power supply test system according to the embodiments of the present application have at least the following beneficial effects:

[0016] In the implementation manner of the present application, first, the MCU outputs a programming signal through the DAC module, and the output end of the DAC module controls the operating state of the closed-loop control circuit through the voltage of the programming signal. The source of the MOS tube is grounded through a current sampling resistor, and the two ends of the current sampling resistor are respectively connected to the non-inverting end and the inverting end of the first error amplifier to form negative feedback. The present application sets a mutual inductor between the first error amplifier and the MOS tube of the closed-loop control circuit, the power supply terminal VBUS is connected to the drain of the MOS tube through the primary side of the mutual inductor, the first secondary side of the mutual inductor is fed back to the input signal of the first error amplifier, and the second secondary side of the mutual inductor is fed back to the driving signal of the first error amplifier to the MOS tube. When the electronic load pulls the high-frequency current, the current of the MOS tube suddenly changes, and the primary side of the mutual inductor generates a potential difference. The first secondary side increases the voltage of the programming signal by sensing the potential difference of the primary side, and the second secondary side can simultaneously increase the driving signal voltage of the MOS tube driven by the first error amplifier by sensing the potential difference of the primary side. Therefore, the rising or falling speed of the current when the electronic load pulls the high-frequency current can be improved by the action of the mutual inductor. When the closed-loop control circuit is in the DC working state, the mutual inductor does not work and will not affect the control accuracy. In addition, the closed-loop control circuit adopts differential feedback to reduce the common-mode interference in the loop and improve the control accuracy. In summary, the present application can improve the dynamic response speed of the electronic load when pulling the high-frequency current, and meet the test requirements of high precision and high dynamic response.

[0017] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present application is further described below with reference to the accompanying drawings and embodiments, wherein:

[0019] Figure 1 A circuit schematic diagram of a control circuit of an electronic load in an embodiment of the present application;

[0020] Figure 2 A circuit schematic diagram of another electronic load control circuit in an embodiment of the present application;

[0021] Figure 3 A circuit schematic diagram of a control circuit of an electronic load of multiple closed-loop control circuits in an embodiment of the present application;

[0022] Figure 4 A circuit schematic diagram of a control circuit of an electronic load corresponding to a constant power circuit in an embodiment of the present application;

[0023] Figure 5 4 is a circuit schematic diagram of a control circuit of an electronic load corresponding to a constant resistance circuit in an embodiment of the present application. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0025] In the description of the present application, it should be understood that the descriptions involving orientation, such as the orientation or positional relationship indicated as up, down, etc., are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0026] In the description of this application, "a plurality" means more than two. If there is a description of "first" or "second", it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0027] In the description of this application, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in this application based on the specific content of the technical solution.

[0028] Electronic load is a device used to test the performance of power supply, with constant current, constant voltage, constant resistance, constant power and combined load test functions. Electronic load can simulate the characteristics of different loads. Since different devices under test have different response speeds to load requirements, the response time is a very important performance parameter for products such as GPU chip power supply, Hall current sensor, high-speed switching power supply, etc.

[0029] The disadvantage of current electronic loads is that the dynamic response speed is insufficient when drawing high-frequency current, and they cannot meet the testing requirements of some products.

[0030] The following uses a constant current and constant voltage circuit to specifically illustrate the shortcomings of electronic loads when drawing high-frequency current. The constant current and constant voltage circuit is a conventional control circuit in electronic loads.

[0031] In the related art, during high-speed dynamic loading, the parasitic inductance of external wiring and internal connections will hinder the slope of the current rise, especially in the constant voltage and constant current circuit architecture of multi-stage MOS tubes in parallel used in most electronic loads. Because the parallel lines are long and short, the internal current rise time of each parallel group will be inconsistent, reducing the dynamic response speed.

[0032] Secondly, when the electronic load is dynamically loaded, the amplitude of the voltage waveform to current conversion will also be attenuated if the wiring and transmission circuit are long. This is because the parasitic capacitance on the line is resistive at high speed, which has a certain voltage division and lag on the signal. After testing, the electronic load in the relevant technology will have an amplitude attenuation of more than 20% when dynamically loaded at about 20k.

[0033] Therefore, the electronic load in the related technology can only achieve a rise time of up to 20us, and may drop to 30-40us in high-voltage and extended-power electronic loads. Therefore, the dynamic response speed is insufficient when pulling high-frequency current and cannot meet the testing requirements of some products.

[0034] In order to solve the problems in the prior art, the embodiments of the present application provide a control circuit of an electronic load, an electronic load and a power supply test system. The control circuit of the electronic load is first introduced below.

[0035] refer to Figure 1 As shown, a control circuit of an electronic load includes: an MCU, a DAC module and a closed-loop control circuit. The signal output end of the MCU is connected to the input end of the DAC module, and the MCU outputs a programming signal through the DAC module. The programming signal is an analog signal output by the DAC and is used to control the current of the closed-loop control circuit.

[0036] Specifically, the closed-loop control circuit includes a first error amplifier U1, a mutual inductor T1, a MOS tube Q1, a current sampling resistor Rs and a power supply terminal VBUS, the output end of the DAC module is connected to the inverting end of the first error amplifier U1, one end of the first secondary side of the mutual inductor T1 is connected to the non-inverting end of the first error amplifier U1, the other end of the first secondary side of the mutual inductor T1 is connected to the inverting end of the first error amplifier U1, the output end of the first error amplifier U1 is connected to one end of the second secondary side of the mutual inductor T1, the other end of the second secondary side of the mutual inductor T1 is connected to the gate of the MOS tube Q1, the drain of the MOS tube Q1 is connected to one end of the primary side of the mutual inductor T1, the other end of the primary side of the mutual inductor T1 is connected to the power supply terminal VBUS, the source of the MOS tube Q1 is grounded through the current sampling resistor Rs, the non-inverting end of the first error amplifier U1 is grounded, the inverting end of the first error amplifier U1 is connected to the common end of the current sampling resistor Rs and the MOS tube Q1, and the output end of the first error amplifier U1 is connected to the inverting end of the first error amplifier U1 through the first capacitor C1.

[0037] In the implementation mode of the present application, first, the MCU outputs a programming signal through the DAC module, and the output end of the DAC module controls the operating state of the closed-loop control circuit through the voltage of the programming signal. The source of the MOS tube Q1 is grounded through the current sampling resistor Rs, and the two ends of the current sampling resistor Rs are respectively connected to the in-phase end and the inverting end of the first error amplifier U1 to form a negative feedback, forming a constant current closed-loop control loop, and the MCU controls the current of the loop by adjusting the voltage of the programming signal. The present application sets a mutual inductor T1 between the first error amplifier U1 and the MOS tube Q1 of the closed-loop control circuit, the power supply end VBUS is connected to the drain of the MOS tube Q1 through the primary side of the mutual inductor T1, the first secondary side of the mutual inductor T1 is fed back to the input signal of the first error amplifier U1, and the second secondary side of the mutual inductor T1 is fed back to the driving signal of the first error amplifier U1 to the MOS tube Q1. When the electronic load pulls the high-frequency current, the current of the MOS tube Q1 suddenly changes, and the primary side of the mutual inductor T1 generates a potential difference. The first secondary side increases the programming signal by sensing the potential difference of the primary side. The voltage of the first error amplifier U1, that is, the voltage between the in-phase terminal and the inverting terminal, and the second secondary side can simultaneously increase the driving signal voltage of the first error amplifier U1 driving the MOS tube Q1, that is, the gate voltage of the MOS tube Q1, by sensing the potential difference of the primary side. Therefore, the rising or falling speed of the current when the electronic load pulls the high-frequency current can be improved through the action of the mutual inductor T1. When the closed-loop control circuit is in the DC working state, the mutual inductor T1 does not work and will not affect the control accuracy. In addition, the closed-loop control circuit adopts differential feedback to reduce common-mode interference in the loop and improve the control accuracy.

[0038] In summary, this application feeds back the high-speed current response of the power side to the programming and control signals, improves the conduction rate of the MOS tube Q1, and increases the current rise time. At the same time, it does not affect the static current accuracy, so that the loop takes into account both high speed and high precision, making the control more accurate, faster and more stable. This application can improve the dynamic response speed of the electronic load when pulling high-frequency current, and meet the test requirements of high precision and high dynamic response.

[0039] It should be noted that the power supply terminal VBUS refers to the voltage of the electronic load connected to the device under test. When the electronic load needs to pull high-frequency current, the control signal slope must be faster, usually in the ns level. The error signal output by the first error amplifier U1 controls the MOS tube Q1 to pull the current, and the current will also change with a very high slope, even if the current changes suddenly. The mutual inductor T1 makes the loop respond faster, pulls a current with a higher slope, and has a higher frequency dynamic response. When the current of the MOS tube Q1 suddenly changes, the primary side of the mutual inductor T1 generates a potential difference through the voltage coupling principle. After the primary side of the mutual inductor T1 generates an induced electromotive force, the first secondary side and the second secondary side will obviously also generate a coupling voltage. The coupling voltage generated by the first secondary side is superimposed on the input end of the first error amplifier U1, increasing the voltage of the programming signal. Similarly, the coupling voltage generated by the second secondary side is superimposed on the output voltage of the first error amplifier U1, thereby increasing the driving voltage of the MOS tube Q1.

[0040] It should be noted that the number of closed-loop control circuits in the present application is not limited, and can be one or multiple in parallel.

[0041] It should be noted that the programming signal output by the DAC module is input to the inverting end of the first error amplifier U1, the non-inverting end of the first error amplifier U1 is grounded, and the closed-loop control circuit uses differential feedback to perform closed-loop control, which can improve the control accuracy compared to the conventional single-ended feedback method. In addition, AC feedback is realized through the first capacitor C1. When the output of the first error amplifier U1 suddenly increases, it is fed back to the reverse end of the first error amplifier U1 through C1, and the output of the first error amplifier U1 decreases, which controls the conduction of the MOS tube Q1 to decrease.

[0042] After testing, the control circuit of the present application can increase the loop current rise time of the electronic load to 0.4u. Compared with the 20u loop current rise time in the related art, it is obvious that the dynamic response speed of the electronic load is greatly improved.

[0043] In some embodiments, reference Figure 2As shown, the closed-loop control circuit also includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a second capacitor C2 and a third capacitor C3. The output end of the DAC module is connected to the inverting end of the first error amplifier U1, the non-inverting end of the first error amplifier U1 is grounded through the second resistor R2, the inverting end of the first error amplifier U1 is connected to the common end of the current sampling resistor Rs and the MOS tube Q1 through the third resistor R3, the non-inverting end of the first error amplifier U1 is connected to the ground end of the current sampling resistor Rs through the fourth resistor R4, the other end of the first secondary side of the mutual inductor T1 is connected to the inverting end of the first error amplifier U1 through the fifth resistor R5, one end of the first secondary side of the mutual inductor T1 is connected to the non-inverting end of the first error amplifier U1 through the sixth resistor R6, the second capacitor C2 is connected in parallel with the second resistor R2, and the third capacitor C3 is connected in parallel with the first resistor R1.

[0044] In this embodiment, by setting the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, the fifth resistor R5, and the sixth resistor R6, by adding resistance to the inverting end and the non-inverting end of the first error amplifier U1, the voltage signal can be increased, the probability of being affected by interference and the Vos of the operational amplifier can be reduced, and the control accuracy of the loop can be further improved. In addition, by setting the second capacitor C2 and the third capacitor C3, the dynamic response at high speed can be accelerated.

[0045] In some embodiments, the resistance values ​​of the first resistor R1 and the second resistor R2 are equal, and the resistance values ​​of the third resistor R3 and the fourth resistor R4 are equal; the first resistor R1 and the second resistor R2, and the third resistor R3 and the fourth resistor R4 satisfy the following relationship:

[0046] Ra / Rb=GBP / f;

[0047] Wherein, Ra is the resistance of the first resistor R1 and the second resistor R2, Rb is the resistance of the third resistor R3 and the fourth resistor R4, GBP is the gain bandwidth product of the first error amplifier U1, and f is the signal frequency.

[0048] In this implementation, by setting the resistances R1, R2, R3, and R4 to satisfy the above relationship, the amplification factor of the loop can be reduced and the frequency of the loop response signal can be increased.

[0049] It should be noted that Ra / Rb is equivalent to the ratio of the first resistor R1 to the third resistor R3, or the ratio of the second resistor R2 to the fourth resistor R4, GBP is the gain-bandwidth product, which is related to the model of the first error amplifier U1, and f is the signal frequency, which is related to the programming signal output by the MCU. Since the signal frequency x the actual closed-loop amplification factor = the gain-bandwidth product, the relationship Ra / Rb=GBP / f can be obtained.

[0050] For example, in the embodiment of the present application, the first resistor R1 and the second resistor R2 are selected to have a resistance value of 4000R, and the third resistor R3 and the fourth resistor R4 are selected to have a resistance value of 500R.

[0051] In some embodiments, reference Figure 3 As shown, there are multiple closed-loop control circuits, and the output ends of the DAC modules are respectively connected to the inverting ends of multiple first error amplifiers U1.

[0052] In this implementation, by providing a plurality of parallel closed-loop control circuits, power expansion can be achieved to meet high-power testing requirements.

[0053] In some embodiments, reference Figure 4 As shown, the closed-loop control circuit also includes a second error amplifier U2, a differential amplifier U3 and a multiplier U4, the output end of the DAC module is connected to the in-phase end of the second error amplifier U2, the output end of the second error amplifier U2 is connected to the inverting end of the first error amplifier U1, the input end of the differential amplifier U3 is respectively connected to the two ends of the current sampling resistor Rs, the output end of the differential amplifier U3 is connected to the first input end of the multiplier U4, the power supply end VBUS is connected to the second input end of the multiplier U4, and the output end of the multiplier U4 is connected to the inverting end of the second error amplifier U2.

[0054] In this embodiment, on the basis of the constant current loop, a constant power closed-loop control circuit is formed by adding a second error amplifier U2, a differential amplifier U3 and a multiplier U4, which can achieve high-precision and high-dynamic response constant power closed-loop control of the electronic load and meet the testing requirements in a constant power scenario.

[0055] It should be noted that the working process of the constant power closed-loop control circuit is as follows: the differential amplifier U3 inputs the current sampling value into the multiplier U4, the multiplier U4 multiplies the voltage sampling value obtained by the power supply terminal VBUS by the current sampling value, and obtains a power feedback value which is input into the second error amplifier U2. The second error amplifier U2 generates an error signal through the power feedback value and the programming signal output by the DAC module, which is input into the first error amplifier U1, thereby forming a constant power closed-loop control.

[0056] In some embodiments, reference Figure 5 As shown, the closed-loop control circuit also includes a dual switch S1 and a reference power supply, wherein a first input terminal of the dual switch S1 is connected to the power supply terminal VBUS, a second input terminal of the dual switch is connected to the reference power supply Vref, and an output terminal of the dual switch is connected to the reference voltage terminal VREF of the DAC module.

[0057] In this embodiment, on the basis of the constant current loop, only one switch is added to realize the switching of constant current and constant resistance. The circuit is simple, the device requirements are low, the cost of the whole test solution is reduced, and it is easier to implement. The present invention realizes a constant resistance circuit by simply improving and transforming the current loop, based on the calibration parameters of the principle constant current loop, without affecting the response speed of the overall current loop. Therefore, it is possible to realize high-precision and high-dynamic response constant resistance closed-loop control of the electronic load, and meet the test requirements in the constant resistance scenario.

[0058] Specifically, the working process of the constant resistance closed-loop control circuit is as follows: when the dual switch S1 is turned to 2, the circuit is in the constant current loop mode. At this time, the reference voltage of the DAC module is Vref, and the MCU outputs a set DAC value to the DAC module. The DAC module outputs a voltage corresponding to the DAC value to the inverting end of the first error amplifier U1. The first error amplifier U1 forms an error signal through differential feedback to control the conduction degree of the MOS tube Q1, thereby realizing a negative feedback constant current closed loop.

[0059] When the dual switch S1 is turned to 1, the reference voltage of the DAC module is the voltage of the power supply terminal VBUS. The resistance value R of the constant resistance circuit is expressed by the following formula R=VBUS / I, where I is the current flowing through the current sampling resistor Rs. From the above formula, it can be seen that as long as VBUS and I are fixed, R is determined, so a constant resistance circuit can be implemented.

[0060] The present application also relates to an electronic load, including the control circuit of the electronic load of the above embodiment.

[0061] The present application also relates to a power supply testing system, including a device under test and an electronic load of the above embodiment, wherein the electronic load is connected to the device under test, and the device under test may be a GPU chip power supply, a Hall current sensor, a high-speed switching power supply or other power supply equipment.

[0062] The embodiments of the present application are described in detail above in conjunction with the accompanying drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present application.

Claims

1. A control circuit for an electronic load, characterized in that: include: MCU; DAC module, the signal output end of the MCU is connected to the input end of the DAC module; A closed-loop control circuit, the closed-loop control circuit comprises a first error amplifier, a mutual inductor, a MOS tube, a current sampling resistor and a power supply terminal VBUS, the output end of the DAC module is connected to the inverting end of the first error amplifier, the opposite-name end of the first secondary side of the mutual inductor is connected to the same-name end of the first error amplifier, the same-name end of the first secondary side of the mutual inductor is connected to the inverting end of the first error amplifier, the output end of the first error amplifier is connected to the opposite-name end of the second secondary side of the mutual inductor, the same-name end of the second secondary side of the mutual inductor is connected to the gate of the MOS tube, the drain of the MOS tube is connected to the opposite-name end of the primary side of the mutual inductor, the same-name end of the primary side of the mutual inductor is connected to the power supply terminal VBUS, the source of the MOS tube is grounded through the current sampling resistor, the same-name end of the first error amplifier is grounded, the inverting end of the first error amplifier is connected to the common end of the current sampling resistor and the MOS tube, and the output end of the first error amplifier is connected to the inverting end of the first error amplifier through a first capacitor.

2. The control circuit of the electronic load according to claim 1, characterized in that: The closed-loop control circuit also includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a second capacitor and a third capacitor. The output end of the DAC module is connected to the inverting end of the first error amplifier through the first resistor, the non-inverting end of the first error amplifier is grounded through the second resistor, the inverting end of the first error amplifier is connected to the common end of the current sampling resistor and the MOS tube through the third resistor, the non-inverting end of the first error amplifier is connected to the ground end of the current sampling resistor through the fourth resistor, the other end of the first secondary side of the mutual inductor is connected to the inverting end of the first error amplifier through the fifth resistor, one end of the first secondary side of the mutual inductor is connected to the non-inverting end of the first error amplifier through the sixth resistor, the second capacitor is connected in parallel with the second resistor, and the third capacitor is connected in parallel with the first resistor.

3. The control circuit of the electronic load according to claim 2, characterized in that: The resistance values ​​of the first resistor and the second resistor are equal, and the resistance values ​​of the third resistor and the fourth resistor are equal; the first resistor and the second resistor, and the third resistor and the fourth resistor satisfy the following relationship: Ra / Rb=GBP / f; Wherein, Ra is the resistance value of the first resistor and the second resistor, Rb is the resistance value of the third resistor and the fourth resistor, GBP is the gain-bandwidth product of the first error amplifier, and f is the signal frequency.

4. The control circuit of the electronic load according to claim 1, characterized in that: There are multiple closed-loop control circuits, and the output end of the DAC module is respectively connected to the inverting ends of multiple first error amplifiers.

5. The control circuit of the electronic load according to claim 1, characterized in that: The closed-loop control circuit also includes a second error amplifier, a differential amplifier and a multiplier. The output end of the DAC module is connected to the non-inverting end of the second error amplifier, the output end of the second error amplifier is connected to the inverting end of the first error amplifier, the input end of the differential amplifier is respectively connected to the two ends of the current sampling resistor, the output end of the differential amplifier is connected to the first input end of the multiplier, the power supply end VBUS is connected to the second input end of the multiplier, and the output end of the multiplier is connected to the inverting end of the second error amplifier.

6. The control circuit of the electronic load according to claim 1, characterized in that: The closed-loop control circuit also includes a dual-way switch and a reference power supply, wherein a first input end of the dual-way switch is connected to the power supply end VBUS, a second input end of the dual-way switch is connected to the reference power supply, and an output end of the dual-way switch is connected to a reference voltage end of the DAC module.

7. An electronic load, characterized in that: A control circuit comprising the electronic load according to any one of claims 1 to 6.

8. A power supply testing system, characterized in that: The device comprises a device under test and the electronic load according to claim 7, wherein the electronic load is connected to the device under test.

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