Constant current constant voltage circuit for electronic load and electronic load

Abstract

The application discloses a constant-current constant-voltage circuit and an electronic load for the electronic load, and relates to the technical field of electronic loads. The constant-current constant-voltage circuit comprises an MCU, a DAC module, a first error amplifier, a plurality of constant-current loops, a power supply end and a first differential amplifier, the plurality of constant-current loops are connected in parallel, the voltage or the current of the plurality of parallel constant-current loops is controlled through the DAC module and the first error amplifier, and the originally parallel circuit of a plurality of small closed loops is changed into the architecture of controlling small closed loops by a large closed loop. The plurality of constant-current loops are connected to the ground through a sampling resistor, the precision and the noise will not be affected by the measured power supply and overcurrent, and the sampling precision is high. The constant-current constant-voltage circuit has strong scalability, the number of the parallel constant-current loops can be infinitely stacked in theory, and is particularly suitable for the case of high voltage and small current.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electronic load, in particular to a constant current and constant voltage circuit for electronic load and electronic load. BACKGROUND

[0002] The constant current and constant voltage circuit is a basic circuit mode of the electronic load. The electronic load needs to change the topology of the internal circuit according to the power density and current size of the power supply during different power supply tests. Most of the electronic loads on the market currently use a constant current loop in parallel current sharing mode. A same programming signal is used to control different constant current loops. The sampling resistance, error amplifier and power tube of each constant current loop must be strictly consistent to achieve current sharing. A same bus voltage is used to ensure that the power of each constant current loop is consistent, thereby realizing large power or large current consumption.

[0003] Therefore, most of the current electronic loads use multiple constant current loops in parallel to realize current sharing or power sharing of each power device. However, such design requires that the sampling resistance, error amplifier and power tube of each constant current loop must be strictly consistent. The Vos of the error amplifier is too large, the difference of the sampling resistance or the inconsistent characteristic curve of the MOS tube / IGBT module will cause uneven changes of each constant current loop, thereby causing nonlinearity of the current point during control, high error and affecting the accuracy. In addition, if any constant current loop has a problem, it will affect the constant current value. At the same time, because the power lines are in parallel, overcurrent will cause a pressure difference, and it is also accompanied by power supply interference, which will cause the reference point of the same programming signal to change, ultimately affecting the accuracy and noise index of the constant current. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a constant current and constant voltage circuit for electronic load and electronic load, which can solve the problems of complex constant current and constant voltage circuit, any constant current loop problem affecting the constant current value, high requirement for devices, accuracy and noise being easily affected, low sampling accuracy of the existing electronic load.

[0005] According to the constant current constant voltage circuit for electronic load of the first aspect of the present application, the following beneficial effects can be achieved:

[0006] According to the constant current constant voltage circuit for electronic load of the first aspect of the present application, the following beneficial effects can be achieved:

[0007] The present application connects multiple constant current loops in parallel, controls the voltage or current of the multiple parallel constant current loops through a DAC module and a first error amplifier, changes the original multiple small closed loop parallel circuits into a large closed loop control small closed loop architecture, and has a simple circuit, low requirements for devices, reduced device cost, and optimized load product efficiency. The multiple constant current loops are grounded through a sampling resistor, the architecture of multiple sampling resistors is changed, only one sampling resistor can be used to more accurately control the total current, because there is only one sampling reference ground, the accuracy and noise will not be affected by the measured power supply and overcurrent, and the sampling accuracy is high. The present application has strong scalability, the number of parallel constant current loops can be infinitely stacked in theory, and is particularly suitable for high voltage and small current conditions. In summary, the present application skillfully uses DAC modules, operational amplifiers, error amplifiers and other devices to build a constant current constant voltage circuit for controlling power devices by setting programming values, has low device cost, high control accuracy, simple circuit and strong scalability.

[0008] According to some embodiments of the present application, the constant current loop comprises a second error amplifier, a MOS tube and a feedback resistor, the output end of the first error amplifier is connected to the non-inverting end of the second error amplifier, the output end of the second error amplifier is connected to the gate of the MOS tube, the drain of the MOS tube is connected to the power supply end, the source of the MOS tube is connected to one end of the feedback resistor, the other end of the feedback resistor is connected to the sampling resistor, and the common end of the feedback resistor and the MOS tube is connected to the non-inverting end of the second error amplifier.

[0009] According to some embodiments of the present invention, the constant current loop further includes a second differential amplifier, wherein the non-inverting input of the second differential amplifier is connected to one end of the feedback resistor connected to the MOS transistor, the inverting input of the second differential amplifier is connected to one end of the feedback resistor connected to the sampling resistor, and the output terminal of the second differential amplifier is connected to the inverting input of the second error amplifier.

[0010] According to some embodiments of the present invention, the first error amplifier, the sampling resistor, and the first differential amplifier all employ high-precision, low-temperature drift components.

[0011] According to some embodiments of the present invention, an ADC module is further included, wherein the output terminal of the first differential amplifier is connected to the input terminal of the ADC module, and the output terminal of the ADC module is connected to the sampling terminal of the MCU.

[0012] According to a second aspect of the present invention, the electronic load includes the constant current and constant voltage circuit for the electronic load described above.

[0013] The electronic load according to the second aspect of the present invention has at least the following beneficial effects:

[0014] This invention connects multiple constant current loops in parallel, using a DAC module and a first error amplifier to control the voltage or current of these parallel loops. This transforms the original circuit of multiple small closed loops in parallel into an architecture where a large closed loop controls smaller closed loops. The circuit is simple, has low requirements for components, reduces component costs, and optimizes the efficiency of the load product. All multiple constant current loops are grounded through a single sampling resistor. By changing the architecture of adding multiple sampling resistors, only one sampling resistor is needed to more accurately control the total current. Because there is only one sampling reference ground, accuracy and noise are not affected by the measured power supply or overcurrent, resulting in high sampling accuracy. This invention has strong scalability; theoretically, the number of parallel constant current loops can be infinitely increased, making it particularly suitable for high-voltage, low-current applications. In summary, this invention cleverly utilizes a DAC module, operational amplifier, error amplifier, and other components to build a constant current and constant voltage circuit that controls power devices by setting programmed values. It features low component cost, high control accuracy, simple circuitry, and strong scalability.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0017] Figure 1 This is a circuit diagram of a constant current circuit for an electronic load in an embodiment of the present invention;

[0018] Figure 2 Circuit schematic diagram of constant voltage circuit for electronic load in embodiments of the present application. DETAILED DESCRIPTION

[0019] Embodiments of the present application are described below in detail, examples of which are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the drawings are exemplary only, for the purpose of explaining the present application, and should not be understood as a limitation of the present application.

[0020] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, etc. is based on the orientation or position relationship shown in the drawings, only for the purpose of facilitating the description of the present application and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0021] In the description of the present application, multiple refers to two or more. If there is a description of first, 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 technical features indicated or the sequence of technical features indicated.

[0022] In the description of the present application, unless otherwise explicitly limited, the words such as arrangement, installation, connection, etc. should be broadly understood, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0023] Reference Figure 1 and Figure 2 As shown in FIGS. 1 and 2, a constant current and constant voltage circuit for an electronic load includes an MCU, a DAC module, a first error amplifier U1, N constant current loops, a power supply terminal VBUS, and a first differential amplifier U2. Specifically, the MCU is connected to the input terminal of the DAC module, the MCU outputs a programming control signal, the DAC module outputs a corresponding voltage according to the programming control signal, the output terminal of the DAC module is connected to the non-inverting terminal of the first error amplifier U1, the output terminal of the first error amplifier U1 is connected to the control terminal of the N constant current loops, respectively, the power supply terminal VBUS is connected to the input terminal of the N constant current loops, respectively, and the output terminal of the N constant current loops is connected to ground through a sampling resistor RL. The function of the first differential amplifier U2 is to obtain the total current or voltage of the constant current loop, as shown in FIG. 3. Figure 1As shown, when the circuit is in constant current mode, the non-inverting input of the first differential amplifier U2 is connected to the sampling resistor RL and the end connected to the constant current loop; the inverting input of the first differential amplifier U2 is connected to the end connected to the sampling resistor RL and grounded; and the output of the first differential amplifier U2 is connected to the inverting input of the first error amplifier. At this time, the first differential amplifier U2 obtains the current flowing through the sampling resistor RL, which is the total current of the N constant current loops. (Reference) Figure 2 As shown, when the circuit is in constant voltage mode, the non-inverting input of the first differential amplifier U2 is connected to the power supply terminal VBUS to obtain the voltage of the constant current loop.

[0024] Specifically, taking constant current loop 1 as an example, it includes a second error amplifier U31, a MOSFET Q1, and a feedback resistor R1. The output of the first error amplifier U1 is connected to the non-inverting input of the second error amplifier U31, and the output of the second error amplifier U31 is connected to the gate of the MOSFET Q1. The drain of the MOSFET Q1 is connected to the power supply terminal VBUS, the source of the MOSFET Q1 is connected to one end of the feedback resistor R1, and the other end of the feedback resistor R1 is connected to the sampling resistor RL. The common terminal of the feedback resistor R1 and the MOSFET Q1 is connected to the non-inverting input of the second error amplifier U31. In this constant current loop, the differential amplifier in the small closed loop is removed, and the second error amplifier U31 directly compares the high side of the feedback resistor R1 with the error signal.

[0025] However, the current distribution between each constant current circuit using the above structure will be uneven, affecting the heating degree of the power device in each unit. To avoid this problem, this application also provides a second differential amplifier U41 in the constant current loop. The non-inverting input of the second differential amplifier U41 is connected to one end of the feedback resistor R1 connected to the MOS transistor Q1. The inverting input of the second differential amplifier U41 is connected to one end of the feedback resistor R1 connected to the sampling resistor RL. The output of the second differential amplifier U41 is connected to the inverting input of the second error amplifier U31.

[0026] The working principle of a constant current circuit is explained below:

[0027] refer to Figure 1 As shown, the MCU outputs a DAC setpoint to the DAC module, and the DAC module outputs the corresponding voltage. At this time, no current is generated. The positive error of the first error amplifier U1 controls the positive input of the subsequent second error amplifiers U31-U3N. When there is no current in the feedback resistor R1-RN, the inverting terminal of the error amplifiers U31-U3N is 0, which controls the conduction of MOSFETs Q1-QN. After conduction, the current feedback resistor R1-RN generates current, which eventually converges to the current sampling resistor RL. Through the amplification of the first differential amplifier U2 and the first error amplifier U1, a closed-loop control is formed, thereby achieving the purpose of constant current.

[0028] refer to Figure 2As shown, the working principle of the constant voltage circuit is similar to that of the constant current circuit, and only the feedback circuit is replaced by a voltage signal.

[0029] In order to realize the collection of voltage and current, the application further comprises an ADC module, the output end of the first differential amplifier U2 is connected to the input end of the ADC module, and the output end of the ADC module is connected to the sampling end of the MCU.

[0030] It should be understood that when the first differential amplifier U2 is connected to the sampling resistor RL, the ADC module feeds back the current of the circuit to the MCU, and when the first differential amplifier U2 is connected to the power supply end VBUS and the ground end, the ADC module feeds back the voltage of the circuit to the MCU.

[0031] The core point of the patent is that only the first error amplifier U1, the sampling resistor RL and the first differential amplifier U2 use high-precision low-temperature drift components. The output current and voltage precision can be ensured to be higher, the error amplifiers U31-U3N and the feedback resistors R1-RN in the current closed loop are not required, low-cost devices such as TL084CDT operational amplifier and cement resistor can be used, and the second differential amplifiers U41-U4N in each current closed loop can be removed.

[0032] In addition, in the prior art, the power lines are connected in parallel, and when the current is too large, a voltage difference will be generated at the reference ground, and at the same time, the power supply will be disturbed, so that the reference point of the same programming signal will change, and finally the accuracy and noise of the constant current will be affected. The circuit of the application has only one reference ground, which perfectly avoids this problem, and the feedback signal is stable, so that the accuracy and noise of the constant current are better.

[0033] The application connects multiple constant current loops in parallel, controls the voltage or current of the multiple parallel constant current loops through a DAC module and a first error amplifier U1, changes the original multiple small closed-loop parallel circuits into a large closed-loop control small closed-loop architecture, and the circuit is simple and has low requirements for devices, thereby reducing the cost of devices and optimizing the efficiency of the load product. The multiple constant current loops are connected to the ground through a sampling resistor RL, and the total current can be controlled more accurately by changing the architecture of the multiple sampling resistors, because there is only one sampling reference ground, the accuracy and noise will not be affected by the measured power supply and overcurrent, and the sampling accuracy is high. The application has strong scalability, and theoretically, the number of parallel constant current loops can be infinitely stacked, and is particularly suitable for high-voltage small-current situations. In summary, the application skillfully uses a DAC module, an operational amplifier, an error amplifier and the like to build a constant current and constant voltage circuit for controlling power devices by setting a programming value, has low device cost, high control accuracy, simple circuit and strong scalability.

[0034] The application also relates to an electronic load comprising the constant current and constant voltage circuit for an electronic load in the above embodiment.

[0035] The embodiments of the present application are described in detail above with reference to the accompanying drawings, but the present application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application.

Claims

1. A constant current and constant voltage circuit for electronic loads, characterized in that, include: MCU; A DAC module, wherein the MCU is connected to the input terminal of the DAC module for outputting control voltage; The first error amplifier, wherein the output terminal of the DAC module is connected to the non-inverting input of the first error amplifier; Multiple constant current loops are provided, and the output of the first error amplifier is connected to the control terminals of the multiple constant current loops respectively. The power supply terminal is connected to the input terminals of multiple constant current loops, and the output terminals of the multiple constant current loops are all grounded through the same sampling resistor. A first differential amplifier, wherein the non-inverting input of the first differential amplifier is connected to the end of the sampling resistor and the constant current loop or the power supply end, the inverting input of the first differential amplifier is connected to the ground end of the sampling resistor, and the output end of the first differential amplifier is connected to the inverting input of the first error amplifier. The constant current loop includes a second error amplifier, a MOSFET, and a feedback resistor. The output terminal of the first error amplifier is connected to the non-inverting input of the second error amplifier. The output terminal of the second error amplifier is connected to the gate of the MOSFET. The drain of the MOSFET is connected to the power supply terminal. The source of the MOSFET is connected to one end of the feedback resistor. The other end of the feedback resistor is connected to the sampling resistor. The common terminal of the feedback resistor and the MOSFET is connected to the non-inverting input of the second error amplifier. The constant current loop further includes a second differential amplifier. The non-inverting input of the second differential amplifier is connected to one end of the feedback resistor connected to the MOS transistor. The inverting input of the second differential amplifier is connected to one end of the feedback resistor connected to the sampling resistor. The output of the second differential amplifier is connected to the inverting input of the second error amplifier.

2. The constant current and constant voltage circuit for electronic loads according to claim 1, characterized in that, The first error amplifier, sampling resistor, and first differential amplifier all use high-precision, low-temperature drift components.

3. The constant current and constant voltage circuit for electronic loads according to claim 1, characterized in that, It also includes an ADC module, with the output of the first differential amplifier connected to the input of the ADC module, and the output of the ADC module connected to the sampling terminal of the MCU.

4. An electronic load, characterized in that, Includes the constant current and constant voltage circuit for electronic loads as described in any one of claims 1 to 3.

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