Voltage-to-current circuit

Abstract

The utility model provides a voltage-to-current circuit, which is characterized in that a current amplification branch and a first input end of an operational amplifier circuit receive an input voltage signal through a first current limiting circuit, and a second input end of the operational amplifier circuit receives a power supply voltage signal; the operational amplifier circuit carries out processing according to an input voltage signal and a power supply voltage signal to obtain an output signal, and the output signal is transmitted to the control end of the current amplification branch, so that the operational amplifier circuit can control the operation state of the current amplification branch, the input voltage is converted into an output current signal, and the output current signal is within a preset range; the voltage-to-current conversion function can be realized according to the operational amplifier circuit and the current amplification branch circuit, the cost is reduced, the system does not need to be matched with an external device for use, and the system complexity is reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of power electronics, and more specifically, particularly relates to a voltage-to-current circuit. Background Art

[0002] In industrial applications, 0 - 20mA / 4 - 20mA current signals are often used for transmission. Because the noise voltage in the industrial environment is generally relatively large, but the power of the noise is very weak, so the noise current is usually less than the nA level. Therefore, the error caused by using current transmission is relatively small. At the same time, the spark energy caused by the on-off of 20mA current is not enough to ignite gas, so the upper limit is generally set at 20mA.

[0003] In the industrial environment, the stability and safety of signal transmission are crucial. To cope with the complex conditions of coexisting high noise voltage and low noise power, and to ensure safe operation in flammable and explosive environments (such as the presence of gas), the industrial community widely uses 0 - 20mA or 4 - 20mA current signals for long-distance and high-precision data transmission. This signal transmission method can not only effectively resist noise interference and reduce errors, but also ensure reliable operation under specific safety standards (such as the spark energy is not enough to ignite gas).

[0004] Currently, integrated chips such as the XTR111 integrated chip can be used to achieve voltage conversion to current. These chips are designed specifically for current signal conversion and have the characteristics of high precision and low noise.

[0005] However, the cost of existing integrated chips is relatively high, and they usually need to be used in conjunction with external triodes and MOS transistors, which increases the complexity of the system. Summary of the Utility Model

[0006] In view of this, the purpose of the utility model is to provide a voltage-to-current circuit for........

[0007] The present application discloses a voltage-to-current circuit, including: a current amplification branch, a first current limiting circuit, a second current limiting circuit, and an operational amplifier circuit;

[0008] One end of the first current limiting circuit serves as the input end of the voltage-to-current circuit and receives an input voltage signal;

[0009] The other end of the first current limiting circuit is respectively connected to the input end of the current amplification branch and the first input end of the operational amplifier circuit;

[0010] The second input end of the operational amplifier circuit is connected to a power supply;

[0011] The output end of the operational amplifier circuit is respectively connected to the control end of the current amplification branch and one end of the second current limiting circuit;

[0012] The other end of the second current limiting circuit is connected to the power supply;

[0013] The output end of the current amplification branch serves as the output end of the voltage-to-current circuit, and outputs a current signal.

[0014] Optionally, in the voltage-to-current circuit, the current amplification branch includes: a first resistor R1, a third resistor R3, and a triode TR1;

[0015] One end of the third resistor R3 serves as the input end of the current amplification branch;

[0016] The other end of the third resistor R3 is respectively connected to one end of the first resistor R1 and the input end of the triode TR1;

[0017] The other end of the first resistor R1 is connected to the power supply;

[0018] The control end of the triode TR1 serves as the control end of the current amplification branch;

[0019] The output end of the triode TR1 serves as the output end of the current amplification branch.

[0020] Optionally, in the voltage-to-current circuit, the triode TR1 is a PNP triode.

[0021] Optionally, in the voltage-to-current circuit, the operational amplifier circuit includes: an operational amplifier D, a first capacitor C1, and a fourth resistor R4;

[0022] The negative-phase input end of the operational amplifier D is connected to one end of the first capacitor C1, and the connection point serves as the first input end of the operational amplifier circuit;

[0023] The positive-phase input end of the operational amplifier D serves as the second input end of the operational amplifier circuit;

[0024] The output end of the operational amplifier D is respectively connected to the other end of the first capacitor C1 and one end of the fourth resistor R4;

[0025] The other end of the fourth resistor R4 serves as the output end of the operational amplifier circuit.

[0026] Optionally, in the voltage-to-current circuit, the operational amplifier D is powered by the power supply.

[0027] Optionally, in the voltage-to-current circuit, the first current limiting circuit includes a second resistor R2;

[0028] Both ends of the second resistor R2 serve as both ends of the first current limiting circuit.

[0029] Optionally, in the voltage-to-current circuit, the second current-limiting circuit includes a fifth resistor R5;

[0030] Both ends of the fifth resistor R5 serve as both ends of the second current-limiting circuit.

[0031] Optionally, in the voltage-to-current circuit, a filter circuit is further included, which is disposed between the second input terminal of the operational amplifier circuit and the power supply.

[0032] Optionally, in the voltage-to-current circuit, the filter circuit includes a sixth resistor R6, a second capacitor C2, and a seventh resistor R7;

[0033] One end of the sixth resistor R6 is connected to one end of the second capacitor C2, and the connection point is connected to the power supply;

[0034] The other end of the sixth resistor R6 is respectively connected to the other end of the second capacitor C2 and one end of the seventh resistor R7, and the connection point is connected to the second input terminal of the operational amplifier circuit;

[0035] The other end of the seventh resistor R7 is connected to signal ground.

[0036] Optionally, in the voltage-to-current circuit, the voltage signal is 0 to 10V;

[0037] The current signal is 0 to 20mA.

[0038] As can be seen from the above technical solutions, a voltage-to-current circuit provided by the present invention is as follows: One end of the first current-limiting circuit serves as the input terminal of the voltage-to-current circuit; the other end of the first current-limiting circuit is respectively connected to the input terminal of the current amplification branch and the first input terminal of the operational amplifier circuit; the second input terminal of the operational amplifier circuit is connected to the power supply; the output terminal of the operational amplifier circuit is respectively connected to the control terminal of the current amplification branch and one end of the second current-limiting circuit; the other end of the second current-limiting circuit is connected to the power supply; the output terminal of the current amplification branch serves as the output terminal of the voltage-to-current circuit; that is to say, the current amplification branch and the first input terminal of the operational amplifier circuit receive the input voltage signal through the first current-limiting circuit, and the second input terminal of the operational amplifier circuit receives the power supply voltage signal; the operational amplifier circuit processes according to the input voltage signal and the power supply voltage signal to obtain an output signal, and this output signal is transmitted to the control terminal of the current amplification branch, so that the operational amplifier circuit can control the operating state of the current amplification branch, realize converting the input voltage into an output current signal, and make the output current signal within a preset range; that is, the function of voltage-to-current can be realized according to the operational amplifier circuit and the current amplification branch, the cost is reduced, and there is no need to cooperate with external devices, reducing the system complexity. Description of the Drawings

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0040] Figure 1 is a schematic diagram of a voltage-to-current circuit provided by an embodiment of the present invention;

[0041] Figure 2 is a schematic diagram of another voltage-to-current circuit provided by an embodiment of the present invention. Detailed implementation manners

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0043] In this application, the terms "include", "comprise", or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article, or device. Without further limitations, the element defined by the phrase "including one..." does not exclude the existence of additional identical elements in the process, method, article, or device including the said element. In addition, the terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of this application and the above accompanying drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances, so that the embodiments of this application described herein can be implemented in an order other than those illustrated or described herein.

[0044] The embodiments of this application provide a voltage-to-current circuit, which is used to solve the problems in the prior art of high cost and usually requiring cooperation with external triodes and MOS transistors, increasing the complexity and cost of the system.

[0045] See Figure 1 , the voltage-to-current circuit includes: a current amplification branch, a first current limiting circuit, a second current limiting circuit, and an operational amplifier circuit.

[0046] That is to say, relevant components can be integrated in the voltage-to-current circuit, aiming to efficiently and safely convert the voltage signal into a current signal.

[0047] One end of the first current-limiting circuit serves as the input end of the voltage-to-current circuit.

[0048] The starting point of the voltage-to-current circuit is the first current-limiting circuit, one end of which directly serves as the input interface of the circuit to receive the external voltage signal. This design not only ensures the effective access of the signal but also protects the subsequent circuit from the impact of excessive current through the current-limiting mechanism.

[0049] The other end of the first current-limiting circuit is respectively connected to the input end of the current amplification branch and the first input end of the operational amplifier circuit.

[0050] The other end of the first current-limiting circuit realizes the signal shunt. On the one hand, it is directly connected to the input end of the current amplification branch, and on the other hand, it is connected to the first input end of the operational amplifier circuit, that is, it realizes the shunting of the signal of the first current-limiting circuit to the current amplification branch and the operational amplifier circuit; such a layout prepares for the subsequent signal processing and amplification.

[0051] The second input end of the operational amplifier circuit is connected to the power supply.

[0052] The operational amplifier circuit plays a crucial role in the voltage-to-current circuit. Its second input end is stably connected to the power supply, providing a reference benchmark for the amplification process. The core function of the operational amplifier circuit is to receive the signal from the first current-limiting circuit, accurately amplify it, and adjust the output according to the preset conditions.

[0053] The output end of the operational amplifier circuit is respectively connected to the control end of the current amplification branch and one end of the second current-limiting circuit.

[0054] The output end of the operational amplifier circuit not only directly drives the control end of the current amplification branch but also is cleverly connected to one end of the second current-limiting circuit. This design realizes the intelligent control of the current amplification branch, ensuring that the current output meets the requirements and is safe and reliable. The other end of the second current-limiting circuit is securely connected to the power supply, further enhancing the safety and stability of the circuit.

[0055] The other end of the second current-limiting circuit is connected to the power supply.

[0056] The output end of the current amplification branch serves as the output end of the voltage-to-current circuit.

[0057] The output end of the current amplification branch becomes the output interface of the entire voltage-to-current circuit, outputting the precisely processed and converted current signal to the external load or the subsequent circuit, perfectly demonstrating the conversion ability and practical value of this circuit.

[0058] That is to say, the input voltage signal and the power supply voltage signal of the operational amplifier circuit are processed and transmitted to the current amplification branch to control the operating state of the current amplification branch, so as to realize the conversion of the input voltage signal into a current signal and make the current signal within a preset range.

[0059] In summary, through the collaborative work of the components carefully designed in this voltage-to-current circuit, an accurate conversion from voltage to current is achieved, which not only ensures the safe and stable operation of the circuit, but also meets diverse application requirements.

[0060] In this embodiment, one end of the first current limiting circuit serves as the input end of the voltage-to-current circuit; the other end of the first current limiting circuit is respectively connected to the input end of the current amplification branch and the first input end of the operational amplifier circuit; the second input end of the operational amplifier circuit is connected to the power supply; the output end of the operational amplifier circuit is respectively connected to the control end of the current amplification branch and one end of the second current limiting circuit; the other end of the second current limiting circuit is connected to the power supply; the output end of the current amplification branch serves as the output end of the voltage-to-current circuit; that is to say, the current amplification branch and the first input end of the operational amplifier circuit receive the input voltage signal through the first current limiting circuit, and the second input end of the operational amplifier circuit receives the power supply voltage signal; the operational amplifier circuit processes according to the input voltage signal and the power supply voltage signal to obtain an output signal, and this output signal is transmitted to the control end of the current amplification branch, so that the operational amplifier circuit can control the operating state of the current amplification branch, realize the conversion of the input voltage into an output current signal, and make the output current signal within a preset range; that is, the function of voltage-to-current can be realized according to the operational amplifier circuit and the current amplification branch, reducing costs and without the need to cooperate with external devices, reducing system complexity.

[0061] Optionally, the current amplification branch includes: a first resistor R1, a third resistor R3, and a triode TR1.

[0062] The current amplification branch is mainly for realizing optimized signal transmission and current control, such as realizing voltage-to-current conversion and current amplification.

[0063] One end of the third resistor R3 serves as the input end of the current amplification branch and is respectively connected to one end of the first current limiting circuit and the first input end of the operational amplifier circuit.

[0064] The third resistor R3 serves as the starting point of the current amplification branch, and one end of it is carefully set at the input end of the current amplification branch. This end is not only connected to the first current limiting circuit to ensure that the current flows within a safe range, but also directly connected to the first input end of the operational amplifier circuit to accurately capture and transmit the input voltage signal through the first current limiting circuit.

[0065] The other end of the third resistor R3 is respectively connected to one end of the first resistor R1 and the input end of the triode TR1.

[0066] On the other hand, the other end of the third resistor R3 is directly connected to the input end of the triode TR1 to provide a necessary signal basis for the operation of the triode TR1, while being connected to one end of the first resistor R1 to form a resistor series structure for signal voltage division processing.

[0067] The other end of the first resistor R1 is connected to the power supply.

[0068] The other end of the first resistor R1 is connected to the power supply, serving as the energy supply source for the entire branch to ensure the stable operation of the circuit. This design not only simplifies the power supply connection method but also effectively manages the current distribution in the branch.

[0069] The third resistor R3 and the first resistor R1 can form a voltage division circuit; the second resistor R2 and the third resistor R3 can also form a voltage division circuit; it can also be said that the first resistor R1, the second resistor R2, and the third resistor R3 together form a voltage division circuit.

[0070] The control end of the triode TR1 serves as the control end of the current amplification branch.

[0071] The output end of the triode TR1 serves as the output end of the current amplification branch, outputting a current signal.

[0072] As the core control element of this branch, the control end of the triode TR1 naturally becomes the control end of the entire current amplification branch. By receiving the signal output by the operational amplifier circuit through its control end, the triode TR1 can be flexibly turned on or off to achieve precise control of the current path.

[0073] The output end of the triode TR1 serves as the output end of the current amplification branch. Here, what is output is not only a current signal but also a precisely regulated electrical signal to meet the requirements of subsequent circuits or devices. This design enables the current amplification branch to play an important role in a complex circuit system, achieving precise signal conversion and transmission.

[0074] Specifically, the triode TR1 can be an NPN triode or a PNP triode, which will not be elaborated here one by one. It depends on the actual situation and is within the protection scope of this application.

[0075] Both PNP and NPN triodes can amplify current.

[0076] The working principle of a PNP triode is opposite to that of an NPN triode. In electronics, the triode TR1 (whether NPN or PNP type) is based on a bipolar junction transistor (BJT), and they have the ability to amplify current or voltage, depending on how they are connected to the circuit.

[0077] In this embodiment, the emitter of the PNP transistor serves as the output terminal of the current amplification branch; the collector of the PNP transistor serves as the input terminal and is connected to the first resistor R1 and the third resistor R3; the base of the PNP transistor serves as the control terminal of the current amplification branch and is respectively connected to the fifth resistor R5 and the fourth resistor R4.

[0078] The NPN transistor is composed of two N-type semiconductors sandwiching a P-type semiconductor, and has three regions: the emitter region, the base region, and the collector region, corresponding to three electrodes: the emitter (E), the base (B), and the collector (C) respectively.

[0079] Principle of current amplification:

[0080] Forward bias of the emitter junction: When the potential of the base (B) is slightly higher than that of the emitter (E) (usually a few tenths of a volt), the emitter junction is in a forward bias state. This enables the majority carriers (electrons) in the emitter region to overcome the potential barrier of the PN junction and enter the base region, forming the emitter current (Ie).

[0081] Reverse bias of the collector junction: At the same time, the potential of the collector (C) is several volts higher than that of the base (B), making the collector junction in a reverse bias state. This biasing state is conducive to the collector collecting the electrons diffused from the base region, forming the collector current (Ic).

[0082] Current control: Since the base region is very thin and has a low doping concentration, only a small part of the electrons injected into the base region recombine with the holes in the base region to form the base current (Ib), while most of the electrons are collected by the collector under the action of the reverse bias electric field of the collector junction, forming the collector current. Therefore, the base current has a strong control effect on the collector current, that is, a small change in the base current can cause a large change in the collector current, thus realizing the amplification of the current.

[0083] Amplification factor:

[0084] The amplification factor of the NPN transistor is usually represented by β (DC current amplification factor) or hFE (AC current amplification factor), which represents the ratio between the collector current (Ic) and the base current (Ib). The β value is generally between several tens and several hundreds, depending on the model and working conditions of the transistor TR1.

[0085] Quiescent operating point: When designing the amplification circuit of the NPN transistor, it is necessary to reasonably set the quiescent operating point (Q point) to ensure that the transistor TR1 operates in the amplification region rather than the cut-off region or the saturation region. The setting of the quiescent operating point will affect the amplification factor, distortion degree, and stability of the circuit.

[0086] Temperature Influence: The amplification factor and performance of an NPN transistor are affected by temperature. When the temperature rises, the β value may increase, which may lead to a decrease in the stability of the circuit. Therefore, temperature compensation measures need to be considered when designing the circuit.

[0087] Bias Circuit: To stabilize the quiescent operating point of the NPN transistor and reduce the influence of temperature on the circuit performance, a bias circuit is usually adopted to provide the base current. The bias circuit can include components such as resistors and capacitors, and the circuit performance is optimized by adjusting the parameters of these components.

[0088] In summary, the NPN transistor is an important current amplification device and has a wide range of applications in electronic circuits. By reasonably designing the circuit and selecting appropriate component parameters, the current amplification effect of the NPN transistor can be fully exerted and stable circuit performance can be achieved.

[0089] For a PNP transistor, when the base (B) is at a negative potential relative to the emitter (E) (i.e., the emitter potential is higher than the base potential), and the collector (C) is also at a relatively high potential relative to the emitter, the transistor TR1 will enter the amplification mode. In this mode, a small change in the base current will cause a large change in the collector current, thereby achieving current amplification.

[0090] Specifically, when the base current increases, it will attract more holes to flow from the emitter to the base, and then more holes will be injected into the collector junction, resulting in a significant increase in the collector current. This control effect of the base current on the collector current is the basic principle of current amplification of the PNP transistor.

[0091] It should be noted that to achieve effective current amplification, the PNP transistor must operate under appropriate bias conditions, that is, the emitter must be forward-biased (relative to the base), and the collector must be reverse-biased (relative to the base). In addition, the circuit design also needs to consider the current gain (β) of the transistor TR1 and other relevant parameters to ensure that the circuit performance meets the requirements.

[0092] In summary, the PNP transistor can be used to amplify current, but its operating principle and bias conditions are different from those of the NPN transistor. In practical applications, the appropriate type of transistor TR1 and circuit design scheme should be selected according to specific requirements.

[0093] Optionally, the operational amplifier circuit includes: operational amplifier D, first capacitor C1, and fourth resistor R4.

[0094] The negative input terminal of the operational amplifier D is connected to one end of the first capacitor C1, and the connection point is used as the first input terminal of the operational amplifier circuit.

[0095] That is to say, the operational amplifier D, as the core of the operational amplifier circuit, is responsible for signal amplification and processing. Its inverting input terminal is closely connected to one end of the first capacitor C1, and this connection point is specifically designated as the first input terminal of the operational amplifier circuit for receiving external input signals.

[0096] The non-inverting input terminal of the operational amplifier D serves as the second input terminal of the operational amplifier circuit; that is to say, the non-inverting input terminal of the operational amplifier D remains independent and directly serves as the second input terminal of the operational amplifier circuit, allowing another signal to be connected, providing the circuit with flexible signal processing capabilities.

[0097] The output terminal of the operational amplifier D is respectively connected to the other end of the first capacitor C1 and one end of the fourth resistor R4; that is to say, the output terminal of the operational amplifier D is simultaneously connected to the other end of the first capacitor C1 and one end of the fourth resistor R4. This connection method not only realizes signal output but also performs certain filtering or phase adjustment through the first capacitor C1, while the fourth resistor R4 is used to limit the output current and protect the subsequent circuit from the impact of excessive current.

[0098] The other end of the fourth resistor R4 serves as the output terminal of the operational amplifier circuit. That is to say, the other end of the fourth resistor R4 is clearly set as the output terminal of the operational amplifier circuit, and the signal output here is the result processed and adjusted by the operational amplifier D and can be directly supplied to the subsequent circuit for use.

[0099] It should be noted that, as Figure 1 shown, 11, 12, 13, 14, and 4 are all pin numbers of the operational amplifier D; IC1D is the current identifier, that is, the current from the first capacitor C1 to the operational amplifier D.

[0100] Optionally, the operational amplifier D is powered by a power supply.

[0101] Specifically, the positive power supply terminal of the operational amplifier D is connected to the power supply; the negative power supply terminal of the operational amplifier D is connected to the signal ground SGND.

[0102] To ensure that the operational amplifier D can work properly, an optional power supply interface is also provided. By receiving stable power supply, the operational amplifier D can continuously and stably output high-quality signals to meet the requirements of various complex circuit systems. This design enables the operational amplifier circuit to be widely used in electronic devices and become a key component for signal processing and amplification.

[0103] In this embodiment, the functions of the operational amplifier circuit can be realized through devices such as the operational amplifier D, resistors, and capacitors. The circuit is simple and the cost is low.

[0104] Optionally, the first current-limiting circuit includes a second resistor R2.

[0105] Both ends of the second resistor R2 serve as both ends of the first current-limiting circuit.

[0106] The number of the second resistors R2 can be multiple or 1.

[0107] Specifically, when the number of the second resistors R2 is 1, one end of the second resistor R2 serves as one end of the first current-limiting circuit, that is, serves as the input end of the voltage-to-current conversion circuit to receive an input voltage signal; the other end of the second resistor R2 serves as the other end of the first current-limiting circuit and is respectively connected to the first input end of the operational amplifier circuit and one end of the current amplification branch.

[0108] When the number of the second resistors R2 is multiple, the second resistors R2 are connected in series and / or in parallel. One floating end after connection serves as one end of the first current-limiting circuit, that is, serves as the input end of the voltage-to-current conversion circuit to receive an input voltage signal; the other floating end after connection serves as the other end of the first current-limiting circuit and is respectively connected to the first input end of the operational amplifier circuit and one end of the current amplification branch.

[0109] By adjusting the resistance value of the second resistor R2, the magnitude of the current passing through the circuit can be effectively limited, thereby protecting the subsequent circuit.

[0110] When an input voltage signal passes through this circuit, the second resistor R2 limits the magnitude of the passing current according to its resistance value, thereby protecting the subsequent sensitive components or circuit parts in the circuit from being damaged by excessive current.

[0111] This design makes the first current-limiting circuit simple, direct and effective, can be flexibly applied in various circuit environments, and provides a strong guarantee for the stability and safety of the circuit. At the same time, the designer can accurately control the current-limiting effect by selecting a suitable resistance value of the second resistor R2 according to actual needs to achieve the best circuit performance.

[0112] Optionally, the second current-limiting circuit includes a fifth resistor R5.

[0113] Both ends of the fifth resistor R5 serve as both ends of the second current-limiting circuit.

[0114] The number of the fifth resistors R5 can be multiple or 1.

[0115] It should be noted that the fifth resistor R5 and the fourth resistor R4 form a voltage-dividing circuit.

[0116] Specifically, when the number of the fifth resistors R5 is 1, one end of the fifth resistor R5 serves as one end of the second current-limiting circuit and is respectively connected to the control end of the current amplification branch and the output end of the operational amplifier circuit; the other end of the fifth resistor R5 serves as the other end of the second current-limiting circuit to receive the power supply voltage.

[0117] When the number of the fifth resistors R5 is multiple, the fifth resistors R5 are connected in series and / or in parallel. One floating end after connection is used as one end of the second current limiting circuit and is respectively connected to the control end of the current amplification branch and the output end of the operational amplifier circuit; the other floating end after connection is used as the other end of the second current limiting circuit and receives the power supply voltage.

[0118] That is to say, the two ends of the fifth resistor R5 are directly designated as the input end and the output end of the second current limiting circuit, so as to form an independent current limiting unit. When current flows through the second current limiting circuit, the fifth resistor R5 will limit the current according to its specific resistance value to ensure that the current passing through this circuit is within a safe and controllable range.

[0119] Such a design not only enhances the safety performance of the circuit, but also improves the flexibility and adaptability of the circuit design. The designer can accurately control the current limiting effect of the second current limiting circuit by adjusting the resistance value of the fifth resistor R5 according to the actual application scenario and requirements, so as to meet the specific requirements of the circuit for current management. In addition, the second current limiting circuit and the first current limiting circuit can cooperate with each other to jointly maintain the stable operation of the entire circuit system.

[0120] Optionally, see Figure 2 , and further includes: a filtering circuit arranged between the second input end of the operational amplifier circuit and the power supply.

[0121] Specifically, one end of the filtering circuit is connected to the power supply; the other end of the filtering circuit is connected to the second input end of the operational amplifier circuit.

[0122] The main function of the filtering circuit is to filter out the high-frequency components in the signal and allow the low-frequency components to pass through. Such a circuit is generally composed of resistors and capacitors, and its working principle is based on the response characteristics of capacitors to signal frequencies. When the frequency of the input signal is low, the impedance of the capacitor is high, and the signal can pass through the resistor to the output end better; when the frequency of the input signal is high, the impedance of the capacitor decreases, resulting in more high-frequency signals bypassing through the capacitor to the ground and thus being filtered out. Therefore, the filtering circuit can effectively remove the high-frequency noise and interference in the signal and retain the required low-frequency signal.

[0123] Optionally, the filtering circuit includes a sixth resistor R6, a second capacitor C2, and a seventh resistor R7.

[0124] One end of the sixth resistor R6 is connected to one end of the second capacitor C2, and the connection point is connected to the power supply.

[0125] The other end of the sixth resistor R6 is respectively connected to the other end of the second capacitor C2 and one end of the seventh resistor R7, and the connection point is connected to the second input end of the operational amplifier circuit.

[0126] The other end of the seventh resistor R7 is connected to the signal ground SGND.

[0127] The sixth resistor R6 and the second capacitor C2 mainly function as filters, that is, the sixth resistor R6 and the second capacitor C2 form an RC low-pass filter circuit; the seventh resistor R7 mainly functions as a voltage divider.

[0128] When the power supply voltage is applied to one end of the sixth resistor R6, the power supply voltage signal will flow through both the sixth resistor R6 and the second capacitor C2 simultaneously.

[0129] The second capacitor C2 presents a low impedance to AC signals (especially high-frequency AC signals), while presenting an open circuit state to DC signals. Therefore, high-frequency AC signals are more likely to flow through the second capacitor C2 and the seventh resistor R7 to the signal ground.

[0130] The sixth resistor R6 presents the same impedance to signals of all frequencies, so it will limit the magnitude of the current passing through it.

[0131] Due to the attenuation effect of the second capacitor C2 on high-frequency signals, the RC low-pass filter circuit allows low-frequency signals to pass through and attenuates high-frequency signals. In this way, the high-frequency components in the output signal are filtered out, leaving only low-frequency components and DC components.

[0132] Regarding Figure 2 the shown circuit schematic diagram, the working principle of the voltage-to-current circuit is described as follows:

[0133] One end of the second resistor R2 receives the input voltage signal, and the other end of the second resistor R2 is respectively connected to the negative input terminal of the operational amplifier D, one end of the first capacitor C1, and one end of the third resistor R3; the other end of the third resistor R3 is respectively connected to one end of the first resistor R1 and the collector of the PNP transistor; the emitter of the PNP transistor serves as the output terminal of the voltage-to-current circuit; one end of the sixth resistor R6 is connected to one end of the second capacitor C2, and the connection point is connected to the power supply; the other end of the sixth resistor R6 is respectively connected to the other end of the second capacitor C2, one end of the seventh resistor R7, and the positive input terminal of the operational amplifier D; the other end of the seventh resistor R7 is connected to the signal ground SGND; the output terminal of the operational amplifier D is respectively connected to the other end of the first capacitor C1 and one end of the fourth resistor R4; the other end of the fourth resistor R4 is respectively connected to the base of the PNP transistor and one end of the fifth resistor R5, and the other end of the fifth resistor R5 is connected to the power supply; the positive power supply terminal of the operational amplifier D is connected to the power supply, and the negative power supply terminal of the operational amplifier D is connected to the signal ground SGND.

[0134] Among them: The resistance value of the first resistor R1 is 120R, that is, 120Ω; the resistance value of the second resistor R2 is 1MΩ; the resistance value of the third resistor R3 is 240KΩ; the resistance value of the fourth resistor R4 is 22KΩ, and the resistance value of the fifth resistor R5 is 10KΩ; the resistance value of the sixth resistor R6 is 240KΩ; the resistance value of the seventh resistor R7 is 1MΩ; the first capacitor C1 is a capacitor of 680pF; the second capacitor C2 is also a capacitor of 680pF. The voltage signal input terminal is VIN, and the current output terminal is IOUT.

[0135] First, explain the principles of virtual short and virtual open of the operational amplifier D:

[0136] Virtual short: Virtual short means that when analyzing the operational amplifier D in the linear state, its two input terminals (the non-inverting input terminal + and the inverting input terminal -) can be regarded as having equal potential, that is, the voltage difference is almost zero. This characteristic is not a real short circuit, but because the open-loop voltage amplification factor of the operational amplifier D is extremely high (generally, the open-loop voltage amplification factor of a general-purpose operational amplifier D is above 80dB, that is, more than 10,000 times), and the output voltage is limited by the power supply voltage, usually between 10V and 14V. Therefore, within the normal working range, the differential input voltage of the operational amplifier D (that is, the voltage difference between the two input terminals) is very small, almost zero, and the two input terminals can be approximately considered to have equal potential, which is the so-called "virtual short". Its influence is: The virtual short characteristic enables the operational amplifier D to effectively reduce errors when processing non-inverting input signals, because the voltages of the two input terminals are equal, which is equivalent to forming a high-precision voltage follower between the signal source and the amplifier.

[0137] Virtual open: Virtual open means that the input resistance of the operational amplifier D is extremely large (generally, the input resistance of a general-purpose operational amplifier D is above 1MΩ), the input current is extremely small, and it can be regarded as an open circuit. This is because the differential input resistance of the operational amplifier D is very large, making the current flowing into the input terminals of the operational amplifier much smaller than the current of the external circuit at the input terminals. Therefore, usually, the two input terminals of the operational amplifier can be regarded as an open circuit. However, it should be noted that this does not mean that the two input terminals are truly open, but they are approximately regarded as open due to the extremely small input current, which is the so-called "virtual open". Its influence is: The virtual open characteristic ensures the pure processing of signals, because the input current is extremely small, so the influence of the operational amplifier D on the input signal is also very small, and it can accurately amplify the input signal.

[0138] That is to say, the virtual short and virtual open of the operational amplifier D are two important characteristics in the linear working state. Virtual short makes the voltages of the two input terminals equal and reduces errors; virtual open ensures the pure processing of signals. These two characteristics play a key role in the application of the operational amplifier D, enabling the operational amplifier D to accurately amplify and process various input signals. When designing a circuit containing the operational amplifier D, it is necessary to fully understand and utilize these two characteristics.

[0139] 1) According to the "virtual open" principle of operational amplifier D, we have:

[0140]

[0141]

[0142] Since R3 >> R1, we have:

[0143]

[0144] 2) According to the "virtual short" principle of operational amplifier D, V1 = V2.

[0145] Combining formulas (1), (2), and (3) can obtain the relationship between VIN and IOUT as follows

[0146]

[0147] Substituting the resistance values of each resistor can obtain the final relational expression as:

[0148] VIN = 500 × IOUT Formula (5)

[0149] That is, formula (5) realizes the function of converting voltage 0 - 10V to current 0 - 20mA.

[0150] At the same time, from formula (5), it can be seen that the output current finally has no calculation relationship with the power supply voltage VCC. Therefore, this circuit is not sensitive to the power supply and has strong anti-interference ability. At the same time, since the current of this circuit directly comes from VCC, VCC can be 15V; theoretically, it can drive a resistor of 15V ÷ 0.02A - 120Ω = 630Ω. That is to say, the resistance value of the subsequent load of this voltage-to-current circuit can be 630Ω; this is what a general circuit cannot achieve.

[0151] It should be noted that the Howland current source circuit can also be used. It uses a Howland current pump or a Howland current source circuit to achieve stable current output. This circuit has the characteristics of simple structure and convenient adjustment; however, it has a high requirement for the stability of the power supply voltage, and power supply fluctuations may affect the stability of the current output; in addition, its load-carrying capacity is relatively weak, which limits its application under large-load conditions; at the same time, since the driving current comes from operational amplifier D, operational amplifier D is easily damaged when the load current is too large.

[0152] In this embodiment, the circuit is simple and low-cost, only requiring the combination of an operational amplifier D and a PNP triode to build. It is insensitive to the power supply, has strong anti-interference ability, and has strong load-carrying capacity. In addition, the current output is cleverly directly output from the emitter of the PNP triode through the power supply, which can prevent the operational amplifier from being damaged due to excessive current, and at the same time can also avoid the temperature drift caused by the operational amplifier heating due to the current passing through the operational amplifier.

[0153] The features described in the respective embodiments of this specification can be replaced or combined with each other. For the same or similar parts between the respective embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and for the relevant parts, reference can be made to the partial description of the method embodiment. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative labor.

[0154] Those skilled in the art can further realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Skilled professionals can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0155] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A voltage-to-current circuit, characterized in that, It includes: a current amplification branch, a first current limiting circuit, a second current limiting circuit, and an operational amplifier circuit; One end of the first current limiting circuit serves as the input end of the voltage-to-current circuit and receives an input voltage signal; The other end of the first current limiting circuit is respectively connected to the input end of the current amplification branch and the first input end of the operational amplifier circuit; The second input end of the operational amplifier circuit is connected to a power supply; The output end of the operational amplifier circuit is respectively connected to the control end of the current amplification branch and one end of the second current limiting circuit; The other end of the second current limiting circuit is connected to the power supply; The output end of the current amplification branch serves as the output end of the voltage-to-current circuit and outputs a current signal.

2. The voltage-to-current circuit according to claim 1, wherein The current amplification branch includes: a first resistor, a third resistor, and a triode; One end of the third resistor serves as the input end of the current amplification branch; The other end of the third resistor is respectively connected to one end of the first resistor and the input end of the triode; The other end of the first resistor is connected to a power supply; The control end of the triode serves as the control end of the current amplification branch; The output end of the triode serves as the output end of the current amplification branch.

3. The voltage-to-current circuit according to claim 2, wherein The triode is a PNP triode.

4. The voltage-to-current circuit according to claim 1, wherein The operational amplifier circuit includes: an operational amplifier, a first capacitor, and a fourth resistor; The negative-phase input end of the operational amplifier is connected to one end of the first capacitor, and the connection point serves as the first input end of the operational amplifier circuit; The positive-phase input end of the operational amplifier serves as the second input end of the operational amplifier circuit; The output end of the operational amplifier is respectively connected to the other end of the first capacitor and one end of the fourth resistor; The other end of the fourth resistor serves as the output end of the operational amplifier circuit.

5. The voltage-to-current circuit according to claim 4, wherein, The operational amplifier is powered by a power supply.

6. The voltage-to-current circuit according to claim 1, wherein The first current limiting circuit includes a second resistor; Both ends of the second resistor serve as both ends of the first current limiting circuit.

7. The voltage-to-current circuit according to claim 1, wherein The second current limiting circuit includes a fifth resistor; Both ends of the fifth resistor serve as both ends of the second current limiting circuit.

8. The voltage-to-current circuit according to any one of claims 1 to 7, characterized in that It further includes a filter circuit provided between the second input end of the operational amplifier circuit and the power supply.

9. The voltage-to-current circuit according to claim 8, wherein, The filter circuit includes a sixth resistor, a second capacitor, and a seventh resistor; One end of the sixth resistor is connected to one end of the second capacitor, and the connection point is connected to the power supply; The other end of the sixth resistor is respectively connected to the other end of the second capacitor and one end of the seventh resistor, and the connection point is connected to the second input end of the operational amplifier circuit; The other end of the seventh resistor is connected to signal ground.

10. The voltage-to-current circuit according to claim 1, wherein The voltage signal is 0 to 10V; The current signal is 0 to 20mA.

Images