CN110058630B - Voltage-current conversion circuit - Google Patents

The invention discloses a voltage-current conversion circuit, which comprises: the input end of the amplifying module is connected with the first resistance element, the output end of the amplifying module is connected with the second resistance element, the input end of the output and negative feedback module is connected with the other end of the second resistance element, the output end of the output and negative feedback module is connected with the input end of the compensating module, and the output end of the compensating module is connected with the input end of the amplifying module; the amplifying module is used for linearly amplifying the first voltage input from the first resistance element to obtain a first amplified voltage and outputting the first amplified voltage to the second resistance element; the output and negative feedback module is used for converting a second voltage input from the second resistance element into a current, outputting the current to the current driving component and carrying out negative feedback on the second voltage by using the voltage at the two ends of the current driving component; and the compensation module is used for carrying out negative feedback on the first voltage according to the voltages at the two ends of the current driving component.

Voltage-current conversion circuit

Technical Field

The invention relates to the technical field of communication, in particular to a voltage-current conversion circuit.

Background

In the application circuit of industrial control and many sensors, when the signal is output in an analog mode, the signal is generally output in a voltage mode. However, when the analog signal is transmitted in a voltage manner over a long distance, a large attenuation is caused, and in order to avoid the attenuation of the analog signal during the transmission, the voltage is usually converted into a current for output.

Referring to fig. 1, a voltage-current (V-I) conversion circuit in the prior art is shown. The amplifier a1 and the resistor R2 constitute a negative feedback amplifier, and when an input voltage is input to the amplifier a1 through the resistor R1, the amplifier a1 linearly amplifies the voltage, and then the amplified voltage is input to the amplifier a2 through the resistor R3. The amplifier A2, the transistor, the resistor R4 and the current driving component Rn form a negative feedback circuit, the amplifier A2 amplifies the voltage input from the resistor R3 and outputs the amplified voltage to the transistor, the transistor converts the input voltage into current under the action of bias voltage of a collector electrode, the current is output to the current driving component Rn through an emitter electrode of the transistor, and the current flowing through the current driving component Rn is the output current. Finally, the resistor R4 feeds back the voltage at the two ends of the current driving component Rn to the amplifier a2, so that when the output voltage of the amplifier a2 changes, that is, the base bias voltage of the transistor changes, at this time, the on-resistance of the transistor changes correspondingly, which causes the output current of the transistor to change accordingly, the divided voltage of Rn changes correspondingly, so that the voltage V3 changes, the input voltage of the amplifier a2 changes, and the output voltage of the amplifier a2 changes accordingly, thereby ensuring that the output current of the transistor keeps constant.

However, in practical use, when the input voltage is constant but the temperature changes, the voltage V3 changes with the temperature, that is, when the ambient temperature becomes high, the voltage V3 decreases, so that the output current of the V-I conversion circuit becomes small; when the ambient temperature becomes lower, the voltage V3 rises, and the output current of the V-I conversion circuit becomes larger.

Therefore, the output current of the voltage-current conversion circuit in the prior art is easily influenced by the ambient temperature, and the temperature drift problem exists.

Disclosure of Invention

The invention provides a voltage-current conversion circuit, which is used for solving the temperature drift problem of the voltage-current conversion circuit in the prior art.

The invention provides a voltage-current conversion circuit in a first aspect, the circuit comprises a first resistance element, an amplifying module, a second resistance element, an output and negative feedback module and a compensation module, wherein:

the input end of the amplifying module is connected with the first resistance element, the output end of the amplifying module is connected with the second resistance element, the input end of the output and negative feedback module is connected with the other end of the second resistance element, the output end of the output and negative feedback module is connected with the input end of the compensating module, and the output end of the compensating module is connected with the input end of the amplifying module;

the amplifying module is used for linearly amplifying the first voltage input from the first resistance element to obtain a first amplified voltage, and outputting the first amplified voltage to the second resistance element;

the output and negative feedback module is used for converting a second voltage input from the second resistance element into a current, outputting the current to the current driving component, and performing negative feedback on the second voltage by using the voltage at two ends of the current driving component; wherein the current is an output current;

and the compensation module is used for carrying out negative feedback on the first voltage according to the voltages at the two ends of the current driving component, so that when the voltages at the two ends of the current driving component are increased, the input voltage of the amplification module is reduced or when the voltages at the two ends of the current driving component are reduced, the input voltage of the amplification module is increased, and the current is kept stable.

In a possible embodiment, the amplifying module is a feedback amplifier.

In a possible embodiment, the output and negative feedback module includes an operational amplifier, a transistor, a third resistive element, and a fourth resistive element, wherein:

the operational amplifier comprises a first negative electrode input end and a first positive electrode input end, the first positive electrode input end is grounded, the first negative electrode input end is connected with the second resistor element, and the output end of the operational amplifier is connected with the base electrode of the transistor;

a collector of the transistor inputs a preset bias voltage, and an emitter of the transistor is connected with an input end of the current driving component;

the first end of the third resistance element is connected with the output end of the current driving component, and the second end of the third resistance element is connected with the ground;

a first end of the fourth resistance element is connected with an output end of the current driving component, and a second end of the fourth resistance element is connected with the first negative electrode input end;

the operational amplifier is used for linearly amplifying the second voltage to obtain a second amplified voltage;

the transistor converts the second amplified voltage into the current under the action of the preset bias voltage, and outputs the current to the current driving component through an emitter of the transistor;

and the fourth resistance element is used for feeding back the voltages at two ends of the current driving component to the first negative electrode input end of the operational amplifier so as to carry out negative feedback on the second voltage.

In a possible embodiment, the compensation module comprises a fifth resistive element, a feedback unit, a sixth resistive element, a seventh resistive element, and an eighth resistive element, wherein:

the first end of the fifth resistance element is connected with the output end of the current driving element, the feedback unit comprises a second negative input end and a second positive input end, the second negative input end is connected with the second end of the fifth resistance element, the first end of the sixth resistance element is connected with the second positive input end, the second end of the sixth resistance element is connected with the ground, the first end of the seventh resistance element is connected with the second positive input end, the second end of the seventh resistance element is connected with the first end of the first resistance element, the first end of the eighth resistance element is connected with the output end of the feedback unit, and the second end of the eighth resistance element is connected with the second end of the first resistance element;

the feedback unit is used for comparing and amplifying a third voltage input from the fifth resistance element and a fourth voltage input from the seventh resistance element and outputting the processed voltage;

the eighth resistance element is used for feeding back the processed voltage to the input end of the amplifying module so as to adjust the first voltage.

In a possible embodiment, the feedback unit is a feedback amplifier.

In a possible embodiment, the first, second, fourth, fifth, sixth, seventh and eighth resistance elements have the same resistance value.

In a possible embodiment, the resistance value is 10K ohms.

In a possible embodiment, the initial voltage has a voltage value of any one of 0 to 5V.

In a possible implementation manner, a resistance value of any one of the first, second, fourth, fifth, sixth, seventh, and eighth resistance elements is greater than a resistance value of the current-driven component, and a resistance value of any one of the first, second, fourth, fifth, sixth, seventh, and eighth resistance elements is greater than a resistance value of the third resistance element.

In a possible embodiment, the amplification factor in the amplification module, the feedback unit and the operational amplifier is 1.

The technical scheme in the embodiment of the invention has the following beneficial effects:

a compensation module is added in the voltage-current conversion circuit in the prior art, wherein the output end of a feedback circuit in the voltage-current conversion circuit in the prior art is connected with the input end of the compensation module, the output end of the compensation module is connected with the input end of the amplification module, so that the negative feedback is carried out on the input voltage of an amplifier A1 according to the voltage at two ends of the current driving component Rn, when the voltage at two ends of the current driving component is increased, the input voltage of the amplifier A1 is reduced or when the voltage at two ends of the current driving component is reduced, the input voltage of the amplifier A1 is increased, thereby the abnormal V-I conversion caused by the temperature is automatically compensated through the closed loop V-I conversion circuit structure with automatic compensation, the output current of the voltage-current conversion circuit is stabilized, and further, compared with the prior art, the circuit structure only needs to add one compensation module to reduce the influence of temperature on the V-I conversion circuit, and the product cost can be effectively reduced.

Drawings

FIG. 1 is a prior art V-I converter circuit;

fig. 2 is a block diagram of a voltage-to-current conversion circuit according to an embodiment of the present invention;

fig. 7 is an example of a voltage-to-current conversion circuit provided in the embodiment of the present invention.

Detailed Description

The invention provides a voltage-current conversion circuit, which is used for solving the temperature drift problem of the voltage-current conversion circuit in the prior art.

In order to solve the technical problems, the general idea of the invention is as follows:

a compensation module is added in the voltage-current conversion circuit in the prior art, wherein the output end of a feedback circuit in the voltage-current conversion circuit in the prior art is connected with the input end of the compensation module, the output end of the compensation module is connected with the input end of the amplification module, so that the negative feedback is carried out on the input voltage of an amplifier A1 according to the voltage at two ends of the current driving component Rn, when the voltage at two ends of the current driving component is increased, the input voltage of the amplifier A1 is reduced or when the voltage at two ends of the current driving component is reduced, the input voltage of the amplifier A1 is increased, thereby the abnormal V-I conversion caused by the temperature is automatically compensated through the closed loop V-I conversion circuit structure with automatic compensation, the output current of the voltage-current conversion circuit is stabilized, and further, compared with the prior art, the circuit structure only needs to add one compensation module to reduce the influence of temperature on the V-I conversion circuit, and the product cost can be effectively reduced.

In order to better understand the technical solutions of the present invention, the following detailed descriptions of the technical solutions of the present invention are provided with the accompanying drawings and the specific embodiments, and it should be understood that the specific features of the embodiments and the examples of the present invention are the detailed descriptions of the technical solutions of the present invention, and are not limitations of the technical solutions of the present invention, and the technical features of the embodiments and the examples of the present invention can be combined with each other without conflict.

In the V-I conversion circuit shown in fig. 1, when the input voltage is constant but the temperature changes, the voltage V3 changes with the temperature. However, through experiments on the V-I conversion circuit shown in fig. 1, it was found that if the voltage V3 changes due to temperature changes, the input voltage of the V-I conversion circuit is changed, so that the voltage V3 and the output current can return to the original values, i.e., when the voltage V3 decreases, the input voltage is increased; when the voltage V3 increases, the input voltage is decreased.

Referring to fig. 7, an example of a voltage-to-current conversion circuit in the embodiment of the present invention is shown, and the circuit shown in fig. 7 is analyzed as follows:

according to the basic circuit law of virtual short-virtual break of the operational amplifier, the operational amplifier A1 can be obtained:

thereby obtaining:

similarly, for the operational amplifier a2, the following are available:

assume that R3 > RL, R3 > Rn, i.e. resistor R3 versus output current I_outThe shunting effect can be ignored, and the following formulas can be listed for the Rn branch and the RL branch:

obtaining:

the following steps are provided:

the following can be obtained:

V2＝I_out·(Rn+RL) (4)

for the operational amplifier a3, the following are available:

substituting equation (1) into equation (2) yields:

substituting equation (3) into equation (6) yields:

substituting equation (5) into equation (6) yields:

in an ideal case, the resistances except the Rn and RL resistances are all equal, and the equation (8) can be obtained:

V_in+(V_in-V3)＝V3

namely, it is

V_in＝V3 (9)

Substituting equation (3) into equation (9) yields:

then, equation (4) is substituted into available:

namely:

as can be seen from equation (10), the output current I_outIndependent of Rn, i.e. output current I_outDoes not change along with the change of Rn, and realizes the stable transformation of V-I.

In practical use, since all resistors have a certain error and a certain temperature effect, and different resistance values at different temperatures, the formula should be:

in the V-I conversion circuit, since the initial voltage changes at any time, the current flowing through the resistor RL also changes at any time, and when the initial voltage changes in a range of 0 to 5V and RL is 10 Ω, the current flowing through RL ranges from 0 to 500 mA. According to the formula P ═ I²The power variation range of R and RL is 0W to 2.5W, the bearing power is relatively large, and the power variation is also relatively large, therefore, the temperature drift problem of RL is not negligible.

The resistors R1, R2, … …, and R9 have large resistance values, so that the current flowing through the resistors is small and the current change is negligible. Meanwhile, the initial voltage changes greatly, the actual change range is 0-5V, the resistance values are all 10K, and the value is U according to the formula²and/R, the power borne by each resistor is 0-2.5 mW, and the power borne by each resistor is very small, so the temperature drift problem of the resistors can be ignored.

In summary, the following steps: when the environment temperature changes or the initial voltage changes, the resistance values of the resistors R1, R2, … … and R9 are unchanged, but the resistance value of the resistor RL changes greatly.

Further, temperature causes the gain of the active device to vary:

neglecting the difference between each resistor, introducing the operational amplifier gain, and changing the formula into:

I_out·RL·G_A11G_A2＝V_in+V4·G_A3＝V_in+(V_in-V3)·G_A3

the voltage V3 is determined by the operational amplifiers a1 and a2, and theoretically the amplification factor of the operational amplifier itself should always be 1, but there are also reasons for thisA situation where temperature causes a gain change. When the amplification factor of the operational amplifiers A1 and A2 changes with temperature, the current I_outAnd will vary accordingly.

The operational amplifier a3 plays a role in the circuit:

when the voltage V3 decreases due to temperature change, the voltage V4 increases, the voltage V4 is fed back to the operational amplifier a1, the voltage V2 increases, and the voltage V3 returns to the original value.

When the voltage V3 increases due to temperature change, the voltage V4 becomes smaller, the voltage V4 is fed back to the operational amplifier a1, the voltage V2 is reduced, and the voltage V3 returns to the original value.

When the temperature is constant, the voltage V3 is equal to the initial voltage, and the voltage V4 is zero.

Regardless of the change of the gains of the operational amplifiers A1 and A2 with temperature and the change of the reference resistor RL with temperature, as long as the gain of the operational amplifier A3 does not change with temperature, the influence of the temperature on other operational amplifiers and the reference resistor RL can be compensated by the method, and the output current I is achieved in the form of a feedback closed loop_outIs not affected by the current change caused by the temperature change.

In the above technical solution, a compensation module is added in the voltage-current conversion circuit in the prior art, and by using the compensation module, the input voltage of the amplifier a1 is negatively fed back according to the voltage across the current-driven element Rn, decreasing the input voltage of the amplifier a1 when the voltage across the current drive component increases or increasing the input voltage of the amplifier a1 when the voltage across the current drive component decreases, such that, the output current of the voltage circuit conversion circuit is stabilized by automatically compensating the abnormal V-I conversion caused by temperature through the closed loop V-I conversion circuit structure of automatic compensation, and further, in order to reduce the influence of temperature on the V-I conversion circuit, compared with the prior art, the circuit structure only needs to add one compensation module, and the product cost can be effectively reduced.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, optical storage, and the like) having computer-usable program code embodied therein.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.