CN102035546A - Voltage current transformer - Google Patents

Abstract

The invention relates to a voltage current transformer which comprises resistors R, a potentiometer RW and an operational amplifier U1, wherein the resistors R comprise a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5 and a resistor R6, the resistor R1 is connected with the resistor R2 and then connected with the negative input end of the operational amplifier U1, one end of the resistor R1 is connected with the potentiometer RW, and the other end of the potentiometer RW is grounded; the other end of the resistor R2 is connected with one end of the resistor R5 and then connected with the output end of the operational amplifier U1, the other end of the resistor R5 is connected with one end of the resistor R4 and one end of the resistor R6, the other end of the resistor R4 is connected with the resistor R3 and then connected with the positive input end of the operational amplifier U1, the other end of the resistor R3 is connected with a voltage signal source Vin, and the other end of the resistor R6 is grounded. The voltage current transformer of the invention has simple circuit and high output precision. An output current is irrelevant to the size of a load. The voltage current transformer integrates simplicity, reliability, high precision and high cost performance.

Description

Voltage current adapter

Technical field

Voltage current adapter of the present invention relates to electronic circuit, and specifically a kind of voltage source converts the change-over circuit of current source to.

Background technology

In the application circuit of Industry Control and many transducers, when simulating signal output, generally be to export at present with voltage.With voltage system length Distance Transmission analog signal the time, the D.C. resistance of signal resistance or transmission line etc. can cause voltage attenuation, and the input resistance of signal receiving end is low more, and voltage attenuation is big more.For fear of the decay of signal in transmission course, has only the input resistance that increases signal receiving end, but the increase of signal receiving end input resistance, the transmission line interference free performance is reduced, be subject to external interference, the signal transmission is unstable, like this when length Distance Transmission analog signal, can not use the voltage way of output, and voltage output is converted to electric current output.In many in addition conventional industrial instruments, connect with current system and also to require output to convert voltage output to electric current output.Voltage current adapter converts the voltage output signal to current output signal exactly, helps the signal long-distance transmission.At existing problem in the above-mentioned prior art, a kind of novel voltage current adapter of research and design, existing problem is very necessary in the prior art thereby overcome.

Summary of the invention

In view of existing problem in the above-mentioned prior art, the objective of the invention is a kind of novel voltage current adapter of research and design, thereby when solving voltage system length Distance Transmission analog signal, the D.C. resistance of signal resistance or transmission line etc. can cause voltage attenuation, the input resistance of signal receiving end is low more, and voltage attenuation is big more.For fear of the decay of signal in transmission course, have only the input resistance that increases signal receiving end, but the increase of signal receiving end input resistance reduces the transmission line interference free performance, is subject to external interference, problems such as signal transmission instability.

Voltage current adapter of the present invention is made up of resistance R, potentiometer RW and operational amplifier U1; It is characterized in that described resistance R comprises R1, R2, R3, R4, six resistance of R5 and R6, resistance R 1 is connected the back and is connected with the negative input end of operational amplifier U1 with resistance R 2, the other end of resistance R 1 connects potentiometer RW, the other end ground connection of potentiometer RW, the other end of resistance R 2 and the output that is connected to operational amplifier U1 after an end of resistance R 5 is connected, the other end of described resistance R 5 is connected with an end of resistance R 4 and resistance R 6, the other end of resistance R 4 be connected with the positive input terminal of operational amplifier U1 again after resistance R 3 is connected, the other end of resistance R 3 connects voltage signal source Vin, the other end ground connection of described resistance R 6.The resistance value of resistance R 1 of the present invention, R2, R3, R4 is identical as far as possible, perhaps R4/R3=R2/R1+RW.Resistance R 4 of the present invention＞＞R5, R4＞＞R6.Voltage signal source Vin=0～5V of the present invention.

Voltage current adapter of the present invention is the current signal that the voltage signal of input is converted to satisfied certain relation, the suitable output constant-source with adjustable of electric current after the conversion, its output current should be able to keep stable and can not change with the variation of load.Basic demand to sort circuit is: 1, output current is directly proportional with input voltage; 2, output current is a constant-current source.Promptly when load resistance changed in prescribed limit, output current remained unchanged; 3, output current is insensitive to the variation of power source change, ambient temperature etc.4, input voltage and output current are altogether.

Voltage current adapter of the present invention requires 0～5V input direct voltage is converted to the output of 0～20mA current source linearly, and basic accuracy is in 0.2%; When loading on 0～250 Ω variation, output current changes should be within specified accuracy simultaneously.This voltage-current converter circuit mainly is made up of operational amplifier U1, resistance R 1, R2, R3, R4, R5, R6 and potentiometer RW.Major advantage is that circuit structure is very succinct, is easy to realize functional requirement, greatly reduces the cost of product simultaneously.

Voltage current adapter operation principle of the present invention is, establishes resistance R 1+RW, R2, R3 and R4 and equates, and output current Iout=Vin/R5 then, promptly output current is proportional to input voltage, and is irrelevant with load resistance R6 size.R6 is a load resistance, and its resistance allows to change within the specific limits.Iout is an output current.To R3, R4 branch road, can list following equation

$V2=V1(1+\frac{R4}{R3})-\mathrm{Vin}\×\frac{R4}{R3}=V1\×(1+\mathrm{\α})-\mathrm{Vin}\×\mathrm{\α}---\left(1\right)$ α＝R4/R3。

If ignore the offset voltage of amplifier U1, when amplifier U1 operate as normal, the in-phase input end of amplifier and the voltage of inverting input equate, to R1+RW, R2 branch road, have

$V1=\frac{V3\×(R1+\mathrm{RW})}{R1+\mathrm{RW}+R2}=\frac{V3}{1+\mathrm{\β}}---\left(2\right)$ β＝R2/R1+RW。

If R4＞＞R5, R4＞＞R6, promptly the shunting action of 4 couples of output current Iout of resistance R can be ignored, to R5, R6 branch road,

$V2=\frac{V3*R6}{R5+R6}=\frac{V3*\mathrm{\γ}}{1+\mathrm{\γ}}---\left(3\right)$ γ＝R6/R5。

With (2), (3) formula substitution (1) formula,

$V2=\frac{V3*(1+\mathrm{\α})}{1+\mathrm{\β}}-\mathrm{Vin}*\mathrm{\α}=\frac{V2(1+1/\mathrm{\γ})*(1+\mathrm{\α})}{1+\mathrm{\β}}-\mathrm{Vin}*\mathrm{\α}$

Solve $V2=\frac{\mathrm{Vin}*\mathrm{\α}}{(1+1/\mathrm{\γ})*(1+\mathrm{\α})*(1+\mathrm{\β})-1}---\left(4\right)$

To the R6 branch road, have $\mathrm{Iout}=\frac{V2}{R6}$

With (4) substitution following formula, can get through deriving

$\mathrm{Iout}=\frac{\mathrm{Vin}*R4}{R3*R5}*\frac{1+\mathrm{\β}}{1+\mathrm{\α}+(\mathrm{\α}-\mathrm{\β})*R6/R5}---\left(5\right)$

Here, α=R4/R3, β=R2/R1+RW, require simultaneously R4＞＞R5, R4＞＞R6.

When this circuit was used for the product of mass, because the components and parts cost control, the influence of other component parameters in inevitable trueness error of resistance value and the circuit often made the circuit available accuracy descend.Even resistance R 1～R4 chooses the resistance of 0.5 class precision, when producing voltage current adapter in batches, when output loading has bigger variation, all may reach 2 grades when the variation of output current Iout is the poorest, promptly output error may reach 2%.This all is definitely unallowed for a lot of users.From (5) formula as seen, as long as α=β, i.e. R2/R1+RW=R4/R3, then output current and load size has nothing to do.In the application of reality, realize the transducer of Vin=0～5V to Iout=0～20mA.By the value of regulator potentiometer RW, condition α=β is satisfied, then exporting Iout will be irrelevant with the size of load R6, direct ratio and input voltage vin, and precision can reach system requirements.

Voltage current adapter of the present invention is simple voltage (Vin)/electric current (Iout) transducer that higher output accuracy is arranged again simultaneously of a kind of circuit.Its output current Iout and load size is irrelevant, is a kind of simple, reliable, high accuracy, voltage current adapter that cost performance is high of collecting.

Description of drawings

The present invention has a width of cloth accompanying drawing,

Fig. 1 is the voltage current adapter electrical schematic diagram.

Embodiment

Specific embodiments of the invention as shown in drawings, described voltage current adapter is made up of resistance R, potentiometer RW and operational amplifier U1; Described resistance R comprises R1, R2, R3, R4, six resistance of R5 and R6, resistance R 1 is connected the back and is connected with the negative input end of operational amplifier U1 with resistance R 2, the other end of resistance R 1 connects potentiometer RW, the other end ground connection of potentiometer RW, the other end of resistance R 2 and the output that is connected to operational amplifier U1 after an end of resistance R 5 is connected, the other end of described resistance R 5 is connected with an end of resistance R 4 and resistance R 6, the other end of resistance R 4 be connected with the positive input terminal of operational amplifier U1 again after resistance R 3 is connected, the other end of resistance R 3 connects voltage signal source Vin, the other end ground connection of described resistance R 6.The resistance value of described resistance R 1, R2, R3, R4 is 50K ohm.Described resistance R 5 and R6 resistance value are 100 ohm.Described voltage signal source Vin=0～5V.

Claims (4)

1. a voltage current adapter is made up of resistance R, potentiometer RW and operational amplifier U1; It is characterized in that described resistance R comprises R1, R2, R3, R4, six resistance of R5 and R6, resistance R 1 is connected the back and is connected with the negative input end of operational amplifier U1 with resistance R 2, the other end of resistance R 1 connects potentiometer RW, the other end ground connection of potentiometer RW, the other end of resistance R 2 and the output that is connected to operational amplifier U1 after an end of resistance R 5 is connected, the other end of described resistance R 5 is connected with an end of resistance R 4 and resistance R 6, the other end of resistance R 4 be connected with the positive input terminal of operational amplifier U1 again after resistance R 3 is connected, the other end of resistance R 3 connects voltage signal source Vin, the other end ground connection of described resistance R 6.

2. voltage current adapter according to claim 1 is characterized in that the resistance value of described resistance R 1, R2, R3, R4 is identical as far as possible, perhaps R4/R3=R2/R1+RW.

3. voltage current adapter according to claim 1, it is characterized in that described resistance R 4＞＞R5, R4＞＞R6.

4. voltage current adapter according to claim 1 is characterized in that described voltage signal source Vin=0～5V.

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