CN212965147U

CN212965147U - Voltage analog signal isolation differential acquisition circuit structure

Info

Publication number: CN212965147U
Application number: CN202022148638.3U
Authority: CN
Inventors: 陈安武; 周龙; 白洪超
Original assignee: Qingdao Ainuo Instrument Co ltd
Current assignee: Qingdao Ainuo Instrument Co ltd
Priority date: 2020-09-25
Filing date: 2020-09-25
Publication date: 2021-04-13
Anticipated expiration: 2030-09-25

Abstract

The utility model relates to a differential acquisition circuit structure is kept apart to voltage analog signal, include: bleeder circuit, difference circuit, buffer circuit, the voltage adjustment circuit that connects gradually, bleeder circuit be used for obtaining the small-signal voltage, difference circuit be used for reducing common mode signal interference, buffer circuit be used for input and output signal to keep apart, the voltage adjustment circuit be used for opto-coupler feedback back current signal adjustment to voltage signal output. The voltage adjusting circuit mainly has the functions of converting a current signal output by the optical coupler into a voltage signal for a later-stage circuit to use, enhancing the load driving capability and reducing the output impedance. The utility model utilizes the linear optical coupling to isolate the analog signal, realizes power supply isolation through the isolation module power supply in the aspect of power supply, and greatly reduces the interference caused by the peripheral circuit; the input link also increases the overvoltage protection function, and a rear-stage circuit can be better protected, so that greater loss is avoided.

Description

Voltage analog signal isolation differential acquisition circuit structure

Technical Field

The utility model belongs to the technical field of electronic equipment inspection detects, concretely relates to differential acquisition circuit structure is kept apart to voltage analog signal.

Background

The analog quantity signal isolation acquisition technology has wide application in the fields of power electronics, electrical testing and the like, a plurality of mature schemes are provided for digital signal isolation at present, but compared with digital signal isolation, the analog signal isolation difficulty is higher, and the scheme cost is much higher.

In the prior art, isolation amplifiers are usually used to isolate analog signals. At present, the linearity of a chip of a domestic isolation amplifier can reach 0.1%, and some foreign isolation amplifiers have stable performance and good linearity, can generally reach or far exceed 0.1%, but have high relative cost. For manufacturers who make common industrial products, the scheme of adopting the foreign isolation amplifier is low in feasibility, cannot realize differential sampling, and is easily interfered by common-mode signals.

In an automatic detection system, it is often necessary to monitor the output voltage parameters of each module in the system to give a fault indication to a circuit that is not working properly, so as to ensure product quality and normal use. However, the actual working environment is relatively harsh, and various electromagnetic interference signals are superimposed on the useful measured signal, which may reduce the accuracy of the measurement.

In addition, for the acquisition of voltage signals, the current technical scheme mainly utilizes a voltage acquisition module to directly acquire or carries out data processing and analysis by a singlechip. Although the scheme has low cost, the application range is limited, and the scheme is only suitable for acquiring and outputting ideal pure signals. For the measurement scheme of the high-frequency alternating current analog signal, transformer isolation is the most common choice, but the direct current signal cannot be acquired. Some isolation amplifiers can achieve better linearity as solutions for isolating analog signals, but the isolation device needs to perform voltage-frequency conversion first, then perform transformer isolation on generated alternating current signals, and then perform frequency-voltage conversion to obtain an isolation effect. However, the integrated isolation amplifier has complex internal circuit, large volume and high cost, and is not suitable for large-scale application.

Disclosure of Invention

For solving the technical problem, the utility model provides a voltage analog quantity signal isolation difference acquisition circuit structure has not only realized analog signal's isolation, has still utilized differential sampling technique, and the preceding stage is the applied voltage stepping mechanism more, carries out the stepping to the signal of different amplitude sizes and measures, measures more accurate, stable, reliable. The utility model discloses the scheme that adopts as follows:

a voltage analog signal isolation differential acquisition circuit structure comprises: bleeder circuit, difference circuit, buffer circuit, the voltage adjustment circuit that connects gradually, bleeder circuit be used for obtaining the small-signal voltage, difference circuit be used for reducing common mode signal interference, buffer circuit be used for input and output signal to keep apart, the voltage adjustment circuit be used for opto-coupler feedback back current signal adjustment to voltage signal output.

For the input high-voltage direct current voltage, the front stage needs to be subjected to voltage division to obtain small-signal voltage, then the small-signal voltage enters the isolation circuit through the rear stage of the differential circuit, the isolated signal enters the single chip microcomputer through the voltage adjusting circuit, and voltage signal reading is carried out through the AD inside the single chip microcomputer. The voltage adjusting circuit mainly has the functions of converting a current signal output by the optical coupler into a voltage signal for a later-stage circuit to use, enhancing the load driving capability and reducing the output impedance.

The utility model has the advantages that:

the utility model discloses utilize linear optical coupling to keep apart analog signal, its principle is that it compares traditional opto-coupler and has increased a light receiving circuit who is used for the feedback and constitute feedback network, has offset the nonlinearity of direct passageway through the nonlinearity of feedback passageway to reach and realize linear isolation.

In the aspect of power supply, power supply isolation is realized through an isolation module power supply, and interference caused by a peripheral circuit is greatly reduced. On the other hand, the front stage of the designed circuit adopts a voltage division and difference network, the voltage division network can be better suitable for signal acquisition with different amplitudes, the sampling precision is higher, the difference network can improve the anti-interference performance, and the accuracy and the stability of the signal acquisition are enhanced.

The input link also increases the overvoltage protection function, and a rear-stage circuit can be better protected, so that greater loss is avoided.

The utility model discloses except realizing analog signal and keeping apart, still utilized differential sampling technique, really realized keeping apart differential sampling, it is lower to compare traditional scheme cost, changes and realizes the scale production.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It should be apparent that the drawings in the following description are illustrative of some embodiments of the invention, and that those skilled in the art will be able to derive other drawings without inventive step from these drawings, which are within the scope of the present application.

Fig. 1 is a schematic structural diagram of an isolated differential acquisition circuit according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a differential circuit according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of an isolation circuit according to an embodiment of the present invention;

fig. 4 is a front-to-back isolated input/output voltage line graph of an embodiment of the present invention.

Detailed Description

The following describes embodiments of the present invention with reference to the drawings.

As shown in fig. 1, it is a schematic structural diagram of an isolated differential acquisition circuit according to an embodiment of the present invention. A voltage analog signal isolation differential acquisition circuit structure comprises: bleeder circuit, difference circuit, buffer circuit, the voltage adjustment circuit that connects gradually, bleeder circuit be used for obtaining the small-signal voltage, difference circuit be used for reducing common mode signal interference, buffer circuit be used for input and output signal to keep apart, the voltage adjustment circuit be used for opto-coupler feedback back current signal adjustment to voltage signal output.

The gain of passageway can be adjusted to the value of adjusting resistance, the embodiment of the utility model provides a gain design is 1, can guarantee like this that the signal is not enlargied but has reduced the interference of common mode signal. As shown in fig. 2, it is a schematic structural diagram of the differential circuit according to the embodiment of the present invention. The differential circuit adopts an in-phase parallel three-operational-amplifier structure, the first stage of the differential circuit mainly comprises an operational amplifier A, B and a matching circuit and is used for improving the input impedance of the whole amplifying circuit, the second stage of the differential circuit comprises an operational amplifier C and a matching circuit, the differential circuit is used for improving the common-mode rejection ratio, and the resistance error determining the gain has no influence on the common-mode rejection ratio, so the resistance error can be ignored. The output voltage is as follows:

Vo＝(R3/R4)*(1+2*R2/R1)*(Vi1-Vi2)；

the differential circuit designed above has the following characteristics:

1) has high input impedance characteristics. The measured signal may be a weak signal of an unstable high internal resistance source, and in order to reduce the influence of the internal resistance of the signal source on the measurement, the input impedance of the amplifier must be increased. Generally, the internal resistance of the signal source is typically 100k Ω, so the amplifier input impedance is preferably chosen to be greater than 1M Ω.

2) And inputting an overvoltage protection function. When the input voltage exceeds the rated voltage, the voltage is clamped within a certain range due to the existence of the protection circuit, so that even if the input end is connected with high voltage by mistake or the sampling circuit has problems, the rear-stage circuit can be protected from being damaged, and the loss is better reduced.

3) High common mode rejection ratio. The signal power frequency interference and the interference of the functions except the measured parameters are generally common mode interference, and the preceding stage adopts a differential amplification form with high CMRR (constant current mirror) so as to better reduce the common mode interference.

4) Has the characteristics of low drift and low noise. The main functions are to reduce the influence of signal source, enhance the ability of measuring signal and stabilize output.

The first stage of the differential circuit is also provided with an overvoltage protection module to improve the safety of the differential circuit. The differential circuit formed by the three operational amplifiers has the advantages of high input impedance, high common mode rejection ratio and the like, so that the differential circuit can be used for designing amplifiers for general instruments.

In order to prevent interference signals from entering the detection board through the acquisition channel and ensure normal work of the single chip microcomputer system, a photoelectric coupler can be used for realizing signal transmission, and a differential circuit realizes interference resistance. The light emitting diode of the photoelectric coupler is a current driving device, the current driving device is used for energy transmission in the form of a current loop, the current loop is a low-impedance circuit, the noise sensitivity is low, and meanwhile, the anti-interference capability of the circuit is improved due to the application of a differential circuit. Although the interference noise has larger voltage amplitude, the energy of the interference noise is small, so that only weak current can be formed, and the light emitting diode of the input part of the photoelectric coupler works in a current state, and can emit light only when current with certain intensity passes through the light emitting diode. Therefore, even a disturbance with a high voltage amplitude is suppressed due to the magnitude of the current formed.

As shown in fig. 3, is a schematic structural diagram of an isolation circuit according to an embodiment of the present invention. The isolation circuit structure comprises an operational amplifier 1, a resistor, a linear optocoupler, a feedback network, an adjusting network and an operational amplifier 2. The output end of the operational amplifier 1 is connected with one end of a light emitting diode of the linear optocoupler after being connected with a resistor in series, one end of a receiving diode of the linear optocoupler is connected with the negative electrode of the operational amplifier to form a feedback network, one end of the other receiving diode is connected with the operational amplifier 2 and is connected with an adjusting network consisting of the resistor and a capacitor in parallel, and finally, a signal is output to the output end of the operational amplifier 2.

The input end Vin is the output Vo at the tail end in fig. 2, the feedback network mainly functions to form negative feedback, when voltage Vin is input, the output of the operational amplifier 1 enables current to flow out of a light emitting diode of the linear optocoupler, and an electric signal driving the light emitting diode is converted into an optical signal. The light emitted therefrom is detected by the receiving diode and generates a photocurrent. At the same time, the input voltage Vin also generates a current, and the resistor thereof mainly plays a role of limiting the current. The operational amplifier 2 and the adjusting network mainly adjust the output current signal into a voltage signal for output, so that a rear-stage singlechip can directly acquire the voltage signal conveniently.

The embodiment of the utility model provides an in, what the signal isolation adopted is the linear opto-coupler of HCNR201 model, and it is the linear opto-coupler of a high accuracy, through external different components and parts, can realize photoelectric isolation converting circuit. The optical coupler is composed of a high-performance light emitting diode and two photodiodes with strict proportional relation, and the principle is that after light emitted by the diodes in the optical coupler is received, one diode can generate output current. A diode is used for feedback to compensate the conducting current of the light emitting LED, thereby improving the linearity and temperature characteristics between the input and output circuits. The structure improves the stability and the linearity of the linear optocoupler, and has the advantages of low cost, low nonlinearity, high frequency bandwidth, stability and flexible design.

Fig. 4 is a linear diagram of input/output voltage before and after isolation according to an embodiment of the present invention. The abscissa is input voltage before isolation, the ordinate is output voltage after isolation, the unit is millivolts, linear contrast is carried out under the condition that the proportion is 1, the linear ratio is about 1.001, and the linearity is better. An isolation circuit composed of a linear optocoupler and peripheral devices thereof is also easily affected by errors of a power supply, errors of other devices and environmental factors, so that the linearity of the circuit is not ideal. The linearity and the precision of the isolation circuit can be better improved by improving the quality of the power supply and replacing the power supply with a precision device.

Finally, it is to be noted that: the above embodiments are only specific embodiments of the present invention, and are not intended to limit the technical solutions of the present invention, and the scope of the present invention is not limited thereto. Those skilled in the art will understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.

Claims

1. The utility model provides a voltage analog signal isolation difference acquisition circuit structure which characterized in that includes: bleeder circuit, difference circuit, buffer circuit, the voltage adjustment circuit that connects gradually, bleeder circuit be used for obtaining the small-signal voltage, difference circuit be used for reducing common mode signal interference, buffer circuit be used for input and output signal to keep apart, the voltage adjustment circuit be used for opto-coupler feedback back current signal adjustment to voltage signal output.

2. The structure of claim 1, wherein the differential circuit is configured with three in-phase parallel operational amplifiers.

3. The structure of claim 2, wherein the differential circuit comprises an operational amplifier A, B and a matching circuit for increasing the input impedance of the whole amplifying circuit in the first stage, and an operational amplifier C and a matching circuit in the second stage, and the differential circuit is used to increase the common mode rejection ratio.

4. The structure of claim 3, wherein the first stage of the differential circuit is further provided with an overvoltage protection module.

5. The structure of claim 1, wherein the isolation circuit comprises: the operational amplifier 1, a resistor, a linear optocoupler, a feedback network, an adjusting network and an operational amplifier 2, wherein the output end of the operational amplifier 1 is connected with one end of a light emitting diode of the linear optocoupler after being connected with the resistor in series, one end of a receiving diode of the linear optocoupler is connected with the negative electrode of the operational amplifier to form the feedback network, one end of the other receiving diode is connected with the operational amplifier 2 and is connected with the adjusting network in parallel, and finally, a signal is output to the output end of the operational amplifier 2.

6. The structure of claim 5, wherein the adjustment network comprises a resistor and a capacitor.

7. The structure of claim 6, wherein the linear optocoupler is a HCNR201 type linear optocoupler.