CN207488351U - Linear photoelectric isolation circuit for inhibiting temperature drift - Google Patents

Abstract

The utility model provides a restrain linear photoelectric isolation circuit of temperature drift, it can include: a signal input source for providing an input signal; the signal conditioning unit is connected with the signal input source and is used for converting the input signal into two signals with the same amplitude and waveform but opposite polarities; the two optical coupling units are connected with the signal conditioning unit and are respectively used for transmitting the two signals; the difference arithmetic unit is connected with the optical coupling unit and is used for carrying out arithmetic processing on the signal output by the optical coupling unit; and the output circuit is connected with the differential operation unit and used for outputting the signal after the operation processing of the differential operation unit. The utility model has the advantages that: the problem of signal gain error caused by temperature deviation and the problem of waveform interference noise in signal isolation transmission are solved, and therefore accurate isolation transmission of signals is achieved. The practical application requirements of the linear photoelectric isolation circuit in the high-voltage industrial field are better met.

Description

A Linear Photoelectric Isolation Circuit for Suppressing Temperature Drift

technical field

The utility model relates to the field of high-voltage electrical equipment testing, in particular to a linear photoelectric isolation circuit for suppressing temperature drift.

Background technique

In the field of high-voltage insulation diagnosis and high-voltage industrial applications, linear photoelectric isolation circuits are often used, and linear photoelectric isolation circuits are required to have high precision. At present, in industrial applications, the combination of V-F conversion and analog optical fiber is often used to realize linear signal isolation. However, using a voltage-frequency conversion chip, the conversion accuracy is not high due to the limitation of its resolution, and the voltage range of the input signal is small. When using a linear optocoupler for isolation, since the linearity and conversion gain of the optocoupler are greatly affected by temperature, there is a large signal transmission error, so it is necessary to further use the conversion algorithm to remove the influence of temperature offset. For a weak signal to be transmitted, the above two forms will cause the original signal waveform to be distorted to varying degrees. At the same time, the circuit structure using isolation transformers for isolation can only be applied under specific frequency or power frequency conditions due to the limitation of the passband of the transformer. For high-voltage amplifiers in the field of high-voltage insulation diagnosis, not only the waveform distortion rate of the transmitted signal is required to be small, but also the amplitude gain of the voltage signal after signal isolation and transmission is required to be stable. At the same time, because the dielectric response method in high-voltage insulation diagnosis needs to be used in a variety of test environments with different temperatures, the isolation circuit is required to have high temperature stability. The above requirements indicate that the existing signal isolation circuit cannot well meet the actual needs.

Utility model content

The technical problem to be solved by the utility model is to provide a linear photoelectric isolation circuit that suppresses temperature drift, which can improve the signal gain error problem caused by temperature drift and the waveform interference noise problem in signal isolation transmission, thereby realizing accurate signal isolation transmission. It better meets the actual application requirements of linear photoelectric isolation circuits in the high-voltage industrial field.

In order to solve the above technical problems, the utility model provides a linear photoelectric isolation circuit for suppressing temperature drift, which may include:

The signal input source is used to provide an input signal;

A signal conditioning unit, connected to the signal input source, for converting the input signal into two signals with the same amplitude and waveform but opposite polarity;

Two optocoupler units, connected to the signal conditioning unit, are used to transmit the two signals respectively;

A differential calculation unit, connected to the two optocoupler units, for performing calculation processing on the signals output by the optocoupler units;

The output circuit is connected to the differential operation unit, and is used to output the signal processed by the differential operation unit.

Wherein, the signal conditioning unit includes an operational amplifier and a low temperature coefficient resistance element connected to the operational amplifier.

Wherein, the two optocoupler units isolate the two signals output by the conditioning unit so that the two signals do not interfere with each other.

Wherein, the optocoupler unit includes a linear optocoupler of a linear optocoupler chip.

Wherein, the differential operation unit includes:

Two operational amplifiers, respectively connected to the two optocoupler units, are used to filter out high-frequency noise and thermal noise in the signals output by the connected optocoupler units;

The instrument operational amplifier, the non-inverting terminal and the inverting terminal of the instrument operational amplifier respectively receive the signals output by the two operational amplifiers, and eliminate the common mode error of the received signals.

Wherein, the signal conditioning unit, the linear optocoupler unit, and the differential operation unit are sequentially connected together in a differential structure.

Wherein, the operational amplifier is OPA227.

Wherein, the linear optocoupler is HCNR201.

Wherein, the instrumentation amplifier is AD620.

The beneficial effects of the utility model embodiment are:

The embodiment of the utility model uses a linear photoelectric isolation circuit that suppresses temperature drift. On the one hand, the problem of signal gain error caused by temperature drift and the problem of waveform interference and noise in signal isolation transmission are improved, thereby realizing accurate signal isolation transmission. . It better satisfies the actual application requirements of linear photoelectric isolation circuits in the high-voltage industrial field; The optocoupler is used for transmission isolation, and the transmission accuracy of the signal is high, and at the same time, it will not introduce high-frequency signal conversion errors; on the one hand, compared with the method of isolation by ordinary linear optocouplers, the utility model can significantly improve the temperature stability of the isolation circuit and reduce the gain error caused by temperature changes; on the other hand, compared with the method of isolation through the transformer, the utility model can significantly improve the passband of the isolation circuit and broaden the application range of the isolation circuit.

Description of drawings

In order 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 that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are only some embodiments of the utility model, and those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a schematic diagram of the functional structure of a linear photoelectric isolation circuit for suppressing temperature drift of the present invention.

Fig. 2 is a schematic diagram of the specific circuit composition of an embodiment of the linear photoelectric isolation circuit for suppressing temperature drift of the present invention.

Fig. 3 is a schematic circuit diagram of an embodiment of the linear optocoupler module HCNR201 in the present invention.

FIG. 4 is a schematic diagram of an embodiment of the feedback circuit in the linear optocoupler module HCNR201 of the present invention.

Detailed ways

The descriptions of the following embodiments are with reference to the accompanying drawings to illustrate the specific embodiments that the present utility model can be used to implement.

Fig. 1 is a schematic diagram of the functional structure of a linear photoelectric isolation circuit that suppresses temperature drift. In Fig. 1, the signal _S0 is sent by the signal input source 10 and processed by the signal conditioning unit 20 to generate two signals S1 and S2 with the same amplitude and waveform but opposite polarities, which are sent to the linear optocoupler unit 30 and S2 respectively. Linear optocoupler unit 31, the signal S1 and signal S2 do not interfere with each other under the action of their respective optocoupler units, the signal S1 is transmitted to the differential calculation unit 40 through the linear optocoupler unit 30, and the signal S2 is transmitted to the differential calculation unit through the linear optocoupler unit 31 Unit 40, the two groups of high-speed operational amplifiers in the differential operation unit 40 filter the high-frequency noise and thermal noise through capacitance integration for the signals S1 and S2 respectively, and then send them to the non-inverting terminals of the instrumentation operational amplifiers in the differential operation unit 40 subtract each other with the inverting terminal to eliminate the common mode error, and finally form a signal S which is sent to the signal output unit 50 .

As an example, in the circuit schematic diagram of a linear photoelectric isolation circuit embodiment shown in Figure 2, the OPA227 is selected as the signal conditioning unit operational amplifier model, the HCNR201 is selected as the linear optocoupler model, and the AD620 is selected as the differential operation unit operational amplifier model. The operating temperature of the circuit varies from -20°C to 85°C.

The signal passes through the signal conditioning circuit composed of U1 and U2, and generates two signals with the same amplitude and waveform but opposite polarity through the operational amplifier OPA227, and sends them to the transmission circuits U3 and U4 respectively. At this time, the functions of capacitors C13 and C15 are to improve The linearity of the transmission signal, filtering out high-frequency noise and thermal noise, and then sending the signal into the two branches of the differential structure respectively.

Among them, the internal block diagram of the linear optocoupler HCNR201 contained in each branch is shown in Figure 3, and its working principle is: pins 1 and 2 are used as input of isolated signals, pins 3 and 4 are used for feedback, pins 5 and 6 pin for output. The current between pins 1 and 2 is denoted as I _F , the current between pins 3 and 4 and between pins 5 and 6 is denoted as I _PD1 and I _PD2 respectively. The input signal is converted from voltage to current, and the change of voltage is reflected in the current IF. IPD1 and IPD2 are basically in a linear relationship with IF, and the linear coefficients are respectively recorded as K1 and K2, namely

K1 and K2 are generally small and vary greatly with temperature, but the design of the chip makes K1 and K2 equal. It can be seen later that in a reasonable peripheral circuit design, what really affects the output/input ratio is the ratio K3 of the two, and the linear optocoupler is using this characteristic to achieve satisfactory linearity.

Some indicators for selecting linear optocoupler HCNR201 for isolation are as follows:

* Linearity: HCNR201: 0.05%;

* Linear coefficient K3: HCNR201: 5%;

*Temperature coefficient: -65ppm//℃;

*Isolation voltage: 1414V;

*Signal bandwidth: DC to greater than 1MHz.

It can be seen from the above that, like ordinary optocouplers, what the linear optocoupler really isolates is the current. To truly isolate the voltage, it is necessary to add auxiliary circuits such as operational amplifiers at the input and output. Next, analyze the typical circuit of the linear optocoupler HCNR201, deduce and explain how to realize feedback and current-voltage, voltage-current conversion in the circuit: set the input terminal voltage to V _in , the output terminal voltage to V _out , and the optocoupler The guaranteed two current transfer coefficients are K1 and K2 respectively. Analyze the extracted part of the circuit diagram in Figure 3 to obtain Figure 4, as shown in Figure 4:

Let the voltage at the negative terminal of the op amp be Vi, and the voltage at the output end of the op amp be Voo. When the op amp is not saturated, the two satisfy the following relationship:

Vo=Voo-GVi (1)

Among them is the output voltage when the input differential mode of the operational amplifier is 0, and G is the gain of the operational amplifier, which is generally relatively large.

Neglecting the input current at the negative terminal of the op amp, it can be considered that the current passing through R1 is IP1. According to the Ohm's law of R1:

The current passing through both ends of R3 is IF, according to Ohm's law:

Among them, Vcc is the voltage of pin 2 of the optocoupler. Considering that the voltage when the LED is turned on is basically unchanged, it is treated as a constant here. According to the characteristics of the optocoupler, namely

K1=IP1/IF (4)

Substituting the expression of sum into the above formula, we can get:

The above formula can be transformed into:

K ₁ R ₁ (V _DD -V _o0 )+K ₁ R ₁ GV _i ＝R ₃ V _in -R ₃ V _i

Substitute the expression into (3) to get:

Considering that G is very large, the following approximation can be made:

Thus, the output is related to the input voltage as follows:

It can be seen that in the above circuit diagram 3, the output is proportional to the input, and the proportional coefficient is only determined by K3, R1, and R2, so in practical applications, R1=R2 is generally selected to achieve the purpose of isolation without amplification.

Returning to the main circuit diagram in Figure 2, the gain value of differential structure branch 1 is determined by the ratio of resistors R1, R5, and R6; the gain value of differential structure branch 2 is determined by the ratio of resistors R7, R9, and R10. The legs have the same gain and the resistive elements all have the same temperature coefficient.

The two-way signals are sent to the circuits of U3 and U4 respectively after passing through the optocoupler unit, pass through the operational amplifier OPA227, and filter out high-frequency noise and thermal noise after capacitance integration.

The last two signals are respectively sent to the non-inverting terminal and the inverting terminal of the instrument amplifier AD620 to subtract each other to eliminate the common mode error, and output the final signal.

In summary, the linear optoelectronic isolation circuit in this embodiment of the present invention can greatly improve the temperature stability of the circuit, and can reduce the transfer gain temperature coefficient of a typical linear optocoupler from 65ppm/°C to about 20ppm/°C . The influence of ambient temperature change on the isolation transmission result is avoided, and the ability to suppress the influence of temperature drift can be high.

What is disclosed above is only a preferred embodiment of the utility model, and of course it cannot limit the scope of rights of the utility model. Therefore, equivalent changes made according to the claims of the utility model still fall within the scope of the utility model.

Claims (9)

1. A linear photoelectric isolation circuit for suppressing temperature drift, characterized in that, comprising: The signal input source is used to provide an input signal; A signal conditioning unit, connected to the signal input source, for converting the input signal into two signals with the same amplitude and waveform but opposite polarity; Two optocoupler units, connected to the signal conditioning unit, are used to transmit the two signals respectively; A differential calculation unit, connected to the two optocoupler units, for performing calculation processing on the signals output by the optocoupler units; The output circuit is connected to the differential operation unit, and is used to output the signal processed by the differential operation unit. 2 . The linear photoelectric isolation circuit for suppressing temperature drift according to claim 1 , wherein the signal conditioning unit comprises an operational amplifier and a low temperature coefficient resistance element connected to the operational amplifier. 3 . 3. The linear photoelectric isolation circuit for suppressing temperature drift according to claim 1, wherein the two optocoupler units isolate the two signals output by the conditioning unit so that the two signals are mutually independent. interference. 4. The linear optoelectronic isolation circuit for suppressing temperature drift according to claim 3, wherein the optocoupler unit comprises a linear optocoupler of a linear optocoupler chip. 5. The linear photoelectric isolation circuit for suppressing temperature drift according to claim 1, wherein the differential operation unit comprises: Two operational amplifiers, respectively connected to the two optocoupler units, are used to filter out high-frequency noise and thermal noise in the signals output by the connected optocoupler units; The instrument operational amplifier, the non-inverting terminal and the inverting terminal of the instrument operational amplifier respectively receive the signals output by the two operational amplifiers, and eliminate the common mode error of the received signals. 6 . The linear optoelectronic isolation circuit for suppressing temperature drift according to claim 1 , wherein the signal conditioning unit, the linear optocoupler unit, and the differential operation unit are sequentially connected together in a differential structure. 7. The linear photoelectric isolation circuit for suppressing temperature drift according to claim 2 or 4, characterized in that the operational amplifier is OPA227. 8. The linear optoelectronic isolation circuit for suppressing temperature drift according to claim 4, characterized in that, the linear optocoupler is HCNR201. 9. The linear photoelectric isolation circuit for suppressing temperature drift according to claim 5, characterized in that, the instrumentation amplifier is AD620.