A high-precision programmable constant current source system

Abstract

The application discloses a high-precision programmable constant current source system, which comprises a micro control module MCU, a DAC digital-analog conversion module, a voltage following module, a voltage sampling module, a circuit anti-interference module, a current amplification module and a load feedback module. The micro control module MCU is connected with the DAC digital-analog conversion module and the load feedback module respectively; the voltage sampling module is connected with the voltage following module and the circuit anti-interference module respectively; the current amplification module is connected with the circuit anti-interference module and the load feedback module. The anti-interference module has the functions of filtering high-frequency interference and coupling circuit. The application mainly adjusts the circuit constant current source by controlling the output voltage of the DAC digital-analog conversion module through the MCU.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electronic circuits, and particularly relates to a programmable constant current source system. BACKGROUND

[0002] A constant current source refers to a power supply with a constant output current, and is a widely used unit circuit, and its prominent feature is that the output value of the current remains unchanged and will not change due to changes in the load. In industrial applications, various non-electric physical quantities measured by transmitters, such as humidity, flow, pressure, temperature, etc., need to be transmitted to the central control room remotely. The current signal has strong anti-interference ability on the transmission line and will not produce voltage drop on the transmission line, so the current signal becomes the mainstream signal transmission method in the industrial field.

[0003] In the industrial field, more and more electronic devices need high-precision, wide-range constant current source devices to provide stable current to drive the devices to work normally. In the circuit control system, the output signal not only needs to have high precision, but more importantly, stability and reliability. However, most of the current constant current source products cannot meet the requirements of high-precision electronic devices, and a few constant current source systems that meet the requirements cannot be widely used due to high price and poor portability. SUMMARY

[0004] In order to solve the above problems, the application provides a high-precision programmable constant current source system.

[0005] The technical scheme adopted by the application is:

[0006] The application discloses a high-precision programmable constant current source system, which comprises a micro control module MCU, a DAC digital-to-analog conversion module, a voltage following module, a voltage sampling module, a circuit anti-interference module, a current amplification module and a load feedback module; the micro control module MCU is connected with the DAC digital-to-analog conversion module and the load feedback module respectively; the voltage sampling module is connected with the voltage following module and the circuit anti-interference module respectively; the current amplification module is connected with the circuit anti-interference module and the load feedback module;

[0007] The micro control module MCU is connected with the DAC digital-to-analog conversion module by using a serial peripheral interface SPI protocol, and is used for sending a control signal to the DAC digital-to-analog conversion module;

[0008] The DAC digital-to-analog conversion module is used for converting the control signal into a voltage signal and outputting the voltage signal to the voltage following module;

[0009] The voltage following module is used for following the voltage signal, and adopts a voltage / current conversion circuit to convert the voltage signal into a current signal;

[0010] The voltage sampling module is connected with the voltage follower module, and is used for collecting a voltage signal and controlling the size of an output current according to the voltage signal;

[0011] The circuit anti-interference module is used for filtering high-frequency interference signals in the system.

[0012] The current amplification module is used for amplifying the output current to obtain an amplified output current.

[0013] The load feedback module is used for feeding back the amplified output current to the micro control module MCU, and has a circuit breaking detection function.

[0014] In some embodiments, the DAC digital-to-analog conversion module adopts an SGM5349 chip.

[0015] In some embodiments, the DAC digital-to-analog conversion module uses a serial peripheral interface SPI communication protocol to realize analysis on a control signal, so as to output a voltage signal Ui.

[0016] When the interface SYNC is at a low level, the micro control module MCU writes data into a register of the DAC digital-to-analog conversion module, the interface SCLK is a serial clock input signal, and the interface SDin is a serial data input signal, and at each rising edge of the interface SCLK clock input signal, data 0 or 1 is written into a 16-bit input shift register.

[0017] In some embodiments, the voltage follower module includes an operational amplifier A1, four voltage dividing resistors divided into two groups, the positive input end of the operational amplifier A1 is connected with the output voltage signal Ui of the DAC digital-to-analog conversion module, the negative input end of the operational amplifier A1 is connected with a resistor R4, and the output end of the operational amplifier A1 is connected with the input end of the current amplification module through a resistor R1.

[0018] In some embodiments, the voltage sampling module includes a sampling resistor R0 and an operational amplifier A4, one end of the sampling resistor R0 is connected with a voltage source DC, the other end is connected with the output end of the operational amplifier A4, the positive input end of the operational amplifier A4 is connected with the negative input end of an operational amplifier A3, and the negative input end of the operational amplifier A4 is connected with the output end of the operational amplifier A4.

[0019] In some embodiments, the circuit anti-interference module includes a capacitor C1 connected with a voltage source, a capacitor C2 connected with an operational amplifier A2, and a capacitor C3 connected with an operational amplifier A3.

[0020] One end of the capacitor C1 is connected with the voltage source DC, and the other end is grounded.

[0021] One end of the capacitor C2 is connected with the output end of the operational amplifier A2, and the other end is connected with the reverse input end of the operational amplifier A2;

[0022] One end of the capacitor C3 is connected with the output end of the operational amplifier A3, and the other end is connected with the sampling resistor R0.

[0023] In some embodiments, the current amplification module comprises two parts of amplification circuit of NPN triode Q2 and P-channel field effect tube Q1;

[0024] The G pole of the P-channel field effect tube Q1 is connected with the output end of the operational amplifier A1 through the resistor R1, the S pole of the P-channel field effect tube Q1 is connected with the resistor R2 and the same direction input end of the operational amplifier A2, and the D pole of the P-channel field effect tube is connected with the reverse input end of the operational amplifier A1 and the resistor R4;

[0025] The base of the NPN triode Q2 is connected with the output end of the operational amplifier A3, the emitter of the NPN triode Q2 is connected with one end of the sampling resistor R0, and the collector of the NPN triode Q2 is connected with the load feedback module.

[0026] In some embodiments, the load feedback module comprises a load RL, one end of the load is connected with the collector of the NPN triode Q2, and the other end is connected with the resistor R4 in series and grounded, so that the potential difference between the input and output ends of the load is zero.

[0027] In some embodiments, the type of the operational amplifier A1 of the voltage follower module is OP177F of AD company of Yadian semiconductor.

[0028] In some embodiments, the operational amplifier A1, the operational amplifier A2, the operational amplifier A3 and the operational amplifier A4 adopt the voltage series negative feedback mode, so that the feedback of the output voltage signal is directly connected to the reverse input end of the operational amplifier A1, so that Ui=U1 and U2=U4.

[0029] The DAC digital-analog conversion module, the voltage follower module, the voltage sampling module, the circuit anti-interference module, the current amplification module and the load feedback module are controlled by the MCU, and can be programmed by software.

[0030] Compared with the prior art, the system has the following beneficial effects: the system can output stable and high-precision current signals, and can quickly detect the loop state. The system circuit hardware structure is simple, the output anti-interference ability is strong, the stability is good, the modular design thought is adopted, the current output range and precision are improved, and good expansibility and portability are also achieved. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1is a schematic diagram of a high-precision adjustable constant current source system of the present application example;

[0032] Figure 2 is a schematic diagram of the circuit principle of the system in the present application example. DETAILED DESCRIPTION

[0033] In order to make the content and purpose of the present application more clear, the embodiments of the present application will be specifically described below in combination with the drawings.

[0034] As shown in Figure 1 , a high-precision programmable constant current source system comprises a micro control module MCU, a DAC digital-analog conversion module, a voltage following module, a voltage sampling module, a circuit anti-interference module, a current amplification module and a load feedback module; the micro control module MCU is connected with the DAC digital-analog conversion module and the load feedback module respectively; the voltage sampling module is connected with the voltage following module and the circuit anti-interference module respectively; the current amplification module is connected with the circuit anti-interference module and the load feedback module;

[0035] The micro control module MCU is connected with the DAC digital-analog conversion module by using a serial peripheral interface SPI protocol, for sending a control signal to the DAC digital-analog conversion module;

[0036] The DAC digital-analog conversion module is used for converting the control signal into a voltage signal and outputting the voltage signal to the voltage following module;

[0037] The voltage following module is used for following the voltage signal, so as to improve the load capacity of the circuit and isolate the circuit; and a voltage / current conversion circuit is adopted to convert the voltage signal into a current signal;

[0038] The voltage sampling module is connected with the voltage following module, for collecting the voltage signal and controlling the size of the output current according to the voltage signal; in some embodiments, the size of the current is 4-20 mA;

[0039] The circuit anti-interference module is used for filtering the high-frequency interference signal in the system;

[0040] The current amplification module is used for amplifying the output current to obtain the amplified output current, expand the application range of the circuit and improve the load capacity of the whole circuit;

[0041] The load feedback module is used for feeding back the amplified output current to the micro control module MCU and has a circuit breaking detection function.

[0042] The circuit anti-interference module has the functions of filtering high-frequency interference and coupling circuit.

[0043] The application mainly adjusts the constant current source of the circuit by controlling the output voltage of the DAC digital-analog conversion module through the micro control module MCU.

[0044] The DAC digital-analog conversion module adopts a domestic SGM5349 chip from Shengbang Microelectronics (Beijing) Co., Ltd.

[0045] In some embodiments, the DAC digital-analog conversion module uses a serial peripheral interface SPI communication protocol to realize the analysis of the control signal, so as to output a voltage signal Ui; when the interface SYNC is at a low level, the micro control module MCU writes data into the register of the DAC digital-analog conversion module, the interface SCLK is a serial clock input signal; and the interface SDin is a serial data input signal, and data 0 or 1 is written into a 16-bit input shift register at each rising edge of the interface SCLK clock input signal.

[0046] In some embodiments, as shown in Figure 2 The current amplification module includes two parts of amplification circuits of an NPN type triode Q2 and a P channel field effect tube Q1.

[0047] The G pole of the P channel field effect tube Q1 is connected to the output end of the operational amplifier A1 through the resistor R1, the S pole of the P channel field effect tube Q1 is connected to the resistor R2 and the same direction input end of the operational amplifier A2, and the D pole of the P channel field effect tube is connected to the reverse input end of the operational amplifier A1 and the resistor R4.

[0048] The base of the NPN type triode Q2 is connected to the output end of the operational amplifier A3, the emitter of the NPN type triode Q2 is connected to one end of the sampling resistor R0, and the collector of the NPN type triode Q2 is connected to the load feedback module.

[0049] In some embodiments, as shown in Figure 2 The circuit anti-interference module includes a capacitor C1 connected to a voltage source, a capacitor C2 connected to the operational amplifier A2 and a capacitor C3 connected to the operational amplifier A3.

[0050] One end of the capacitor C1 is connected to the voltage source DC, and the other end is grounded.

[0051] One end of the capacitor C2 is connected to the output end of the operational amplifier A2, and the other end is connected to the reverse input end of the operational amplifier A2.

[0052] One end of the capacitor C3 is connected to the output end of the operational amplifier A3, and the other end is connected to the sampling resistor R0.

[0053] In some embodiments, the capacitor C1, the capacitor C2 and the capacitor C3 are all 220 pf capacitors.

[0054] The circuit anti-interference module makes the current generated by the constant current source slowly increase, so as to avoid that the load current changing too fast will cause a very large induced voltage.

[0055] In some embodiments, as shown in FIG. 2, the voltage sampling module comprises a sampling resistor R0 and an operational amplifier A4; one end of the sampling resistor R0 is connected with a voltage source DC, and the other end is connected with the output end of the operational amplifier A4; the positive input end of the operational amplifier A4 is connected with the negative input end of the operational amplifier A3; and the negative input end of the operational amplifier A4 is connected with the output end of the operational amplifier A4. Figure 2

[0056] The operational amplifier A1 of the voltage following module is OP177F of AD company of Yadian semiconductor.

[0057] In some embodiments, as shown in FIG. 2, the load feedback module comprises a load RL; one end of the load RL is connected with the collector of an RL NPN type triode Q2, and the other end is connected with the resistor R4 in series and grounded, so that the potential difference between the input and output ends of the load is zero. The change of the load will not affect the system current value. Figure 2

[0058] In some embodiments, as shown in FIG. 2, the voltage sampling module comprises a sampling resistor R0 and an operational amplifier A4; one end of the sampling resistor R0 is connected with a voltage source DC, and the other end is connected with the output end of the operational amplifier A4; the positive input end of the operational amplifier A4 is connected with the negative input end of the operational amplifier A3; and the negative input end of the operational amplifier A4 is connected with the output end of the operational amplifier A4. Figure 2

[0059] As shown in FIG. 2, the operational amplifier A1, the operational amplifier A2, the operational amplifier A3 and the operational amplifier A4 adopt the voltage series negative feedback mode, so that the feedback of the output voltage signal is directly connected with the negative input end of the operational amplifier A1, so that Ui=U1 and U2=U4. Figure 2

[0060] The DAC digital-to-analog conversion module, the voltage following module, the voltage sampling module, the circuit anti-interference module, the current amplification module and the load feedback module are controlled by the MCU, and can be programmed by software.

[0061] ​​​​In some embodiments, a high-precision programmable constant current source system, voltage current conversion circuit in the selection of AD company's OP177F ultra-high precision operational amplifier, the maximum input bias voltage is 25μV, the maximum temperature drift is 0.3μV / ℃, the maximum bias current is 2.2nA, the maximum temperature drift is 40pA / ℃. Power switch MOS tube Q1 selects CN2305, current amplification triode Q2 selects 2SC945, R2, R4 selects 0.1% high precision 10KΩ precision resistor, R1, R3 selects 0.1% high precision 100Ω precision resistor, sampling resistor R0 selects RS02BR low temperature drift 250Ω precision wire wound resistor, C1 takes 0.1uF, C2 takes 220pF, C3 takes 220pF. Ui adjustment range is 5 to 10V. Then the output current value range of this constant current source is 4mA to 20mA.

[0062] When the control signal Ui is switched to high level (for example, 5V), the gate of MOS tube Q1 jumps to high level, at this time Q1's gate source voltage VGS is 5V, Q1 is turned on, its drain and source are equivalent to short circuit state, the drain voltage becomes 5V. At this time, capacitors C1, C2 and C3 are in charging state, with the continuous charging of C1, R2 and R4 are in series to form a loop, and the current values of the two are the same. During this charging process, the base voltage of triode Q2 gradually rises, and the collector to emitter gradually changes from cut-off to full conduction. Sampling resistor R0 and load RL are in series, and the current values of the two are equal. The output current of the constant current source slowly rises to the set value with the charging of the capacitor.

[0063] According to the specific needs of adjusting the value of the charging capacitor and the sampling resistor R0, the output range of the constant current source can be controlled. The op-amps A1, A2 and A3 form a multi-stage voltage follower, and the source voltage U2 of the MOS tube Q1 is the same as the voltage U4 at one end of the sampling resistor R0 after multi-stage following. R2 and R4 are in series, and the current values flowing through the two are equal:

[0064]

[0065]

[0066]

[0067] The voltage across the sampling resistor R0 is:

[0068]

[0069] The operational amplifier has the characteristics of "virtual short" and "virtual open". According to the characteristics of the op-amp:

[0070]

[0071]

[0072] At this time, the resistance of R4 is the same as that of R2, and the potential difference across R0 is equal to Ui:

[0073]

[0074] R4 = R2

[0075] The sampling resistor R0 is connected in series with the load RL, and the current is equal:

[0076]

[0077] As can be seen, the output of the circuit is a constant current, which does not change with the load, and the output voltage and load current are linearly related, realizing the stable output of the constant current source.

[0078] The above is only a specific embodiment of the present application, but cannot limit the present application to only these descriptions. Any person skilled in the art, without departing from the concept of the present application, can make equivalent replacements or changes according to the technical solution and concept of the present application, which should be covered within the protection scope of the present application.

Claims

1. A high-precision programmable constant current source system, characterized in that, It includes a microcontroller module (MCU), a DAC (digital-to-analog converter) module, a voltage follower module, a voltage sampling module, a circuit anti-interference module, a current amplification module, and a load feedback module; the MCU is connected to the DAC module and the load feedback module respectively; the voltage sampling module is connected to the voltage follower module and the circuit anti-interference module respectively; the current amplification module is connected to the circuit anti-interference module and the load feedback module respectively; The microcontroller module (MCU) is connected to the DAC (digital-to-analog converter) module via the serial peripheral interface (SPI) protocol, and is used to send control signals to the DAC module. The DAC digital-to-analog converter module is used to convert the control signal into a voltage signal and output the voltage signal to the voltage follower module; The DAC digital-to-analog converter module uses the serial peripheral interface SPI communication protocol to parse the control signal and output the voltage signal Ui; when the interface SYNC is low, the microcontroller module MCU writes data into the register of the DAC digital-to-analog converter module, and the interface SCLK is the serial clock input signal; On each rising edge of the interface SCLK clock input signal, the serial data input signal SDin of the interface is written to the 16-bit input shift register, where data 0 or 1 is written. The voltage follower module is used to follow the voltage signal and uses a voltage / current conversion circuit to convert the voltage signal into a current signal. The voltage follower module includes an operational amplifier A1 and four voltage divider resistors divided into two groups. The positive input terminal of the operational amplifier A1 is connected to the output voltage signal Ui of the DAC digital-to-analog converter module, the inverting input terminal of the operational amplifier A1 is connected to a resistor R4, and the output terminal of the operational amplifier A1 is connected to the input terminal of the current amplification module through a resistor R1. The voltage sampling module is connected to the voltage follower module and is used to acquire voltage signals and control the output current based on the voltage signals. The voltage sampling module includes a sampling resistor R0 and an operational amplifier A4. One end of the sampling resistor R0 is connected to the voltage source DC, and the other end is connected to the output terminal of the operational amplifier A4. The positive input terminal of the operational amplifier A4 is connected to the inverting input terminal of the operational amplifier A3, and the inverting input terminal of the operational amplifier A4 is connected to the output terminal of the operational amplifier A4. The circuit anti-interference module is used to filter high-frequency interference signals in the system. The circuit anti-interference module includes a capacitor C1 connected to a voltage source, a capacitor C2 connected to operational amplifier A2, and a capacitor C3 connected to operational amplifier A3. One end of capacitor C1 is connected to the DC voltage source, and the other end is grounded. One end of capacitor C2 is connected to the output terminal of operational amplifier A2, and the other end is connected to the inverting input terminal of operational amplifier A2. One end of capacitor C3 is connected to the output terminal of operational amplifier A3, and the other end is connected to the sampling resistor R0. The current amplification module is used to amplify the output current to obtain the amplified output current. The current amplification module includes two amplification circuits: an NPN transistor Q2 and a P-channel field-effect transistor Q1. The gate (G) of the P-channel field-effect transistor Q1 is connected to the output terminal of operational amplifier A1 through resistor R1. The source (S) of the P-channel field-effect transistor Q1 is connected to resistor R2 and the non-inverting input terminal of operational amplifier A2. The drain (D) of the P-channel field-effect transistor Q1 is connected to the inverting input terminal of operational amplifier A1 and resistor R4. The base of the NPN transistor Q2 is connected to the output terminal of operational amplifier A3. The emitter of the NPN transistor Q2 is connected to one end of the sampling resistor R0. The collector of the NPN transistor Q2 is connected to the load feedback module. The load feedback module is used to feed back the amplified output current to the microcontroller module MCU, and has an open circuit detection function. The load feedback module includes a load RL, one end of which is connected to the collector of RLNPN transistor Q2, and the other end is connected in series with resistor R4 and grounded, so that the potential difference between the input and output terminals of the load is zero.

2. The high-precision programmable constant current source system according to claim 1, characterized in that, The DAC digital-to-analog converter module uses the SGM5349 chip.

3. The high-precision programmable constant current source system according to claim 1, characterized in that, The operational amplifier A1 of the voltage follower module is an OP177F from Analog Devices, Inc.

4. The high-precision programmable constant current source system according to claim 1, characterized in that, Operational amplifiers A1, A2, A3, and A4 employ a voltage series negative feedback method.

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