A constant power supply device for magnetospheric space electric field instrument

Abstract

The present invention belongs to the technical field of electric field instruments, and specifically relates to a constant power supply device for a magnetospheric space electric field instrument, the device comprising an FPGA control circuit, a digital-to-analog converter, a summing amplifier circuit, a control circuit, a floating ground reference circuit, and a load driving circuit. The device realizes accurate current-to-voltage conversion through a DAC controlled by an FPGA, and realizes voltage output in positive and negative directions through a summing amplifier circuit. The floating ground reference circuit ensures that the output voltage is stable relative to the floating ground in space, and the load driving circuit outputs a stable voltage to the load. The device is simple to control and has strong adaptability. It realizes accurate control of power supply output through FPGA, can withstand changes in load impedance, ensures the stability of power supply output, realizes voltage output in positive and negative directions, and meets the needs of different loads.

Description

Technical Field

[0001] The invention belongs to the technical field of electric field instruments, and in particular relates to a constant power supply device for a magnetosphere space electric field instrument. Background Art

[0002] The space electromagnetic environment is an important space environment background parameter. At the same time, the disturbance of the electromagnetic field is also closely related to various space weather events. The development of space electric field detection experimental means can detect the changing characteristics of space electric fields and electromagnetic waves and provide data for space weather forecasts. Develop space electric detection experimental means to detect the changing characteristics of space electric fields and electromagnetic waves, systematically study the important role of space electric fields in the dynamic process of near-Earth space disturbances, and strive to discover new manifestations of space electric fields and electromagnetic waves in the propagation process of important space disturbances, provide analytical data for space weather, and verify the rationality and accuracy of space weather forecast models.

[0003] In space electric field detection, the double-probe measurement method is often used. This method is to extend two rods into space, and install electrically insulated metal balls or metal cylinders at their respective ends as probes, i.e., electric field sensors. When the potentials on the two probes are consistent with the potentials of the plasmas around them, the potential difference between the two probes is measured and divided by the distance between the two probes to obtain the electric field component along the extended rod direction.

[0004] In this measurement method, since the probe is surrounded by the surrounding plasma, a plasma sheath is generated. The equivalent sheath resistance of the plasma sheath is usually relatively high, which will seriously affect the detection accuracy. In order to solve this problem, it is usually necessary to apply a weak current of the nanoampere level to the probe to reduce the impedance of the sheath resistance and improve the measurement accuracy. Moreover, applying a constant current bias to the probe can also enable the probe to better keep consistent with the surrounding plasma potential. Therefore, the voltage-controlled precision constant current source circuit is a key technology in the dual-probe measurement method.

[0005] According to the measurement needs, the following requirements are put forward for the constant current source: it can output the corresponding constant DC current according to the output instruction of FPGA; the direction of the current can be determined by the control signal; the output current is in the pA range, with a maximum of ±530nA; the output load of the constant current source should be a grounded load; it should be able to withstand large changes in load resistance; the output current is less affected by the power supply voltage.

[0006] Some existing constant current source circuits have the following problems: the minimum output current is usually above the uA level, and some professional dedicated constant current source circuits that can provide nA level have complex circuits and large equipment size. Some constant current source circuits also require a high-precision reference voltage source, and the output load of the constant current source is not a grounded load, etc.

[0007] For example, in the article "Design and Implementation of a High-Precision Digital Control DC Current Source", a digital control constant current source circuit is introduced. This circuit can achieve an adjustable current output of 20mA-3000mA. The characteristics of this circuit are that it requires a high-precision reference voltage source, has high requirements for the stability of the power supply voltage, and cannot achieve bidirectional constant current output. In "Design of Digital Control Constant Current Source", a constant current source design is mentioned, but the output current accuracy of this design depends on the sampling resistor. For weak currents, a high-resistance precision resistor is required, making the design difficult to implement. Summary of the invention

[0008] The purpose of the present invention is to provide a constant power supply device for a magnetospheric space electric field instrument, aiming to overcome the problems of existing constant current sources such as large output current, complex circuits, and large size that cannot meet the needs of electric field detection, thereby providing a constant current output of pA level controlled by a single-chip microcomputer, which can control the current direction on the load with a control signal, and realize a bidirectional constant current output through a FPGA-controlled digitally controlled constant current source device for a space-borne electric field instrument. The output current accuracy of the device is independent of the power supply voltage, does not require a high-precision reference voltage source, and reduces the complexity and cost of the circuit.

[0009] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a constant power supply device for a magnetospheric space electric field instrument, comprising: an FPGA control circuit, a digital-to-analog converter DAC, a summing amplifier circuit, a floating ground reference circuit and a load driving circuit; the floating ground reference circuit adjusts the resistance in the summing amplifier circuit , , , , The output voltage is determined by the resistance value, the formula is:

[0010] ;

[0011] Among them, the control signal output end of the FPGA control circuit is connected to the digital-to-analog converter DAC; the output end of the digital-to-analog converter is connected to the input end of the summing amplifier circuit; the output signal of the summing amplifier circuit uses a floating reference point as a reference, and the output signal is connected to the load driving circuit; the output end of the load driving circuit is connected to the load.

[0012] Preferably, the digital-to-analog converter DAC has a 16-bit resolution, the full-scale output current is determined by an external reference input voltage VREF, and the output voltage polarity is opposite to the polarity of VREF.

[0013] Preferably, the FPGA control circuit is used to output corresponding digital signals according to instructions.

[0014] Preferably, the digital-to-analog converter DAC converts the digital signal into an analog signal and controls the magnitude of the output voltage.

[0015] Preferably, the summing amplifier circuit is used to realize the switching of the positive and negative directions of the output voltage, and the magnitude of the output voltage is set by adjusting the resistance value.

[0016] Preferably, the floating ground reference circuit is used to ensure that the output voltage is stable relative to the spatial floating ground.

[0017] Preferably, the load driving circuit is used to withstand changes in load resistance and output a stable voltage to the load.

[0018] Technical effects and advantages of the present invention: Compared with the prior art, the constant power supply device for the magnetospheric space electric field instrument proposed by the present invention has the following advantages:

[0019] The device of the present invention comprises an FPGA control circuit, a digital-to-analog converter, a summing amplifier circuit, a control circuit, a floating ground reference circuit and a load driving circuit. The device realizes accurate current-to-voltage conversion through a DAC controlled by an FPGA, and realizes voltage output in positive and negative directions through a summing amplifier circuit. The floating ground reference circuit ensures that the output voltage is stable relative to the floating ground in space, and the load driving circuit outputs a stable voltage to the load. The device is simple to control and has strong adaptability. It realizes accurate control of power supply output through FPGA, can withstand changes in load impedance, ensures the stability of power supply output, realizes voltage output in positive and negative directions, and meets the needs of different loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a constant power supply device for a magnetospheric space electric field instrument of the present invention;

[0021] Figure 2 It is a schematic diagram of the FPGA control circuit of the present invention;

[0022] Figure 3 An interface circuit diagram of the output signal of the digital-to-analog converter of the present invention;

[0023] Figure 4 is a schematic diagram of a summing amplifier circuit of the present invention;

[0024] Figure 5 FIG. 1 is a circuit diagram of a floating ground reference circuit according to the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] The present invention provides a constant power supply device for a magnetospheric space electric field instrument, aiming to overcome the problems of existing constant current sources such as large output current, complex circuits, and large size that cannot meet the needs of electric field detection, thereby providing a constant current output of pA level controlled by a single-chip microcomputer, which can control the current direction on the load with a control signal, and realize a bidirectional constant current output through a digitally controlled constant current source device controlled by an FPGA for use in a space-borne electric field instrument. The output current accuracy of the device is independent of the power supply voltage, does not require a high-precision reference voltage source, and reduces the complexity and cost of the circuit, as follows:

[0027] like Figure 1 As shown, it includes: an FPGA control circuit 1, a digital-to-analog converter DAC2, a summing amplifier circuit 3, a floating ground reference circuit 4 and a load driving circuit 5;

[0028] Specifically, the control signal output end of the FPGA control circuit 1 is connected to the digital-to-analog converter DAC2. The digital-to-analog converter DAC2 has a 16-bit resolution. The full-scale output current is determined by the external reference input voltage VREF, and the output voltage polarity is opposite to the polarity of VREF. The FPGA control circuit 1 is used to output the corresponding digital signal according to the instruction, and the digital-to-analog converter DAC2 converts the digital signal into an analog signal and controls the output voltage.

[0029] Specifically, the output end of the digital-to-analog converter DAC2 is connected to the input end of the summing amplifier circuit 3. The summing amplifier circuit 3 is used to realize the positive and negative direction switching of the output voltage. The magnitude of the output voltage is set by adjusting the relevant resistance value.

[0030] Specifically, the floating ground reference circuit 4 is used to ensure that the output voltage is stable relative to the spatial floating ground. The floating ground reference circuit (4) adjusts the resistance in the summing amplifier circuit (3). , , , , The output voltage is determined by the resistance value, the formula is:

[0031] ;

[0032] The importance of floating ground reference circuit 4 is that the magnetosphere is covered by plasma, the satellite operates in the magnetosphere, and the entire system uses the satellite as the reference ground; the magnetosphere space electric field instrument uses spherical dual probe technology. When the spherical probe is in different plasma environments, the potential of the probe relative to the satellite changes greatly. Therefore, for the pre-signal processing of the electric field instrument, its reference ground is relative to the potential of the electric field instrument probe itself, not the potential of the satellite. In other words, the voltage difference between the output voltage of the electric field instrument signal processing preamplifier and the floating ground is 0 volts. By introducing the floating ground, the dynamic range of the preamplifier is increased, allowing it to handle larger voltages;

[0033] like Figure 5 As shown, the probe potential signal sent by the electric field meter preamplifier is sent to the drive circuit after passing through the first-order low-pass filter, and then sent to the power supply system after passing through the first-order low-pass filter output. Since the maximum output DC voltage of the preamplifier is set to ±260 V, a general amplifier cannot drive such a large voltage. Therefore, the drive circuit is mainly a power amplifier circuit composed of an NPN transistor and a bipolar junction PNP transistor. The BUL45D2G produced by ON Semiconductor and the FMMT560 produced by DIODES are selected in the present invention.

[0034] The load driving circuit 5 is a power amplifier circuit, which is an amplifier circuit for the purpose of outputting high power. The power amplifier circuit does not simply pursue the output of high voltage or high current, but requires it to output as much power as possible under the condition of a certain voltage. When the input signal is greater than zero, it is mainly the emitter of the Q4 transistor that drives the load, and when the input signal is less than zero, it is mainly the emitter of the Q3 transistor that drives the load.

[0035] Specifically, the output signal of the summing amplifier circuit 3 is based on a floating reference point, and the output signal is connected to the load driving circuit 5; the output end of the load driving circuit 5 is connected to the load, and the load driving circuit 5 is used to withstand a large change in load resistance and output a stable voltage to the load.

[0036] like Figure 2 As shown, the constant current source control circuit consists of a digital-to-analog converter controlled by an FPGA and an addition-subtraction circuit. The FPGA generates a signal to control the DAC, which converts the digital signal into an analog signal and then sends it to the back end for further processing. The reference voltage is +5 volts.

[0037] FPGA: FPGA (Field Programmable Gate Array) is the heart of this circuit and it communicates with external devices through pins like SDI, CLK, LDAC, RS and CS.

[0038] DAC: The digital-to-analog converter (DAC) receives data from the FPGA and converts it into an analog voltage output. VREF_A and VDD provide reference voltage and power for the DAC.

[0039] Analog amplifier: An operational amplifier is used to amplify or attenuate the input signal. Its two input terminals are connected to VREF_BIAS and RFB_BIAS respectively, and the output is connected to AGND.

[0040] Capacitor C6: Capacitor C6 is used for filtering purposes to help eliminate noise and stabilize circuit performance.

[0041] Power and ground: There are several different power and ground nodes in the circuit, including +5VD, +VREF, -VREF, +VREF_BIAS, -VREF_BIAS reference voltage. These power and ground lines ensure proper power supply and signal transmission between various components.

[0042] In addition, the generation of bias current and voltage is mainly controlled by a 16-bit digital-to-analog converter (DAC). The DAC chip model can be AD5544, and the full-scale output current is determined by the applied external reference input voltage (VREF). When used with an external current-to-voltage precision amplifier, the integrated feedback resistor (RFB) can provide temperature tracking and full-scale voltage output.

[0043] like Figure 3 As shown in the figure:

[0044] VREF_BIAS is coupled to the inverting input of operational amplifier U4 through resistor R9 and C2.

[0045] RFB_BIAS is coupled to the non-inverting input of operational amplifier U4 through resistor R10 and C5.

[0046] V_PROBE (from the E-field meter probe) is coupled to the non-inverting input of operational amplifier U4 through resistor R8 and C3.

[0047] Amplifier: Operational amplifier U4 is a bipolar operational amplifier with high common-mode rejection ratio and low bias current. It is used as a follower to improve the signal driving capability.

[0048] Switch: Q1 and Q2 form a complementary symmetrical switch to control the current flowing through R11. When VREF_BIAS is greater than RFB_BIAS, Q1 is turned on and Q2 is turned off; when VREF_BIAS is less than RFB_BIAS, Q2 is turned on and Q1 is turned off. This design ensures that current is provided to the load only when the voltage difference between VREF_BIAS and RFB_BIAS reaches a certain threshold.

[0049] Load: The output is connected to the load BIAS through resistor R12. The output range is from +V_MAX to -V_MAX, depending on the state of the switch and the load impedance.

[0050] Bias: AGND is the analog ground, and all analog signals use this as a reference point. +10V and -10V are the positive and negative power supplies of operational amplifier U4, respectively.

[0051] Isolation: Capacitors C1, C4, and C5 provide AC isolation, preventing DC components from affecting the operation of the circuit.

[0052] The design goal of the entire circuit is to selectively provide current to the load based on the relative size between VREF_BIAS and RFB_BIAS. At the same time, the signal driving capability is improved through the operational amplifier U4, and the AC isolation is achieved by using capacitors.

[0053] VREF_BIAS is the reference voltage, usually 5V, RFB_BIAS is the signal generated by the DAC, usually between -5V and 0V, and V_PROBE is the voltage detected by the electric field meter probe. By setting a reasonable resistance value, the output voltage of the operational amplifier U4 can be between 1 and 20 times the reference voltage VREF_BIAS relative to the probe voltage, and both positive and negative voltages can be obtained. By setting a suitable resistance value, the required output voltage can be obtained, which is very flexible, and then the output voltage is applied to the probe through the driver. V_MAX is the maximum voltage that can be detected by the onboard electric field instrument probe.

[0054] According to the data setup and data hold time requirements defined in the interface timing specification, when The chip select pin starts inputting data when it is at a low level. The data is input into the register one by one through the SDI pin at the rising edge of CLK. When the data in the shift register is aligned normally, The positive edge of 0 starts the transfer of new data to the target DAC register, which is determined by the decoding of address bits A1 and A0. When the positive edge of returns to logic high, the AD5544 checks the last 18 bits (address + data) input to the serial register one by one. At this time, the internally generated load strobe transfers the serial register data content (D15 bit to D0 bit) to the decoded DAC input register address (determined by A1 bit to A0 bit). The DAC output voltage is determined by VREF and digital data, and the formula is as follows:

[0055]

[0056] D is the input data. It can be seen from the above formula that the output voltage polarity is opposite to the polarity of the DC reference voltage VREF.

[0057] The circuit principle of the summing amplifier is as follows Figure 4 As shown:

[0058] VREF_BIAS1: This is the first reference voltage source, which applies voltage to the negative input terminal (marked "-") of the op amp through resistor R1. Resistor R1 determines the amount of current that flows into the negative input terminal of the op amp.

[0059] RFB_BIAS: This is the second reference voltage source that is applied to the positive input (marked "+") of the op amp through resistor R2. Resistor R2 also determines the amount of current that flows into the positive input of the op amp.

[0060] V_PROBE: This is a third voltage source, usually a probe or test signal, that is applied to the positive input of the op amp through resistor R3. Resistor R3 allows the user to adjust the amplitude of the input signal.

[0061] Operational amplifier U1: This is a high gain operational amplifier whose purpose is to amplify the differential input signal (i.e. VREF_BIAS1 - VFB_BIAS + V_PROBE). Since the open loop gain of the operational amplifier is very high, theoretically very high amplification can be achieved.

[0062] Output: The output of the op amp is connected to the load resistor Rf and then returned to ground through capacitor C2. The output signal can be changed by adjusting the value of Rf.

[0063] C1 and C3: These two capacitors are connected between the positive and negative input terminals of the operational amplifier and the ground respectively, acting as bypasses and helping to suppress high-frequency noise.

[0064] C2: This capacitor is connected between the output of the operational amplifier and ground, and also acts as a bypass, helping to suppress high-frequency noise at the output.

[0065] Vn2 and Vp3: These may be virtual locations or test points used to measure intermediate voltages in the circuit.

[0066] Furthermore, from the knowledge of the amplifier circuit, we can get: ;

[0067] Solving the above formula we can get:

[0068]

[0069] Therefore, you can set , , , , The value of bias voltage is used to set the value of bias voltage. Generally speaking, ,and , substituting the resistance value into the above formula:

[0070]

[0071] V1 is the reference voltage VREF of the digital-to-analog converter = +5V, V2 is the output voltage Vout of the digital-to-analog converter, ranging from -5V to 0V, V3 = Vsphere, and the value of Vout can be obtained by substituting the value into the above formula:

[0072]

[0073] That is, the output voltage is ± V, The value is generally between 1 and 20, and can be flexibly set according to specific scientific research needs. By setting the appropriate resistance value, the required output voltage can be obtained, which is very flexible, and then the output voltage is applied to the probe through the driver.

[0074] Voltage resolution, that is, the step voltage is ; Current resolution, that is, the step current is: , R is the resistance value between the output end of the load driving circuit and the load.

[0075] In summary, in this embodiment, the control instructions output by FPGA are used to achieve the corresponding precise constant current output; the change of current direction can be conveniently controlled by the FPGA control signal to achieve bidirectional constant current output; due to the special design of the constant current source circuit, the output current accuracy is independent of the power supply voltage, and the stability of the power supply voltage is not required to be high; the load is a grounded load, and the circuit can withstand a large load impedance change; the circuit scale is small, which reduces the complexity and cost of the circuit.

[0076] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A constant power supply device for a magnetospheric space electric field instrument, characterized in that: include: FPGA control circuit (1), digital-to-analog converter (2), summing amplifier circuit (3) and load driving circuit (5); Wherein, the control signal output end of the FPGA control circuit (1) is connected to the digital-to-analog converter (2); The output end of the digital-to-analog converter (2) is connected to the input end of the summing amplifier circuit (3); The output signal of the summing amplifier circuit (3) uses a floating reference point as a reference, and the output signal is connected to a load driving circuit (5); the output end of the load driving circuit (5) is connected to a load; It also includes a floating ground reference circuit (4) for ensuring that the output voltage is stable relative to the spatial floating ground; the summing amplifier circuit (3) includes a first reference voltage signal V1, a second reference voltage signal V2, and a third reference voltage signal V3; wherein the first reference voltage signal applies a voltage to the negative input terminal of the operational amplifier through a resistor R1, the second reference voltage signal applies a voltage to the negative input terminal of the operational amplifier through a resistor R2, and the third reference voltage signal applies a voltage to the positive input terminal of the operational amplifier through a resistor R3; the output of the operational amplifier is connected to a load resistor ; The output of operational amplifier U1 is connected to the load resistor , The other end of is connected to the negative input terminal of the operational amplifier U1; one end of the resistor R3 is connected to the resistor R4, and the other end of the resistor R4 is grounded; The floating ground reference circuit (4) adjusts the resistance in the summing amplifier circuit (3) , , , , The output voltage is determined by the resistance value, the formula is: , V1 is the reference voltage of the digital-to-analog converter, V2 is the output voltage of the digital-to-analog converter, which is generated by the FPGA control circuit (1), and V3 is the voltage obtained by the electric field meter probe.

2. A constant power supply device for a magnetospheric space electric field instrument according to claim 1, characterized in that: The digital-to-analog converter (2) has a 16-bit resolution, and the full-scale output current is determined by an external reference input voltage.

3. A constant power supply device for a magnetospheric space electric field instrument according to claim 2, characterized in that: The FPGA control circuit (1) is used to output corresponding digital signals according to instructions.

4. A constant power supply device for a magnetospheric space electric field instrument according to claim 3, characterized in that: The digital-to-analog converter (2) converts the digital signal into an analog signal and controls the magnitude of the output voltage.

5. A constant power supply device for a magnetospheric space electric field instrument according to claim 4, characterized in that: The summing amplifier circuit (3) is used to realize the switching of the positive and negative directions of the output voltage, and the magnitude of the output voltage is set by adjusting the resistance value.

6. A constant power supply device for a magnetospheric space electric field instrument according to claim 5, characterized in that: The floating ground reference circuit (4) is used to ensure that the output voltage is stable relative to the spatial floating ground.

7. A constant power supply device for a magnetospheric space electric field instrument according to claim 6, characterized in that: The load driving circuit (5) is used to withstand changes in load resistance and output a stable voltage to the load.

Images