CN112817359B - High-stability constant current source with wide load range - Google Patents
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- G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is DC
- G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is DC using semiconductor devices in series with the load as final control devices
- G05F1/561—Voltage to current converters
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Abstract
The invention discloses a high-stability constant current source with a wide load range, which comprises a control voltage module, a power dissipation module, a V/I conversion module and an auxiliary module. The control voltage module is a D/A control circuit, adopts a high-stability D/A chip AD5791, is controlled by an FPGA, and outputs and is connected to the voltage input end of the V/I conversion module; the power dissipation module is used for dissipating extra power provided by the power supply when the load is low, the safety and the high stability of the circuit are ensured, and the power output is connected to the power input end of the V/I conversion module; the V/I conversion module converts voltage into current through a feedback circuit built by an operational amplifier, a BJT and a sampling resistor, and a power output end and a power ground are respectively connected to two ends of a load; the auxiliary modules comprise a power supply control module, a current direction control module, a Field Programmable Gate Array (FPGA), a man-machine interaction module and the like; in addition, a control algorithm for improving the current accuracy is also provided.
Description
Technical Field
The invention relates to the technical field of constant current sources, in particular to a high-stability constant current source with a wide load range.
Background
The most important module in the constant current source is a V/I conversion module that proportionally converts the controllable voltage signal into a target current value. The non-inverting input end of the traditional constant current source operational amplifier is connected with a control voltage signal, the inverting input end of the traditional constant current source operational amplifier is connected with the negative electrode of a sampling resistor, and the output end of the traditional constant current source operational amplifier is connected with the base electrode of a triode; the collector of the triode is connected with the positive electrode of the power supply, and the emitter of the triode is connected with the positive electrode of the load resistor; the negative electrode of the load resistor is connected with the positive electrode of the sampling resistor; the negative pole of the sampling resistor is connected with the analog ground and the power ground. In practical application, the emitter and the collector of the base electrode of the triode are formed by large capacitors, so that the gain of an operational amplifier loop is unstable, and an oscillation phenomenon occurs; because the sampling resistor, the operational amplifier, the triode and the like have the characteristics of temperature drift and long-term drift, the stability is insufficient; when the load resistance is small, a large amount of power is dissipated on the triode, so that heat is generated, and the stability is greatly reduced and even the instrument is damaged.
At present, no scheme is disclosed for solving the problem of power dissipation when the load resistance is small, so as to obtain a stable constant current source.
Disclosure of Invention
In view of this, the invention provides a high-stability constant current source with a wide load range, and a power dissipation module is added to effectively improve the stability and the load range of the constant current source.
In order to achieve the purpose, the technical scheme of the invention is as follows: a high-stability constant current source with a wide load range comprises a control voltage module, a power dissipation module and a V/I conversion module.
The control voltage module is a D/A control circuit and is controlled by the FPGA, and the output end of the control voltage module is connected to the voltage input end of the V/I conversion module.
The power dissipation module is used for dissipating the extra power provided by the power supply, the safety and the high stability of the circuit are ensured, and the power output of the power dissipation module is connected to the power input end of the V/I conversion module.
The V/I conversion module converts voltage into current through a feedback circuit built by an operational amplifier, a BJT and a sampling resistor, and a power output end and a power ground of the V/I conversion module are respectively connected to two ends of a load.
Furthermore, the control voltage module utilizes a D/A converter AD5791 to construct a D/A control circuit, a digital end of the D/A converter AD5791 is connected to an IO pin of the FPGA through an isolation chip, the control voltage module is placed in the thermostat, and the temperature change does not exceed 1 ℃ after the start-up is stable.
Further, the power dissipation module includes a first operational amplifier U1, a first power amplifier, and a parallel BJT array.
The non-inverting input end of the first operational amplifier U1 is connected with a fixed reference voltage, the inverting input end of the U1 is connected with the power output end of the parallel BJT array through an isolation resistor R12, and the output end of the U1 is connected with the base of the parallel BJT array after amplifying power through a power amplifier L2.
The parallel BJT array comprises n parallel PNP type triodes, wherein the base electrode of each PNP type triode is directly short-circuited as an array base electrode; the collectors of all PNP type triodes are directly short-circuited and then serve as POWER supply ends of the array, and the POWER supply ends are connected with the anodes of the POWER supplies; and the emitters of all the PNP type triodes are respectively connected with a balance resistor and then are in short circuit to form the power output end of the array.
The power output of the array serves as the power output of the power dissipation module.
Furthermore, the V/I conversion module adopts a combination mode of a second operational amplifier U3, a second power amplifier, a PNP type triode Q7 and a sampling resistor;
the voltage output end of the control voltage module is connected to the inverting input end of a second operational amplifier U3 after passing through a follower and an inverter, the non-inverting input end of the second operational amplifier U3 is connected to the voltage sampling B end of a sampling resistor R21 after passing through an isolation resistor R22, and the output end of the second operational amplifier U3 is connected to the base electrode of Q7 after amplifying power through a second power amplifier; the collector of the Q7 is connected with the power output end of the power dissipation module, and the emitter of the Q7 is connected with the power current A end of the sampling resistor R21; a end of the sampling resistor R21 is connected with the analog ground, and B end is connected with the load positive interface SC +; the load interface SC is connected to power ground.
Further, the second operational amplifier adopted by the V/I conversion module is OPA189, the temperature drift is 0.005 uV/DEG C, and the open-loop gain is 170 dB;
furthermore, a sampling resistor R21 adopted by the V/I conversion module is VPR221Z, the temperature drift is 0.05 ppm/DEG C, and the long-term stability is 50ppm/2000 h;
has the advantages that:
the invention designs a high-stability constant current source with a wide load range, and a power dissipation module is added, wherein the power dissipation module is used for dissipating extra power provided by a power supply when the load is low, so that the safety and the high stability of a circuit are ensured; the invention designs the operational amplifier stability compensation circuit, and effectively improves the stability and the load range of the constant current source.
Drawings
FIG. 1 is a schematic diagram of a wide-load-range high-stability constant current source according to an embodiment of the present invention
Fig. 2 is a circuit diagram of a voltage control module according to an embodiment of the present invention.
Fig. 3 is a circuit diagram of a power dissipation module according to an embodiment of the invention.
Fig. 4 is a circuit diagram of a V/I conversion module according to an embodiment of the invention.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
The invention provides a high-stability constant current source structure with a wide load range, which comprises a control voltage module, a power dissipation module, a V/I conversion module and an auxiliary module as shown in figure 1.
The control voltage module is a D/A control circuit and is controlled by the FPGA, and the output end of the control voltage module is connected to the voltage input end of the V/I conversion module.
The power dissipation module is used for dissipating the extra power provided by the power supply, the safety and the high stability of the circuit are ensured, and the power output of the power dissipation module is connected to the power input end of the V/I conversion module.
The V/I conversion module converts voltage into current through a feedback circuit built by an operational amplifier, a BJT and a sampling resistor, and a power output end and a power ground of the V/I conversion module are respectively connected to two ends of a load.
The control voltage module is used for converting a value set in the FPGA into control voltage; the power dissipation module is used for dissipating the extra power provided by the power supply when the load is low; the V/I conversion module is used for converting the control voltage signal into power current; the auxiliary module is used for auxiliary control of man-machine interaction, current direction and the like.
The control voltage module utilizes a D/A converter AD5791 to implement a D/A conversion function. AD5791 has 20-bit resolution, temperature drift of 0.05 ppm/deg.C, and long-term linear stability of 0.19 LSB; the external reference voltage chip adopts MAX6350, the temperature drift is 0.5 ppm/DEG C, and the long-term stability is 30ppm/1000 h. The control voltage module is placed in the thermostat, and the temperature change does not exceed 1 ℃ after the start-up is stable. Comprehensive calculation shows that the drift of the control voltage module is not more than 1ppm within 10h, and the control voltage module has extremely high stability.
The circuit diagram of the control voltage module is shown in fig. 2 and is a conventional connection mode of an AD5791, a digital end of a D/A conversion chip AD5791 is connected to an FPGA pin through an isolation chip, a reference pin is symmetrically connected to an external reference through a follower formed by a double-channel operational amplifier, and an output pin and the operational amplifier are combined to be used as control voltage to be output; the reference chip is powered by a 5V single power supply, the output range of the control voltage is 0-5V, the output range of the actual control voltage is 0-4V, the corresponding output power current range is 0-2A, the resolution of the control voltage is 5/2^20 ^ 4.77uV, and the resolution of the equivalent power current is 2.38 uA.
The power dissipation module is shown in fig. 3, wherein a 12V power supply is connected to an ultra-low noise LDO chip, a reference voltage of 3V is generated by the ultra-low noise LDO chip U6, and the reference voltage is connected to a non-inverting input terminal of the first operational amplifier U1 after passing through an isolation resistor, and the rest of the LDO chip is a classic circuit design of the LDO chip; the power dissipation module comprises a first operational amplifier U1, a first power amplifier and a parallel BJT array; the inverting input end of the first operational amplifier U1 is connected with the current output end of the parallel BJT array through an isolation resistor (the emitters of all BJTs of the parallel BJT array are connected together through a shunt power resistor to be used as the current output end of the parallel BJT array); the output end of the first operational amplifier U1 is connected to the base terminal of the parallel BJT array after amplifying the current through a power amplifier U2(LT 1010). The parallel BJT array comprises n parallel PNP type triodes, wherein the base electrode of each PNP type triode is directly short-circuited as an array base electrode; the collectors of all PNP type triodes are directly short-circuited and then serve as POWER supply ends of the array, and the POWER supply ends are connected with the anodes of the POWER supplies; the emitters of all the PNP type triodes are respectively connected with a balance resistor and then are in short circuit to form a power output end of the array; the power output end of the parallel BJT array is connected to the inverting input end of a first operational amplifier U1 through a resistor R12, meanwhile, the output end of a second operational amplifier U1 is connected with the inverting input end of the first operational amplifier U1 through a capacitor C4, a resistor R6 and a capacitor C5 are connected between the non-inverting input end and the inverting input end of a second operational amplifier U1, and the output end of the second operational amplifier U1 is connected with the non-inverting input end of the U1 through a capacitor C1; a resistor R2 and a capacitor C2 are connected in parallel between the pin out at the output end 3 and the pin input at the input end 8 of the first power amplifier U2, and a resistor R5 is connected between the pin 1 and the pin 2 of the first power amplifier U2, which are conventional connections of the first power amplifier U2.
According to the feedback loop formed by the first operational amplifier U1 and the parallel BJT array, when the voltage at the current output end is higher than 3V relatively, the output voltage of the first operational amplifier U1 will decrease, resulting in the output voltage of the power amplifier U2 decreasing, resulting in the base current of the parallel BJT array decreasing, resulting in the equivalent resistance of the BJT array increasing. Since the rear end of the power current is a constant current source, the emitter current of the BJT array is not changed, so the voltage drop on the BJT array is increased, and the voltage of the current output end is reduced. Therefore, negative feedback closed-loop control is completed, the voltage of the current output end relative to the analog ground is consistent with the reference voltage of 3V, and the voltage between the collector and the emitter of the BJT in the V/I conversion module can be ensured to be constant. The BJT power dissipation in the V/I conversion module is reduced, the safe operation is ensured, and meanwhile, the stability of the output current can be greatly improved.
In the alternating current path, the power dissipation module has a large capacitance between the bases of the parallel BJT array (the output of the first operational amplifier U1 and the first power amplifier U2) and the analog ground, and a large capacitance also exists between the inverting input terminal of the operational amplifier and the analog ground, and the direct connection causes oscillation of the operational amplifier U1. The controllable loop gain is realized through the configuration of the resistor and the capacitor in the circuit, and the stable operation of the circuit is ensured.
The V/I conversion module is shown in fig. 4, and adopts a combination of a second operational amplifier U3, a second power amplifier, a PNP triode Q7 and a sampling resistor; in order to improve the precision and stability of the constant current source, the analog ground is isolated from the power ground, and the analog ground is advanced to the voltage detection end of the sampling resistor, so that the base current of the BJT in the power dissipation module and the V/I conversion module can be led out before entering the sampling resistor, and the output current cannot be influenced. The negative feedback loop of the operational amplifier needs to be inverted. After the voltage generated by the control voltage module is improved by the input resistance of the follower (U5B), the voltage is reduced from 0-4V to-1-0V by the inverting amplifier (U5A) and is connected to the inverting input end of the second operational amplifier U3; the non-inverting input end of the second operational amplifier U3 is connected with the load side voltage detection end of the sampling resistor through an isolation resistor, and the output end of the second operational amplifier U3 is connected with the base end of the triode Q7 after amplifying current through a second power amplifier U4(LT 1010). The non-inverting input end of the second operational amplifier U3 is connected with the voltage sampling end B of the sampling resistor R21 through the isolation resistor R22, and the output end of the second operational amplifier U3 is connected with the base electrode of the Q7 after amplifying power through the second power amplifier; the collector of the Q7 is connected with the power output end of the power dissipation module, and the emitter of the Q7 is connected with the power current A end of the sampling resistor R21; a end of the sampling resistor R21 is connected with the analog ground, and B end is connected with the load positive interface SC +; the load interface SC is connected to power ground. The second power amplifier U4 also has a conventional connection. The output terminal of the second operational amplifier U3 is connected to the non-inverting input terminal of U3 through a capacitor C11, and the output terminal of the second operational amplifier U3 is connected to the inverting input terminal of U3 through a capacitor C7. Other conventional connections are shown in fig. 3. According to the feedback loop formed by the second operational amplifier and the transistor Q7, when the output current is larger than the voltage drop of the control voltage generated on the sampling resistor (0.5 Ω), the voltage (negative value) at the non-inverting input terminal of the operational amplifier U3 will decrease, resulting in the decrease of the output voltage of the second power amplifier U4, resulting in the decrease of the base current of Q7, resulting in the decrease of the emitter current (output current) of Q7. Thus, negative feedback closed-loop control is completed, and the output current is proportional to the control voltage (the sampling resistance is 0.5 omega).
In the V/I conversion module, the OPA189 adopted by the second operational amplifier U3 has extremely low temperature drift of 0.005 uV/DEG C and extremely high open loop gain of 170 dB. The temperature drift is low, the temperature drift of the output voltage and the control voltage of the operational amplifier U3 is reduced, and the stability is improved; the open-loop gain high energy reduces the voltage drop on the sampling resistor and the deviation of the control voltage, and improves the precision.
The V/I conversion module has a large capacitance between the base of the transistor Q7 (the output of the second operational amplifier U3 and the second power amplifier U4) and the analog ground in the ac path, and the direct connection will cause the operational amplifier U1 to oscillate. The controllable loop gain is realized through the configuration of the resistor and the capacitor in the circuit, and the stable operation of the circuit is ensured.
The control algorithm can reduce the dissipation power on the power dissipation module, reduce the temperature rise in the instrument caused by the dissipation power and improve the stability. Before conducting current each time, the control algorithm comprises the steps that 1) when the current value set by an operator is finished, after the control current is conducted, the control current is conducted by current of 24V and 10mA, the relay 2 is conducted, the voltage difference between the positive pole of the power voltage and the simulated ground is measured, and the load resistance value is calculated; and (3) closing the relay 2, selecting a proper power voltage gear according to the load resistance value and the set current value, setting a control voltage value corresponding to the target current value, and conducting the current.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (5)
1. The high-stability constant current source with the wide load range is characterized by comprising a control voltage module, a power dissipation module and a V/I conversion module;
the control voltage module is a D/A control circuit, the control voltage module is controlled by an FPGA, and the output end of the control voltage module is connected to the voltage input end of the V/I conversion module;
the power dissipation module is used for dissipating extra power provided by the power supply to ensure the safety and high stability of the circuit, and the power output of the power dissipation module is connected to the power input end of the V/I conversion module;
the power dissipation module comprises a first operational amplifier U1, a first power amplifier and a parallel BJT array;
the non-inverting input end of the first operational amplifier U1 is connected with a fixed reference voltage, the inverting input end of the U1 is connected with the power output end of the parallel BJT array through an isolation resistor R12, and the output end of the U1 is connected with the base electrode of the parallel BJT array after amplifying power through a power amplifier U2;
the parallel BJT array comprises n parallel PNP type triodes, wherein the base electrode of each PNP type triode is directly short-circuited as an array base electrode; the collectors of all PNP type triodes are directly short-circuited and then serve as POWER supply ends of the array, and the POWER supply ends are connected with the anodes of the POWER supplies; the emitters of all the PNP type triodes are respectively connected with a balance resistor and then are in short circuit to form a power output end of the array;
the power output end of the array is used as the power output end of the power dissipation module;
the V/I conversion module converts voltage into current through a feedback circuit built by an operational amplifier, a BJT and a sampling resistor, and a power output end and a power ground of the V/I conversion module are respectively connected to two ends of a load.
2. The constant current source of claim 1, wherein the control voltage module utilizes a D/a converter AD5791 to construct a D/a control circuit, a digital terminal of the D/a converter AD5791 is connected to an IO pin of the FPGA through an isolation chip, the control voltage module is placed in a thermostat, and a temperature change after startup is stable does not exceed 1 ℃.
3. The constant current source of claim 1 or 2, wherein the V/I conversion module employs a combination of a second operational amplifier U3, a second power amplifier, a PNP transistor Q7, and a sampling resistor;
the voltage output end of the control voltage module is connected to the inverting input end of a second operational amplifier U3 after passing through a follower and a phase inverter, the non-inverting input end of the second operational amplifier U3 is connected to the voltage sampling B end of a sampling resistor R21 after passing through an isolation resistor R22, and the output end of the second operational amplifier U3 is connected to the base electrode of Q7 after amplifying power through a second power amplifier; the collector of the Q7 is connected with the power output end of the power dissipation module, and the emitter of the Q7 is connected with the power current A end of the sampling resistor R21; a end of the sampling resistor R21 is connected with the analog ground, and B end is connected with the load positive interface SC +; the load interface SC is connected to power ground.
4. The constant current source of claim 1, wherein the second operational amplifier employed by the V/I conversion module is OPA189, the temperature drift is 0.005 uV/c, and the open loop gain is 170 dB.
5. The constant current source of claim 1, wherein the sampling resistor R21 used by the V/I conversion module is VPR221Z, the temperature drift is 0.05ppm/° c, and the long-term stability is 50ppm/2000 h.
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| CN114040557B (en) * | 2021-11-04 | 2022-09-20 | 中船重工安谱（湖北）仪器有限公司 | Array type dielectric barrier glow discharge device |
| CN114390750A (en) * | 2021-12-13 | 2022-04-22 | 四维生态科技（杭州）有限公司 | LED driving system for plant illumination and plant illumination system |
| CN117472132B (en) * | 2023-11-10 | 2024-12-31 | 湖南恩智测控技术有限公司 | Constant current source and related method, constant voltage source and related method, device and medium |
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| CN102005941B (en) * | 2010-10-28 | 2012-12-12 | 广西大学 | Piezoelectric ceramics driving power supply for adjusting numerical control potentiometer |
| CN103257662B (en) * | 2012-03-14 | 2014-12-24 | 美芯晟科技（北京）有限公司 | Linear constant-current modulation circuit |
| CN102637054B (en) * | 2012-04-21 | 2013-12-25 | 吉林大学 | 50-ampere power consumption balanced-type high-power constant-current source |
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