CN220105580U - A carbon resistance temperature sensor constant current source circuit for low temperature measurement - Google Patents

Abstract

A constant current source circuit of a carbon resistance temperature sensor for low-temperature measurement belongs to the technical field of contact low-temperature measurement and solves the problem of inaccurate low-temperature measurement caused by joule heat generated by the carbon resistance temperature sensor; comprising the following steps: the first operational amplifier U8, the second operational amplifier U9, the capacitor C123, the capacitor C124, the resistor R23 and the power supply circuit; the constant current source circuit outputs excitation current by adopting the first operational amplifier U8, and the second operational amplifier U9 collects the output excitation current in real time for feedback adjustment, so that the stability and reliability of the output excitation current are ensured; the first operational amplifier U8 adopts an operational amplifier with a high common mode rejection ratio, so that the anti-interference performance of low-temperature measurement is improved, and the precision is higher; the power supply circuit adopts a chopper type 220-12/AC-DC module, and an FC-LX1D filter is arranged in front of the chopper type 220-12/AC-DC module, so that the noise of the power supply circuit is reduced, and the power supply circuit is suitable for occasions sensitive to the noise.

Description

A carbon resistance temperature sensor constant current source circuit for low temperature measurement

Technical field

The utility model belongs to the technical field of contact low-temperature measurement and relates to a carbon resistance temperature sensor constant current source circuit used for low-temperature measurement.

Background technique

Carbon resistance temperature sensors are often used to measure the temperature of liquid helium (5 to 80K) due to their extremely high sensitivity. Carbon resistance temperature sensors require an external power source to be driven. Because the carbon resistance temperature sensor has a resistance of several thousand ohms at low temperatures, when the current is larger, its own heating power will be very high and Joule heat will be generated. When Joule heat is too large, it will cause larger measurement errors. Errors may even cause measurement errors in severe cases, so the carbon resistance temperature sensor needs to be driven by a small current. Therefore, it is necessary to design a stable and reliable constant current source to limit the Joule heat generated by the carbon resistance temperature sensor.

Utility model content

The purpose of this utility model is how to design a stable and reliable constant current source to solve the problem of inaccurate low temperature measurement caused by the Joule heat generated by the carbon resistance temperature sensor.

The utility model solves the above technical problems through the following technical solutions:

A carbon resistance temperature sensor constant current source circuit for low temperature measurement, including: a first operational amplifier U8, a second operational amplifier U9, a capacitor C123, a capacitor C124, a resistor R23, and a power supply circuit; the first operational amplifier U8 The 1 ^# pin is connected to ground, the 4 ^# pin of the first operational amplifier U8 is connected to the reference voltage, the 8 ^# pin of the first operational amplifier U8 and the 5 ^# pin of the first operational amplifier U8 are both connected to the power supply circuit, and one end of the capacitor C123 Connect to the 8 ^# pin of the first operational amplifier U8, the other end of the capacitor C123 is connected to the ground, one end of the capacitor C124 is connected to the 5 ^# pin of the first operational amplifier U8, the other end of the capacitor C124 is connected to the ground, the first operational amplifier U8 The 7 ^# pin is connected to one end of the resistor R23, the other end of the resistor R23 is connected to the 3 ^# pin of the second operational amplifier U9, the 4 ^# pin of the second operational amplifier U9 and the 7 ^# pin of the second operational amplifier U9 Both are connected to the power supply circuit, the 6 ^# pin of the second operational amplifier U9 is connected to the 6 ^# pin of the first operational amplifier U8, the 2 ^# pin of the second operational amplifier U9 is connected to the 6 ^# pin of the second operational amplifier U9 ; The common connection point between the resistor R23 and the 3 ^# pin of the second operational amplifier U9 is used as the output end of the constant current source circuit.

Further, the model of the first operational amplifier U8 is AD8221, and the model of the second operational amplifier U9 is AD8638.

Further, the power supply circuit includes: a first voltage conversion circuit, a second voltage conversion circuit, and a third voltage conversion circuit; the input terminal of the first voltage conversion circuit is connected to the 220V AC power supply, and the output terminal of the first voltage conversion circuit is connected to the 220V AC power supply. Connect the second voltage conversion circuit and the third voltage conversion circuit respectively; the 8 ^# pin of the first operational amplifier U8 is connected to the output end of the second voltage conversion circuit, and the 5 ^# pin of the first operational amplifier U8 is connected to the third voltage The output end of the conversion circuit; the 7 ^# pin of the second operational amplifier U9 is connected to the output end of the second voltage conversion circuit, and the 4 ^# pin of the second operational amplifier U9 is connected to the output end of the third voltage conversion circuit.

Further, the first voltage conversion circuit includes: step-down chopper module V1, filter V2, fuse F1, electrolytic capacitor CE1, electrolytic capacitor CE2, capacitor C54, capacitor C55, voltage stabilizing diode TVS9, voltage stabilizing diode TVS10; The 3 ^# pin of the filter V2 is connected to the live wire of the 220V AC power supply, the 2 ^# pin of the filter V2 is connected to the neutral wire of the 220V AC power supply, the 1 ^# pin of the filter V2 is connected to ground, and the 4 ^# pin of the filter V2 is connected to the ground. The pin is connected to the 3 ^# pin of the step-down chopper module V1, the 5 ^# pin of the filter V2 is connected to the 2 ^# pin of the step-down chopper module V1, the 1 ^# pin of the filter V2 is connected to the ground, and the electrolytic capacitor CE1 The negative pole of the electrolytic capacitor CE1 is connected to the 4 ^# pin of the step-down chopper module V1, the positive pole of the electrolytic capacitor CE1 is connected to the 6 ^# pin of the step-down chopper module V1, and the negative pole of the electrolytic capacitor CE2 is connected to the 6 ^# pin of the step-down chopper module V1. , the positive electrode of the electrolytic capacitor CE2 is connected to the 8 ^# pin of the step-down chopper module V1, and the two ends of the capacitor C54 are connected to the 4 ^# pin of the step-down chopper module V1 and the 6 ^# pin of the step-down chopper module V1 respectively. The two ends of the capacitor C55 are connected to the 6 ^# pin of the step-down chopper module V1 and the 8 ^# pin of the step-down chopper module V1 respectively. The 6 ^# pin of the step-down chopper module V1 is connected to ground, and one end of the zener diode TVS9 Connect to the 4 ^# pin of the step-down chopper module V1, the other end of the zener diode TVS9 is connected to ground, one end of the zener diode TVS10 is connected to the 8 ^# pin of the step-down chopper module V1, and the other end of the zener diode TVS10 Grounded, the 8 ^# pin of the step-down chopper module V1 serves as the output end of the +12V power supply and is connected to the input end of the second voltage conversion circuit, and the 4 ^# pin of the step-down chopper module V1 serves as the output end of the -12V power supply and is connected to the ground. The input terminal of the third voltage conversion circuit is connected.

Further, the step-down chopper module V1 adopts a chopper-type 220-12/AC-DC module, and the filter V2 adopts an FC-LX1D filter.

Further, the second voltage conversion circuit includes: a first linear voltage stabilizing chip V3, a capacitor C56, a capacitor C57, a capacitor C58, a capacitor C59, a capacitor C60, a capacitor C61, a resistor R30 and a resistor R31; Pins 13 ^# , 15 ^# , and 16 ^# of the pressure chip V3 are connected together and then connected to the output end of the +12V power supply of the first voltage conversion circuit. One end of the capacitor C58 is connected to the first linear voltage regulator chip V3. The 13 ^# pin and the other end of the capacitor C58 are connected to the ground. One end of the capacitor C59 is connected to the 13 ^# pin of the first linear voltage regulator chip V3. The other end of the capacitor C59 is connected to the ground. One end of the capacitor C60 and the capacitor C61 are connected together and then connected. The 14 ^# pin of the first linear voltage stabilizing chip V3, the other ends of the capacitor C60 and the capacitor C61 are all connected to ground. After the resistor R30 and the resistor R31 are connected in series, the non-series end of the resistor R30 is connected to the 1 ^# pin of the first linear voltage stabilizing chip V3. Connection, the non-series end of resistor R31 is grounded, the common point of resistor R30 and resistor R31 in series is connected to the ^# 3 pin of the first linear regulator chip V3, and one of the parallel common terminals of capacitor C56 and capacitor C57 connected in parallel is connected to the first linear regulator chip. The 1 ^# pin of the pressure chip V3 and the other parallel common terminal are connected to the ground. The 1 ^# pin and the 20 ^# pin of the first linear voltage regulator chip V3 are connected together. The 6 ^# pin of the first linear voltage regulator chip V3, The 7 ^# pin and the 10 ^# pin are grounded, and the 1 ^# pin of the first linear voltage stabilizing chip V3 serves as the +5V power output terminal of the first linear voltage stabilizing chip V3.

Further, the model of the first linear voltage regulator chip V3 is TPS7A4701.

Further, the third voltage conversion circuit includes: a second linear voltage stabilizing chip V4, a capacitor C62, a capacitor C63, a capacitor C64, a capacitor C65, a capacitor C66, a capacitor C67, a capacitor C68, a resistor R32, and a resistor R33; The 13 ^# pin, 15 ^# pin, and 16 ^# pin of the two linear voltage regulator chips V4 are connected together and then connected to the output end of the -12V power supply of the first voltage conversion circuit. One end of the capacitor C65 is connected to the second linear voltage regulator The 13 ^# pin of the chip V4 and the other end of the capacitor C65 are connected to the ground. One end of the capacitor C66 is connected to the 13 ^# pin of the second linear voltage regulator chip V4. The other end of the capacitor C66 is connected to the ground. One of the capacitor C67 and the capacitor C68 is connected in parallel. The parallel common terminal is connected to the 14 ^# pin of the second linear voltage regulator chip V4, and the other parallel common terminal is connected to ground. The two ends of the capacitor C64 are connected to the 20 ^# pin and 3 ^# pin of the second linear voltage regulator chip V4 respectively. After the resistor R32 and the resistor R33 are connected in series, the non-series end of the resistor R32 is connected to the 20 ^# pin of the second linear voltage stabilizing chip V4, and the non-series connection end of the resistor R33 is connected to the 7 ^# pin and 21 ^# of the second linear voltage stabilizing chip V4. Pin connection, the common point ^of resistor R32 and resistor R33 ^{in series} is connected to pin 3 of the second linear voltage regulator chip V4, and one of the parallel common terminals of capacitor C62 and capacitor C63 connected in parallel is connected to pin 20 of the second linear voltage regulator chip V4. pin, the other parallel common terminal is grounded, the 20 ^# pin of the second linear voltage stabilizing chip V4 is connected to the 1 ^# pin, and the 20 ^# pin of the second linear voltage stabilizing chip V4 is used as the second linear voltage stabilizing chip -5V power output of V4.

Further, the model of the second linear voltage regulator chip V4 is TPS7A3301.

The advantages of this utility model are:

(1) The constant current source circuit of the present invention uses the first operational amplifier U8 to output the excitation current, and uses the second operational amplifier U9 to collect the output excitation current in real time for feedback adjustment, ensuring the stability and reliability of the output excitation current;

(2) The first operational amplifier U8 uses an operational amplifier with a high common-mode rejection ratio, which improves the anti-interference performance of low-temperature measurements and results in higher accuracy;

(3) The power supply circuit adopts the chopper-type 220-12/AC-DC module, and sets the FC-LX1D filter in front of the chopper-type 220-12/AC-DC module, which reduces the noise of the power supply circuit and is suitable for Noise sensitive situations.

Description of the drawings

Figure 1 is a schematic diagram of a carbon resistance temperature sensor constant current source circuit for low temperature measurement according to an embodiment of the present invention;

Figure 2 is a schematic diagram of the first voltage conversion circuit of the constant current source circuit of the carbon resistance temperature sensor used for low-temperature measurement according to the embodiment of the present invention;

Figure 3 is a schematic diagram of the second voltage conversion circuit of the carbon resistance temperature sensor constant current source circuit used for low-temperature measurement according to the embodiment of the present invention;

Figure 4 is a schematic diagram of the third voltage conversion circuit of the carbon resistance temperature sensor constant current source circuit used for low-temperature measurement according to the embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present utility model more clear, the technical solutions in the embodiments of the present utility model will be clearly and completely described below in conjunction with the embodiments of the present utility model. Obviously, the described embodiments are Some embodiments of the present invention are not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present utility model.

The technical solution of the present utility model will be further described below in conjunction with the accompanying drawings and specific embodiments of the description:

Embodiment 1

As shown in Figure 1, the carbon resistance temperature sensor constant current source circuit for low-temperature measurement in this embodiment includes: a first operational amplifier U8, a second operational amplifier U9, a capacitor C123, a capacitor C124, and a resistor R23; the first The 1 ^# pin of the operational amplifier U8 is connected to ground, the 4 ^# pin of the first operational amplifier U8 is connected to the reference voltage VDD_R, the 8 ^# pin of the first operational amplifier U8 is connected to the +5V power supply, and the 5 ^# pin of the first operational amplifier U8 Connect to the -5V power supply, one end of the capacitor C123 is connected to the 8 ^# pin of the first operational amplifier U8, the other end of the capacitor C123 is connected to ground, one end of the capacitor C124 is connected to the 5 ^# pin of the first operational amplifier U8, and the other end of the capacitor C124 is connected to the -5V power supply. One end is connected to ground, the 7 ^# pin of the first operational amplifier U8 is connected to one end of the resistor R23, the other end of the resistor R23 is connected to the 3 ^# pin of the second operational amplifier U9, and the 4 ^# pin of the second operational amplifier U9 is connected to - 5V power supply, the 7 ^# pin of the second operational amplifier U9 is connected to the +5V power supply, the 6 ^# pin of the second operational amplifier U9 is connected to the 6 ^# pin of the first operational amplifier U8, and the 2 ^# pin of the second operational amplifier U9 pin is connected to the 6 ^# pin of the second operational amplifier U9; the common point of the connection between the resistor R23 and the 3 ^# pin of the second operational amplifier U9 is used as the output end of the constant current source circuit.

The model of the first operational amplifier U8 is AD8221. AD8221 is a programmable high-performance instrument amplifier with excellent common-mode rejection performance. The sensor interface circuit is composed of an operational amplifier with a high common-mode rejection ratio. When designing the measurement circuit, the anti-interference performance of the low-temperature measurement system can be improved; the AD8221 has the advantages of low noise and programmable gain, making it very suitable for bridge circuit signal measurement and other fields that require high DC characteristics.

The model of the second operational amplifier U9 is AD8638. AD8638 is a wide-bandwidth, automatic zero-adjusting amplifier with low offset voltage, low offset drift, low noise, low cost and high precision.

The working principle of constant current source circuit:

For example, the input reference voltage VDD_R is 2.5V, the output terminal of the first operational amplifier U8 gets a voltage of 2.5V, and the designed resistance value of R23 is 250KΩ, then the output of the constant current source circuit is 10μA, so the constant current source circuit is carbon The resistance temperature sensor provides a stable 10μA excitation; the function of the second operational amplifier U9 is to collect the output value of the constant current source circuit in real time and send it to the first operational amplifier U8 for feedback adjustment to stabilize the output value of the constant current source circuit. at 10µA.

As shown in Figure 2-4, it is the power supply circuit of the constant current source circuit, including: a first voltage conversion circuit, a second voltage conversion circuit, and a third voltage conversion circuit. The function of the first voltage conversion circuit is to convert the 220V AC input into It is ±12V DC. The function of the second voltage conversion circuit is to convert +12V DC into +5V DC. The function of the third voltage conversion circuit is to convert -12V DC into -5V DC.

As shown in Figure 2, it is the circuit schematic diagram of the first voltage conversion circuit, including: step-down chopper module V1, filter V2, fuse F1, electrolytic capacitor CE1, electrolytic capacitor CE2, capacitor C54, capacitor C55, and zener diode TVS9, Zener diode TVS10; the step-down chopper module V1 adopts the chopper type 220-12/AC-DC module, the filter V2 adopts the FC-LX1D filter, and the FC-LX1D filter is suitable for noise comparison Sensitive occasions.

The 3 ^# pin of the filter V2 is connected to the live wire of the 220V AC power supply, the 2 ^# pin of the filter V2 is connected to the neutral wire of the 220V AC power supply, the 1 ^# pin of the filter V2 is connected to ground, and the 4 ^# pin of the filter V2 is connected to the ground. The pin is connected to the 3 ^# pin of the step-down chopper module V1, the 5 ^# pin of the filter V2 is connected to the 2 ^# pin of the step-down chopper module V1, the 1 ^# pin of the filter V2 is connected to the ground, and the electrolytic capacitor CE1 The negative pole of the electrolytic capacitor CE1 is connected to the 4 ^# pin of the step-down chopper module V1, the positive pole of the electrolytic capacitor CE1 is connected to the 6 ^# pin of the step-down chopper module V1, and the negative pole of the electrolytic capacitor CE2 is connected to the 6 ^# pin of the step-down chopper module V1. , the positive electrode of the electrolytic capacitor CE2 is connected to the 8 ^# pin of the step-down chopper module V1, and the two ends of the capacitor C54 are connected to the 4 ^# pin of the step-down chopper module V1 and the 6 ^# pin of the step-down chopper module V1 respectively. The two ends of the capacitor C55 are connected to the 6 ^# pin of the step-down chopper module V1 and the 8 ^# pin of the step-down chopper module V1 respectively. The 6 ^# pin of the step-down chopper module V1 is connected to ground, and one end of the zener diode TVS9 Connect to the 4 ^# pin of the step-down chopper module V1, the other end of the zener diode TVS9 is connected to ground, one end of the zener diode TVS10 is connected to the 8 ^# pin of the step-down chopper module V1, and the other end of the zener diode TVS10 Grounded, the 8 ^# pin of the step-down chopper module V1 serves as the output end of the +12V power supply and is connected to the input end of the second voltage conversion circuit, and the 4 ^# pin of the step-down chopper module V1 serves as the output end of the -12V power supply and is connected to the ground. The input terminal of the third voltage conversion circuit is connected. The external 220V AC power is first connected to the FC-LX1D filter through a fuse. After filtering, it is connected to the step-down chopper module V1 to convert the 220V AC power into ±12V power output.

As shown in Figure 3, it is the circuit schematic diagram of the second voltage conversion circuit, including: first linear voltage stabilizing chip V3, capacitor C56, capacitor C57, capacitor C58, capacitor C59, capacitor C60, capacitor C61, resistor R30, resistor R31 ; The model of the first linear voltage regulator chip V3 is TPS7A4701. TPS7A4701 is an ultra-low noise (4μV RMS) LDO that can provide 1A load and provide positive output voltage. The external feedback resistor configures the output voltage of TPS7A4701. This stabilizer Pressure chips are suitable for high-precision measurement circuits.

The 13 ^# pin, 15 ^# pin, and 16 ^# pin of the first linear voltage stabilizing chip V3 are connected together and then connected to the output end of the +12V power supply of the first voltage conversion circuit, and one end of the capacitor C58 is connected to the first The 13 ^# pin of the linear voltage stabilizing chip V3 and the other end of the capacitor C58 are connected to the ground. One end of the capacitor C59 is connected to the 13 ^# pin of the first linear voltage stabilizing chip V3. The other end of the capacitor C59 is connected to the ground. One end of the capacitor C60 and the capacitor C61 After connecting together, connect the 14 ^# pin of the first linear voltage stabilizing chip V3, the other ends of the capacitor C60 and the capacitor C61 are grounded, the resistor R30 and the resistor R31 are connected in series, and then the non-series end of the resistor R30 is connected to the first linear voltage stabilizing chip The 1 ^# pin of V3 is connected, the non-series end of the resistor R31 is connected to the ground, the common point of the resistor R30 and the resistor R31 is connected in series to the 3 ^# pin of the first linear voltage regulator chip V3, one of the parallel common points of the capacitor C56 and the capacitor C57 is connected in parallel. Terminate the 1 ^# pin of the first linear voltage stabilizing chip V3, and the other parallel common terminal is connected to ground. The 1 ^# pin and the 20 ^# pin of the first linear voltage stabilizing chip V3 are connected together. The first linear voltage stabilizing chip V3 The 6 ^# pin, 7 ^# pin and 10 ^# pin are grounded, and the 1 ^# pin of the first linear voltage stabilizing chip V3 is used as the +5V power output end of the first linear voltage stabilizing chip V3.

As shown in Figure 4, it is the circuit schematic diagram of the third voltage conversion circuit, including: the second linear voltage regulator chip V4, capacitor C62, capacitor C63, capacitor C64, capacitor C65, capacitor C66, capacitor C67, capacitor C68, resistor R32 , resistor R33; the model of the second linear voltage regulator chip V4 is TPS7A3301. The TPS7A3301 linear voltage regulator is an ultra-low noise (16μVRMS, 72dBPSRR) linear voltage regulator that supports a maximum input voltage of -36V and can provide a load of up to 1A. powered by.

The 13 ^# pin, 15 ^# pin, and 16 ^# pin of the second linear voltage stabilizing chip V4 are connected together and then connected to the output end of the -12V power supply of the first voltage conversion circuit, and one end of the capacitor C65 is connected to the second The 13 ^# pin of the linear voltage regulator chip V4 and the other end of the capacitor C65 are connected to the ground. One end of the capacitor C66 is connected to the 13 ^# pin of the second linear voltage regulator chip V4. The other end of the capacitor C66 is connected to the ground. After the capacitor C67 is connected in parallel with the capacitor C68 One of the parallel common terminals is connected to the 14 ^# pin of the second linear voltage stabilizing chip V4, the other parallel common terminal is connected to ground, and the two ends of the capacitor C64 are respectively connected to the 20 ^# pin and the 3 ^# pin of the second linear voltage stabilizing chip V4. Pin connection, after resistor R32 and resistor R33 are connected in series, the non-series end of resistor R32 is connected to the 20 ^# pin of the second linear voltage stabilizing chip V4, and the non-series connection end of the resistor R33 is connected to the 7 ^# pin of the second linear voltage stabilizing chip V4. And 21 ^# pin connection, resistor R32 and resistor R33 are connected in series and the common point is connected to the 3 ^# pin of the second linear voltage stabilizing chip V4. One of the parallel common terminals after the capacitor C62 and capacitor C63 are connected in parallel is connected to the second linear voltage stabilizing chip V4. The 20 ^# pin and the other parallel common terminal are connected to the ground. The 20 ^# pin of the second linear voltage stabilizing chip V4 is connected to the 1 ^# pin. The 20 ^# pin of the second linear voltage stabilizing chip V4 is used as the second linear The -5V power output terminal of the voltage stabilizing chip V4.

The above embodiments are only used to illustrate the technical solution of the present invention, but not to limit it; although the present utility model has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still implement the foregoing implementations. The technical solutions described in the examples are modified, or some of the technical features are equivalently replaced; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims (9)

1. A carbon resistance temperature sensor constant current source circuit for low temperature measurement, comprising: the first operational amplifier U8, the second operational amplifier U9, the capacitor C123, the capacitor C124, the resistor R23 and the power supply circuit; 1 of the first operational amplifier U8 ^# Pin is grounded, 4 of the first operational amplifier U8 ^# Pin is connected with reference voltage, 8 of first operational amplifier U8 ^# Pin and 5 of first operational amplifier U8 ^# Pins are connected with a power supply circuit, one end of a capacitor C123 is connected with 8 of a first operational amplifier U8 ^# The other end of the capacitor C123 is grounded, and one end of the capacitor C124 is connected with 5 of the first operational amplifier U8 ^# Pin is connected, the other end of the capacitor C124 is grounded, 7 of the first operational amplifier U8 ^# The pin is connected with one end of a resistor R23, and the other end of the resistor R23 is connected with 3 of a second operational amplifier U9 ^# Pin connection, 4 of second operational amplifier U9 ^# Pin and 7 of second operational amplifier U9 ^# Pins are connected with a power supply circuit, 6 of a second operational amplifier U9 ^# Pin 6 with first op amp U8 ^# Pin connection, 2 of second operational amplifier U9 ^# Pin 6 with second operational amplifier U9 ^# The pins are connected; resistor R23 and 3 of second operational amplifier U9 ^# The common point of connection of the pins is used as the output end of the constant current source circuit.

2. The constant current source circuit according to claim 1, wherein the first operational amplifier U8 has a model AD8221 and the second operational amplifier U9 has a model AD8638.

3. The constant current source circuit according to claim 1, wherein the power supply circuit includes: a first voltage conversion circuit, a second voltage conversion circuit, a third voltage conversion circuit; the input end of the first voltage conversion circuit is connected with a 220V alternating current power supply, and the output end of the first voltage conversion circuit is respectively connected with the second voltage conversion circuit and the third voltage conversion circuit; 8 of the first operational amplifier U8 ^# The pin is connected with the output end of the second voltage conversion circuit, 5 of the first operational amplifier U8 ^# The pin is connected with the output end of the third voltage conversion circuit; 7 of the second operational amplifier U9 ^# The pin is connected with the output end of the second voltage conversion circuit and 4 of the second operational amplifier U9 ^# The pin is connected with the output end of the third voltage conversion circuit.

4. The constant current source circuit according to claim 3, wherein the first voltage conversion circuit includes: step-down chopper module V1, filter V2, fuse F1, electrolytic capacitor CE2, capacitor C54, capacitor C55, zener diode TVS9, zener diode TVS10; 3 of the filter V2 ^# Pin is connected with the live wire of 220V alternating current power supply, 2 of filter V2 ^# The pin is connected with the zero line of 220V alternating current power supply, 1 of the filter V2 ^# Pin is grounded, 4 of the filter V2 ^# Pin and 3 of step-down chopper module V1 ^# Pin connection, 5 of filter V2 ^# Pin and step-down chopper module V1 2 ^# Pin connection, 1 of filter V2 ^# The pin is grounded, and the cathode of the electrolytic capacitor CE1 is connected with 4 of the buck chopper module V1 ^# Pin, positive electrode of electrolytic capacitor CE1 is connected with 6 of step-down chopper module V1 ^# Pin, cathode of electrolytic capacitor CE2 is connected with 6 of step-down chopper module V1 ^# Pin, positive electrode of electrolytic capacitor CE2 is connected with 8 of step-down chopper module V1 ^# Pin, two ends of capacitor C54 are respectively connected with 4 of step-down chopper module V1 ^# 6 of pin and step-down chopper module V1 ^# Pin, two ends of capacitor C55 are respectively connected with 6 of step-down chopper module V1 ^# Pin and step-down chopper V1 8 ^# Pin, step-down chopper module V1 6 ^# The pin is grounded, one end of the voltage stabilizing diode TVS9 and 4 of the step-down chopper module V1 ^# The other end of the voltage stabilizing diode TVS9 is grounded, and one end of the voltage stabilizing diode TVS10 is connected with 8 of the step-down chopper module V1 ^# The other end of the voltage stabilizing diode TVS10 is grounded, and the pin is connected with 8 of the step-down chopper module V1 ^# The pin is used as the output end of the +12V power supply and is connected with the input end of the second voltage conversion circuit, and the 4 of the buck chopper module V1 ^# The pin is used as the output end of the-12V power supply and is connected with the input end of the third voltage conversion circuit.

5. The constant current source circuit according to claim 4, wherein the step-down chopper module V1 is a chopper 220-12/AC-DC module, and the filter V2 is an FC-LX1D filter.

6. The constant current source circuit according to claim 4, wherein the second voltage conversion circuit includes: the first linear voltage stabilizing chip V3, the capacitor C56, the capacitor C57, the capacitor C58, the capacitor C59, the capacitor C60, the capacitor C61, the resistor R30 and the resistor R31; 13 of the first linear voltage stabilizing chip V3 ^# Pins, 15 ^# Pins, 16 ^# The pins are connected together and then connected with the output end of the +12V power supply of the first voltage conversion circuit, one end of the capacitor C58 is connected with 13 of the first linear voltage stabilizing chip V3 ^# The other end of the pin and the capacitor C58 is grounded, and one end of the capacitor C59 is connected with 13 of the first linear voltage stabilizing chip V3 ^# The other end of the pin and the capacitor C59 is grounded, one end of the capacitor C60 and one end of the capacitor C61 are connected together and then connected with 14 of the first linear voltage stabilizing chip V3 ^# The other ends of the pin, the capacitor C60 and the capacitor C61 are grounded, and after the resistor R30 and the resistor R31 are connected in series, the non-series end of the resistor R30 and 1 of the first linear voltage stabilizing chip V3 ^# Pin connection, non-series grounding of the resistor R31, and 3 of the first linear voltage stabilizing chip V3 connected with the series common point of the resistor R30 and the resistor R31 ^# Pin, one of the parallel common terminals of the capacitor C56 and the capacitor C57 is connected in parallel with 1 of the first linear voltage stabilizing chip V3 ^# Pin, anotherA common ground connected in parallel, 1 of the first linear voltage stabilizing chip V3 ^# Pins and 20 ^# Pins are connected together, 6 of the first linear voltage stabilizing chip V3 ^# Pins, 7 ^# Pin and 10 ^# Pin grounding, 1 of first linear voltage stabilizing chip V3 ^# The pin is used as the +5V power supply output end of the first linear voltage stabilizing chip V3.

7. The constant current source circuit according to claim 6, wherein the first linear voltage regulator chip V3 has a type TPS7a4701.

8. The constant current source circuit according to claim 4, wherein the third voltage conversion circuit includes: the second linear voltage stabilizing chip V4, a capacitor C62, a capacitor C63, a capacitor C64, a capacitor C65, a capacitor C66, a capacitor C67, a capacitor C68, a resistor R32 and a resistor R33; 13 of the second linear voltage stabilizing chip V4 ^# Pins, 15 ^# Pins, 16 ^# The pins are connected together and then connected with the output end of the-12V power supply of the first voltage conversion circuit, one end of the capacitor C65 is connected with 13 of the second linear voltage stabilizing chip V4 ^# The other end of the pin and the capacitor C65 is grounded, and one end of the capacitor C66 is connected with 13 of the second linear voltage stabilizing chip V4 ^# The other end of the pin and the capacitor C66 is grounded, and one of the parallel common terminals after the capacitor C67 and the capacitor C68 are connected in parallel is connected with 14 of the second linear voltage stabilizing chip V4 ^# The pin and the other parallel common ground are grounded, and two ends of the capacitor C64 are respectively connected with 20 of the second linear voltage stabilizing chip V4 ^# Pin and 3 ^# The pin is connected, after the resistor R32 is connected in series with the resistor R33, the non-series end of the resistor R32 is connected with 20 of the second linear voltage stabilizing chip V4 ^# Pin connection, non-series connection end of resistor R33 and 7 of second linear voltage stabilizing chip V4 ^# Pin and 21 ^# Pin connection, resistor R32 and resistor R33 are connected in series and commonly connected with 3 of second linear voltage stabilizing chip V4 ^# Pin, one of the parallel common terminals of capacitor C62 and capacitor C63 is connected in parallel with 20 of the second linear voltage stabilizing chip V4 ^# Pin, another parallel common ground, 20 of the second linear voltage stabilizing chip V4 ^# Pin and 1 ^# Pins are connected together20 of the second Linear Voltage-stabilizing chip V4 ^# The pin is used as the-5V power supply output end of the second linear voltage stabilizing chip V4.

9. The constant current source circuit according to claim 8, wherein the second linear voltage regulator chip V4 has a type TPS7a3301.