Frequency converter

Abstract

The embodiment of the invention provides a frequency converter comprising a main control circuit which is electrically connected with an isolation amplification circuit, a communication circuit and a keyboard circuit; the isolation amplifying circuit is electrically connected to the driving circuit; the isolation amplifying circuit comprises an optical isolation amplifying chip, the input end of the optical isolation amplifying chip is electrically connected to a main control circuit, and the two output ends of the optical isolation amplifying chip are electrically connected to the positive input end and the negative input end of a first power operational amplifier through a first current-limiting resistor and a second current-limiting resistor respectively; and the output end of the first power operational amplifier is electrically connected to the driving circuit. The frequency converter realizes electrical isolation through the optical isolation amplification chip in the isolation amplification circuit, and is provided with the current-limiting resistor, so that the influence of pulse electromagnetic interference on the circuit can be effectively reduced, the soft fault occurrence probability is reduced, the circuit stability and the equipment reliability are improved, the service life of the equipment is prolonged, and the maintenance and repair cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of frequency converters, and in particular to a frequency converter. Background Art

[0002] Variable-frequency Drive (VFD) is a power control device that uses frequency conversion technology and microelectronics technology to control AC motors by changing the frequency of the motor's working power supply.

[0003] The inverter is mainly composed of rectification (AC to DC), filtering, inversion (DC to AC), braking unit, drive unit, detection unit, microprocessor unit, etc. The inverter adjusts the voltage and frequency of the output power supply by the internal IGBT opening and closing, and provides the required power supply voltage according to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation. In addition, the inverter has many protection functions, such as over-current, over-voltage, overload protection, etc. With the continuous improvement of industrial automation, inverters have also been widely used.

[0004] The current frequency converter needs to change the output power pulse frequency during operation, and many components in the circuit are easily affected by pulse electromagnetic interference, which can easily cause soft faults in circuit operation. Therefore, the present application proposes a frequency converter to at least partially solve the problems that may exist in the prior art. Summary of the invention

[0005] In view of the above problems, the present invention is proposed to provide a frequency converter that overcomes the above problems or at least partially solves the above problems, including:

[0006] A frequency converter, comprising:

[0007] A main control circuit, which is electrically connected to an isolation amplifier circuit, a communication circuit and a keyboard circuit;

[0008] The isolation amplifier circuit is electrically connected to the drive circuit;

[0009] Wherein, the isolation amplifier circuit comprises: an optical isolation amplifier chip, whose input end is electrically connected to the main control circuit, and whose two output ends are electrically connected to the positive input end and the negative input end of the first power amplifier through a first current limiting resistor and a second current limiting resistor respectively;

[0010] The output terminal of the first power operational amplifier is electrically connected to the driving circuit.

[0011] Optionally, it also includes an AI input circuit and an AO output circuit;

[0012] The AI ​​input circuit and the AO output circuit are electrically connected to the main control circuit.

[0013] Optionally, the communication circuit is RS485, comprising: an RS485 chip, whose input end is electrically connected to the main control circuit, whose A output end provides an RS485+ interface, and whose B output end provides an RS485- interface;

[0014] Wherein, the A output terminal is electrically connected to a pull-up resistor and a first filter capacitor, and is connected to an RS485+ interface via a third current limiting resistor;

[0015] The B output terminal is electrically connected to a pull-down resistor and a second filter capacitor, and is connected to an RS485 interface via a fourth current limiting resistor;

[0016] The A output terminal and the B output terminal are also electrically connected to a third filter capacitor.

[0017] Optionally, the keyboard circuit includes a common anode digital tube, a control end of which is electrically connected to a first triode, and an input end of which is electrically connected to a displacement buffer and a diode indicator light.

[0018] Optionally, the input end of the AI ​​input circuit to the output end of the AI ​​input circuit includes sequentially from the inductor to the first RC filter unit, to the fourth current limiting resistor, to the fifth current limiting resistor, to the + input end of the first front-stage operational amplifier, from the output end of the first front-stage operational amplifier to the - input end of the first front-stage operational amplifier and the sixth current limiting resistor, to the seventh current limiting resistor, to the + input end of the first rear-stage operational amplifier and the second RC filter unit, the output end of the first rear-stage operational amplifier to one end of the eighth current limiting resistor, and the other end of the eighth current limiting resistor is the output end of the AI ​​input circuit;

[0019] The other end of the eighth current limiting resistor is electrically connected to the -input terminal of the first post-stage operational amplifier.

[0020] Optionally, the AO output circuit comprises:

[0021] A second front-stage operational amplifier, whose + input terminal is electrically connected to the main control circuit through a ninth current-limiting resistor and a tenth current-limiting resistor connected in series, and whose output terminal is connected in series with an eleventh current-limiting resistor; a second front-stage operational amplifier, whose - input terminal is connected between the first voltage-dividing resistor and the second voltage-dividing resistor, the first voltage-dividing resistor is electrically connected to one end of the eleventh current-limiting resistor, and the other end of the eleventh current-limiting resistor provides a first output terminal of the AO output circuit;

[0022] A second post-stage operational amplifier, a + input terminal thereof, is electrically connected to the eleventh current limiting resistor through a twelfth current limiting resistor; a - input terminal of the second post-stage operational amplifier is grounded through a third voltage-dividing resistor, and is electrically connected to the emitter of the first transistor through a fourth voltage-dividing resistor; an output terminal of the second post-stage operational amplifier is electrically connected to the base of the first transistor through the twelfth current-limiting resistor;

[0023] The + input terminal of the second post-stage operational amplifier is electrically connected to the second output terminal of the AO output circuit through a thirteenth current-limiting resistor;

[0024] The second output end of the AO output circuit is also electrically connected to the emitter of the first transistor.

[0025] Optionally, a relay circuit is also included, which includes: a push-pull amplifier circuit, whose control end is electrically connected to the main control circuit, and whose output end is electrically connected to the trigger end of the relay, wherein the relay also provides a normally open end, a normally closed end and a common end.

[0026] The embodiments of the present invention have the following advantages:

[0027] In an embodiment of the present invention, the main control circuit is electrically connected to an isolation amplifier circuit, a communication circuit and a keyboard circuit; the isolation amplifier circuit is electrically connected to a drive circuit; wherein the isolation amplifier circuit comprises: an optical isolation amplifier chip, whose input end is electrically connected to the main control circuit, and whose two output ends are electrically connected to the positive input end and the negative input end of the first power amplifier through a first current limiting resistor and a second current limiting resistor, respectively; the output end of the first power amplifier is electrically connected to the drive circuit. The frequency converter realizes electrical isolation through the optical isolation amplifier chip in the isolation amplifier circuit, and sets a current limiting resistor, which can effectively reduce the impact of pulse electromagnetic interference on the circuit, reduce the probability of soft failure, improve circuit stability and equipment reliability, extend equipment life, and reduce maintenance and repair costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings required for use in the description of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0029] Figure 1 It is a schematic diagram of a module structure of a frequency converter provided by an embodiment of the present invention;

[0030] Figure 2 It is a schematic structural diagram of the first part of a main control circuit of a frequency converter provided by an embodiment of the present invention;

[0031] Figure 3 It is a schematic structural diagram of the first part of a main control circuit of a frequency converter provided by an embodiment of the present invention;

[0032] Figure 4 It is a schematic diagram of a communication circuit structure of a frequency converter provided by an embodiment of the present invention;

[0033] Figure 5It is a schematic diagram of the structure of an AO output circuit of a frequency converter provided by one embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of the structure of an AI input circuit of a frequency converter provided by an embodiment of the present invention;

[0035] Figure 7 It is a schematic diagram of a relay circuit structure of a frequency converter provided by an embodiment of the present invention;

[0036] Figure 8 This is a schematic diagram of the structure of an isolation amplifier circuit of a frequency converter provided by an embodiment of the present invention;

[0037] Fig. 9 It is a schematic diagram of a keyboard circuit structure of a frequency converter provided by an embodiment of the present invention;

[0038] Fig.10 The present invention is a schematic diagram of a drive circuit structure of a frequency converter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Embodiment 1

[0041] Reference Figures 1 to 10 As shown, a frequency converter provided by an embodiment of the present invention includes: a main control circuit 100, which is electrically connected to an isolation amplifier circuit 200, a communication circuit 300 and a keyboard circuit 400; the isolation amplifier circuit 200 is electrically connected to a drive circuit 500; wherein the isolation amplifier circuit 200 includes: an optical isolation amplifier chip U16, such as Figure 8 As shown, TLP7820 is preferred, its input end is electrically connected to the main control circuit 100, and its two output ends are electrically connected to the positive input end and negative input end of the first power amplifier U13, LF353 / SO-8 through the first current limiting resistor R38 and the second current limiting resistor R39 respectively; the output end of the first power amplifier U13, LF353 / SO-8 is electrically connected to the driving circuit 500. The optical isolation amplifier chip U16, its power supply end is electrically connected to a three-terminal regulator, its positive input end is electrically connected to the main control circuit 100, the output end corresponding to U, V, and W in the MCU main control unit, and the negative input end of the optical isolation amplifier chip U16 is grounded.

[0042] In this embodiment, a frequency converter is proposed, and an isolation amplifier circuit 200 is used in the circuit design. Its core component, the optical isolation amplifier chip U16, can electrically isolate the main control circuit 100 and the drive circuit 500. It can effectively prevent the conduction of pulse electromagnetic interference between these two key circuits, because optical isolation transmits information through optical signals, and optical signals are not affected by electromagnetic interference. The optical isolation amplifier chip U16 is preferably TLP7820, in which the input and output ends are in an isolated state, and are driven by light internally, and are not affected by external electromagnetic influences. For example, when the main control circuit 100 generates electromagnetic interference when changing the output power supply pulse frequency, the optical isolation amplifier chip U16 can prevent these interferences from being transmitted to the drive circuit 500, and vice versa.

[0043] A first current limiting resistor R38 and a second current limiting resistor R39 are provided between the optical isolation amplifier chip U16 and the first power amplifier U13. When an instantaneous overcurrent caused by pulse electromagnetic interference occurs in the circuit, the current limiting resistor can limit the current size, protect the optical isolation amplifier chip U16 and the first power amplifier U13 from large current shocks, thereby reducing soft faults caused by electromagnetic interference. The frequency converter achieves electrical isolation by isolating the optical isolation amplifier chip in the amplifier circuit and providing a current limiting resistor. It can effectively reduce the impact of pulse electromagnetic interference on the circuit, reduce the probability of soft faults, improve circuit stability and equipment reliability, extend equipment life, and reduce maintenance and repair costs.

[0044] It should be noted that a soft fault refers to an abnormal operating state that occurs accidentally during the operation of the device due to environmental or other unknown reasons, and without any hardware failure.

[0045] Embodiment 2

[0046] A frequency converter, wherein Figure 1 As shown, it also includes an AI input circuit 600 and an AO output circuit 700 ; the AI ​​input circuit 600 and the AO output circuit 700 are electrically connected to the main control circuit 100 .

[0047] like Figure 6As shown, the input end of the AI ​​input circuit 600 to the output end of the AI ​​input circuit 600 includes, in sequence, from the inductor L2, to the first RC filter unit, to the fourth current limiting resistor R93, to the fifth current limiting resistor R88, to the + input end of the first front-stage operational amplifier, from the output end of the first front-stage operational amplifier to the - input end of the first front-stage operational amplifier and the sixth current limiting resistor R277, to the seventh current limiting resistor R284, to the + input end of the first rear-stage operational amplifier and the second RC filter unit, the output end of the first rear-stage operational amplifier to one end of the eighth current limiting resistor R284, the other end of the eighth current limiting resistor R284 is the output end of the AI ​​input circuit 600; the other end of the eighth current limiting resistor R284 is electrically connected to the - input end of the first rear-stage operational amplifier.

[0048] In this embodiment, the AI ​​input circuit 600 is used to provide a dry contact circuit for an external input interface. Starting from the input end, the inductor L2 can block high-frequency interference signals, and multiple current-limiting resistors and RC filter units work together. For example, Figure 6 As shown, the first RC filter unit composed of capacitor C44 and resistor R94, the sixth current limiting resistor R277, the seventh current limiting resistor R284 and the second RC filter unit composed of capacitor C133 and resistor R276 can perform multiple filtering and current limiting processes on the input signal. This makes the analog signal input to the main control circuit 100 purer and more stable, effectively reduces the influence of external interference on the input signal, and improves the recognition and processing accuracy of the inverter for the input analog signal.

[0049] The structure of the first front-stage operational amplifier and the first rear-stage operational amplifier further enhances the signal amplification and processing capabilities, and can appropriately amplify weak input signals to meet the signal strength requirements of the main control circuit 100, ensuring that the signal will not fail due to interference.

[0050] As a preferred implementation, the AO output circuit 700 includes: a second front-stage operational amplifier, whose + input terminal is electrically connected to the main control circuit 100 through a ninth current limiting resistor R255 and a tenth current limiting resistor R258 connected in series, and whose output terminal is connected in series with an eleventh current limiting resistor R256; the second front-stage operational amplifier, whose - input terminal is connected between a first voltage-dividing resistor R257 and a second voltage-dividing resistor R270, the first voltage-dividing resistor R257 is electrically connected to one end of the eleventh current limiting resistor R256, and the other end of the eleventh current limiting resistor R256 provides a first output terminal AO1-U of the AO output circuit 700; a second rear-stage operational amplifier, whose + input terminal The -input terminal of the second post-stage operational amplifier is grounded through a third voltage-dividing resistor R260, and is electrically connected to the emitter of the first transistor Q2 through a fourth voltage-dividing resistor R83; the output terminal of the second post-stage operational amplifier is electrically connected to the base of the first transistor Q2 through a twelfth current-limiting resistor R271; the +input terminal of the second post-stage operational amplifier is electrically connected to the second output terminal AO1-I of the AO output circuit 700 through a thirteenth current-limiting resistor R81; the second output terminal AO1-I of the AO output circuit 700 is also electrically connected to the emitter of the first transistor Q2.

[0051] In the above-mentioned AO output circuit 700, by setting a plurality of current limiting resistors (such as the ninth current limiting resistor R255, the tenth current limiting resistor R258, the eleventh current limiting resistor R256, etc.), the current size can be limited to protect the circuit components from the impact of abnormally large currents. This can ensure the safety of the circuit when outputting signals, especially when the output signal changes or encounters interference, to prevent overcurrent from causing damage to the circuit.

[0052] The use of voltage-dividing resistors (such as the first voltage-dividing resistor R257, the second voltage-dividing resistor R270, the third voltage-dividing resistor R260, the fourth voltage-dividing resistor R83, etc.) can accurately control the voltage value of the output signal. The cooperation of the second front-stage operational amplifier and the second rear-stage operational amplifier can appropriately amplify and adjust the output signal, so that the AO output circuit 700 can output a more accurate analog signal. This is very important for inverter application scenarios that require precise output control (such as high-precision motor speed regulation, etc.), which can improve the quality and control accuracy of the inverter output signal, thereby improving the performance of the entire system. The introduction of the first transistor Q2 increases the flexibility and control ability of the circuit, and the output signal can be further adjusted and optimized according to the working state of the circuit, ensuring that the two output terminals AO1-U and AO1-I of the AO output circuit 700 output signals that meet the requirements, thereby improving the stability and reliability of the inverter output signal.

[0053] Embodiment 3

[0054] The communication circuit 300 is RS485, including: an RS485 chip, whose input end is electrically connected to the main control circuit 100, whose A output end provides an RS485+ interface, and whose B output end provides an RS485- interface; wherein, the A output end is electrically connected to a pull-up resistor R326 and a first filter capacitor C49, and is connected to the RS485+ interface through a third current limiting resistor R72; the B output end is electrically connected to a pull-down resistor R327 and a second filter capacitor C50, and is connected to the RS485- interface through a fourth current limiting resistor R75; the A output end and the B output end are also electrically connected to a third filter capacitor C79. Long-distance transmission can be performed through the above-mentioned RS485 communication, which can reach more than 1km; through the above-mentioned pull-up resistor R326 and the pull-down resistor R327 parallel filter capacitor, since the capacitor characteristic is that the voltage at both ends cannot suddenly change, it can hinder the voltage change rate. After being connected in parallel with the pull-up and pull-down resistors, the signal in the circuit can be filtered to make the output signal smoother. In addition, the pull-up and pull-down resistors can provide a discharge path for the capacitor, preventing the accumulation of charge on the capacitor from affecting the normal operation of the circuit or causing damage to other components.

[0055] As a preferred implementation method, Fig. 9 As shown, the keyboard circuit 400 includes a common anode digital tube, whose control end is electrically connected to a triode, such as Fig. 9 As shown, multiple control electrodes at the upper end of the above-mentioned common anode digital tube are respectively connected to multiple triodes, from Q12, Q15, Q17, Q18, and Q19, whose input ends are electrically connected to the displacement buffer U11, preferably 74HC595 and a diode indicator light, which are used to indicate the corresponding state of the display, and the operation of the corresponding display keyboard is displayed through the above-mentioned common anode digital tube, such as setting frequency, time and other parameters, and the above-mentioned 74HC595 is used as a displacement buffer for storing parameters.

[0056] As a preferred implementation method, Figure 7 As shown, a relay circuit is also included, which includes: a push-pull amplifier circuit, whose control end is electrically connected to the main control circuit 100, and whose output end is electrically connected to the trigger end of the relay, wherein the relay also provides a normally open end, a normally closed end and a common end.

[0057] The above relay circuit enables the inverter to have a new control dimension. The push-pull amplifier circuit, as a bridge connecting the main control circuit 100 and the relay trigger end, can effectively amplify the control signal output by the main control circuit 100 to ensure reliable triggering of the relay. The main control circuit 100 can control the on and off of the relay according to the operating state and preset parameters of the inverter to achieve flexible control of external devices or circuits; through the relay having a normally open end, a normally closed end and a common end, this structure can achieve a variety of safety protection and backup functions in circuit design. In normal operation, the normally open end or the normally closed end can be used to connect different circuit paths to achieve specific functional logic. When an abnormal situation occurs in the circuit (such as overload, short circuit, etc.), the relay can quickly switch the state to protect the inverter and related equipment from damage. For example, if the internal temperature of the inverter is detected to be too high, the main control circuit 100 can control the relay to switch to the backup cooling circuit connected to the normally closed end, start additional cooling measures, and thus ensure the stable operation of the system. For example, in some scenarios where it needs to be used in conjunction with multiple motors or different power devices, the relay can select the appropriate circuit connection method according to the instructions of the main control circuit 100 to achieve effective control of different devices, thereby improving the compatibility and adaptability of the inverter in complex systems.

[0058] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0059] It should be understood by those skilled in the art that the embodiments of the embodiments of the present invention may be provided as methods, devices, or computer program products. Therefore, the embodiments of the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the embodiments of the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0060] The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of the methods, terminal devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing terminal device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1A device that provides the functions specified in a block or multiple blocks.

[0061] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing terminal device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0062] These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device so that a series of operating steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing instructions for executing on the computer or other programmable terminal device to implement the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0063] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0064] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or terminal device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or terminal device including the elements.

[0065] The frequency converter provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A frequency converter, characterized in that: include: A main control circuit, which is electrically connected to an isolation amplifier circuit, a communication circuit and a keyboard circuit; The isolation amplifier circuit is electrically connected to the drive circuit; Wherein, the isolation amplifier circuit comprises: an optical isolation amplifier chip, whose input end is electrically connected to the main control circuit, and whose two output ends are electrically connected to the positive input end and the negative input end of the first power amplifier through a first current limiting resistor and a second current limiting resistor respectively; The output terminal of the first power operational amplifier is electrically connected to the driving circuit.

2. The frequency converter according to claim 1, characterized in that: It also includes AI input circuit and AO output circuit; The AI ​​input circuit and the AO output circuit are electrically connected to the main control circuit.

3. The frequency converter according to claim 1 or 2, characterized in that: The communication circuit is RS485, comprising: an RS485 chip, whose input end is electrically connected to the main control circuit, whose A output end provides an RS485+ interface, and whose B output end provides an RS485- interface; Wherein, the A output terminal is electrically connected to a pull-up resistor and a first filter capacitor, and is connected to an RS485+ interface via a third current limiting resistor; The B output terminal is electrically connected to a pull-down resistor and a second filter capacitor, and is connected to an RS485 interface via a fourth current limiting resistor; The A output terminal and the B output terminal are also electrically connected to a third filter capacitor.

4. The frequency converter according to claim 1, characterized in that: The keyboard circuit comprises a common anode digital tube, a control end of which is electrically connected to a first triode, and an input end of which is electrically connected to a displacement buffer and a diode indicator light.

5. The frequency converter according to claim 2, characterized in that: The input end of the AI ​​input circuit to the output end of the AI ​​input circuit includes sequentially from the inductor to the first RC filter unit, to the fourth current limiting resistor, to the fifth current limiting resistor, to the + input end of the first front-stage operational amplifier, from the output end of the first front-stage operational amplifier to the - input end of the first front-stage operational amplifier and the sixth current limiting resistor, to the seventh current limiting resistor, to the + input end of the first rear-stage operational amplifier and the second RC filter unit, the output end of the first rear-stage operational amplifier to one end of the eighth current limiting resistor, and the other end of the eighth current limiting resistor is the output end of the AI ​​input circuit; The other end of the eighth current limiting resistor is electrically connected to the -input terminal of the first post-stage operational amplifier.

6. The frequency converter according to claim 2, characterized in that: The AO output circuit comprises: A second front-stage operational amplifier, whose + input terminal is electrically connected to the main control circuit through a ninth current-limiting resistor and a tenth current-limiting resistor connected in series, and whose output terminal is connected in series with an eleventh current-limiting resistor; a second front-stage operational amplifier, whose - input terminal is connected between the first voltage-dividing resistor and the second voltage-dividing resistor, the first voltage-dividing resistor is electrically connected to one end of the eleventh current-limiting resistor, and the other end of the eleventh current-limiting resistor provides a first output terminal of the AO output circuit; A second post-stage operational amplifier, a + input terminal thereof, is electrically connected to the eleventh current limiting resistor through a twelfth current limiting resistor; a - input terminal of the second post-stage operational amplifier is grounded through a third voltage-dividing resistor, and is electrically connected to the emitter of the first transistor through a fourth voltage-dividing resistor; an output terminal of the second post-stage operational amplifier is electrically connected to the base of the first transistor through the twelfth current-limiting resistor; The + input terminal of the second post-stage operational amplifier is electrically connected to the second output terminal of the AO output circuit through a thirteenth current-limiting resistor; The second output end of the AO output circuit is also electrically connected to the emitter of the first transistor.

7. The frequency converter according to claim 1, characterized in that: It also includes a relay circuit, which includes: a push-pull amplifier circuit, whose control end is electrically connected to the main control circuit, and whose output end is electrically connected to the trigger end of the relay, wherein the relay also provides a normally open end, a normally closed end and a common end.

Images