CN214900173U

CN214900173U - Compressor control circuit

Info

Publication number: CN214900173U
Application number: CN202120701119.7U
Authority: CN
Inventors: 刘湘; 张琴兰
Original assignee: TCL Air Conditioner Zhongshan Co Ltd
Current assignee: TCL Air Conditioner Zhongshan Co Ltd
Priority date: 2021-04-06
Filing date: 2021-04-06
Publication date: 2021-11-26
Anticipated expiration: 2031-04-06

Abstract

The application discloses a compressor control circuit. The circuit that this application embodiment provided includes: busbar voltage detection module and control module, wherein, busbar voltage detection module with control module connects, control module includes: the voltage comparison device comprises a reference voltage unit, a voltage comparison unit and a micro control unit, wherein the reference voltage unit is connected with the voltage comparison unit, and the voltage comparison unit is connected with the micro control unit. According to the embodiment of the application, after the shutdown instruction for controlling the compressor to be shut down is received, the current bus voltage of the compressor is obtained instead of the shutdown operation, and the compressor is controlled to be shut down only when the current bus voltage is smaller than or equal to the voltage threshold. The bus voltage over-high protection caused by shutdown is effectively avoided.

Description

Compressor control circuit

Technical Field

The application relates to the technical field of compressors, in particular to a compressor control circuit.

Background

With the issuance of new energy efficiency standards in China, various air conditioner manufacturers adopt high-energy-efficiency compressors to pursue higher energy efficiency, but the permanent magnet materials and coils used by the high-energy-efficiency compressors are different from those of a common compressor, the counter electromotive force of the high-energy-efficiency compressors is also higher, the counter electromotive force of the compressors is also higher when the compressors are shut down at the same frequency such as 100Hz, the conventional air conditioners are provided with a bus voltage overhigh protection logic for protecting devices on a control panel from high-voltage impact, namely protection is reported when the bus voltage is detected to be greater than a certain set threshold value, so that the high-back-electromotive-force compressors report faults when the compressors are shut down at high frequency each time, the devices on the control panel are frequently impacted to cause the service life of the devices to be damaged, and the use of other functions is also influenced due to the overhigh protection of the bus voltage.

SUMMERY OF THE UTILITY MODEL

In order to solve the above technical problem or at least partially solve the above technical problem, the present application provides a compressor control circuit.

According to an aspect of an embodiment of the present application, there is provided a compressor control circuit, including: busbar voltage detection module and control module, wherein, busbar voltage detection module with control module connects, control module includes: the voltage comparison device comprises a reference voltage unit, a voltage comparison unit and a micro control unit, wherein the reference voltage unit is connected with the voltage comparison unit, and the voltage comparison unit is connected with the micro control unit;

the bus voltage detection module is used for performing first voltage reduction operation on the current first bus voltage of the compressor under the condition that the compressor receives a stop instruction to obtain a second bus voltage, and inputting the second bus voltage into the control module;

the voltage comparison unit is used for acquiring the voltage threshold from the reference voltage unit, comparing the second bus voltage with the voltage threshold to obtain a comparison result, and inputting the comparison result into the micro control unit;

and the micro control unit is used for controlling the compressor to stop under the condition that the second bus voltage is determined to be less than or equal to the voltage threshold according to the comparison result.

Further, the circuit further comprises: the device comprises a voltage input module, a filtering module and a PFC module, wherein the voltage input module is connected with the filtering module, and the filtering module is connected with the PFC module;

the filtering module is used for filtering the voltage input by the voltage input module and inputting the filtered voltage into the PFC module;

and the PFC module is used for rectifying and boosting the filtered voltage to obtain a third voltage, and inputting the third voltage into the bus voltage detection module.

Further, the voltage input module includes: the filter module comprises a first voltage input end and a second voltage input end, wherein the first voltage input end and the second voltage input end are connected with the filter module.

Further, the filtering module includes: the fuse protector comprises a fuse, a first inductor, a thermistor, a first capacitor and a second capacitor;

the input end of the fuse is connected with the first voltage input end of the voltage input module, the output end of the fuse is connected with the input end of the first inductor, the output end of the first inductor is respectively connected with the input end of the thermistor and the output end of the second capacitor, and the output end of the thermistor is connected with the PFC module;

the input end of the first capacitor is connected with the second voltage input end of the voltage input module, the output end of the first capacitor is connected with the input end of the second capacitor, and the output end of the second capacitor is connected with the PFC module.

Further, the PFC module comprises: the bidirectional trigger diode, the second inductor, the disposable fuse, the insulated gate bipolar transistor, the diode and the polar capacitor are connected in series;

the first access end of the bidirectional trigger diode is connected with the output end of a thermistor in the filter module, the second access end of the bidirectional trigger diode is respectively connected with the output end of a second capacitor in the filter module and the second voltage input end of the voltage input module, the third access end of the bidirectional trigger diode is connected with the output end of the disposable fuse, and the output end of the bidirectional trigger diode is connected with the input end of a second inductor;

the output end of the second inductor is connected with the input end of the diode, the output end of the diode is respectively connected with the anode of the polar capacitor, the bus voltage detection module, the output end of the second inductor is also connected with the collector of the insulated gate bipolar transistor, the emitter of the insulated gate bipolar transistor is connected with the input end of the disposable fuse, and the cathode of the polar capacitor is grounded.

Further, the bus voltage detection module includes: the direct-current power supply and the voltage reduction module are connected, the voltage reduction module comprises a plurality of resistors connected in series, the plurality of resistors connected in series are used for executing a first voltage reduction operation on the first bus voltage to obtain a second bus voltage, and the first bus voltage is the sum of the voltage of the direct-current power supply and the third voltage.

Further, the reference voltage unit includes: the power supply, the fifth resistor, the sixth resistor and the voltage follower are connected;

the input end of the sixth resistor is connected with the power supply, and the output end of the sixth resistor is respectively connected with the non-inverting input end of the voltage follower, the input end of the fifth resistor and the output end node of the fifth resistor;

wherein the inverting input end of the voltage follower and the input end of the voltage follower are connected to the voltage comparison module.

Further, the voltage comparing unit includes: the circuit comprises a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a third capacitor, a fourth capacitor, a voltage comparator and a triode;

the input end of the seventh resistor is connected with the output end of the voltage reduction unit in the bus voltage detection module, and the output section of the seventh resistor is respectively connected with the input end of the third capacitor and the non-inverting input end of the voltage comparator;

the reverse input end of the voltage comparator is connected with the output end of a voltage follower in the reference voltage module, the output end of the voltage comparator is respectively connected with the output end of an eighth resistor and the base electrode of the triode, the output end of the eighth resistor is connected with the input end of a tenth resistor, the output end of the tenth resistor is connected with the collector electrode of the triode, and the emitter electrode of the triode is grounded;

the output end of the tenth resistor is further connected with the input end of the ninth resistor, and the output end of the ninth resistor is respectively connected with the fourth capacitor and the micro control unit.

According to another aspect of the embodiments of the present application, there is also provided a storage medium including a stored program that executes the above steps when the program is executed.

According to another aspect of the embodiments of the present application, there is also provided an electronic apparatus, including a processor, a communication interface, a memory, and a communication bus, where the processor, the communication interface, and the memory complete communication with each other through the communication bus; wherein: a memory for storing a computer program; a processor for executing the steps of the method by running the program stored in the memory.

Embodiments of the present application also provide a computer program product containing instructions, which when run on a computer, cause the computer to perform the steps of the above method.

Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages: according to the embodiment of the application, after the shutdown instruction for controlling the compressor to be shut down is received, the current bus voltage of the compressor is obtained instead of the shutdown operation, and the compressor is controlled to be shut down only when the current bus voltage is smaller than or equal to the voltage threshold. The bus voltage over-high protection caused by shutdown is effectively avoided.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

Fig. 1 is a block diagram of a compressor control circuit according to an embodiment of the present disclosure;

FIG. 2 is a schematic diagram of a compressor control circuit according to an embodiment of the present disclosure;

FIG. 3 is a flow chart of a compressor control method according to an embodiment of the present disclosure;

fig. 4 is a block diagram of a compressor control device according to an embodiment of the present application.

Detailed Description

In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application, it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments, and the illustrative embodiments and descriptions thereof of the present application are used for explaining the present application and do not constitute a limitation to the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another similar entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The embodiment of the application provides a compressor control circuit, a compressor control method, a compressor control device, electronic equipment and a storage medium. The embodiment of the utility model provides a method can be applied to the electronic equipment of arbitrary needs, for example, can be for electronic equipment such as server, terminal, do not do specific limit here, for the description convenience, follow-up electronic equipment for short.

Fig. 1 is a schematic block diagram of a compressor control circuit according to an embodiment of the present disclosure, and as shown in fig. 1, the compressor control circuit according to the embodiment of the present disclosure includes: a bus voltage detection module 40 and a control module 50;

the bus voltage detection module 40 is configured to, when the compressor receives a shutdown instruction, perform a first voltage reduction operation on a current first bus voltage of the compressor to obtain a second bus voltage, and input the second bus voltage to the control module 50;

and a control module 50 for controlling the compressor to stop if the second bus voltage is less than or equal to the voltage threshold.

As shown in fig. 1, the circuit in the embodiment of the present application further includes: the power supply comprises a voltage input module 10, a filtering module 20 and a PFC module 30, wherein the voltage input module 10 is connected with the filtering module 20, and the filtering module 20 is connected with the PFC module 30;

the filtering module 20 is configured to filter the voltage input by the voltage input module, and input the filtered voltage to the PFC module;

and the PFC module 30 is configured to rectify and boost the filtered voltage to obtain a third voltage, and input the third voltage to the bus voltage detection module.

As shown in fig. 2, the voltage input module in the embodiment of the present application includes: the filter module comprises a first voltage input end L and a second voltage input end N, wherein the first voltage input end L and the second voltage input end N are both connected with the filter module.

As shown in fig. 2, the filtering module of the embodiment of the present application includes: the fuse FU, the first inductor L1, the thermistor PTC, the first capacitor C1 and the second capacitor C2;

the input end of the fuse FU is connected with a first voltage input end L of the voltage input module, the output end of the fuse FU is connected with the input end of a first inductor L1, the output end of the first inductor L1 is respectively connected with the input end of a thermistor PTC and the output end of a second capacitor C2, and the output end of the thermistor PTC is connected with the PFC module;

the input end of the first capacitor L1 is connected to the second voltage input end N of the voltage input module, the output end of the first capacitor C1 is connected to the input end of the second capacitor C2, and the output end of the second capacitor C2 is connected to the PFC module.

As shown in fig. 2, the PFC module in the embodiment of the present application includes: the bidirectional trigger diode DB, the second inductor L2, the disposable fuse RS, the insulated gate bipolar transistor IGBT, the diode D and the polar capacitor E;

the first access end of the bidirectional trigger diode DB is connected with the output end of a thermistor in the filter module, the second access end of the bidirectional trigger diode DB is respectively connected with the output end of a second capacitor in the filter module and the second voltage input end of the voltage input module, the third access end of the bidirectional trigger diode DB is connected with the output end of the disposable fuse RS, and the output end of the bidirectional trigger diode DB is connected with the input end of a second inductor L2;

the output end of the second inductor L2 is connected with the input end of a diode D, the output end of the diode D is respectively connected with the anode of a polar capacitor E and a bus voltage detection module, the output end of the second inductor L2 is also connected with the collector of an insulated gate bipolar transistor IGBT, and the emitter of the insulated gate bipolar transistor IGBT is connected with the input end of a disposable fuse RS and is grounded with the cathode of the polar capacitor E.

As shown in fig. 2, the bus voltage detection module includes: the direct-current power supply VDC and the voltage reduction module are connected, wherein the voltage reduction module comprises a plurality of resistors connected in series, the plurality of resistors connected in series are used for executing first voltage reduction operation on first bus voltage to obtain second bus voltage, and the first bus voltage is the sum of the voltage of the direct-current power supply and third voltage.

The voltage reduction module in the embodiment of the present application includes four resistors connected in series, where the four resistors are a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4; the first voltage reduction operation referred to in the embodiment of the present application specifically includes: and reducing the resistance values of the four series resistors. Because the current that direct current power VCC provided is fixed, consequently the resistance that reduces the resistance can realize the step-down to first busbar voltage.

The input end of the first resistor R1 is connected with the output end of the diode D in the PFC module and the direct-current power supply VDC respectively, the output end of the first resistor R1 is connected with the input end of the second resistor R2, the output end of the second resistor R2 is connected with the input end of the third resistor R3, the output end of the third resistor R3 is connected with the input end of the fourth resistor R4 and the voltage comparison module respectively, and the output end of the fourth resistor R4 is grounded.

It is understood that the second bus voltage is a sum of the voltage of the dc power VDC and the third voltage, and is a voltage dropped by the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4.

In an embodiment of the present application, the control module includes: the device comprises a reference voltage unit, a voltage comparison unit and a micro control unit, wherein the reference voltage unit is connected with the voltage comparison unit, and the voltage comparison unit is connected with the micro control unit;

the voltage comparison unit is used for acquiring a voltage threshold value from the reference voltage unit, comparing the voltage of the second bus with the voltage threshold value to obtain a comparison result, and inputting the comparison result into the micro control unit;

As shown in fig. 2, the reference voltage unit in the embodiment of the present application includes: a power supply VCC, a fifth resistor R5, a sixth resistor R6, and a voltage follower IC 2;

the input end of a sixth resistor R6 is connected with a power supply VCC, the output end of the sixth resistor R6 is respectively connected with the non-inverting input end of a voltage follower IC2, the input end of a fifth resistor R5 and the output end node of the fifth resistor R5;

the inverting input terminal of the voltage follower IC2 and the input terminal of the voltage follower IC2 are connected to the voltage comparison module.

It is understood that the voltage threshold is a voltage obtained by the voltage follower IC2 after the voltage of the power source VCC is divided by the fifth resistor R5 and the sixth resistor R6.

As shown in fig. 2, the voltage comparing unit in the embodiment of the present application includes: a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, a third capacitor C3, a fourth capacitor C4, a voltage comparator IC1 and a triode Q1;

the input end of the seventh resistor R7 is connected with the output end of the third resistor R3 in the bus voltage detection module, and the output end of the seventh resistor R7 is respectively connected with the input end of the third capacitor C3 and the non-inverting input end of the voltage comparator IC 1;

the reverse input end of the voltage comparator IC1 is connected with the output end of the voltage follower IC2 in the reference voltage module, the output end of the voltage comparator IC1 is respectively connected with the output end of the eighth resistor R8 and the base electrode of the triode Q1, the output end of the eighth resistor R8 is connected with the input end of the tenth resistor R10, the output end of the tenth resistor R10 is connected with the collector electrode of the triode Q1, and the emitter electrode of the triode Q1 is grounded;

the output end of the tenth resistor R10 is further connected to the input end of the ninth resistor R9, and the output end of the ninth resistor R9 is connected to the fourth capacitor C4 and the micro-control unit, respectively.

In this embodiment, the micro control unit is an MCU (microcontroller unit), a TZ pin is provided in the micro control unit, after the comparator IC1 compares the second bus voltage with the voltage threshold, the comparator outputs a pull-up signal, so the TZ pin detected by the MCU is always at a high level, and when the voltage at the forward input terminal of the comparator (the second bus voltage) is higher than the voltage at the reverse input terminal (the voltage threshold), the triode Q1 inputs a low level and outputs a high level.

In the embodiment of the application, when a compressor stop command is received, the current operation frequency is judged firstly, and if the current operation frequency is smaller than or equal to a preset frequency threshold, the compressor executes the stop command and stops immediately. If the current running frequency is greater than the preset frequency threshold, the TZ of the micro control unit detects whether level conversion exists or not (the pin is set to be triggered by a level falling edge in a program), if the level conversion is detected, the current bus voltage value is judged to be smaller than the preset bus voltage threshold, an instruction for closing the compressor is sent out, the compressor is turned off in interruption, the TZ pin is set to be an interruption pin triggered by the outside in the program, namely once the pin is detected to have the level conversion, a preset interruption service function is entered immediately, and a shutdown command is executed in the interruption service function, so that the bus voltage is shut down immediately when being lower than the preset voltage value, almost no time delay is needed, and the bus voltage can not be shut down when being overshot to be too high. If no level conversion is detected, the current bus voltage value is judged to be larger than the preset bus voltage threshold value, and then no instruction for closing the compressor is sent out, so that the bus voltage is prevented from being directly shut down at a higher point.

According to an aspect of an embodiment of the present application, there is provided an embodiment of a method for controlling a compressor, and fig. 3 is a flowchart of the method for controlling a compressor according to the embodiment of the present application, as shown in fig. 3, the method includes:

step S11, receiving a stop instruction, wherein the stop instruction is used for instructing the compressor to stop running;

step S12, responding to the stop command, and performing first voltage reduction operation on the current first bus voltage of the compressor to obtain a second bus voltage;

in the embodiment of the present application, the first voltage reduction operation is performed on the current first bus voltage of the compressor to obtain the second bus voltage, and the method includes the following steps a1-a 2:

step A1, detecting the current running frequency of the compressor;

and step A2, performing a first voltage reduction operation on the current first bus voltage of the compressor to obtain a second bus voltage under the condition that the current running frequency is greater than a preset frequency threshold. The first voltage reduction operation referred to in the embodiment of the present application specifically includes: and reducing the resistance values of the four series resistors. Because the current that direct current power VCC provided is fixed, consequently the resistance that reduces the resistance can realize the step-down to first busbar voltage.

In the embodiment of the present application, when the current operating frequency is greater than the preset frequency threshold, it indicates that there is a possibility that the compressor is stopped at the current moment to damage internal components of the compressor, and if the compressor is stopped, the function of the compressor may be affected subsequently. Therefore, when the current operating frequency is greater than the preset frequency threshold, the first bus voltage inside the compressor needs to be acquired, and the acquired first bus voltage is reduced to obtain the second voltage.

And step S13, controlling the compressor to stop when the second bus voltage is less than or equal to the voltage threshold.

In the embodiment of the application, if the current operating frequency rain is larger than the preset frequency threshold and the second bus voltage is smaller than the voltage threshold, the bus voltage overhigh protection caused by shutdown can not occur.

In another embodiment of the present application, after detecting the current operating frequency of the compressor, the method further includes the following step a 3:

and step A3, controlling the compressor to stop when the current running frequency is less than or equal to the preset frequency threshold.

In the embodiment of the present application, when the current operating frequency is less than or equal to the preset frequency threshold, it indicates that the shutdown of the compressor at the current time does not cause damage to the internal components of the compressor. Therefore, when the current running frequency is less than or equal to the preset frequency threshold value, the compressor can be directly controlled to immediately execute the stop operation.

In another embodiment of the present application, after performing the first step-down operation on the current first bus voltage of the compressor to obtain the second bus voltage, the method further includes the following steps B1-B2:

step B1, under the condition that the voltage of the second bus is larger than the voltage threshold, the compressor continues to operate;

and step B2, in the running process of the compressor, carrying out second voltage reduction operation on the second bus voltage, and controlling the compressor to stop until the obtained third bus voltage is less than or equal to the voltage threshold. The second voltage reduction operation referred to in the embodiment of the present application specifically includes: and the resistance values of the four series resistors are reduced again so as to realize the voltage reduction of the second bus voltage.

In the embodiment of the application, after the current operating frequency of the compressor is obtained, the current operating frequency is compared with a preset frequency threshold, if the current operating frequency is greater than the preset frequency threshold, and the second bus voltage is greater than a voltage threshold, the compressor needs to be controlled to continue to operate at the moment, the resistance value of the voltage reduction unit in the bus voltage detection module is adjusted to execute the voltage reduction operation, and the compressor is controlled to stop until the obtained third bus voltage is less than or equal to the voltage threshold.

It should be noted that, when the current operating frequency is greater than the preset frequency threshold and the second bus voltage is greater than the voltage threshold, the shutdown may cause damage to devices of the circuit board in the compressor.

According to the embodiment of the application, after the shutdown instruction for controlling the compressor to be shut down is received, the current bus voltage of the compressor is obtained instead of the shutdown operation, and the compressor is controlled to be shut down only when the current bus voltage is smaller than or equal to the voltage threshold. The bus voltage over-high protection caused by shutdown is effectively avoided.

Fig. 4 is a block diagram of a compressor control apparatus according to an embodiment of the present application, which may be implemented as part or all of an electronic device by software, hardware, or a combination of the two. As shown in fig. 4, the apparatus includes:

a receiving module 41, configured to receive a shutdown instruction, where the shutdown instruction is used to instruct the compressor to stop operating;

a response module 42, configured to respond to the shutdown instruction, perform a first voltage reduction operation on a current first bus voltage of the compressor, so as to obtain a second bus voltage;

a control module 43 for controlling the compressor to stop if the second bus voltage is less than or equal to a voltage threshold.

The above description is only for the preferred embodiment of the present application, and is not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application are included in the protection scope of the present application.

The above description is merely exemplary of the present application and is presented to enable those skilled in the art to understand and practice the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A compressor control circuit, comprising: busbar voltage detection module and control module, wherein, busbar voltage detection module with control module connects, control module includes: the voltage comparison device comprises a reference voltage unit, a voltage comparison unit and a micro control unit, wherein the reference voltage unit is connected with the voltage comparison unit, and the voltage comparison unit is connected with the micro control unit;

the voltage comparison unit is used for acquiring a voltage threshold value from the reference voltage unit, comparing the second bus voltage with the voltage threshold value to obtain a comparison result, and inputting the comparison result into the micro control unit;

2. The circuit of claim 1, further comprising: the device comprises a voltage input module, a filtering module and a PFC module, wherein the voltage input module is connected with the filtering module, and the filtering module is connected with the PFC module;

3. The circuit of claim 2, wherein the voltage input module comprises: the filter module comprises a first voltage input end and a second voltage input end, wherein the first voltage input end and the second voltage input end are connected with the filter module.

4. The circuit of claim 3, wherein the filtering module comprises: the fuse protector comprises a fuse, a first inductor, a thermistor, a first capacitor and a second capacitor;

5. The circuit of claim 4, wherein the PFC module comprises: the bidirectional trigger diode, the second inductor, the disposable fuse, the insulated gate bipolar transistor, the diode and the polar capacitor are connected in series;

6. The circuit of claim 5, wherein the bus voltage detection module comprises: the direct-current power supply and the voltage reduction module are connected, the voltage reduction module comprises a plurality of resistors connected in series, the plurality of resistors connected in series are used for executing a first voltage reduction operation on the first bus voltage to obtain a second bus voltage, and the first bus voltage is the sum of the voltage of the direct-current power supply and the third voltage.

7. The circuit of claim 6, wherein the reference voltage unit comprises: the power supply, the fifth resistor, the sixth resistor and the voltage follower are connected;

8. The circuit of claim 7, wherein the voltage comparison unit comprises: the circuit comprises a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a third capacitor, a fourth capacitor, a voltage comparator and a triode;