Speed measuring circuit and brushless motor

Abstract

The embodiment of the utility model provides a speed measuring circuit and a brushless motor, and the circuit comprises an induction circuit which is coupled with the brushless motor; the acquisition module is used for acquiring alternating-current signals associated with the rotating speed of the brushless motor; the inverting amplification circuit is respectively connected with the induction circuit and a biasing circuit and is used for amplifying the alternating current signal according to the bias voltage provided by the biasing circuit; and the comparison circuit is respectively connected with the inverting amplification circuit and the biasing circuit, and is used for obtaining a square wave signal with the same rotating frequency as the brushless rotating machine according to the bias voltage and the amplified alternating current signal, so as to obtain the rotating speed information of the brushless motor. The problem that an additional auxiliary device is needed when the rotating speed of the brushless motor is measured in the prior art is solved. Through cooperative work of the induction circuit, the anti-phase amplification circuit and the comparison circuit, a variable magnetic field generated when a motor rotor rotates can be accurately detected, an alternating current signal related to the rotating speed is generated, and the rotating speed of the motor is obtained according to the alternating current signal.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of brushless motor, and particularly relates to a speed measurement circuit and a brushless motor. BACKGROUND

[0002] With the development of modern industrial automation and intelligence, brushless motors have been widely used in various application fields such as unmanned aerial vehicles, electric vehicles, household appliances and industrial robots due to their high efficiency, long service life, low maintenance and high reliability. A brushless DC motor (BLDC) is a kind of DC motor, which controls the rotation of the rotor through an electronic commutator (instead of a mechanical brush). Compared with brush motors, brushless motors have higher efficiency, longer service life, lower maintenance requirements and higher reliability. The speed measurement of brushless motors is one of the key technologies in their control and application, and accurate speed measurement is essential for precise control of the motor.

[0003] In the related art, the speed measurement methods of brushless motors mainly include Hall effect sensors, optical encoders and magnetic encoders. Although these methods can meet the demand of speed measurement to some extent, they also have some shortcomings. For example, the Hall effect sensor needs to install multiple Hall elements inside the motor, which increases the complexity and cost of the motor; although the optical encoder and the magnetic encoder have high precision, they are highly sensitive to the external environment and are easily affected by dust, oil stains and other pollution, resulting in unstable measurement results. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present disclosure is to provide a speed measurement circuit and a brushless motor to solve the problems in the related art.

[0005] The first aspect of the present disclosure provides a speed measurement circuit, wherein the speed measurement circuit is used for the speed measurement of a brushless motor; the speed measurement circuit comprises:

[0006] an induction circuit coupled with the brushless motor, for obtaining an alternating current signal associated with the speed of the brushless motor;

[0007] an inverting amplification circuit connected with the induction circuit and a bias circuit respectively, for amplifying the alternating current signal according to a bias voltage provided by the bias circuit;

[0008] a comparison circuit connected with the inverting amplification circuit and the bias circuit respectively, for obtaining a square wave signal with the same rotation frequency as the brushless motor according to the bias voltage and the amplified alternating current signal, so as to obtain the speed information of the brushless motor.

[0009] In the embodiments of the first aspect, the induction circuit comprises:

[0010] an inductive inductor coupled to the brushless motor, one end of the inductive inductor coupled to a first input of the inverting amplifier circuit, another end of the inductive inductor coupled to a second input of the inverting amplifier circuit via a first capacitor.

[0011] In an embodiment of the first aspect, the biasing circuit comprises:

[0012] a first resistor, one end of the first resistor grounded, another end of the first resistor coupled to the first input of the inverting amplifier circuit;

[0013] a second resistor, one end of the second resistor coupled to a first external power source, another end of the first resistor coupled to the first input.

[0014] In an embodiment of the first aspect, the biasing circuit further comprises a second capacitor, one end of the second capacitor grounded, another end of the second capacitor coupled to the first input.

[0015] In an embodiment of the first aspect, the inverting amplifier circuit comprises:

[0016] an inverting amplifier, comprising a non-inverting input, an inverting input, and an inverting output; the non-inverting input coupled to the biasing circuit;

[0017] an input resistor, one end of the input resistor coupled to the inductive inductor, another end of the input resistor coupled to the inverting input;

[0018] a first feedback resistor, one end of the first feedback resistor coupled to the inverting input, another end of the first feedback resistor coupled to the inverting output.

[0019] In an embodiment of the first aspect, the inverting amplifier circuit further comprises a third capacitor, one end of the third capacitor coupled to the inverting input, another end of the third capacitor coupled to the inverting output.

[0020] In an embodiment of the first aspect, the comparison circuit comprises:

[0021] a comparator, the comparison circuit comprising a first signal input, a second signal input, and a comparison output; the first signal input coupled to the biasing circuit, the second signal input coupled to the first output of the inverting amplifier circuit;

[0022] a second feedback resistor, one end of the second feedback resistor coupled to the first signal input, another end of the second feedback resistor coupled to the comparison output.

[0023] In an embodiment of the first aspect, the comparison circuit comprises a fourth capacitor coupled between the first output of the inverting amplification circuit and the second signal input.

[0024] In an embodiment of the first aspect, a master unit is further included, coupled to the comparison circuit, for obtaining the speed information of the brushless motor according to the square wave signal.

[0025] The second aspect of the present disclosure provides a brushless motor, wherein the brushless motor comprises the speed measurement circuit according to any one of the above embodiments.

[0026] The present disclosure has the following advantages: the problem of requiring additional auxiliary devices for measuring the speed of a brushless motor in the prior art is solved. Through the cooperative work of the induction circuit, the inverting amplification circuit and the comparison circuit, the changing magnetic field generated when the motor rotor rotates can be accurately detected, an alternating current signal related to the speed can be generated, and the speed of the motor can be obtained according to the alternating current signal. The speed measurement circuit can be adapted to various application scenarios, and the actual speed of the motor during operation can be accurately measured even if the motor is integrated inside a product. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 FIG. 1 shows a structural block diagram of a speed measurement circuit according to an embodiment of the present disclosure.

[0028] Figure 2 FIG. 2 shows a schematic diagram of the circuit connection of a speed measurement circuit according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0029] The embodiments of the present disclosure are described below with reference to specific examples. Those skilled in the art can easily understand other advantages and effects of the present disclosure from the disclosed information. The present disclosure can also be implemented or applied in different specific embodiments or application modules, and the details in the present disclosure can be modified or changed according to different views and application modules without departing from the spirit of the present disclosure. It should be noted that the embodiments in the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0030] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the present disclosure. The present disclosure can be embodied in various different forms, and is not limited to the embodiments described herein.

[0031] In the description of the present disclosure, the expressions "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like mean that the specific features, structures, materials or characteristics represented in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. Also, the specific features, structures, materials or characteristics represented can be combined in an appropriate manner in any one or a group of embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples represented in the present disclosure and the features of the different embodiments or examples without contradiction.

[0032] In addition, the terms "first", "second", are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "a group" is two or more, unless specifically limited.

[0033] In order to clearly illustrate the present disclosure, devices irrelevant to the description are omitted, and the same reference numerals are given to the same or similar constituent elements throughout the description.

[0034] Throughout the description, when it is said that a device is "connected" to another device, it includes not only the case of "direct connection", but also the case of "indirect connection" in which other elements are placed therebetween. In addition, when it is said that a device "includes" a certain constituent element, unless specifically stated to the contrary, other constituent elements are not excluded, but it means that other constituent elements can also be included.

[0035] Although the terms first, second, and the like are used herein to refer to various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first interface and a second interface, and the like are indicated. Furthermore, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including" mean that the features, steps, operations, elements, modules, items, species, and / or groups thereof are present, but do not exclude the presence or addition of one or more other features, steps, operations, elements, modules, items, species, and / or groups thereof. The terms "or" and "and / or" as used herein are to be interpreted as inclusive, or meaning either or any combination. Therefore, "A, B or C" or "A, B and / or C" means "any of the following: A; B; C; A and B; A and C; B and C; A, B and C". This exception occurs only when the combination of elements, functions, steps or operations is inherently mutually exclusive.

[0036] The professional terms used herein are used only to refer to specific embodiments and are not intended to limit the present disclosure. The singular form used herein includes the plural form unless the context clearly indicates the opposite. The meaning of "include" used in the specification is to embody specific features, regions, integers, steps, operations, elements, and / or components, and is not to exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0037] Although not differently defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. Terms defined in commonly used dictionaries are to be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the presently disclosed message, unless defined otherwise, and should not be over-interpreted as ideally or very formally defined.

[0038] With the development of modern industrial automation and intelligence, brushless motors have been widely used in various application fields such as unmanned aerial vehicles, electric vehicles, household appliances, industrial robots, etc. due to their high efficiency, long service life, low maintenance and high reliability. The speed measurement of brushless motor is one of the key technologies in its control and application, and accurate speed measurement is essential for precise control of the motor.

[0039] Traditional brushless motor speed measurement methods include various ways, each of which needs to increase additional auxiliary devices to realize the measurement of the speed. For example, a reflective sticker is pasted on the motor rotor, and an infrared laser emitter and receiver are used. When the rotor rotates, the reflective sticker reflects the laser, and the receiver detects the reflected signal. The speed is measured by calculating the number of reflected signals received per unit time. Alternatively, a stroboscopic lamp is used to irradiate the rotor. When the stroboscopic frequency of the stroboscopic lamp is synchronized with the rotation frequency of the rotor, the rotor appears to be stationary. By adjusting the frequency of the stroboscopic lamp, the point of synchronization with the rotation frequency of the rotor is found, and thus the speed is measured. However, the above two methods need to paste a reflective sticker on the rotor, which increases the installation complexity and cost. In addition, the reflective sticker is easily contaminated, which affects the measurement accuracy. For example, a grating disc is installed on the motor rotor shaft, and the grating disc has light transmission holes or reflective stripes. A photoelectric gate is used to detect the pulse signal generated when the light transmission hole or reflective stripe passes, and the speed is measured by calculating the number of pulses generated per unit time. Alternatively, a radial magnet is installed on the motor rotor shaft, and a magnetic encoder sensor is used to detect the pulse signal generated when the magnet passes, and the speed is measured by calculating the number of pulses generated per unit time. Alternatively, a permanent magnet is installed on the motor rotor, and a Hall sensor is used to detect the pulse signal generated when the permanent magnet passes, and the speed is measured by calculating the number of pulses generated per unit time. The disadvantages of the above methods are that the grating disc and the photoelectric gate or the radial magnet and the magnetic encoder sensor or the permanent magnet and the Hall sensor need to be installed on the rotor shaft, which increases the complexity and cost of the motor. In addition, the installed elements are easily contaminated by dust, oil stains and other contaminants or affected by the external environment, which affects the measurement accuracy.

[0040] In view of the deficiencies in the prior art, an embodiment of the present disclosure provides a speed measurement circuit, wherein an induction circuit is coupled with a brushless motor to generate an alternating current signal related to the speed by detecting a changing magnetic field generated when the motor rotor rotates. This method does not require additional auxiliary devices such as reflective stickers, grating discs, magnets, etc. on the motor rotor, simplifying the installation process and reducing the cost. The induction circuit is non-contact, which does not affect the mechanical structure of the motor, avoiding the mechanical complexity and potential failure points caused by the installation of auxiliary devices in traditional methods.

[0041] In Figure 1 In an example, the speed measurement circuit includes an induction circuit 200, an inverting amplification circuit 400, and a comparison circuit 500.

[0042] The induction circuit 200 is coupled with the brushless motor 100; and is configured to obtain an alternating current signal related to the speed of the brushless motor 100;

[0043] The inverting amplifier circuit 400 is connected to the induction circuit 200 and a bias circuit 300, respectively, for amplifying the AC signal according to the bias voltage provided by the bias circuit 300.

[0044] The comparison circuit 500 is connected to the inverting amplifier circuit 400 and the bias circuit 300, respectively, for obtaining a square wave signal with the same frequency as the rotation frequency of the brushless motor according to the bias voltage and the amplified AC signal, so as to obtain the rotation speed information of the brushless motor 100.

[0045] Specifically, in some embodiments, the main components of the brushless motor 100 include: a stator composed of a plurality of electromagnetic coils, which generates a magnetic field through electric current. A rotor, usually composed of a permanent magnet, is subjected to force in the magnetic field generated by the stator, thereby producing rotation. The induction circuit 200 generates an AC signal related to the rotation speed by detecting the changing magnetic field generated when the rotor of the brushless motor 100 rotates. The induction circuit 200 is arranged near the rotor of the brushless motor 100 to detect the change of the magnetic field generated by the permanent magnet on the rotor. When the rotor of the brushless motor 100 rotates, the permanent magnet on the rotor moves near the induction coil, causing the magnetic field in the coil to change. The frequency of the changing magnetic field is the same as the rotation frequency of the rotor. The changing magnetic field generates an induced electromotive force (voltage) in the induction coil. The frequency of the induced electromotive force is the same as the frequency of the changing magnetic field, so the frequency of the induced electromotive force is also the same as the rotation frequency of the rotor. The induced electromotive force generated in the induction coil is the AC signal related to the rotation speed.

[0046] The AC voltage generated by the induction circuit 200 is usually small, so the AC signal output by the induction circuit 200 is amplified by the inverting amplifier circuit 400. The inverting amplifier circuit 400 needs a bias circuit 300 to ensure that the input signal is within the linear range of the inverting amplifier circuit 400 and to avoid the output signal being truncated. The bias circuit 300 is used to move the voltage value of the input signal to the linear operating region of the inverting amplifier circuit 400.

[0047] The comparison circuit 500 is connected to the bias circuit 300 to obtain the reference voltage provided by the bias circuit 300; the comparison circuit 500 is used to compare the AC signal amplified by the inverting amplifier circuit 400 with the reference voltage. When the AC signal exceeds the reference voltage, the comparison circuit 500 outputs a high level; when the AC signal is lower than the reference voltage, the comparison circuit 500 outputs a low level. Since the output of the comparison circuit 500 follows the change of the AC signal, the frequency of the square wave signal is also the same as the frequency of the AC signal, i.e. the same as the rotation frequency of the rotor of the brushless motor 100.

[0048] Optionally, in Figure 2 In an example, the induction circuit 200 includes:

[0049] An inductive inductor L1 is coupled to the brushless motor 100, one end of the inductive inductor L1 is coupled to the first input end of the inverting amplifier circuit 400, and the other end of the inductive inductor L1 is coupled to the second input end of the inverting amplifier circuit 400 via a first capacitor C1.

[0050] Specifically, the inductive inductor L1 is placed near the rotor of the brushless motor 100. When the rotor rotates, the permanent magnet on the rotor moves near the inductive inductor L1, causing the external magnetic field in which the inductive inductor L1 is located to change. According to Faraday's law of electromagnetic induction, the changing magnetic field generates an induced electromotive force (voltage) in the inductive inductor L1, thereby generating an alternating voltage related to the rotational speed in the inductive inductor L1. The first capacitor C1 is used to filter out the direct current component that may exist in the inductive inductor L1, ensuring that the signal transmitted to the inverting amplifier circuit 400 is a pure alternating signal. The first capacitor C1 can also filter out high-frequency noise, improving the purity and stability of the signal.

[0051] Optionally, in some embodiments, the biasing circuit 300 further comprises a second resistor R2. Figure 2 In an example, the biasing circuit 300 comprises a first resistor R1 and a second resistor R2.

[0052] One end of the first resistor R1 is grounded, and the other end of the first resistor R1 is coupled to the first input end of the inverting amplifier circuit 400.

[0053] One end of the second resistor R2 is coupled to the first external power supply, and the other end of the first resistor R1 is coupled to the first input end.

[0054] Specifically, the first resistor R1 and the second resistor R2 form a voltage divider network to generate a stable DC bias voltage from the first external power supply. The input voltage of the inverting amplifier circuit 400 usually needs to be within a certain range between the power supply voltage and the ground potential. In order to ensure that the operational amplifier is working within the linear range, the bias voltage should be set within the common-mode input voltage range of the operational amplifier. In this embodiment, the power supply voltage is the first external power supply. For most operational amplifiers, the common-mode input voltage range is usually around power supply voltage / 2. For example, if the power supply voltage is 5V, the bias voltage should be set to 2.5V. In some embodiments, the power supply voltage is 3.3V, and the bias voltage is 1.65V.

[0055] Optionally, in some embodiments, the biasing circuit 300 further comprises a second capacitor C2. Figure 2 In an example, the biasing circuit 300 further comprises a second capacitor C2, one end of the second capacitor C2 is grounded, and the other end of the second capacitor C2 is coupled to the first input end.

[0056] Specifically, the capacitor has the characteristic of passing AC and blocking DC. High-frequency noise is easily shorted to ground through the capacitor, thereby being filtered out. This can reduce the influence of noise on the input end of the operational amplifier and improve the purity and stability of the signal. Therefore, the second capacitor C2 is used in the bias circuit 300 to filter out high-frequency noise and stabilize the DC bias voltage.

[0057] Optionally, in Figure 2 In an example, the inverting amplification circuit 400 comprises an inverting amplifier IC1A, an input resistor R3, and a first feedback resistor R4.

[0058] The inverting amplifier IC1A comprises a positive input end, a negative input end, and an inverting output end; the positive input end is coupled to the bias circuit 300;

[0059] One end of the input resistor R3 is coupled to the sensing circuit 200, and the other end of the input resistor R3 is coupled to the negative input end;

[0060] One end of the first feedback resistor R4 is coupled to the negative input end, and the other end of the first feedback resistor R4 is coupled to the inverting output end.

[0061] Specifically, the stable DC bias voltage provided by the bias circuit 300 ensures the normal operation of the inverting amplifier IC1A. The input resistor R3 is used to ensure the stability of signal transmission. The feedback resistor forms a negative feedback path, feeding back the signal at the inverting output end of the inverting amplifier IC1A to the negative input end. Through the negative feedback mechanism, it is ensured that the amplifier remains linear during amplification, avoiding signal distortion and saturation phenomena. The inverting amplifier outputs an amplified AC signal, the amplitude and phase of which are related to the input signal, but the signal is amplified and inverted.

[0062] Optionally, in Figure 2 In an example, the inverting amplification circuit 400 further comprises a third capacitor C3, one end of the third capacitor C3 is coupled to the negative input end, and the other end of the third capacitor C3 is coupled to the inverting output end.

[0063] Specifically, the third capacitor C3 is used to filter out high-frequency noise and prevent oscillation caused by high-frequency signals, ensuring the stability of the inverting amplifier IC1A.

[0064] Optionally, in Figure 2 In an example, the comparison circuit 500 comprises a comparator IC1B and a second feedback resistor R5.

[0065] The comparison circuit 500 comprises a first signal input end, a second signal input end, and a comparison output end; the first signal input end is coupled to the bias circuit 300, and the second signal input end is coupled to the first output end of the inverting amplification circuit 400;

[0066] One end of the second feedback resistor R5 is coupled to the first signal input end, and the other end of the second feedback resistor R5 is coupled to the comparison output end.

[0067] Specifically, in some embodiments, when the voltage outputted by the inverting amplification circuit 400 is greater than the bias voltage, the comparator IC1B outputs a high level. When the voltage outputted by the inverting amplification circuit 400 is less than the bias voltage, the comparator IC1B outputs a low level. The frequency of the amplified alternating current signal is the same as the rotation frequency of the rotor of the brushless motor 100. Therefore, the frequency of the square wave signal outputted by the comparator IC1B, which alternates between a high level and a low level, is also the same as the rotation frequency of the brushless motor 100.

[0068] By adjusting the size of the second feedback resistor R5, the voltage returned to the first signal input end of the comparator IC1B can be changed, thereby changing the position of the detection level. Specifically, when the value of the second feedback resistor R5 increases, the voltage returned to the first signal input end of the comparator IC1B also increases, enabling the comparator IC1B to adapt to different input signal amplitudes.

[0069] Optionally, when the comparator IC1B outputs a high level, part of the high level signal is fed back to the first signal input end through the second feedback resistor R5, causing the bias voltage to slightly increase, further stabilizing the high level output. Conversely, when the comparator IC1B outputs a low level, part of the low level signal is fed back to the first signal input end through the second feedback resistor R5, causing the bias voltage to slightly decrease, further stabilizing the low level output.

[0070] Optionally, in Figure 2 In an example, the comparison circuit 500 includes a fourth capacitor C4 coupled between the first output end of the inverting amplification circuit 400 and the second signal input end. The fourth capacitor C4 filters out the direct current component in the alternating current signal outputted by the inverting amplification circuit 400.

[0071] Optionally, a master control unit is further included, coupled to the comparison circuit 500, for obtaining the rotation speed information of the brushless motor 100 according to the square wave signal.

[0072] Specifically, the master control unit can be in communication connection with the comparison circuit 500, and the master control unit receives the square wave signal output by the comparison circuit 500 through an input interface. The frequency of the square wave signal is the same as the rotation frequency of the rotor of the brushless motor 100. A counter or timer inside the master control unit is used to measure the frequency or period of the square wave signal. According to the measured frequency or period, the master control unit calculates the rotation speed of the brushless motor 100. The master control unit outputs the calculated rotation speed information to a display device, a communication interface or other control system through an output interface. In this embodiment, the connection diagram of the master control unit is not shown, but those skilled in the art can understand its specific implementation in combination with related technologies.

[0073] In yet another embodiment of the present disclosure, a brushless motor 100 is provided, wherein the speed measurement circuit in any of the above embodiments is included.

[0074] The above embodiments are only illustrative of the principles and effects of the present disclosure, and are not intended to limit the present disclosure. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present disclosure. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed by the present disclosure shall still be covered by the protection scope of the present disclosure.

Claims

1. A speed measurement circuit, characterized by A rotation speed measurement for a brushless motor; the speed measurement circuit comprises: a sensing circuit coupled to the brushless motor; for obtaining an alternating current signal associated with the rotation speed of the brushless motor; an inverting amplifier circuit connected to the sensing circuit and a biasing circuit respectively; for amplifying the alternating current signal according to a bias voltage provided by the biasing circuit; the biasing circuit comprises: a first resistor, one end of the first resistor is connected to ground, and the other end of the first resistor is coupled to a first input terminal of the inverting amplifier circuit; a second resistor, one end of the second resistor is coupled to a first external power supply, and the other end of the second resistor is coupled to the first input terminal; the sensing circuit comprises: a sensing inductor coupled to the brushless motor, one end of the sensing inductor is coupled to the first input terminal of the inverting amplifier circuit, and the other end of the sensing inductor is coupled to a second input terminal of the inverting amplifier circuit via a first capacitor; the inverting amplifier circuit comprises: an inverting amplifier, comprising a positive phase input terminal, a negative phase input terminal and an inverting output terminal; the positive phase input terminal is coupled to the biasing circuit; an input resistor, one end of the input resistor is coupled to the sensing circuit, and the other end of the input resistor is coupled to the negative phase input terminal; a first feedback resistor, one end of the first feedback resistor is coupled to the negative phase input terminal, and the other end of the first feedback resistor is coupled to the inverting output terminal; a third capacitor, one end of the third capacitor is coupled to the negative phase input terminal, and the other end of the third capacitor is coupled to the inverting output terminal; a comparison circuit connected to the inverting amplifier circuit and the biasing circuit respectively; for obtaining a square wave signal with the same rotation frequency as the brushless motor according to the bias voltage and the amplified alternating current signal, so as to obtain the rotation speed information of the brushless motor; the comparison circuit comprises: a comparator, the comparison circuit comprises a first signal input terminal, a second signal input terminal and a comparison output terminal; the first signal input terminal is coupled to the biasing circuit, and the second signal input terminal is coupled to a first output terminal of the inverting amplifier circuit; a second feedback resistor, one end of the second feedback resistor is coupled to the first signal input terminal, and the other end of the second feedback resistor is coupled to the comparison output terminal.

2. The speed measurement circuit of claim 1, wherein The biasing circuit further comprises a second capacitor, one end of the second capacitor is connected to ground, and the other end of the second capacitor is coupled to the first input terminal.

3. The speed measurement circuit of claim 1, wherein The comparison circuit comprises a fourth capacitor, the fourth capacitor is coupled between the first output terminal of the inverting amplifier circuit and the second signal input terminal.

4. The speed measurement circuit of claim 1, wherein Further comprising a master control unit coupled to the comparison circuit; for obtaining the rotation speed information of the brushless motor according to the square wave signal.

5. A brushless electric motor characterized by The speed measurement circuit comprises any one of claims 1-4.

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