Motor rotating speed signal acquisition circuit and related device

Abstract

The application relates to a motor rotating speed signal acquisition circuit and related equipment, in particular to a motor rotating speed signal acquisition circuit, a motor rotating speed detection device and a brushless synchronous motor. The motor rotating speed signal acquisition circuit comprises a first power supply, a second power supply, a rotating speed signal acquisition and isolation circuit, a frequency conversion circuit and a voltage adjustment circuit. The first power supply supplies power for a rotating speed measurement sensor, the second power supply supplies power for the frequency conversion circuit and the voltage adjustment circuit, the rotating speed signal acquisition and isolation circuit acquires and isolates a square wave signal, the frequency conversion circuit converts the square wave signal into a direct current signal, and the voltage adjustment circuit converts the direct current signal into a motor rotating speed signal matched with an input voltage range of a processing unit. The application further comprises a motor rotating speed detection device comprising the acquisition circuit and a brushless synchronous motor comprising the detection device. The application realizes the effect of detecting a motor rotating speed value by effectively acquiring and processing a motor rotating speed signal.

Description

Technical Field

[0001] This application relates to the field of motor speed acquisition, and particularly to a motor speed signal acquisition circuit and related equipment, especially to a motor speed signal acquisition circuit, a motor speed detection device, and a brushless synchronous motor. Background Technology

[0002] In the industrial sector, electric motors are widely used as crucial power equipment, especially brushless synchronous motors, which play a key role in numerous industrial scenarios. With the continuous improvement of industrial automation, the precise monitoring and control of motor operating status has become increasingly important, and accurate acquisition of motor speed is fundamental to achieving precise control. Particularly during the starting of a brushless synchronous motor, the excitation device needs to apply excitation in a timely manner based on the motor speed and issue control signals to lock the starter cabinet. Therefore, accurately obtaining motor speed information is crucial to ensuring the smooth starting process of a brushless synchronous motor.

[0003] In related technologies, motor speed measurement methods are based on the rotor induction principle, which obtains speed information by detecting the induced signal generated by the rotor windings in a rotating magnetic field. However, for brushless synchronous motors, since their rotor structure has no windings, it is impossible to generate an induced current loop, therefore this method is not applicable to brushless synchronous motors.

[0004] The aforementioned technologies have the drawback that the rotational speed of a brushless synchronous motor cannot be measured using rotor induction methods. Utility Model Content

[0005] In order to effectively acquire and process motor speed signals and detect motor speed values, this application provides a motor speed signal acquisition circuit and related equipment.

[0006] On the one hand, this application provides a motor speed signal acquisition circuit, which adopts the following technical solution: A first power supply and a second power supply, wherein the rated voltage of the first power supply is greater than the rated voltage of the second power supply, the first power supply is used to power the speed measurement sensor S1, and the second power supply is used to power the frequency conversion circuit and the voltage adjustment circuit; a speed signal acquisition and isolation circuit is connected to the frequency conversion circuit, the speed signal acquisition and isolation circuit includes the speed measurement sensor S1 and an isolation unit, the speed measurement sensor S1 is used to acquire a square wave signal related to the motor speed; the isolation unit is disposed between the speed measurement sensor S1 and the frequency conversion circuit, and is used to isolate the speed measurement sensor S1 from the frequency conversion circuit and the voltage adjustment circuit; A frequency conversion circuit, connected to the speed signal acquisition and isolation circuit and the voltage adjustment circuit, is used to receive the square wave signal and convert the square wave signal into a DC signal; A voltage adjustment circuit is used to connect to the frequency conversion circuit and the processing unit. The voltage adjustment circuit receives the DC signal and converts the DC signal into a motor speed signal that matches the input voltage range of the processing unit.

[0007] By adopting the above scheme, the stability of the entire circuit is ensured by dual power supply and isolation unit. At the same time, the square wave signal related to the motor speed is acquired by the speed measurement sensor S1. After passing through the frequency conversion circuit and voltage adjustment circuit, the motor speed signal adapted to the processing unit is finally output, realizing the effective acquisition and isolation of the motor speed signal.

[0008] Optionally, the isolation unit includes a high-speed optocoupler U1, a first resistor R1, and a second resistor R2. The first pin of the high-speed optocoupler U1 is connected to the first end of the first resistor R1, the second end of the first resistor R1 is connected to the first power supply, the second pin of the high-speed optocoupler U1 is connected to the first pin of the speed measurement sensor S1 to receive the square wave signal, the third pin of the high-speed optocoupler U1 is grounded, the fourth pin of the high-speed optocoupler U1 is connected to the frequency conversion circuit to send the square wave signal, and the fourth pin of the high-speed optocoupler U1 is also connected to the first end of the second resistor R2. The second end of the second resistor R2 is connected to the second power supply, and the fifth pin of the high-speed optocoupler U1 is connected to the second end of the second resistor R2.

[0009] By adopting the above scheme, the isolation unit, through the cooperation of high-speed optocoupler U1, first resistor R1 and second resistor R2, achieves efficient isolation between the speed measurement sensor S1 and the subsequent frequency conversion circuit and voltage adjustment circuit, ensuring stable transmission of square wave signal and enhancing the circuit's anti-interference capability.

[0010] Optionally, the isolation unit further includes a first capacitor C1, with a first end of the first capacitor C1 connected to a first end of the second resistor R2, and a second end of the first capacitor C1 connected to the frequency conversion circuit to transmit the square wave signal.

[0011] Using the above scheme, the square wave signal is filtered by adding a first capacitor C1.

[0012] Optionally, the frequency conversion circuit includes a second capacitor C2 and a timing capacitor C. t Inductive resistor R S Timing resistor R t Load resistor R LThe system comprises a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a main control chip U2, wherein the first pin of the main control chip U2 is connected to the load resistor R. L The first terminal, the second pin of the main control chip U2, is connected to the sensing resistor R. S At the first end, the fifth pin of the main control chip U2 is connected to the timing resistor R. t The first terminal is connected to the timing capacitor C t The first terminal of the main control chip U2 is connected to the first terminal of the third resistor R3. The second terminal of the third resistor R3 is connected to the second power supply. The seventh terminal of the main control chip U2 is connected to the first terminals of the fourth resistor R4 and the fifth resistor R5, respectively. The eighth terminal of the main control chip U2 is connected to the second power supply. The second capacitor C2 is connected in parallel with the load resistor R. L At both ends, the load resistor R L The timing capacitor C t The sensing resistor R S The second terminal of the fourth resistor R4 is grounded, and the third and fourth pins of the main control chip U2 are also grounded. The fifth resistor R5 and the timing resistor R t The second end of each is connected to the second power source.

[0013] By adopting the above scheme, the square wave signal is converted into a DC signal through the synergistic effect of the main control chip U2 and related components, thus achieving effective signal conversion and stable output.

[0014] Optionally, the frequency conversion circuit is used to convert the square wave signal into the DC signal, wherein the internal circuit of the main control chip U2 converts the square wave signal into a current pulse proportional to the frequency, and the sensing resistor R S The timing resistor R is used to set the amplitude of the current pulse. t and the timing capacitor C t Used to set the width of the current pulse, the current pulse passing through the load resistor R L The load resistor R generates a pulse voltage. L A low-pass filter circuit is formed by connecting it in parallel with the second capacitor C2. The low-pass filter circuit smooths the pulse voltage and converts it into the DC signal.

[0015] Using the above scheme, through the conversion of the internal circuit of the main control chip U2, and the sensing resistor R S Timing resistor R t Timing capacitor C tThe settings for the amplitude and width of the current pulse by components such as the load resistor R ensure the stability and accuracy of the current pulse. L The low-pass filter circuit formed with the second capacitor C2 further smooths the pulse voltage and effectively removes high-frequency interference components.

[0016] Optionally, the voltage adjustment circuit includes a sixth resistor R6, a seventh resistor R7, and a single-supply operational amplifier U3. The first pin of the single-supply operational amplifier U3 is connected to the processing unit to output the motor speed signal. The second pin of the single-supply operational amplifier U3 is grounded. The third pin of the single-supply operational amplifier U3 is connected to the frequency conversion circuit to receive the DC signal. The fourth pin of the single-supply operational amplifier U3 is connected to the second terminal of the sixth resistor R6. The first terminal of the sixth resistor R6 is connected to the frequency conversion circuit. The fifth pin of the single-supply operational amplifier U3 is connected to the second power supply. The first terminal of the seventh resistor R7 is connected to the first pin of the single-supply operational amplifier U3. The second terminal of the seventh resistor R7 is connected to the fourth pin of the single-supply operational amplifier U3.

[0017] By adopting the above scheme, the DC signal is converted into a motor speed signal that matches the input voltage range of the processing unit through the cooperation of the single-supply operational amplifier U3 and related resistors, ensuring that the output motor speed signal can meet the requirements of the processing unit.

[0018] Optionally, the voltage adjustment circuit is used to convert the DC signal into the motor speed signal, wherein the sixth resistor R6 and the seventh resistor R7 form a negative feedback loop, and the voltage adjustment circuit sets the gain of the single-supply operational amplifier U3 by adjusting the resistance ratio of the seventh resistor R7 to the sixth resistor R6, thereby converting the DC signal into the motor speed signal.

[0019] By adopting the above scheme, the gain of the single-supply operational amplifier U3 can be set by flexibly adjusting the resistance ratio of the seventh resistor R7 to the sixth resistor R6, thereby realizing the adjustment and conversion of DC signals and further improving the accuracy and reliability of signal conversion.

[0020] Optionally, the voltage adjustment circuit further includes a first diode D1 and a second diode D2, the anode of the first diode D1 is connected to the anode of the second diode D2, and the anode of the first diode D1 is also grounded, and the cathodes of the first diode D1 and the second diode D2 are both connected to the first pin of the single-supply operational amplifier U3.

[0021] By adopting the above scheme, the added first diode D1 and second diode D2 can clamp and protect the motor speed signal output by the single-supply operational amplifier U3.

[0022] On the other hand, this application also provides a motor speed detection device, which adopts the following technical solution: A motor speed detection device integrates the motor speed signal acquisition circuit and the processing unit into the motor speed detection device.

[0023] By adopting the above technical solution, the motor speed signal acquisition circuit and processing unit are integrated into the motor speed detection device to form a complete system, which provides a guarantee for the stable operation and control of the motor.

[0024] On the other hand, this application also provides a brushless synchronous motor, which adopts the following technical solution: A brushless synchronous motor, wherein the motor speed detection device is installed inside the brushless synchronous motor.

[0025] By adopting the above technical solution, the brushless synchronous motor obtains the motor speed value by installing a motor speed detection device and transmits the motor speed value to the excitation controller, thereby improving the accuracy and reliability of the brushless synchronous motor operation control.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. The stability of the entire circuit is ensured by the independent power supply and isolation unit of the dual power supply. At the same time, the square wave signal related to the motor speed is obtained by the speed measurement sensor S1. After the frequency conversion circuit and voltage adjustment circuit, the motor speed signal adapted to the processing unit is finally output, realizing the effective acquisition and isolation of the motor speed signal. 2. By integrating the motor speed signal acquisition circuit and processing unit into the motor speed detection device, a complete system is formed, which provides a guarantee for the stable operation and control of the motor; 3. By installing a motor speed detection device, the brushless synchronous motor obtains the motor speed value and transmits the motor speed value to the excitation controller, thereby improving the accuracy and reliability of the brushless synchronous motor operation control. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the motor speed signal acquisition circuit in Embodiment 1 of this application.

[0028] Figure 2 This is a circuit diagram of the motor speed signal acquisition circuit in Embodiment 1 of this application.

[0029] Explanation of reference numerals in the attached diagram: 10, First power supply; 20, Second power supply; 30, Speed ​​signal acquisition and isolation circuit; 40, Frequency conversion circuit; 50, Voltage adjustment circuit. Detailed Implementation

[0030] The following is in conjunction with the appendix Figure 1 and appendix Figure 2 This application will be described in further detail.

[0031] Example 1 This application discloses a motor speed signal acquisition circuit.

[0032] Reference Figure 1 The motor speed signal acquisition circuit includes a first power supply 10, a second power supply 20, a speed signal acquisition and isolation circuit 30, a frequency conversion circuit 40, and a voltage adjustment circuit 50. The speed signal acquisition and isolation circuit 30 is connected to the frequency conversion circuit 40. The isolation unit is located between the speed measurement sensor S1 and the frequency conversion circuit 40. The frequency conversion circuit 40 is connected to the speed signal acquisition and isolation circuit 30 and the voltage adjustment circuit 50. The voltage adjustment circuit 50 is connected to the frequency conversion circuit 40 and the processing unit. After the speed measurement sensor S1 acquires a square wave signal, it is sent to the frequency conversion circuit 40 via the isolation unit. The frequency conversion circuit 40 converts the square wave signal into a DC signal. The voltage adjustment circuit 50 then converts the DC signal into a motor speed signal that matches the input voltage range of the processing unit, for example, the input voltage range of the processing unit is 0V to 3V.

[0033] The first power supply 10 can be a DC power supply, such as a common DC battery pack or a switching power supply. The rated voltage of the first power supply 10 is greater than the rated voltage of the second power supply 20, providing a stable power supply to the speed measurement sensor S1 to ensure that the speed measurement sensor S1 can work normally. The second power supply 20 can also be a DC power supply to provide a suitable voltage to the frequency conversion circuit 40 and the voltage adjustment circuit 50, ensuring the stable operation of these two circuits.

[0034] Reference Figure 2The speed signal acquisition and isolation circuit 30 includes a speed measurement sensor S1 and an isolation unit. The speed measurement sensor S1 can be an inductive sensor of model NJ5-18GM-N-V1. The isolation unit includes a high-speed optocoupler U1, a first capacitor C1, a first resistor R1, and a second resistor R2. The high-speed optocoupler U1 can be a high-speed optocoupler of model TLP2304. The first pin of the high-speed optocoupler U1 is connected to the first terminal of the first resistor R1, and the second terminal of the first resistor R1 is connected to the first power supply 10. The first resistor R1 limits current and protects the high-speed optocoupler U1 from damage by excessive current. The second pin of the high-speed optocoupler U1 is connected to the first pin of the speed measurement sensor S1 to receive a square wave signal. The second pin of the speed measurement sensor S1 and the third pin of the high-speed optocoupler U1 are both grounded. The fourth pin of the high-speed optocoupler U1 is connected to the first end of the second resistor R2. The second end of the second resistor R2 is connected to the second power supply 20. The fifth pin of the high-speed optocoupler U1 is connected to the second end of the second resistor R2. The first end of the first capacitor C1 is connected to the first end of the second resistor R2. The second end of the first capacitor C1 is connected to the frequency conversion circuit 40 to transmit a square wave signal.

[0035] The speed measurement sensor S1 senses the movement of the metal parts on the motor rotor in a non-contact manner and generates a square wave signal synchronized with the motor speed. The speed measurement sensor S1 sends the square wave signal from its first pin to the second pin of the high-speed optocoupler U1. The second pin of the high-speed optocoupler U1 receives the square wave signal and then sends it from its fourth pin to the frequency conversion circuit 40. The high-frequency optocoupler isolator isolates the speed sensor S1 from the frequency conversion circuit 40 and the voltage adjustment circuit 50. The first capacitor C1 shapes the square wave signal to ensure that the square wave signal sent to the frequency conversion circuit 40 has good waveform and stability.

[0036] Reference Figure 2 The frequency conversion circuit 40 includes a second capacitor C2 and a timing capacitor C. t Inductive resistor R S Timing resistor R t Load resistor R L The circuit consists of three resistors: R3, R4, R5, and the main control chip U2. The main control chip U2 can be an LM231 voltage-to-frequency converter, capable of receiving square wave signals and generating current pulses. The first pin of the main control chip U2 is connected to the load resistor R. L The first terminal, the second pin of the main control chip U2, is connected to the sensing resistor R. SThe first terminal, the fifth pin of the main control chip U2, is connected to the timing resistor R. t The first terminal is connected to the timing capacitor C t The first terminal is connected to the first terminal of the third resistor R3, the second terminal of the third resistor R3 is connected to the second power supply 20, the seventh terminal of the main control chip U2 is connected to the first terminals of the fourth resistor R4 and the fifth resistor R5 respectively, the eighth terminal of the main control chip U2 is connected to the second power supply 20, and the second capacitor C2 is connected in parallel with the load resistor R. L The two ends of the load resistor R L Timing capacitor C t Inductive resistor R S The second terminal of the fourth resistor R4 is grounded, and the third and fourth pins of the main control chip U2 are also grounded. The fifth resistor R5 and the timing resistor R t The second end of each is connected to the second power supply 20.

[0037] After receiving the square wave signal at pin 6 of the main control chip U2, the internal circuit of the main control chip U2 converts the square wave signal into a current pulse proportional to the frequency, and the sensing resistor R... S The amplitude of the current pulse is set by adjusting the sensing resistor R. S The resistance value can change the magnitude of the current pulse. Timing resistor R t and timing capacitor C t This setting determines the width of the current pulse, thus controlling its duration. The current pulse passes through the load resistor R. L Generate pulse voltage, load resistor R L A low-pass filter circuit is formed in parallel with the second capacitor C2. This circuit smooths the pulse voltage and converts it into a DC signal. For example, when the current pulse output by the main control chip U2 contains high-frequency noise, the low-pass filter circuit can filter out this noise, making the output DC signal more stable.

[0038] Reference Figure 2 The voltage adjustment circuit 50 includes a sixth resistor R6, a seventh resistor R7, a first diode D1, a second diode D2, and a single-supply operational amplifier U3. The first pin of the single-supply operational amplifier U3 is connected to the processing unit to output the motor speed signal, the second pin of the single-supply operational amplifier U3 is grounded, and the third pin of the single-supply operational amplifier U3 is connected to the load resistor R. L The second terminal is used to receive the DC signal. The fourth pin of the single-supply operational amplifier U3 is connected to the second terminal of the sixth resistor R6, and the first terminal of the sixth resistor R6 is connected to the load resistor R. LThe first terminal of the single-supply operational amplifier U3 is connected to the fifth pin of the second power supply 20. The first terminal of the seventh resistor R7 is connected to the first pin of the single-supply operational amplifier U3, and the second terminal of the seventh resistor R7 is connected to the fourth pin of the single-supply operational amplifier U3. The anode of the first diode D1 is connected to the anode of the second diode D2, and the anode of the first diode D1 is also grounded. The cathodes of both the first diode D1 and the second diode D2 are connected to the first pin of the single-supply operational amplifier U3. The first diode D1 can be a fast recovery diode, and the second diode D2 can be a Zener diode.

[0039] The voltage adjustment circuit 50 is used to convert the DC signal into a motor speed signal. The sixth resistor R6 and the seventh resistor R7 form a negative feedback loop. The voltage adjustment circuit 50 adjusts the ratio of the resistance values ​​of the seventh resistor R7 and the sixth resistor R6 to set the gain of the single-supply operational amplifier U3, thereby converting the DC signal into a motor speed signal and sending the motor speed signal to the processing unit.

[0040] Frequency conversion circuit 40 can convert square wave signals into DC signals through the main control chip U2 and passive components in frequency conversion circuit 40, as expressed by the following formula: Where V represents the voltage of the DC signal, f N R represents the frequency of the input square wave signal. L R represents the load resistor. S R represents an inductive resistor. t Indicates a timing resistor, C t This indicates a timing capacitor.

[0041] The implementation principle of a motor speed signal acquisition circuit in Embodiment 1 of this application is as follows: Through reasonable power distribution and multi-stage circuit conversion, the acquisition of motor speed signals is achieved. The speed measurement sensor S1 acquires a square wave signal related to the motor speed. An isolation unit isolates the speed measurement sensor S1 from the frequency conversion circuit 40. The frequency conversion circuit 40 converts the square wave signal into a DC signal, and the voltage adjustment circuit 50 converts the DC signal into a motor speed signal suitable for the processing unit.

[0042] Example 2 Embodiment 2 of this application also discloses a motor speed detection device, including the motor speed signal acquisition circuit and processing unit in Embodiment 1 above.

[0043] The processing unit can be a microcontroller or digital signal processor with an analog-to-digital converter (ADC) interface. The processing unit uses its built-in ADC module to periodically sample the motor speed signal received from the voltage regulation circuit. The ADC converts continuous analog voltage values ​​into discrete digital quantities, which are then parsed by a pre-programmed algorithm within the processing unit, thus converting the motor speed signal into a motor speed value.

[0044] The implementation principle of the motor speed detection device in Embodiment 2 of this application is as follows: The motor speed detection device combines a motor speed signal acquisition circuit and a processing unit to form a complete system. The motor speed signal acquisition circuit acquires the motor speed signal, and the processing unit processes and applies the signal, providing a guarantee for the stable operation and control of the motor.

[0045] Example 3 Embodiment 3 of this application also discloses a brushless synchronous motor having the motor speed detection device described in Embodiment 2 above. The motor speed detection device is installed near the rotor of the brushless synchronous motor to obtain the motor speed value.

[0046] The implementation principle of a brushless synchronous motor in Embodiment 3 of this application is as follows: The brushless synchronous motor obtains its speed value by installing a motor speed detection device and transmits the motor speed value to the excitation controller. The excitation controller determines whether the brushless synchronous motor is stalled based on the received motor speed value and determines the timing for engaging the excitation coil. In addition, the excitation controller can also control the on / off state of the star-point starter cabinet based on the motor speed value.

[0047] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A motor speed signal acquisition circuit, characterized in that, The motor speed signal acquisition circuit, used for connection to the processing unit, includes: A first power supply (10) and a second power supply (20), wherein the rated voltage of the first power supply (10) is greater than the rated voltage of the second power supply (20), the first power supply (10) is used to power the speed measuring sensor S1, and the second power supply (20) is used to power the frequency conversion circuit (40) and the voltage adjustment circuit (50). A speed signal acquisition and isolation circuit (30) is connected to a frequency conversion circuit (40). The speed signal acquisition and isolation circuit (30) includes a speed measurement sensor S1 and an isolation unit. The speed measurement sensor S1 is used to acquire a square wave signal related to the motor speed. The isolation unit is located between the speed measurement sensor S1 and the frequency conversion circuit (40) and is used to isolate the speed measurement sensor S1 from the frequency conversion circuit (40) and the voltage adjustment circuit (50). The frequency conversion circuit (40) is connected to the speed signal acquisition and isolation circuit (30) and the voltage adjustment circuit (50) and is used to receive the square wave signal and convert the square wave signal into a DC signal. A voltage adjustment circuit (50) is used to connect to the frequency conversion circuit (40) and the processing unit. The voltage adjustment circuit (50) receives the DC signal and converts the DC signal into a motor speed signal that matches the input voltage range of the processing unit.

2. The motor speed signal acquisition circuit according to claim 1, characterized in that, The isolation unit includes a high-speed optocoupler U1, a first resistor R1, and a second resistor R2. The first pin of the high-speed optocoupler U1 is connected to the first end of the first resistor R1, the second end of the first resistor R1 is connected to the first power supply (10), the second pin of the high-speed optocoupler U1 is connected to the first pin of the speed measurement sensor S1 to receive the square wave signal, the third pin of the high-speed optocoupler U1 is grounded, the fourth pin of the high-speed optocoupler U1 is connected to the frequency conversion circuit (40) to send the square wave signal, and the fourth pin of the high-speed optocoupler U1 is also connected to the first end of the second resistor R2. The second end of the second resistor R2 is connected to the second power supply (20), and the fifth pin of the high-speed optocoupler U1 is connected to the second end of the second resistor R2.

3. The motor speed signal acquisition circuit according to claim 2, characterized in that, It also includes a first capacitor C1, the first end of which is connected to the first end of the second resistor R2, and the second end of which is connected to the frequency conversion circuit (40) to transmit the square wave signal.

4. The motor speed signal acquisition circuit according to claim 1, characterized in that, The frequency conversion circuit (40) includes a second capacitor C2 and a timing capacitor C. t Inductive resistor R S Timing resistor R t Load resistor R L The system comprises a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a main control chip U2, wherein the first pin of the main control chip U2 is connected to the load resistor R. L The first terminal, the second pin of the main control chip U2, is connected to the sensing resistor R. S At the first end, the fifth pin of the main control chip U2 is connected to the timing resistor R. t The first terminal is connected to the timing capacitor C t The first end of the main control chip U2 is connected to the first end of the third resistor R3, the second end of the third resistor R3 is connected to the second power supply (20), the seventh pin of the main control chip U2 is connected to the first end of the fourth resistor R4 and the first end of the fifth resistor R5 respectively, the eighth pin of the main control chip U2 is connected to the second power supply (20), and the second capacitor C2 is connected in parallel with the load resistor R L At both ends, the load resistor R L The timing capacitor C t The sensing resistor R S The second terminal of the fourth resistor R4 is grounded, and the third and fourth pins of the main control chip U2 are also grounded. The fifth resistor R5 and the timing resistor R t The second end of each is connected to the second power supply (20).

5. The motor speed signal acquisition circuit according to claim 4, characterized in that, The frequency conversion circuit (40) is used to convert the square wave signal into the DC signal. The internal circuit of the main control chip U2 converts the square wave signal into a current pulse proportional to the frequency. The sensing resistor R... S The timing resistor R is used to set the amplitude of the current pulse. t and the timing capacitor C t Used to set the width of the current pulse, the current pulse passing through the load resistor R L The load resistor R generates a pulse voltage. L A low-pass filter circuit is formed by connecting it in parallel with the second capacitor C2. The low-pass filter circuit smooths the pulse voltage and converts it into the DC signal.

6. The motor speed signal acquisition circuit according to claim 1, characterized in that, The voltage adjustment circuit (50) includes a sixth resistor R6, a seventh resistor R7, and a single-supply operational amplifier U3. The first pin of the single-supply operational amplifier U3 is connected to the processing unit to output the motor speed signal. The second pin of the single-supply operational amplifier U3 is grounded. The third pin of the single-supply operational amplifier U3 is connected to the frequency conversion circuit (40) to receive the DC signal. The fourth pin of the single-supply operational amplifier U3 is connected to the second end of the sixth resistor R6. The first end of the sixth resistor R6 is connected to the frequency conversion circuit (40). The fifth pin of the single-supply operational amplifier U3 is connected to the second power supply (20). The first end of the seventh resistor R7 is connected to the first pin of the single-supply operational amplifier U3. The second end of the seventh resistor R7 is connected to the fourth pin of the single-supply operational amplifier U3.

7. The motor speed signal acquisition circuit according to claim 6, characterized in that, The voltage adjustment circuit (50) is used to convert the DC signal into the motor speed signal. The sixth resistor R6 and the seventh resistor R7 form a negative feedback loop. The voltage adjustment circuit (50) adjusts the ratio of the resistance values ​​of the seventh resistor R7 to the sixth resistor R6 to set the gain of the single-supply operational amplifier U3, thereby converting the DC signal into the motor speed signal.

8. The motor speed signal acquisition circuit according to claim 6, characterized in that, It also includes a first diode D1 and a second diode D2. The anode of the first diode D1 is connected to the anode of the second diode D2, and the anode of the first diode D1 is also grounded. The cathodes of the first diode D1 and the second diode D2 are both connected to the first pin of the single-supply operational amplifier U3.

9. A motor speed detection device, characterized in that, It includes the motor speed signal acquisition circuit and processing unit as described in any one of claims 1 to 8.

10. A brushless synchronous motor, characterized in that, It has the motor speed detection device as described in claim 9.

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