Motor driving circuit with built-in counter electromotive force sampling and brushless motor

Abstract

The invention relates to a motor drive circuit with built-in counter electromotive force sampling and a brushless motor, which are characterized in that circuit optimization design is carried out based on an MOS drive circuit, and a counter electromotive force waveform is directly connected to the inside of a main control chip from a pre-drive circuit to be processed, so that an external circuit of the chip on a circuit board is simplified, signal interference is reduced, and the reliability of the circuit board is improved. And the IO pin occupation of the main control chip is reduced. Compared with a traditional square wave driving scheme, a plurality of sampling resistors, capacitors and other elements outside the main control chip are reduced, the number of IO pins occupying the main control chip is reduced, interference of a sampling circuit to a weak driving circuit is reduced, EMI external radiation interference of the whole driving scheme is reduced, the accuracy of counter electromotive force sampling is improved, and the driving efficiency is improved. Therefore, the cost performance of the whole back electromotive force sampling scheme is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of circuit design, and relates to a motor driving circuit with built-in back electromotive force sampling and a brushless motor. BACKGROUND

[0002] There are two driving modes for the brushless motor, one is square wave driving, and the other is rotating wave driving. The two driving modes and effects are different, and the hardware circuits are naturally different. The rotating wave driving needs to sample the phase current size of the motor, needs to use an operational amplifier circuit to amplify the phase current signal and sample, and after sampling is completed, the back electromotive force waveform is given to the MCU chip for calculation and output of the next driving waveform. The square wave driving samples the three-phase voltage waveform of the brushless motor, judges the zero-crossing point through the phase relationship between the phase voltages, that is, the commutation point of the brushless motor, and if the zero-crossing point is detected, the next driving waveform is switched, and the brushless motor is always rotated in this way. However, part of the rotating wave driving scheme also needs to sample the back electromotive force waveform to judge the headwind and tailwind of the motor. The existing back electromotive force sampling circuit needs to be connected to the IO (input / output) pin of the MCU chip after being divided by the voltage of the three-phase line UVW (three-phase phase sequence identifier) of the motor, which needs to build the back electromotive force sampling circuit outside the MCU chip and connect the wire to the MCU chip to perform detection, and there is a technical problem of high sampling cost. SUMMARY

[0003] In view of the problems in the above-mentioned traditional technology, the application provides a motor driving circuit with built-in back electromotive force sampling and a brushless motor, which can effectively reduce the sampling cost and improve the sampling accuracy.

[0004] In order to achieve the above-mentioned purpose, the embodiments of the application adopt the following technical solutions: On the one hand, a motor driving circuit with built-in back electromotive force sampling is provided, which comprises a main control chip, a MOS tube circuit and a MOS tube driving circuit. The main control chip comprises a chip body and a chip built-in sampling circuit. The chip built-in sampling circuit comprises a voltage dividing network, an RC filter network and a sampling comparison module. The chip body is connected to the sampling comparison module and the MOS tube driving circuit respectively. The MOS tube driving circuit is connected to the MOS tube circuit and the voltage dividing network respectively. The voltage dividing network is connected to the sampling comparison module through the RC filter network. The MOS tube driving circuit inputs the back electromotive force signal from the three-phase winding of the brushless motor into the voltage dividing network, and then reduces the voltage to the low voltage range suitable for the internal circuit of the main control chip through the voltage dividing network. After the reduced back electromotive force signal is filtered of high-frequency noise and interference signals through the RC filter network, the zero-crossing trigger signal is directly output to the chip body through the sampling comparison module. The chip body is used to output the corresponding commutation instruction according to the zero-crossing trigger signal. The commutation instruction is used to drive the rotation of the brushless motor.

[0005] In one of the embodiments, the sampling comparison module comprises a comparator and / or an analog-to-digital converter, the comparator is used to compare the filtered back electromotive force signal with a preset threshold voltage, and directly output a zero-crossing trigger signal to the chip body; the analog-to-digital converter is used to convert the filtered back electromotive force signal into a digital signal and then output to the chip body, and the chip body calculates and outputs the zero-crossing trigger signal according to the received back electromotive force signal.

[0006] In one of the embodiments, the chip-embedded sampling circuit further comprises a resistor R1, and the sampling comparison module is connected to the chip body through the resistor R1.

[0007] In one of the embodiments, the voltage dividing network comprises resistors R2, R3, R4, R8, R9 and R10, the resistor R2 and the resistor R8 are connected in series, the resistor R3 and the resistor R9 are connected in series, the resistor R4 and the resistor R10 are connected in series, one end of the resistor R8 is used to access the back electromotive force signal of the U-phase winding output by the MOS tube driving circuit, one end of the resistor R9 is used to access the back electromotive force signal of the V-phase winding output by the MOS tube driving circuit, and one end of the resistor R10 is used to access the back electromotive force signal of the W-phase winding output by the MOS tube driving circuit. The other end of the resistor R2, the other end of the resistor R3 and the other end of the resistor R4 are all connected to the negative input end of the sampling comparison module, the other end of the resistor R8 is further connected to the first positive input end of the sampling comparison module and the first filtering branch of the RC filtering network, the other end of the resistor R9 is further connected to the second positive input end of the sampling comparison module and the second filtering branch of the RC filtering network, and the other end of the resistor R10 is further connected to the third positive input end of the sampling comparison module and the third filtering branch of the RC filtering network.

[0008] In one of the embodiments, the first filtering branch of the RC filtering network comprises a resistor R5 and a capacitor C1, one end of the resistor R5 and one end of the capacitor C1 are both connected to the other end of the resistor R8, and the other end of the resistor R5 and the other end of the capacitor C1 are both grounded.

[0009] In one of the embodiments, the second filtering branch of the RC filtering network comprises a resistor R6 and a capacitor C2, one end of the resistor R6 and one end of the capacitor C2 are both connected to the other end of the resistor R9, and the other end of the resistor R6 and the other end of the capacitor C2 are both grounded.

[0010] In one of the embodiments, the third filtering branch of the RC filtering network comprises a resistor R7 and a capacitor C3, one end of the resistor R7 and one end of the capacitor C3 are both connected to the other end of the resistor R10, and the other end of the resistor R7 and the other end of the capacitor C3 are both grounded.

[0011] In another aspect, a brushless motor is also provided, which is driven by the motor drive circuit with built-in back electromotive force sampling of any of the above.

[0012] One of the above technical solutions has the following advantages and beneficial effects: The motor drive circuit with built-in back electromotive force sampling and the brushless motor are optimized in circuit design based on the MOS drive circuit, the back electromotive force waveform is directly connected from the pre-drive circuit to the internal processing of the master control chip, the external circuit of the chip on the circuit board is simplified, the signal interference is reduced, and the IO pin occupation of the master control chip is reduced. Compared with the traditional square wave drive scheme, the number of IO pins of the master control chip is reduced, the number of IO pins of the master control chip is reduced, the interference of the sampling circuit to the weak drive circuit is reduced, the external radiation interference of the whole drive scheme is reduced, the precision of the back electromotive force sampling is improved, and the performance price ratio of the whole back electromotive force sampling scheme is improved. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0014] Figure 1 It is a module structure diagram of the existing brushless motor drive circuit scheme; Figure 2 It is a working principle diagram of the existing brushless motor drive circuit scheme; Figure 3 It is a circuit structure diagram of the related circuit module of the existing brushless motor drive circuit scheme, wherein, Figure 3 (a) is a MOS tube circuit, Figure 3 (b) is a MOS tube drive circuit, Figure 3 (c) is a master control chip, Figure 3 (d) is a back electromotive force sampling circuit; Figure 4 It is a module structure diagram of the motor drive circuit with built-in back electromotive force sampling in an embodiment; Figure 5 It is a circuit module structure diagram of the motor drive circuit with built-in back electromotive force sampling in an embodiment, wherein, Figure 5 (a) is a MOS tube circuit, Figure 5 (b) is a MOS tube drive circuit, Figure 5 (c) is a master control chip,Figure 5 (d) is a chip built-in sampling circuit; Figure 6 Figure 1 is a schematic diagram of a circuit structure of a chip built-in sampling circuit in one embodiment. DETAILED DESCRIPTION

[0015] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not intended to limit the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0016] It should be noted that the term "embodiment" mentioned herein means that the specific features, structures or characteristics described in conjunction with the embodiment can be included in at least one embodiment of the present application. The phrase is shown at various places in the specification does not necessarily refer to the same embodiment, nor is it independent or alternative to other embodiments. Those skilled in the art can understand that the embodiments described herein can be combined with other embodiments. The term "and / or" used herein refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0017] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0018] As shown in Figure 1, the existing brushless motor drive circuit scheme, working principle and related circuit module structure are shown respectively, and the related circuit module structure includes but is not limited to Figures 1 to 3 (c) the main control chip (such as CPU or MCU), Figure 3 (a) MOS (metal-oxide semiconductor field effect transistor) tube circuit, Figure 3 (b) MOS drive circuit and Figure 3 (d) back electromotive force sampling circuit, these circuit parts are used together to realize the driving of the brushless motor. It can be easily seen that the back electromotive force sampling circuit is placed outside the main control chip, and this external back electromotive force sampling circuit design needs 9 resistors and 3 capacitors, which has high device and patch cost and large circuit board area. If the sampling signal is outside the main control chip, the back electromotive force needs to be reduced and filtered before being input to the IO pin of the main control chip to detect the zero crossing point, and three sampling signals need to occupy three IO pins of the main control chip, which wastes the limited number of available IO pins on the main control chip and increases the chip packaging cost. Figure 3 ​

[0019] In one embodiment, as shown in Figure 4 A motor driving circuit with built-in back electromotive force sampling is provided, including a master control chip, a MOS tube circuit and a MOS tube driving circuit. The master control chip includes a chip body and a chip built-in sampling circuit, and the chip built-in sampling circuit includes a voltage dividing network, an RC filter network and a sampling comparison module. The chip body is connected to the sampling comparison module and the MOS tube driving circuit respectively, the MOS tube driving circuit is connected to the MOS tube circuit and the voltage dividing network respectively, and the voltage dividing network is connected to the sampling comparison module through the RC filter network. After the back electromotive force signal from the three-phase winding of the brushless motor is input into the voltage dividing network through the MOS tube driving circuit, the voltage is reduced to a low voltage range suitable for the internal circuit of the master control chip through the voltage dividing network, and after the reduced back electromotive force signal is filtered of high-frequency noise and interference signals through the RC filter network, a zero-crossing trigger signal is directly output to the chip body through the sampling comparison module, and the chip body is used to output a corresponding commutation instruction according to the zero-crossing trigger signal. The commutation instruction is used to drive the rotation of the brushless motor.

[0020] It can be understood that the chip body can be but is not limited to CPU, MCU or DSP. In this embodiment, the improvement is the design of the back electromotive force sampling circuit, which uses a new chip built-in sampling circuit built in the master control chip to directly realize the connection of the back electromotive force signal of the three-phase winding of the brushless motor output by the MOS tube driving circuit to the chip body. The explanation and description of parts such as MOS tube circuit, chip body and MOS tube driving circuit can be understood in the same way by referring to the same circuit module in the traditional brushless motor driving circuit scheme, which will not be repeated here.

[0021] It can be understood that the three-phase voltage signal of the brushless motor is a square wave signal with different phases, and the higher the speed of the motor, the faster the frequency of the waveform. At the same time, the square wave signal has irregular and strong energy noise signals, and the square wave drive is two-by-two conduction (i.e. one phase is floating at any time), so any driving phase can easily cause interference on the other two-phase sampling circuit, i.e. signal crosstalk. This interference not only affects the phase-to-phase, but also affects other traces on the circuit board, especially the ADC (analog-to-digital converter) sampling circuit, operational amplifier circuit and input detection circuit, etc. weak driving circuit. Moreover, square wave drive is highly dependent on back electromotive force sampling signal, and if the sampling signal is disturbed, the rotation of the brushless motor will be abnormal.

[0022] In the embodiment, on the drive circuit board of the brushless motor, the switch of the MOS tube circuit can be pushed by the pre-drive circuit, the back electromotive force waveform of the brushless motor can be directly observed from the MOS drive circuit, the back electromotive force waveform can be directly connected to the chip body (such as CPU or MCU) inside the main control chip through the branch of the pre-drive circuit, and then the back electromotive force circuit is reduced and filtered through an analog circuit, and then taken out from the IO pin inside the main control chip. The IO pin can be the input of the sampling comparison module (such as the input of the comparator or the channel of the analog-to-digital converter), and the zero-crossing point of the motor is detected through the comparator or the analog-to-digital converter to realize the commutation rotation of the brushless motor. Because the MOS drive circuit can observe the back electromotive force waveform of the brushless motor, the back electromotive force waveform of the brushless motor can no longer be output from the outside of the main control chip by setting multiple devices and occupying multiple IO pins. The pre-drive circuit can use the die (Die) of the pre-drive module manufactured by other chip manufacturers and be combined and sealed on the main control chip to complete the hardware implementation.

[0023] The above-mentioned motor drive circuit with built-in back electromotive force sampling is designed by optimizing the circuit based on the MOS drive circuit, the back electromotive force waveform is directly connected from the pre-drive circuit to the inside of the main control chip for processing, so as to simplify the external circuit of the chip on the circuit board, reduce the interference of the signal, and reduce the occupation of the IO pin of the main control chip. Compared with the traditional square wave drive scheme, the number of multiple sampling resistors and capacitors and other elements outside the main control chip is reduced, the number of IO pins of the main control chip is reduced, the interference of the sampling circuit to the weak drive circuit is reduced, the EMI radiation interference of the whole drive scheme is reduced, the precision of the back electromotive force sampling is improved, and the cost performance of the whole back electromotive force sampling scheme is improved.

[0024] In one embodiment, as shown in Figure 5 and 6 The sampling comparison module includes a comparator and / or an analog-to-digital converter. The comparator is used to compare the filtered back electromotive force signal with a preset threshold voltage, and directly output a zero-crossing trigger signal to the chip body. The analog-to-digital converter is used to convert the filtered back electromotive force signal into a digital signal and output it to the chip body. The chip body calculates and outputs the zero-crossing trigger signal according to the received back electromotive force signal.

[0025] It can be understood that Figure 5 (a) is a MOS tube circuit, Figure 5 (b) is a MOS tube drive circuit, Figure 5 (c) is a main control chip, Figure 5(d) is a sampling circuit built-in the chip. In the embodiment, the sampling comparison module can be implemented by a comparator, or by an analog-to-digital converter, or by both the comparator and the analog-to-digital converter. When the sampling comparison module includes both the comparator and the analog-to-digital converter, the two devices can be connected in parallel to the circuit, and can be configured by a corresponding configuration interface of the chip to flexibly select which device to use to process the filtered signal. Through the design of the sampling comparison module, the zero-crossing detection of the motor can be efficiently and flexibly implemented.

[0026] In one embodiment, as shown in Figure 5 and 6 , the sampling circuit built-in the chip further includes a resistor R1, and the sampling comparison module is connected to the chip through the resistor R1. It can be understood that in the embodiment, the resistor R1 can also be used to limit the current and match the impedance between the sampling comparison module and the chip, further improving the stability and reliability of the circuit.

[0027] In one embodiment, as shown in Figure 5 and 6 , the voltage division network includes resistors R2, R3, R4, R8, R9, and R10. The resistor R2 and the resistor R8 are connected in series, the resistor R3 and the resistor R9 are connected in series, and the resistor R4 and the resistor R10 are connected in series. One end of the resistor R8 is used to access the back electromotive force signal of the U-phase winding output by the MOS tube driving circuit (such as OUT U), one end of the resistor R9 is used to access the back electromotive force signal of the V-phase winding output by the MOS tube driving circuit (such as OUT V), and one end of the resistor R10 is used to access the back electromotive force signal of the W-phase winding output by the MOS tube driving circuit (such as OUT W). The other end of the resistor R2, the other end of the resistor R3, and the other end of the resistor R4 are all connected to the negative input end (such as CMP0 N) of the sampling comparison module. The other end of the resistor R8 is also connected to the first positive input end (such as CMP0 P[0]) of the sampling comparison module and the first filter branch of the RC filter network, the other end of the resistor R9 is also connected to the second positive input end (such as CMP0 P[1]) of the sampling comparison module and the second filter branch of the RC filter network, and the other end of the resistor R10 is also connected to the third positive input end (such as CMP0 P[2]) of the sampling comparison module and the third filter branch of the RC filter network.

[0028] It can be understood that in the embodiment, the above-mentioned voltage division network with a relatively simple circuit structure design can efficiently complete the voltage reduction processing of the signals corresponding to each phase, while simplifying the circuit structure. Those skilled in the art can select the number of added voltage division resistors according to the actual application scenario to meet the specific voltage reduction processing requirements, or replace resistors with different resistance values to meet the specific voltage reduction processing requirements.

[0029] In one embodiment, as shown in Figure 5 and 6 , the first filter branch of the RC filter network includes a resistor R5 and a capacitor C1, one end of the resistor R5 and one end of the capacitor C1 are both connected to the other end of the resistor R8, the other end of the resistor R5 and the other end of the capacitor C1 are both grounded.

[0030] In one embodiment, as shown in Figure 5 and 6 , the second filter branch of the RC filter network includes a resistor R6 and a capacitor C2, one end of the resistor R6 and one end of the capacitor C2 are both connected to the other end of the resistor R9, the other end of the resistor R6 and the other end of the capacitor C2 are both grounded.

[0031] In one embodiment, as shown in Figure 5 and 6 , the third filter branch of the RC filter network includes a resistor R7 and a capacitor C3, one end of the resistor R7 and one end of the capacitor C3 are both connected to the other end of the resistor R10, the other end of the resistor R7 and the other end of the capacitor C3 are both grounded.

[0032] It can be understood that the above-mentioned RC filter network is used in the three embodiments described above, which is a relatively simple circuit structure design, which can efficiently complete the filtering processing of each corresponding signal, and further simplify the circuit structure. Those skilled in the art can select to increase the number of access of the filtering RC device according to the actual application scene under the filtering processing requirement of each corresponding signal, and adjust the adaptability of series-parallel connection structure to meet the specific filtering processing requirement.

[0033] In order to more clearly and intuitively show the working implementation of the motor drive circuit with built-in back electromotive force sampling of any of the above, taking the circuit structure shown in Figure 6 as an example, the working process of the built-in sampling circuit of the chip is based on the three-stage processing of "voltage reduction-filtering-detection" of the back electromotive force signal, which is as follows: Signal access: When the brushless motor is running, the back electromotive force signal (from the UVW three-phase winding) generated at the output end of the MOS drive circuit is directly input to the input end of the built-in sampling circuit of the chip through internal wiring.

[0034] Voltage reduction processing: The input back electromotive force signal is first subjected to a voltage division network composed of resistors R2 to R4, resistors R8 to R10, to reduce the high voltage signal (such as the phase voltage when the motor is running) to a low voltage range (such as 0V to 3.3V) that can be tolerated by the internal circuit of the main control chip (such as CPU).

[0035] Filtering: the voltage-reduced back electromotive force signal is filtered by an RC filter network (consisting of capacitors C1-C3 and resistors R5-R7) to remove high-frequency noise and interference signals from the square wave signal, resulting in a smooth DC or low-frequency AC signal.

[0036] Zero-crossing detection: the filtered signal is input to a sampling comparison module (CMP|ADC). If the sampling comparison module uses a comparator (CMP), the zero-crossing trigger signal is directly output to the chip body of the main control chip by comparing with a preset threshold voltage. If the sampling comparison module uses an ADC, the input analog signal (i.e., the filtered signal) is converted into a digital signal and input to the chip body of the main control chip through resistor R1. The zero-crossing time is calculated by the internal algorithm of the main control chip, and then the zero-crossing trigger signal is output.

[0037] Brushless motor commutation control: the zero-crossing trigger signal triggers the main control chip to output corresponding commutation instructions to control the MOS tube circuit to switch the conduction phase, thereby realizing the continuous rotation of the brushless motor.

[0038] In the traditional scheme, back electromotive force sampling needs to be separately built outside the main control chip, and a separate voltage division and filtering circuit consisting of 9 resistors and 3 capacitors is needed (as described in the background art). In the above technical solution of the present application, these resistors (e.g., R1-R10) and capacitors (e.g., C1-C3) are integrated inside the main control chip, directly eliminating all passive components of the external sampling circuit (such as the traditional back electromotive force sampling circuit), reducing the cost of devices and the cost of surface mounting, and reducing the area of the circuit board.

[0039] In the traditional scheme, three back electromotive force sampling signals need to be input to the main control chip through three external IO pins. In the above technical solution of the present application, the three back electromotive force sampling signals are directly transmitted to the sampling comparison module (CMP|ADC) of the built-in sampling circuit inside the main control chip through internal wiring, without the need for external IO pins, saving the pin resources of the main control chip and reducing the packaging cost of the chip (reducing the number of pins can reduce the packaging size). In the traditional scheme, the wiring of the back electromotive force sampling circuit outside the main control chip is easily affected by the electromagnetic interference of the motor drive circuit (such as the switching of MOS tubes) and the crosstalk of other weak drive circuits (such as operational amplifiers and ADC circuits). In the above technical solution of the present application, the sampling circuit is built-in, and the signal path is completely located inside the main control chip, avoiding interference from external wiring. The built-in RC filter network is closer to the sampling module, and the filtering effect is more stable, which can effectively suppress the noise in the square wave signal, reduce the influence of interference on zero-crossing detection, and improve the sampling accuracy. After reducing the external elements and wiring of the main control chip, the electromagnetic radiation (EMI) of the entire drive scheme is significantly reduced, and the interference to the peripheral circuit is also reduced accordingly.

[0040] In one embodiment, a brushless motor is also provided, which is driven by the motor drive circuit with built-in back-EMF sampling of any of the above.

[0041] It can be understood that the specific explanation and description of the motor drive circuit with built-in back-EMF sampling in the present embodiment can be understood in the same way by referring to the explanation and description of the motor drive circuit with built-in back-EMF sampling in any of the above embodiments, which will not be repeated here. The above brushless motor can achieve more reliable and accurate driving performance with a smaller volume of the driving circuit by applying the above motor drive circuit with built-in back-EMF sampling.

[0042] The technical features of the above embodiments can be combined in any way. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the present application.

[0043] The above embodiments only express several embodiments of the present application, which are described in detail and specifically, but should not be considered as a limitation to the protection scope of the present application. It should be pointed out that for those skilled in the art, some modifications and improvements can be made without departing from the concept of the present application, which are all within the protection scope of the present application.

Claims

1. A motor drive circuit with built-in back EMF sampling, characterized in that, It includes a main control chip, a MOSFET circuit, and a MOSFET driver circuit. The main control chip includes a chip body and a chip-built sampling circuit. The chip-built sampling circuit includes a voltage divider network, an RC filter network, and a sampling comparison module. The chip body is connected to the sampling comparison module and the MOSFET driver circuit. The MOSFET driver circuit is connected to the MOSFET circuit and the voltage divider network. The voltage divider network is connected to the sampling comparison module through the RC filter network. The MOSFET drive circuit inputs the back EMF signal from the three-phase windings of the brushless motor into the voltage divider network. The voltage divider network then reduces the voltage to a low voltage range suitable for the internal circuitry of the main control chip. After the back EMF signal is reduced, it is filtered by an RC filter network to remove high-frequency noise and interference signals. Finally, the sampling and comparison module directly outputs a zero-crossing trigger signal to the chip body. The chip body then outputs the corresponding commutation command based on the zero-crossing trigger signal. The commutation command is used to drive the rotation of the brushless motor.

2. The motor drive circuit with built-in back EMF sampling according to claim 1, characterized in that, The sampling and comparison module includes a comparator and / or an analog-to-digital converter. The comparator is used to compare the filtered back EMF signal with a preset threshold voltage and directly output a zero-crossing trigger signal to the chip body. The analog-to-digital converter is used to convert the filtered back EMF signal into a digital signal and output it to the chip body. The chip body calculates and outputs the zero-crossing trigger signal based on the received back EMF signal.

3. The motor drive circuit with built-in back EMF sampling according to claim 2, characterized in that, The chip's built-in sampling circuit also includes a resistor R1, and the sampling comparison module is connected to the chip body through the resistor R1.

4. The motor drive circuit with built-in back EMF sampling according to claim 2 or 3, characterized in that, The voltage divider network includes resistors R2, R3, R4, R8, R9, and R10. Resistors R2 and R8 are connected in series, resistors R3 and R9 are connected in series, and resistors R4 and R10 are connected in series. One end of resistor R8 is used to connect to the back electromotive force signal of the U-phase winding output by the MOSFET driver circuit. One end of resistor R9 is used to connect to the back electromotive force signal of the V-phase winding output by the MOSFET driver circuit. One end of resistor R10 is used to connect to the back electromotive force signal of the W-phase winding output by the MOSFET driver circuit. The other ends of resistors R2, R3, and R4 are all connected to the negative input of the sampling comparison module. The other end of resistor R8 is also connected to the first positive input of the sampling comparison module and the first filtering branch of the RC filter network. The other end of resistor R9 is also connected to the second positive input of the sampling comparison module and the second filtering branch of the RC filter network. The other end of resistor R10 is also connected to the third positive input of the sampling comparison module and the third filtering branch of the RC filter network.

5. The motor drive circuit with built-in back EMF sampling according to claim 4, characterized in that, The first filtering branch of the RC filter network includes a resistor R5 and a capacitor C1. One end of the resistor R5 and one end of the capacitor C1 are both connected to the other end of the resistor R8. The other ends of the resistor R5 and the other ends of the capacitor C1 are both grounded.

6. The motor drive circuit with built-in back EMF sampling according to claim 4, characterized in that, The second filtering branch of the RC filter network includes a resistor R6 and a capacitor C2. One end of the resistor R6 and one end of the capacitor C2 are both connected to the other end of the resistor R9, and the other ends of the resistor R6 and the other ends of the capacitor C2 are both grounded.

7. The motor drive circuit with built-in back EMF sampling according to claim 4, characterized in that, The third filtering branch of the RC filter network includes resistor R7 and capacitor C3. One end of resistor R7 and one end of capacitor C3 are both connected to the other end of resistor R10, and the other ends of resistor R7 and capacitor C3 are both grounded.

8. A brushless motor, characterized in that, Driven by the motor drive circuit with built-in back EMF sampling as described in any one of claims 1 to 7.

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