Brushless DC motor drive circuit and starting control method thereof

Abstract

A DC brushless motor drive circuit and a startup control method thereof. The DC brushless motor drive circuit comprises: a driving power stage circuit for providing a startup probe signal to excite a DC brushless motor in a startup mode, thereby causing a rotor of the DC brushless motor to perform trial rotation; a current unidirectional circuit, a reverse terminal of which is coupled to the DC brushless motor, for detecting a back electromotive force generated by the DC brushless motor during trial rotation in the startup mode, generating a detection signal, and limiting the voltage at a forward terminal of the current unidirectional circuit to not exceed a clamping voltage; a bias circuit, coupled to a forward terminal of the current unidirectional circuit, for biasing the current unidirectional circuit in a forward operating state; and a sensing circuit, coupled to the forward terminal, for generating a sensing signal based on the detection signal to indicate a trial rotation state of the DC brushless motor.

Description

Technical Field

[0001] The present invention relates to a DC brushless motor driving circuit, and in particular to a DC brushless motor driving circuit capable of detecting extremely small back electromotive force. Background Art

[0002] During startup, conventional brushless DC motor drive circuits typically use resistors to divide the voltage to extract the back EMF of each motor phase. This voltage is then used to determine the motor rotor position and accurately control the current in each phase during normal operation. The magnitude of the signal extracted during startup is proportional to the back EMF voltage. A smaller back EMF voltage results in a smaller signal, making it difficult for the IC to interpret. Conversely, an excessively large back EMF, while easier to interpret, requires significant perturbations in the motor rotor, which are difficult to detect.

[0003] In view of this, the present invention addresses the above-mentioned deficiencies in the prior art and proposes an innovative DC brushless motor drive circuit and a startup control method thereof. Summary of the Invention

[0004] In one aspect, the present invention provides a brushless DC motor drive circuit for driving a brushless DC motor. The brushless DC motor drive circuit includes: a drive power stage circuit for providing a start-up detection signal in a startup mode to excite the brushless DC motor, thereby causing a rotor of the brushless DC motor to test rotate; a current unidirectional circuit having a reverse terminal coupled to the brushless DC motor for detecting a back electromotive force generated during the test rotation of the brushless DC motor in the startup mode, generating a detection signal at a forward terminal of the current unidirectional circuit, and limiting the voltage of the forward terminal to not exceed a clamping voltage when the voltage at the reverse terminal exceeds the voltage at the forward terminal; a bias circuit coupled to the forward terminal for biasing the current unidirectional circuit in a forward operating state and providing the clamping voltage; and a sensing circuit coupled to the forward terminal for generating a sensing signal based on the detection signal to indicate a test rotation state of the brushless DC motor.

[0005] In one embodiment, the brushless DC motor has a plurality of coils, and the driving power stage circuit provides a plurality of operating currents to the corresponding plurality of coils in a normal mode after the startup mode ends according to the sensing signal, thereby controlling the rotation of the rotor.

[0006] In one embodiment, the current unidirectional circuit has multiple unidirectional control elements, and each of the unidirectional control elements senses the corresponding back electromotive force in the startup mode to generate the corresponding detection signal; wherein the sensing circuit generates corresponding multiple sensing signals based on the multiple detection signals to indicate the position relationship of the rotor of the DC brushless motor at a certain point in time.

[0007] In one embodiment, the current unidirectional circuit has at least one unidirectional control element, which includes one of the following: a diode, the forward end and the reverse end of the diode being respectively coupled to the forward end and the reverse end of the current unidirectional circuit; a first MOSFET element, configured as a MOSFET diode in a diode-connected manner, the forward end and the reverse end of the MOSFET diode being respectively coupled to the forward end and the reverse end of the current unidirectional circuit; or a second MOSFET element, wherein the first end and the second end of the second MOSFET element are respectively coupled to the forward end and the reverse end of the current unidirectional circuit, when the voltage of the reverse end of the current unidirectional circuit exceeds the voltage of the forward end of the current unidirectional circuit, the MOSFET element is controlled to be non-conductive, and when the voltage of the reverse end of the current unidirectional circuit does not exceed the voltage of the forward end of the current unidirectional circuit, the MOSFET element is controlled to be conductive.

[0008] In one embodiment, the driving power stage circuit includes a plurality of half-bridge power elements to correspondingly generate the plurality of operating currents.

[0009] In one embodiment, before the start-up mode begins, the sensing circuit controls the multiple lower bridge elements of the multiple groups of half-bridge power elements so that one end of the multiple coils is electrically connected to a ground potential to calibrate the forward conduction voltage of the multiple unidirectional control elements.

[0010] In another aspect, the present invention provides a startup control method for a brushless DC motor drive circuit, wherein the brushless DC motor drive circuit is used to drive a brushless DC motor. The startup control method for the brushless DC motor drive circuit includes: providing a startup probe signal in a startup mode to excite the brushless DC motor, thereby causing a rotor of the brushless DC motor to test rotate; detecting a back electromotive force generated by the brushless DC motor during the test rotation in a unidirectional current control manner in the startup mode to generate a detection signal; limiting the detection signal to not exceed a clamping voltage; and generating a sensing signal based on the detection signal to indicate a test rotation state of the brushless DC motor.

[0011] In one embodiment, the brushless DC motor has a plurality of coils, and a driving power stage circuit provides a plurality of operating currents to the corresponding plurality of coils in a normal mode after the startup mode ends according to the sensing signal, thereby controlling the rotation of the rotor.

[0012] In one embodiment, the startup control method of the brushless DC motor drive circuit further includes: in the startup mode, detecting the multiple back electromotive forces corresponding to the multiple coils in a current unidirectional control manner to generate corresponding multiple detection signals; and generating corresponding multiple sensing signals based on the multiple detection signals to indicate the position relationship of the rotor of the brushless DC motor at a certain point in time.

[0013] An advantage of the present invention is that the present invention can extract proportional back electromotive force through the current unidirectional circuit and bias it at a positive level to facilitate the controller to read it, and can block high voltage to avoid damage to the controller.

[0014] Another advantage of the present invention is that the bias circuit can clamp high voltage to avoid damage to the controller.

[0015] Another advantage of the present invention is that the present invention can detect extremely small back electromotive force, and the rotor of the DC brushless motor only needs to be slightly disturbed, without generating a large disturbance.

[0016] The following detailed description through specific embodiments will make it easier to understand the purpose, technical content, characteristics and effects achieved by the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. 1 is a schematic diagram showing a brushless DC motor driving circuit according to an embodiment of the present invention.

[0018] Figure 2 It is a schematic diagram showing detection waveforms of extremely small back electromotive force in a conventional DC brushless motor driving circuit and the DC brushless motor driving circuit of the present invention.

[0019] Figure 3 The flowchart shows a startup control method of a brushless DC motor driving circuit according to an embodiment of the present invention.

[0020] Figures 4A-4C FIG. 1 is a schematic diagram illustrating an embodiment of a unidirectional control element in a unidirectional current circuit of a brushless DC motor driving circuit according to an embodiment of the present invention.

[0021] Explanation of symbols in the figure

[0022] 10: Brushless DC motor drive circuit

[0023] 101: Controller

[0024] 1011: Sensing circuit

[0025] 102: Driving power stage circuit

[0026] 1021: Driver

[0027] 10211: High-side driver

[0028] 10212: Low-voltage side driver

[0029] 1022: Power stage circuit

[0030] 103: One-way current circuit

[0031] 1031, 1031w, 1031v, 1031u: Reverse end

[0032] 1032, 1032w, 1032v, 1032u: Forward-facing end

[0033] 104: Bias Circuit

[0034] 1041: Node

[0035] 20: Brushless DC motor

[0036] 30: Starting control method of DC brushless motor drive circuit

[0037] 301, 302, 303, 3031, 304, 305, 306, 3061, 307: Steps

[0038] C1: capacitor

[0039] eu, ev, ew: back electromotive force

[0040] GATE: control terminal

[0041] ia, ib, ic: resistance

[0042] Lu, Lv, Lw: Phase inductance

[0043] N: Neutral point

[0044] M1, M2, M3: MOSFET components

[0045] Qh1, Qh2, Qh3: upper bridge power components

[0046] Ql1, Ql2, Ql3: lower bridge power components

[0047] Ru, Rv, Rw: Phase resistance

[0048] Vbu, Vbv, Vbw: detection signal

[0049] Vsu, Vsv, Vsw: voltage DETAILED DESCRIPTION

[0050] The drawings in the present invention are schematic diagrams, mainly intended to illustrate the coupling relationship between various circuits and the relationship between various signal waveforms. The circuits, signal waveforms and frequencies are not drawn according to scale.

[0051] Figure 1 FIG. 1 is a schematic diagram showing a brushless DC motor driving circuit according to an embodiment of the present invention. Figure 1 As shown, a brushless DC motor drive circuit 10 of the present invention is used to drive a brushless DC motor 20. The brushless DC motor drive circuit 10 includes a controller 101, a drive power stage circuit 102, a current unidirectional circuit 103, and a bias circuit 104. The brushless DC motor 20 has multiple coils. For example, a three-phase brushless DC motor has U-phase, V-phase, and W-phase coils. Figure 1 Only a three-phase brushless DC motor is shown, but the present invention is not limited to three-phase brushless DC motors and can also be applied to two-phase brushless DC motors, five-phase brushless DC motors, or other multi-phase brushless DC motors. Controller 101 includes a sensing circuit 1011. In one embodiment, sensing circuit 1011 can be an analog circuit that directly processes analog signals, or it can include an analog-to-digital conversion circuit that converts analog signals into digital signals and then processes the digital signals. The driving power stage circuit 102 is used to provide a starting probe signal to at least one coil of the brushless DC motor 20 in a starting mode to excite the brushless DC motor 20 and cause a rotor of the brushless DC motor 20 to test rotate. After the test rotation, the starting probe signal is stopped, and the current unidirectional circuit 103 detects the back electromotive force generated by the brushless DC motor 20 during the test rotation to obtain relevant information about the corresponding coil.

[0052] In a preferred embodiment, the driving power stage circuit 102 provides a starting probe signal to at least one coil of the brushless DC motor 20 during the startup mode to excite the brushless DC motor 20 and cause the rotor of the brushless DC motor 20 to test rotate. After the test rotation, the starting probe signal is stopped, and the current unidirectional circuit 103 detects the back electromotive force generated by each phase during the test rotation of the brushless DC motor 20 to determine the time point position relationship of the rotor and provides it to the driving power stage circuit 102. Based on the time point position relationship of the rotor indicated by the sensed signal, the driving power stage circuit 102 provides multiple operating currents in the normal mode after the startup mode ends to supply the corresponding U-phase, V-phase, and W-phase coils to control the rotation of the rotor.

[0053] For example, the reverse terminal 1031 of the unidirectional current circuit 103 is coupled to the brushless DC motor 20 to detect the back electromotive forces ew, ev, and eu generated during the test run of the brushless DC motor 20 during the startup mode. Detection signals Vbw, Vbv, and Vbu are generated at the forward terminal 1032 of the unidirectional current circuit 103. When the voltage at the reverse terminal 1031 exceeds the voltage at the forward terminal 1032, the voltage at the forward terminal of the unidirectional current circuit 103 is limited to a clamping voltage, such as, but not limited to, +5V, to protect the controller 101. This eliminates the need for high-voltage-resistant electronic components in the controller 101. The voltage at the forward end 1032 of the so-called current limiting unidirectional circuit 103 does not exceed a clamping voltage to prevent the controller 101 from being exposed to a high voltage exceeding a preset voltage. Therefore, in one embodiment, the clamping voltage is related to the upper voltage tolerance limit of the controller 101. For example, a clamping voltage lower than the upper voltage tolerance limit of the controller 101 can be selected.

[0054] The reverse end 1031 of the current unidirectional circuit 103 includes, for example Figure 1 1031w, 1031v, 1031u shown, and the forward end of the current unidirectional circuit 103 includes, for example Figure 1 The function of the current unidirectional circuit 103 is to control the current to flow only from the forward end 1032 to the reverse end 1031, and to prevent the current from flowing from the reverse end 1031 to the forward end 1032. From another perspective, when the voltage of the reverse end 1031 exceeds the voltage of the forward end 1032, the reverse end 1031 and the forward end 1032 are not conductive. When the voltage of the reverse end 1031 does not exceed the voltage of the forward end 1032, the reverse end 1031 and the forward end 1032 are conductive.

[0055] The current unidirectional circuit 103 has at least one unidirectional control element, and each unidirectional control element senses the corresponding back electromotive force ew, ev, eu in the startup mode and generates the corresponding detection signal Vbw, Vbv, Vbu. Figure 1 As shown, in one embodiment, the unidirectional control element may be a diode, and the forward end and the reverse end of the diode are respectively coupled to the forward end 1032 and the reverse end 1031 of the current unidirectional circuit 103. In one embodiment, the diode may include but is not limited to a PN diode, a Schottky diode, or a Zener diode.

[0056] Figures 4A-4C FIG. 1 is a schematic diagram showing an embodiment of a unidirectional control element in a current unidirectional circuit of a brushless DC motor drive circuit according to an embodiment of the present invention. Figure 4A and Figure 4BAs shown, in another embodiment, the unidirectional control element can be a first MOSFET element (such as M1, M2), which is configured as a MOSFET diode in a diode-connected manner, and the forward end and the reverse end of the MOSFET diode are respectively coupled to the forward end 1032 and the reverse end 1031 of the current unidirectional circuit 103. Taking NMOS as an example, Figure 4A As shown, the gate and drain of the NMOSFET element M1 are coupled to the forward end of the NMOSFET diode, and the source of the NMOSFET element M1 is coupled to the reverse end of the NMOSFET diode. Figure 4B As shown, the gate and drain of the PMOSFET element M2 are coupled to the reverse end of the PMOSFET diode, and the source of the PMOSFET element M2 is coupled to the forward end of the PMOSFET diode.

[0057] like Figure 4C As shown, in another embodiment, the unidirectional control element may be a second MOSFET element (such as M3), wherein the first end and the second end of the second MOSFET element M3 are respectively coupled to the forward end 1032 and the reverse end 1031 of the current unidirectional circuit 103. When the voltage of the reverse end 1031 of the current unidirectional circuit 103 exceeds the voltage of the forward end 1032 of the current unidirectional circuit 103, the MOSFET element is controlled to be non-conducting through the control end GATE. When the voltage of the reverse end 1031 of the current unidirectional circuit 103 does not exceed the voltage of the forward end 1032 of the current unidirectional circuit 103, the MOSFET element is controlled to be conducting.

[0058] Please continue reading Figure 1The bias circuit 104 is coupled to a forward terminal 1032 of the current unidirectional circuit 103 to bias the current unidirectional circuit 103 in a forward operating state and to provide the aforementioned clamping voltage. In one embodiment, the other terminal of the bias circuit 104 is coupled to a clamping voltage such as but not limited to +5V. In one embodiment, the bias circuit 104 may include at least one resistor. The aforementioned at least one resistor is commonly coupled to a node 1041, and the node 1041 is further coupled to a clamping voltage such as but not limited to +5V. The sensing circuit 1011 is coupled to the forward terminal 1032 to generate a sensing signal based on the detection signals Vbw, Vbv, and Vbu to indicate a trial rotation state of the DC brushless motor 20. The voltages of the reverse terminal 1031 of each unidirectional control element are voltages Vsw, Vsv, and Vsu, respectively. In one embodiment, the sensing circuit 1011 generates a plurality of corresponding sensing signals based on the detection signals Vbw, Vbv, and Vbu, indicating the positional relationship of the rotor of the brushless DC motor 20 at a given point in time, thereby determining the test rotation status of the brushless DC motor 20. Based on the sensing signals, the driving power stage circuit 102 provides a plurality of operating currents to the corresponding coils in a normal mode after the startup mode ends, thereby controlling the rotation of the rotor.

[0059] The driving power stage circuit 102 includes a driver 1021 and a power stage circuit 1022. Driver 1021 is coupled to the power stage circuit 1022. Driver 1021 may include a high-side driver 10211 and a low-side driver 10212. Power stage circuit 1022 may include a plurality of half-bridge power elements to generate the plurality of operating currents. The aforementioned half-bridge power elements include upper-bridge power elements Qh1, Qh2, and Qh3, and lower-bridge power elements Ql1, Ql2, and Ql3. Upper-bridge power element Qh1 is connected in series with lower-bridge power element Ql1 and resistor ia. Upper-bridge power element Qh2 is connected in series with lower-bridge power element Ql2 and resistor ib. Upper-bridge power element Qh3 is connected in series with lower-bridge power element Ql3 and resistor ic. Resistors ia, ib, and ic are commonly coupled to ground potential. Upper-bridge power elements Qh1, Qh2, and Qh3 are commonly coupled to capacitor C1. The high-side driver 10211 is coupled to the upper-bridge power element Qh1, while the low-side driver 10212 is coupled to the lower-bridge power element Ql1. The nodes between the upper-bridge power elements Qh1, Qh2, and Qh3 and the lower-bridge power elements Ql1, Ql2, and Ql3 are respectively coupled to the corresponding phase inductors Lw, Lv, and Lu of the brushless DC motor 20.

[0060] The brushless DC motor 20 includes a W-phase inductor Lw and a phase resistor Rw, a V-phase inductor Lv and a phase resistor Rv, and a U-phase inductor Lu and a phase resistor Ru. The phase inductor Lw is connected in series with the phase resistor Rw, the phase inductor Lv is connected in series with the phase resistor Rv, and the phase inductor Lu is connected in series with the phase resistor Ru. The phase resistors Rw, Rv, and Ru of each phase are commonly coupled to a neutral point N. Before the start-up mode begins, the sensing circuit 1011 controls the lower bridge elements Ql1, Ql2, and Ql3 of the multiple half-bridge power devices so that one end of the multiple coils is electrically connected to a ground potential. This calibrates the forward conduction voltages of the multiple unidirectional control devices and records the voltages in the sensing circuit 1011. In one embodiment, the lower bridge elements Ql1, Ql2, and Ql3 of the multiple half-bridge power devices are sequentially controlled so that one end of the multiple coils is electrically connected to a ground potential. This calibrates the forward conduction voltages of the multiple unidirectional control devices. In another embodiment, the multiple lower bridge components Ql1, Ql2, and Ql3 of multiple sets of half-bridge power components can be simultaneously controlled so that one end of the multiple coils is simultaneously electrically connected to a ground potential, thereby simultaneously correcting the forward conduction voltages of multiple unidirectional control components. In yet another embodiment, the multiple lower bridge components Ql1, Ql2, and Ql3 of multiple sets of half-bridge power components can be randomly controlled so that one end of the multiple coils is randomly electrically connected to a ground potential, thereby randomly correcting the forward conduction voltages of multiple unidirectional control components.

[0061] Figure 2 Schematic diagram showing the detection waveforms of extremely small back electromotive force in a conventional DC brushless motor drive circuit and the DC brushless motor drive circuit of the present invention. The voltages Vsw, Vsv, and Vsu at the reverse end 1031 of each unidirectional control element, the detection signal Vbv measured by the conventional method, and the detection signal Vbv measured by the DC brushless motor drive circuit of the present invention are shown in FIG. Figure 2 As shown. Figure 2 It can be seen that, with the same startup probe signal, the amplitude of the back EMF measured by the conventional method is only 5mV, while the amplitude of the back EMF measured by the DC brushless motor drive circuit of the present invention can be maintained at the original amplitude of 500mV. This can improve the signal resolution and make it easier for the controller to interpret the back EMF. In addition, the back EMF measured by the DC brushless motor drive circuit of the present invention can be biased at a positive level (for example, but not limited to +0.7V) for the controller to interpret. If it is not biased at a positive level, a negative back EMF may be generated, which requires the use of a negative voltage controller. However, negative voltage controllers have the disadvantage of being difficult to manufacture.

[0062] Figure 3 FIG. 1 is a flow chart showing a method for starting a brushless DC motor drive circuit according to an embodiment of the present invention. Figure 3As shown, the startup control method 30 for a brushless DC motor drive circuit of the present invention includes step 301. Before the start-up mode begins, the plurality of lower-bridge components of the plurality of half-bridge power components are controlled so that one end of the plurality of coils is electrically connected to a ground potential to calibrate the forward conduction voltage of the plurality of unidirectional control components. Then, in step 302, during a startup mode, a startup probe signal is provided to excite the brushless DC motor, causing a rotor of the brushless DC motor to test rotate. Next, in step 303, during the startup mode, a back electromotive force generated by the brushless DC motor during the test rotation is detected using a unidirectional current control method to generate a detection signal. In one embodiment, step 303 may include step 3031. During the startup mode, the plurality of back electromotive forces corresponding to the plurality of coils are detected using a unidirectional current control method to generate the corresponding plurality of detection signals. Next, in step 304, the detection signal is limited to not exceed a clamping voltage. Next, in step 305, the current unidirectional circuit is biased in a forward operating state. Next, in step 306, a sensing signal is generated based on the detection signal to indicate a test rotation state of the brushless DC motor. In one embodiment, step 306 may include step 3061, generating a corresponding plurality of sensing signals based on a plurality of the detection signals to indicate a positional relationship of the rotor of the brushless DC motor at a given point in time. Next, in step 307, based on the sensing signals, multiple operating currents are provided to corresponding coils in a normal mode after the startup mode ends, thereby controlling the rotation of the rotor.

[0063] As described above, the present invention utilizes a unidirectional current circuit to extract proportional back EMF and bias it at a positive level for interpretation by the controller, while also blocking high voltages to prevent damage to the controller. The present invention also utilizes a bias circuit to clamp a fixed voltage, preventing damage to the controller. Furthermore, the present invention can detect extremely small back EMFs, requiring only slight perturbations of the brushless DC motor's rotor, rather than significant disturbances.

[0064] The present invention has been described above with respect to the preferred embodiments, but the above description is only for those skilled in the art to easily understand the content of the present invention and is not intended to limit the broadest scope of the present invention. The various embodiments described are not limited to individual applications, but can also be applied in combination. For example, two or more embodiments can be used in combination, and part of the components in one embodiment can also be used to replace the corresponding components in another embodiment. In addition, under the same spirit of the present invention, those skilled in the art can think of various equivalent changes and various combinations. For example, the present invention refers to "processing or calculating or generating an output result according to a certain signal", which is not limited to the signal itself, but also includes, when necessary, performing voltage-to-current conversion, current-to-voltage conversion, and / or ratio conversion on the signal, and then processing or calculating the converted signal to generate an output result. It can be seen that under the same spirit of the present invention, those skilled in the art can think of various equivalent changes and various combinations, and there are many combinations, which are not listed here one by one. Therefore, the scope of the present invention should cover the above and all other equivalent changes.

Claims

1. A brushless DC motor drive circuit for driving a brushless DC motor, the brushless DC motor drive circuit comprising: a driving power stage circuit for providing a starting probe signal in a starting mode to excite the brushless DC motor and cause a rotor of the brushless DC motor to test rotate; a current unidirectional circuit having a reverse terminal coupled to the brushless DC motor to detect a back electromotive force generated by the brushless DC motor during test rotation in the startup mode, generate a detection signal at a forward terminal of the current unidirectional circuit, and limit the voltage of the forward terminal to not exceed a clamping voltage when the voltage at the reverse terminal exceeds the voltage at the forward terminal; a bias circuit coupled to the forward terminal for biasing the current unidirectional circuit in a forward operating state and for providing the clamping voltage; as well as A sensing circuit is coupled to the forward end and is used to generate a sensing signal according to the detection signal to indicate a test rotation state of the brushless DC motor. The brushless DC motor has a plurality of coils, and the driving power stage circuit provides a plurality of operating currents to the corresponding coils in a normal mode after the start-up mode ends according to the sensing signal, thereby controlling the rotation of the rotor. The current unidirectional circuit has a plurality of unidirectional control elements, and each of the unidirectional control elements senses the corresponding back electromotive force in the startup mode to generate the corresponding detection signal. The sensing circuit generates a plurality of corresponding sensing signals based on the plurality of detection signals to indicate the position relationship of the rotor of the brushless DC motor at a certain point in time. The driving power stage circuit includes multiple sets of half-bridge power elements to generate the multiple operating currents accordingly. Before the start-up mode begins, the sensing circuit controls the multiple lower bridge elements of the multiple sets of half-bridge power elements so that one end of the multiple coils is electrically connected to a ground potential to calibrate the forward conduction voltage of the multiple unidirectional control elements.

2. The brushless DC motor driving circuit as claimed in claim 1 , wherein the current unidirectional circuit comprises at least one unidirectional control element, the unidirectional control element comprising: a diode, wherein a forward end and a reverse end of the diode are respectively coupled to the forward end and the reverse end of the current unidirectional circuit; or a first MOSFET element configured as a MOSFET diode in a diode connection manner, wherein a forward end and a reverse end of the MOSFET diode are respectively coupled to the forward end and the reverse end of the current unidirectional circuit; or a second MOSFET element, wherein a first end and a second end of the second MOSFET element are respectively coupled to the forward end and the reverse end of the current unidirectional circuit; when the voltage of the reverse end of the current unidirectional circuit exceeds the voltage of the forward end of the current unidirectional circuit, the MOSFET element is controlled to be non-conductive; when the voltage of the reverse end of the current unidirectional circuit does not exceed the voltage of the forward end of the current unidirectional circuit, the MOSFET element is controlled to be conductive.

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