Control circuit and control method of PWM (Pulse Width Modulation) speed regulation fan

Abstract

The invention provides a control circuit of a PWM (Pulse Width Modulation) speed regulation fan. The control circuit comprises an overvoltage protection circuit, a power conversion circuit and a driving control circuit, the power supply is connected to the power conversion circuit through the overvoltage protection circuit, the overvoltage protection circuit is used for adjusting fluctuation of an external power supply, and the power conversion circuit is used for providing power for the driving control circuit; the control circuit is connected with the PWM speed regulation circuit through the low-pass filter circuit and the fault restart circuit; the control circuit is used for outputting a fixed PWM signal after reading a rotating speed requirement from the speed regulation circuit, converting the PWM signal into an analog quantity speed regulation signal, inputting the analog quantity speed regulation signal into the PWM speed regulation circuit, and regulating the speed of the PWM signal through the PWM speed regulation circuit; and the fault restarting circuit is used for restarting the fan after the fan is subjected to stalling or overcurrent protection. Wide-frequency and wide-voltage-range PWM speed regulation is realized, and overvoltage protection is carried out at the same time.

Description

Technical Field

[0001] This invention relates to the field of wind turbine control technology, specifically to a control circuit and control method for a PWM speed-regulating wind turbine. Background Technology

[0002] The existing speed control port circuit has the following main problems:

[0003] 1. The speed regulation frequency of PWM signals is limited, which is related to the turn-on and turn-off delays of components such as transistors; 2. The speed regulation voltage range of the PWM signal is limited and is related to the power supply voltage of the microcontroller; 3. It lacks isolation capabilities; 4. Susceptible to damage from external power fluctuations. Summary of the Invention

[0004] In view of this, the embodiments of this specification provide a control circuit and control method for a PWM speed-regulating fan. This achieves wide-frequency, wide-voltage-range PWM speed regulation, while simultaneously implementing overvoltage protection in the hardware circuit.

[0005] The embodiments in this specification provide the following technical solutions: A control circuit for a PWM speed-regulating fan includes: The circuit includes an overvoltage protection circuit, a power conversion circuit, and a drive control circuit. The drive control circuit includes a control circuit, a PWM speed regulation circuit, a low-pass filter circuit, and a fault restart circuit. The 28V DC power supply is connected to the power conversion circuit through the overvoltage protection circuit. The overvoltage protection circuit is used to regulate external power fluctuations, and the power conversion circuit is used to provide power to the drive control circuit. The control circuit is connected to the PWM speed control circuit through a low-pass filter circuit and a fault restart circuit; The control circuit reads the speed requirement from the speed control circuit and outputs a fixed PWM signal. The PWM signal is then converted into an analog speed control signal by a low-pass filter circuit and input to the PWM speed control circuit. The PWM speed control circuit then adjusts the speed of the PWM signal. The fault restart circuit is used to restart the fan after it experiences a stall or overcurrent protection failure.

[0006] Furthermore, the PWM speed control circuit includes: The seventh high-speed optocoupler U7, the twenty-ninth resistor R29, the thirtieth resistor R30, and the seventh Zener diode D7; The positive input terminal of the seventh high-speed optocoupler U7 is connected to the twenty-ninth resistor R29, and then connected to the +5V power supply. The negative input terminal of the seventh high-speed optocoupler U7 is connected to one end of the thirtieth resistor R30 and the seventh Zener diode D7, and the other end of the thirtieth resistor R30 is connected to the speed control input KZ.

[0007] Furthermore, the low-pass filter circuit includes: The eighth resistor R8 and the thirteenth capacitor C13; One end of the eighth resistor R8 is connected to one end of the thirteenth capacitor C13 and the voltage adjustment terminal, respectively, and the other end of the thirteenth capacitor C13 is grounded.

[0008] Furthermore, the overvoltage protection circuit includes: The first PNP transistor Q1, the second P-channel field-effect transistor Q2, the first Zener diode ZD1, and the third resistor R3; The first PNP transistor Q1 and the third resistor R3 are both connected in parallel across the gate and source terminals of the second P-channel MOSFET Q2, and the first Zener diode ZD1 is connected to the base of the first PNP transistor Q1.

[0009] Furthermore, the fault restart circuit includes: the twelfth field-effect transistor Q12, the thirteenth transistor Q13, the fourteenth resistor R14, the fifteenth resistor R15, the sixteenth resistor R16, and the seventeenth resistor R17; The gate of the twelfth field-effect transistor Q12 is connected to the collector of the thirteenth transistor Q13 through the fifteenth resistor R15. The drain of the twelfth field-effect transistor Q12 is connected to the +5V power supply, and the source of the twelfth field-effect transistor Q12 is connected to VDD. The fourteenth resistor R14 is connected in series between the +5V power supply and the fifteenth resistor R15; The emitter of the thirteenth transistor Q13 is grounded, and the base of the thirteenth transistor Q13 is connected to one end of the sixteenth resistor R16 and the seventeenth resistor R17. The other end of the seventeenth resistor R17 is grounded.

[0010] A control method for a PWM speed-regulating fan, the method realizing wide-frequency and wide-voltage range PWM speed regulation of the fan based on a control circuit, including the following steps: Receives externally input PWM speed control signals; The externally input PWM speed control signal is isolated and its level is converted by the PWM speed control circuit to obtain a PWM signal that matches the level of the internal control circuit of the fan. The duty cycle of the PWM signal after level matching is read by the control circuit, and the speed requirement is obtained. Based on the speed requirement, a fixed-frequency PWM control signal is output through the control circuit; A low-pass filter circuit is used to convert a fixed-frequency PWM control signal into an analog speed regulation signal. The analog speed control signal is input to the fan drive chip, which then controls the fan speed.

[0011] Furthermore, the externally input PWM speed control signal is isolated and its level is converted by the PWM speed control circuit, including: When the high-level voltage of the externally input PWM speed control signal is in the range of 3.3V to 5.1V and the seventh Zener diode D7 is not turned on, the input voltage is divided by the twenty-ninth resistor R29 and the thirtieth resistor R30. Configure the resistance values ​​of the 29th resistor R29 and the 30th resistor R30 in a fixed ratio so that the voltage difference applied between the positive and negative terminals of the input of the 7th high-speed optocoupler U7 after voltage division is lower than the turn-on threshold voltage of the 7th high-speed optocoupler U7. By using the total resistance of the twenty-ninth resistor R29 and the thirtieth resistor R30, the current flowing into the input terminal of the seventh high-speed optocoupler U7 is limited to below the minimum threshold current of the seventh high-speed optocoupler U7, so that the seventh high-speed optocoupler U7 remains off and outputs a high level. When the high-level voltage of the externally input PWM speed control signal is in the range of 5.1V to 15V, the cathode voltage of the seventh Zener diode D7 reaches the reverse breakdown voltage of the seventh Zener diode D7, and turns on the seventh Zener diode D7. The cathode potential of the seventh Zener diode D7 is clamped at a stable clamping voltage value, which is lower than the minimum turn-on voltage required at the input terminal of the seventh high-speed optocoupler U7. Through the 29th resistor R29 and the 7th Zener diode D7, the voltage difference between the positive and negative input terminals of the 7th high-speed optocoupler U7 is made lower than the stable clamping voltage value, and the 7th high-speed optocoupler U7 is kept off, outputting a high level.

[0012] Furthermore, the frequency range of the PWM signal is 1kHz to 50kHz, and the voltage range of the PWM signal is 3.3V to 15V for the high level and 0V to 0.8V for the low level.

[0013] Furthermore, it also includes: When power supply fluctuations occur, overvoltage protection circuitry protects against overvoltage, including: The power supply voltage is monitored through an overvoltage protection circuit. When the power supply voltage exceeds the stable voltage value of the first Zener diode ZD1, the first PNP transistor Q1 is turned on, and the gate-source voltage of the second P-channel MOSFET Q2 is turned off after it reaches zero.

[0014] Furthermore, it also includes: When the fan experiences a stall or overcurrent protection failure, it is restarted via a fault restart circuit, including: The control circuit controls the thirteenth transistor Q13 to turn off for a set period of time and then turn it back on. The twelfth field-effect transistor Q12 is turned off for a set time period and then turned on again, so that the power supply pin of the fan drive chip is powered off and then powered on again.

[0015] Compared with the prior art, the beneficial effects that at least one technical solution adopted in the embodiments of this specification can achieve include at least: Attached Figure Description To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a general structural diagram of the control circuit of the PWM speed-regulating fan according to an embodiment of the present invention; Figure 2 This is a circuit diagram of the PWM speed control circuit according to an embodiment of the present invention; Figure 3 This is a circuit diagram of the overvoltage protection circuit according to an embodiment of the present invention; Figure 4 This is a circuit diagram of a low-pass filter circuit according to an embodiment of the present invention; Figure 5 This is a circuit diagram of the fault restart circuit according to an embodiment of the present invention. Detailed Implementation

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

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] The circuit design of this invention converts the external speed control input signal into a PWM signal with a high level of 5V and a low level of 0V. It then reports the required speed status information to the MCU core controller (control circuit). After reading the speed requirement, the MCU outputs a fixed 20kHz PWM signal, which is then low-pass filtered and converted into a 0V–5V analog speed control signal. This analog signal is then sent to the driver chip to achieve real-time speed control. Simultaneously, this circuit design has isolation protection functions, improving circuit stability.

[0020] like Figure 1 As shown, the circuit includes an overvoltage protection circuit, a power conversion circuit, and a drive control circuit. The drive control circuit includes a control circuit, a PWM speed regulation circuit, a low-pass filter circuit, and a fault restart circuit. The 28V DC power supply is connected to the power conversion circuit through the overvoltage protection circuit. The overvoltage protection circuit is used to regulate external power fluctuations, and the power conversion circuit is used to provide power to the drive control circuit. The control circuit is connected to the PWM speed control circuit through a low-pass filter circuit and a fault restart circuit; The control circuit reads the speed requirement from the speed control circuit and outputs a fixed PWM signal. The PWM signal is then converted into an analog speed control signal by a low-pass filter circuit and input to the PWM speed control circuit. The PWM speed control circuit then adjusts the speed of the PWM signal. The fault restart circuit is used to restart the fan after it experiences a stall or overcurrent protection failure.

[0021] like Figure 2 As shown, the PWM speed control circuit includes: the seventh high-speed optocoupler U7, the twenty-ninth resistor R29, the thirtieth resistor R30, and the seventh Zener diode D7.

[0022] The positive input terminal of the seventh high-speed optocoupler U7 is connected to the twenty-ninth resistor R29, and then connected to the +5V power supply. The negative input terminal of the seventh high-speed optocoupler U7 is connected to one end of the thirtieth resistor R30 and the seventh Zener diode D7, and the other end of the thirtieth resistor R30 is connected to the speed control input KZ.

[0023] Due to the conduction mode of the seventh high-speed optocoupler U7, when the voltage is between 3.3V and 15V, it can be isolated by the isolation circuit composed of the seventh high-speed optocoupler U7 and the seventh Zener diode D7. The maximum reverse input DC voltage of the seventh high-speed optocoupler U7 is 5V. When the high-level voltage of the input PWM signal exceeds 10V, the seventh high-speed optocoupler U7 is at risk of damage. Therefore, the seventh Zener diode D7 is added to limit the high level of the input PWM signal, limiting the high level of the PWM signal from 5.1V to 15V to 5.1V. The seventh high-speed optocoupler U7 remains off, and the MCU port remains high. When the high level of the PWM signal is between 3.3V and 5.1V, in order to ensure that the optocoupler is in the off state, the voltage drop at the input terminal of the optocoupler should be kept between 0V and 0.8V. At the same time, it should be ensured that the input current is lower than the minimum threshold current (about 1.2mA). The series resistor value should be greater than 667Ω. The twenty-ninth resistor R29 is selected as 100Ω, and the thirtieth resistor R30 is selected as 1KΩ.

[0024] The PWM speed control circuit was redesigned using components such as the seventh high-speed optocoupler U7 and the seventh Zener diode D7, achieving wide-frequency input and adaptability to a wide voltage range for the fan speed control circuit.

[0025] like Figure 3As shown, the overvoltage protection circuit includes: a first PNP transistor Q1, a second P-channel MOSFET Q2, a first Zener diode ZD1, and a third resistor R3.

[0026] The first PNP transistor Q1 and the third resistor R3 are both connected in parallel across the gate and source terminals of the second P-channel MOSFET Q2, and the first Zener diode ZD1 is connected to the base of the first PNP transistor Q1.

[0027] To regulate external power supply fluctuations, hardware overvoltage protection is implemented using components such as the second P-channel MOSFET Q2, the first PNP transistor Q1, the first Zener diode ZD1, and resistors. An overvoltage protection circuit is designed using the first PNP transistor Q1, the second P-channel MOSFET Q2, and the first Zener diode ZD1 to provide overvoltage protection for the fan, thereby enhancing its reliability.

[0028] The fan control circuit uses a 28V power supply. When the power supply voltage exceeds approximately 37V, the voltage across the first Zener diode ZD1 stabilizes at 36V, the first PNP transistor Q1 reaches the turn-on condition, the third resistor R3 is short-circuited, the gate-source voltage of the second P-channel MOSFET Q2 is 0V, the second P-channel MOSFET Q2 is turned off, and the power supply to the subsequent stage is cut off, thus achieving the overvoltage protection function.

[0029] like Figure 4 As shown, the low-pass filter circuit includes the eighth resistor R8 and the thirteenth capacitor C13.

[0030] One end of the eighth resistor R8 is connected to one end of the thirteenth capacitor C13 and the voltage adjustment terminal, respectively, and the other end of the thirteenth capacitor C13 is grounded.

[0031] Because it is necessary to ensure that the input PWM signal is not distorted, Figure 2 The seventh high-speed optocoupler, U7, uses a high-speed optocoupler with a transmission rate of 1Mb / s to ensure consistency between the external input and the 1kHz-50kHz wide-frequency PWM signal information (including duty cycle, rising edge position, and falling edge position) at the microcontroller pins. After reading the speed control signal, the microcontroller outputs a PWM signal with a specified duty cycle frequency of 20kHz, which is then converted into a 0V-5V analog signal after RC low-pass filtering and input to the driver chip. In summary, this PWM speed control circuit can achieve speed regulation using a wide-frequency PWM of 1kHz-50kHz.

[0032] The control circuit of the PWM speed-regulating fan in this embodiment of the invention can achieve wide frequency range PWM speed regulation (1kHz to 50kHz), wide voltage range PWM speed regulation (low level 0V to 0.8V, high level 3.3V to 15V), and can isolate the input speed regulation signal from the internal control circuit of the fan. It can implement overvoltage protection in the hardware circuit; when the power supply voltage exceeds 37V, the power supply to the subsequent stage is cut off, achieving overvoltage protection and possessing high reliability.

[0033] like Figure 5 As shown, the fault restart circuit includes: 12th field-effect transistor Q12, 13th transistor Q13, 14th resistor R14, 15th resistor R15, 16th resistor R16 and 17th resistor R17.

[0034] The gate of the twelfth field-effect transistor Q12 is connected to the collector of the thirteenth transistor Q13 through the fifteenth resistor R15. The drain of the twelfth field-effect transistor Q12 is connected to the +5V power supply. The source of the twelfth field-effect transistor Q12 is connected to VDD. The fourteenth resistor R14 is connected in series between the +5V power supply and the fifteenth resistor R15. The emitter of the thirteenth transistor Q13 is grounded. The base of the thirteenth transistor Q13 is connected to one end of the sixteenth resistor R16 and the seventeenth resistor R17. The other end of the seventeenth resistor R17 is grounded.

[0035] To ensure the reliability of the wind turbine and prevent false protection activation, the wind turbine is restarted after a stall or overcurrent protection event. Since the driver chip does not restart after protection, a fault restart circuit is designed to achieve fault restart. After fault protection, the thirteenth microcontroller controls transistor Q13 to turn off for 5 seconds and then on, thereby controlling the twelfth MOSFET Q12 to turn off for 5 seconds and then on. The driver chip's VDD power supply pin is powered down for 5 seconds and then on, causing the wind turbine to restart, thus achieving fault restart.

[0036] In another embodiment of the present invention, the control method for the PWM speed-regulating fan is based on Figure 1 The control circuit achieves wide-frequency and wide-voltage range PWM speed regulation of the fan, including the following steps: Receives externally input PWM speed control signals; The externally input PWM speed control signal is isolated and its level is converted by the PWM speed control circuit to obtain a PWM signal that matches the level of the internal control circuit of the fan. The duty cycle of the PWM signal after level matching is read by the control circuit, and the speed requirement is obtained. Based on the speed requirement, a fixed-frequency PWM control signal is output through the control circuit; A low-pass filter circuit is used to convert a fixed-frequency PWM control signal into an analog speed regulation signal. The analog speed control signal is input to the fan drive chip, which then controls the fan speed.

[0037] Through high-speed optocoupler U7 transmission and low-pass filter circuit (R8, C13), it can stably and without distortion process external PWM speed control signals from 1kHz to 50kHz and convert them into analog signals. This overcomes the frequency limitation caused by the delay of components such as transistors in traditional circuits, and realizes wide frequency range speed control. The system utilizes a specific PWM speed control circuit (U7, R29, R30, D7) to safely and reliably receive and process PWM signals with a wide voltage range of 3.3V to 15V (high level) and 0V to 0.8V (low level), solving the voltage adaptability problem caused by the limitation of the microcontroller's power supply voltage in traditional circuits. The use of the seventh high-speed optocoupler U7 for signal input isolation effectively isolates electrical interference and potential high-voltage risks between external circuits and the internal control circuit of the fan, improving system safety and anti-interference capabilities, and achieving electrical isolation and signal fidelity. The system integrates signal reception, isolation conversion, MCU intelligent processing, filtering, and drive control, forming a complete closed loop, improving the real-time performance and accuracy of speed control, and enhancing system integration and controllability.

[0038] Specifically, the PWM speed control circuit isolates and levels the externally input PWM speed control signal, including: When the high-level voltage of the externally input PWM speed control signal is in the range of 3.3V to 5.1V and the seventh Zener diode D7 is not turned on, the input voltage is divided by the twenty-ninth resistor R29 and the thirtieth resistor R30. Configure the resistance values ​​of the 29th resistor R29 and the 30th resistor R30 in a fixed ratio so that the voltage difference applied between the positive and negative terminals of the input of the 7th high-speed optocoupler U7 after voltage division is lower than the turn-on threshold voltage of the 7th high-speed optocoupler U7. By using the total resistance of the twenty-ninth resistor R29 and the thirtieth resistor R30, the current flowing into the input terminal of the seventh high-speed optocoupler U7 is limited to below the minimum threshold current of the seventh high-speed optocoupler U7, so that the seventh high-speed optocoupler U7 remains off and outputs a high level. When the high-level voltage of the externally input PWM speed control signal is in the range of 5.1V to 15V, the cathode voltage of the seventh Zener diode D7 reaches the reverse breakdown voltage of the seventh Zener diode D7, and turns on the seventh Zener diode D7. The cathode potential of the seventh Zener diode D7 is clamped at a stable clamping voltage value, which is lower than the minimum turn-on voltage required at the input terminal of the seventh high-speed optocoupler U7. Through the 29th resistor R29 and the 7th Zener diode D7, the voltage difference between the positive and negative input terminals of the 7th high-speed optocoupler U7 is made lower than the stable clamping voltage value, and the 7th high-speed optocoupler U7 is kept off, outputting a high level.

[0039] Furthermore, the frequency range of the PWM signal is 1kHz to 50kHz, and the voltage range of the PWM signal is 3.3V to 15V for the high level and 0V to 0.8V for the low level.

[0040] For the two high-level ranges of 3.3V-5.1V and 5.1V-15V, two precise hardware mechanisms—resistor network voltage division and current limiting, and Zener diode clamping—are used respectively to ensure that the optocoupler input is always reliably off. This eliminates the risk of the optocoupler being accidentally turned on or damaged due to input voltage fluctuations, specifically achieving stable adaptation across a wide voltage input range. In particular, the seventh Zener diode (D7) clamps high levels above 5.1V, effectively protecting the seventh high-speed optocoupler (U7), whose maximum reverse input voltage is only 5V, preventing damage under high voltage input and improving the circuit's durability and reliability.

[0041] Furthermore, it also includes: When power supply fluctuations occur, overvoltage protection circuitry protects against overvoltage, including: The power supply voltage is monitored through an overvoltage protection circuit. When the power supply voltage exceeds the stable voltage value of the first Zener diode ZD1, the first PNP transistor Q1 is turned on, and the gate-source voltage of the second P-channel MOSFET Q2 is turned off after it reaches zero.

[0042] The overvoltage protection circuit (Q1, Q2, ZD1, R3) monitors the power supply voltage in real time and quickly and automatically cuts off the power supply to the downstream stage when the voltage exceeds a set threshold (e.g., approximately 37V). This is a hardware-based fast response mechanism that is more timely and reliable than software protection, effectively solving the problem of susceptibility to damage from external power fluctuations in existing technologies and enhancing the survivability of the wind turbine in harsh power environments.

[0043] Furthermore, it also includes: When the fan experiences a stall or overcurrent protection failure, it is restarted via a fault restart circuit, including: The control circuit controls the thirteenth transistor Q13 to turn off for a set period of time and then turn it back on. The twelfth field-effect transistor Q12 is turned off for a set time period and then turned on again, so that the power supply pin of the fan drive chip is powered off and then powered on again.

[0044] When the fan experiences stall or overcurrent protection failure, a power-down-delay-power-on reset sequence is automatically executed via the fault restart circuit (Q12, Q13, etc.). This avoids situations where the driver chip locks up and requires manual intervention, achieving automatic recovery after a fault, reducing maintenance needs, and improving the overall operating efficiency and reliability of the equipment.

[0045] Beneficial effects of the embodiments of the present invention: The PWM speed-regulating fan control circuit of this invention can be applied to small brushless DC axial fans, realizing PWM speed regulation of the fan at a frequency of 1kHz to 50kHz. The high-level speed regulation voltage can adapt to the range of 3.3V to 15V, and the low-level speed regulation voltage can adapt to the range of 0V to 0.8V. At the same time, the power supply circuit is specifically designed to realize overvoltage protection. While realizing wide-frequency and wide-voltage range PWM speed regulation, it also realizes overvoltage protection function in hardware circuit. It has the advantages of wide applicability and high stability, and can be widely used in aerospace, industry, environmental protection, power system, electronics, shipbuilding and other fields.

[0046] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical solutions, and technical solutions in this invention can be freely combined and used.

Claims

1. A control circuit for a PWM speed controlled fan, characterized in that Comprising: Overvoltage protection circuit, power conversion circuit and drive control circuit, the drive control circuit includes control circuit, PWM speed regulation circuit, low-pass filter circuit and fault restart circuit; 28V DC power supply is connected to the power conversion circuit through the overvoltage protection circuit, the overvoltage protection circuit is used to adjust the external power supply fluctuation, and the power conversion circuit is used to provide power supply for the drive control circuit; The control circuit is connected with the PWM speed regulation circuit through the low-pass filter circuit and the fault restart circuit; The control circuit is used to read the speed requirement from the speed regulation circuit, output fixed PWM signal, convert the PWM signal into analog speed regulation signal through the low-pass filter circuit, input the analog speed regulation signal into the PWM speed regulation circuit, and regulate the speed of the PWM signal through the PWM speed regulation circuit; The fault restart circuit is used to restart the fan after the fan occurs locked-rotor or over-current protection.

2. The control circuit for a PWM speed controlled fan of claim 1 wherein, The PWM speed regulation circuit comprises: Seventh high-speed optocoupler U7, twenty-ninth resistor R29, thirtieth resistor R30 and seventh zener diode D7; The input positive terminal of the seventh high-speed optocoupler U7 is connected with the twenty-ninth resistor R29 and then connected to +5V power supply; The input negative terminal of the seventh high-speed optocoupler U7 is connected with one end of the thirtieth resistor R30 and the seventh zener diode D7, and the other end of the thirtieth resistor R30 is connected with speed regulation input KZ.

3. The control circuit for a PWM blower motor as set forth in claim 1, wherein The low-pass filter circuit comprises: Eighth resistor R8 and thirteenth capacitor C13; One end of the eighth resistor R8 is connected with one end of the thirteenth capacitor C13 and voltage regulation end respectively, and the other end of the thirteenth capacitor C13 is grounded.

4. The control circuit for a PWM blower motor as set forth in claim 1, wherein The overvoltage protection circuit comprises: First PNP transistor Q1, second P-channel field effect transistor Q2, first zener diode ZD1 and third resistor R3; The first PNP transistor Q1 and the third resistor R3 are both connected in parallel between the gate and source of the second P-channel field effect transistor Q2, and the first zener diode ZD1 is connected with the base of the first PNP transistor Q1.

5. The control circuit for a PWM blower motor as set forth in claim 1, wherein The fault restart circuit comprises: twelfth field effect transistor Q12, tenth three transistor Q13, fourteenth resistor R14, fifteenth resistor R15, sixteenth resistor R16 and seventeenth resistor R17; The gate of the twelfth field effect transistor Q12 is connected with the collector of the tenth three transistor Q13 through the fifteenth resistor R15, the drain of the twelfth field effect transistor Q12 is connected with +5V power supply, and the source of the twelfth field effect transistor Q12 is connected with VDD; The fourteenth resistor R14 is connected in series between +5V power supply and the fifteenth resistor R15; The emitter of the tenth three transistor Q13 is grounded, the base of the tenth three transistor Q13 is connected with one end of the sixteenth resistor R16 and the seventeenth resistor R17, and the other end of the seventeenth resistor R17 is grounded.

6. A control method of a PWM speed-regulated fan, which implements PWM speed regulation of the fan over a wide frequency and wide voltage range based on the control circuit according to any one of claims 1 to 5, characterized by, The method comprises the following steps: Receiving external input PWM speed regulation signal; The PWM speed regulation circuit isolates and converts the level of the externally input PWM speed regulation signal, and a PWM signal with a level matched with the internal control circuit of the fan is obtained; The duty cycle of the PWM signal with the matched level is read by the control circuit, and a speed requirement is obtained; Based on the speed requirement, the control circuit outputs a PWM control signal with a fixed frequency; The low-pass filter circuit converts the PWM control signal with the fixed frequency into an analog quantity speed regulation signal; The analog quantity speed regulation signal is input into a fan drive chip, and the speed of the fan is controlled by the fan drive chip.

7. The control method according to claim 6, characterized by, The PWM speed regulation circuit isolates and converts the level of the externally input PWM speed regulation signal, and a PWM signal with a level matched with the internal control circuit of the fan is obtained; When the high-level voltage of the externally input PWM speed regulation signal is in the range of 3.3V to 5.1V and the seventh voltage stabilizing diode D7 is not turned on, the input voltage is divided by the twenty-ninth resistor R29 and the thirtieth resistor R30; The resistance values of the twenty-ninth resistor R29 and the thirtieth resistor R30 are proportionally configured, so that the voltage difference applied between the positive terminal and the negative terminal of the input terminal of the seventh high-speed optocoupler U7 after voltage division is lower than the opening threshold voltage of the seventh high-speed optocoupler U7; The total resistance value of the twenty-ninth resistor R29 and the thirtieth resistor R30 limits the current flowing into the input terminal of the seventh high-speed optocoupler U7 to be below the minimum threshold current of the seventh high-speed optocoupler U7, so that the seventh high-speed optocoupler U7 remains off and outputs a high level; When the high-level voltage of the externally input PWM speed regulation signal is in the range of 5.1V to 15V, the cathode voltage of the seventh voltage stabilizing diode D7 reaches the reverse breakdown voltage of the seventh voltage stabilizing diode D7, and the seventh voltage stabilizing diode D7 is turned on; The cathode potential of the seventh voltage stabilizing diode D7 is clamped at a stable clamping voltage value, wherein the stable clamping voltage value is lower than the minimum conduction voltage required by the input terminal of the seventh high-speed optocoupler U7; The twenty-ninth resistor R29 and the seventh voltage stabilizing diode D7 make the voltage difference applied between the positive terminal and the negative terminal of the input terminal of the seventh high-speed optocoupler U7 lower than the stable clamping voltage value, and the seventh high-speed optocoupler U7 remains off and outputs a high level.

8. The control method according to claim 6, characterized by, The frequency range of the PWM signal is 1kHz to 50kHz, and the voltage range of the PWM signal is 3.3V to 15V for the high level and 0V to 0.8V for the low level.

9. The control method according to claim 6, characterized by, Further comprising: When the power supply fluctuates, the overvoltage protection circuit protects against overvoltage, comprising: The overvoltage protection circuit monitors the power supply voltage; When the power supply voltage exceeds the stable voltage value of the first voltage stabilizing diode ZD1, the first PNP transistor Q1 is turned on, and the gate-source voltage of the second P-channel field effect transistor Q2 is zero after being turned off.

10. The control method according to claim 6, characterized by, Further comprising: When the fan is stalled or overcurrent protection occurs, the fault restart circuit is restarted, comprising: The control circuit controls the tenth three transistor Q13 to be off for a set period of time and then turned on again; The twelfth field effect transistor Q12 is turned off to the set time period and then turned on, so that the power supply pin of the driving chip of the fan is powered off and then powered on.

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