A dual-control circuit for a fan and a multi-channel fan control device

Abstract

An embodiment of the present invention discloses a dual-control circuit for a fan and a multi-channel fan control device, which is externally connected to at least one fan and includes a main board. A fan controller, at least two fan interfaces, and at least one of the dual-control circuits for the fan are provided on the main board; one dual-control circuit for the fan is connected to two fan interfaces; each dual-control circuit for the fan is connected to the fan controller; the fan controller outputs a PWM control signal, and the dual-control circuit for the fan divides the PWM control signal into two paths and outputs them to the corresponding fan interfaces to control the rotation of the externally connected fans. The dual-control circuit for the fan detects the states of the fans externally connected to the two fan interfaces, and selects to convert the first rotation speed signal or the second rotation speed signal into a rotation speed feedback signal and transmit it to the fan controller. In this way, one dual-control circuit for the fan can control two PWM fans at the same time, doubling the number of fans, and solving the problem that the number setting of the existing PWM fan interfaces is limited by the fan controller.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to a dual-control circuit for a fan and a multi-channel fan control device. Background Art

[0002] At present, common motherboards in a computer generally have two PMW (Pulse Width Modulation, the English "pulse width modulation") fan interfaces, and high-end motherboards have 2 to 5 PWM fan interfaces. If there are more fan interfaces, the extra fan interfaces are not PWM fan interfaces and may be DC fan interfaces. There are generally two types of fan controllers. One can support two PWM fan interfaces, and the other can support five PWM fan interfaces. When developing and designing a motherboard, either a fan controller that supports two PWM fan interfaces is selected, or a fan controller that supports five PWM fan interfaces is selected.

[0003] As Figure 1 shown, a group of PWM control signals output by the fan controller (i.e., the waveform on the line pointing to the fan interface) can only be output through one PWM fan interface to control one PWM fan, and the rotation speed signal corresponding to the rotation speed after the PWM fan feedback control (i.e., the waveform on the line pointing to the fan controller) is given to the fan controller. If the motherboard needs to design 3 or 4 PWM fan interfaces, a fan controller that supports five PWM fan interfaces must be selected; if the motherboard needs to design 6 or more PWM fan interfaces, there is currently no corresponding fan controller available, nor is there a relevant control circuit. Summary of the Invention

[0004] In view of the above technical problems, embodiments of the present invention provide a dual-control circuit for a fan and a multi-channel fan control device to solve the problem that the number setting of existing PWM fan interfaces is limited by the fan controller.

[0005] An embodiment of the present invention provides a dual-control circuit for a fan, which includes a fan controller, a first fan interface, and a second fan interface. The dual-control circuit for a fan includes a unidirectional transmission module, a feedback control module, and an output module; the unidirectional transmission module is connected to the first fan interface, the feedback control module, and the fan controller, the feedback control module is connected to the second fan interface and the fan controller, and the output module is connected to the first fan interface, the second fan interface, and the fan controller.

[0006] The output module transmits the PWM control signal to the first fan interface and the second fan interface respectively;

[0007] When the unidirectional transmission module detects that a fan is externally connected to the first fan interface, it converts the corresponding first rotation speed signal into a rotation speed feedback signal and transmits it to the fan controller;

[0008] When the feedback control module detects that a fan is externally connected to the first fan interface, it disconnects the connection between the second fan interface and the fan controller; when it detects that only a fan is externally connected to the second fan interface, it connects the second fan interface to the fan controller, converts the corresponding second rotational speed signal into the rotational speed feedback signal, and transmits it to the fan controller.

[0009] Optionally, in the fan dual-control circuit, the unidirectional transmission module includes a first MOS transistor, a second MOS transistor, a first resistor, and a second resistor;

[0010] The gate of the first MOS transistor is connected to the drain of the second MOS transistor and one end of the first resistor; the drain of the first MOS transistor is connected to the output module and the first feedback pin of the fan controller; the gate of the second MOS transistor is connected to one end of the second resistor and the third pin of the first fan interface, the source electrodes of the first MOS transistor and the second MOS transistor are both grounded, and the other ends of the first resistor and the second resistor are both connected to the second power supply terminal.

[0011] Optionally, in the fan dual-control circuit, the feedback control module includes a third MOS transistor, a fourth MOS transistor, a third resistor, a first capacitor, a second capacitor, and a diode;

[0012] The source of the third MOS transistor is connected to the drain of the first MOS transistor and the first feedback pin of the fan controller, the drain of the third MOS transistor is connected to the drain of the fourth MOS transistor and one end of the first capacitor; the gate of the third MOS transistor is connected to the other end of the first capacitor, the positive electrode of the diode, one end of the second capacitor, and one end of the third resistor; the other end of the third resistor is connected to the negative electrode of the diode and the third pin of the first fan interface, the gate of the fourth MOS transistor is connected to the other end of the first capacitor, and the source of the fourth MOS transistor is connected to the third pin of the second fan interface.

[0013] Optionally, in the fan dual-control circuit, the output module includes a fourth resistor; one end of the fourth resistor is connected to the first control pin of the fan controller and the fourth pin of the first fan interface, and the other end of the fourth resistor is connected to the fourth pin of the second fan interface.

[0014] Optionally, in the fan dual-control circuit, the output module includes an AND gate and a third capacitor; one input pin of the AND gate is connected to the other input pin of the AND gate, the fourth pin of the first fan interface, and the first control pin of the fan controller; the output pin of the AND gate is connected to the fourth pin of the second fan interface, the power supply pin of the AND gate is connected to the first power supply terminal and one end of the third capacitor, the other end of the third capacitor is grounded, and the ground pin of the AND gate is grounded.

[0015] Optionally, in the fan dual-control circuit, both the first MOS transistor and the second MOS transistor are NMOS transistors, and the resistance values of the first resistor and the second resistor are both 10 KΩ.

[0016] Optionally, in the dual-fan control circuit, the third MOS transistor and the fourth MOS transistor are both NMOS transistors, the resistance value of the third resistor is 10 MΩ, and the capacitance value of the second capacitor is 2.2 uF.

[0017] In a second aspect of the embodiments of the present invention, a multi-channel fan control device is provided, which is externally connected to at least one fan. The multi-channel fan control device includes a main board, on which a fan controller, at least two fan interfaces, and at least one of the dual-fan control circuits are provided; one dual-fan control circuit is connected to two fan interfaces; each dual-fan control circuit is connected to the fan controller;

[0018] The fan controller outputs a PWM control signal, and the dual-fan control circuit outputs the PWM control signal in two paths to the corresponding fan interfaces to control the rotation of the externally connected fans. The dual-fan control circuit detects the states of the fans externally connected to the two fan interfaces, and selects to convert the first rotation speed signal or the second rotation speed signal into a rotation speed feedback signal and transmit it to the fan controller.

[0019] Optionally, in the multi-channel fan control device, a peripheral circuit of the fan controller is further provided on the main board. The peripheral circuit is connected to the fan controller and the dual-fan control circuit. The peripheral circuit pulls up the voltage on the control line between the fan controller and the dual-fan control circuit, and also divides the voltage on the feedback line between the fan controller and the dual-fan control circuit.

[0020] Optionally, in the multi-channel fan control device, the peripheral circuit includes a first pull-up resistor, a second pull-up resistor, and a pull-down resistor;

[0021] One end of the first pull-up resistor is connected to the first control pin of the fan controller, the fourth pin of the first fan interface, and the output module; the other end of the first pull-up resistor is connected to the first power supply terminal; one end of the second pull-up resistor is connected to one end of the pull-down resistor, the first feedback pin of the fan controller, the unidirectional transmission module, and the feedback control module; the other end of the second pull-up resistor is connected to the second power supply terminal, and the other end of the pull-down resistor is grounded.

[0022] In the technical solution provided by the embodiment of the present invention, the multi-channel fan control device is externally connected to at least one fan, and includes a main board. A fan controller, at least two fan interfaces, and at least one of the fan dual-control circuits are arranged on the main board; one fan dual-control circuit is connected to two fan interfaces; each fan dual-control circuit is connected to the fan controller; the fan controller outputs a PWM control signal, and the fan dual-control circuit divides the PWM control signal into two paths and outputs them to the corresponding fan interfaces to control the rotation of the externally connected fans. The fan dual-control circuit detects the states of the fans externally connected to the two fan interfaces, and selects to convert the first rotation speed signal or the second rotation speed signal into a rotation speed feedback signal and transmit it to the fan controller. In this way, one fan dual-control circuit can control two PWM fans at the same time, doubling the number of fans, and solving the problem that the number setting of the existing PWM fan interfaces is limited by the fan controller. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a control schematic diagram of an existing fan controller;

[0024] Figure 2 It is a structural block diagram of the multi-channel fan control device in the embodiment of the present invention;

[0025] Figure 3 It is a circuit diagram of the multi-channel fan control device in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. For the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0027] Please refer to Figure 2, the multi-channel fan control device provided by the embodiment of the present invention is externally connected with at least one fan. The multi-channel fan control device includes a main board, on which a fan controller 10, at least one fan dual-control circuit 20, and at least two fan interfaces (FAN1, FAN2,..., FANn, where n is a positive integer) are provided; one fan dual-control circuit 20 is connected to two fan interfaces (or can be only connected to one fan interface); each fan dual-control circuit 20 is connected to the fan controller 10. The fan controller 10 outputs a PWM control signal FAN_PWM1, and the fan dual-control circuit 20 outputs the PWM control signal FAN_PWM1 in two paths to the corresponding fan interfaces to control the rotation of the externally connected fans. The fan dual-control circuit 20 detects the states of the fans externally connected to the two fan interfaces, and selects to convert the first rotation speed signal FAN_TACH1 or the second rotation speed signal FAN_TACH2 into a rotation speed feedback signal R_FAN_TAC1 and transmits it to the fan controller 10.

[0028] An external circuit 30 of the fan controller 10 is also provided on the main board. The external circuit 30 is connected to the fan controller 10 and the fan dual-control circuit 20. The external circuit 30 pulls up the control line between the fan controller 10 and the fan dual-control circuit 20. Since the fan can only be driven by a periodic pulse signal, pulling up can avoid noise or interference from generating false drive signals and causing the fan to rotate falsely. The external circuit 30 also divides the voltage of the feedback line between the fan controller 10 and the fan dual-control circuit 20, so as to avoid burning out the fan controller 10 due to the too high voltage of the feedback rotation speed feedback signal R_FAN_TAC1. The number of the external circuits 30 is the same as the number of the fan dual-control circuits 20.

[0029] It should be understood that the main board can be a computer main board, an industrial control main board, an all-in-one main board, a server main board, etc. that require two or more PWM fans. One fan dual-control circuit 20 can realize the function of controlling two PWM fans with a group of PWM control signals. By adjusting the duty cycle of the PWM control signal FAN_PWM1, the rotation speed of the fan can be adjusted. The fan controller 10 has multiple pairs of adjustment pins (i.e., the first control pin and the first feedback pin). One fan dual-control circuit 20 is paired with two fan interfaces (named the first fan interface and the second fan interface respectively). One fan dual-control circuit 20 is connected to a group of adjustment pins. The number of fan dual-control circuits 20 can be increased or decreased according to requirements ( Figure 2 taking two as an example, and the corresponding signal and interface numbers increase when increasing), then the fan dual-control circuit 20 is connected to the corresponding group of adjustment pins. The circuit structures of each fan dual-control circuit 20 are the same, only the connected adjustment pins and fan interfaces are different. Here, one fan dual-control circuit 20 is taken as an example.

[0030] Please refer to Figure 3, the dual - control circuit 20 of the fan includes a unidirectional transmission module 21, a feedback control module 22, and an output module 23; the unidirectional transmission module 21 is connected to the first fan interface FAN1, the feedback control module 22, and the fan controller 10, the feedback control module 22 is connected to the second fan interface FAN2 and the fan controller 10, and the output module 23 is connected to the first fan interface FAN1, the second fan interface FAN2, and the fan controller 10.

[0031] The output module 23 transmits the PWM control signal FAN_PWM1 to the first fan interface FAN1 and the second fan interface FAN2 respectively to drive the corresponding externally - connected fans to rotate; when the unidirectional transmission module 21 detects that a fan is externally connected to the first fan interface FAN1, it converts the corresponding first rotational speed signal FAN_TACH1 into a rotational speed feedback signal R_FAN_TAC1 and transmits it to the fan controller 10; if the unidirectional transmission module 21 detects that no fan is externally connected to the first fan interface FAN1, it does not work, that is, it will not output any signal. When the feedback control module 22 detects that a fan is externally connected to the first fan interface FAN1, regardless of whether a fan is externally connected to the second fan interface FAN2 at this time, it disconnects the connection between the second fan interface FAN2 and the fan controller 10; if it detects that only a fan is externally connected to the second fan interface FAN2, it connects the second fan interface FAN2 to the fan controller 10, and converts the corresponding second rotational speed signal FAN_TACH2 into the rotational speed feedback signal R_FAN_TAC1 and transmits it to the fan controller 10.

[0032] The peripheral circuit 30 includes a first pull - up resistor RQ1, a second pull - up resistor RQ2, and a pull - down resistor RQ3; one end of the first pull - up resistor RQ1 is connected to the first control pin of the fan controller 10, the 4th pin of the first fan interface FAN1, and the output module 23; the other end of the first pull - up resistor RQ1 is connected to the first power supply terminal +5VS (providing a first voltage of +5V); one end of the second pull - up resistor RQ2 is connected to one end of the pull - down resistor RQ3, the first feedback pin of the fan controller 10, the unidirectional transmission module 21, and the feedback control module 22; the other end of the second pull - up resistor RQ2 is connected to the second power supply terminal +12VS, and the other end of the pull - down resistor RQ3 is grounded.

[0033] Among them, the resistance value of the first pull-up resistor RQ1 is 4.7 KΩ, the resistance value of the second pull-up resistor RQ2 is 4.7 KΩ, and the resistance value of the pull-down resistor RQ3 is 22 KΩ. When the fan controller 10 outputs the PWM control signal FAN_PWM1, the voltage on the control line changes correspondingly; when there is no PWM control signal FAN_PWM1 output, the first pull-up resistor RQ1 pulls up the voltage on the control line to a high level. The second pull-up resistor RQ2 and the pull-down resistor RQ3 form a voltage-dividing circuit to divide the rotational speed feedback signal R_FAN_TAC1 transmitted on the feedback line.

[0034] The unidirectional transmission module 21 includes a first MOS transistor Q1, a second MOS transistor Q2, a first resistor R1, and a second resistor R2; the gate of the first MOS transistor Q1 is connected to the drain of the second MOS transistor Q2 and one end of the first resistor R1; the drain of the first MOS transistor Q1 is connected to the output module 23, the first feedback pin of the fan controller 10, and one end of the second pull-up resistor RQ2; the gate of the second MOS transistor Q2 is connected to one end of the second resistor R2 and the 3rd pin of the first fan interface FAN1, the sources of the first MOS transistor Q1 and the second MOS transistor Q2 are both grounded, and the other ends of the first resistor R1 and the second resistor R2 are both connected to the second power supply terminal (providing a second voltage of +12V).

[0035] Among them, both the first MOS transistor Q1 and the second MOS transistor Q2 are NMOS transistors, and the resistance values of the first resistor R1 and the second resistor R2 are both 10 KΩ. The first fan interface FAN1 is a PWM fan interface, and the models it can adopt include RWA-211046-B10 and WFEA60-104L2.

[0036] When the first fan rotates, the 3rd pin of the first fan interface FAN1 outputs a corresponding first rotational speed signal FAN_TACH1 (indicating the rotational speed of the fan, a square wave signal). When the first rotational speed signal FAN_TACH1 is at a high level, Q2 conducts and Q1 cuts off, and the rotational speed feedback signal R_FAN_TAC1 is divided by the second pull-up resistor RQ2 and the pull-down resistor RQ3 (high level); when the first rotational speed signal FAN_TACH1 is at a low level, Q2 cuts off, and the gate of Q1 is pulled up by R1 and conducts, and the rotational speed feedback signal R_FAN_TAC1 is at a low level; thus, a square wave signal corresponding to the waveform of the first rotational speed signal FAN_TACH1 is output.

[0037] When the first fan does not rotate, there is no first rotational speed signal FAN_TACH1 output. At this time, the gate of Q2 is pulled up to a high level by R2 and continuously conducts, and the rotational speed feedback signal R_FAN_TAC1 is not affected by the 3rd pin of the first fan interface FAN1.

[0038] The feedback control module 22 includes a third MOS transistor Q3, a fourth MOS transistor Q4, a third resistor R3, a first capacitor C1, a second capacitor C2, and a diode D1. The source of the third MOS transistor Q3 is connected to the drain of the first MOS transistor Q1 and the first feedback pin of the fan controller 10. The drain of the third MOS transistor Q3 is connected to the drain of the fourth MOS transistor Q4 and one end of the first capacitor C1. The gate of the third MOS transistor Q3 is connected to the other end of the first capacitor C1, the positive electrode of the diode D1, one end of the second capacitor C2, and one end of the third resistor R3. The other end of the third resistor R3 is connected to the negative electrode of the diode D1 and the third pin of the first fan interface FAN1. The gate of the fourth MOS transistor Q4 is connected to the other end of the first capacitor C1. The source of the fourth MOS transistor Q4 is connected to the third pin of the second fan interface FAN2.

[0039] Among them, both the third MOS transistor Q3 and the fourth MOS transistor Q4 are NMOS transistors. The resistance value of the third resistor R3 is 10 MΩ, and the capacitance value of the second capacitor C2 is 2.2 uF.

[0040] When the gate voltages of Q3 and Q4 are high, the third pin of the second fan interface FAN2 is connected to the first feedback pin of the fan controller 10. On the contrary, when the gate voltages of Q3 and Q4 are low, the connection between the third pin of the second fan interface FAN2 and the first feedback pin of the fan controller 10 is disconnected.

[0041] When the fan externally connected to the first fan interface FAN1 rotates, a first rotation speed signal FAN_TACH1 is generated. It is delayed through R3 and C2 and quickly discharged through D1. Since the first rotation speed signal FAN_TACH1 is a square wave with continuously changing high and low levels, the gate voltages of Q3 and Q4 always cannot reach the turn-on voltage of the NMOS transistor, that is, they remain low, causing Q3 and Q4 to be cut off, and disconnecting the connection between the third pin of the second fan interface FAN2 and the first feedback pin of the fan controller 10. At this time, regardless of whether a fan is externally connected to the second fan interface FAN2 or not, its feedback signal will not be transmitted to the fan controller 10. This is because both fans are driven by the same PWM control signal FAN_PWM1 (FAN_PWM2 is the same as it), and only the rotation speed of one of them needs to be detected.

[0042] When there is no external fan connected to the first fan interface FAN1, the first tach signal FAN_TACH1 will not be generated at this time. It is equivalent that the first tach signal FAN_TACH1 is pulled up to a high level by R2 at this time. Since the first tach signal FAN_TACH1 remains at a high level continuously, D1 will not discharge. After the high level passes through R3 and C2 with a time delay, the gate voltages of Q3 and Q4 are controlled to be at a high level and maintained, then Q3 and Q4 conduct, and the third pin of the second fan interface FAN2 is connected to the first feedback pin of the fan controller 10. In this way, the fan connected to the second fan interface FAN2 can transmit its second tach signal FAN_TACH2 as the tach feedback signal R_FAN_TAC1 to the fan controller 10.

[0043] The output module 23 includes a fourth resistor R4; one end of the fourth resistor R4 is connected to the first control pin of the fan controller 10 and the fourth pin of the first fan interface FAN1, and the other end of the fourth resistor R4 is connected to the fourth pin of the second fan interface FAN2. The fourth resistor R4 is a 0-ohm resistor.

[0044] If two fans are connected simultaneously, the PWM control signal FAN_PWM1 may have impedance mismatch due to the change of the load. A NAND gate can be reserved on the main board to strengthen the PWM control signal FAN_PWM1. Then the output module 23 includes a NAND gate U and a third capacitor C3; one input pin of the NAND gate U is connected to the other input pin of the NAND gate U, the fourth pin of the first fan interface FAN1, and the first control pin of the fan controller 10; the output pin of the NAND gate U is connected to the fourth pin of the second fan interface FAN2, the power pin of the NAND gate U is connected to the first power supply terminal (providing a first voltage of +5V) and one end of the third capacitor C3, the other end of the third capacitor C3 is grounded, and the ground pin of the NAND gate U is grounded.

[0045] It should be understood that the fourth resistor R4, the NAND gate U, and the third capacitor C3 are all soldered on the main board for reservation, and different connection methods are selected according to actual requirements; that is, when the fourth resistor R4 is selected, the NAND gate U and the third capacitor C3 are not connected to other devices; when the NAND gate U and the third capacitor C3 are selected, the fourth resistor R4 is not connected to other devices.

[0046] In summary, the fan dual-control circuit and the multi-channel fan control device provided by the present invention can simultaneously control two PWM fans through a group of PWM fan control signals. The number of controllable fan interfaces is twice the number of PWM control signals of the fan controller, so as to achieve a multiple increase in the number of fans, and solve the problem that the number setting of the existing PWM fan interfaces is limited by the fan controller. At the same time, it can also detect whether external fans are connected to the two fan interfaces, and select the output path of the tach feedback signal according to the situation of the external fans.

[0047] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A dual-control circuit for a fan, characterized in that, The dual - control circuit of the fan is connected to the fan controller, the first fan interface and the second fan interface. The dual - control circuit of the fan includes a unidirectional transmission module, a feedback control module and an output module. The unidirectional transmission module is connected to the first fan interface, the feedback control module and the fan controller. The feedback control module is connected to the second fan interface and the fan controller. The output module is connected to the first fan interface, the second fan interface and the fan controller. The output module transmits the PWM control signal to the first fan interface and the second fan interface respectively. When the unidirectional transmission module detects that a fan is externally connected to the first fan interface, it converts the corresponding first rotation speed signal into a rotation speed feedback signal and transmits it to the fan controller. When the feedback control module detects that a fan is externally connected to the first fan interface, it disconnects the connection between the second fan interface and the fan controller. When it detects that only a fan is externally connected to the second fan interface, it connects the second fan interface to the fan controller, converts the corresponding second rotation speed signal into the rotation speed feedback signal and transmits it to the fan controller. The unidirectional transmission module includes a first MOS transistor, a second MOS transistor, a first resistor and a second resistor. The gate of the first MOS transistor is connected to the drain of the second MOS transistor and one end of the first resistor. The drain of the first MOS transistor is connected to the output module and the first feedback pin of the fan controller. The gate of the second MOS transistor is connected to one end of the second resistor and the 3rd pin of the first fan interface. The sources of the first MOS transistor and the second MOS transistor are both grounded. The other ends of the first resistor and the second resistor are both connected to the second power supply terminal. The feedback control module includes a third MOS transistor, a fourth MOS transistor, a third resistor, a first capacitor, a second capacitor and a diode. The source of the third MOS transistor is connected to the drain of the first MOS transistor and the first feedback pin of the fan controller. The drain of the third MOS transistor is connected to the drain of the fourth MOS transistor and one end of the first capacitor. The gate of the third MOS transistor is connected to the other end of the first capacitor, the positive pole of the diode, one end of the second capacitor and one end of the third resistor. The other end of the third resistor is connected to the negative pole of the diode and the 3rd pin of the first fan interface. The gate of the fourth MOS transistor is connected to the other end of the first capacitor. The source of the fourth MOS transistor is connected to the 3rd pin of the second fan interface.

2. The dual-control circuit for a fan according to claim 1, characterized in that, The output module includes a fourth resistor. One end of the fourth resistor is connected to the first control pin of the fan controller and the 4th pin of the first fan interface. The other end of the fourth resistor is connected to the 4th pin of the second fan interface.

3. The dual-control circuit for a fan according to claim 1, characterized in that, The output module includes an AND gate and a third capacitor. One input pin of the AND gate is connected to the other input pin of the AND gate, the 4th pin of the first fan interface and the first control pin of the fan controller. The output pin of the AND gate is connected to the 4th pin of the second fan interface. The power supply pin of the AND gate is connected to the first power supply terminal and one end of the third capacitor. The other end of the third capacitor is grounded. The ground pin of the AND gate is grounded.

4. The dual-control circuit for a fan according to claim 1, characterized in that, Both the first MOS transistor and the second MOS transistor are NMOS transistors. The resistance values of the first resistor and the second resistor are both 10KΩ.

5. The dual-control circuit for a fan according to claim 1, characterized in that, Both the third MOS transistor and the fourth MOS transistor are NMOS transistors. The resistance value of the third resistor is 10MΩ. The capacitance value of the second capacitor is 2.2uF.

6. A multi-channel fan control device, externally connected to at least 1 fan, characterized in that, It includes a main board, on which a fan controller, at least 2 fan interfaces and at least 1 fan dual-control circuit as described in any one of claims 1-5 are provided; one fan dual-control circuit is connected to 2 fan interfaces; each fan dual-control circuit is connected to the fan controller; The fan controller outputs a PWM control signal, and the fan dual-control circuit outputs the PWM control signal in two paths to the corresponding fan interfaces to control the rotation of the externally connected fans. The fan dual-control circuit detects the states of the fans externally connected to the 2 fan interfaces, and selects to convert the first rotation speed signal or the second rotation speed signal into a rotation speed feedback signal and transmit it to the fan controller.

7. The multi-channel fan control device according to claim 6, characterized in that, The main board is also provided with a peripheral circuit of the fan controller. The peripheral circuit is connected to the fan controller and the fan dual-control circuit. The peripheral circuit pulls up the voltage on the control line between the fan controller and the fan dual-control circuit, and also divides the voltage on the feedback line between the fan controller and the fan dual-control circuit.

8. The multi-channel fan control device according to claim 7, characterized in that, The peripheral circuit includes a first pull-up resistor, a second pull-up resistor and a pull-down resistor; One end of the first pull-up resistor is connected to the first control pin of the fan controller, the 4th pin of the first fan interface and the output module; the other end of the first pull-up resistor is connected to the first power supply terminal; one end of the second pull-up resistor is connected to one end of the pull-down resistor, the first feedback pin of the fan controller, the unidirectional transmission module and the feedback control module; the other end of the second pull-up resistor is connected to the second power supply terminal, and the other end of the pull-down resistor is grounded.

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