Heat dissipation circuit and electronic equipment

Abstract

The utility model discloses a heat dissipation circuit and electronic equipment. The heat dissipation circuit comprises a fan, a controller, a first switch branch, a second switch branch and a third switch branch. The controller outputs a first level signal and a second level signal. The first switch branch is switched on in response to a first level signal and switched off in response to a second level signal; the second switch branch is turned off in response to the first level signal and turned on in response to the second level signal. The third switch branch responds to the first switch branch to be switched on and the second switch branch to be switched off, the positive electrode of the fan is connected with the positive electrode of the first power supply, and the negative electrode of the fan is grounded. And the third switch branch also responds to the conduction of the first switch branch and the second switch branch, establishes the connection between the negative electrode of the fan and the positive electrode of the first power supply, and enables the positive electrode of the fan to be grounded. Through the mode, impurities and dust attached to the air inlet of the electronic equipment can be reversely blown away, so that the air inlet of the electronic equipment is prevented from being blocked, and the heat dissipation function can be reliably achieved.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of electronic circuits, and in particular to a heat dissipation circuit and an electronic device. Background Art

[0002] During the operation of electronic equipment (such as inverters), a certain amount of heat is usually generated, which in turn causes the temperature to rise and may affect the normal operation of the electronic equipment. Based on this, it is usually necessary to set up a corresponding heat dissipation method to dissipate the heat of the electronic equipment to maintain the reliable operation of the electronic equipment. At present, common heat dissipation methods include air cooling, which is to use fans to force air to flow around the internal components of the inverter, thereby taking away the heat emitted by the components.

[0003] However, in the current heat dissipation method, when the electronic device is running for a long time, impurities and dust in the air will adhere to the air inlet of the electronic device, causing the air inlet of the electronic device to be blocked, the air intake volume to be reduced, the heat dissipation effect to be reduced, and even the performance and life of the electronic device to be affected. Utility Model Content

[0004] The embodiments of the present application provide a heat dissipation circuit and an electronic device, which can blow away impurities and dust attached to the air inlet of the electronic device in the opposite direction to prevent the air inlet of the electronic device from being blocked, thereby realizing the heat dissipation function more reliably.

[0005] In a first aspect, an embodiment of the present application provides a heat dissipation circuit, including:

[0006] fan;

[0007] A controller configured to output a first level signal and a second level signal;

[0008] a first switch branch connected to the controller and configured to be turned on in response to the first level signal and turned off in response to the second level signal;

[0009] a second switch branch connected to the controller and configured to be turned off in response to the first level signal and turned on in response to the second level signal;

[0010] a third switch branch connected between the first switch branch and the fan, connected between the fan and the first power supply, and connected between the second switch branch and the second power supply;

[0011] The third switch branch is configured to connect the positive electrode of the fan to the positive electrode of the first power source and ground the negative electrode of the fan in response to the first switch branch being turned on and the second switch branch being turned off;

[0012] The third switch branch is further configured to establish a connection between the negative electrode of the fan and the positive electrode of the first power supply and ground the positive electrode of the fan in response to the first switch branch and the second switch branch being turned on.

[0013] In some embodiments, the controller is further configured to output a pulse width modulation signal;

[0014] The heat dissipation circuit further includes a voltage conversion branch, which is respectively connected to a third power source and the controller and is configured to convert the third power source into the first power source in response to the pulse width modulation signal.

[0015] In some embodiments, the first switch branch includes a first switch tube;

[0016] The first end of the first switch tube is connected to the controller, the second end of the first switch tube is grounded, and the third end of the first switch tube is connected to the third switch branch.

[0017] In some embodiments, the first switch tube is an NMOS tube, and the first switch branch further includes a first resistor, a second resistor and a first capacitor;

[0018] The first resistor and the second resistor are connected in series between the controller and the ground, the connection point between the first resistor and the second resistor is connected to the gate of the NMOS tube, and the first capacitor is connected in parallel with the first resistor;

[0019] The gate of the NMOS tube is the first end of the first switch tube, the source of the NMOS tube is the second end of the first switch tube, and the drain of the NMOS tube is the third end of the first switch tube.

[0020] In some embodiments, the second switch branch includes a second switch tube;

[0021] A first end of the second switch tube is connected to the controller, a second end of the second switch tube is connected to the third switch branch, and a third end of the second switch tube is grounded.

[0022] In some embodiments, the second switch tube is a PNP transistor, and the second switch branch further includes a third resistor and a first voltage regulator diode;

[0023] The third resistor is connected between the base and the emitter of the PNP transistor, the anode of the first voltage stabilizing diode is grounded, and the cathode of the first voltage stabilizing diode is connected to the base of the PNP transistor;

[0024] Among them, the base of the PNP type transistor is the first end of the second switch tube, the emitter of the PNP type transistor is the second end of the second switch tube, and the collector of the PNP type transistor is the third end of the second switch tube.

[0025] In some embodiments, the third switch branch includes a relay, the relay includes a coil, a first set of contacts, and a second set of contacts, the first set of contacts includes a first common contact, a first normally closed contact, and a first normally open contact, the second set of contacts includes a second common contact, a second normally closed contact, and a second normally open contact;

[0026] The coil is connected between the second power supply and the second switch branch, the first common contact is connected to the positive pole of the fan, the first normally closed contact and the second normally open contact are connected and connected to the first power supply, the first normally open contact and the second normally closed contact are connected and connected to the first switch branch, and the second common contact is connected to the negative pole of the fan.

[0027] In some embodiments, the voltage conversion branch includes a PMOS tube, a first diode, a first inductor and a second capacitor;

[0028] The gate of the PMOS tube is connected to the controller, the source of the PMOS tube is connected to the third power supply, the drain of the PMOS tube is connected to the first end of the first inductor and the cathode of the first diode, the second end of the first inductor is connected to the first end of the second capacitor and outputs the first power supply, and the anode of the first diode and the second end of the second capacitor are both grounded.

[0029] In some embodiments, the voltage conversion branch further includes a third capacitor, a fourth capacitor, a fifth capacitor, a fourth resistor and a fifth resistor;

[0030] The third capacitor is connected between the third power supply and ground, the fourth resistor is connected between the gate and source of the PMOS tube, the fourth capacitor and the fifth resistor are connected in series between the source and drain of the PMOS tube, and the fifth capacitor is connected between the second end of the first inductor and ground.

[0031] In a second aspect, an embodiment of the present application provides an electronic device, including a housing, an air inlet and an air outlet provided on the housing, and the heat dissipation circuit as described above.

[0032] Compared with the prior art, the heat dissipation circuit of the embodiment of the present application includes a fan, a controller, a first switch branch, a second switch branch and a third switch branch. The controller outputs a first level signal and a second level signal. When the first switch branch is turned on in response to the first level signal and the second switch branch is turned off in response to the second level signal, the third switch branch establishes a connection between the positive pole of the fan and the positive pole of the first power supply, and the negative pole of the fan is grounded, and the fan rotates forward to achieve the heat dissipation function. When the first switch branch is turned on in response to the first level signal and the second switch branch is turned on in response to the second level signal, the third switch branch establishes a connection between the negative pole of the fan and the positive pole of the first power supply, and the positive pole of the fan is grounded, and the fan reverses to blow away impurities and dust attached to the air inlet of the electronic device in the opposite direction, thereby preventing the air inlet of the electronic device from being blocked, so that the heat dissipation function can be achieved more reliably. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplary descriptions are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0034] Figure 1 This is a schematic diagram of the structure of the heat dissipation circuit provided in the embodiment of the present application. Figure 1 ;

[0035] Figure 2 This is a schematic diagram of the structure of the heat dissipation circuit provided in the embodiment of the present application. Figure 2 ;

[0036] Figure 3 is with Figure 2 The structure shown corresponds to circuit structure 1;

[0037] Figure 4 is with Figure 2 The structure shown corresponds to circuit structure 2. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and in detail in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] It should be noted that, when an element is described as being “connected to” another element, it may be directly connected to the other element, or one or more intervening elements may exist therebetween.

[0040] In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as there is no structural conflict between them.

[0041] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of the heat dissipation circuit provided in the embodiment of the present application. Figure 1 As shown, the heat dissipation circuit 100 includes a first switch branch 10 , a second switch branch 20 , a third switch branch 30 , a controller 40 and a fan M1 .

[0042] The controller 40 is configured to output a first control signal and a second control signal. The controller 40 may be a microcontroller unit (MCU) or a digital signal processing (DSP) controller. In one embodiment, the first control signal and the second control signal are both level signals, that is, the first control signal is a high level signal or a low level signal, and the second control signal is a high level signal or a low level signal.

[0043] The first switch branch 10 is connected to the controller 40. The first switch branch 10 is configured to be turned on or off in response to a first control signal. For example, in one embodiment, when the first control signal is a high level signal, the first switch branch 10 is turned on; when the first control signal is a low level signal, the first switch branch 10 is turned off.

[0044] The second switch branch 20 is connected to the controller 40. The second switch branch 20 is configured to be turned on or off in response to the second control signal. For example, in one embodiment, when the second control signal is a high level signal, the second switch branch 20 is turned off; when the second control signal is a low level signal, the second switch branch 20 is turned on.

[0045] The third switch branch 30 is connected between the first switch branch 10 and the fan M1 , between the fan M1 and the first power source V1 , and between the second switch branch 20 and the second power source V2 .

[0046] The third switch branch 30 is configured to establish a connection between the positive electrode of the fan M1 and the positive electrode of the first power supply V1, and to ground the negative electrode of the fan M1 to GND in response to the first switch branch 10 being turned on and the second switch branch 20 being turned off. Specifically, based on the second switch branch 20 being turned off, the second power supply V2 cannot supply power to the third switch branch 30, so that the third switch branch 30 is turned off. At this time, the positive electrode of the fan M1 is connected to the positive electrode of the first power supply V1 through the third switch branch 30. At the same time, based on the first switch branch 10 being turned on, the negative electrode of the fan M1 is grounded to GND through the third switch branch 30 and the first switch branch 10. In this case, the fan M1 rotates forward, and the heat dissipation function can be achieved.

[0047] The third switch branch 30 is also configured to establish a connection between the negative pole of the fan M1 and the positive pole of the first power supply V1 in response to the first switch branch 10 and the second switch branch 20 being turned on, and to connect the positive pole of the fan M1 to the ground GND. Specifically, based on the conduction of the second switch branch 20, the second power supply V2 can supply power to the third switch branch 30 to turn on the third switch branch 30, at which time the negative pole of the fan M1 is connected to the positive pole of the first power supply V1 through the third switch branch 30. At the same time, based on the conduction of the first switch branch 10, the positive pole of the fan M1 is connected to the ground GND of the first switch branch 10 through the third switch branch 30. In this case, the fan M1 reverses, and can blow away impurities and dust attached to the air inlet of the electronic device in the opposite direction, which is conducive to preventing the air inlet of the electronic device from being blocked, so that the heat dissipation function can be achieved more reliably.

[0048] In one embodiment, if Figure 2 As shown, the heat dissipation circuit 100 further includes a voltage conversion branch 50 .

[0049] The voltage conversion branch 50 is respectively connected to the third power source V3 and the controller 40. The voltage conversion branch 50 is configured to convert the third power source V1 into the first power source V1 in response to a third control signal output by the controller 40.

[0050] In one embodiment, the third control signal is a pulse width modulation signal. By adjusting the duty cycle of the pulse width modulation signal, the voltage of the first power source V1 can be adjusted.

[0051] In one embodiment, the voltage conversion branch 50 is configured as a step-down branch to reduce the voltage of the third power source V1 and generate the first power source V1 to meet the power supply requirement of the fan M1 .

[0052] Please refer to Figure 3 , Figure 3 An example is shown with Figure 2 A circuit structure corresponding to the structure shown in FIG. Figure 3 As shown, the first switch branch 10 includes a first switch tube Q1.

[0053] The first end of the first switch tube Q1 is connected to the controller 40 , the second end of the first switch tube Q1 is grounded GND, and the third end of the first switch tube Q1 is connected to the third switch branch 30 .

[0054] In this embodiment, the first switch tube Q1 is an NMOS tube, wherein the gate of the NMOS tube is the first end of the first switch tube Q1, the source of the NMOS tube is the second end of the first switch tube Q1, and the drain of the NMOS tube is the third end of the first switch tube Q1.

[0055] In addition, the first switch tube Q1 can be any controllable switch, such as an insulated gate bipolar transistor (IGBT) device, an integrated gate commutated thyristor (IGCT) device, a gate turn-off thyristor (GTO) device, a silicon controlled rectifier (SCR) device, a junction gate field effect transistor (JFET) device, a MOS controlled thyristor (MCT) device, etc.

[0056] In one embodiment, the first switch branch 10 further includes a first resistor R1 , a second resistor R2 , and a first capacitor C1 .

[0057] The first resistor R1 and the second resistor R2 are connected in series between the controller 40 and the ground GND, the connection point between the first resistor R1 and the second resistor R2 is connected to the gate of the first switch Q1, and the first capacitor C1 is connected in parallel with the first resistor R1.

[0058] Specifically, the first resistor R1 and the second resistor R2 are used to divide the voltage of the first level signal output by the controller 40, and drive the first switch Q1 to turn on based on the divided voltage on the first resistor R1. The first capacitor C1 is used to filter the spike pulse to reduce the risk of damage to the first switch Q1.

[0059] In one embodiment, the second switch branch 20 includes a second switch tube Q2 .

[0060] The first end of the second switch tube Q2 is connected to the controller 40 , the second end of the second switch tube Q2 is connected to the third switch branch 30 , and the third end of the second switch tube Q2 is grounded GND.

[0061] In this embodiment, the second switch tube Q2 is a PNP transistor as an example, wherein the base of the PNP transistor is the first end of the second switch tube Q2, the emitter of the PNP transistor is the second end of the second switch tube Q2, and the collector of the PNP transistor is the third end of the second switch tube Q2.

[0062] In addition, the second switch tube Q2 can be any controllable switch, such as an insulated gate bipolar transistor (IGBT) device, an integrated gate commutated thyristor (IGCT) device, a gate turn-off thyristor (GTO) device, a silicon controlled rectifier (SCR) device, a junction gate field effect transistor (JFET) device, a MOS controlled thyristor (MCT) device, etc.

[0063] In one embodiment, the second switch branch 20 further includes a third resistor R3 and a first zener diode DW1 .

[0064] The third resistor R3 is connected between the base and the emitter of the second switch tube Q2 , the anode of the first voltage zener diode DW1 is grounded GND, and the cathode of the first voltage zener diode DW1 is connected to the base of the second switch tube Q2 .

[0065] Specifically, the first voltage zener diode DW1 is used to be reversely broken down when the voltage at the emitter of the second switch tube Q2 is too large, so as to clamp the voltage at the emitter of the second switch tube Q2, thereby reducing the risk of the second switch tube Q2 being damaged due to excessive voltage, which is beneficial to protecting the second switch tube Q2.

[0066] In one embodiment, the third switch branch 30 includes a relay. The relay includes a coil KM, a first set of contacts and a second set of contacts. The first set of contacts includes a first common contact S11, a first normally closed contact S12 and a first normally open contact S13, and the second set of contacts includes a second common contact S21, a second normally closed contact S22 and a second normally open contact S23.

[0067] Among them, the coil KM is connected between the second power supply V2 and the second switch branch 20, the first common contact S11 is connected to the positive pole of the fan M1, the first normally closed contact S12 and the second normally open contact S23 are connected and connected to the first power supply V1, the first normally open contact S13 and the second normally closed contact S22 are connected and connected to the first switch branch 10, and the second common contact S21 is connected to the negative pole of the fan M1.

[0068] Specifically, when the second power supply V2 does not supply power to the coil KM, the coil KM loses power, and the corresponding third switch branch 30 is turned off. At this time, the first common contact S11 remains short-circuited with the first normally closed contact S12, and the second common contact S21 remains short-circuited with the second normally closed contact S22.

[0069] When the second power source V2 supplies power to the coil KM, the coil KM is energized, and the corresponding third switch branch 30 is turned on. At this time, the first common contact S11 is switched to short-circuit with the first normally open contact S13 (the connection between the first common contact S11 and the first normally closed contact S12 is disconnected at this time), and the second common contact S21 is switched to short-circuit with the second normally open contact S23 (the connection between the second common contact S21 and the second normally closed contact S22 is disconnected at this time).

[0070] In one embodiment, the voltage conversion branch 50 includes a PMOS transistor Q3 , a first diode D1 , a first inductor L1 , and a second capacitor C2 .

[0071] The gate of the PMOS tube Q3 is connected to the controller 40, the source of the PMOS tube Q3 is connected to the third power supply V3, the drain of the PMOS tube Q3 is connected to the first end of the first inductor L1 and the cathode of the first diode D1, the second end of the first inductor L1 is connected to the first end of the second capacitor C2 and outputs the first power supply V1, and the anode of the first diode D1 and the second end of the second capacitor C2 are both grounded GND.

[0072] Specifically, when the third control signal output by the controller 40 is at a high level, the PMOS transistor Q3 is turned on, the third power source V3 charges the first inductor L1 and the second capacitor C2 through the PMOS transistor Q3, and the first diode D1 is reversely cut off.

[0073] When the third control signal output by the controller 40 is at a low level, the PMOS tube Q3 is turned off, the first diode D1 is forward-conducted for freewheeling, and the first inductor L1, the second capacitor C2 and the first diode D1 form a discharge loop of the first inductor L1.

[0074] The third control signal is a pulse width modulation signal, which generates the first power source V1 at the second end of the first inductor L1 through the alternating switching process between high level and low level. The ratio between the voltage of the first power source V1 and the voltage of the third power source V3 is the duty cycle of the pulse width modulation signal. It can be seen that when the third power source V3 remains unchanged, the voltage of the first power source V1 can be adjusted by adjusting the duty cycle of the pulse width modulation signal.

[0075] In one embodiment, the voltage conversion branch 50 further includes a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a fourth resistor R4 and a fifth resistor R5.

[0076] Among them, the third capacitor C3 is connected between the third power supply V3 and the ground GND, the fourth resistor R4 is connected between the gate and the source of the PMOS tube Q3, the fourth capacitor C4 and the fifth resistor R5 are connected in series between the source and the drain of the PMOS tube Q3, and the fifth capacitor C5 is connected between the second end of the first inductor L1 and the ground GND.

[0077] Specifically, the third capacitor C3 and the fifth capacitor C5 are used for filtering and energy storage. The fourth capacitor C4 and the fifth resistor R5 are used for absorbing peak pulses to protect the PMOS tube Q3.

[0078] exist Figure 3 In the illustrated embodiment, when the first control signal and the second control signal output by the controller 40 are both high level signals, the first switch tube Q1 is turned on (corresponding to the first switch branch 10 being turned on), and the second switch tube Q2 is turned off (corresponding to the second switch branch 20 being turned off).

[0079] At this time, on the one hand, based on the second switch tube Q2 being turned off, the second power supply V2 and the loop where the coil KM is located are disconnected, and the coil KM loses power. The first common contact S11 remains short-circuited with the first normally closed contact S12, and the second common contact S21 remains short-circuited with the second normally closed contact S22. The positive pole of the fan M1 is connected to the first power supply V1 through the first common contact S11 and the first normally closed contact S12. On the other hand, based on the first switch tube Q1 being turned on, the negative pole of the fan M1 is connected to the ground GND through the second common contact S21, the second normally closed contact S22 and the first switch tube Q1. In this case, the fan M1 rotates forward and can achieve the heat dissipation function.

[0080] When the first control signal output by the controller 40 is a high level signal and the second control signal is a low level signal, the first switch tube Q1 and the second switch tube Q2 are both turned on (correspondingly, the first switch branch 10 and the second switch branch 20 are both turned on).

[0081] At this time, on the one hand, based on the conduction of the second switch tube Q2, the second power supply V2 and the loop where the coil KM is located are connected, and the coil KM is energized. The first common contact S11 is switched to short-circuit with the first normally open contact S13, and the second common contact S21 is short-circuited with the second normally open contact S23 (such as Figure 4 As shown). The negative pole of the fan M1 is connected to the first power source V1 through the second common contact S21 and the second normally open contact S23. On the other hand, based on the conduction of the first switch tube Q1, the positive pole of the fan M1 is connected to the ground GND of the first switch tube Q1 through the first common contact S11, the first normally open contact S13. In this case, the fan M1 is reversed, and the impurities and dust attached to the air inlet of the electronic device can be blown away in the opposite direction, which is helpful to prevent the air inlet of the electronic device from being blocked, so that the heat dissipation function can be achieved more reliably.

[0082] The embodiment of the present application further provides an electronic device, which includes a housing, an air inlet and an air outlet provided on the housing, and a heat dissipation circuit 100 in any embodiment of the present application.

[0083] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

[0084] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them. Under the idea of ​​the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order. It should be understood by ordinary technicians in this field that they can still modify the technical solutions recorded in the above embodiments, or replace some of the technical features by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A heat dissipation circuit, characterized in that: include: fan; A controller configured to output a first level signal and a second level signal; a first switch branch connected to the controller and configured to be turned on in response to the first level signal and turned off in response to the second level signal; a second switch branch connected to the controller and configured to be turned off in response to the first level signal and turned on in response to the second level signal; a third switch branch connected between the first switch branch and the fan, connected between the fan and the first power supply, and connected between the second switch branch and the second power supply; The third switch branch is configured to connect the positive electrode of the fan to the positive electrode of the first power source and ground the negative electrode of the fan in response to the first switch branch being turned on and the second switch branch being turned off; The third switch branch is further configured to establish a connection between the negative electrode of the fan and the positive electrode of the first power supply and ground the positive electrode of the fan in response to the first switch branch and the second switch branch being turned on.

2. The heat dissipation circuit according to claim 1, characterized in that: The controller is also used to output a pulse width modulation signal; The heat dissipation circuit further includes a voltage conversion branch, which is respectively connected to a third power source and the controller and is configured to convert the third power source into the first power source in response to the pulse width modulation signal.

3. The heat dissipation circuit according to claim 1 or 2, characterized in that: The first switch branch includes a first switch tube; The first end of the first switch tube is connected to the controller, the second end of the first switch tube is grounded, and the third end of the first switch tube is connected to the third switch branch.

4. The heat dissipation circuit according to claim 3, characterized in that: The first switch tube is an NMOS tube, and the first switch branch further includes a first resistor, a second resistor and a first capacitor; The first resistor and the second resistor are connected in series between the controller and the ground, the connection point between the first resistor and the second resistor is connected to the gate of the NMOS tube, and the first capacitor is connected in parallel with the first resistor; The gate of the NMOS tube is the first end of the first switch tube, the source of the NMOS tube is the second end of the first switch tube, and the drain of the NMOS tube is the third end of the first switch tube.

5. The heat dissipation circuit according to claim 1 or 2, characterized in that: The second switch branch includes a second switch tube; A first end of the second switch tube is connected to the controller, a second end of the second switch tube is connected to the third switch branch, and a third end of the second switch tube is grounded.

6. The heat dissipation circuit according to claim 5, characterized in that: The second switch tube is a PNP type triode, and the second switch branch further includes a third resistor and a first voltage regulator diode; The third resistor is connected between the base and the emitter of the PNP transistor, the anode of the first voltage stabilizing diode is grounded, and the cathode of the first voltage stabilizing diode is connected to the base of the PNP transistor; Among them, the base of the PNP type transistor is the first end of the second switch tube, the emitter of the PNP type transistor is the second end of the second switch tube, and the collector of the PNP type transistor is the third end of the second switch tube.

7. The heat dissipation circuit according to claim 1 or 2, characterized in that: The third switch branch includes a relay, the relay includes a coil, a first group of contacts and a second group of contacts, the first group of contacts includes a first common contact, a first normally closed contact and a first normally open contact, the second group of contacts includes a second common contact, a second normally closed contact and a second normally open contact; The coil is connected between the second power supply and the second switch branch, the first common contact is connected to the positive pole of the fan, the first normally closed contact and the second normally open contact are connected and connected to the first power supply, the first normally open contact and the second normally closed contact are connected and connected to the first switch branch, and the second common contact is connected to the negative pole of the fan.

8. The heat dissipation circuit according to claim 2, characterized in that: The voltage conversion branch includes a PMOS tube, a first diode, a first inductor and a second capacitor; The gate of the PMOS tube is connected to the controller, the source of the PMOS tube is connected to the third power supply, the drain of the PMOS tube is connected to the first end of the first inductor and the cathode of the first diode, the second end of the first inductor is connected to the first end of the second capacitor and outputs the first power supply, and the anode of the first diode and the second end of the second capacitor are both grounded.

9. The heat dissipation circuit according to claim 8, characterized in that: The voltage conversion branch further includes a third capacitor, a fourth capacitor, a fifth capacitor, a fourth resistor and a fifth resistor; The third capacitor is connected between the third power supply and ground, the fourth resistor is connected between the gate and source of the PMOS tube, the fourth capacitor and the fifth resistor are connected in series between the source and drain of the PMOS tube, and the fifth capacitor is connected between the second end of the first inductor and ground.

10. An electronic device, characterized in that: It comprises a shell, an air inlet and an air outlet arranged on the shell, and a heat dissipation circuit as described in any one of claims 1 to 9.

Images