Motor protection circuit and ventilation equipment

Abstract

The invention discloses a motor protection circuit and ventilation equipment, which is characterized in that a first power supply input end is connected with a normally open contact of a first relay and a first end of a coil, a second power supply input end is connected with a normally closed contact of the first relay, and a third power supply input end is connected with a second end of the coil; therefore, when the first power supply input end, the second power supply input end and the third power supply input end receive abnormal power supply input signals, the first optocoupler, the second optocoupler, the first triode, the second triode, the third triode or the fourth triode can be controlled to be switched on and off through the relay. According to the invention, damage to the motor caused by wrong connection of the power supply can be avoided, the operation safety of the motor is improved, and the service life of the motor is prolonged.

Description

Technical Field

[0001] The invention relates to the field of motors, and in particular to a motor protection circuit and ventilation equipment. Background Art

[0002] The motor usually includes at least three terminals, namely, a high-end terminal, a low-end terminal and a common terminal. When the user connects the motor, he / she connects according to the color of the terminal and the instruction manual.

[0003] However, the above method is prone to wrong wiring, which can easily cause damage to the motor. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a motor protection circuit and ventilation equipment, which can avoid motor damage caused by wrong wiring and improve the reliability and life of the motor.

[0005] In a first aspect, the present invention provides a motor protection circuit, including a first power input terminal, a second power input terminal, a third power input terminal, a first relay, a second relay, a third relay, a first optical coupler, a second optical coupler, a first transistor, a second transistor, a third transistor and a fourth transistor;

[0006] The first power input terminal is respectively connected to the normally open contact of the first relay, the first end of the first relay coil and the first end of the first optical coupler;

[0007] The second power input terminal is respectively connected to the normally closed contact of the first relay and the first terminal of the second optical coupler;

[0008] The third power input terminal is respectively connected to the second end of the first relay coil, the second end of the first optocoupler and the second end of the second optocoupler;

[0009] The third end of the first optical coupler is respectively connected to the base of the first transistor, the collector of the third transistor and the base of the fourth transistor, the collector of the first transistor is connected to the second end of the coil of the second relay, the emitter of the third transistor is grounded, the first end of the coil of the second relay is connected to the power supply, the normally open contact of the second relay is connected to the common contact of the first relay, the normally closed contact of the second relay is connected to the first drive circuit of the motor, and the fourth end of the first optical coupler is connected to the power supply;

[0010] The third end of the second optocoupler is respectively connected to the base of the second transistor, the base of the third transistor and the collector of the fourth transistor, the collector of the second transistor is connected to the second end of the coil of the third relay, the emitter of the second transistor is grounded, the first end of the third relay is connected to the power supply, the normally open contact of the third relay is connected to the common contact of the first relay, the normally closed contact of the third relay is connected to the second drive circuit of the motor, and the fourth end of the second optocoupler is connected to the power supply.

[0011] In a second aspect, the present invention provides a ventilation device, comprising a motor and a motor protection circuit as described in any one of the above items.

[0012] In an embodiment of the present application, by connecting the first power input terminal to the normally open contact of the first relay and the first end of the coil, connecting the second power input terminal to the normally closed contact of the first relay, and connecting the third power input terminal to the second end of the coil, so that when the first power input terminal, the second power input terminal and the third power input terminal receive abnormal power input signals, the first optocoupler, the second optocoupler, the first transistor, the second transistor, the third transistor or the fourth transistor can be controlled by utilizing relays, and then the driving circuit of the motor is controlled by the second relay and the third relay to achieve control of the operation of the motor. The present application can avoid damage to the motor due to incorrect power connection and improve the operating safety and life of the motor.

[0013] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a circuit diagram of a motor protection circuit in one embodiment of the present invention;

[0015] Figure 2 is a circuit diagram of a motor protection circuit in another embodiment of the present invention;

[0016] Figure 3 is a circuit diagram of a voltage conversion module in one embodiment of the present invention;

[0017] Figure 4 It is a schematic diagram of the structure of a ventilation device in one embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present application more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0019] It should be clear that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0021] When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of ventilation equipment and methods consistent with some aspects of the present application as detailed in the attached claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects, and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0022] In addition, in the description of this application, unless otherwise specified, "several" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0023] like Figure 1 As shown, the present invention provides a motor protection circuit, comprising: a first power input terminal H, a second power input terminal L, a third power input terminal COM, a first relay KY3, a second relay KY1, a third relay KY2, a first optical coupler U1, a second optical coupler U2, a first transistor Q1, a second transistor Q2, a third transistor Q3 and a fourth transistor Q4;

[0024] The first power input terminal H is respectively connected to the normally open contact of the first relay KY3, the first end of the coil of the first relay KY3 and the first end of the first optical coupler U1;

[0025] The second power input terminal L is connected to the normally closed contact of the first relay KY3 and the first end of the second optical coupler U2 respectively;

[0026] The third power input terminal COM is respectively connected to the second end of the first relay KY3 coil, the second end of the first optical coupler U1 and the second end of the second optical coupler U2;

[0027] The third end of the first optocoupler U1 is respectively connected to the base of the first transistor Q1, the collector of the third transistor Q3 and the base of the fourth transistor Q4, the collector of the first transistor Q1 is connected to the second end of the coil of the second relay KY1, the emitter of the third transistor Q3 is grounded, the first end of the coil of the second relay KY1 is connected to the power supply, the normally open contact of the second relay KY1 is connected to the common contact 220V_LOM of the first relay KY3, the normally closed contact of the second relay KY1 is connected to the first drive circuit of the motor, and the fourth end of the first optocoupler U1 is connected to the power supply.

[0028] The third end of the second optocoupler U2 is respectively connected to the base of the second transistor Q2, the base of the third transistor Q3 and the collector of the fourth transistor Q4, the collector of the second transistor Q2 is connected to the second end of the coil of the third relay KY2, the emitter of the second transistor Q2 is grounded, the first end of the third relay KY2 is connected to the power supply, the normally open contact of the third relay KY2 is connected to the common contact 220V_LOM of the first relay KY3, the normally closed contact of the third relay KY2 is connected to the second drive circuit of the motor, and the fourth end of the second optocoupler U2 is connected to the power supply.

[0029] The first power input terminal H and the second power input terminal L can be used to connect to the 220V live wire, and the third power input terminal COM can be used to connect to the 220V neutral wire. Usually, only one end of the first power input terminal H and the second power input terminal L has a 220V input.

[0030] The first optocoupler U1 and the second optocoupler U2 are used to electrically isolate the input power supply signal, thereby ensuring the safety of subsequent components such as transistors and relays.

[0031] The first driving circuit is used to drive the motor to run at a first speed, and the second driving circuit is used to drive the motor to run at a second speed, wherein the first speed may be greater than the second speed.

[0032] The first drive circuit and the second drive circuit may be common motor drive circuits.

[0033] The following is an explanation of the wiring protection principle of the motor protection circuit in the embodiment of the present application. In the embodiment of the present application, the first drive circuit is used to drive the motor to run at high speed, and the second drive circuit is used to drive the motor to run at low speed;

[0034] When the first power input terminal H inputs the mains 220V_L, the second power input terminal L is not input, and the third power input terminal COM inputs the mains 220V_N, the first relay KY3 is energized, the first optocoupler U1 is turned on, the second optocoupler U2 is not turned on, the third transistor Q3 does not conduct because the base does not receive power due to the second optocoupler U2 not conducting, the base of the first transistor Q1 receives power due to the optocoupler U1 being turned on, the first transistor Q1 is turned on, driving the second relay KY1 to energize, and the first power input terminal H (mains 220V control live wire) is connected to 220V_LCOM, and the motor runs in high gear.

[0035] When the second power input terminal L inputs the mains 220V_L, the first power input terminal H is not input, and the third power input terminal COM inputs the mains 220V_N, the first relay KY3 is not energized, the second optocoupler U2 is turned on, the collector of the third transistor Q3 and the base of the fourth transistor Q4 are not turned on because the first optocoupler U1 is not energized, the base of the second transistor Q2 is energized because the second optocoupler U2 is turned on, the second transistor Q2 is turned on, driving the third relay KY2 to energize, the second power input terminal L (mains 220V control live wire) is connected to 220V_LCOM, and the motor runs at low gear.

[0036] When both the first power input terminal H and the second power input terminal L are powered off, the circuit has no power input and stops working.

[0037] When the second power input terminal L and the first power input terminal H input the mains 220V_L at the same time, and the third power input terminal COM inputs the mains 220V_N, the first relay KY3 is energized, the first optocoupler U1 and the second optocoupler U2 are both turned on, the base and collector of the third transistor Q3 and the fourth transistor Q4 are energized due to the conduction of the first optocoupler U1 and the second optocoupler U2, the third transistor Q3 and the fourth transistor Q4 are turned on, and under the action of the collector saturation voltage drop Uce, the base voltages of the first transistor Q1 and the second transistor Q2 are clamped by the Uce saturation voltage drop, which is lower than the conduction voltage Vbe of the transistor, so the first transistor Q1 and the second transistor Q2 are not turned on, the second relay KY1 and the third relay KY2 are not energized, the motor cannot be powered on normally, and therefore the motor does not run, thereby preventing the high and low gears of the motor from being connected to the power supply at the same time, causing damage to the motor.

[0038] When the first power input terminal H is connected to the mains 220V_L, the second power input terminal L is connected to the mains 220V_N, and the third power input terminal COM is connected to the mains 220V_L, the first relay KY3 is not energized. Since the first power input terminal H and the third power input terminal COM are both connected to the mains 220V_L, the first optocoupler U1 is not conducting, and the second power input terminal L is input to the mains 220V_N, and the third power input terminal COM is both connected to the mains 220V_L, so the second optocoupler U2 is turned on. Since the first optocoupler U1 is not conducting, the collector of the third transistor Q3 and the base of the fourth transistor Q4 are not energized and therefore are not conducting. The base of the second transistor Q2 is energized due to the conduction of the second optocoupler U2, and the second transistor Q2 is turned on, driving the third relay KY2 to energize, and the motor runs at a low gear.

[0039] When the first power input terminal H is connected to the mains 220V_N, the second power input terminal L is connected to the mains 220V_L, and the third power input terminal COM is connected to the mains 220V_N, the first relay KY3 is not energized, because the first power input terminal H and the third power input terminal COM are both connected to the mains 220V_N, so the first optocoupler U1 is not turned on; and the second power input terminal L inputs the mains 220V_L, and the third power input terminal COM is both connected to the mains 220V_N, so the second optocoupler U2 is turned on, and because the first optocoupler U1 is not turned on, the collector of the third transistor Q3 and the base of the fourth transistor Q4 are not energized and therefore are not turned on, and the base of the second transistor Q2 is energized due to the conduction of the optocoupler U2, and the second transistor Q2 is turned on, driving the third relay KY2 to attract, and the motor runs at a low gear.

[0040] Please refer to Table 1, which is a schematic diagram of the operating status of the motor when the first power input terminal, the second power input terminal, and the third power input terminal are connected to the neutral wire (N), the live wire (L), or no power is supplied in one embodiment of the present application.

[0041]

[0042] In this embodiment, when the first power input terminal, the second power input terminal, and the third power input terminal are connected to different power sources, the motor can be protected and will not be damaged due to incorrect wiring.

[0043] In an embodiment of the present application, by connecting the first power input terminal to the normally open contact of the first relay and the first end of the coil, connecting the second power input terminal to the normally closed contact of the first relay, and connecting the third power input terminal to the second end of the coil, so that when the first power input terminal, the second power input terminal and the third power input terminal receive abnormal power input signals, the first optocoupler, the second optocoupler, the first transistor, the second transistor, the third transistor or the fourth transistor can be controlled by utilizing relays, and then the driving circuit of the motor is controlled by the second relay and the third relay to achieve control of the operation of the motor. The present application can avoid damage to the motor due to incorrect power connection and improve the operating safety and life of the motor.

[0044] In one embodiment, the motor protection circuit may further include a first thermistor, wherein a first end of the first thermistor is connected to the first power input end, and a second end of the first thermistor is respectively connected to a normally open contact of the first relay, a first end of the first relay coil, and a first end of the first optocoupler.

[0045] The first thermistor is a sensor resistor whose resistance value changes with temperature. The first thermistor can control the magnitude of the current in the loop according to the change of the ambient temperature. The first thermistor in the embodiment of the present application can be a positive temperature coefficient thermistor.

[0046] In the embodiment of the present application, a thermistor is connected in series to the first power input terminal, so that when the ambient temperature rises, the thermistor is used to reduce the current in the loop, thereby avoiding damage to the relay due to excessive temperature.

[0047] like Figure 2 As shown, in one embodiment, the motor protection circuit may further include a first diode D2, a second diode D4, a first resistor R5, a second resistor R6, a third resistor R7 and a fourth resistor R8;

[0048] The anode of the first diode D2 is respectively connected to the normally open contact of the first relay KY3 and the first end of the coil of the first relay KY3, the cathode of the first diode D2 is respectively connected to the first end of the first resistor R5 and the first end of the first optical coupler U1, the second end of the first resistor R5 is respectively connected to the third power input terminal COM, the second end of the first optical coupler U1 and the second end of the third resistor R7, and the first end of the third resistor R7 is connected to the third power input terminal COM;

[0049] The anode of the second diode D4 is respectively connected to the normally closed contact of the first relay KY3 and the second power input terminal L, the cathode of the second diode D4 is respectively connected to the first end of the second resistor R6 and the first end of the second optocoupler U2, the second end of the second resistor R6 is respectively connected to the third power input terminal COM, the second end of the second optocoupler U2 and the second end of the fourth resistor R8, and the first end of the fourth resistor R8 is connected to the third power input terminal COM.

[0050] In the embodiment of the present application, by connecting a resistor in parallel to the input end of the optocoupler, it is possible to prevent the optocoupler from malfunctioning and causing incorrect signal transmission. At the same time, by connecting a diode and a resistor in series at the input end of the optocoupler, the resistor is used to limit the current input to the optocoupler, and the diode is used to ensure the unidirectional input of the power supply signal, thereby improving the safety and life of the optocoupler.

[0051] like Figure 2 As shown, in one embodiment, it also includes a first capacitor E4 and a second capacitor E5;

[0052] The first end of the first capacitor E4 is connected to the third end of the first optical coupler U1, and the second end of the first capacitor E4 is grounded; the second capacitor E5 is connected to the third end of the second optical coupler U2, and the second end of the second capacitor E5 is grounded.

[0053] The first capacitor E4 and the second capacitor E5 may be electrolytic capacitors;

[0054] In the embodiment of the present application, the signal output by the optocoupler is filtered by the first capacitor E4 and the second capacitor E5 to avoid malfunction of the transistor and improve the accuracy of motor control.

[0055] Optionally, the motor protection circuit of this embodiment may further include resistors R3-R4 and R9-R12, wherein resistor R3 is arranged between the power supply and the fourth end of the first optocoupler U1, resistor R9 is arranged between the third end of the first optocoupler U1 and the base of the transistor Q1, resistor R10 is arranged between the third end of the second optocoupler U2 and the base of the third transistor Q3, resistor R11 is arranged between the third end of the first optocoupler U1 and the base of the fourth transistor Q4, and resistor R4 is arranged between the power supply and the first optocoupler U2.

[0056] Resistors R3-R4 and R9-R12 are used to limit the current of the signal input to the base of the transistor to avoid damage to the transistor due to excessive current, thereby improving the safety of the transistor operation.

[0057] In one embodiment, a third thermistor RT3 is further included; a first end of the third thermistor RT3 is connected to the third power input end, and a second end of the third thermistor RT3 is connected to the common end of the motor.

[0058] Thermistors can be used to implement high temperature protection for motors, thereby improving their operating safety and lifespan.

[0059] In one embodiment, it also includes a voltage conversion module for converting the power supply voltage into a target voltage; the first input terminal of the voltage conversion module is connected to the common contact of the first relay, and the second input terminal of the voltage conversion module is connected to the third power supply input terminal.

[0060] The voltage conversion module can use an existing voltage conversion circuit to convert the voltage of the power supply into a target voltage. The target voltage can be determined according to the voltage used by each circuit module of the motor protection circuit, and in the embodiment of the present application, it can be a DC voltage. The voltage conversion module can use an existing AC to DC circuit and a voltage conversion circuit to achieve the conversion of the target voltage.

[0061] When the first power input terminal H inputs the mains 220V_L, the second power input terminal L is not input, and the third power input terminal COM inputs the mains 220V_N, the first relay KY3 is energized, the first input terminal of the voltage conversion module inputs the mains 220V_L through the normally open contact of the first relay KY3, and the second input terminal of the voltage conversion module inputs the mains 220V_N. The voltage conversion module works normally and converts the power supply voltage into the target voltage VCC, thereby powering each circuit module of the motor protection circuit.

[0062] When the second power input terminal L inputs the mains 220V_L, the first power input terminal H is not input, and the third power input terminal COM inputs the mains 220V_N, the first relay KY3 is not energized, the first input terminal of the voltage conversion module inputs the mains 220V_L through the normally closed contact of the first relay KY3, and the second input terminal of the voltage conversion module inputs the mains 220V_N, the voltage conversion module works normally, converts the power supply voltage into the target voltage VCC, thereby powering the various circuit modules of the motor protection circuit.

[0063] When both the first power input terminal H and the second power input terminal L are powered off, the voltage conversion module has no power signal input, the motor protection circuit lacks power, and the motor stops running.

[0064] When the second power input terminal L and the first power input terminal H simultaneously input the AC power 220V_L, and the third power input terminal COM inputs the AC power 220V_N, the first relay KY3 is energized, the first input terminal of the voltage conversion module inputs the AC power 220V_L through the normally open contact of the first relay KY3, and the second input terminal of the voltage conversion module inputs the AC power 220V_N. The voltage conversion module works normally and converts the power supply voltage into the target voltage VCC, thereby powering each circuit module of the motor protection circuit.

[0065] When the first power input terminal H is connected to the mains 220V_L, the second power input terminal L is connected to the mains 220V_N, and the third power input terminal COM is connected to the mains 220V_L, the first relay KY3 is not energized, the first input terminal of the voltage conversion module is connected to the mains 220V_N through the normally closed contact of the first relay KY3, and the second input terminal of the voltage conversion module is connected to the mains 220V_N through the second power input terminal L. The voltage conversion module works normally and converts the power supply voltage into the target voltage VCC, thereby powering each circuit module of the motor protection circuit.

[0066] When the first power input terminal H is connected to the mains 220V_N, the second power input terminal L is connected to the mains 220V_L, and the third power input terminal COM is connected to the mains 220V_N, the first relay KY3 is not energized, the first input terminal of the voltage conversion module is connected to the mains 220V_L through the normally closed contact of the first relay KY3, and the second input terminal of the voltage conversion module is connected to the mains 220V_N. The voltage conversion module works normally and converts the power supply voltage into the target voltage VCC, thereby powering each circuit module of the motor protection circuit.

[0067] like Figure 3 As shown, the voltage conversion module includes a rectifier bridge DB1, a voltage conversion chip U3, a sampling resistor RS1, an inductor L2, a voltage regulator tube DZ1 and a third diode D2;

[0068] The first end of the rectifier bridge DB1 is connected to the common contact of the first relay, the second end of the rectifier bridge DB1 is connected to the third power input terminal COM, the third end of the rectifier bridge DB1 is connected to the drain terminal of the voltage conversion chip U3, the fourth end of the rectifier bridge DB1 is grounded, the sampling end of the voltage conversion chip U3 is connected to the first end of the inductor L2 through the sampling resistor RS1, and the second end of the inductor L2 is connected to the anode of the third diode D2; the power supply end of the voltage conversion chip U3 is connected to the anode of the voltage regulator tube, and the cathode of the voltage regulator tube DZ1 is connected to the cathode of the third diode D2.

[0069] The voltage conversion chip U3 may be a step-down circuit.

[0070] The 220V AC is rectified into a high-voltage DC voltage of 310V by the rectifier bridge DB1, and then converted into a low-voltage DC voltage by the step-down circuit to supply power to other components on the motor protection circuit. The voltage conversion module of this embodiment has a wide input voltage range (AC 85V to 265V), is suitable for power grids with large voltage fluctuations, and has a relatively low cost compared to isolated power supplies.

[0071] Optionally, the voltage conversion module may also include a filtering module, which includes capacitors C1-C2, electrolytic capacitors E1-E3, inductor L1 and resistor R2, the positive electrode of the electrolytic capacitor E1 is respectively connected to the third end of the rectifier bridge DB1, the first end of the inductor L1 and the first end of the resistor R2, the second end of the inductor L1 is respectively connected to the drain end of the voltage conversion chip U3, the second end of the resistor R2 and the positive electrode of the electrolytic capacitor E2, and the negative electrodes of the electrolytic capacitors E1-E2 are grounded; the first end of the capacitor C1 is connected to the second end of the sampling resistor RS1, the second end of the capacitor C1 is connected to the power supply end of the voltage conversion chip U3, the positive electrode of the electrolytic capacitor E3 and the first end of the capacitor C2 are connected to the anode of the third diode D2, and the negative electrode of the electrolytic capacitor E3 and the second end of the capacitor C2 are grounded.

[0072] By using capacitors, electrolytic capacitors, inductors and resistors to form a filter module, the power signal of the voltage conversion module is filtered to improve the reliability of the output power signal.

[0073] In one embodiment, it also includes a fuse F1, a varistor ZNR, a second thermistor RT1, and an X capacitor XC1;

[0074] A first end of the fuse F1 is connected to the common contact of the first relay, a second end of the fuse F1 is respectively connected to a first end of the varistor ZNR, a first end of the second thermistor RT1 and a first end of the X capacitor XC1, a second end of the varistor ZNR and a second end of the second thermistor RT1 are connected to the third power input terminal COM, and a second end of the X capacitor XC1 is connected to a first end of the rectifier bridge DB1.

[0075] The 220V AC power supply passes through the short-circuit fuse F1, and then is protected by the lightning surge protection varistor ZNR1 and the second thermistor RT1 before being input into the rectifier bridge DB1 for rectification. By utilizing the fuse F1, the varistor ZNR1 and the second thermistor RT1, short-circuit protection, temperature protection and under-voltage protection of the input power supply are achieved, thereby improving power supply reliability.

[0076] like Figure 4 As shown, an embodiment of the present application further provides a ventilation device 100, comprising a motor protection circuit 110 and a motor 120 as described in any one of the above items.

[0077] The motor 120 may be a single-phase two-speed adjustable motor.

[0078] In one embodiment, the ventilation equipment may include a fresh air fan, an air curtain, a fan or an air cabinet.

[0079] The present invention is not limited to the above-mentioned embodiments. If various changes or modifications to the present invention do not depart from the spirit and scope of the present invention, and if these changes and modifications fall within the scope of the claims and equivalent technologies of the present invention, the present invention is also intended to include these changes and modifications.

Claims

1. A motor protection circuit, characterized in that: It includes a first power input terminal, a second power input terminal, a third power input terminal, a first relay, a second relay, a third relay, a first optical coupler, a second optical coupler, a first transistor, a second transistor, a third transistor and a fourth transistor; The first power input terminal is respectively connected to the normally open contact of the first relay, the first end of the first relay coil and the first end of the first optical coupler; The second power input terminal is respectively connected to the normally closed contact of the first relay and the first terminal of the second optical coupler; The third power input terminal is respectively connected to the second end of the first relay coil, the second end of the first optocoupler and the second end of the second optocoupler; The third end of the first optical coupler is respectively connected to the base of the first transistor, the collector of the third transistor and the base of the fourth transistor, the collector of the first transistor is connected to the second end of the coil of the second relay, the emitter of the third transistor is grounded, the first end of the coil of the second relay is connected to the power supply, the normally open contact of the second relay is connected to the common contact of the first relay, the normally closed contact of the second relay is connected to the first drive circuit of the motor, and the fourth end of the first optical coupler is connected to the power supply; The third end of the second optical coupler is respectively connected to the base of the second triode, the base of the third triode and the collector of the fourth triode, the collector of the second triode is connected to the second end of the coil of the third relay, the emitter of the second triode is grounded, the first end of the third relay is connected to the power supply, the normally open contact of the third relay is connected to the common contact of the first relay, the normally closed contact of the third relay is connected to the second drive circuit of the motor, and the fourth end of the second optical coupler is connected to the power supply; The first driving circuit is used to drive the motor to run at a first speed, and the second driving circuit is used to drive the motor to run at a second speed; wherein the first speed is greater than the second speed.

2. The motor protection circuit according to claim 1, characterized in that: It also includes a first thermistor, a first end of the first thermistor is connected to the first power input end, and a second end of the first thermistor is respectively connected to the normally open contact of the first relay, the first end of the first relay coil and the first end of the first optocoupler.

3. The motor protection circuit according to claim 1, characterized in that: Also includes a first diode, a second diode, a first resistor, a second resistor, a third resistor and a fourth resistor; The anode of the first diode is connected to the normally open contact of the first relay and the first end of the first relay coil respectively, the cathode of the first diode is connected to the first end of the first resistor and the first end of the first optocoupler respectively, the second end of the first resistor is connected to the third power input terminal, the second end of the first optocoupler and the second end of the third resistor respectively, and the first end of the third resistor is connected to the third power input terminal; The anode of the second diode is respectively connected to the normally closed contact of the first relay and the second power supply input terminal, the cathode of the second diode is respectively connected to the first end of the second resistor and the first end of the second optocoupler, the second end of the second resistor is respectively connected to the third power supply input terminal, the second end of the second optocoupler and the second end of the fourth resistor, and the first end of the fourth resistor is connected to the third power supply input terminal.

4. The motor protection circuit according to claim 1, characterized in that: Also includes a first capacitor and a second capacitor; The first end of the first capacitor is connected to the third end of the first optical coupler, and the second end of the first capacitor is grounded; the second capacitor is connected to the third end of the second optical coupler, and the second end of the second capacitor is grounded.

5. The motor protection circuit according to claim 1, characterized in that: It also includes a voltage conversion module for converting the power supply voltage into a target voltage; the first input terminal of the voltage conversion module is connected to the common contact of the first relay, and the second input terminal of the voltage conversion module is connected to the third power supply input terminal.

6. The motor protection circuit according to claim 5, characterized in that: The voltage conversion module includes a rectifier bridge, a voltage conversion chip, a sampling resistor, an inductor, a voltage regulator tube and a third diode; The first end of the rectifier bridge is connected to the common contact of the first relay, the second end of the rectifier bridge is connected to the third power supply input end, the third end of the rectifier bridge is connected to the drain end of the voltage conversion chip, the fourth end of the rectifier bridge is grounded, the sampling end of the voltage conversion chip is connected to the first end of the inductor through a sampling resistor, the second end of the inductor is connected to the anode of the third diode; the power supply end of the voltage conversion chip is connected to the anode of the Zener diode, and the cathode of the Zener diode is connected to the cathode of the third diode.

7. The motor protection circuit according to claim 6, characterized in that: It also includes a fuse, a varistor, a second thermistor and an X capacitor; A first end of the fuse is connected to a common contact of the first relay, a second end of the fuse is respectively connected to a first end of the varistor, a first end of the second thermistor and a first end of the X capacitor, a second end of the varistor and a second end of the second thermistor are connected to the third power input terminal, and a second end of the X capacitor is connected to a first end of the rectifier bridge.

8. The motor protection circuit according to claim 1, characterized in that: It also includes a third thermistor; a first end of the third thermistor is connected to the third power input end, and a second end of the third thermistor is connected to the common end of the motor.

9. A ventilation device, characterized in that: The invention comprises a motor and a motor protection circuit as claimed in any one of claims 1 to 8.

10. The ventilation device according to claim 9, characterized in that The ventilation equipment includes a fresh air fan, an air curtain, a fan or an air cabinet.

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