TWI614984B - Fan motor power failure automatic brake circuit - Google Patents

Abstract

The invention relates to a circuit for a fan motor power-off automatic braking, comprising an energy storage unit, a motor driving circuit, a control unit and a resistor unit connected to an input power source, wherein the energy storage unit is electrically connected to the motor driving circuit, Receiving and storing an operating voltage, the motor driving circuit has a plurality of upper and lower arm switch assemblies and a first and second driving unit, and the control unit is electrically connected to the lower arm switch assemblies and the first and second driving respectively The unit, when the power storage unit is powered off, provides the operating voltage to the upper arm switch assemblies to be turned on, so that the upper arm switch assemblies form a closed loop with the motor coils to brake.

Description

Fan motor power failure automatic brake circuit

The invention relates to a circuit for automatically braking a fan motor, and in particular to a circuit for automatically braking a fan motor with an automatic braking function.

In recent years, the use of digital-based microcontrollers (MCUs) combined with power electronic switch drive circuits for electronic product design has become a common technology in the industry. However, when the electronic product is operated, the digital microcontroller and the power electronic switch may generate a large amount of heat due to the high frequency operation; therefore, the heat dissipation requirement of the electronic product will become a very important design issue. At present, the more common heat dissipation method is to drive the heat of the electronic product by the operation of the fan system. However, based on the fan control and the safe operation of the user, the fan system usually combines a brake circuit so that when the power is cut off. Stop the operation of the fan system to ensure the accuracy of the fan control and the safety of the user.

Referring to FIG. 1 , a conventional fan brake circuit 1 includes a bridge driver 11 , a controller 13 , a brake circuit 14 , and a motor coil L . An input power source Vin is connected to the bridge driver 11 , the controller 13 , and The braking circuit 14 is required to provide power for the above-mentioned components, and the bridge driver 11 is composed of two upper arm switches M1 and M2 and two lower arm switches M3 and M4, so when the fan is powered off, the brake is transmitted through the brake. The control of the circuit 14 is performed to perform an immediate stop operation to achieve the effect of braking. However, in the conventional fan brake circuit 1, the controller 13 is required to perform the pulse width modulation signal (PULSE WIDTH MODULATION; PWM) cutting control on the two lower arm switches M3 and M4, and the controller 13 is turned into the upper arm switch. M1, M2 do the pulse width modulation signal cutting control, but the temperature of the two upper arm switches M1, M2 and the control resistor rises, so it is necessary to increase the electronic components (such as resistors) to solve the above problem of temperature rise, and The lower arm switches M3 and M4 are electrically connected to the braking circuit 14, which is bound to increase the cost and increase the circuit connection complexity due to the setting of the braking circuit 14.

Therefore, in order to effectively solve the above problems, an object of the present invention is to provide a braking function for a circuit through a resistor unit, and an operating voltage is supplied to a motor driving circuit when an energy storage unit is powered off. A plurality of upper arm switch assemblies, such that the upper arm switch assembly and a motor coil form a closed loop to achieve the effect of braking, and the fan motor is powered off and automatically brakes the circuit.

Another object of the present invention is to provide a circuit having a fan motor power-off automatic brake that achieves cost savings.

In order to achieve the above object, the present invention provides a circuit for a fan motor power-off automatic braking, comprising an energy storage unit, a motor driving circuit, a control unit and a resistor unit, wherein the energy storage unit receives and stores an operating voltage. The motor drive circuit has a plurality of upper arm switch assemblies, a plurality of lower arm switch assemblies, a first drive unit, and a second drive unit, and a first end of the upper arm switch assemblies is electrically connected to the energy storage unit and receives the operation a second end of the voltage is electrically connected to a first end of the lower arm switch assembly and the motor coil, and a second end of the lower arm switch assembly is connected to a ground end, and A first end of the first and second driving units are electrically connected to a third end of the upper arm switch assembly, and the control unit is electrically connected to a third end of the lower arm switch and the first end, a second end of the driving unit, and one end of the resistor unit is electrically connected to an input power source, and the other end of the resistor unit is electrically connected to a third end of the first and second driving units, and the first and second drives are A fourth terminal means electrically connected to the ground terminal, wherein when the fan is off, the upper arm switching component receives such The operating voltage provided by the energy storage unit is turned on, and the lower arm switch assembly does not receive the operating voltage and is not turned on, so that the upper arm switch assembly and the motor coil form a closed loop to achieve the braking effect, and Effectively achieve cost savings.

In one implementation, the upper arm switch assembly has a first upper arm switch assembly and a second upper arm switch assembly, the first end of the first and second upper arm switch members being electrically connected to the energy storage unit, the first The second ends of the two upper arm switch assemblies are electrically connected to opposite ends of the motor coil, and the third ends of the first and second upper arm switch assemblies are electrically connected to the first and second driving units respectively. One end.

In one implementation, the lower arm switch assembly has a first lower arm switch assembly and a second lower arm switch assembly, and the first ends of the first and second lower arm switch assemblies are electrically connected to the motor coils respectively The second ends of the first and second lower arm switch assemblies are electrically connected to the ground end, and the third ends of the first and second lower arm switch assemblies are electrically connected to the control unit respectively.

In one implementation, the resistor unit is a resistor, and one end of the resistor unit is electrically connected to the input power source, and the other end of the resistor unit is electrically connected to the third end of the first and second driving units.

In one implementation, the control unit is a central processing unit or a microcontroller.

In one implementation, the first driving unit includes a first transistor, a first resistor, a second resistor, a third resistor, a fourth resistor, and a first capacitor, the first transistor Having a base, an emitter, and a collector, the collector is electrically connected to one end of the second resistor, the emitter is electrically connected to one end of the third resistor and the ground, the third resistor The other end is electrically connected to one end of the first capacitor, one end of the first resistor, the other end of the second resistor, and the third end of the first upper arm switch assembly, and the first resistor The other end of the first capacitor is connected to the other end of the resistor unit. One end of the fourth resistor is electrically connected to the base, and the other end of the fourth resistor is electrically connected to the control unit.

In one implementation, the second driving unit includes a second transistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, and a second capacitor, the second transistor Having a base, an emitter, and a collector, the collector of the second transistor is electrically connected to one end of the seventh resistor, and the emitter of the second transistor is electrically connected to the sixth resistor One end of the sixth resistor and one end of the second capacitor, one end of the fifth resistor, the other end of the seventh resistor, and the third end of the second upper arm switch group The other end of the second resistor is electrically connected to the other end of the second resistor, and the other end of the second resistor is electrically connected to the base of the second transistor. The other end is electrically connected to the control unit.

In one implementation, the resistor unit is a 0 ohm resistor.

2‧‧‧Circuit motor power failure automatic brake circuit

21‧‧‧ Energy storage unit

22‧‧‧Motor drive circuit

221‧‧‧First upper arm switch assembly

222‧‧‧Second upper arm switch assembly

2211, 2221‧‧‧ first end

2212, 2222‧‧‧ second end

2213, 2223‧‧‧ third end

223‧‧‧First lower arm switch assembly

224‧‧‧Second lower arm switch assembly

2231, 2241‧‧‧ first end

2232, 2242‧‧‧ second end

2233, 2243‧‧‧ third end

225‧‧‧First drive unit

226‧‧‧Second drive unit

2251, 2261‧‧‧ first end

2252, 2262‧‧‧ second end

2253, 2263‧‧‧ third end

2254, 2264‧‧‧ fourth end

24‧‧‧Control unit

25‧‧‧Resistor unit

L‧‧‧Motor coil

Vin‧‧‧Input power supply

Vcc‧‧‧ operating voltage

Vs‧‧‧ working voltage

GND‧‧‧ ground terminal

M1‧‧‧First MOS transistor

M2‧‧‧Second upper MOS transistor

M3‧‧‧First MOS transistor

M4‧‧‧Second MOS transistor

Q1‧‧‧First transistor

Q2‧‧‧Second transistor

R1‧‧‧ first resistor

R2‧‧‧second resistor

R3‧‧‧ third resistor

R4‧‧‧ fourth resistor

R5‧‧‧ fifth resistor

R6‧‧‧ sixth resistor

R7‧‧‧ seventh resistor

R8‧‧‧ eighth resistor

R9‧‧‧ ninth resistor

R10‧‧‧10th Resistor

R11‧‧‧Eleventh Resistor

R12‧‧‧12th resistor

R13‧‧‧13th resistor

C1‧‧‧First Capacitor

C2‧‧‧second capacitor

C3‧‧‧ third capacitor

C4‧‧‧fourth capacitor

Figure 1 is a schematic diagram of a conventional circuit of a fan brake circuit.

Figure 2 is a block diagram showing an embodiment of the present invention.

Figure 3 is a circuit diagram of an embodiment of the present invention.

The above object of the present invention, as well as its structural and functional features, will be described in accordance with the preferred embodiments of the drawings.

The present invention provides a circuit 2 for a fan motor to be powered off and automatically braked. Please refer to FIGS. 2 and 3 for a block and circuit diagram showing a preferred embodiment of the present invention; Applied to a fan (such as an axial fan or a centrifugal fan; not shown), the circuit 2 includes an energy storage unit 21, a motor drive circuit 22, a control unit 24, and a resistor unit 25, the energy storage unit 21 is shown as a capacitor in the embodiment, the energy storage unit 21 is configured to receive and store an operating voltage Vcc (eg, 12 volts), and the motor driving circuit 22 has a plurality of upper arm switch components, a plurality of lower arm switch components, and a first One The upper arm switch assembly is shown in the embodiment as two upper arm switch assemblies, and the upper arm switch assembly has a first upper arm switch assembly 221 and a second upper arm switch assembly 222. The first and second upper arm switch assemblies 221, 222 each have a first end 2211, 2221, a second end 2212, 2222, and a third end 2213, 2223, and the first and second upper arm switch members 221, 222 The first ends 2211, 2221 (ie, the first ends 2211, 2221 of the upper arm switch assemblies) are electrically connected to the energy storage unit 21 and receive the operating voltage Vcc, the first and second upper arm switch assemblies 221, 222 The second ends 2212, 2222 (the second ends 2212, 2222 of the upper arm switch assemblies) are electrically connected to opposite ends of the motor coil L, and the third ends of the first and second upper arm switch assemblies 221, 222 2213, 2223 (ie, the third ends 2213, 2223 of the upper arm switch assemblies) are electrically connected to a first end 2251 of the first driving unit 225 and a first end 2261 of the second driving unit 226, respectively.

The lower arm switch assemblies are shown in the present embodiment as two lower arm switch assemblies having a first lower arm switch assembly 223 and a second lower arm switch assembly 224, the first and second The lower arm switch assemblies 223, 224 each have a first end 2231, 2241, a second end 2232, 2242, and a third end 2233, 2243. The first end 2231 of the first and second lower arm switch assemblies 223, 224 2241 (the first ends 2231, 2241 of the lower switch assemblies) are electrically connected to the second ends 2212, 2222 of the first and second upper arm switch assemblies 221, 222, respectively, the first and second lower arm switch assemblies 223 The second ends 2232, 2242 of the 224 (the second ends 2232, 2242 of the lower switch components) are connected to a ground GND, and the third ends 2233 of the first and second lower arm switch assemblies 223, 224, 2243 (the third ends 2233, 2243 of the lower arm closing assemblies) are electrically connected to the control unit 24, respectively. The first and second driving units 225 and 226 each have the first end 2251, 2261, a second end 2252, 2262, a third end 2253, 2263 and a fourth end 2254, 2264. The first and second driving The first ends 2251, 2261 of the units 225, 226 are electrically connected to the third ends 2213, 2223 of the upper arm switch assemblies, respectively, and the second ends 2252, 2262 of the first and second drive units 225, 226 respectively Electrically connected to the control unit 24, the third ends 2253, 2263 of the first and second driving units 225, 226 are electrically connected to the other end of the resistor unit 25, the first and second driving units 225, 226 The four ends 2254 and 2264 are electrically connected to the ground GND, and one end of the resistor unit 25 is electrically connected to an input power source Vin, and the input power source Vin (such as 12 volts) is used to supply power.

In addition, the resistor unit 25 is a resistor, and in the embodiment, the resistor unit 25 is a 0 ohm resistor. The control unit 24 is a central processing unit (CPU) or a micro control unit (MCU), and the control unit 24 has a plurality of pins, wherein the four pins of the control unit 24 respectively Connecting the second ends 2252, 2262 of the first and second driving units 225, 226 and the third ends 2233, 2243 of the first and second lower arm switch assemblies 223, 224, and the four pins of the foregoing control unit 24 The first and second driving units 225 and 226 respectively drive the switching operations of the corresponding first and second upper arm switching components 221 and 222 to output a pulse width modulation (PWM) signal (for example, the switch is turned on or The switch is non-conducting) and controlling the switching action of the first and second lower arm switch assemblies 223, 224 (eg, the switch is conducting or the switch is non-conducting), and the other pin of the control unit 24 (such as the fifth pin) And electrically connected to a Hall element (not shown) for receiving the Hall signal transmitted by the Hall element, and another pin of the control unit 24 (such as the sixth pin) receives an operating voltage Vs (such as 5 volts). Therefore, the circuit has a braking function through the foregoing resistor unit 25 of the present invention, and the operating voltage Vcc is supplied to the first and second upper arm switch assemblies 221, 222 of the motor driving circuit 22 when the energy storage unit 21 is powered off. Turning on, the first and second upper arm switch assemblies 221, 222 and the motor coil L are short-circuited to form a closed loop to achieve the braking effect. With the circuit 2 of the present invention, when the fan is powered off, the fan blade rotates (or operates) due to its own inertia, and the motor coil L on the closed circuit is made according to Faraday's law. Inductive current is generated to close the coil. This induced current will cause the motor coil L to generate a reverse magnetic field to prevent the fan blade from running, so that the fan can quickly stop braking.

Please refer to FIG. 3 for details. The first driving unit 225 includes a first transistor Q1, a first resistor R1, a second resistor R2, and a third resistor R3. a fourth resistor R4 and a first capacitor C1. The first transistor Q1 is represented as a BJT (Bipolar Junction Transistor) transistor in the embodiment, and the first transistor Q1 has a base, an emitter and a a collector, the collector of the first transistor Q1 is electrically connected to one end of the second resistor R2, and the emitter of the first transistor Q1 is electrically connected to one end of the third resistor R3 and the ground GND. The other end of the third resistor R3 (ie, the first end 2251 of the first driving unit 225) and one end of the first capacitor C1, one end of the first resistor R1, and the other end of the second resistor R2 The third end 2213 of the first upper arm switch assembly 221 is electrically connected in common, and the other end of the first resistor R1 is commonly connected with the other end of the first capacitor C1 with respect to the other end of the resistor unit 25. One end of the fourth resistor R4 is electrically connected to the base of the first transistor Q1, and the other end thereof is electrically A pin (such as a first pin) is connected to the control unit 24.

The second driving unit 226 includes a second transistor Q2, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8 and a second capacitor C2. The second transistor Q2 has a base, an emitter and a collector. The collector of the second transistor Q2 is electrically connected to one end of the seventh resistor R7, and the emitter of the second transistor Q2 is electrically connected. One end of the sixth resistor R6 is connected to the ground GND, the other end of the sixth resistor R6 (ie, the first end 2261 of the second driving unit 226) and one end of the second capacitor C2, the fifth One end of the resistor R5, the other end of the seventh resistor R7, and the third end 2223 of the second upper arm switch group 222 are electrically connected in common, and the other end of the fifth resistor R5 and the second capacitor C2 are electrically connected. The other end of the second resistor R8 is electrically connected to the other end of the second transistor Q2, and the other end of the eighth resistor R8 is electrically connected to the other end of the control unit 24 Foot (such as the second pin).

The first upper arm switch assembly 221 includes a first upper MOS transistor M1, and the second upper arm switch unit 222 includes a second upper MOS transistor M2. The first and second upper MOS transistors M1 and M2 are in this embodiment. Expressed as a P-type MOSFET, and the sources of the first and second upper MOS transistors M1, M2 (ie, the first ends 2211 of the first and second upper arm switch assemblies 221, 222) 2221) is connected in common with one end of the energy storage unit 21 (ie, the positive pole of the energy storage unit 21), and the other end of the energy storage unit 21 (ie, the negative pole of the energy storage unit 21) is electrically connected to the ground GND, wherein The energy storage unit 21 is electrically connected to a rectifying and stabilizing circuit (not shown). The rectifying and stabilizing circuit rectifies and receives the input power supply Vin (such as 12 volts), and outputs the operating voltage Vcc (such as 12). The volts are given to the energy storage unit 21, and the gates of the first and second upper MOS transistors M1, M2 (ie, the third ends 2213, 2223 of the first and second upper arm switch assemblies) are electrically connected to the corresponding ones. One end of the first and second capacitors C1, C2. The first lower arm switch module 223 includes a first lower MOS transistor M3, a ninth resistor R9, a tenth resistor R10 and a third capacitor C3. The first lower MOS transistor M3 is in the implementation. The example is represented as an N-type MOSFET (NMOS) transistor, and the drain of the first lower MOS transistor M3 (ie, the first end 2231 of the first lower arm switch component 223) is electrically connected to the first The drain of the upper MOS transistor M1 (ie, the second end 2212 of the first upper arm switch assembly) and one end of the motor coil L, the gate of the first lower MOS transistor M3 is electrically connected to the ninth and tenth resistors One end of the R9, R10 and one end of the third capacitor C3, the other end of the third capacitor C3 is electrically connected together with the other end of the tenth resistor and the ground GND, and the other end of the ninth resistor R9 That is, the third end 2233 of the first lower arm switch assembly 223 is connected to another pin (such as the third pin) corresponding to the control unit 24.

In addition, the second lower arm switch assembly 224 includes a second lower MOS transistor M4, an eleventh resistor R11, a twelfth resistor R12 and a fourth capacitor C4, and the second lower MOS device The crystal M4 is represented as an N-type metal oxide half field effect (NMOS) transistor in this embodiment, and the second lower MOS transistor M4 is germanium. The pole (ie, the first end 2241 of the second lower arm switch assembly 224) is electrically connected to the drain of the second upper MOS transistor M2 (ie, the second end 2222 of the second upper arm switch assembly 222) and the motor coil The other end of the second lower MOS transistor M4 is electrically connected to one end of the eleventh and twelfth resistors R11 and R12 and one end of the fourth capacitor C4, and the other end of the fourth capacitor C4 is The other end of the twelfth resistor and the ground GND are electrically connected together, and the other end of the eleventh resistor R11 (ie, the third end 2243 of the second lower arm switch assembly 224) is connected to the corresponding control unit. Another pin of 24 (such as the fourth pin), and the source of the first and second lower MOS transistors M3, M4 (ie, the second end 2242 of the second lower arm switch assembly 224) and a tenth One end of the three resistors R13 is electrically connected, and the other end of the thirteenth resistor R13 is electrically connected to the ground GND.

Therefore, when the fan is to be started, the motor driving circuit 22 can receive the input power source Vin, and control the first and second driving units 225 and 226 to drive the corresponding first and second respectively by the PWM signal outputted by the control unit 24. The switching operation of the MOS transistors M1 and M2 and the switching operation of the first and second MOS transistors M3 and M4 are performed to control the fan operation and the fan rotation speed, and the energy storage unit 21 receives the received operating voltage Vcc. The storage (ie, the energy storage unit 21 is charged); if the control unit 24 does not receive the operating voltage Vs and fails to operate when the fan is powered off, the four pin potentials of the PWM signal outputted from the control unit 24 are O. Volts, the first and second transistors Q1, Q2, the first and second lower MOS transistors M3, M4 of the first and second driving units 225, 226 are also non-conducting, at this time, the first and second MOS The gates of the transistors M1 and M2 are respectively pulled down to a low potential (ie, 0 volts) by being connected to the negative electrodes of the energy storage unit with respect to the third and sixth resistors R3 and R6, and simultaneously stored by the energy storage unit 21. Operating voltage Vcc (ie 12 volts) will be provided to the first The sources of the two upper MOS transistors M1 and M2 are such that the source voltages of the first and second upper MOS transistors M1 and M2 are discharged through the energy storage unit 21 to a high potential of 12 volts. The voltage between the source and the gate of the MOS transistors M1 and M2 is minus 12 volts (-12V), and the first The two upper MOS transistors M1 and M2 are turned on (that is, the sources of the first and second upper MOS transistors M1 and M2 are turned on), so that the first and second MOS transistors M1 and M2 and the motor coil L are both The short circuit of the terminal forms a closed loop, and the blade itself operates by the inertia of the fan after the power is turned off, so that an induced current is generated in the motor coil L on the closed circuit, and the induced current will cause the motor coil L to generate a reverse magnetic field to prevent the blade from running. So that the fan can quickly stop reaching the brake effect.

Therefore, the circuit structure design in which the resistor unit 25 and the other end of the first capacitor C1 are not connected in series with the operating voltage Vcc by the input power source Vin of the present invention and the other end of the first resistor R1, so that the circuit is designed 2 with a braking function, and the operating voltage Vcc is supplied to the first and second upper arm switch assemblies 221, 222 of the motor drive circuit 22 when the energy storage unit 21 is powered off, so that the first and second upper arm switches are turned on. The components 221, 222 and the motor coil L form a closed loop to achieve the effect of braking. In addition, the design of the circuit 2 of the present invention makes it possible to effectively improve the lower arm switch assembly of the conventional motor brake circuit, and requires additional electronic components to implement the brake, so that the present invention can effectively achieve cost-saving effects.

2‧‧‧Circuit motor power failure automatic brake circuit

21‧‧‧ Energy storage unit

22‧‧‧Motor drive circuit

221‧‧‧First upper arm switch assembly

222‧‧‧Second upper arm switch assembly

2211, 2221‧‧‧ first end

2212, 2222‧‧‧ second end

2213, 2223‧‧‧ third end

223‧‧‧First lower arm switch assembly

224‧‧‧Second lower arm switch assembly

2231, 2241‧‧‧ first end

2232, 2242‧‧‧ second end

2233, 2243‧‧‧ third end

225‧‧‧First drive unit

226‧‧‧Second drive unit

2251, 2261‧‧‧ first end

2252, 2262‧‧‧ second end

2253, 2263‧‧‧ third end

2254, 2264‧‧‧ fourth end

24‧‧‧Control unit

25‧‧‧Resistor unit

L‧‧‧Motor coil

Vin‧‧‧Input power supply

Vcc‧‧‧ operating voltage

Vs‧‧‧ working voltage

Claims (8)

A circuit for a fan motor to be powered off automatically includes: an energy storage unit that receives and stores an operating voltage; a motor drive circuit having a plurality of upper arm switch assemblies, a plurality of lower arm switch assemblies, a first drive unit, and a a second driving unit, the first end of the upper arm switch assembly is electrically connected to the energy storage unit and receives the operating voltage, and a second end thereof is opposite to a first end of the lower arm switch assembly and the motor The coils are electrically connected to each other, and a second end of the lower arm switch assembly is connected to a ground end, and a first end of the first and second drive units is electrically connected to a first arm of the upper arm switch assembly a third end; a control unit electrically connected to a third end of the lower arm switch and a second end of the first and second driving units; a resistor unit electrically connected to an input power source at one end thereof One end is electrically connected to a third end of the first and second driving units, and a fourth end of the first and second driving units is electrically connected to the ground end; and when the fan is powered off, the upper arm Switch assembly Receiving the energy storage unit to provide the operating voltage is turned on, the lower arm switching assembly such does not receive the operation voltage does not conduct, so that such upper arm switching brake assembly and a closed loop is formed with the motor coil. The circuit of the fan motor power-off automatic brake according to claim 1, wherein the upper arm switch assembly has a first upper arm switch assembly and a second upper arm switch assembly, and the first and second upper arm switch members The first end is electrically connected to the energy storage unit, and the second ends of the first and second upper arm switch assemblies are electrically connected to opposite ends of the motor coil respectively. The third ends of the first and second upper arm switch assemblies are electrically connected to the first ends of the first and second driving units, respectively. The circuit of the fan motor power-off automatic brake according to claim 2, wherein the lower arm switch assembly has a first lower arm switch assembly and a second lower arm switch assembly, the first and second lower arms The first ends of the switch assembly are electrically connected to opposite ends of the motor coil, and the second ends of the first and second lower arm switch assemblies are electrically connected to the ground end, respectively, the first and second lower arm switch assemblies The third ends are electrically connected to the control unit respectively. The circuit of the fan motor power-off automatic brake according to claim 3, wherein the resistor unit is a resistor, one end of the resistor unit is electrically connected to the input power source, and the other end of the resistor unit is opposite to the first The third ends of the first and second driving units are electrically connected. The circuit of the fan motor power-off automatic brake according to claim 1, wherein the control unit is a central processing unit or a microcontroller. The circuit of the fan motor power-off automatic brake according to the second aspect of the invention, wherein the first driving unit comprises a first transistor, a first resistor, a second resistor, a third resistor, a fourth resistor and a first capacitor, the first transistor has a base, an emitter and a collector, the collector is electrically connected to one end of the second resistor, and the emitter is electrically connected And a first end of the third resistor The third end is electrically connected to the other end, and the other end of the first resistor is connected to the other end of the resistor unit, and one end of the fourth resistor is electrically connected to the base, and the other One end is electrically connected to the control unit. The circuit of the fan motor power-off automatic brake according to the sixth aspect of the invention, wherein the second driving unit comprises a second transistor, a fifth resistor, a sixth resistor, a seventh resistor, An eighth resistor and a second capacitor, the second transistor has a base, an emitter and a collector, and the collector of the second transistor is electrically connected to one end of the seventh resistor, The emitter of the second transistor is electrically connected to one end of the sixth resistor and the ground, the other end of the sixth resistor and one end of the second capacitor, one end of the fifth resistor, and the seventh The other end of the resistor and the third end of the second upper arm switch group are electrically connected in common, and the other end of the fifth resistor and the second capacitor are connected to the other end of the resistor unit, the eighth resistor One end of the second transistor is electrically connected to the base of the second transistor, and the other end of the second electrode is electrically connected to the control unit. The circuit of the fan motor power-off automatic brake according to claim 4, wherein the resistor unit is a 0 ohm resistor.