CN1989680A - Brushless DC motor and electric device using the same - Google Patents

Abstract

A brushless DC motor comprising: a stator assembly having drive coils for multiple phases; a rotor assembly having permanent magnets; and a built-in printed wiring board (PWB), the printed The wiring board has a drive circuit for energizing the drive coil. The drive circuit includes: a MOSFET for supplying power to a drive coil; a gate driver for controlling the MOSFET; and a pre-driver for supplying a PWM signal to the gate pole drive. The PWB includes a power module formed by integrating a MOSFET and a gate driver with a molding resin. The power module includes a setting part for setting the electric strength of the MOSFET.

Description

Brushless DC motor and electrical devices using it

technical field

The present invention relates to a brushless DC motor having a drive circuit (or excitation circuit) incorporated therein, and an electric device using the motor.

Background technique

Small brushless DC motors with a shaft output ranging from 20 watts to 50 watts are used to drive blowers used in air conditioners and various home appliances. Generally, this motor includes a driver (or exciter) having various electronic components on its printed wiring board.

FIG. 13 shows a cross-sectional view of a conventional brushless DC motor 101 . The stator molding assembly 103 includes the following components:

Stator core 120, the stator core 120 is formed by laminating electromagnetic steel plates;

driving coils (or exciting coils) 121 for multiple phases and wound on the stator core 120; and

An unsaturated polyester resin that accommodates the stator core 120 and the drive coil 121 together in one unit.

The first end of the stator molding assembly 103 is covered with a metal bracket 104 . The second end of the stator molding assembly 103 and the central portion of the bracket 104 have bearing retainers.

The rotor assembly 119 includes the following components:

a rotor yoke 118 formed by laminating electromagnetic steel sheets;

The multi-pole permanent magnet 117, the multi-pole permanent magnet 117 is set to the outer wall of the rotor yoke 118, and faces the inner wall of the stator core 120, and there is a given distance between the multi-pole permanent magnet 117 and the inner wall of the stator core 120 gap;

shaft 105 which is press fit in the center of the yoke 118; and

A bearing 114 rotatably supports the shaft 105 .

A printed wiring board (PWB) 113 has a driving circuit for driving the coil 121 , and the printed wiring board 113 is rigidly mounted to the stator mold assembly 103 . An end of the coil 121 is connected to the PWB 113 through a pin 122 . Components such as metal-oxide-semiconductor field-effect transistor (MOSFET) array 110, pre-driver (or pre-driver) 112, and many other discrete components (not shown) are soldered to PWB 113 and used for sensing permanent magnet 117. A magnetic sensor 125 for a magnetic pole is also soldered to the PWB 113 . The insulating plate 115 is placed between the PWB 113 and the bracket 104 so that the PWB 113 is insulated from the bracket 104 .

FIG. 14 shows a plan view of a printed wiring board assembly (PWB Assy) 107 . Components such as MOSFET array 110 , pre-driver 112 , three gate drivers 111 , and many other discrete components 131 are mounted on PWB 113 . Lead assembly 102 is provided to PWB 113 for receiving input and providing output of PWB 113 . Discrete components 131 include resistors and capacitors.

The MOSFET array 110 is formed by unifying six MOSFETs into one array, and drives the coil 121 . Each of the MOSFETs has an avalanche resistance so that it is not easily damaged when a pulse-like voltage exceeding a withstand voltage such as a surge voltage of the MOSFET is applied. The use of MOSFET array 110 thus advantageously ensures reliability.

On the other hand, in order to increase the electrical strength of MOSFET so as to increase its reliability, it is necessary to strictly set various factors such as the rate of change of voltage between drain and source "dV/dt", the rate of change of drain current "dI /dt", turn-on delay time "td" (on), cut-off delay time "td" (off). To achieve this, discrete components such as resistors, capacitors, and diodes require at least 4-6 pieces at each gate, requiring from 4*6=24 to 6*6=36 pieces of discrete components. Auxiliary components other than these quantities would bring the total quantity to almost 100 pieces, thus hindering the miniaturization of the PWB.

As switching elements, MOSFETs are replaced with IGBTs so that the drive circuit is formed by a monolithic integrated circuit. This structure is disclosed in Unexamined Japanese Patent Publication No. H03-270677. Although this structure allows miniaturization of the PWB, improvement in reliability due to avalanche resistance peculiar to MOSFETs cannot be expected.

Contents of the invention

The brushless DC motor of the present invention comprises the following components:

a stator assembly having drive coils (excitation coils) for multiple phases;

a rotor assembly having permanent magnets; and

A printed wiring board (PWB) that houses the motor and has a drive circuit mounted thereon for driving (or energizing) the drive coil.

The drive circuit includes: a MOSFET, the MOSFET is used to supply power to the drive coil; a gate driver, the gate driver is used to control the MOSFET; and a pre-driver, the pre-driver is used for PWM (pulse width modulation) ) signal is supplied to the gate driver.

The PWB includes a power module formed by integrating a MOSFET and a gate driver with molded resin, and the power module is characterized by including a setting portion that sets an electrical voltage of the MOSFET. strength.

The structure discussed above allows to propose a reliable brushless DC motor which is compact, light in weight, and easy to wire and install. Therefore, the present invention can also provide an electric device using the brushless DC motor.

Description of drawings

Figure 1 shows the appearance of a brushless DC motor according to a first embodiment of the present invention;

Figure 2 shows a cross-sectional view of the motor shown in Figure 1;

Figure 3 shows a circuit diagram of the motor shown in Figure 1;

Figure 4 shows a cross-sectional view of the power module of the brushless DC motor shown in Figure 1;

Figure 5 shows a plan view of the printed wiring board assembly of the motor shown in Figure 1;

Figure 6 shows a circuit diagram detailing one phase of the motor shown in Figure 1;

FIG. 7 shows a timing diagram illustrating the relationship between the input signal and the output signal of the gate driver of the motor shown in FIG. 1;

FIG. 8 shows a timing diagram detailing an enlarged portion around time "t1" shown in FIG. 7;

Figure 9 shows a time diagram illustrating a relationship similar to that shown in Figure 7, however, the time diagram has a larger time interval between time "t2" and time "t3" than that shown in Figure 7 Shorter;

Figure 10 shows a timing diagram detailing the situation when the threshold voltage of the MOSFET is increased;

FIG. 11 shows the appearance of an electronic device according to a second embodiment of the present invention;

Figure 12 shows a circuit diagram of the electronic device shown in Figure 11;

Figure 13 shows a cross-sectional view of a conventional brushless DC motor; and

FIG. 14 shows a plan view of a printed wiring board assembly of the conventional brushless DC motor shown in FIG. 13 .

Detailed ways

Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

Fig. 1 shows the appearance of a brushless DC motor according to a first embodiment of the present invention. The spindle motor assembly 3 is covered with a cover-shaped bracket 4 , and a shaft 5 extends through the bracket 4 . The lead assembly 2 extends from the side (or lateral face) of the stator molding assembly 3 .

Fig. 2 shows a sectional view of the brushless DC motor according to the first embodiment. Stator molding assembly 3 includes the following components:

Stator core 20, the stator core 20 is formed by laminating electromagnetic steel sheets (or electromagnetic steel sheets);

drive coils 21 for multiple phases and wound on the stator core 20; and

An unsaturated polyester resin that encapsulates the stator core 20 and the drive coil 21 together in one unit.

The first end of the stator molding assembly 3 is covered with a metal bracket 4 . The second end of the stator molding assembly 3 and the center portion of the bracket 4 have bearing retainers.

The rotor assembly 19 includes the following components:

a rotor yoke 18 formed by laminating electromagnetic steel sheets;

Multi-pole permanent magnet 17, this multi-pole permanent magnet 17 is arranged on the outer wall of rotor yoke 18, and faces the inner wall of stator core body 20, and there is a given space between multi-pole permanent magnet 17 and the inner wall of stator core body 20 gap;

shaft 5 which is press fit in the center of the yoke 18; and

A bearing 14 rotatably supports the shaft 5 .

A printed wiring board (PWB) 13 has a drive circuit for driving the coil 21 , and the printed wiring board 13 is rigidly mounted to the stator mold assembly 3 . An end of the coil 21 is connected to the PWB 13 through a pin 22 . Components such as MOSFET array 10, pre-driver (or pre-driver) 12 and many other discrete components (not shown) are soldered to PWB 13, and magnetic sensor 25 for sensing the pole of permanent magnet 17 is also soldered to on PWB13. The insulating plate 15 is placed between the PWB 13 and the bracket 4 so that the PWB 13 is insulated from the bracket 4 .

The power module 10 installed on the PWB 13 dissipates heat to the bracket 4 through the high thermal conductivity resin 16 , and the high thermal conductivity resin 16 adopts silicon-based resin with excellent thermal conductivity. Since silicone-based resin is elastic, it can absorb dispersion of the space between the power module 10 and the bracket 4 .

Fig. 3 shows a circuit diagram of the brushless DC motor according to the first embodiment. The drive circuit 6 receives the following voltages: a high DC voltage Vdc supplied from a high voltage DC power supply 9 , a control voltage Vcc from a control power supply 23 , and a control signal voltage Vsp of a speed control signal 24 . The drive circuit 6 outputs a motor rotation signal FG to be used for speed control.

The drive circuit 6 includes the following components (or elements):

Three magnetic sensors 25, the three magnetic sensors 25 are used to sense the magnetic pole position of the rotor;

A pre-driver 12, the pre-driver 12 is used to receive signals from the magnetic sensor 25 and generate a PWM signal;

Three gate drivers 11 for receiving signals from the pre-driver 12 and generating control signals for the MOSFET 8; and

Six MOSFETs 8 are connected in a three-phase bridge.

The magnetic sensor 25 usually adopts a Hall element or a Hall integrated circuit (IC). The output current is sensed by current sense resistor 26 and fed back to pre-driver 12 .

Three gate drivers 11 and six MOSFETs 8 are unified (or integrated) into one unit, thereby forming a power module 10. FIG. 4 shows a cross-sectional view of the power module 10 . The gate driver 11 and MOSFET 8 are rigidly soldered to the frame 28, and bond wires 30 connect the gate driver 11 to the MOSFET 8, and lead electrodes 27 to these two components. All these elements are molded in epoxy 29 as a unit.

FIG. 5 shows a plan view of a printed wiring board (PWB) assembly 7 . The power module 10 , the pre-driver 12 and the discrete components 31 are mounted on the PWB 13 , which also includes a lead assembly 2 for receiving inputs and providing outputs of the PWB 13 . The discrete components 31 include resistors, capacitors, and the like.

FIG. 6 shows a part of the circuit diagram of the brushless DC motor according to the first embodiment, and this diagram details one phase of the entire circuit diagram shown in FIG. 3 . MOSFET 8 shown in Figure 3 is actually formed by MOSFET Q1 in series with MOSFET Q2 and receives a high DC voltage Vdc. MOSFET Q1 includes freewheeling diode D1 and gate capacitor C1 as passive components. MOSFET Q2 also includes freewheeling diode D2 and gate capacitor C2 as passive components.

The gate driver 11 comprises hysteresis comparators HS1, HS2, a level shifting circuit LS1, resistors R1, R2, R3, R4, and output electronic switches SW1, SW2, SW3, SW4. The gate driver 11 receives the PWM signal generated in the pre-driver 12 as input signals HIN, LIN, and supplies output signals HO, LO to respective gates of MOSFET Q1 and MOSFET Q2.

Fig. 7 shows a time (timing) diagram illustrating the relationship between the input signal HIN, LIN and the output signal HO, LO. During the period "t"<t1, both input signals HIN and LIN stay at low level, so that the output electronic switches SW1, SW3 on the upper side are turned off and the switches SW2, SW4 on the lower side are turned on. Therefore, the output signals HO and LO are kept at low level, and MOSFET Q1 and MOSFET Q2 stay in the cut-off state.

Next, when "t"=t1, the input signal HIN rises to a high level, and the input signal LIN remains at a low level. The switch SW1 is thus turned on, and the switch SW2 is turned off. The output signal HO rises to a high level to turn on MOSFET Q1. MOSFET Q2 remains off. At this time, the charge stored in the boot capacitor C3 is supplied to the gate of the MOSFET Q1 through the resistor R1, and the output signal HO rises with a certain time constant. MOSFET Q1 stays in the off state until the output signal HO reaches the threshold voltage Vth of MOSFET Q1, and when "t" = t10, i.e. when the signal HO reaches the voltage Vth, MOSFET Q1 turns on, which causes a high DC supply to the driving coil 21 Voltage Vdc.

Next, when "t"=t2, the input signal HIN falls to a low level, and the output signal LIN remains at a low level. Switch SW1 is thereby turned off, and switch SW2 is turned on, and output signal HO falls with a time constant determined by resistor R2 and gate capacitor C1 of MOSFET Q1. MOSFET Q1 stays in the conduction (ON) state until the output signal HO becomes lower than the threshold voltage Vth of MOSFET Q1, and when the output signal HO becomes lower than the threshold voltage, that is, when "t" = t20, MOSFET Q1 becomes Cut-off (OFF) state.

When "t"=t3, the input signal HIN remains at a low level, and the input signal LIN rises to a high level, so that the switch SW3 is turned on, and the switch SW4 is turned off. The output signal LO rises with a time constant determined by capacitor C2 and resistor 3 . MOSFET Q2 stays in the off state until the output signal LO reaches the threshold voltage Vth of MOSFET Q2, and when "t" = t30, that is, when the signal LO reaches the voltage Vth, MOSFET Q2 is turned on.

When "t"=t4, the input signal HIN remains at a low level, and the input signal LIN falls to a low level. The switch SW3 is thereby turned off, and the switch SW4 is turned on. Output signal LO falls with a time constant determined by gate capacitor C2 of MOSFET Q2, and resistor 4. MOSFET Q2 stays in the on state until the output signal LO becomes lower than the threshold voltage Vth of MOSFET Q2, and when "t" = t40, that is, when the signal LO becomes lower than the voltage Vth, MOSFET Q2 is turned off (i.e., off open).

Then, when "t" = t5, the state becomes the same state as occurred when "t" = t2, and the sequence of states discussed above is repeated.

FIG. 8 magnifies a part of t1 shown in FIG. 7 and additionally shows changes in the terminal voltage VU of the driving coil. When "t" = t1, when the input signal HIN changes from low level to high level, the transmission (or transfer) time of hysteresis comparator HS1, level shifting circuit LS1 and output electronic switch SW1 (omitted in Fig. 7 After this transmission time), the output signal HO starts to rise at "t" = t11.

The output signal HO then reaches the threshold voltage Vth, and the MOSFET Q1 is turned on; however, in practice, the signal HO hardly changes at a voltage of about the threshold voltage Vth during the transition period when the MOSFET Q1 changes from the off state to the on state . Because MOSFET Q1's state transition from off to on changes the voltage between its drain and source, Q1's gate capacitor C1 becomes significantly larger (mirror effect). In more detail, when "t"=t12, the output signal HO reaches the threshold voltage Vth, and the MOSFET Q1 starts to turn on, and the terminal voltage of the driving coil starts to rise. During the rise of voltage VU, signal HO is almost unchanged due to the image effect. When "t"=t13, the voltage VU reaches about the high DC voltage Vdc, and the signal HO starts to rise further because the mirror effect no longer works. At this time, the rate of change "dV/dt" of the voltage VU becomes larger in a shorter time between t12 and t13.

The rate of change "dV/dt" of voltage VU is determined by the time constant based on resistor R1 and the feedback capacitance between the gate and drain of MOSFET Q1, so the rate of change "dV/dt" can be adjusted by adjusting resistor R1 and feedback capacitance Capacitance is set. Usually, the rate of change "dV/dt" is set by means of the value of resistor R1 which can be easily adjusted. For example, in the case of a home appliance equipped with a motor, the resistor R1 is adjusted so that the rate of change "dV/dt" becomes about 2 kV/μsec.

The previous description mentioned the case where the state of MOSFET Q1 transitions from off to on; however, when the state of MOSFET Q1 transitions from on to off, the rate of change of the terminal voltage VU of the driving coil can be set "dV/ dt", the rate of change "dV/dt" in this case can be set by adjusting resistor R2.

Similar settings can be made for MOSFET Q2 as discussed above, i.e. the "dV/dt" at which Q2 transitions from off to on can be set by adjusting resistor R3 and the "dV/dt" at which Q2 transitions from on to off dV/dt” can be set by adjusting resistor R4.

As discussed above, the resistors R1, R2, R3, R4 serve as a setting section for setting the rate of change of the voltage between the drain and the source of MOSFET Q1 and MOSFET Q2. Next, the current "dI/dt" will be described later.

In Fig. 8, while the voltage VU is changing, the rate of change of the drain current "dI/dt" at the state transition of MOSFET Q1 from off to on can be observed. During a change in voltage VU, signal HO is almost constant around the threshold voltage Vth of MOSFET Q1 because the mirror effect acts as previously discussed; however, it actually varies slightly. The slight change in the rate of change around the threshold voltage Vth and the transconductance of MOSFET Q1 determines the rate of change of the drain current "dI/dt" of MOSFET Q1. A slight change in the rate of change of signal HO around threshold voltage Vth can be determined by resistor R1 or capacitor C1 between the gate and source of MOSFET Q1. In other words, the adjustment of resistor R1 or the mutual conductance of MOSFET Q1 can set the rate of change of the drain current "dI/dt" of MOSFET Q1. However, as resistor R1 is used to set the rate of change of voltage "dV/dt", capacitor C1 or transconductance is used to set the rate of change of drain current "dI/dt".

The previous description mentioned the case where the state of MOSFET Q1 transitions from off to on; however, when the state of MOSFET Q1 transitions from on to off, the rate of change of the drain current "dI/dt" can be set, That is, the rate of change "dV/dt" in this case can be set by adjusting the capacitor C1 or the mutual conductance.

A similar setting can be made for MOSFET Q2 as discussed above, i.e. the "dI/dt" of Q2 can be set by adjusting the capacitor C2 and the transconductance of MOSFET Q2.

As discussed above, the capacitors C1, C2, or the transconductance of MOSFET Q1 or MOSFET Q2, can be used as a setting section, which is used to set the rate of change of the drain current of MOSFET Q1 or MOSFET Q2 "dI/dt ".

Figure 9 illustrates how the motor operates when t2 is close to t3 in the circuit shown in Figure 6 . More specifically, the input signal HIN transitions from high level to low level at "t" = t2, and the input signal LIN transitions from low level to high level at "t" = t3. Figure 9 thus shows the operation when t2 is close to t3, i.e. when the output voltage LO starts to rise, the output signal HO starts to fall at "t" = t2 and is still above the threshold at "t" = t3 Voltage Vth. In this case, if MOSFET Q2 is turned on before MOSFET Q1 is turned off, pass-through current flows from Q1 to Q2, damaging the MOSFETs.

In order to prevent the flow of such passing current, the relationship between the resistors R1 and R2 used as the setting section should be adjusted in advance to R1>>R2 so that "t"=t20 can occur before "t"=t30.

The time interval between "t" = t2 (at this time the input signal HIN changes from high level to low level) and "t" = t3 (at this time the input signal LIN changes from low level to high level) is usually called is the dead time (or dead time). This dead time is prepared to be sufficiently long with respect to the delay time generally occurring in the gate driver 11, MOSFET 8 and nearby components. However, since the drive coil is not excited when the dead time lasts for a long time, motors used in fans of home appliances (whose shaft output power ranges from 20 watts to 50 watts) sometimes cause noise and Vibration trouble. This dead time should therefore be minimized, so that the values of the resistors R1 , R2 and the capacitance of the gate capacitor should be carefully studied in advance.

Figure 10 illustrates the operation when the threshold voltage Vth of MOSFET Q1 itself is increased from Vth1 to Vth2. In this case, the turn-on to turn-off delay time of MOSFET Q1 becomes shorter, and the turn-on delay time of MOSFET Q2 becomes longer. Said preparations allow to propose a brushless DC motor even when the dead time is extremely short in the circuit diagram shown in FIG. 6, namely when "t"=t2 (at "t"=t2 When the input signal HIN changes from high level to low level) close to "t" = t3 (input signal LIN changes from low level to high level at "t" = t3), there is no need to worry about MOSFET Q1 cut-off MOSFET Q2 was turned on before.

As discussed above, the brushless DC motor of the present invention includes a power module formed by integrating at least a MOSFET and a gate driver into one unit through molding resin; and a driving circuit including the power module. A setting section built into one of the power module, gate driver, or MOSFET can set the electrical strength of the MOSFET. The foregoing structure allows obtaining a reliable brushless DC motor characterized by compactness, light weight, and ease of wiring and installation.

Example 2

Next, an electric device having a brushless DC motor according to the present invention will be described with reference to FIGS. 11 and 12. FIG. Fig. 11 shows the structure of an electric device (outdoor unit of an air conditioner) according to a second embodiment of the present invention.

In FIG. 11 , an outdoor unit 51 according to a second embodiment of the present invention is divided into a compressor chamber 56 and a heat exchanger chamber 59 by a partition plate 54 standing on a bottom plate 52 . Compressor 55 is placed within chamber 56 . Heat exchanger 57 and blower motor 58 are placed in chamber 59 . A box 60 carrying electronic components is placed on the insulating plate 54 .

The fan motor 58 is formed by the brushless DC motor 1 explained in Embodiment 1, and the blower mounted on the motor shaft, and the fan motor 58 is supplied with a high DC voltage Vdc and a control voltage from the power supply 53 accommodated in the case 60 Vcc. Rotation of the fan motor 58 causes the blower to rotate, which generates wind for cooling the heat exchanger chamber 59 . As discussed in Embodiment 1, since the brushless DC motor includes a drive circuit incorporated therein, the motor 1 is compact in size and easy to wire and install, so that the motor 1 completes and reduces costs for electrical devices such as air conditioners it works.

Fig. 12 shows a simple circuit diagram of an electrical device (outdoor unit of an air conditioner) according to a second embodiment of the present invention. In FIG. 12, a commercial power supply 62 supplies power to a power supply 53 including a rectifier, a smoothing capacitor, a switching power supply, and other components. The power supply 53 outputs a high DC voltage Vdc and a control voltage Vcc to the fan motor 58 . The high DC voltage Vdc is also supplied to the inverter 61 for driving the compressor 55 .

The switching on and off of the inverter 61 causes a surge current (not shown) to be superimposed on the high DC voltage Vdc, so that the voltage may exceed the withstand voltage of the MOSFET incorporated in the fan motor 58 . However, the MOSFET itself has an avalanche resistance large enough to withstand overvoltage for a short period of time so that the MOSFET does not break down. A reliable fan motor can thus be achieved.

In this second embodiment, an outdoor unit of an air conditioner is taken as an example of an electric device; however, the present invention can be applied to a blower used in an indoor unit of an air conditioner as well as the indoor unit itself, and has advantages similar to those of the outdoor unit. advantage.

Industrial Applicability

The brushless DC motor of the present invention includes a stator assembly including driving coils for multiple phases; a rotor assembly having permanent magnets; and a built-in printed wiring board (PWB) having A drive circuit for energizing the drive coil is mounted thereon. The drive circuit includes a MOSFET that supplies power to the drive coil, a gate driver that controls the MOSFET, and a pre-driver that supplies a PWM signal to the gate driver. The PWB has a power module mounted thereon, and the power module is formed by integrating at least a MOSFET and a gate driver with molding resin. The power module includes a setting part therein or in the gate driver or in the MOSFET for setting the electric strength of the MOSFET. The invention further includes an electrical device having the brushless DC motor. The structure discussed above makes the motor reliable, compact in size, light in weight, and makes the motor easy to install and wire. This structure can also provide an electrical device using the brushless DC motor.

Claims (16)

1. A brushless DC motor, comprising: a stator assembly having drive coils for multiple phases; a rotor assembly having permanent magnets; and a printed wiring board (PWB) built into the motor and having a drive circuit for driving the drive coil, Wherein the drive circuit includes: (a) a MOSFET for powering the drive coil; (b) a gate driver for controlling the MOSFET; and (c) a pre-driver for supplying the PWM signal to the gate driver, Wherein the PWB includes a power module formed by integrating a MOSFET and a gate driver with molding resin, and the power module includes a device in one of the power module, the gate driver, and the MOSFET. The setting part is used for setting the electric strength of the MOSFET. 2. The brushless DC motor according to claim 1, wherein the PWB further includes the pre-driver. 3. The brushless DC motor according to claim 1, wherein the setting portion includes at least one of a resistor and a capacitor. 4. The brushless DC motor according to claim 1, wherein the drive circuit further includes a magnetic sensor for sensing a magnetic pole position of the permanent magnet, and the magnetic sensor is provided to the PWB . 5. The brushless DC motor according to claim 1, further comprising a metal bracket, wherein the power module dissipates heat to the bracket through a high thermal conductivity resin. 6. The brushless DC motor according to claim 5, wherein the high thermal conductivity resin is a silicon-based resin. 7. The brushless DC motor according to claim 1, wherein the power module is formed by connecting a MOSFET to a gate driver with a bonding wire and then sealing it with epoxy. 8. The brushless DC motor according to claim 1, wherein the setting section sets a rate of change of a voltage between a drain and a source of the MOSFET to a predetermined value. 9. The brushless DC motor according to claim 1, wherein the setting section sets a drain current change rate of the MOSFET to a predetermined value. 10. The brushless DC motor according to claim 1, wherein the setting section sets the on/off delay time of the MOSFET to a predetermined value. 11. The brushless DC motor according to claim 10, wherein the setting section further sets a threshold voltage of a gate of the MOSFET to a predetermined value. 12. The brushless DC motor according to claim 1, wherein said MOSFET has a given avalanche resistance. 13. An electrical device comprising the brushless DC motor according to claim 1. 14. The electric device according to claim 13, the electric device being an air conditioner, and the brushless DC motor being a fan motor. 15. The electrical device according to claim 13, further comprising a power source and another device other than a brushless DC motor, wherein two of said motor and said other device are connected to the power source. 16. The electric device according to claim 15, wherein the electric device is an outdoor unit of an air conditioner, the brushless DC motor is a fan motor, and the other device is a compressor.

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