JP2685046B2 - Brushless motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor.
The drive circuit of the three-phase brushless motor
You. One of conventional drive systems for brushless motors
The switching transistor is used to turn off the power.
A switching method that performs switching (phase switching) is known
I have. This switching method has a sharp
Depending on the current change, especially the rising of the current, the stator and
Vibrations of the rotor and rotor occur at high frequencies, which
Large acoustic noise is generated. In order to prevent the generation of this acoustic noise,
Conventionally, as shown in FIG. 11, one end of each is commonly connected.
The other ends of the stator coils L1, L2, L3 connected to
Capacitor C1, which has a relatively large capacity such as a capacitor
Current waveform by connecting in common via C2 and C3
I was trying to lick it. [0004] As in the prior art, the
The method using the sensors C1, C2, C3 is the number of rotations of the motor.
Is not effective at low speed, and the motor speed is high
At times, a phase delay occurs in the energizing current, and reactive current flows,
There is a drawback that the efficiency of the motor decreases. As another drive system of the brushless motor,
A linear drive method that uses a sinusoidal current is known.
Have been. This linear drive system produces acoustic noise.
Although it does not occur, the motor efficiency is significantly better than the switching method.
It drops significantly. Therefore, an object of the present invention is to provide switching
Motor efficiency equivalent to drive system, phase switching
Of a brushless motor with reduced acoustic noise due to
It is to provide a circuit. Another object of the present invention is to use a conventional motor machine.
No need to change the mechanical structure, only drive circuit
Can be realized by changing the brushless motor drive
To provide a path. SUMMARY OF THE INVENTION The present invention is directed to a rotor mug.
Magnet from the net, the stator coil, and the rotor magnet
For position detection that generates a detection signal with a waveform according to the change in the bundle
For a three-phase brushless motor with three Hall elements
In each of the three Hall elements,
First, second and third of three phases with a phase difference of 120 °
Class that clamps the level of the detection signal (A, B, C) of
Of the clamp circuit and the clamped first and second detection signals.
By synthesizing the waveforms (a, b), energization of the first phase
Clamped second and third detection signals forming a waveform
By combining the waveforms (b, c) of
Clamped first and third detection signals forming a radio wave shape
By combining the waveforms (a, c) of the No.
An energization waveform generating circuit for forming an energization waveform, a first phase, a second phase
Phase and third phase energization waveforms are amplified respectively and stator coil
And an amplifier circuit to supply the
The mutual zero crossing points of the waveform are 120 ° apart in electrical angle
And the zero crossing of the second-phase and third-phase energization waveforms of each other
The points have a deviation of 120 ° in electrical angle, the first phase, the second phase,
Each of the third-phase energization waveforms has its maximum level,
It at the minimum level, its mid-level including the zero-cross point
Each has a flat part, and the flat part of the maximum level and the maximum level.
Compared to a small level flat part, the length of the flat part in the middle part is larger.
The inclination of the detection signal is clamped between the flat parts
The first phase, the second phase, and the
The energization waveform of the third phase is different from that of the other phase at each slope.
Bra that is characterized by crossing the slope of the energization waveform of
It is a series motor. Wave of output signals (A, B, C) of the Hall element
The shape is a waveform according to the change in magnetic flux from the rotor magnet.
Become. The distance between the rotor magnet and the Hall element,
Position or size of the non-magnetized part of the trochanter magnet
Due to the above, the waveform of the output signal of the Hall element is almost trapezoidal.
It becomes wavy. The output signal of this Hall element was clamped
By combining the waveforms (a, b, c)
By extracting the waveform of the edge of the child, the energization signal
The edge portion is formed. In addition, the zero cross point of the energization waveform
The flat part of the middle level including the flat part of the maximum level
And the flat part at the minimum level are sufficiently small. Follow
The edge part of the energization signal is
Since it does not become steep, prevent the generation of acoustic noise.
Can be. Also, using the output waveform of the Hall element
Causes a change in the phase of the drive signal even if the rotation speed changes.
In addition, a trapezoidal wavy drive with an intermediate level flat part
Since it is a dynamic signal, the efficiency of the motor does not decrease. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.
explain. The description of this example should follow the order below.
Is done. a. Waveform shaping of output signal of Hall element b. Energization waveform generation circuit c. Generation of switching pulses d. Energization waveform generation operation e. Other Examples f. Modifications a. Waveform shaping of output signal of Hall element FIG. 1 shows a waveform shaping circuit of output signal of Hall element,
1a, 1b, 1c are magnets from the rotor magnet.
Figure 3 shows a Hall element that produces an output voltage proportional to the bundle. E
The power from the power supply terminal 2 is applied to the rule elements 1a, 1b, 1c.
The drive current formed by the voltage Vs and the resistor 3 is common
Supplied. In this example, the voltage Vs is applied to the stator coil.
It is equal to the voltage supplied. Output of each of the Hall elements 1a, 1b, 1c
The signals are operational amplifiers 4a, 5a, 4b, 5b, 4c, 5c.
Is amplified by By the operational amplifiers 4a, 4b, 4c
The differential signal is converted to a single-ended signal
The signals are inverted by the operational amplifiers 5a, 5b and 5c.
The detection signal A is obtained from the operational amplifier 4a, and the operational amplifier 5
The detection signal A * is obtained from a. * Indicates inversion, and
The output signals A and A * are signals with opposite phases. In the drawings,
It is shown by adding-on the letters of the signal. Operational amplifier 4b and
The detection signals B and C are respectively obtained from 4c, and the operational amplifier 5
Detection signals B and C from b and 5c, which are in opposite phase to the detection signals B and C
And C * are obtained respectively. FIG. 2 shows the detection signals A, B and C, respectively.
You. The solid line waveform is the detection signal A, and the one-dot chain line waveform is
The detection signal B, and the broken line waveform is the detection signal C. This
These detection signals are trapezoidal waves with a center level of Vs / 2.
Signal with a phase difference of 120 ° in electrical angle.
is there. In addition, the slope waveform of the edge part of these detection signals
Is the size of the non-magnetized area of the rotor magnet,
Waveform corresponding to the gap between magnet and hall element
Becomes The detection signal A is the diode clamp circuit 6a.
And the detection signal A * is supplied to the diode clamp.
Is supplied to the drive circuit 7a. Similarly, the detection signals B, B *,
C and C * are diode clamp circuits 6b and 7b,
It is supplied to 6c and 7c. These diode clamps
The circuits 6a, 6b, 6c use the maximum level of the detection signal as a terminal.
Specify the clamp voltage from 8 and turn on the diode clamp.
The paths 7a, 7b and 7c show the minimum level of the detection signal at the terminal 9
Specify the clamp voltage from. The terminal 8 has (3/4
・ Vs-Vf) (Vf is the forward voltage of the diode.
A clamp voltage of (voltage drop) is supplied, and (1
A clamp voltage of / 4 · Vs + Vf) is supplied. this
Output signals of each of the clamp circuits 6a, 7a, ... 7c
Are operational amplifiers 10a, 11a as buffer amplifiers,
It is supplied to 10b, 11b, 10c, 11c. Therefore, the output of the operational amplifier 10a is
In 2B, as shown by the solid line, Vs / 2 is the center level.
The maximum value is (3/4 · Vs) and the minimum value is (1/4
A Vs) trapezoidal detection signal a is generated. Computational amplification
The output of each of the instruments 10b and 10c has a similar central level.
Trapezoidal detection signal b having maximum, minimum and maximum values and
c occurs. Detection signal a of opposite phase to detection signals a, b, c
*, B *, c * are the operational amplifiers 11a, 11b, 11c
It is output from each. These detection signals a, b, c and a *, b
An energization waveform of the stator coil is generated from * and c *. Ma
In addition, the switch from the detection signals A, A *, B, B *, C, C *
A ching pulse is formed. B. Energization Waveform Generation Circuit FIG. 3 shows an energization waveform generation circuit in this embodiment.
You. In FIG. 3, L1, L2 and L3 are stator coils
Are shown respectively. This one embodiment has a three-phase bidirectional energization configuration.
So, one end of each of the stator coils L1, L2, L3
The other ends of the output terminals 30a, 30 are connected to each other.
b, 30c. These three stator coils
Circuits for generating the respective energization waveforms of L1, L2, L3
Three sets of road structures are provided. First the stator coil L1
The circuit configuration for generating the energization waveform of
You. The detection signal a of the hall element 1a and the
Of the inverted signal b * of the detection signal b of the scroll element 1b
Is the maximum value detection circuit 12a consisting of a diode and a resistor.
Supplied. The signal a and the signal from the maximum value detection circuit 12a
The higher level signal is output with respect to b *
You. The output signal of this maximum value detection circuit 12a is for buffer
And calculation for diode forward voltage (Vf) cancellation
It is supplied to the amplifier 14a. A signal obtained by inverting the detection signal a and the detection signal b.
Minimum value detection of each signal b * consisting of diode and resistor
It is supplied to the circuit 13a. From the minimum value detection circuit 13a
Signal of lower level with respect to signal a and signal b *
Is output. The output signal of this minimum value detection circuit 13a is
Performance for buffer and diode forward voltage cancellation
It is supplied to the operational amplifier 15a. The output signal of the operational amplifier 14a is an operational amplifier.
16a and the output signal of the operational amplifier 15a.
Signal is supplied to the operational amplifier 17a. Operational amplifier 16a
And 17a are inverting amplifiers for level shift. Performance
The input signal of the operational amplifier 16a is directly connected to Vs / 4 from the terminal 18.
Current voltage is added to the input signal of the operational amplifier 17a
The DC voltage of (3/4) Vs is added from 19. Calculation
The output signal of the amplifier 16a is supplied to the analog switch 20a.
Is supplied, and the output signal of the operational amplifier 17a is switched to the analog switch.
Is supplied to the switch 21a. The output signal of the analog switch 20a is
Analog via operational amplifier 22a
It is supplied to the switch 24a. This analog switch 2
An npn-type transistor in which the output signal of 4a constitutes an output stage
Is supplied to the base of the switch 26a. Analog switch
The output signal of the switch 21a is the operational amplifier 23a and the analog switch.
Output stage pnp transistor 2 via switch 25a
It is supplied to the base of 8a. Analog switch 20a and
Switching pulse from the terminal 31
Is turned on when is at the high level, the analog switch 21a and
And 25a are switching pulses from the terminal 32.
Turns on when is at high level. The emitter of the transistor 26a is an npn type
Connected to the base of the transistor 27a,
The emitter of 28a is the base of the pnp transistor 29a.
Connected to The collector of the transistor 27a is the power supply
It is connected to the power supply terminal of the voltage Vs and is connected to the transistor 29a.
The collector is grounded. Emitter of transistor 27a
And the emitters of the transistors 29a are connected to each other,
It is derived as the output terminal 30a. This output terminal 30a
Is connected to the input terminals of the operational amplifiers 22a and 23a.
A negative feedback path is provided. Therefore, the output terminal 30a
Includes the transistor base-emitter voltage drop.
First, equal to the input voltage of the operational amplifiers 22a and 23a
Output voltage is generated. Output voltage generated at the above-mentioned output terminal 30a
A circuit configuration similar to that for generating
It is provided in association with each of 30b and 30c. Output voltage taken to the output terminal 30b
Are formed from the signals b and c *. Also, output terminal
The output voltage output to 30c is signal c or signal a *
Formed from Each time to form these output voltages
References to the road part with the respective symbols b and c added
A number is attached and the explanation is omitted. However, 3
3 is a switch for controlling the analog switches 20b and 24b.
It shows the input terminal of the itching pulse, and 34 is an analog
A switching pulse for controlling the switches 21b and 25b
35 indicates an analog switch 20c.
And the input terminal of the switching pulse for controlling 24c
Shown at 36 is the control of the analog switches 21c and 25c.
The input terminal of the control pulse is shown. C. Generation of switching pulse Switching supplied to each of the terminals 31 to 36 described above
The pulse is generated by the switching pulse generating circuit shown in FIG.
Formed. In FIG. 4, 41, 42, 43, 4
4,45,46,51,52,53,54,55,56
Indicate the level comparators, respectively. Input of one of the level comparators 41 to 46
The reference voltage (3/4) Vs is supplied to the input terminal. these
Level comparators 41 to 46 are connected to the other input terminals.
Input voltage level supplied is lower than (3/4) VS
Sometimes it produces a high level output, and in the opposite
Generates bell output. Level comparators 51-56
The reference voltage (1/4) Vs is supplied to the other input terminal of
You. These level comparators 51 to 56 are
The level of the input voltage supplied to the input terminal is (1/4) V
Generates high level output when higher than s, and vice versa
The low level output is generated. Husband of level comparators 41, 42, 43
The other input terminal and the level comparators 51, 52,
The Hall elements 1a, 1 are connected to one of the input terminals of 53, respectively.
Detection signals A, B, C from b, 1c are supplied. Ma
The other of the level comparators 44, 45, 46
Input terminal and husband of level comparators 54, 55, 56
The detection signals A *, B *, which are inverted to the respective one input terminals,
C * is supplied. The level comparator 5 is connected to the AND gate 61.
The output of 1 and the output of the level comparator 55 are supplied.
You. Of the other AND gates 62, 63, 64, 65, 66
The output of the level comparator is as follows, respectively.
Supplied. AND gate 62: of level comparators 41 and 45
Output AND gate 63: of level comparators 52 and 56
Output AND gate 64: of level comparators 42 and 46
Output AND gate 65: of level comparators 53 and 54
Output AND gate 66: of level comparators 43 and 44
Outputs AND gates 61, 62, 63, 64, 6
Terminals where switching pulses are generated from 5 and 66 respectively
31, 32, 33, 34, 35, 36 are derived. Regarding the above switching pulse generation circuit
The switching pulse output to terminals 31 and 32.
The generation of the scan will be described with reference to FIG. Shown in FIG.
Signal A (shown by the solid line) and signal B * (the one-dot chain line)
, And reference voltages (1/4) Vs and (3 /
4) Depending on the level relationship with Vs, a level comparator
The output of 41 is high level at (A <(3/4) Vs)
The output of the level comparator 45 becomes (B * <(3
/ 4) Vs) becomes high level, level comparator
The output of 51 is high level at (A> (1/4) Vs)
The output of the level comparator 55 becomes (B * >> (1
It becomes a high level at / 4) Vs). Therefore, the AND game
Switch formed by the terminal 61 and generated at the terminal 31.
Formed by an AND gate 62 and a terminal 3
The switching pulses generated in 2 are shown in FIG. 5, respectively.
It becomes These switching pulses are high
Analog switch 20a, 24a and analog switch
The switches 21a and 25a are turned on. D. Energization Waveform Generation Operation Referring to FIG. 6, the output voltage immediately generated at the output terminal 30a
The generation of the energization waveform will be described. Signal a and signal b
* Is supplied to the maximum value detection circuit 12a, and both signals can be used.
The signal shown in FIG. 6A having a higher level is an operational amplifier.
It occurs at the output of 14a. Also, the signals a and b * are
It is supplied to the minimum value detection circuit 13a, and the signals of both are smaller.
The signal shown in FIG. 6B having a certain level is the operational amplifier 15
occurs at the output of a. Output signal of operational amplifier 14a (Fig.
6A) has a maximum level of (1/2) Vs as a central level.
Signal with (3/4) Vs and minimum value of (1/4) Vs
is there. The output signal of the operational amplifier 15a (FIG. 6B) is the same.
Signal of the level. The output of the operational amplifier 16a is
The signal shown in FIG. 6A is the level of (1/4) Vs, the rising direction
6C by being shifted and inverted.
As shown in, the signal at the level of [(1/2) Vs-Vs] is
Issue occurs. The output of the operational amplifier 17a is shown in FIG. 6B.
The signal shown shifts to the level of (1/4) Vs, decreasing
As shown in FIG.
, A signal of the level of [0 to (1/2) Vs] is generated.
You. Switching from terminal 31 as shown in FIG. 6E
Depending on the pulse, the signal shown in FIG.
Section is the output of analog switch 20a, 24a
Will be issued. The switching pattern shown in FIG.
The low-level section of the signal shown in FIG.
Are output to the outputs of the analog switches 21a and 25a.
You. Therefore, the output terminal 30a is an analog switch.
Therefore, in Fig. 6G, which is a combination of two gated signal waveforms,
The indicated output voltage is generated. An output formed in the same manner as the output voltage described above.
The output voltage is taken out to each of the output terminals 30b and 30c.
You. In FIG. 6H, the solid line waveform is output to the output terminal 30a.
The generated output voltage is shown, and the broken line waveform appears at the output terminal 30b.
Indicates the generated output voltage and the waveform of the one-dot chain line is output terminal 3
The output voltage generated at 0c is shown. This is shown in Figure 6H
So that the stator coils L1, L2 and L3 each have 120 °
Energization is performed sequentially for each slightly larger energization section. As shown in FIG. 3, the stator coil L1 and
The current flowing through L2 is represented by I1, and the stator coil L1 and
When the current flowing through L3 is represented by I2, the output terminal 30a is V
s, the output terminal 30b is (1/2) Vs, and the output terminal 3
In the section where the voltage 0c is 0, (I1> I2). This
Next, I1 gradually decreases, I2 gradually increases, and
The voltage at the output terminal 30b and the voltage at the output terminal 30c are equal
When it becomes (1/2) Vs, it becomes (I1 = I2). Soshi
, I1 further decreases, I2 further increases,
(I1 <I2). In other words, the phase switching is gradually
Sound is generated due to abrupt current change during phase switching.
The occurrence of scratches is prevented. Also, every 120 °
The energization section overlaps at the time of phase switching
Cancels the torque drop due to phase switching
can do. Furthermore, the energization waveform is (1/2) Vs
In the section where the level is constant, the stator coils L1, L
In 2, L3, no current flows through one stator coil
The motor efficiency is improved and torque unevenness is prevented.
Have been. In the above embodiment, the stator coils L1,
Regarding the voltage Vs applied to L2 and L3, (1/2)
Vs amplitude detection signals a, b, and c are formed. Only
However, when the amplitudes of the detection signals a, b, and c are represented by V1,
(V1 = Vs / 2n) (n: integer) for detection signal of amplitude
Even if this detection signal is amplified to form a signal for energization
good. E. Other Embodiments FIGS. 7 and 8 show another embodiment of the present invention. Other fruits
In the example, the detection signals A, B and C of the three Hall elements (Fig.
2A) (see 2A)
Using the generated signals α, β, and γ shown in FIG. 9A, a conduction wave is generated.
It is what creates a shape. That is, the signal α is (AB)
And the signal β is formed by (B-C).
Signal γ is formed by (C−A). One-phase communication
The generation of the radio wave form will be described. FIG. 7 shows an example of an adder circuit for generating the signal α.
Is shown. This adding circuit is composed of an operational amplifier 70.
The detection signal A and the detection signal B as input signals.
And the inverted signal B * is supplied. Therefore, this addition
The signal α (= A + B = AB) is formed by the arithmetic circuit.
You. This signal α is similar to the other signals β and γ (1 /
2) It has a central level of Vs. In FIG. 8, the input terminal 71 is
A signal α is provided. This signal α is the operational amplifier 72 and
It is supplied to the operational amplifier 73. The operational amplifier 72 is (+
V2 / 2) Level-shifted and inverted signal
Generates α2. The operational amplifier 73 has a (-V2 / 2) level.
Generates a signal α1 which is bell-shifted and inverted
You. FIG. 9B shows the signal α which is different by the level of V2.
The waveforms of 1 and the signal α2 are displayed. The signal α2 is sent to the analog switch 74 and the level.
To the comparator 76. Signal α1 is analog
It is supplied to the switch 75 and the level comparator 77.
You. The level comparator 76 is based on the level of the signal α2.
High level during a period greater than quasi level (1/2) Vs
The switching pulse shown in FIG. 9C is generated. Level
In the comparator 77, the level of the signal α1 is the reference level.
It becomes high level in a period smaller than (1/2) Vs.
The switching pulse shown in D is generated. Level comparison
When the switching pulse from the oscillator 76 is at high level
The analog switch 74 is turned on and the output terminal 78
Is higher than (1/2) Vs in the waveform of the signal α2.
The waveform of a large section is extracted. Level comparator
While the switching pulse from 77 is high level,
The analog switch 75 is turned on, and the signal is output to the output terminal 79.
Within the α1 waveform, the level is smaller than (1/2) Vs
The waveform between is taken out. Each of the output terminals 78 and 79 has a front
Through the output circuit similar to the one described above, the stator coil
It is connected. Depending on the output circuit, output terminals 78 and 7
The combined voltage of the output voltages generated in each of FIG.
It becomes what is shown in E. Energization waveform shown in FIG. 9E
Is the same as the energization waveform (FIG. 6G) in the above-described embodiment.
Waveform. Therefore, the steep current change during phase switching
Is prevented, and the energized sections overlap and
In addition, there is a section where no current flows through one stator coil.
Is done. In this other embodiment, the inclination angle of the energization waveform and
Conduction angle wave, amount of offset between signals α1 and α2, level
It is set by the reference level of the comparator. F. Modifications The present invention is not limited to the three-phase bidirectional energization method, but the three-phase unidirectional
For energizing brushless motor drive circuits
Can be applied to For reference, the waveform diagram of FIG.
Current wave in the case of brushless motor of 90 ° direction energization method
Shows the generation of shapes. FIG. 10A shows the detection of two Hall elements.
Signals A and B are shown. The detection signals A and B are the same as those described above.
As in the one embodiment, the amplitude is set to Vs, for example. And
The maximum value of both detection signals A and B is detected, and
The signal shown in is formed and the minimum value of both is detected.
Then, the signal shown in FIG. 10C is formed. From the detection signals A and B of the Hall element, FIG.
The switching pulses shown in FIG.
Generated. While the signal shown in FIG. 10B is inverted,
Level-shifted signal to switch shown in FIG. 10D
The waveform in the high-level period of the pulse is extracted. same
Similarly, the signal shown in FIG.
Switching pulse shown in FIG. 10E from the switched signal
The waveform in the high level period is extracted. Switchon
By combining the two waveforms
The energization waveform shown is obtained. In FIG. 10G, the solid line and
The energization waveforms shown by the broken lines are supplied to the stator coil.
You. Energization shown in FIGS. 10F and 10G
The waveform is such that the current changes slowly when switching phases.
And has features similar to those of the above-described one embodiment and other embodiments.
Things. According to the present invention, the current at the time of phase switching is changed.
The change is gradual, and the acoustic
It is possible to prevent the occurrence of noise. This invention is
The slope waveform of the energization waveform
Since it is a slanted part, a capacitor is not required and it is low cost
It can be configured as well as the motor rotation
Even when the number is low, it is possible to reliably prevent the generation of acoustic noise.
Can be. The present invention also relates to a linear drive system.
As described above, there is an advantage that the motor efficiency does not decrease. Furthermore,
This invention changes the mechanical structure of a brushless motor.
It is not necessary to realize, and it can be realized by replacing only the drive circuit
Can be. Furthermore, according to the present invention, the energization waveform is switched off.
It becomes the center level near the replacement point, and in that case,
No current flows through the stator coil. Therefore, this invention
Is to prevent torque unevenness due to back electromotive force.
In addition, it prevents waste of current flowing during periods when there is no magnetic flux,
Efficiency can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a connection diagram of a waveform shaping circuit for an output signal of a Hall element according to an embodiment of the present invention. FIG. 2 is a waveform diagram showing an output waveform of a Hall element. FIG. 3 is a connection diagram of a conduction waveform generation circuit according to an embodiment of the present invention. FIG. 4 is a connection diagram of a switching pulse generation circuit according to an embodiment of the present invention. FIG. 5 is a waveform diagram used to explain a switching pulse generating operation. FIG. 6 is a waveform diagram used to describe an energization waveform generation operation. FIG. 7 is a connection diagram of another embodiment of the present invention. FIG. 8 is a connection diagram of another embodiment of the present invention. FIG. 9 is a waveform diagram used for explaining an energization waveform generating operation according to another embodiment of the present invention. FIG. 10 is a waveform diagram used for explaining an energization waveform generating operation of still another embodiment of the present invention. FIG. 11 is a connection diagram for explaining a conventional technique. [Explanation of reference symbols] L1, L2, L3 ... Stator coils, 1a, 1b, 1
c ... Hall element, 6a, 6b, 6c, 7a, 7b,
7c ... Diode clamp circuit, 12a, 12b,
12c ... Maximum value detection circuit, 13a, 13b, 13c
... Minimum value detection circuits, 20a, 20b, 20c, 21
a, 21b, 21c, 24a, 24b, 24c, 25
a, 25b, 25c ... Analog switch, 30a,
30b, 30c ... Output terminals

Claims (1)

(57) [Claims] A three-phase brushless motor having a rotor magnet, a stator coil, and three Hall elements for position detection that generate a detection signal having a waveform corresponding to a change in magnetic flux from the rotor magnet. And a clamp circuit for clamping the levels of three-phase first, second and third detection signals output from each of the Hall elements and having a phase difference of 120 ° in electrical angle, and the clamped first and second The first-phase energization waveform is formed by synthesizing the waveforms of the detection signals of, and the second-phase energization waveform is formed by synthesizing the clamped waveforms of the second and third detection signals. An energization waveform generation circuit that forms an energization waveform of a third phase by combining the clamped waveforms of the first and third detection signals; and energization of the first phase, the second phase, and the third phase. Waveform An amplifier circuit for amplifying and supplying each to the stator coil is provided, and the zero cross points of the energization waveforms of the first phase and the second phase have a deviation of 120 ° in electrical angle. Phase and third
The mutual zero crossing points of the phase conduction waveforms are 120 ° in electrical angle
The first-phase, second-phase, and third-phase energization waveforms each have a flat portion at its maximum level, its minimum level, and its intermediate level including the zero-cross point, and
The length of the flat portion of the intermediate portion is sufficiently small as compared with the flat portion of the maximum level and the flat portion of the minimum level, and the distance between the flat portions is substantially the same as the inclined portion of the clamped detection signal. The brushless motor is characterized in that the energization waveforms of the first phase, the second phase, and the third phase are connected to each other by the inclined part of each of the inclined parts and cross the inclined parts of the energized waveforms of the other phases. 2. The brushless motor according to claim 1, wherein the position on the time axis where the inclined portions of the first-phase, second-phase, and third-phase energization waveforms cross substantially coincides with the zero-cross point of the clamped detection signal. A brushless motor characterized by: