JPH11136988A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce reactive current during low speed rotation of rotor in variable speed control of a brushless motor. SOLUTION: The brushless motor comprises a current detection resistor 47 detecting a first voltage corresponding to the conduction current of the stator coil 4, a second detecting section in an r.p.m. detection type current limit circuit 46 detecting a second voltage corresponding to the rotational speed of the rotor, and the r.p.m. detection type current limit circuit 46 for comparing the first and second voltages and reducing the driving of the stator coil 4 through a variable speed control circuit 49 it the conduction current of the stator coil 4 exceeds a specified level when the rotational speed of the rotor is lower than a specified level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed controllable brushless motor.

[0002]

2. Description of the Related Art In recent years, DC motors have been recognized for their good controllability not only in the acoustic field but also in the information and industrial fields, and their use has been expanding at an extremely rapid pace. Among them, a brushless motor has no contact portion such as a brush and a commutator, and has an advantage of a long service life. Therefore, its use as an industrial motor in which reliability is particularly important is expanding.

Under these circumstances, the driving method of small axial fans has been switched from AC to DC in recent years, and DC axial fans using brushless motors have been increasing. As the mounting density of industrial equipment such as computer-related equipment increases, the DC axial flow fan is required for cooling the fan, and the fan itself is required to have high reliability.

That is, when the motor stops due to some external factor, not only is it possible to prevent the stator coil from being burned out, but also by issuing an alarm to the main body of the device to prevent the accident from occurring and to eliminate the factor. In such a case, it is required to return automatically and rotate normally.

At the same time, quietness in the office is required, and when there is not much heat generation from the equipment, it is possible to reduce the air flow by lowering the rotation of the motor, and to increase the air flow by increasing the rotation of the motor when the temperature rise due to the heat generation becomes large. A motor with a shift control has been required.

A conventional brushless motor is disclosed in Japanese Patent Laid-Open No. 2-12.
Japanese Patent Application Laid-Open No. 3989 or Japanese Utility Model Application Laid-Open No. 5-55798 is known. A conventional brushless motor includes a speed control circuit that detects the rotation of a rotor rotationally driven by a stator coil with a magnetic detection element and feeds it back, and drives the stator coil so that the rotor rotates at a set rotation speed. It operates by controlling the speed.

As shown in FIG. 8, this brushless motor has a magnetic detecting element 1 and a stator coil burnout prevention device 50.
And a speed control circuit, which also uses the charge / discharge characteristics of the capacitor to prevent burnout of the stator coil and control the variable speed.

The speed control circuit includes, for example, a position signal amplifier circuit 2, an output circuit 3, a stator coil 4, a rotation detection circuit 5, a discharge transistor 6, a cutoff / return circuit 11, a capacitor 12, and a variable speed control circuit 49. It is configured.

The stator coil burnout prevention device 50 includes a charge / discharge circuit 7, an inversion detection transistor 8, a second flip-flop circuit 9, a second comparator circuit 10, and an inverter circuit 13.

The stator coil burnout prevention device 50
When the motor stops due to some external factor, the excessive current supplied to the stator coil 4 is prevented from flowing to prevent the stator coil 4 from burning.

The variable speed control circuit 49 comprises a charging circuit 14, a first comparator circuit 15, a first flip-flop circuit 16, a pulse circuit 17, and an OR circuit 18.

When the motor is started, the potential of the capacitor 12 is 0 V, as shown in FIG.
The output of the second comparator circuit 10 becomes Lo, and a reset pulse is output from the pulse circuit 17 to reset the first flip-flop circuit 16. Therefore, the OR circuit 1
The output of 8 becomes Hi, the cutoff / return circuit 11 is turned on, and the output circuit 3 is turned off. Therefore, no current flows through the stator coil 4.

FIG. 5B shows the output waveform of the first flip-flop circuit 16, FIG. 5C shows the output waveform of the second comparator circuit 10, FIG.
(E) shows the output waveform of the output circuit 3.

At this time, the charging circuit 14 operates and the capacitor 1
2 is supplied with electric charge. Then, when the potential of the capacitor 12 reaches the predetermined first set potential Vs, the first comparator circuit 15 operates to invert the first flip-flop circuit 16 to stop charging. Then, the output of the OR circuit 18 becomes Lo, the cutoff / return circuit 11 is turned off, and the output circuit 3
Is turned ON. As a result, the stator coil 4 is energized and the rotor rotates.

When the rotor rotates, a pulse is output from the rotation detecting circuit 5 to discharge the electric charge of the capacitor 12 by the discharging transistor 6, reset the first flip-flop circuit 16 and supply the electric charge to the capacitor 12 again.

As described above, since the output pulse of the rotation detecting circuit 5 is periodically generated, the potential of the capacitor 12 does not reach the predetermined third set potential Voff for shutting off the output circuit 3, and the output circuit is not driven. 3 energizes the stator coil 4 while repeating ON / OFF, and the motor keeps rotating.

If the charging current of the charging circuit 14 is appropriately selected using the variable resistor 20, the ON / OFF duty ratio of the output circuit 3 changes, and the rotation speed of the rotor can be changed. Since the charging current of the charging circuit 14 is set to a sufficiently large value as compared with the charging current and the discharging current of the charging / discharging circuit 7, only the charging circuit 14 contributes during normal rotation, and the motor is driven by some external factor. When stopped, only the charge / discharge circuit 7 contributes.

When the motor stops due to some external factor, the output pulse of the rotation detecting circuit 5 is not generated, so that the capacitor 12 is further charged by the charging / discharging circuit 7. When the potential of the capacitor 12 rises to a predetermined third set potential Voff that cuts off the output circuit 3, the output of the second comparator circuit 10 becomes Hi and the cutoff / return circuit 11 is turned on through the OR circuit 18, and the output circuit 3 is turned on. It is turned off, and no current is supplied to the stator coil 4.

When the charging further proceeds and reaches a predetermined fourth set potential Vh of the capacitor 12, the inversion detecting transistor 8
Then, the charging / discharging circuit 7 is discharged through the second flip-flop circuit 9. Then capacitor 1
The potential of 2 starts to drop.

The potential of the capacitor 12 is set to a predetermined first
When the voltage drops to a predetermined second set potential Von lower than the set potential Vs, the output of the second comparator circuit 10 becomes Lo.
And the pulse circuit 17 generates a reset pulse to reset the first flip-flop circuit 16.

Such an operation is repeated until an external factor is removed. From the above, when the motor stops due to some external factor, the capacitor 1
The current supplied to the stator coil 4 is cut based on the electric potential of the stator coil 2 to prevent the stator coil 4 from burning.

[0022]

When a DC power is supplied to a brushless motor and the brushless motor is rotated, an induced voltage is generated in the stator coil 4. The induced voltage is not uniform since it is related to the amount of the magnetic flux of the rotor magnet in the motor interlinked with the stator coil 4 and the rate of change, and has a voltage waveform as shown in FIG.

Even during normal rotation, the reactive current is large before and after the peak of the induced voltage. Actually, due to the delay due to the inductive L component of the stator coil 4, the reactive current is larger after the peak of the induced voltage than before.

This reactive current is defined as torque (motor output)
Current that does not contribute to In a conventional brushless motor, in pulse width modulation control (PWM control) in which variable speed control is performed using the charge and discharge characteristics of the capacitor 12, as the number of rotations decreases, the induced voltage waveform of the motor decreases, and this induced voltage is reduced. There is a problem that the current efficiency is extremely deteriorated because a portion after the peak of the voltage waveform is used.

As shown in FIG. 7, a current waveform for each energization condition is a full energization waveform without an OFF section, and b is 1/3.
It can be seen that 2/3 section energization with an OFF section and c is 1/3 section energization with a 2/3 OFF section, and that the current increases as the energization section becomes shorter (the rotation speed decreases). This is because the induced voltage is low, and there is a problem that the reactive current increases particularly at the end of the section.

An object of the present invention is to provide a brushless motor having a reduced reactive current when the number of revolutions is reduced.

[0027]

According to the present invention, there is provided a brushless motor comprising: a first detecting unit for detecting a first voltage corresponding to a current supplied to a stator coil; and a second voltage corresponding to a rotation speed of a rotor. And a second detection unit for detecting that an energizing current exceeding a specified value has flowed through the stator coil when the rotation speed of the rotor is a specified low speed by comparing the first voltage and the second voltage. Current limiting means for reducing the driving of the stator coil by the speed control circuit.

According to the present invention, it is possible to reduce the reactive current when the number of revolutions is reduced.

[0029]

According to the first aspect of the present invention, a rotation of a rotor driven by the stator coil is detected and fed back to a speed control circuit for driving the stator coil. A brushless motor that operates so that the rotor rotates at a rotation speed, a first detection unit that detects a first voltage corresponding to a current supplied to the stator coil, and a second detection unit that detects a first voltage according to a rotation speed of the rotor. A second detecting unit for detecting the voltage of the second voltage; and comparing the first voltage with the second voltage, and when the rotation speed of the rotor is a specified low speed, an energizing current exceeding a specified value flows through the stator coil. And a current limiting means for reducing the driving of the stator coil by the speed control circuit, and the induced voltage waveform is reduced when the rotation speed is reduced. In the pulse width modulation control Ri can reduce the reactive current due to use past the peak of the waveform.

According to a second aspect of the present invention, a rotational position of the rotor is detected by a magnetic detecting element, and a speed control circuit includes a position signal amplifying circuit for amplifying an output signal of the magnetic detecting element; An output circuit that supplies the output of the position signal amplifier circuit to the stator coil, a rotation detection circuit that outputs a pulse in synchronization with the output of the position signal amplifier circuit, and charges a capacitor according to a set rotation speed A charging circuit, a first comparator circuit for stopping charging of the capacitor when a potential of the capacitor reaches a predetermined first set potential due to a charging current of the charging circuit, and an output pulse of the rotation detection circuit. A discharge transistor for discharging a charge of a capacitor, a first flip-flop circuit whose output is reset by an output pulse of the rotation detection circuit, A pulse circuit that generates a reset pulse and outputs the reset pulse to the first flip-flop circuit when the potential of the first flip-flop circuit drops to a predetermined second set potential lower than the first set potential; An OR circuit for performing a logical sum of an output of the discharge transistor and an output of the discharge transistor; and a cutoff / return circuit for switching whether or not to supply the output of the position signal amplifier circuit to the output circuit with the output of the OR circuit. A first detecting unit is configured by interposing a current detecting resistor in series with a power supply circuit of the output circuit, and a current limiting unit is connected to an output side of the rotation detecting circuit by an interruption /
The brushless motor according to claim 1, wherein the brushless motor is connected between the input side of the return circuit and the input side.

According to a third aspect of the present invention, the rotational position of the rotor is detected by a magnetic detecting element, and the speed control circuit includes a position signal amplifying circuit for amplifying an output signal of the magnetic detecting element; An output circuit that supplies the output of the position signal amplifier circuit to the stator coil, a rotation detection circuit that outputs a pulse in synchronization with the output of the position signal amplifier circuit, and charges or charges a capacitor with an output pulse of the rotation detection circuit. A charge / discharge circuit for discharging, a two-output comparator for comparing the potential of the capacitor with a reference potential, outputting one output to the charge / discharge circuit, and switching whether or not to supply the output to the output circuit with the other output; And a first detection unit is configured by interposing a current detection resistor in series with a power supply circuit of the output circuit, and a current limiting unit is connected to an output side of the rotation detection circuit and an input side of the output circuit. It is obtained by a brushless motor according to claim 1, wherein connected between.

According to a fourth aspect of the present invention, there is provided the brushless motor according to any one of the first to third aspects, wherein the second voltage is a fixed bias. Hereinafter, a brushless motor of the present invention will be described based on specific embodiments.

(Embodiment 1) In a brushless motor according to Embodiment 1, the rotation of a rotor driven by a stator coil is detected by a magnetic detection element and fed back, so that the rotor rotates at a set rotation speed. The speed is controlled by a speed control circuit that drives the stator coil in such a manner as to perform the operation.

As shown in FIG. 1, the brushless motor comprises a magnetic detecting element 1 and a stator coil burnout preventing device 50.
, A speed control circuit, a current limiting means (for example, a rotation speed detecting type current limiting circuit 46), and a first detecting unit.

The speed control circuit includes, for example, a position signal amplifier circuit 2, an output circuit 3, a stator coil 4, a rotation detection circuit 5, a discharge transistor 6, a cutoff / return circuit 11, a capacitor 12, and a variable speed control circuit 49. It is configured.

The first detecting section is constituted, for example, by interposing a current detecting resistor 47 in series with the power supply circuit of the output circuit 3. The stator coil burnout prevention device 50 includes a charge / discharge circuit 7, an inversion detection transistor 8, a second flip-flop circuit 9, a second comparator circuit 10, and an inverter circuit 13.

The variable speed control circuit 49 comprises a charging circuit 14, a first comparator circuit 15, a first flip-flop circuit 16, a pulse circuit 17, and an OR circuit 18.

The charging circuit 14 includes transistors 21 and 22 and 24 and 2 constituting a current mirror circuit.
5, a variable resistor 20, and a transistor 23. The transistor 23 is set so that charging is turned ON / OFF. The collector of the transistor 25 is connected to the positive side of the capacitor 12.

The first comparator circuit 15 includes transistors 26 and 27 forming a current mirror circuit,
Transistors 28 and 29 constituting differential amplifier circuit
, A constant current source 30, and resistors 31 and 32. A predetermined first set potential Vs is set by the resistors 31 and 32, and the base of the transistor 28 is connected to the positive side of the capacitor 12. I have.

The first flip-flop circuit 16 includes transistors 34, 35, 36, 37, and 38, resistors 39 and 40, and constant current sources 33 and 41. The base of the transistor 34 is a transistor. 2
7, the base of the transistor 37 is connected to the output side of the rotation detecting circuit 5, respectively.

The pulse circuit 17 includes transistors 43 and 44, a capacitor 45 using the capacitance between the transistors, and a constant current source 42. The collectors of the transistors 43 and 44 are connected to the base of the transistor 38, respectively. The base of the transistor 43 is connected to the output of the second comparator circuit 10 by the transistor 44.
Are connected to the output side of the inverter circuit 13, respectively.

The first input terminal of the OR circuit 18 is connected to the collectors of the transistors 34 and 35, and the second input terminal is connected to the second input terminal.
Respectively connected to the output side of the comparator circuit 10 of
The output terminal is connected to the input side of the shutoff / return circuit 11.

As shown in FIG. 2, the rotation speed detection type current limiting circuit 46 includes a charging / discharging circuit 63, an integrating circuit 64, and a current limiting circuit 65, and is predetermined by the output of the rotation detecting circuit 5. The current limit value is set so that the voltage drop of the current detection resistor 47 does not exceed it.

The charge / discharge circuit 63 comprises a constant current circuit 51, a transistor 52 and a capacitor 53. The integration circuit 64 includes a diode 54, a capacitor 55, and a resistor 56.

The current limiting circuit 65 includes a comparator 57,
62, a transistor 60, and resistors 58, 59, 61. The second detection unit that detects a voltage corresponding to the rotation speed of the rotor includes, for example, a rotation speed detection type current limiting circuit 4.
6 except for the comparator 62.

When the motor is started, the potential of the capacitor 12 is 0 V as shown in FIG.
As shown in FIG. 1, the output of the second comparator circuit 10 becomes Lo and a reset pulse is output from the pulse circuit 17 to reset the first flip-flop circuit 16. Therefore, the output of the OR circuit 18 becomes Hi, the cutoff / return circuit 11 is turned on, and the output circuit 3 is turned off. Therefore, no current flows through the stator coil 4.

FIG. 5B shows the output waveform of the first flip-flop circuit 16, FIG. 5C shows the output waveform of the second comparator circuit 10, FIG.
(E) shows the output waveform of the output circuit 3.

At this time, the charging circuit 14 works and supplies electric charge to the capacitor 12. Then, as shown in FIG. 5A, the potential of the capacitor 12 becomes a predetermined first set potential V.
At s, the first comparator circuit 15 operates to invert the first flip-flop circuit 16 to stop charging. Then, the output of the OR circuit 18 becomes Lo, the cutoff / return circuit 11 is turned off, and the output circuit 3 is turned on. As a result, the stator coil 4 is energized and the rotor rotates.

As shown in FIG. 1, when the rotor rotates,
A pulse is output from the rotation detection circuit 5 in synchronization with the output signal amplified by the position signal amplification circuit 2 by detecting the rotation position of the rotor with the magnetic detection element 1. In accordance with this pulse, the charge of the capacitor 12 is discharged by the discharging transistor 6 and the first flip-flop circuit 16 is reset to supply the charge to the capacitor 12 again.

As described above, since the output pulse of the rotation detecting circuit 5 is periodically generated, as shown in FIG.
Without reaching the set potential Voff of the output circuit 3.
Energizes the stator coil 4 while repeating ON / OFF, and the motor continues to rotate.

If the charging current of the charging circuit 14 is appropriately selected using the variable resistor 20 shown in FIG.
The duty ratio of the FF changes and the rotation speed of the rotor can be changed.

Since the charging current of the charging circuit 14 is set to a sufficiently large value compared to the charging current and the discharging current of the charging / discharging circuit 7, only the charging circuit 14 contributes during normal rotation, and the motor operates in a certain manner. When the operation is stopped by an external factor, only the charge / discharge circuit 7 contributes.

The pulse generated by the rotation detection circuit 5 is also output to a rotation speed detection type current limiting circuit 46. As shown in FIG. 2, each time the output pulse of the rotation detection circuit 5 is received by the transistor 52, the charge of the capacitor 53 is discharged. As the rotation speed becomes slower, the interval between the discharge outputs becomes wider.

Therefore, the potential of the capacitor 55 constituting the integrating circuit 64 rises. When this potential rises to a predetermined potential Vref1, the comparator 57 operates to turn on the transistor 60. As a result, the bias (second voltage) of the non-inverting input terminal of the comparator 62 drops to a point divided by the resistors 58, 59 and 61, and the current detection resistor 47 is supplied by a current flowing through the stator coil 4 exceeding a specified value. (First voltage) rises, and at this point, the current is limited. The output of the comparator 62, which compares the first voltage and the second voltage, is input to the cutoff / return circuit 11, so that no current is supplied to the stator coil 4.

When the capacitor 55 is discharged and the potential of the capacitor 55 falls below the potential Vref1, the comparator 57 does not operate, the transistor 60 is turned off, the comparator 62 does not operate, and the current limit is released.
The current is supplied to the stator coil 4 again.

As shown in FIG. 3, the current at this time has a smaller reactive current at the end of the section than the conventional current waveform d. Note that the potential of the capacitor 53 is not high at the time of starting or when the number of rotations is high.
Since the potential of No. 5 does not rise, and therefore the comparator 57 does not operate, the transistor 60 is turned off and the comparator 62 does not actually operate.

As described above, the first detector for detecting the first voltage corresponding to the current supplied to the stator coil and the second detector for detecting the second voltage corresponding to the rotation speed of the rotor. And the current limiting means, the first voltage and the second voltage are compared, and when the rotation speed of the rotor is a specified low speed, it is determined that an energizing current that exceeds a specified value flows through the stator coil. Thus, the driving of the stator coil by the speed control circuit can be reduced.

More specifically, the rotation speed detection type current limiting circuit 4
By providing 6 and the current detection resistor 47, it is possible to reduce the reactive current when the number of rotations is reduced and to increase the current efficiency.

(Embodiment 2) In a brushless motor according to Embodiment 2, the rotation of a rotor driven by a stator coil is detected by a magnetic detection element and fed back, so that the rotor rotates at a set rotation speed. The speed is controlled by a speed control circuit that drives the stator coil in such a manner as to perform the operation.

As shown in FIG. 4, the brushless motor has a magnetic detecting element 1, a rotation detecting circuit 5, a speed control circuit, a first detecting section, and current limiting means (for example, a rotational speed detecting type current limiting circuit 46). It is composed of

This speed control circuit comprises, for example, a position signal amplifier circuit 2, an output circuit 3, a stator coil 4, and a variable speed control circuit 71. The first detection unit is configured by interposing a current detection resistor 47 in series with a power supply circuit of the output circuit 3, for example.

As shown in FIG. 2, the rotation speed detection type current limiting circuit 46 includes a charging / discharging circuit 63, an integrating circuit 64, and a current limiting circuit 65, and is predetermined by the output of the rotation detecting circuit 5. The current limit value is set so that the voltage drop of the current detection resistor 47 does not exceed it.

However, in the second embodiment, the cutoff / return circuit 11 shown in FIG. 2 is not provided between the rotation speed detection type current limiting circuit 46 and the output circuit 3, and the rotation speed detection type current limiting circuit 4
The output of the comparator 62 in 6 is directly input to the output circuit 3.

The charge / discharge circuit 63 comprises a constant current circuit 51, a transistor 52 and a capacitor 53. The integration circuit 64 includes a diode 54, a capacitor 55, and a resistor 56.

The current limiting circuit 65 includes a comparator 57,
62, a transistor 60, and resistors 58, 59, 61. The second detection unit that detects a voltage corresponding to the rotation speed of the rotor includes, for example, a rotation speed detection type current limiting circuit 4.
6 except for the comparator 62.

As shown in FIG. 4, the variable speed control circuit 71 comprises a constant current circuit 79, a diode 80 and a transistor 8
1, a capacitor 82, a two-output type comparator 83, and an inverter 84.

By appropriately changing the current value of the constant current circuit 79, the rotation speed of the rotor can be changed. The capacitor 82 constituting the variable speed control circuit 71 is related only to a general speed control function which is not related to the function of preventing the stator coil from burning.

The variable speed control circuit 71 comprises a charge / discharge circuit 66 comprising a constant current circuit 79, a diode 80, a transistor 81 and a capacitor 82.
This constitutes an M-type variable speed control circuit.

That is, the potential of the capacitor 82 is discharged by the pulse output of the rotation detecting circuit 5 and becomes a sawtooth wave. The peak value of this waveform is a predetermined value Vr
When the voltage becomes higher than ef2, the comparator 83 operates to stop charging the capacitor 82 and to drive the output circuit 3 via the inverter 84.

For this reason, if the value of Vref2 is low, the ON section becomes long (high rotation speed), and if the value of Vref2 is high, the ON section becomes short (low rotation speed). The pulse generated by the rotation detection circuit 5 is also output to a rotation speed detection type current limiting circuit 46.

As shown in FIG. 2, each time the pulse output is received by the transistor 52, the charge of the capacitor 53 is discharged. As the rotation speed becomes slower, the interval between the discharge outputs becomes wider.

Therefore, the potential of capacitor 55 forming integration circuit 64 rises. When this potential rises to a predetermined potential Vref1, the comparator 57 operates to turn on the transistor 60. As a result, the bias (second voltage) of the non-inverting input terminal of the comparator 62 drops to a point divided by the resistors 58, 59 and 61, and the current detection resistor 47 is supplied by a current flowing through the stator coil 4 exceeding a specified value. (First voltage) rises, and at this point, the current is limited. The output of the comparator 62, which compares the first voltage and the second voltage, is input to the output circuit 3 so that no current is supplied to the stator coil 4.

When the capacitor 55 is discharged and the potential of the capacitor 55 falls below the potential Vref1, the comparator 57 does not operate, the transistor 60 is turned off, the comparator 62 does not operate, and the current limit is released.
The current is supplied to the stator coil 4 again.

At this time, as shown in FIG. 3, the reactive current at the end of the section is smaller than that of the conventional current waveform d, as shown in FIG. At the time of start-up or when the number of revolutions is high, the potential of the capacitor 53 does not rise because the potential of the capacitor 53 is not high, and therefore the comparator 57 does not operate, so that the transistor 60 is turned off and the comparator 62 does not actually operate.

As described above, the first detecting section for detecting the first voltage corresponding to the current flowing through the stator coil and the second detecting section for detecting the second voltage corresponding to the rotation speed of the rotor. And the current limiting means, the first voltage and the second voltage are compared, and when the rotation speed of the rotor is a specified low speed, it is determined that an energizing current that exceeds a specified value flows through the stator coil. Thus, the driving of the stator coil by the speed control circuit can be reduced.

More specifically, the rotation speed detection type current limiting circuit 4
By providing 6 and the current detection resistor 47, it is possible to reduce the reactive current when the number of rotations is reduced and to increase the current efficiency.

In each embodiment, the bias (second voltage) of the non-inverting input terminal of the comparator 62 of the current limiting means is used.
The bias is changed by the resistors 58, 59 and 61 by the operation of the comparator 57, but the same effect is obtained even when the second voltage is fixed.

[0078]

As described above, according to the brushless motor of the present invention, the first detector for detecting the first voltage corresponding to the current flowing through the stator coil and the second detector corresponding to the rotation speed of the rotor are provided. A second detection unit for detecting the first voltage and a current limiting means, the first voltage and the second voltage are compared, and the rotation speed of the rotor is regulated to the stator coil at a prescribed low speed. It is possible to detect that an energizing current exceeding the value flows, and it is possible to reduce the driving of the stator coil by the speed control circuit.

Specifically, by providing a rotation speed detection type current limiting circuit and a current detection resistor, it is possible to reduce the reactive current when the rotation speed of the rotor in the variable speed control is a specified low speed, and to reduce the current efficiency. A high brushless motor can be provided.

The same effect can be obtained even when the second voltage of the current limiting means is a fixed bias. Specifically, the same effect is obtained even when the bias of the non-inverting input terminal of the comparator of the rotation speed detection type current limiting circuit is a fixed bias.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a brushless motor according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a rotation speed detection type current limiting circuit according to each embodiment of the present invention.

FIG. 3 is a diagram showing a current waveform according to each embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a brushless motor according to a second embodiment of the present invention.

FIG. 5 is a diagram showing waveforms at various parts of the brushless motor according to the first embodiment of the present invention;

FIG. 6 is a diagram showing a waveform of an induced voltage of a conventional brushless motor.

FIG. 7 shows a conventional current waveform.

FIG. 8 is a block diagram showing a configuration of a conventional brushless motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic detection element 2 Position signal amplification circuit 3 Output circuit 4 Stator coil 5 Rotation detection circuit 6 Discharge transistor 7 Charge / discharge circuit 8 Inversion detection transistor 9 Second flip-flop circuit 10 Second comparator circuit 11 Cutoff / return circuit REFERENCE SIGNS LIST 12 capacitor 13 inverter 14 charging circuit 15 first comparator circuit 16 first flip-flop circuit 17 pulse circuit 18 OR circuit 46 rotation speed detection type current limiting circuit 47 current detection resistor 49 variable speed control circuit 50 stator coil burnout prevention device 51 Constant current circuit 52 Transistor 53, 55 Capacitor 54 Inverter 56, 61 Resistance 57, 62 Comparator 58, 59 Resistance 63 Charge / discharge circuit 64 Integration circuit 66 Charge / discharge circuit 65 Current limiting circuit 71 Variable speed control circuit 79 Constant current circuit 8 0 Diode 81 Transistor 82 Capacitor 83 Two-output type comparator 84 Inverter

Claims (4)

[Claims] A brushless motor that operates so that the rotor rotates at a set rotation speed by detecting and feeding back the rotation of a rotor that is rotationally driven by the stator coil to a speed control circuit that drives the stator coil. A first detection unit that detects a first voltage according to a current flowing through the stator coil; a second detection unit that detects a second voltage according to a rotation speed of the rotor; And comparing the first voltage with the second voltage to detect that an energizing current exceeding a specified value flows through the stator coil when the rotation speed of the rotor is a specified low speed, and driving the stator coil by the speed control circuit Brushless motor provided with current limiting means for reducing power consumption. 2. A speed control circuit for detecting a rotational position of a rotor with a magnetic detecting element, a position signal amplifying circuit for amplifying an output signal of the magnetic detecting element, and an output of the position signal amplifying circuit to a stator coil. An output circuit for supplying, a rotation detection circuit for outputting a pulse in synchronization with an output of the position signal amplification circuit, a charging circuit for charging a capacitor according to a set rotation speed, and a charging current for the charging circuit. A first comparator circuit that stops charging the capacitor when the potential of the capacitor reaches a predetermined first set potential, and a discharge transistor that discharges the charge of the capacitor with an output pulse of the rotation detection circuit. A first flip-flop circuit whose output is reset by an output pulse of the rotation detection circuit, and wherein the potential of the capacitor is the first setting A pulse circuit that generates a reset pulse when the voltage drops to a predetermined second set potential lower than the second level and outputs the reset pulse to the first flip-flop circuit; An OR circuit for performing an OR operation with an output; and a shutoff / return circuit for switching whether or not to supply the output of the position signal amplifying circuit to the output circuit with the output of the OR circuit. 2. The power supply circuit of the output circuit, wherein a current detection resistor is interposed in series, and current limiting means is connected between an output side of the rotation detection circuit and an input side of the cutoff / return circuit. Brushless motor. 3. A rotational position of the rotor is detected by a magnetic detecting element, a speed control circuit includes: a position signal amplifying circuit for amplifying an output signal of the magnetic detecting element; and an output of the position signal amplifying circuit to a stator coil. An output circuit for supplying, a rotation detection circuit that outputs a pulse in synchronization with an output of the position signal amplification circuit, a charge / discharge circuit that charges or discharges a capacitor with an output pulse of the rotation detection circuit, A two-output comparator that compares a potential with a reference potential and outputs one output to the charge / discharge circuit and switches whether to supply the output to the output circuit with the other output, and the first detection unit includes: 2. The output circuit according to claim 1, wherein a current detection resistor is interposed in series with a power supply circuit of the output circuit, and current limiting means is connected between an output side of the rotation detection circuit and an input side of the output circuit. Brushless motor. 4. The brushless motor according to claim 1, wherein the second voltage is a fixed bias.