JPH1098893A - Device for driving dc brushless motor and dc brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a reverse current from flowing to the side of a power supply without filtering a high-frequency-switched motor starting current into a direct current by a method wherein a capacitor which repeats a changing operation and a discharge operation at a pulse modulation cycle and which prevents the reverse current from flowing to a power supply for drive at the modulation cycle is connected across the power supply for drive of a driving coil and a ground. SOLUTION: A driving device is constituted in such a way that a high ripple current capacitor 55 which repeats a charging operating and a discharge operation at a pulse modulation cycle and which prevents a reverse current from flowing to a power supply for drive at the modulation cycle is connected across a power supply 52 for drive of a driving coil and a ground 54. As a result, the capacitor 55 repeats the charging operation and the discharge operation with reference to the high-frequency switching operation of a driving coil current, and it can function as an adjusting tank. As a result, without filtering a high-frequency-switched power supply 52 for motor drive into a direct current, the reverse current does not flow to the side of the power supply, and the driving device is operated normally so as to enhance its reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC brushless motor driving device and a DC brushless motor, and more particularly, to a driving device such as a high-speed polygon scanner used in a laser printer, a digital copying machine, a laser FAX, or the like. In particular, it is possible to prevent the reverse current from flowing to the power supply side without smoothing and DC converting the motor drive current that has been subjected to high frequency switching, and without newly providing a choke coil, a capacitor and a diode. The present invention relates to a DC brushless motor drive device and a DC brushless motor that can be completed, and can achieve downsizing, cost reduction, and stabilization of the drive device.

[0002]

2. Description of the Related Art Heretofore, there has been known a DC brushless motor driving apparatus that controls a rotation speed by turning on and off a current of a driving coil at a cycle shorter than a cycle of a position detection signal. This conventional drive device for a current brushless motor has an advantage that the drive efficiency can be increased in principle. The disadvantage of the conventional DC brushless motor driving device is disclosed in Japanese Patent Application Laid-Open No. 58-99289. Here, there are described problems such as the occurrence of a disturbance electromagnetic wave due to the high frequency switching of the drive coil current and the generation of a beat sound from the drive coil when switching is performed at a relatively low frequency. Further, although not disclosed, if a general bipolar transistor is used as the energizing switching element of the drive coil, the loss of the switching element due to the high frequency switching increases, so that the high frequency switching that should have been provided to increase the efficiency is performed. In practice, there is a problem that efficiency is reduced.

Further, when a current of a drive coil formed of an inductance element is subjected to a high-frequency switching operation, a back electromotive voltage V is generated when the current is off. This back electromotive voltage V is expressed by the following equation (1).

[0004]

(Equation 1)

Where V is a back electromotive voltage, i is a drive coil, and L
Is the inductance of the coil, and t is the time. As described above, the reverse voltage V generated when the current of the drive coil is turned off by the high-frequency switching operation increases as the switching speed increases, and as a result, the reverse voltage V passes through the diode included to protect the switching element. There is a problem that the directional current flows to the power supply side and the driving device does not operate normally. For a conventional DC brushless motor drive device that solves the problem that the reverse current flows to the power supply side and the drive device does not operate normally,
For example, there is one reported in JP-A-58-99289. Here, by using a choke coil, a capacitor, a diode, and the like, the high-frequency switched motor drive current is smoothed and converted to DC, so that a reverse current can be made difficult to flow to the power supply side, and the drive device operates normally. It has the advantage of being able to.

[0006]

However, in such a conventional DC brushless motor driving apparatus, a choke coil, a capacitor, a diode, and the like must be newly provided in order to smooth the motor driving current and make it DC. However, there is a problem that the cost of the driving device increases accordingly. In addition, in order to smooth the motor drive current and make it DC, as described above, a new choke coil, capacitor, diode, etc. must be provided.
In particular, since the choke coil and the capacitor are composed of large-sized elements, there is a problem that the driving device is enlarged accordingly.

Accordingly, the present invention can prevent a reverse current from flowing to the power supply side without smoothing and DC-converting a high-frequency switched motor drive current, and newly install a choke coil, a capacitor and a diode. It is an object of the present invention to provide a DC brushless motor drive device and a DC brushless motor which can be omitted and can realize a reduction in size, cost, and stability of the drive device.

[0008]

According to the first aspect of the present invention,
To solve the above problem, a speed control circuit that compares a target speed signal with a rotation speed signal of a rotor and outputs a speed control voltage signal; and a speed control voltage signal output from the speed control circuit, A pulse width modulation circuit that converts the pulse width into a pulse width corresponding to the control voltage signal and outputs a speed control pulse signal; an energization switching circuit that outputs an energization switching signal that switches energization of the drive coil according to a position detection signal output from the motor; A switching circuit for energizing a drive coil with an output pulse width of the pulse width modulation circuit by combining an energization switching signal output from the energization switching circuit and a speed control pulse signal output from the pulse width modulation circuit. In the brushless motor driving device, the switching element for energizing the driving coil of the switching circuit has a turn-off time of a pulse. It consists of a switching element that is 1/50 or less of the width modulation cycle, and repeats charging and discharging with a pulse modulation cycle between the drive power supply and the ground of the drive coil, and prevents the reverse current from flowing in the drive power supply with the modulation cycle. It is characterized in that a capacitor for preventing the noise is connected.

According to a second aspect of the present invention, in order to solve the above-mentioned problem, in the first aspect of the present invention, a modulation frequency of the pulse width modulation circuit is approximately 20 kHz. According to a third aspect of the present invention, in order to solve the above problem, in the first or second aspect of the present invention, a motor drive current detection circuit that detects a drive current of the motor and outputs a motor drive current detection voltage; The motor drive current detection voltage output from the motor drive current detection circuit is compared with the current limit reference voltage. If the motor drive current detection voltage is higher than the current limit reference voltage, the speed control output from the speed control circuit is output. A current limiting circuit for limiting the motor drive current by invalidating the voltage signal and limiting the pulse width of the speed control pulse signal output from the pulse width modulation circuit.

According to a fourth aspect of the present invention, in order to solve the above-mentioned problems, in the first to third aspects of the present invention, a time constant circuit for gradually changing a motor start signal given by a binary voltage change; A logical product circuit for calculating a logical product of a signal obtained by pulse width modulation of the output from the time constant circuit and a speed control pulse signal obtained by pulse width modulating the speed control voltage signal output from the speed control circuit; A soft start circuit for gradually increasing the motor drive current by gradually changing the pulse width.

According to a fifth aspect of the present invention, in order to solve the above-mentioned problems, the driving device according to the first to fourth aspects is configured to be integrated with or substantially integrated with a motor. First, the operation of the first aspect will be described.
Conventionally, a current-driven bipolar transistor has a low switching speed, and particularly when turned off, a delay due to accumulation of charges is large. This delay tends to increase as the electric current increases due to the accumulation of electric charges due to the accumulation of electric charges. For this reason, bipolar transistors are not well suited for high current, high speed switching. On the other hand, when the switching element for energizing the driving coil of the switching circuit is configured by a switching element whose turn-off time is 1/50 or less of the pulse width modulation cycle, the switching speed is about 10 times or more that of the bipolar transistor. Therefore, it is suitable for high-current high-speed switching. That is, when this switching element is used, the loss of the switching element can be reduced, so that the efficiency can be improved.
However, when a high-frequency switching operation is performed on the current of the drive coil formed by the inductance element, the back electromotive voltage generated when the current is off increases.
As can be seen from the above equation (1), the larger the switching speed is, the larger the value becomes. Therefore, a reverse current flows to the power supply side through a diode provided to protect the switching element, which causes a problem that the drive device does not operate normally.

Therefore, in the first aspect of the present invention, charging and discharging are repeated between the drive power supply of the drive coil and the ground (GND) in a pulse modulation cycle, and a reverse current flows in the drive power supply in the modulation cycle. To connect a capacitor to prevent
The capacitor can repeatedly function as a regulating tank by repeatedly discharging and charging with respect to the high frequency switching of the driving coil current. For this reason, the capacitor repeatedly discharges and charges the high frequency switching of the driving coil current to function as a regulating tank, thereby smoothing the high frequency switched motor driving current.
Since it is possible to prevent the current from flowing to the power supply side without converting to a direct current, the drive device can be operated normally to improve its reliability, and no new choke coil, capacitor and diode are provided. Therefore, it is possible to reduce the size and cost of the driving device. Further, since the drive coil energizing switching element is configured to have a turn-off time of 1/50 or less of the pulse width modulation cycle,
Efficiency can be increased by suppressing the loss of the switching element.

Next, the operation of the present invention will be described. The modulation frequency is a human audible frequency band (20 Hz to
If the frequency is at 20 KHz), noise is generated, and the higher the modulation frequency, the more easily the back electromotive voltage V and the disturbance electromagnetic wave are generated. Therefore, in the invention according to claim 2, since the modulation frequency of the pulse width modulation circuit is set to approximately 20 kHz, the generation of the back electromotive voltage V from the drive coil, the generation of the electromagnetic interference wave, and the generation of the beat noise are suppressed. Can be.

Next, the operation of the present invention will be described. If the resistance of the drive coil of the motor is small, a large current flows at the time of startup, and the drive coil and the switching element may be broken, which is not preferable. Also, the current flowing through the high ripple current type capacitor that prevents reverse current is proportional to the drive current, and the allowable ripple current of the capacitor is proportional to the capacitor capacity (size). Since a large capacitor is required, the size of the circuit board is increased by the size of the large capacitor, and the cost is undesirably increased.

Therefore, according to the present invention, the motor drive current detection voltage is compared with the current limit reference voltage, and when the motor drive current detection voltage is higher than the current limit reference voltage, the output from the speed control circuit is output. Since the motor drive current is limited by disabling the speed control voltage signal and limiting the pulse width of the speed control pulse signal output from the pulse width modulation circuit, the motor drive current can be limited. Even if the resistance of the drive coil of the motor is reduced, it is possible to prevent the drive coil and the switching element from being damaged at startup, and to prevent the reverse flow without providing a large capacitor. Can be reduced. Therefore, the size and cost of the circuit board can be further reduced.

Next, the operation of the present invention will be described. Normally, the start signal of the motor is given by a binary voltage change. However, the speed control pulse signal immediately after the start causes the motor to operate at full speed with the maximum pulse width, and the current detection is delayed. Does not work, and a large current may flow to break the drive coil and the switching element, which is not preferable.

Therefore, according to the present invention, a time constant circuit for gradually changing a motor start signal given by a binary voltage change, a signal obtained by pulse-width-modulating an output from the time constant circuit, and An AND circuit that calculates the logical product of the speed control pulse signals obtained by pulse-width-modulating the speed control voltage signal output from the speed control circuit, and gradually increasing the motor drive current by gradually changing the pulse width immediately after startup. To have a soft-start circuit,
Since the pulse width immediately after startup is gradually changed and the motor drive current can be gradually increased, it is possible to make it difficult for a large current to flow through the drive coil and the switching element.
It is possible to prevent the drive coil and the switching element from being broken by a large current.

According to the fifth aspect of the present invention, the first to fourth aspects are provided.
Since the driving device is integrally or substantially integrally formed with the motor, the current supply wiring to the driving coil can be minimized, so that the generation of the electromagnetic interference caused by the high-frequency high-current switching can be suppressed.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing a configuration of a DC brushless motor driving device according to a first embodiment of the present invention (claims 1 and 2). The illustrated example is a case where the present invention is applied to a three-phase brushless motor. As shown in FIG. 1, a drive device for a DC brushless motor according to the present invention includes a speed control circuit 1 that compares a target speed signal 1a of a motor with a rotation speed signal 1b of a rotor and outputs a speed control voltage signal 1c; The speed control voltage signal 1c output from the speed control circuit 1 is
A pulse width modulation circuit 2 that converts the pulse width into a pulse width corresponding to the speed control voltage signal 1c and outputs a speed control pulse signal 2a, and energization that switches energization of a drive coil of the motor 5 by a position detection signal 3a output from the motor 5. Switching signal 3
b, and the energization switching signal 3b output from the energization switching circuit 3 and the speed control pulse signal 2a output from the pulse width modulation circuit 2 so that the energization of the drive coil is controlled by the pulse width modulation circuit. And a switching circuit 4 which operates with an output pulse width of 2.

FIG. 2 is a block diagram showing the configuration of the speed control circuit 1 shown in FIG.
It is a speed-phase control circuit composed of two loops of speed and phase. As shown in FIG. 2, a target speed signal 1a which is a highly accurate reference clock signal generated by a crystal oscillation line or the like.
The rotation speed signal 1b of the rotor, which is obtained by amplifying and waveform-shaping the output of the frequency generator and the Hall element signal in proportion to the rotation speed, is input to the frequency comparison circuit 11 and the phase comparison circuit 12. Each of the comparison circuits 11 and 12 compares the frequency and the phase of the target speed signal 1a and the rotation speed signal 1b, and outputs error signals 1d and 1e with respect to the target speed. The error signals 1d and 1e of the comparison circuits 11 and 12 are added to the addition circuit 13
After that, the speed control voltage signal 1c is output after being reduced-compensated by the smoothing circuit 14 and the phase compensation circuit 15.

FIG. 3 is a block diagram showing the configuration of the pulse width modulation circuit 2 shown in FIG. As shown in FIG. 3, the speed control voltage signal 1c is a triangular wave signal 21 of the oscillation circuit 21.
is compared with a by the comparison circuit 22 and modulated into a pulse waveform. At this time, the oscillation frequency of the oscillation circuit 21 becomes the modulation frequency, and this modulation frequency has a shorter cycle than the cycle of the position detection signal.

FIG. 4 is a block diagram showing the configuration of the power supply switching circuit 3 shown in FIG. As shown in FIG. 4, a position detection circuit 31 for a three-phase DC brushless motor includes a position detection signal 3 from a Hall element or the like arranged in the motor 5.
is input, and the energization switching signal 3 b generated by the logic circuit 32 is output to the switching circuit 4. next,
5 is a circuit diagram showing a configuration of the switching circuit 4 shown in FIG. 1, and FIG. 6 is a circuit diagram showing a configuration of a switching element for energizing a driving coil of the switching circuit 5 shown in FIG. FIG. 5 shows a three-phase full-wave drive type switching circuit. Here, the switching element 41 for energizing the drive coil selected by the energization switching signal 3b is turned on.
Since the speed control pulse signal 2a is input to all the inputs of the drive coil energizing switching element 41, the drive coil 51 is energized with the pulse width of the speed control pulse signal 2a. 5 and 6, reference numeral 42 denotes a diode, and reference numerals 52 to 55 denote a power supply, a current detection element, a ground,
It is a capacitor.

Next, FIG. 7 is a diagram showing a switching waveform of the bipolar transistor, and FIG. 8 is a diagram showing a comparison of switching time between the bipolar transistor and the MOSFET. As can be seen from FIGS. 7 and 8, the switching of the current-driven bipolar transistor is slow, and particularly when the transistor is turned off, the delay due to charge accumulation becomes large. The delay due to charge accumulation tends to increase as the amount of charge accumulation increases and the current increases, causing heat generation of the element, leading to a reduction in efficiency. For this reason, bipolar transistors are not well suited for high current, high speed switching. On the other hand, a voltage-driven MOSFET has a switching speed that is about 10 times or more that of a bipolar transistor, and is suitable for high-speed switching of a large current. Therefore, MOSF
When ET is used, the loss of the switching element can be reduced, so that the efficiency can be increased. Therefore, in the present embodiment, for example, a MOSFET is used as the switching element whose turn-off time is 1/50 or less of the pulse width modulation cycle.

However, when the current of the drive coil, which is an inductance element, is subjected to a high-frequency switching operation,
The back electromotive voltage V generated when the switch is off increases. The back electromotive voltage V increases as the switching speed increases, as shown in the above-described equation (1). As a result, the reverse current flows through the diode 42 for protecting the switching element 41 to drive. There is a problem that the current flows to the power supply 52 side and the drive device does not operate normally.

On the other hand, this embodiment (described in claim 1)
Then, a high ripple current type capacitor 55 for preventing the reverse current from flowing to the drive power supply in the modulation cycle is connected between the drive power supply 52 of the drive coil and the ground 54 by repeating charge and discharge in the pulse modulation cycle. With this configuration, the capacitor 55 can repeatedly function as an adjustment tank by repeatedly discharging and charging in response to high-frequency switching of the drive coil current. Therefore, the capacitor 55 repeatedly discharges and charges the reverse current against the high frequency switching of the drive coil current to function as an adjustment tank, thereby smoothing and DC converting the high frequency switched motor drive power supply 52. And it can be prevented from flowing to the power supply 52 side, so that the drive device can operate normally and its reliability can be improved, and it is not necessary to newly provide a choke coil, a capacitor, a diode, and the like. Therefore, the size and cost of the driving device can be reduced. Furthermore, since the switching element 41 for energizing the drive coil is constituted by a MOSFET including a switching element whose turn-off time is 1/50 or less of the pulse width modulation period, the loss of the switching element can be suppressed and the efficiency can be increased.

When the modulation frequency is in the human audible frequency band (20 Hz to 20 kHz), noise occurs, and as the modulation frequency increases, the back electromotive voltage V and obstacle electromagnetic waves tend to be generated, which is not preferable. Thus, in the present embodiment (claim 2), the modulation frequency of the pulse width modulation circuit 2 is set to approximately 20 kHz. Therefore, it is possible to suppress the back electromotive voltage V from the drive coil 51, the generation of the obstructive electromagnetic wave, and the generation of the beat noise.

(Second Embodiment) If the resistance of the drive coil of the motor 5 is small, a large current flows at the time of startup, and the drive coil 51 and the switching element 44 may be broken, which is not preferable. The current flowing through the high ripple current type capacitor 55 for preventing the reverse current is proportional to the drive current, and the allowable ripple current of the capacitor 55 is
Since it is proportional to the capacitance (size) of the capacitor, when the drive current increases, a larger capacitor 55 is required. Therefore, the circuit board becomes large in size corresponding to the large capacitor, and the cost increases, which is not preferable.

FIG. 9 is a block diagram showing a configuration of a motor drive current detection circuit and a current limit circuit of a DC brushless motor drive device according to a second embodiment of the present invention. First,
The motor drive current detection voltage signal 7a detected by the DC detection resistor of the current detection circuit 71 and smoothed by the smoothing circuit 72 is
The current limit reference voltage 7b is compared with the comparison circuit 73. When the motor drive current detection voltage 7a becomes higher than the current limit reference voltage 7b, the speed limit voltage signal 1c is invalidated and the pulse width of the speed limit pulse signal 2a is reduced. The limitation limits the motor drive current.

As described above, in this embodiment (claim 3), the motor drive current detection voltage is compared with the current limit reference voltage, and if the motor drive current detection voltage is higher than the current limit reference voltage, the speed is reduced. The motor drive current is limited by disabling the speed control voltage signal output from the control circuit 1 and limiting the motor drive current by limiting the pulse width of the speed control pulse signal output from the pulse width modulation circuit 2. can do. For this reason, even if the resistance of the drive coil 51 of the motor 5 becomes small, it is possible to prevent the drive coil 51 and the switching element 41 from being destroyed at the time of starting, and to prevent the reverse current without providing a large capacitor. Current type capacitor 55
Can be reduced in capacitance. Therefore, the size and cost of the circuit board can be further reduced.

(Third Embodiment) Normally, the motor start signal is given by a binary voltage change, but the speed control pulse signal 2a immediately after the start is used to drive the motor at full speed with the maximum pulse width. Since the delay occurs, the comparison circuit 73 of the current control circuit 1 does not work, and a large current flows, which may destroy the drive coil 51 and the switching element 44, which is not preferable.

FIG. 10 is a block diagram showing a configuration of a time constant circuit, a logical product circuit, and a soft start circuit of a DC brushless motor driving apparatus according to a third embodiment of the present invention.
1 is a time chart at the time of activation of the drive device of the DC brushless motor shown in FIG. A motor start signal 8a given by a binary voltage change is generated by a time constant circuit 81.
Gradually rise or fall. At this time, the output 8b of the constant circuit 81 is compared with the triangular wave signal 21a of the oscillation circuit 21 of the pulse width modulation circuit 2 by the comparison circuit 82, and the pulse wave 8c
Is modulated. The logical product output 8d of the pulse wave 8c and the speed control pulse signal 2a is newly added to the speed control pulse signal 2a.
By doing so, it is possible to perform a soft start in which the pulse width immediately after startup is gradually changed to gradually increase the motor drive current. With this soft start circuit,
The drive coil 51 and the switching element 41 can be prevented from being broken.

As described above, in the present embodiment (claim 4), the time constant circuit 81 for gradually changing the motor start signal 89 given by the binary voltage change, and the output from the time constant circuit 81 is pulsed. An AND circuit 83 for calculating the logical product of the width-modulated signal and the speed control pulse signal obtained by pulse-width-modulating the speed control voltage signal output from the speed control circuit 1, and gradually changing the pulse width immediately after the start-up Since the configuration is such that a soft start circuit that gradually increases the motor drive current is provided, the pulse width immediately after startup is gradually changed, and the motor drive current can be gradually increased. Element 41
It is possible to make it difficult for a large current to flow, and it is possible to prevent the driving coil 51 and the switching element 41 from becoming large current from being destroyed.

(Fourth Embodiment) FIG. 12 is a sectional view showing the structure of a DC brushless motor according to a fourth embodiment of the present invention. In the illustrated example, an example is shown in which the drive circuits and the brushless motors of the above embodiments are provided integrally with a polygon scanner. In FIG. 12, reference numeral 110 denotes a housing.
11 are vertically fitted and fixed. This fixed shaft 111
A radial bearing surface 112 (dynamic pressure air bearing) is provided on the outer periphery of the bearing, and a pair of herringbone grooves 113 and 114 for generating dynamic pressure are formed on the radial bearing surface 112 at regular intervals in the circumferential direction. . Also, the radial bearing surface 11
2 is opposed to the inner peripheral surface of the cylindrical rotating shaft 115, and the inner peripheral surface of the radial bearing surface 112 is separated from the inner peripheral surface by a predetermined distance, so that the rotating shaft 115 can rotate with respect to the fixed shaft 111. I have. A mirror receiving flange 116 is formed on the upper portion of the rotating shaft 115, and a mirror retainer 117 is provided.
And a polygon mirror 118 are attached. The mirror retainer 117 holds a magnet 121 constituting an axial magnetic bearing 119 at the center thereof.
The axial bearing 119 includes three magnets 120, 121, and 122 that repel each other on the axis of the fixed shaft 111, and the magnet 120 is mounted on the upper case 123 above the magnet 121, and the magnet 122 is fixed to the fixed shaft 1.
11, the rotation shaft 115,
The rotating body including the mirror retainer 117, the polygon mirror 118, and the magnet 121 is urged to float upward from the fixed shaft 111, and is supported in a non-contact manner. On the other hand, reference numeral 124 denotes an axial gap type face-to-face brushless motor for driving the polygon mirror 118. The motor 124 includes a rotor magnet assembly 125 fixed to the rotating shaft 115, a drive coil 51 opposed to the lower surface thereof, and spaced apart from the rotor magnet assembly 125 by a predetermined distance in the axial direction. The rotor magnet assembly 125 is a motor component in which a field magnet 125a is integrally mounted on the rotating shaft 115 by a yoke 125b. The drive coil 51 is mounted on a coil board 126 of the drive device, and the coil board 126 is attached to the housing 110 via a wiring 127.

As described above, in this embodiment (Claim 5), since the drive devices of the first to third embodiments are integrally or substantially integrally formed with the motor, the current supply wiring to the drive coil 51 is provided. Can be minimized, so that the generation of a disturbance electromagnetic wave due to high-current high-frequency switching can be suppressed.

[0035]

According to the present invention, it is possible to prevent a reverse current from flowing to the power supply side without smoothing and DC-converting a high-frequency switched motor drive current. This eliminates the need for providing a diode, and has the effect that the drive device can be reduced in size, reduced in cost, and stabilized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a drive device of a DC brushless motor according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a speed control circuit shown in FIG.

FIG. 3 is a block diagram showing a configuration of a pulse width modulation circuit shown in FIG.

FIG. 4 is a block diagram showing a configuration of an energization switching circuit shown in FIG. 1;

FIG. 5 is a circuit diagram showing a configuration of a switching circuit shown in FIG. 1;

FIG. 6 is a circuit diagram showing a configuration of a switching element of the switching circuit shown in FIG.

FIG. 7 is a diagram showing switching waveforms of a bipolar transistor.

FIG. 8 is a diagram showing a comparison of switching time between a bipolar transistor and a MOSFET.

FIG. 9 is a block diagram showing a configuration of a motor drive current detection circuit and a current limit circuit of a DC brushless motor drive device according to a second embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of a time constant circuit, a logical product circuit, and a soft start circuit of a DC brushless motor driving device according to a third embodiment of the present invention.

11 is a time chart when the motor of the drive device for the DC brushless motor shown in FIG. 10 is started.

FIG. 12 is a cross-sectional view illustrating a structure of a DC brushless motor according to a fourth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 speed control circuit 1a target speed signal 1b rotation speed signal 1c speed control voltage signal 1d, 1e error signal 2 pulse width modulation circuit 2a speed control pulse signal 3 conduction switching circuit 3a conduction switching signal 4 switching circuit 5 motor 7a motor drive current detection Voltage signal 7b Current limit reference voltage signal 8a Motor start signal 8b Output 8c Pulse wave 8d Logical product output 11 Frequency comparison circuit 12 Phase comparison circuit 13 Addition circuit 14 Smoothing circuit 15 Phase compensation circuit 21 Oscillation circuit 21a Triangular wave signal 22 Comparison circuit 31 Position Detection circuit 32 Logic circuit 41 Switching element 42 Diode 44 Fixed resistor 51 Drive coil 52 Drive power supply 53 Current detection element 54 Grounding 55 Capacitor 71 Current detection circuit 72 Smoothing circuit 73 Comparison circuit 81 Time constant circuit 82 Comparison circuit 8 AND circuit 110 housing 124 brushless motor 126 coil substrate 127 wiring

Claims (5)

[Claims] A speed control circuit for comparing a target speed signal with a rotor speed signal to output a speed control voltage signal;
A pulse width modulation circuit that converts a speed control voltage signal output from the speed control circuit into a pulse width corresponding to the speed control voltage signal and outputs a speed control pulse signal; and a driving coil that is driven by a position detection signal output from the motor. An energization switching circuit that outputs an energization switching signal for switching the energization of the motor; and a combination of the energization switching signal output from the energization switching circuit and the speed control pulse signal output from the pulse width modulation circuit, to energize the drive coil by the pulse. In a DC brushless motor driving device having a switching circuit that performs switching with an output pulse width of a width modulation circuit, a switching element for energizing a driving coil of the switching circuit is a switching element whose turn-off time is 1/50 or less of a pulse width modulation cycle. Configure and charge and discharge between the drive power supply of the drive coil and ground with pulse modulation cycle Repeatedly driving device for a DC brushless motor, characterized in that formed by connecting a capacitor to prevent the reverse current flows through a modulation cycle to the driving power source. 2. The DC brushless motor driving device according to claim 1, wherein a modulation frequency of the pulse width modulation circuit is approximately 20 kHz. A motor drive current detection circuit for detecting a drive current of the motor and outputting a motor drive current detection voltage;
The motor drive current detection voltage output from the motor drive current detection circuit is compared with the current limit reference voltage. If the motor drive current detection voltage is higher than the current limit reference voltage, the speed control output from the speed control circuit is output. 3. A current limiting circuit for limiting a motor drive current by invalidating a voltage signal and limiting a pulse width of a speed control pulse signal output from the pulse width modulation circuit. DC brushless motor drive device. 4. A time constant circuit for gradually changing a motor start signal given by a binary voltage change, a signal obtained by pulse width modulation of an output from the time constant circuit, and a speed control output from the speed control circuit. A logical product circuit for calculating a logical product of a voltage signal and a speed control pulse signal obtained by pulse width modulation, and a soft start circuit for gradually increasing a motor drive current by gradually changing a pulse width immediately after startup. The driving device for a DC brushless motor according to claim 3, wherein 5. A direct current brushless motor characterized in that the driving device according to claim 1 is formed integrally or substantially integrally with a motor.