JP2007166839A - Motor drive circuit, motor drive method, and cooling device using the motor drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive circuit capable of flexibly executing torque control, when a motor is started. <P>SOLUTION: The motor drive circuit 100 generates a pulse-modulated drive signal SD for controlling the energizing period of a coil in a fan motor 120 as a drive target and controls the rotational frequency. A time-constant circuit 10 generates a first start-control voltage Vstrt1, whose voltage value changes together with the lapse of time, when the fan motor 120 is started. An amplifier 20 inversely amplifies the first start-control voltage Vstrt1, outputted from the time constant circuit 10 so as to output it as a second start-control voltage Vstrt2. A drive signal generating circuit 30 combines a rotation control voltage Vcnt, set corresponding to the torque target value of the motor, with the first/second start-control voltages Vstrt1, Vstrt2 so as to generate a pulse-modulated drive signal SD, having duty ratio that corresponds to one among the three voltages. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a motor drive technique, and more particularly to control at the time of startup.

  In order to rotate a single-phase motor or a multi-phase motor with a desired torque, a technique of widely controlling the energization period of the motor coil by a pulse signal such as a pulse width modulation signal is widely used.

  When driving the stopped motor is started, if a switching voltage having a pulse width corresponding to the target torque is suddenly applied to the motor coil, a current flows suddenly through the motor coil. When the motor is started, particularly when its rotational speed is close to 0, since there is no power generation function, the current flowing through the coil is a value obtained by dividing the applied voltage by the winding resistance. The resistance value of the coil is designed to be very low in order to reduce power loss, and the coil current may exceed the rating of the drive circuit and the coil itself, which may affect the reliability of the circuit.

  Further, the counter electromotive voltage generated in the coil is proportional to the time change rate of the current flowing in the coil. Therefore, as described above, when the coil current rapidly increases, a very large counter electromotive voltage is generated, which may exceed the rating of the drive circuit.

  For this reason, immediately after the start of the motor start, soft start control for gradually increasing the current flowing through the coil is performed (see, for example, Patent Documents 1 and 2). In the soft start control described in Patent Document 1, a soft start voltage whose voltage value gradually increases with time is generated, and this soft start voltage is compared with a triangular voltage or a sawtooth waveform, and the duty ratio is moderate. A pulse modulation signal that increases rapidly is generated, and the coil energization time is gradually increased to perform soft start.

JP-A-7-95792 Japanese Patent Laid-Open No. 2001-45790

  However, with soft start control as described in the patent literature, the energization time of the motor can only be increased monotonously.

  The present invention has been made in view of such problems, and an object thereof is to provide a motor drive circuit capable of realizing soft start control with a high degree of freedom.

  One embodiment of the present invention relates to a motor drive circuit that generates a pulse-modulated drive signal that defines an energization time of a coil of a motor to be driven and controls the number of rotations of the motor. The motor drive circuit amplifies the first start control voltage output from the time constant circuit that generates a first start control voltage whose voltage value changes with time at the start of the motor, and the second start An amplifier that outputs as a control voltage and a rotation control voltage that is set according to the target value of the motor torque are combined with the first and second start control voltages, and has a duty ratio according to one of the three voltages. A drive signal generation circuit for generating a pulse-modulated drive signal.

  According to this aspect, the duty ratio of various pulse-modulated drive signals can be set variously by synthesizing the three voltages, the first control voltage, the second control voltage, and the rotation control voltage. The degree of freedom of rotation control at the time can be improved. In the present specification, “amplification” includes attenuation with a gain lower than 1, and “amplifier” includes an attenuator.

  The amplifier may be a variable gain amplifier. The amplifier may be an inverting amplifier that inverts and amplifies the first start control voltage, or may be a non-inverting amplifier that non-inverts and amplifies the first start control voltage. By controlling the gain of the amplifier, it is possible to freely perform rotation control at the time of starting the motor.

  The drive signal generation circuit includes a pulse modulation comparator that generates a pulse modulation signal by comparing the rotation control voltage with a predetermined periodic voltage, and a first control pulse signal by comparing the first activation control voltage with the periodic voltage. A first comparator that generates a second control pulse signal by comparing the second start-up control voltage with a periodic voltage, and a pulse modulation signal that is logically related to the first and second control pulse signals. And a synthesis circuit that generates a drive signal by synthesizing by calculation.

  In the pulse modulation comparator, the first comparator, and the second comparator, a pulse modulation signal is generated using a triangular voltage or a sawtooth-shaped periodic voltage. Since the output signal of each comparator is a logic signal that takes either the high level or the low side, the duty ratio of the drive signal is set to the duty ratio of the pulse signal output from the three comparators by synthesizing by a logical operation. Can be set to either.

  The synthesis circuit includes a first logic block that performs a logical operation on the pulse modulation signal generated by the pulse modulation comparator and the second control pulse signal generated by the second comparator, and the first control pulse signal generated by the first comparator. May be included in the second logic block to be combined with the output signal of the first logic block.

  The drive signal generation circuit includes a voltage selection circuit that selects one of the three voltages based on the magnitude relationship between the rotation control voltage and the first and second control voltages, and a voltage output from the voltage selection circuit. And a pulse width modulation comparator that generates a pulse modulated drive signal by comparison with the periodic voltage.

  The motor drive circuit may be integrated on a single semiconductor substrate. “Integrated integration” includes the case where all of the circuit components are formed on a semiconductor substrate and the case where the main components of the circuit are integrated. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the motor drive circuit as one LSI, the circuit area can be reduced.

  Another aspect of the present invention is a cooling device. This apparatus includes a fan motor and a motor drive circuit that drives the fan motor.

  Yet another embodiment of the present invention is an electronic device. This electronic apparatus includes the above-described cooling device. According to this aspect, the object to be cooled inside the electronic device can be suitably cooled according to the temperature.

  Yet another embodiment of the present invention is a motor driving method. This method is a motor driving method that generates a pulse-modulated drive signal that defines the energization time of a coil of a motor to be driven and controls the rotation speed of the motor. A step of generating a first startup control voltage that varies, a step of amplifying the first startup control voltage and outputting as a second startup control voltage, and a rotation control voltage set in accordance with a target value of the torque of the motor, Synthesizing with the first and second start-up control voltages, and generating a pulse-modulated drive signal having a duty ratio corresponding to one of the three voltages.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the present invention, soft start control with a high degree of freedom can be realized.

(First embodiment)
Embodiments of the present invention relate to a motor drive circuit used in a cooling device for cooling an electronic computer such as a desktop computer or a notebook personal computer or a workstation, or an electronic device such as a refrigerator.

  FIG. 1 is a circuit diagram showing a configuration of a cooling device 200 according to the first embodiment of the present invention. The cooling device 200 includes a motor drive circuit 100, an H bridge circuit 110, and a fan motor 120.

  The fan motor 120 is a single-phase full-wave motor in the present embodiment, and is disposed to face a cooling object (not shown). The fan motor 120 is controlled in rotation by controlling the coil current, that is, the energized state by the switching signals Vsw1 and Vsw2 generated by the motor driving circuit 100 and the H bridge circuit 110.

  The H bridge circuit 110 includes a first high side transistor MH1, a second high side transistor MH2, a first low side transistor ML1, and a second low side transistor ML2. The H bridge circuit 110 corresponds to an output stage for driving the fan motor 120. The first high-side transistor MH1 and the first low-side transistor ML1 are connected in series between the power supply voltage terminal 112 and the ground terminal GND, and constitute a transistor pair (hereinafter referred to as a first transistor pair). Similarly, the second high side transistor MH2 and the second low side transistor ML2 also constitute a transistor pair (hereinafter referred to as a second transistor pair). In the present embodiment, the first high-side transistor MH1 and the second high-side transistor MH2 are P-channel MOSFETs. The first low side transistor ML1 and the second low side transistor ML2 are N-channel MOSFETs.

  The first high side transistor MH1 and the second high side transistor MH2 constituting the first transistor pair are alternately turned on and off alternately. On / off of the first high-side transistor MH1 and the first low-side transistor ML1 is controlled by a first high-side drive signal SDH1 and a first low-side drive signal SDL1 that are applied to the gates of the transistors.

  The voltage at the connection point of the first high-side transistor MH1 and the first low-side transistor ML1 is applied to one end of the coil of the fan motor 120 as the first switching signal Vsw1. When the first high-side transistor MH1 is on, the first switching signal Vsw1 becomes the power supply voltage Vdd, and when the first low-side transistor ML1 is on, the first switching signal Vsw1 becomes the ground potential (0V).

  On / off of the second high-side transistor MH2 and the second low-side transistor ML2 constituting the second transistor pair is controlled by a second high-side drive signal SDH2 and a second low-side drive signal SDL2 applied to the gates of the transistors. The voltage at the connection point of the two transistors is applied to the other end of the coil of the fan motor 120 as the second switching signal Vsw2. The second switching signal Vsw2 is controlled to have a phase opposite to that of the first switching signal Vsw1.

  Note that the four transistors constituting the H-bridge circuit 110 may be integrated and incorporated in the motor drive circuit 100. Further, a diode for preventing reverse connection may be provided in the sources of the first high-side transistor MH1 and the second high-side transistor MH2 and the power source (not shown) that outputs the power supply voltage Vdd.

  A rotation control voltage Vcnt that is set according to a target torque value of the fan motor 120 is input to the motor drive circuit 100 from the outside. The rotation control voltage Vcnt may be generated inside the motor drive circuit 100. The motor drive circuit 100 generates pulse-modulated drive signals SDH1, SHL1, SDH2, and SDL2 that define the energization time of the coil of the fan motor 120 to be driven based on the rotation control voltage Vcnt, and outputs the output signal H. Output to the bridge circuit 110. The motor drive circuit 100 includes a time constant circuit 10, an amplifier 20, and a drive signal generation circuit 30, and is a functional IC integrated on a single semiconductor substrate.

  The time constant circuit 10 generates a first activation control voltage Vstrt1 whose voltage value changes with time when the fan motor 120 is activated. The time constant circuit 10 can be used in various configurations such as a type in which a capacitor is charged with a constant current or a type in which a digital signal having a ramp waveform is converted into a digital signal, and the circuit configuration is particularly limited. There is no.

  The amplifier 20 amplifies the first start control voltage Vstrt1 generated by the time constant circuit 10 and outputs it as the second start control voltage Vstrt2. In the present embodiment, the amplifier 20 is an inverting amplifier. The amplifier 20 includes an operational amplifier 22, a first resistor R1, and a second resistor R2. One end of the first resistor R1 is connected to the inverting input terminal of the operational amplifier 22, and the first start control voltage Vstrt1 is applied to the other end. The second resistor R <b> 2 has one end connected to the output terminal of the operational amplifier 22 and the other end connected to the inverting input terminal of the operational amplifier 22. A fixed voltage is applied to the non-inverting input terminal of the operational amplifier 22.

  In the present embodiment, the first activation control voltage Vstrt1 is a voltage that gradually increases with time at the start of driving of the motor. Therefore, the second activation control voltage Vstrt2 gradually decreases with time.

  In the amplifier 20, it is desirable that at least one of the first resistor R1 and the second resistor R2 be a variable resistor and the amplifier 20 be a variable gain amplifier. In this case, it is desirable that the gain of the amplifier 20 can be controlled by a control circuit (not shown).

  The drive signal generation circuit 30 combines the rotation control voltage Vcnt with the first start control voltage Vstrt1 and the second start control voltage Vstrt2, and generates a pulse-modulated signal having a duty ratio corresponding to one of the three voltages. To do. Hereinafter, a specific configuration example of the drive signal generation circuit 30 will be described.

  The drive signal generation circuit 30 includes a comparator 32, a drive signal generation unit 34, a synthesis circuit 50, a pulse modulation (Pulse Width Modulation) comparator (hereinafter referred to as a PWM comparator) 40, a first comparator 42, a second comparator 44, and an oscillator 46. Including.

  The comparator 32 compares Hall signals H + and H− output from a Hall element (not shown), and generates a frequency generation signal (hereinafter referred to as an FG signal) whose high level and low level change according to the phase of the rotor of the fan motor 120. Generate.

  The drive signal generator 34 generates drive signals SDH1, SDH2, SDL1, and SDL2 based on the FG signal. In the present embodiment, the motor drive circuit 100 controls the energization period of the fan motor 120 by a pulse width modulation method. In the motor drive control by this pulse width modulation method, in the present embodiment, the low side transistors ML1 and ML2 are turned on and off alternately according to the phase switching of the fan motor 120, and the high side transistors MH1 and MH2 are pulse width modulated. It is assumed that switching control is performed based on the received signal. However, the present invention is not limited to this, and the low-side transistor may be driven by a pulse-width modulated signal, or the high-side and low-side transistors may be driven by a pulse-width modulated signal.

  For example, when the FG signal is at a high level, the drive signal generation unit 34 turns on the first high-side transistor MH1 and the second low-side transistor ML2, and turns off the second high-side transistor MH2 and the first low-side transistor ML1. A drive signal SD is generated. Here, the transition of the signal level is delayed so that the first high-side transistor MH1 and the first low-side transistor ML1 are not turned on at the same time, or the second high-side transistor MH2 and the second low-side transistor ML2 are not turned on at the same time. It is desirable to provide it.

  The drive signals SDL1 and SDL2 output from the drive signal generator 34 are output to the first low side transistor ML1 and the second low side transistor ML2 on the low side, respectively. As a result, the first low-side transistor ML1 and the second low-side transistor ML2 are alternately turned on and off according to the high level and low level of the FG signal.

  On the other hand, the drive signals SDH 1 and SDH 2 output from the drive signal generation unit 34 are output to the synthesis circuit 50. The synthesizing circuit 50 performs pulse width modulation on the drive signals SDH1 and SDH2 generated by the drive signal generation unit 34 and outputs them to the first high-side transistor MH1 and the second high-side transistor MH2. The synthesis circuit 50 will be described later. Next, pulse width modulation will be described.

  The oscillator 46 generates a triangular or sawtooth periodic voltage Vsaw having a predetermined frequency. The PWM comparator 40 generates a pulse modulation signal (hereinafter referred to as PWM signal Vpwm) by comparing the rotation control voltage Vcnt with the periodic voltage Vosc. In the present embodiment, the rotation control voltage Vcnt is input to the non-inverting input terminal of the PWM comparator 40, and the periodic voltage Vosc is input to the inverting input terminal. As a result, the PWM signal Vpwm is at a high level when Vcnt> Vosc, and is at a low level when Vcnt <Vosc. The high level time of the PWM signal Vpwm becomes longer as the control voltage Vcnt becomes higher.

  The first comparator 42 generates the first control pulse signal Vp1 by comparing the first activation control voltage Vstrt1 with the periodic voltage Vosc. In the present embodiment, the first activation control voltage Vstrt1 is input to the non-inverting input terminal of the first comparator 42, and the periodic voltage Vosc is input to the inverting input terminal. As a result, the first control pulse signal Vp1 is at a high level when Vstrt1> Vosc, and is at a low level when Vstrt1 <Vosc. The high level time of the first control pulse signal Vp1 becomes longer as the first activation control voltage Vstrt1 becomes higher.

  On the other hand, the second comparator 44 generates the second control pulse signal Vp2 by comparing the second activation control voltage Vstrt2 with the periodic voltage Vosc. In the present embodiment, the second activation control voltage Vstrt2 is input to the non-inverting input terminal of the second comparator 44, and the periodic voltage Vosc is input to the inverting input terminal. As a result, the second control pulse signal Vp2 is at a high level when Vstrt2> Vosc, and is at a low level when Vstrt2 <Vosc. The high level time of the second control pulse signal Vp2 becomes longer as the second activation control voltage Vstrt2 becomes higher.

  In the present embodiment, the first activation control voltage Vstrt1 gradually increases with time and the second activation control voltage Vstrt2 gradually decreases with time at the start of driving of the motor. Therefore, the first control pulse signal Vp1 , The duty ratio of the second control pulse signal Vp2 decreases with time.

  In the present embodiment, the PWM signal Vpwm, the first comparator 42, and the second comparator 44 have a high level corresponding to the on state of the low side transistor constituting the H bridge circuit 110, and a low level corresponding to the off state of the low side transistor. It shall be.

  In the PWM comparator 40, the first comparator 42, and the second comparator 44, which signal is input to the inverting input terminal and the non-inverting input terminal is a design matter, and is not limited to this embodiment.

  The PWM signal Vpwm, the first control pulse signal Vp1, and the second control pulse signal Vp2 output from the PWM comparator 40, the first comparator 42, and the second comparator 44, respectively, are input to the synthesis circuit 50. Hereinafter, the configuration and operation of the synthesis circuit 50 will be described.

  FIG. 2 is a circuit diagram illustrating a configuration example of the synthesis circuit 50. In the present embodiment, the synthesis circuit 50 includes a first logic block 52, a second logic block 54, a third logic block 56, and a fourth logic block 58.

  In the present embodiment, the first logic block 52 performs a logical operation on the PWM signal Vpwm generated by the PWM comparator 40 and the second control pulse signal Vp2 generated by the second comparator 44. The first logic block 52 includes an OR gate, and outputs a logical sum of the PWM signal Vpwm and the second control pulse signal Vp2.

  The output signal S1 of the first logic block 52 is a signal giving priority to a signal having a long high level period, that is, a signal in which the torque of the fan motor 120 is set high, of the PWM signal Vpwm and the second control pulse signal Vp2. It becomes.

  The second logic block 54 combines the first control pulse signal Vp1 generated by the first comparator 42 with the output signal S1 of the first logic block 52. In the present embodiment, the second logic block 54 includes an AND gate, and outputs a logical product of the output signal S1 of the first logic block 52 and the first control pulse signal Vp1.

  The output signal S1 of the second logic block 54 is a signal in which the high-level period is short among the output signal S1 of the first logic block 52 and the second control pulse signal Vp2, that is, the torque of the fan motor 120 is set low. This signal gives priority to the signal.

  The output signal S2 of the second logic block 54 thus generated has a pulse width having a duty ratio corresponding to any one of the rotation control voltage Vcnt, the first start control voltage Vstrt1, and the second start control voltage Vstrt2. It becomes a modulated signal.

  The third logic block 56 combines the first high-side drive signal SDH1 output from the drive signal generator 34 with the output signal S2 of the second logic block 54. The third logic block 56 includes an AND gate, and outputs a logical product of the first high-side drive signal SDH1 and the output signal S2 of the second logic block 54. The output signal of the third logic block 56 is output to the gate of the first high-side transistor MH1 as a pulse width modulated drive signal SDH1 '.

  Similarly to the third logic block 56, the fourth logic block 58 includes an AND gate, and synthesizes the second high-side drive signal SDH2 output from the drive signal generator 34 with the output signal S2 of the second logic block 54. And outputs the logical product of the two signals. The output signal of the fourth logic block 58 is output to the gate of the second high side transistor MH2 as a pulse width modulated drive signal SDH2 '.

  In addition, when the size of the transistors constituting the H bridge circuit 110 is large and driving capability is required, a pre-driver circuit having sufficient driving capability is required before the H bridge circuit 110. Not shown.

  The operation of the motor drive circuit 100 configured as described above will be described. FIGS. 3A to 3D are time charts showing the operating state of the motor drive circuit 100 according to the present embodiment when the motor is started. FIG. 3A shows the rotation control voltage Vcnt, the first start control voltage Vstrt1, and the second start control voltage Vstrt2. 2B shows the duty ratio of the PWM signal Vpwm, the first control pulse signal Vp1, and the second control pulse signal Vp2. FIG. 2C shows the duty ratio of the output signal S1 of the first logic block 52. FIG. 4D shows the duty ratio of the output signal S2 of the second logic block 54.

  At time t0, the start of driving the fan motor 120 is instructed, and the time constant circuit 10 gradually increases the first activation control voltage Vstrt1. Contrary to the increase in the first activation control voltage Vstrt1, the second activation control voltage Vstrt2 output from the amplifier 20 decreases with time.

  When the first activation control voltage Vstrt1 becomes higher than the bottom level of the periodic voltage Vosc output from the oscillator 46 at time t1, the duty ratio of the first control pulse signal Vp1 starts to gradually increase. Similarly, when the second activation control voltage Vstrt2 becomes lower than the peak level of the periodic voltage Vosc, the duty ratio of the second control pulse signal Vp2 starts to decrease. The duty ratio of the PWM signal Vpwm is fixed because the rotation control voltage Vcnt is constant.

  As described above, since the output signal S1 of the first logic block 52 is the logical sum of the second control pulse signal Vp2 and the PWM signal Vpwm, the larger one of the two signals is reflected in the duty ratio. As a result, as shown in FIG. 3C, the duty ratio of the output signal S1 of the first logic block 52 is the maximum value (for example, 100%) during the period from time t0 to t1, and gradually after time t1. It goes down. After time t3 when the duty ratio of the second control pulse signal Vp2 falls below the duty ratio of the PWM signal Vpwm, the duty ratio of the output signal S1 becomes equal to the duty ratio of the PWM signal Vpwm.

  Since the output signal S2 of the second logic block 54 is a logical product of the first control pulse signal Vp1 and the output signal S1 of the first logic block 52, the smaller one of the two signals is reflected in the duty ratio. As a result, as shown in FIG. 3D, the duty ratio of the output signal S2 of the second logic block 54 is the minimum value (for example, 0%) during the period from time t0 to t1, and gradually after time t1. It goes down. After time t2 when the duty ratio of the first control pulse signal Vp1 exceeds the duty ratio of the PWM signal Vpwm, the duty ratio of the output signal S2 becomes equal to the duty ratio of the output signal S1 of the first logic block 52.

  On / off of the low-side transistors ML1 and ML2 of the H-bridge circuit 110 is PWM-controlled based on the duty ratio of the output signal S2 of the first logic block 52. As a result, according to the motor drive circuit 100 according to the present embodiment, the conduction time with respect to the coil of the fan motor 120 is set gradually longer by PWM control during the period from time t1 to time t2. Once the target value torque is exceeded, the coil conduction time is gradually shortened at time t2, and the target value torque is set at time t3.

  According to the motor drive circuit 100 according to the present embodiment, the first control pulse signal Vp1 and the second control pulse that are pulse width modulated based on the first start control voltage Vstrt1 and the second start control voltage Vstrt2 obtained by amplifying the first start control voltage Vstrt1. A signal Vp2 is generated, and these pulse signals are combined with the PWM signal Vpwm to control the motor torque. As a result, various activation controls can be performed according to the type of fan motor 120.

  For example, as shown in FIG. 3D, once the fan motor 120 is driven with a large duty ratio exceeding the target torque, and then the duty ratio is decreased, the fan motor 120 with a large friction at the time of stop is provided. It can drive suitably.

  Further, when the amplifier 20 of the motor driving circuit 100 is a variable gain amplifier, the slope of the second start control voltage Vstrt2 can be controlled, and the speed at which the duty ratio of the first control pulse signal Vp1 increases is controlled. can do.

  For example, in this embodiment, the operation when the gain of the amplifier 20 is set high is shown in FIGS. When the gain of the amplifier 20 is high, the second activation control voltage Vstrt2 decreases rapidly. As a result, the duty ratio of the second control pulse signal Vp2 also decreases more quickly than in FIG. As a result, as shown in FIG. 4D, the duty ratio of the second control pulse signal Vp2 set based on the second activation control voltage Vstrt2 is not reflected in the output signal S2 of the second logic block 54. In this case, the torque of the fan motor 120 can be gradually increased to the target torque, and an operation equivalent to a normal soft start can be executed.

  Moreover, according to the motor drive circuit 100 according to the present embodiment, the fan motor 120 can be started to rotate at full torque. In this case, for example, the first activation control voltage Vstrt1 that is the output of the time constant circuit 10 is increased at a very high speed. As a result, the duty ratio at the time of startup rises to nearly 100%, so that it starts to rotate at full torque. Thereafter, when the second activation control voltage Vstrt2 decreases, the duty ratio is gradually set lower toward the target value.

  Furthermore, according to the motor drive circuit 100 according to the present embodiment, torque control of the fan motor 120 can be suitably performed, and noise can be reduced.

(Second Embodiment)
In the first embodiment, the case where the H bridge circuit 110 is PWM driven by logically synthesizing the three signals Vpwm1, Vp1, and Vp2 that are pulse width modulation signals has been described. On the other hand, in the second embodiment, the pulse width modulation is performed after the three voltages Vcnt, the first start control voltage Vstrt1, and the second start control voltage Vstrt2 are combined.

  FIG. 5 is a circuit diagram showing a part of the configuration of the motor drive circuit 100b according to the second embodiment of the present invention. In addition, about the member which is not illustrated in FIG. 5, it can comprise similarly to FIG.

  In the present embodiment, the drive signal generation circuit 30b of the motor drive circuit 100b includes a voltage selection circuit 60 and a pulse width modulator 70. The voltage selection circuit 60 receives the rotation control voltage Vcnt, the first start control voltage Vstrt1, and the second start control voltage Vstrt2. The voltage selection circuit 60 selects any one of the three voltages based on the magnitude relationship among the rotation control voltage Vcnt, the first activation control voltage Vstrt1, and the second activation control voltage Vstrt2.

  For example, the voltage selection circuit 60 includes a maximum value circuit 62 and a minimum value circuit 64. The maximum value circuit 62 outputs the larger one of the rotation control voltage Vcnt and the second activation control voltage Vstrt2. The minimum value circuit 64 outputs the lower voltage of the output voltage V1 of the maximum value circuit 62 and the first activation control voltage Vstrt1. The output voltage V2 of the minimum value circuit 64 is output to the pulse width modulator 70. The output voltage V2 of the voltage selection circuit 60 has a voltage value corresponding to one of the three input voltages Vcnt, Vstrt1, and Vstrt2 that is selected based on the magnitude relationship.

  The pulse width modulator 70 includes an oscillator 72 and a PWM comparator 74. The oscillator 72 generates a periodic voltage Vosc. The PWM comparator 74 compares the periodic voltage Vosc with the output voltage V2 of the voltage selection circuit 60, and outputs a signal that is at a high level when V2> Vosc and at a low level when V2 <Vosc. The output voltage V3 of the pulse width modulator 70 corresponds to the signal S2 in the synthesis circuit 50 shown in FIG.

  The output voltage V3 of the pulse width modulator 70 is logically synthesized with the first high-side drive signal SDH1 and the second high-side drive signal SDH2 output from the drive signal generator 34, and the first high-side transistor MH1 and the second high-side drive signal SDH2. It is output to the side transistor MH2.

FIGS. 6A to 6C are time charts showing operation states at the start of the motor drive circuit 100 of FIG. 5 according to the second embodiment.
As shown in FIG. 5B, the output voltage V2 of the voltage selection circuit 60 has the same voltage value as the first activation control voltage Vstrt1 during the period from time t0 to time t2. Thereafter, during the period from time t2 to t3, the voltage value becomes the same as the second activation control voltage Vstrt2, and after time t3, the voltage value becomes the same as the rotation control voltage Vcnt.

  As shown in FIG. 5C, the duty ratio of the output voltage V3 of the pulse width modulator 70 gradually increases after time t1 when the voltage V2 exceeds the bottom level of the periodic voltage Vosc. Thereafter, after exceeding the duty ratio corresponding to the target torque, the duty ratio decreases during the period of time t2 to t3. After time t3, the duty ratio is set corresponding to the target torque.

  According to the motor drive circuit 100b according to the second embodiment, similarly to the motor drive circuit 100 according to the first embodiment, the gain of the amplifier 20 and the time constant of the time constant circuit 10 are set. The fan motor 120 can be driven with various duty ratios.

(Third embodiment)
FIG. 7 is a circuit diagram showing a part of the configuration of a motor drive circuit 100c according to the third embodiment. The motor drive circuit 100c according to the present embodiment further includes a second PWM comparator 48 that compares a predetermined reference voltage Vref and a periodic voltage Vosc in addition to the motor drive circuit 100 of FIG. The reference voltage Vref may be input from the outside of the motor drive circuit 100c, or may be generated inside the motor drive circuit 100, but the voltage value is preferably controllable.

  The second PWM comparator 48 compares the reference voltage Vref and the periodic voltage Vosc, and outputs a second PWM signal Vpwm2 that is at a high level when Vref> Vosc and at a low level when Vref <Vosc. The duty ratio of the second PWM signal Vpwm2 is set according to the reference voltage Vref and becomes a constant value. The second PWM signal Vpwm2 is output to the synthesis circuit 50 together with the PWM signal Vpwm1, the first control pulse signal Vp1, and the second control pulse signal Vp2.

  The synthesizing circuit 50 synthesizes the pulse modulation signal Vpwm1 with the first control pulse signal Vp1, the second control pulse signal Vp2, and the second PWM signal Vpwm2 by a logical operation, and further generates a drive signal SDH1 generated by the drive signal generation unit 34. Combined with SDH2, drive signals SDH1 'and SDH2' are output.

  The configuration of the synthesis circuit 50 may be the same as that shown in FIG. That is, the synthesis circuit 50 of FIG. 2 includes the first logic block 52 and the second logic block 54, but further includes a third logic block, and has four pulse signals Vpwm1, Vp1, Vp2, and Vpwm2. By performing logic synthesis in order, a signal having a duty ratio of any of the four pulse signals can be generated.

  FIG. 8 shows an example of duty ratio control that can be realized by the motor drive circuit 100c according to the third embodiment. In the example of FIG. 8, the period from time t0 to t1 is set to a duty ratio according to the first activation control voltage Vstrt1, and the period from time t1 to t2 is set to the duty ratio according to the reference voltage Vref. During the period of t3, the duty ratio is set according to the second activation control voltage Vstrt2, and after time t3, the duty ratio is set according to the rotation control voltage Vcnt.

  According to the present embodiment, by generating a pulse signal (Vpwm2) with a fixed duty ratio and combining it with other pulse signals, a constant torque is set before setting the target torque at the start of motor driving. Can be rotated for a certain period of time.

  Furthermore, more complex motor start control is possible depending on the setting of the reference voltage Vref, the setting of the time constant of the time constant circuit 10, the gain of the amplifier 20, and the like.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  For example, in the present embodiment, the case where one amplifier 20 is used has been described. However, more amplifiers may be provided, and the third and fourth start control voltages Vstrt may be generated to set the duty ratio. In this case, more complicated torque control is possible.

  In the embodiment, the case where the amplifier 20 is configured as an inverting amplifier has been described. However, the present invention is not limited to this, and may be configured as a non-inverting amplifier. In this case, the duty ratio of the PWM signal can be increased at a two-stage speed.

  In the motor drive circuit according to the embodiment, the case where the time constant circuit changes the first start control voltage Vstrt1 when the motor is started has been described. However, when the motor is stopped, the first start control voltage Vstrt1 is gradually decreased. May be. In this case, torque control when the motor is stopped can be flexibly performed.

  In the embodiment, the case where the motor drive circuit 100 is integrated in one LSI has been described. However, the present invention is not limited to this, and some components are provided as discrete elements or chip components outside the LSI. It may be provided or constituted by a plurality of LSIs. For example, the H bridge circuit 36 may be configured using a discrete power transistor, or may be built in the motor drive circuit 100.

  In addition, the transistor used in the embodiment may be configured by replacing the bipolar transistor and the FET with each other or by replacing the P-channel and N-channel transistors.

  In the embodiment, the case of driving a single-phase motor has been described, but the present invention is not limited to this. That is, the present invention can also be applied to a motor drive circuit that drives a three-phase motor or the like.

  In the embodiment, the motor drive circuit 100 has been described with respect to driving a fan motor. However, the motor to be driven by the motor drive circuit according to the present invention is not limited to the fan motor, and other single motors. It can be widely applied to phase and multiphase motors.

  In the circuit described in the embodiment, the setting of the high level and low level logic values of the signal is an example, and can be freely changed by appropriately inverting it with an inverter or the like. Further, replacement of the AND gate and the OR gate according to this can be easily conceived by those skilled in the art.

It is a circuit diagram which shows the structure of the cooling device which concerns on 1st Embodiment. It is a circuit diagram which shows the structural example of a synthetic | combination circuit. 3A to 3D are time charts showing operation states of the motor drive circuit of FIG. 1 when the motor is started. 4A to 4D are time charts showing an operation state when the gain of the amplifier is set high. It is a circuit diagram which shows a part of structure of the motor drive circuit which concerns on 2nd Embodiment. 6A to 6C are time charts showing operation states of the motor drive circuit of FIG. 5 when the motor is started. It is a circuit diagram which shows a part of structure of the motor drive circuit which concerns on 3rd Embodiment. It is a time chart which shows an example of duty ratio control realizable by the motor drive circuit of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Motor drive circuit, 110 H bridge circuit, 112 Power supply voltage terminal, 120 Fan motor, 200 Cooling device, 10 Time constant circuit, 20 Amplifier, 30 Drive signal generation circuit, 32 Comparator, 34 Drive signal generation part, 40 PWM comparator, 42 first comparator, 44 second comparator, 46 oscillator, 50 synthesis circuit, 52 first logic block, 54 second logic block, 56 third logic block, 58 fourth logic block, 60 voltage selection circuit, 62 maximum value circuit 64 minimum value circuit, 70 pulse width modulator, SDH1 first high side drive signal, SDH2 second high side drive signal, SDL1 first low side drive signal, SDL2 second low side drive signal, MH1 first high side Transistor, ML1 first low side transistor, MH2 second high side transistor, ML2 second low side transistor, Vsw1 first switching signal, Vsw2 second switching signal, Vstrt1 first start control voltage, Vstrt2 second start control voltage, Vp1 first Control pulse signal, Vp2 second control pulse signal.

Claims (10)

A motor drive circuit that generates a pulse-modulated drive signal that defines the energization time of a coil of a motor to be driven, and controls the rotational speed of the motor,
A time constant circuit for generating a first start control voltage whose voltage value changes with time when the motor is started;
An amplifier that amplifies the first start-up control voltage output from the time constant circuit and outputs it as a second start-up control voltage;
A pulse-modulated drive signal having a duty ratio corresponding to one of the three voltages by combining a rotation control voltage set according to a target value of the torque of the motor with the first and second start-up control voltages A drive signal generation circuit for generating
A motor drive circuit comprising:   The motor driving circuit according to claim 1, wherein the amplifier is a variable gain amplifier.   The motor driving circuit according to claim 1, wherein the amplifier is an inverting amplifier that inverts and amplifies the first activation control voltage.   The motor driving circuit according to claim 1, wherein the amplifier is a non-inverting amplifier that non-inverting amplifies the first start-up control voltage. The drive signal generation circuit includes:
A pulse modulation comparator that generates a pulse modulation signal by comparing the rotation control voltage with a predetermined periodic voltage; and
A first comparator that generates a first control pulse signal by comparing the first activation control voltage with the periodic voltage;
A second comparator for generating a second control pulse signal by comparing the second activation control voltage with the periodic voltage;
A synthesis circuit that generates the drive signal by synthesizing the pulse modulation signal with the first and second control pulse signals by a logical operation;
The motor drive circuit according to claim 1, comprising: The synthesis circuit is:
A first logic block that logically operates the pulse modulation signal generated by the pulse modulation comparator with a second control pulse signal generated by the second comparator;
A second logic block that combines the first control pulse signal generated by the first comparator with an output signal of the first logic block;
The motor drive circuit according to claim 5, comprising: The drive signal generation circuit includes:
A voltage selection circuit that selects any one of three voltages based on the magnitude relationship between the rotation control voltage and the first and second control voltages;
A pulse width modulation comparator for generating the pulse-modulated drive signal by comparing the voltage output from the voltage selection circuit with a predetermined periodic voltage;
The motor drive circuit according to claim 1, comprising:   8. The motor drive circuit according to claim 1, wherein the motor drive circuit is integrated on a single semiconductor substrate. A fan motor,
The motor drive circuit according to any one of claims 1 to 7, which drives the fan motor;
A cooling device comprising: A motor drive method for generating a pulse-modulated drive signal that defines the energization time of a coil of a motor to be driven, and for controlling the rotational speed of the motor,
Generating a first start control voltage whose voltage value changes with time at the start of the motor;
Amplifying the first start control voltage and outputting as a second start control voltage;
A pulse-modulated drive signal having a duty ratio corresponding to one of the three voltages by combining a rotation control voltage set according to a target value of the torque of the motor with the first and second start-up control voltages Generating
A motor driving method comprising:

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