JP2007267552A - Motor driving circuit, its method, and disk drive using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the erroneous detection of a zero cross point at the time of modulating the pulses of a motor prior to drive. <P>SOLUTION: A pulse width modulation signal generating circuit 50 generates a PWM signal Spwm whose duty ratio changes according to the target toque of the motor 110. A counterelectromotive detection circuit 20 detects a zero cross point by comparing a phase voltage Vu generated in a U-phase coil Lu with a midpoint voltage Vcom. A switching control circuit 30 receives the PWM signal Spwm and a counterelectromotive detection signal BEMF<SB>-</SB>EDGE, controls the sequence of the ON-OFF state of a switching circuit 10, and also controls the switching of at least one hand of a high-side switch and a low-side switch included in the switching circuit 10. The counterelectromotive detection circuit 20 sets the detection timing, based on the PWM signal Spwm, and outputs a specified level of counterelectromotive detection signal BEMF<SB>-</SB>EDGE at its detection timing when the comparison results between the counterelectromotive voltage Vu and the midpoint voltage Vcom fulfills specified conditions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for controlling rotation of a rotor, and more particularly to a motor drive circuit that controls rotation of a motor including a stator having a plurality of coils and a magnetic rotor.

  In an electronic device using a disk-type medium such as a portable CD (Compact Disc) device or a DVD (Digital Versatile Disc), a brushless DC motor is used to rotate the disk. Brushless direct current (DC) motors generally include a rotor with a permanent magnet and a stator with a plurality of star-connected coils of a phase, and the coil is excited by controlling the current supplied to the coil. The rotor is driven by rotating relative to the stator. In order to detect the rotational position of the rotor, the brushless DC motor generally includes a sensor such as a Hall element or an optical encoder, and switches the current supplied to the coil of each phase according to the position detected by the sensor. And apply an appropriate torque to the rotor.

  In order to further reduce the size of the motor, a sensorless motor that detects the rotational position of the rotor without using a sensor such as a Hall element has also been proposed (for example, see Patent Documents 1 and 2). For example, a sensorless motor monitors the counter electromotive voltage (inductive voltage) generated in the coil by measuring the potential of the midpoint wiring of the motor (hereinafter referred to as the midpoint voltage). By detecting, position information is obtained.

  Here, in order to monitor the counter electromotive voltage of a certain phase coil, it is necessary to set the non-driving state in accordance with the timing at which the zero cross point occurs. In this non-driving state, the driver (switching circuit) connected to the phase coil stops switching driving and is set to a high impedance state. When the motor is driven by a 180-degree energization method or the like, since current always flows through the phase coil, it is necessary to predict the timing at which the zero cross point occurs and set the high impedance state according to the prediction result. . For example, Patent Document 3 describes a related technique.

JP-A-3-207250 Japanese Patent Laid-Open No. 10-243865 Japanese Patent Laid-Open No. 11-75388

  In some cases, the voltage applied to the motor coil is controlled by pulse modulation in order to continuously change the current flowing in the motor coil in a sine wave shape or an arch shape. FIGS. 1A to 1C are time charts showing how a zero-cross point is detected when pulse modulation driving is performed. FIG. 1A shows a pulse-modulated signal PWM, and FIG. 1B shows a phase voltage (hereinafter also referred to as a counter electromotive voltage Vu) and a midpoint voltage Vcom generated in a coil to be detected at a zero cross point. FIG. 6C shows a waveform diagram of the back electromotive force detection signal BEMF_EDGE.

  As shown in FIG. 1B, the back electromotive voltage Vu generated in the coil that is the detection target of the zero cross point includes the timing of the transition from OFF to ON of the pulse-modulated signal shown in FIG. Alternatively, a noise component appears at the timing from on to off. Due to this noise component, the back electromotive force detection signal obtained by comparing the phase voltage Vu and the midpoint voltage Vcom repeats a high level and a low level, and the zero cross point is erroneously detected. The erroneous detection of the zero cross point is nothing but an erroneous detection of the rotor position, and causes problems such as deterioration in rotational accuracy and defective rotation.

  The present invention has been made in view of such a situation, and an object thereof is to provide a technique for preventing erroneous detection of a zero cross point when driving a motor by pulse modulation.

  One embodiment of the present invention relates to a motor drive circuit that drives a multiphase motor by supplying a drive current. This motor drive circuit is provided for each coil of the multiphase motor, and a plurality of switching circuits for applying a high level or low level voltage to one end of the connected coil, and at least the target torque of the multiphase motor A pulse modulation signal generation circuit that generates a pulse modulation signal whose duty ratio changes, and a counter electromotive voltage generated in at least one coil of the multiphase motor is compared with a midpoint voltage of the coil to detect a zero cross point; A back electromotive detection circuit that outputs a back electromotive detection signal, a pulse modulation signal from the pulse modulation signal generation circuit, and a back electromotive detection signal from the back electromotive detection circuit are received. High-side switch included in multiple switching circuits based on the pulse modulation signal as well as controlling the sequence of switching circuits on / off And comprising a switching control circuit for controlling switching of at least one of the low-side switch, the. The back electromotive force detection circuit sets the detection timing based on the pulse modulation signal from the pulse modulation signal generation circuit, and when the comparison result between the back electromotive voltage and the midpoint voltage satisfies a predetermined condition at the set detection timing, A back electromotive force detection signal of a predetermined level is output.

  According to this aspect, the detection timing of the zero cross point can be set to a timing with less influence of noise in synchronization with the pulse modulation signal itself that causes a noise component in the back electromotive voltage, and the zero cross point is erroneously detected. Can be prevented. “Pulse modulation” refers to modulation using a signal in which the ratio between the high-level and low-level periods of the pulse, that is, the duty ratio, such as pulse width modulation, pulse frequency modulation, and pulse position modulation.

  The back electromotive detection circuit may set the detection timing based on the level transition timing of the pulse modulation signal. In this case, the timing of the edge of the pulse modulation signal or the timing obtained by delaying the edge by a predetermined time can be set as the detection timing.

  The back electromotive force detection circuit may set the detection timing to the timing at which the level of the pulse modulation signal transitions from a level corresponding to ON of a switch included in the plurality of switching circuits to a level corresponding to OFF. The noise component generated in the back electromotive force due to pulse modulation becomes almost maximum immediately after the on / off state of the switch connected to a coil different from the coil in which the back electromotive voltage to be detected appears, and then attenuates. I often go. Thus, by setting the timing immediately before the switch on / off transition is set to the detection timing, it is possible to perform zero-cross detection with a small noise component.

  The back electromotive force detection circuit may output a back electromotive force detection signal when the magnitude relationship between the back electromotive voltage and the midpoint voltage satisfies a predetermined condition at a detection timing. The predetermined condition may be set when the back electromotive voltage is higher than the midpoint voltage or when the back electromotive voltage is lower than the midpoint voltage, depending on the driving state of the motor.

  The back electromotive force detection circuit may include a comparator that compares the back electromotive voltage with the midpoint voltage, and a comparison value output unit that receives an output signal of the comparator and outputs a value at the detection timing. The comparison value output unit may be a latch circuit that latches the output signal of the comparator in accordance with the pulse modulation signal.

  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 embodiment of the present invention is a disk device. This apparatus includes a spindle motor that rotates a disk and the above-described motor drive circuit that drives the spindle motor.
According to this aspect, it is possible to suitably prevent erroneous detection of the zero cross point by the motor drive circuit, and it is possible to stably rotate the spindle motor.

  Yet another aspect of the present invention is a motor driving method for driving a polyphase motor by supplying a driving current. In this driving method, a step of generating a pulse modulation signal whose duty ratio changes at least according to a target torque of the multiphase motor, and a back electromotive voltage generated in at least one coil of the multiphase motor A counter-electromotive detection step for detecting a zero-cross point in comparison with the voltage and generating a counter-electromotive detection signal of a predetermined level, and controlling the sequence of the coil to be driven based on the counter-electromotive detection signal, and a pulse modulation signal And applying a high-level or low-level switching signal to the coil to be driven. In the back electromotive force detection step, the detection timing is set based on the pulse modulation signal, and when the comparison result between the back electromotive voltage and the midpoint voltage satisfies a predetermined condition at the set detection timing, the back electromotive detection signal is set to a predetermined level. And

  According to this aspect, the detection timing of the zero cross point can be set to a timing with less influence of noise in synchronization with the pulse modulation signal itself that causes a noise component in the back electromotive voltage, and the zero cross point is erroneously detected. Can be prevented.

  According to the present invention, when the motor is driven by pulse modulation, the zero cross point can be accurately detected.

  FIG. 2 is a block diagram showing a configuration of the motor drive circuit 100 according to the embodiment. The motor drive circuit 100 controls the rotation by supplying a drive current to a sensorless brushless DC motor (hereinafter simply referred to as “motor 110”). In the present embodiment, the motor 110 to be driven is a three-phase DC motor including U-phase, V-phase, and W-phase coils Lu, Lv, and Lw.

  The motor drive circuit 100 includes switching circuits 10u, 10v, and 10w, which are collectively referred to as a switching circuit 10, a back electromotive force detection circuit 20, a switching control circuit 30, a window generation circuit 40, and a pulse width modulation signal generation circuit 50. . The motor drive circuit 100 is integrally integrated as a functional IC on one semiconductor substrate. For example, the motor drive circuit 100 drives the multiphase motor 110 by PWM (Pulse Width Modulation) so that a desired torque can be obtained. Furthermore, the duty ratio of the PWM drive may be changed so that the current flowing through the coil of each phase becomes an arch shape or a sine wave shape by the 180-degree energization method.

  The switching circuits 10u, 10v, and 10w are provided for each of the coils Lu, Lv, and Lw of the motor 110. The switching circuits 10u, 10v, and 10w include, for example, a high-side switch and a low-side switch connected in series between a power supply voltage and a ground potential, and a connection point between the two switches is connected to the coil. The drive signal DRV_H (U, V, W) and the drive signal DRV_L (U, V, W) are input to the control terminals of the high side switch and the low side switch, respectively. The switching circuits 10u, 10v, and 10w apply a high level voltage to one end of a connected coil when the high side switch is on and a low level voltage when the low side switch is on. Further, the high-side switch and the low-side switch are simultaneously turned off to set the high impedance state.

  The back electromotive force detection circuit 20 compares the back electromotive voltage generated in at least one coil of the motor 110 with the midpoint voltage of the coil to detect a zero cross point, and outputs a back electromotive force detection signal BEMF_EDGE. In the present embodiment, the back electromotive force detection circuit 20 monitors the back electromotive voltage Vu and the midpoint voltage Vcom generated in the U-phase coil Lu, and generates a back electromotive force detection signal BEMF_EDGE. The generated back electromotive force detection signal BEMF_EDGE is output to the switching control circuit 30 and the window generation circuit 40. Details of the back electromotive force detection circuit 20 will be described later.

  The pulse width modulation signal generation circuit 50 generates a pulse width modulation signal (hereinafter referred to as a PWM signal Spwm) whose duty ratio changes at least according to the target torque of the motor 110. The pulse width modulation signal generating circuit 50 compares the level of the triangular wave or sawtooth wave periodic signal Sosc with the level of the signal Strq indicating the torque, and changes the period of the high level and low level of the PWM signal Spwm according to the magnitude relationship. . Note that the pulse width modulation signal generation circuit 50 may be configured by either an analog circuit or a digital circuit.

  The pulse width modulation signal generation circuit 50 generates a PWM signal Spwm by synthesizing a target torque and a sinusoidal or arched control waveform in order to gently change the coil current flowing through the coils Lu, Lv, and Lw. May be.

  The switching control circuit 30 receives the PWM signal Spwm from the pulse width modulation signal generation circuit 50 and the back electromotive detection signal BEMF_EDGE from the back electromotive detection circuit 20. The switching control circuit 30 controls the sequence of the on / off states of the plurality of switching circuits 10u, 10v, and 10w based on the back electromotive detection signal BEMF_EDGE. Furthermore, the switching control circuit 30 performs switching control of at least one of the high-side switch and the low-side switch included in the plurality of switching circuits 10u, 10v, and 10w based on the PWM signal Spwm.

  The switching control circuit 30 includes a drive timing generation circuit 32 and a drive signal synthesis circuit 34. The drive timing generation circuit 32 receives the back electromotive force detection signal BEMF_EDGE. The drive timing generation circuit 32 generates a drive signal DRV having a cycle that is 1/6 of the cycle Tp1 of the back electromotive detection signal BEMF_EDGE.

  The drive signal synthesis circuit 34 synthesizes the drive signal DRV and the PWM signal Spwm to output drive signals DRV_H (u, v, w) and DRV_L (u, v, w), and the switching circuits 10 u, 10 v, 10 w. Control the state of

  Prior to the detection of the zero cross point by the back electromotive force detection circuit 20, the window generation circuit 40 stops the switching of the switching circuit 10u connected to the coil Lu that is the target of back electromotive force detection and sets the window signal to high impedance. WINDOW is generated. In the present embodiment, the predetermined level is a high level. The window generation circuit 40 can be omitted when there is a period in which no current flows in the coil Lu, which is the target of back electromotive force detection, when conducting 120-degree energization.

  The window signal WINDOW is output to the drive signal synthesis circuit 34 of the switching control circuit 30. During the period when the window signal WINDOW is at a high level, the drive signal synthesis circuit 34 stops switching of the switching circuit 10u connected to the terminal where the back electromotive voltage Vu to be monitored for detection of the zero cross point is generated, and the high impedance Set to state. That is, during the period in which the window signal WINDOW is at a high level, a phase that is not intentionally driven is set in order to detect the zero cross point. In the present embodiment, in the non-driving period Tp3, the U phase is set to a phase that is not driven.

  Next, the back electromotive force detection circuit 20 will be described in detail. In addition to the back electromotive voltage Vu and the midpoint voltage Vcom, the back electromotive force detection circuit 20 according to the present embodiment receives the PWM signal Spwm from the pulse width modulation signal generation circuit 50. The back electromotive detection circuit 20 sets the detection timing of the zero cross point based on the PWM signal Spwm. The back electromotive force detection circuit 20 outputs a back electromotive force detection signal BEMF_EDGE that becomes a high level when the comparison result between the back electromotive voltage Vu and the midpoint voltage Vcom satisfies a predetermined condition at the set detection timing.

  The back electromotive detection circuit 20 sets the detection timing based on the level transition timing of the PWM signal Spwm. As a detection timing setting method, a method of setting the positive edge or negative edge of the PWM signal Spwm as the detection timing, a method of setting the detection timing by delaying the positive edge or the negative edge by a predetermined time, and the like are effective.

  In the present embodiment, the back electromotive force detection circuit 20 determines the timing at which the level of the PWM signal Spwm changes from the level corresponding to the on state of the switches included in the plurality of switching circuits 10u, 10v, and 10w to the level corresponding to the off state. Set the detection timing. For example, when the low level of the PWM signal Spwm corresponds to the switch off and the high level corresponds to the switch on, the negative edge of the PWM signal Spwm is set as the detection timing. The back electromotive force detection circuit 20 outputs a high level back electromotive force detection signal BEMF_EDGE when Vu> Vcom is satisfied at the detection timing thus set.

  FIG. 3 is a circuit diagram illustrating a configuration example of the back electromotive force detection circuit 20. The back electromotive detection circuit 20 includes a comparator 22 and a comparison value output unit 24. The back electromotive force detection circuit 20 compares the phase voltage Vu of the U-phase coil Lu with the midpoint voltage Vcom, and outputs a comparison signal Scmp that becomes high level when Vu> Vcom.

  The comparison value output unit 24 receives the comparison signal Scmp that is the output of the comparator 22 and outputs the value at the detection timing as the back electromotive detection signal BEMF_EDGE. The comparison value output unit 24 can be configured by a latch circuit that latches the output signal of the comparator 22 in accordance with the negative edge of the PWM signal Spwm. The comparison signal Scmp is input to the input terminal D of the D latch circuit which is the comparison value output unit 24.

  The negative edge detection circuit 26 detects a negative edge of the PWM signal Spwm, and outputs a negative edge signal NEDGE that becomes a high level at each detection. The negative edge signal NEDGE is input to the clock terminal of the comparison value output unit 24.

  The operation of the motor drive circuit 100 configured as described above will be described. 4A to 4L are time charts showing the operation of the motor drive circuit 100 according to the embodiment. The vertical and horizontal axes in FIGS. 1A to 1L are enlarged or reduced as appropriate for easy understanding, and the waveforms shown are also simplified for easy understanding. Yes. FIGS. 4A to 4C are waveforms showing driving states of the U-phase, V-phase, and W-phase coils Lu, Lv, and Lw by the switching circuits 10u, 10v, and 10w. FIG. 6D shows the back electromotive detection signal BEMF_EDGE detected by the back electromotive detection circuit 20, FIG. 5E shows the drive signal DRV generated by the drive timing generation circuit 32, and FIG. The window signal WINDOW generated by the window generation circuit 40 is shown. Further, (g) to (l) in the figure show driving signals DRV_H and DRV_L for the high-side switch and the low-side switch of the switching circuits 10u to 10w.

  As shown in FIGS. 4A to 4C, in the present embodiment, the drive current is driven so as to have an arch waveform. However, the present invention is not limited to this, and may be a sine wave as described above. In the present embodiment, the back electromotive force detection signal BEMF_EDGE is generated for each zero cross point where the back electromotive voltage Vu intersects the midpoint voltage Vcom as shown in FIG. The drive timing generation circuit 32 generates the drive signal DRV shown in FIG. 5E, which is 1/6 times the cycle Tp1 of the back electromotive detection signal BEMF_EDGE. As shown in the figure, the drive signal DRV may be given a delay Td with respect to the back electromotive force detection signal BEMF_EDGE. By adjusting the delay Td, the motor drive is optimized.

  Based on the drive signal DRV generated by the drive timing generation circuit 32, the drive signal synthesis circuit 34 controls drive signals DRV_H (U, V, W), DRV_L (U, V) for controlling on / off of the switching circuits 10u to 10w. , W). This driving sequence is appropriately set according to the energization angle and the like.

  In the drive signal DRV_HU shown in FIG. 4G, the high level corresponds to the on state of the high side switch of the switching circuit 10u, and the low level corresponds to the off state. The same applies to the drive signals DRV_H (V, W) and DRV_L (U, V, W) shown in FIGS. Further, the ON state of at least one of the high side switch and the low side switch is pulse width modulated so as to obtain the drive waveforms shown in FIGS. The side switch or low side switch alternately turns on and off at a high frequency.

  Each time the back electromotive detection signal BEMF_EDGE is output, the drive signal synthesis circuit 34 changes the on / off states of the drive signals DRV_H and DRV_L of the switching circuits 10u to 10w according to a predetermined drive sequence.

  The window signal WINDOW shown in FIG. 6F is set to the high level by the window generation circuit 40 prior to the time when the zero cross point occurs. The drive signal synthesizing circuit 34 sets the drive signals DRV_HU and DRV_LU output to the switching circuit 10u to the low level while the window generation circuit 40 is at the high level, turns off the high side switch and the low side switch, and sets the high impedance state. In the same figure (g) and (j), the period during which the high impedance state is set in order to detect the zero cross point is indicated by hatching. When the window signal WINDOW becomes high level and one end of the coil Lu is set to a high impedance state, the zero cross point can be detected, and the back electromotive detection signal BEMF_EDGE is generated.

  FIGS. 5A to 5E are waveform diagrams illustrating how the zero cross point is detected in the motor drive circuit 100 according to the embodiment. 5A shows the PWM signal Spwm, FIG. 5B shows the phase voltage Vu and the midpoint voltage Vcom, FIG. 5C shows the comparison signal Scmp, and FIG. 5D shows the negative edge signal NEDGE. (E) shows the back electromotive force detection signal BEMF_EDGE.

  The PWM signal Spwm alternately repeats a high level and a low level with a duty ratio corresponding to the torque. In the U-phase phase voltage Vu set to the non-driven state, a pulsed counter electromotive voltage is generated according to switching control of the other phase coils Lv and Lw based on the PWM signal Spwm. As shown in FIG. 4B, the phase voltage Vu has a counter electromotive voltage when the PWM signal Spwm is at a high level, and a voltage near 0 V when the PWM signal Spwm is at a low level. Here, the signal transition of the PWM signal Spwm and the change of the phase voltage Vu have a delay due to the propagation time of the signal. Therefore, the phase voltage Vu falls to around 0 V later than the timing at which the negative edge of the PWM signal Spwm occurs. Note that the midpoint voltage Vcom shown in FIG. 2B is a signal that alternately repeats the illustrated voltage level and low level, but is shown here as a straight line for simplicity.

  In the phase voltage Vu shown in FIG. 5B, a noise component appears at the timing when the PWM signal Spwm is at a high level and a pulse voltage is applied to the other phase coils Lv and Lw. The comparison signal Scmp obtained by comparing the phase voltage Vu and the midpoint voltage Vcom by this noise component repeats a high level and a low level as shown in FIG. This comparison signal Scmp is latched at the detection timing at which the negative edge signal NEDGE appears, and is output as the back electromotive force detection signal BEMF_EDGE shown in FIG. The back electromotive detection signal BEMF_EDGE generated in this way is a more stable signal than the back electromotive detection signal BEMF_EDGE shown in FIG.

  In the motor drive circuit 100 according to the present embodiment, the detection timing of the zero cross point is set in synchronization with the PWM signal Spwm that causes a noise component in the counter electromotive voltage Vu. As a result, the detection timing of the zero cross point can be set appropriately at a time when the influence of noise is small, and erroneous detection of the zero cross point can be prevented.

  Further, as shown in FIG. 5C, the noise component generated in the counter electromotive voltage by the pulse modulation is immediately after turning on the switch connected to a coil different from the coil in which the counter electromotive voltage to be detected appears. In many cases, it becomes almost maximum and then decays. In the present embodiment, the back electromotive force detection circuit 20 determines the timing at which the level of the PWM signal Spwm transitions from a level corresponding to ON of the switches included in the plurality of switching circuits 10u, 10v, and 10w to a level corresponding to OFF. Since the detection timing is set, zero cross detection can be performed with a small noise component.

  Next, an example of application of the motor drive circuit 100 according to the present embodiment will be described. FIG. 6 is a block diagram showing a configuration of a disk device 200 on which the motor drive circuit 100 of FIG. 2 is mounted. The disk device 200 is a unit that performs recording and reproduction processing on an optical disk such as a CD or a DVD, and is mounted on an electronic device such as a CD player, a DVD player, or a personal computer. The disk device 200 includes a pickup 210, a signal processing unit 212, a disk 214, a motor 110, and a motor driving circuit 100.

  The pickup 210 writes desired data by irradiating the disk 214 with a laser, or reads the data written on the disk 214 by reading reflected light. The signal processing unit 212 performs necessary signal processing such as amplification processing, A / D conversion, or D / A conversion on data read and written by the pickup 210. The motor 110 is a spindle motor provided for rotating the disk 214. Since the disk device 200 as shown in FIG. 6 is particularly required to be downsized, a sensorless type that does not use a Hall element or the like is used as the motor 110. The motor drive circuit 100 according to the present embodiment can be suitably used to stably drive such a sensorless spindle motor.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art 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.

  In the embodiment, the case of driving a three-phase motor has been described. However, the present invention can also be suitably used for driving a sensorless motor other than the three-phase motor. For example, a five-phase motor may be used. In the embodiment, the case where the zero-cross point is detected by comparing the U-phase counter electromotive voltage Vu with the midpoint voltage Vcom has been described, but the present invention is not limited to this. For example, the back electromotive force detection circuit 20 may be provided for each of the U phase, the V phase, and the W phase to generate the back electromotive force detection signal BEMF_EDGE.

  In the embodiment, the zero cross point is detected by detecting the state where Vu> Vcom in the process of increasing the phase voltage Vu. However, the present invention is not limited to this, and the back electromotive force detection circuit 20 may detect the zero cross point by detecting a state where Vu <Vcom in the process of decreasing the phase voltage Vu.

  In the embodiment, the negative edge of the PWM signal Spwm is set to the detection timing of the zero cross point, but the present invention is not limited to this, and the back electromotive detection circuit 20 determines the time defined in synchronization with the pulse modulation signal. What is necessary is just to set to a detection timing. For example, the back electromotive force detection circuit 20 may set the time after a predetermined time from the positive edge as the detection timing. In this case, an appropriate zero cross point can be detected by adjusting the predetermined time.

  In the embodiment, the case where the motor is driven by the PWM method with 180 degree energization has been described. However, the present invention is not limited to this, and the present invention is widely used for a motor driving circuit that adopts a pulse modulation method. Can do.

  The high-level and low-level logic settings of the signals described in the embodiment are merely examples, and various modifications can be considered for the configuration of the logic circuit block, and such modifications are also included in the scope of the present invention.

FIGS. 1A to 1C are time charts showing how a zero-cross point is detected when pulse modulation driving is performed. It is a block diagram which shows the structure of the motor drive circuit which concerns on embodiment. It is a circuit diagram which shows the structural example of a back electromotive force detection circuit. 4A to 4L are time charts showing the operation of the motor drive circuit according to the embodiment. FIGS. 5A to 5E are waveform diagrams showing how the zero cross point of the motor drive circuit according to the embodiment is detected. FIG. 3 is a block diagram showing a configuration of a disk device on which the motor drive circuit of FIG. 2 is mounted.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Motor drive circuit, 10 Switching circuit, 20 Back electromotive detection circuit, 22 Comparator, 24 Comparison value output part, 30 Switching control circuit, 32 Drive timing generation circuit, 34 Drive signal synthesis circuit, 40 Window generation circuit, 50 Pulse width modulation Signal generation circuit, 110 motor, 210 pickup, 212 signal processing unit, 214 disc.

Claims (9)

A motor drive circuit that drives a multiphase motor by supplying a drive current,
A plurality of switching circuits that are provided for each coil of the multiphase motor and apply a high-level or low-level voltage to one end of the connected coils;
A pulse modulation signal generation circuit that generates a pulse modulation signal whose duty ratio changes according to a target torque of at least the multiphase motor;
A counter electromotive voltage generated in at least one coil of the multiphase motor is compared with a midpoint voltage of the coil to detect a zero cross point and output a counter electromotive detection signal;
A sequence of on / off states of the plurality of switching circuits based on the back electromotive detection signal, upon receiving the pulse modulation signal from the pulse modulation signal generating circuit and the back electromotive detection signal from the back electromotive detection circuit And a switching control circuit that controls switching of at least one of a high-side switch and a low-side switch included in the plurality of switching circuits based on the pulse modulation signal;
With
The back electromotive force detection circuit sets a detection timing based on the pulse modulation signal from the pulse modulation signal generation circuit, and the comparison result between the back electromotive voltage and the midpoint voltage is a predetermined value at the set detection timing. A motor drive circuit that outputs the back electromotive force detection signal at a predetermined level when the condition is satisfied.   The motor drive circuit according to claim 1, wherein the back electromotive detection circuit sets the detection timing based on a level transition timing of the pulse modulation signal.   The back electromotive force detection circuit sets a timing at which the level of the pulse modulation signal transits from a level corresponding to ON of a switch included in the plurality of switching circuits to a level corresponding to OFF, as the detection timing. The motor drive circuit according to claim 2, wherein   The back electromotive force detection circuit outputs the back electromotive force detection signal when the magnitude relationship between the back electromotive voltage and the midpoint voltage satisfies a predetermined condition at the detection timing. The motor drive circuit according to any one of the above. The back electromotive detection circuit is
A comparator that compares the back electromotive voltage with the midpoint voltage;
A comparison value output unit that receives an output signal of the comparator and outputs a value at the detection timing;
The motor drive circuit according to claim 1, further comprising:   6. The motor drive circuit according to claim 5, wherein the comparison value output unit is a latch circuit that latches an output signal of the comparator in accordance with the pulse modulation signal.   7. The motor driving circuit according to claim 1, wherein the motor driving circuit is integrated on a single semiconductor substrate. A spindle motor that rotates the disk;
The motor drive circuit according to any one of claims 1 to 6, which drives the spindle motor;
A disk device comprising: A motor driving method for driving by supplying a driving current to a multiphase motor,
Generating a pulse modulation signal whose duty ratio changes according to at least a target torque of the multiphase motor;
Back electromotive force generated in at least one coil of the multiphase motor is compared with a midpoint voltage of the coil to detect a zero cross point and generate a back electromotive force detection signal of a predetermined level;
Controlling a sequence of a coil to be driven based on the back electromotive detection signal, and applying a high-level or low-level switching signal to the coil to be driven based on the pulse modulation signal;
With
The counter electromotive detection step sets a detection timing based on the pulse modulation signal, and the counter electromotive force is detected when a comparison result between the counter electromotive voltage and the midpoint voltage satisfies a predetermined condition at the set detection timing. A method of setting a detection signal to the predetermined level.

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