JP5537147B2 - Motor drive circuit, position control system using the same, and electronic equipment - Google Patents

Description

  The present invention relates to a motor drive circuit.

  A voice coil motor (VCM) is used to position the focus lens of the camera. The voice coil motor includes a permanent magnet and a voice coil. When a current is supplied to the voice coil, the voice coil linearly moves according to the current.

  In addition, the voice coil motor is used in a wide range of applications such as HDD head positioning, camera zoom, aperture, shutter, printer (printing machine), processing machine actuator, and XY stage.

JP 2000-21030 A

In general, a constant current circuit is used for driving the voice coil motor. The constant current circuit is provided in series with the coil of the voice coil motor. When the voice coil motor is driven directly using the power supply voltage Vdd of the circuit, the power consumption P of this system is
P = Vdd × I _COIL
It becomes. For example, when Vdd = 4.5V and I _COIL = 100 mA, the power consumption is 450 mW, most of which is heat loss, and there is room for improvement.

  The present invention has been made in view of these problems, and one of the exemplary purposes of an aspect thereof is to provide a drive circuit for a voice coil motor capable of reducing power consumption.

  One embodiment of the present invention relates to a drive circuit for a voice coil motor. This drive circuit includes a DC / DC converter that converts an input voltage into a predetermined voltage. The voice coil of the voice coil motor is used as an inductance element of the DC / DC converter.

  According to this aspect, since the drive current can be controlled while applying an optimum voltage to the voice coil by voltage conversion of the DC / DC converter, it is possible to drive with high efficiency.

  Another aspect of the present invention is also a voice coil motor drive circuit. This drive circuit applies a switching transistor provided between a first fixed voltage terminal to which a first voltage is applied and a first terminal of a voice coil of a voice coil motor, and a first terminal and a second voltage of the voice coil are applied. A rectifying element provided between the second fixed voltage terminal, a capacitor provided between the second terminal of the voice coil and the second fixed voltage terminal, and a control unit for controlling on / off of the switching transistor, .

  According to this aspect, since the drive circuit and the voice coil motor operate as a step-down DC / DC converter using the voice coil of the voice coil motor as an inductance element, high efficiency can be obtained.

The driving circuit according to an aspect may further include a constant current circuit provided between the second terminal and the second fixed voltage terminal of the voice coil. The control unit may control ON / OFF of the switching transistor so that the voltage between both ends of the constant current circuit becomes a predetermined value.
By stabilizing the voltage across the constant current circuit to the minimum value at which it operates, the efficiency of the circuit can be increased.

The driving circuit according to an aspect may further include a detection resistor provided between the second terminal and the second fixed voltage terminal of the voice coil. The control unit may control ON / OFF of the switching transistor so that the voltage across the detection resistor becomes a predetermined value.
In this case, the current flowing through the voice coil can be controlled according to the voltage across the detection resistor without using a constant current circuit.

  Still another embodiment of the present invention is also a voice coil motor drive circuit. This drive circuit has a switching transistor provided between a first terminal of a voice coil of a voice coil motor, a first fixed voltage terminal to which a first voltage is applied, and one end thereof connected to the first fixed voltage terminal. A capacitor, a rectifying element provided between the first terminal of the voice coil and the other end of the capacitor, and a controller for controlling on / off of the switching transistor.

  According to this aspect, since the drive circuit and the voice coil motor operate as a step-up DC / DC converter using the voice coil of the voice coil motor as an inductance element, the voice coil motor can be driven based on a very low voltage.

  The driving circuit according to an aspect may further include a constant current circuit provided between the other end of the capacitor and the fixed voltage terminal. The control unit may control ON / OFF of the switching transistor so that the voltage between both ends of the constant current circuit becomes a predetermined value.

  The driving circuit according to an aspect may further include a detection resistor provided between the other end of the capacitor and the fixed voltage terminal. The control unit may control ON / OFF of the switching transistor so that the voltage across the detection resistor becomes a predetermined value.

  Yet another aspect of the present invention is a position control system. The position control system includes a voice coil motor and a drive circuit according to any one of the above-described modes for driving the voice coil motor.

  Yet another embodiment of the present invention is an electronic device with an imaging function. This electronic apparatus includes the above-described position control system for positioning the autofocus lens.

  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 an aspect of the present invention, a highly efficient motor drive circuit is provided.

It is a circuit diagram which shows the structure of the position control system using the drive circuit which concerns on 1st Embodiment. It is a wave form diagram which shows operation | movement of the drive circuit of FIG. FIGS. 3A and 3B are circuit diagrams showing the configuration of the drive circuit according to the comparison technique. It is a circuit diagram which shows the structure of the position control system which concerns on a 1st modification. It is a circuit diagram which shows the structure of the position control system which concerns on a 2nd modification. It is a circuit diagram which shows the structure of the position control system using the drive circuit which concerns on 2nd Embodiment. FIG. 7 is a circuit diagram showing a modification of the drive circuit in FIG. 6.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected in addition to the case where the member A and the member B are physically directly connected. It includes the case of being indirectly connected through another member that does not affect the connection state.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through another member that does not affect the connection state.

(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of a position control system 1 using a drive circuit 4 according to the first embodiment. The position control system 1 includes a voice coil motor (hereinafter referred to as VCM) 2 and a drive circuit 4. The position control system 1 is mounted on, for example, an electronic device with an imaging function, such as a digital camera or video camera, or a mobile phone with an imaging function, and is used for autofocusing or positioning of other lenses.

  In the VCM 2, the position of the mover changes according to the drive current flowing through the voice coil L1. The driving circuit 4 supplies a driving voltage to the voice coil L1 and supplies a driving current corresponding to the target position.

  The drive circuit 4 includes a switching transistor SW1, a synchronous rectification transistor SW2, a capacitor C1, a control circuit 10, and a constant current circuit 6. The switching transistor SW1, the synchronous rectification transistor SW2, and the control circuit 10 are integrated as a control IC 100 on one semiconductor substrate.

The first terminal T1 of the voice coil L1 is connected to the switching terminal P3 of the control IC 100. The power supply voltage Vdd is applied as the first voltage to the first fixed voltage terminal P1. The switching transistor SW1 is a P-channel MOSFET, and is provided between the first fixed voltage terminal P1 and the first terminal T1 of the voice coil L1 of the VCM2. The ground voltage V _GND is applied as the second voltage to the second fixed voltage terminal P2. The synchronous rectification transistor SW2 is an N-channel MOSFET, and is provided between the first terminal T1 and the second fixed voltage terminal P2 of the voice coil L1. Instead of the synchronous rectification transistor SW2, a rectification diode may be used in which the cathode is disposed on the first terminal T1 side of the voice coil L1 and the anode is disposed on the second fixed voltage terminal P2 side. The capacitor C1 is provided between the second terminal T2 and the second fixed voltage terminal P2 of the voice coil L1.

  The control circuit 10 controls on / off of the switching transistor SW1 based on the feedback signal FB input to the feedback terminal P4. The switching frequency of the switching transistor SW1 is preferably designed to be higher than the audible band.

The control circuit 10 includes a pulse width modulator 12 and a driver 19. The pulse width modulator 12 generates a pulse signal S _PWM whose duty ratio is adjusted so that the feedback signal FB matches a predetermined target value. Driver 19 based on the pulse signal _{S PWM,} complementarily turned on, to turn off the synchronous rectification transistor SW2 and the switching transistor SW1.

The pulse width modulator 12 includes an error amplifier 14, an oscillator 16, and a PWM comparator 18. The error amplifier 14 amplifies an error between the feedback signal FB and the reference voltage Vref, and generates an error voltage V _ERR corresponding to the error. The oscillator 16 generates a periodic signal V _OSC having a triangular wave shape or a sawtooth wave _shape . The PWM comparator 18 compares the error voltage V _ERR with the periodic signal V _OSC and generates a pulse signal S _PWM . The configuration of the pulse width modulator 12 is not limited to this, and other types of modulators may be used.

The constant current circuit 6 is provided between the second terminal T2 and the second fixed voltage terminal P2 of the voice coil L1. The constant current circuit 6 generates a drive current I _DRV to be passed through the voice coil L1. The voltage Vs across the constant current circuit 6 is input to the feedback terminal P4 as the feedback signal FB. That is, the control circuit 10 controls the switching transistors SW1 and SW2 to be turned on and off so that the voltage Vs across the constant current circuit 6 becomes the predetermined value Vref.

A command value corresponding to the target position of the mover (voice coil L1) of the VCM 2 is input to the constant current circuit 6. The drive current I _DRV generated by the constant current circuit 6 is defined according to the command value. The constant current circuit 6 may be integrated in the control IC 100.

The constant current circuit 6 can generate a predetermined drive current _IDRV when the voltage Vs between both ends thereof is higher than a predetermined threshold, and cannot generate it when it is low. Therefore, the reference voltage Vref is set as low as possible with a value higher than this threshold value. As a result, it is possible to cause the constant current circuit 6 to stably generate the drive current I _DRV and to increase the efficiency of the circuit.

  The above is the configuration of the position control system 1. Next, the operation will be described.

  The drive circuit 4 and the VCM 2 in FIG. 1 function as a so-called synchronous rectification step-down DC / DC converter. In this DC / DC converter, a voice coil L1 of VCM2 is used as an inductance element for storing magnetic energy.

  FIG. 2 is a waveform diagram showing the operation of the drive circuit 4 of FIG.

  As a result of the drive circuit 4 and VCM2 operating as a DC / DC converter, an output voltage Vout obtained by stepping down the power supply voltage Vdd appears at the second terminal T2 of VCM2. In the configuration of FIG. 1, feedback control is performed so that the output voltage Vout becomes equal to the reference voltage Vref.

A switching voltage SWOUT that alternately repeats the power supply voltage Vdd (first voltage) and the ground voltage V _GND (second voltage) is applied to the first terminal T1 of the VCM2. The output voltage Vout stabilized according to the reference voltage Vref is applied to the second terminal T2. A voltage _VL between both ends of the voice coil L1 is a difference (Vout−SWOUT) between the output voltage Vout and the switching voltage SWOUT.

At this time, a coil current _IL flows through the voice coil L1. The coil current I _L, the pulsating driving current I _DRV the constant current circuit 6 is generated as an average value. As a result, the mover of the VCM 2 is positioned according to the drive current I _DRV .

  The above is the operation of the drive circuit 4. The advantage of the drive circuit 4 becomes clear by comparison with a comparative technique. FIGS. 3A and 3B are circuit diagrams showing the configuration of the drive circuit according to the comparison technique.

In FIG. 3A, a constant current circuit 206 as a drive circuit is provided in series with the voice coil L1 of the VCM 202. In this topology, the circuit loss increases when the power supply voltage Vdd is high. For example, if Vdd = 4.5 V and I _DRV = 100 mA, the power consumption of the circuit is 450 mW. Most of the power consumption is a heat loss in the constant current circuit 6.

In FIG. 3B, the step-down DC / DC converter 208 converts the power supply voltage Vdd into a lower DC voltage Vdc. Then, the VCM 202 is driven using the DC voltage Vdc. For example, assuming that the DC voltage Vdc is 2 V, the drive current I _DRV is 100 mA, and the conversion efficiency of the DC / DC converter 208 is 100%, the power consumption is reduced to 200 mW. In the topology of FIG. 3B, since an inductance element is required for the DC / DC converter 208, the circuit area and cost are increased.

  On the other hand, according to the drive circuit 4 of FIG. 1, the VCM 2 can be driven with lower power consumption than that of FIG. Further, since the voice coil L1 of the VCM2 is used as the inductance element for the DC / DC converter, an increase in circuit area and cost can be suppressed.

  Subsequently, some modified examples will be described.

  FIG. 4 is a circuit diagram showing a configuration of the position control system 1a according to the first modification. The drive circuit 4a in FIG. 4 includes a detection resistor R1 instead of the constant current circuit 6 in FIG. The detection resistor R1 is provided between the second terminal T2 of the voice coil L1 and the second fixed voltage terminal (ground terminal).

  The voltage Vs across the detection resistor R1 is fed back to the feedback terminal P4. The reference voltage Vref is set according to a command value indicating the target position of the mover (voice coil L1) of the VCM2. The control IC 100 controls the ON / OFF duty ratio of the switching transistor SW1 and the synchronous rectification transistor SW2 so that the voltage Vs matches the reference voltage Vref. The detection resistor R1 may be built in the control IC 100.

The operation of the drive circuit 4a in FIG. 4 will be described. When feedback is applied so that the voltage Vs across the detection resistor R1 matches the reference voltage Vref, the detection resistor R1
I _DRV = Vref / R1
The drive current I _DRV given by As a result, the voice coil L1, the coil current I _L for pulsating the drive current I _DRV around value flows, it is possible to position the mover in VCM2 the target position. The frequency and amplitude of the pulsating flow are determined according to the switching frequency of the switching transistor SW1, the capacity of the position control system 1, and the inductance value of the voice coil L1, and by optimizing those parameters, the position control system 1 The effect on accuracy can be made sufficiently small.

  The modification of FIG. 4 has an advantage that the circuit can be simplified compared to the configuration of FIG. 1 in addition to the advantage of the circuit of FIG.

FIG. 5 is a circuit diagram showing a configuration of a position control system 1b according to the second modification. The configuration of the drive circuit 4b in FIG. 5 is obtained by reversing the configuration of the drive circuit 4a in FIG. That is, the ground voltage V _GND is applied as the first voltage to the first fixed voltage terminal P1, and the power supply voltage Vdd is applied as the second voltage to the second fixed voltage terminal P2. The switching transistor SW1 is an N-channel MOSFET, and the synchronous rectification transistor SW2 is a P-channel MOSFET.

  Also in this modified example, high-efficiency motion can be realized as in the position control system 1a of FIG. Further, the detection resistor R1 may be replaced with the constant current circuit 6 in FIG.

(Second Embodiment)
In the first embodiment, the technology for driving the VCM 2 with high efficiency in a system to which a somewhat high power supply voltage Vdd is supplied has been described. In contrast, in the second embodiment, a technique for suitably driving the VCM 2 in a system to which a very low power supply voltage Vdd is supplied will be described.

  FIG. 6 is a circuit diagram showing a configuration of the position control system 1 using the drive circuit 4c according to the second embodiment. The drive circuit 4c and VCM2 in FIG. 6 function as a so-called diode rectification type step-up DC / DC converter. In this DC / DC converter, a voice coil L1 of VCM2 is used as an inductance element for storing magnetic energy.

Specifically, the switching transistor SW1 is provided between the first terminal T1 of the voice coil L1 of the VCM 2 and the first fixed voltage terminal P1 to which the ground voltage V _GND that is the first voltage is applied. One end T3 of the capacitor C1 is connected to a first fixed voltage terminal (ground terminal), and a ground voltage V _GND is applied. The rectifier diode D1 is provided in such a direction that the first terminal T1 of the VCM2 is on the anode side and the other end T4 of the capacitor C1 is on the cathode side. Instead of the rectifying diode D1, a synchronous rectifying transistor that is turned on / off complementarily to the switching transistor SW1 may be provided.

  The control circuit 10 controls on / off of the switching transistor SW1.

  The constant current circuit 6 is provided between the other end T4 of the capacitor C1 and the first fixed voltage terminal P1. The control circuit 10 controls on / off of the switching transistor SW1 so that the voltage Vs across the constant current circuit 6 becomes a predetermined value. As in the first embodiment, a detection resistor R1 may be provided instead of the constant current circuit 6.

  The above is the configuration of the drive circuit 4c. Next, the operation will be described.

In the drive circuit 4c of FIG. 6, since the position control system 1c operates as a step-up DC / DC converter, a voltage Vout higher than the power supply voltage Vdd is generated at the other end T4 of the capacitor C1. And the voice coil L1, the driving current _{I DRV} for pulsating the drive current _{I DRV} as mean flow, the movable element of VCM2 is positioned at the target position.

  In the comparison technique shown in FIG. 3A, when the power supply voltage Vdd is very low, for example, 0.3 V, the VCM 2 cannot be driven. On the other hand, according to the drive circuit 4c in FIG. 6, the VCM 2 can be driven. Further, since the voice coil L1 is used as the inductance element of the DC / DC converter, an increase in circuit area and cost can be suppressed.

  The power supply voltage Vdd ′ for the control IC 100 needs to be supplied with a voltage that is somewhat higher than the power supply voltage Vdd for the first fixed voltage terminal P1, but the control IC 100 does not consume a large current. The current capability of the power supply that generates the second power supply voltage Vdd ′ may be low. As this power source, another power source of an electronic device on which the position control system 1d is mounted may be used, or a charge pump circuit or the like may be used.

  FIG. 7 is a circuit diagram showing a modification of the drive circuit of FIG. The drive circuit 4d in FIG. 7 has a configuration obtained by inverting the drive circuit 4c in FIG. 6 upside down, and the other configurations are the same.

  The position control system 1d of FIG. 7 can also drive the VCM 2 based on the low power supply voltage Vdd.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and various modifications may exist in each of those constituent elements, each processing process, and a combination thereof. Hereinafter, such modifications will be described.

  Instead of the pulse width modulator 12 of FIGS. 1, 4, 5, 6, and 7, a pulse frequency modulator (PFM) may be used.

  In the embodiment, the case where the VCM is driven has been described. However, the present invention is not limited to this, and can be used for driving various other types of motors (actuators) in which torque and position control are performed by a direct current value flowing through the coil. .

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Position control system, 2 ... VCM, 4 ... Drive circuit, 6 ... Constant current circuit, SW1 ... Switching transistor, SW2 ... Synchronous rectification transistor, D1 ... Rectifier diode, 10 ... Control circuit, 12 ... Pulse width modulator, 14 ... Error amplifier, 16 ... Oscillator, 18 ... PWM comparator, 19 ... Driver, T1 ... First terminal, T2 ... Second terminal, C1 ... Capacitor, L1 ... Voice coil, P1 ... First fixed voltage terminal, P2 ... Second Fixed voltage terminal, P3... Switching terminal, P4... Feedback terminal, 100... Control IC, R1.

Claims (4)

A drive circuit for a voice coil motor,
A switching transistor provided between a first fixed voltage terminal to which a first voltage is applied and a first terminal of a voice coil of the voice coil motor;
A rectifying element provided between the first terminal of the voice coil and a second fixed voltage terminal to which a second voltage is applied;
A capacitor provided between the second terminal of the voice coil and the second fixed voltage terminal;
A constant current circuit provided between the second terminal of the voice coil and the second fixed voltage terminal;
A control unit for controlling on and off of the switching transistor so that a voltage between both ends of the constant current circuit becomes a predetermined value ;
A drive circuit comprising: A drive circuit for a voice coil motor,
A switching transistor provided between a first terminal of a voice coil of the voice coil motor and a first fixed voltage terminal to which a first voltage is applied;
A capacitor having one end connected to the first fixed voltage terminal;
A rectifying element provided between the first terminal of the voice coil and the other end of the capacitor;
A constant current circuit provided between the other end of the capacitor and a fixed voltage terminal;
A control unit for controlling on and off of the switching transistor so that a voltage between both ends of the constant current circuit becomes a predetermined value ;
A drive circuit comprising: A voice coil motor,
The drive circuit according to claim 1 or 2 , which drives the voice coil motor;
A position control system comprising:   An electronic apparatus with an imaging function, comprising the position control system according to claim 3 for positioning an autofocus lens.

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