JP2006204017A - Voltage generating circuit and stepping motor drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage generating circuit in which steep change in voltage value can be sufficiently suppressed, and a stepping motor drive circuit using the same. <P>SOLUTION: The stepping motor drive circuit 1 includes the voltage generating circuit 10, a triangular wave generating circuit 20, a comparator 30, a gate drive circuit 40, and an H-bridge circuit 50. The voltage generating circuit 10 includes a current control circuit 12, a capacitor (capacitive element) 14, and an operational amplifier 16. The current control circuit 12 generates a current having waveform that changes stepwise along a sine wave. The current control circuit 12 is connected with the capacitor 14. The capacitor 14 is charged with the above current generated in the current control circuit 12, and the current is discharged from the capacitor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a voltage generation circuit and a stepping motor drive circuit.

  When driving a zoom / focus optical lens in a digital camera (DSC: Digital Still Camera) or a digital video camera (DVC: Digital Video Camera), a two-phase bipolar stepping motor with easy position control is used. When the stepping motor is driven, a pseudo sine wave current having a phase difference of 90 degrees is applied to the two poles.

  As a drive circuit for the stepping motor, for example, there is one described in Patent Document 1. FIG. 7 is a block diagram showing a drive circuit described in the document. There are two signal paths from the control circuit 101, a path P <b> 1 connected to the bridge circuit 103 through the gate drive circuit 102 and a path P <b> 2 toward the D / A conversion circuit 104. The path P1 is a signal path for controlling the MOSFET gate in the bridge circuit for switching between positive and negative of the current flowing in the coil serving as the motor load and switching by pulse width modulation (PWM) control. The path P2 is a signal path that controls a block that generates a pseudo sine wave.

  Next, the PWM control drive of the stepping motor in FIG. 7 will be briefly described. The PWM control for flowing the pseudo sine wave current to the stepping motor is based on a full-wave rectified pseudo Sin function reference voltage output from an electrical variable resistor (EVR) circuit in the D / A conversion circuit 104. Requires a triangular wave. A configuration example of the EVR circuit is shown in FIG. As shown in FIG. 9 (lower left in the figure), the pseudo Sin function reference voltage exhibits a voltage waveform that changes stepwise (stepwise) when viewed on a fine time scale. The voltage value change amount in each step is weighted so that the voltage waveform as a whole follows the Sin function. Therefore, the amount of change in voltage value at each time scale, that is, the height of the staircase, decreases as it approaches the extreme value (maximum value) of the parabola. This voltage is generated by dividing the reference voltage VREF by a weighted resistor in the EVR circuit of FIG. At that time, the place where the resistance is divided is switched by a switch.

Thus, from the EVR circuit, step-like pseudo Sin function reference voltages _{V 1} is output as a full-wave rectifier-like waveform (see FIG. 10, FIG. 11). A voltage value obtained by adding the triangular wave generated by the triangular wave generating circuit 105 to the reference voltage is input to the positive phase input of the comparator 106. As shown in FIG. 10, the output of the comparator 106 is transmitted through the gate drive circuit 102 to the gate of the high-side P channel of the H bridge circuit 103 that directly controls the current flowing through the motor. A sense resistor _RS is connected between the N-channel source of the H-bridge circuit 103 and GND. In addition, the voltage value on the upper side of the sense resistor R _{S in} the drawing, that is, the source side of the N-channel MOSFET is connected to the negative phase input of the comparator 106, thereby forming feedback. Therefore, the P channel is chopped so that a pseudo sine wave current flows through the motor driving coil of the inductance load.

By the way, since the pseudo sine wave is a waveform that rises stepwise for each time scale divided in equal time intervals as described above, the presence of a step edge whose current value changes sharply is a problem of noise generation. It has become. In the conventional drive circuit, the step edge of the pseudo-Sin function reference voltage is blunted by attaching a capacitor to the output terminal of the EVR, whereby the pseudo-sinusoidal current value applied to the motor drive coil changes sharply. It was relaxed (Patent Document 2).
Japanese Patent Laid-Open No. 5-114848 JP 2002-78386 A

  As shown in FIG. 12, the smoothness of the step edge can be increased by increasing the capacitance of the capacitor. However, if the capacity is increased too much, the voltage does not rise to a required value at each step, and a sine wave reference voltage cannot be obtained. Further, even if the capacitance value is optimized, it is difficult to sufficiently suppress the abrupt voltage value change at the initial stage (rising portion) when each step changes.

  The present invention has been made in view of the above circumstances, and provides a voltage generation circuit capable of sufficiently suppressing a steep voltage value change and a stepping motor drive circuit using the voltage generation circuit.

  In order to solve the above problems, a voltage generation circuit according to the present invention includes a current control circuit that generates a current having a waveform that changes stepwise along a sine wave, and the current control circuit connected to the current control circuit. And a capacitor element that is charged and discharged by the current generated in step 1.

  In this voltage generation circuit, a current having a waveform that changes stepwise is generated by a current control circuit, and the capacitive element is charged or discharged by the current. At this time, since the current is constant in each step of the staircase, the change in voltage applied to the capacitive element is linear. Therefore, as the current changes along the sine wave, a voltage having a waveform that forms a sine wave in a linear approximation is generated. Thereby, a voltage generation circuit capable of sufficiently suppressing a steep voltage value change is realized.

  The current control circuit includes a voltage generation circuit that generates a voltage having a waveform that changes stepwise along a sine wave, and a conversion circuit that converts the voltage generated in the voltage generation circuit into a current. May be. In this case, a current waveform that changes stepwise along a sine wave can be obtained with a simple configuration.

  The current control circuit may include a direction control circuit that controls a direction in which the current obtained in the conversion circuit flows. In this case, charging and discharging of the capacitive element can be easily switched by switching the direction of the current by the direction control circuit.

  The stepping motor drive circuit according to the present invention generates a current having a pseudo sine wave waveform based on the voltage generation circuit and the voltage waveform generated by the voltage generation circuit, and supplies the current to the stepping motor. And a current supply circuit.

  In this drive circuit, a pseudo sine wave current waveform is generated based on the voltage waveform generated by the voltage generation circuit described above. For this reason, a current waveform constituting a sine wave in a linear approximation is obtained. Therefore, since a current in which a steep change is sufficiently suppressed can be supplied to the stepping motor, a drive circuit capable of sufficiently reducing noise is realized.

  According to the present invention, a voltage generation circuit capable of sufficiently suppressing a steep voltage value change and a stepping motor drive circuit using the voltage generation circuit are realized.

  Hereinafter, preferred embodiments of a voltage generation circuit and a stepping motor drive circuit according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

  FIG. 1 is a block diagram showing an embodiment of a voltage generation circuit and a stepping motor drive circuit according to the present invention. The stepping motor drive circuit 1 includes a voltage generation circuit 10, a triangular wave generation circuit 20, a comparator 30, a gate drive circuit 40, and an H bridge circuit 50. The voltage generation circuit 10 generates a pseudo sine wave reference voltage. The triangular wave generation circuit 20, the comparator 30, the gate drive circuit 40, and the bridge circuit 50 constitute a current supply circuit. The current supply circuit generates a current having a pseudo sine waveform based on the reference voltage generated by the voltage generation circuit 10 and supplies the current to a stepping motor (not shown).

  The voltage generation circuit 10 includes a current control circuit 12, a capacitor 14 (capacitance element), and an operational amplifier 16. The current control circuit 12 generates a current having a waveform that changes stepwise along a sine wave. A capacitor 14 is connected to the current control circuit 12. Specifically, the capacitor 14 has one end connected to the output end of the current control circuit 12 and the other end grounded. The capacitor 14 is charged and discharged by the current generated in the current control circuit 12.

  The configuration of the current control circuit 12 will be described with reference to FIG. The current control circuit 12 includes a voltage generation circuit 122, a conversion circuit 124, and a direction control circuit 126. The voltage generation circuit 122 generates a voltage having a waveform that changes stepwise along a sine wave. As this voltage generation circuit 122, for example, an EVR circuit (see FIG. 8) can be used. The EVR circuit is composed of a multi-stage resistance divider circuit, and by switching the switches at a time scale corresponding to the desired sine wave period and amplitude, it is stepped along the pseudo sine wave voltage, that is, along the sine wave. Outputs changing voltage.

  A conversion circuit 124 is connected to the voltage generation circuit 122. The conversion circuit 124 is a V / I conversion circuit that converts the voltage generated in the voltage generation circuit 122 into a current. In addition, a direction control circuit 126 is connected to the conversion circuit 124. The direction control circuit 126 controls the direction in which the current obtained in the conversion circuit 124 flows. That is, the direction control circuit 126 can switch between positive and negative (whether discharge or suction is only) in the direction of the output current.

  Returning to FIG. 1, the operational amplifier 16 is also connected to the current control circuit 12. Specifically, the positive phase input terminal of the operational amplifier 16 is connected to the output terminal of the current control circuit 12 and one end of the capacitor 14. The operational amplifier 16 has a negative phase input terminal and an output terminal connected to each other, and constitutes a voltage follower. In the present embodiment, the output from the operational amplifier 16 is the output of the entire voltage generation circuit 10.

A positive phase input terminal of a comparator 30 is connected to the voltage generation circuit 10. A triangular wave generating circuit 20 is also connected to the positive phase input terminal. The triangular wave generation circuit 20 generates a triangular wave that is added to the pseudo sine wave reference voltage generated by the voltage generation circuit 10. In addition, a gate drive circuit 40 is connected to the comparator 30, and a bridge circuit 50 is connected to the gate drive circuit 40. The gate drive circuit 40 controls driving of the gate of the high-side P channel in the bridge circuit 50 according to the output from the comparator 30. In the bridge circuit 50, a sense resistor _RS is provided, one end of which is connected to the N-channel source and the other end is grounded. The N-channel source (and one end of the sense resistor _RS ) is connected to the reverse-phase input terminal of the comparator 30, thereby forming feedback. The P channel performs chopping so that a pseudo sinusoidal current flows through the coil 52 for driving the stepping motor.

Next, the operation of the stepping motor drive circuit 1 will be described with reference to FIGS. First, the voltage generation circuit 122 generates a voltage V ₁ having a waveform that changes stepwise along a sine wave of full-wave rectification. This voltage V ₁ is converted into a current I ₁ by the conversion circuit 124. The waveform of this current I ₁ also changes stepwise along a sine wave of full-wave rectification, like the voltage V ₁ . The direction of the current I ₁ is switched between positive and negative by the direction control circuit 126 every quarter period of the sine wave. Therefore, the waveform of the current I ₂ output from the direction control circuit 126 is as shown in FIG. Current I ₂ when the positive charged capacitor 14, when the negative capacitor 14 is discharged.

Here, since the current I ₂ has a waveform that changes stepwise, the current I ₂ takes a constant value at each step of the step. That is, the capacitor 14 is charged and discharged with a constant current as shown in FIG. Therefore, the change of the voltage V ₂ applied to the capacitor 14, as shown in FIG. 4 (a) and 4 (b), the linear. FIGS. 4 (a) shows a part of the waveform of the voltage _{V 2.} FIG. 4B shows an enlarged waveform of a portion surrounded by a circle in FIG. Thus, the voltage V ₂ with linearly approximately configuration a waveform of sine wave is obtained. That is, the waveform of the voltage V _2, a continuous waveform obtained by connecting line segments each other corresponding to each step of stepped current waveform outputted from the current control circuit 12 full-wave rectification shaped sinusoidal overall It constitutes a wave. The slope of each line segment depends on the current value at the corresponding step.

This voltage V ₂ is input to the positive phase input terminal of the comparator 30 through the operational amplifier 16. A triangular wave output from the triangular wave generation circuit 20 is also input to the same input terminal. Thus, the comparator 30, and the voltage V ₂ and the triangular wave are added together. The voltage obtained by the addition is compared with the voltage applied to the sense resistor _RS of the bridge circuit 50, and the result is output from the comparator 30 as a gate driving signal. The signal is transmitted to the bridge circuit 50 through the gate drive circuit 40. Thus, the waveform of current I _L flowing through the pseudo sinusoidal coil 52, similarly to the voltage V _2, becomes the linearly varies along the sinusoidal wave (see Figure 3).

  Next, effects of the voltage generation circuit 10 and the stepping motor drive circuit 1 will be described. In the voltage generation circuit 10, as described above, a pseudo sine wave is generated using a linear voltage change obtained by charging the capacitor 14 with a constant current output from the current control circuit 12. . As a result, a voltage waveform having no step edge is obtained in principle, so that the voltage generation circuit 10 capable of sufficiently suppressing a steep voltage value change is realized.

  Therefore, the voltage generation circuit 10 can be suitably used as a circuit for generating the pseudo sine wave reference voltage in the stepping motor driving circuit. A steep voltage value change in the reference voltage leads to noise generation in the stepping motor. However, if the voltage generation circuit 10 is used, noise in the stepping motor can be reduced.

  Actually, the stepping motor drive circuit 1 generates a pseudo sine wave current waveform based on the pseudo sine wave reference voltage generated by the voltage generation circuit 10. As a result, it is possible to supply a current in which a steep change is sufficiently suppressed to the stepping motor. For this reason, the stepping motor drive circuit 1 that can drive the stepping motor while sufficiently suppressing noise is realized.

  The current control circuit 12 includes a voltage generation circuit 122 and a conversion circuit 124 that converts a voltage generated in the voltage generation circuit 122 into a current. With this configuration, the current waveform can be obtained by generating a voltage having a similar waveform and converting it into a current without directly generating a current waveform that changes stepwise along the sine wave. A voltage waveform that changes stepwise along a sine wave can be easily generated using a conventionally used circuit such as an EVR circuit. Therefore, the current control circuit 12 capable of generating a current waveform that changes stepwise along a sine wave with a simple configuration is realized.

  The current control circuit 12 has a direction control circuit 126. With this configuration, it is possible to easily switch between charging and discharging of the capacitor 14 by switching the direction of the current by the direction control circuit 126.

  In addition, the voltage generation circuit 10 includes an operational amplifier 16. Thereby, the pseudo sine wave reference voltage can be stably supplied to the comparator 30. However, it is not essential to provide the operational amplifier 16 in the voltage generation circuit 10. That is, the current control circuit 12 and the capacitor 14 may be directly connected to the positive phase input terminal of the comparator 30.

  The voltage generation circuit and the stepping motor drive circuit according to the present invention are not limited to the above-described embodiment, and various modifications are possible. For example, as shown in FIG. 5, in the current control circuit 12, a constant current generation circuit 128 may be used instead of the voltage generation circuit 122 and the conversion circuit 124 (see FIG. 2). The constant current generating circuit 128 directly generates a current waveform that changes stepwise along a sine wave. FIG. 6 shows a configuration example of the constant current generation circuit 128. In this constant current generating circuit 128, current mirror circuits are provided in multiple stages, and a desired constant current value can be obtained by opening / closing a reference voltage VREF and a switch.

1 is a block diagram showing an embodiment of a voltage generation circuit and a stepping motor drive circuit according to the present invention. It is a block diagram which shows the structure of the current control circuit in FIG. It is a figure for demonstrating operation | movement of the drive circuit of FIG. It is a figure for demonstrating operation | movement of the drive circuit of FIG. It is a block diagram which shows the modification of the current control circuit of FIG. FIG. 6 is a circuit diagram showing a configuration example of a constant current generation circuit 128 in FIG. 5. It is a block diagram which shows the conventional stepping motor drive circuit. FIG. 8 is a circuit diagram illustrating a configuration example of an EVR circuit in FIG. 7. It is a figure for demonstrating PWM control drive. It is a figure for demonstrating generation | occurrence | production of the pseudo sine wave current in the drive circuit of FIG. It is a figure which shows the waveform of the pseudo | simulation sine wave reference voltage and load current which generate | occur | produce in the drive circuit of FIG. It is a figure for demonstrating the problem of the drive circuit of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stepping motor drive circuit 10 Voltage generation circuit 12 Current control circuit 14 Capacitor 16 Operational amplifier 20 Triangular wave generation circuit 30 Comparator 40 Gate drive circuit 50 Bridge circuit 52 Coil 122 Voltage generation circuit 124 Conversion circuit 126 Direction control circuit 128 Constant current generation circuit

Claims (4)

A current control circuit for generating a current having a waveform that changes stepwise along a sine wave;
A capacitive element connected to the current control circuit and charged and discharged by the current generated in the current control circuit;
A voltage generation circuit comprising: The voltage generation circuit according to claim 1,
The current control circuit is
A voltage generation circuit for generating a voltage having a waveform that changes stepwise along a sine wave;
A conversion circuit for converting the voltage generated in the voltage generation circuit into a current;
A voltage generating circuit. The voltage generation circuit according to claim 2,
The voltage control circuit includes a direction control circuit that controls a direction in which the current obtained in the conversion circuit flows. A voltage generation circuit according to any one of claims 1 to 3,
A current supply circuit that generates a current having a pseudo sine waveform based on the voltage waveform generated by the voltage generation circuit, and supplies the current to the stepping motor;
A stepping motor drive circuit comprising:

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