JP2012075198A - Drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of motor output fluctuations due to power voltage fluctuations.SOLUTION: A comparator COMP10 compares a triangular wave of PWM carrier frequency to a threshold voltage and generates a PWM signal of a duty ratio corresponding to the threshold voltage. By switching a plurality of transistors with the PWM signal, a driving current from a power supply is output to a motor. Also, by changing the threshold voltage according to the power voltage, the duty ratio of the PWM signal can be changed according to the power voltage.

Description

  The present invention relates to a drive circuit that drives a motor.

  There are various types of motors, but there is a wide variety of motors that have a permanent magnet on the rotor and control the phase of current supply to multiple coils on the stator side to form a rotating magnetic field and rotate the rotor. Has been.

  Such a current supply to the permanent magnet motor is generally performed by switching a plurality of transistors. For example, an H-bridge configuration is adopted in which a pair of arms each having two transistors connected in series with a power source and a ground are provided, and a coil is disposed between the midpoints of the two arms. With this configuration, by turning on the upper transistor of one arm and the lower transistor of the other arm, a current on one side flows through the coil, and the upper transistor of the other arm and the lower transistor of one arm are turned on. By turning on, the phase of the current flowing through the coil can be controlled by causing the current on the other side to flow through the coil. And while providing a coil in a different position of a stator and providing H bridge correspondingly and controlling the electric current phase supplied to a coil, a motor can be driven.

JP 2009-207218 A JP 2006-288056 A JP-A-8-37798

  Here, in the drive circuit using the H bridge as described above, the current from the power source is supplied to the motor via the transistor. Therefore, when the power supply voltage fluctuates, the driving state of the motor changes. For example, if the power supply voltage is high, the motor output is large, and if the power supply voltage is low, the motor output is small.

  The present invention is a drive circuit for driving a motor, which compares a triangular wave of a PWM carrier frequency with a threshold voltage to generate a PWM signal having a duty ratio corresponding to the threshold voltage, and the PWM An output circuit that outputs a driving current from a power source to a motor by switching a plurality of transistors according to a signal, wherein the threshold voltage changes according to the voltage of the power source.

  The threshold voltage is preferably generated by dividing the power supply voltage from the power supply by resistance.

  Thus, according to the present invention, it is possible to suppress a change in motor output when the motor is PWM driven and the power supply voltage changes.

It is a block diagram which shows the whole structure. It is a figure which shows the structural example of an output circuit. It is a figure which shows the structure which produces | generates a PWM signal. It is a figure which shows the operation | movement waveform of each point of the structure which produces | generates a PWM signal. It is a figure which shows the structure which produces | generates a drive control signal from a PWM signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an overall configuration, and the system includes a driver 100 and a motor 200. The input signal is input to the driver 100, and the driver 100 supplies a driving current corresponding to the input signal to the motor 200. Thereby, the rotation of the motor 200 is controlled according to the input signal. Examples of the motor 200 include a motor for generating vibration of a mobile phone.

  Here, the driver 100 includes the comparator 10, and a rotation state signal corresponding to the rotor position from the Hall element 30 provided in the motor 200 is supplied to one end of the comparator 10. A reference value voltage is supplied to the other end of the comparator 10, and the comparator 10 detects that the rotation state signal has reached the reference value.

  The output of the comparator 10 is supplied to the output control circuit 12. The output control circuit 12 latches the output signal of the comparator 10 with a predetermined clock, and can repeatedly obtain two rectangular waves whose phases are 180 degrees and whose phases are inverted from the rotation state signal. This is used as two 180-degree drive waveforms. Then, a PWM drive control signal is generated by taking AND of a PWM signal (PWM input) having a predetermined duty ratio from this drive waveform. As described above, the output control circuit 12 determines the drive waveform (phase) in accordance with the comparator output and obtains the PWM-converted drive control signals (OUT1, OUT2). Then, the generated drive control signal is supplied to the output circuit 14.

  The output circuit 14 is composed of a plurality of transistors, and controls the current from the power source by switching them to generate a motor driving current and supplies it to the motor 200.

  FIG. 2 shows a configuration of a part of the output circuit 14 and one coil 22 of the motor 200. Thus, the output circuit 14 has an H-bridge configuration, and consists of an arm composed of two transistors Q1 and Q2 connected in series between the power supply VCC and the ground, and two transistors Q3 and Q4 connected in series. An arm is provided, and coil 22 is connected between the intermediate point of transistors Q1 and Q2 and the intermediate point of transistors Q3 and Q4. Then, by turning on the transistors Q1 and Q4 and turning off the transistors Q2 and Q3, a current in one direction flows through the coil 22, turning off the transistors Q1 and Q4 and turning on the transistors Q2 and Q3. A current in the direction is supplied to drive the coil 22.

  The motor 200 is a portable vibration motor and has a coil 22 and a rotor 26. The number of permanent magnets corresponding to the number of poles is provided in the rotor 26, and for example, the rotor 26 is disposed at a position where the N pole and the S pole face each other (positions different from each other by 180 degrees). A stable position is determined according to the magnetic field from the two coils 22.

  Therefore, by supplying an alternating current to the coil 22, the rotor 26 can be moved and rotated by the current phase. Further, by stopping the change of the current phase at the timing of the specific current phase, the rotor can be stopped at a position corresponding to the current phase at that time.

  The motor 200 is provided with a hall element 30 and generates a rotation state signal in accordance with the magnetic field from the permanent magnet of the rotor 26. As described above, when N and S are one each, a sine wave in which one rotation of the rotor 26 is one cycle is obtained as a rotation state signal, and the rotation state signal from the Hall element 30 is supplied to the comparator 10. The

  Here, the present embodiment has a configuration in which the duty ratio of the PWM signal is automatically changed when the power supply voltage VCC varies, and this configuration will be described with reference to FIG. The circuit of FIG. 3 is included in the output control circuit 12 of FIG.

  The constant current source CC10 is connected to one end (upper end) of the capacitor C10, and the other end (lower end) of the capacitor C10 is connected to the ground. A transistor Q10 is connected between both ends of the capacitor C10.

  The upper end of the capacitor C10 is connected to the negative input end of the comparator COMP10, and the upper end voltage Vc of the capacitor C10 is supplied thereto. On the other hand, a threshold voltage Vd obtained by dividing the power supply voltage VCC by two resistors R1 and R2 is input to the positive input terminal of the comparator COMP10.

  The operation of such a circuit will be described with reference to FIG. First, the PWM input is a pulse signal having a carrier frequency of PWM, and a signal having a predetermined frequency. The transistor Q10 is turned on by this PWM input.

  Since the constant current is supplied to the capacitor C10 from the constant current source CC10, the upper end voltage Vc of the capacitor C10 is charged by the constant current from the constant current source CC10 and gradually rises with the transistor Q10 turned off. To do. When the transistor Q10 is turned on, the capacitor C10 is discharged to the ground, and the upper end voltage Vc is maintained at the ground voltage until the transistor Q10 is turned on. Therefore, the upper end voltage of the capacitor C10 is a sawtooth triangular wave. It is not always necessary to use a sawtooth wave, but a triangular wave that gradually discharges by inserting a resistor in the discharge path can also be used.

  The comparator COMP10 compares the threshold voltage Vd supplied to the positive input terminal with the upper end voltage Vc of the capacitor C10, and outputs a PWM signal that becomes H level during the period when the upper end voltage Vc exceeds the threshold voltage Vd. To do. Therefore, a PWM signal whose duty ratio is determined by the threshold voltage Vd is obtained at the output of the comparator COMP10.

  Here, in the present embodiment, since the threshold voltage Vd is created by dividing the power supply voltage VCC, the threshold voltage Vd is a voltage proportional to the power supply voltage VCC. Therefore, the threshold voltage Vd varies according to the power supply voltage VCC. Therefore, when the power supply voltage VCC rises and the threshold voltage Vd becomes Vd ′ in the figure, the PWM signal has a small duty ratio as indicated by a broken line in the figure.

  As shown in FIG. 2, since the power supply voltage VCC is applied to the coil 22 of the motor, a large current flows through the coil 22 when the power supply voltage VCC is high. On the other hand, in this embodiment, when the power supply voltage VCC is high, the duty ratio of the PWM signal is automatically reduced. Therefore, fluctuations in the motor output due to fluctuations in the power supply voltage VCC can be suppressed.

  Thus, according to the present embodiment, fluctuations in motor output due to fluctuations in the power supply voltage VCC can be suppressed with a relatively simple configuration.

  Note that it is preferable that the duty ratio of the PWM signal is varied so that the fluctuation of the threshold voltage Vd and the magnitude of the fluctuation of the power supply voltage VCC do not fluctuate the motor output with respect to the fluctuation of the power supply voltage VCC. However, complete alignment is difficult, and it is sufficient that the influence can be improved in the fluctuation of the allowable range of the power supply voltage VCC. A sufficient effect can be obtained by setting the values of the resistors R1 and R2 to appropriate values.

  Further, the duty ratio can be changed by changing the values of the resistors R1 and R2. Therefore, when an appropriate duty ratio is set in the operating state of the motor, the resistance values of the resistors R1 and R2 can be changed and the threshold voltage Vd may be set as needed.

  FIG. 5 shows a configuration example of PWM conversion of the drive control signal. In this way, by taking the logical product of both signals by the AND gate AND10, a drive control signal obtained by PWM conversion can be obtained.

  10 Comparator, 12 Output control circuit, 14 Output circuit, 22 Coil, 26 Rotor, 30 Hall element, 100 Driver, 200 Motor.

Claims (2)

A drive circuit for driving a motor,
A comparator that compares the triangular wave of the PWM carrier frequency with a threshold voltage and generates a PWM signal having a duty ratio according to the threshold voltage;
An output circuit that outputs a driving current from a power source to a motor by switching a plurality of transistors by the PWM signal;
Including
The drive circuit according to claim 1, wherein the threshold voltage changes according to a voltage of the power source. The drive circuit according to claim 1,
The drive circuit according to claim 1, wherein the threshold voltage is generated by dividing a power supply voltage from the power supply.

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