JP4979273B2 - Motor drive circuit - Google Patents

Description

  The present invention relates to a motor drive circuit, and more particularly to a linear drive motor drive circuit.

  FIG. 4 shows an example of a motor drive circuit according to the prior art.

  The motor 1 is a single-phase brushless motor having a coil 2. The motor 1 rotates in response to a drive signal S1 applied to the coil 2. The hall element 3 detects the rotational phase of the motor 1 and outputs a detection signal S2. The hall amplifier 4 amplifies the detection signal S2 and outputs an amplified detection signal S3. The output amplifier 5 amplifies the amplification detection signal S3 according to the power supply voltage V1 and outputs the drive signal S1. Thus, the motor 1, the hall element 3, the hall amplifier 4, and the output amplifier 5 form a feedback loop to linearly drive the motor 1.

  In such a motor drive circuit, the rotational speed of the motor 1 depends on the power supply voltage V1. In other words, the rotational speed of the motor 1 becomes faster when the power supply voltage V1 is set larger, and becomes slower when the power supply voltage V1 is set lower.

Examples of related technical literatures include the following patent literatures.
JP-A-5-30780

  In the motor drive circuit described above, the amplitude of the drive signal S1 is fixed even when the power supply voltage V1 is switched.

  FIG. 5 shows a waveform diagram of the drive signal S1.

  First, FIG. 5A shows a waveform diagram of the drive signal S1 when the amplitude of the drive signal S1 is appropriate with respect to the power supply voltage V1. In general, the drive signal S1 is designed to be slightly distorted by the power supply voltage V1.

  On the other hand, FIG. 5B shows a waveform diagram of the drive signal S1 when the power supply voltage V1 is set large so that the rotational speed of the motor 1 is faster than that in FIG. As described above, the amplitude of the drive signal S1 is fixed even when the power supply voltage V1 is switched. In this case, since the drive signal S1 is less than the power supply voltage V1, the motor 1 has insufficient drive capability and cannot reach the set rotation speed. Further, in the output amplifier 5, heat corresponding to the potential difference between the power supply voltage V1 and the drive signal S1 is generated, and it is necessary to take measures against heat dissipation.

  On the other hand, FIG. 5C shows a waveform diagram of the drive signal S1 when the power supply voltage V1 is set to be small so that the rotation speed of the motor 1 is slower than that of FIG. In this case, the drive signal S1 is greatly distorted in a region exceeding the power supply voltage V1 and becomes a substantially rectangular wave shape. For this reason, the change of the drive signal S1 becomes steep and noise is generated.

  Further, the Hall element 3 had variations in internal resistance, temperature characteristics, etc., from element to element. For this reason, the amplitude of the detection signal S2 output from the Hall element 3 varies, and the same problem as described above occurs.

  In view of the above, a motor drive circuit according to the present invention includes a detection circuit that detects a rotational phase of a motor and outputs a detection signal, an amplification circuit that amplifies the detection signal and outputs an amplified detection signal, and the amplification An output amplifier that amplifies the detection signal in accordance with a power supply voltage and outputs a drive signal; and a motor that is driven in accordance with the drive signal, wherein the detection signal is a ratio between a saturation time and a non-saturation time of the drive signal. Is amplified according to the power supply voltage so as to maintain a constant value.

  A voltage conversion circuit that outputs a conversion voltage corresponding to the power supply voltage; and an amplification factor setting amplifier that uses the conversion voltage as one input and the amplification detection signal as the other input. The output of the amplifier is characterized by changing the gain of the amplifier circuit.

  The power supply voltage is switched according to a target motor rotation speed.

Further, the detection signal is detected by a Hall element constituting the detection circuit,
The hall current flowing through the hall element is adjusted so as not to exceed a predetermined value.

  In the motor drive circuit according to the present invention, the voltage amplification factor of the operational amplifier changes according to the power supply voltage so that the ratio between the saturation time and the non-saturation time of the drive signal is kept constant. Even if the speed is changed, the gain of the drive signal suitable for the set power supply voltage can be obtained. For this reason, generation of heat and noise can be prevented.

  Further, since the amplification factor of the operational amplifier is controlled according to the amplification detection signal and the set voltage corresponding to the power supply voltage, the gain of the amplification detection signal can be set to an optimum value. Furthermore, the influence of variations in the Hall elements can be reduced.

  Further, even if the motor speed is set by the power supply voltage, heat generation and noise can be prevented.

  Even if the internal resistance and temperature characteristics of the Hall element vary, damage to the Hall element can be prevented.

  Hereinafter, the motor drive circuit according to the present invention will be described in detail.

  FIG. 1 shows an example of a motor drive circuit according to the present invention. In such a drive circuit, the motor 1, the hall element 3, the hall amplifier 4, and the output amplifier 5 form a feedback loop to linearly drive the motor 1. Here, the rotational speed of the motor 1 is controlled according to the power supply voltage V 1 applied to the output amplifier 5. Here, the power supply voltage V1 is adjusted by the speed control circuit 6 to a value corresponding to the set rotational speed and output. The power supply voltage V1 is connected to the power supply connection terminal of the Hall amplifier via the voltage conversion circuit 7 and the amplification factor setting amplifier 8. The Hall current I1 flowing through the Hall element is controlled by the Hall current circuit 9 so as to be a predetermined amount or less. The motor drive circuit according to the present invention will be specifically described below.

  The motor 1 is a single-phase brushless motor having a coil 2. The motor 1 has a rotor magnet attached to a rotor, and rotates according to a drive signal S 1 applied to the coil 2.

  The hall element 3 is disposed at an appropriate portion through which the rotor magnet of the motor 1 passes, and detects the rotational phase of the motor 1 and outputs a detection signal S2. The Hall element 3 is made of, for example, gallium arsenide (GaAs) or indium antimony (InSb). Here, the Hall element 3 detects the rotational phase of the motor 1 using the Hall effect. That is, a Hall current I1 flows through the Hall element 3. When a magnetic field based on the rotation of the motor 1 is applied in a direction perpendicular to the direction of the Hall current I1, both the Hall current I1 and the magnetic field are applied. The detection signal S2 corresponding to the magnitude of the magnetic field is generated in a direction perpendicular to the direction. By the way, the internal resistance of the Hall element 3 varies from element to element, and the internal resistance varies with temperature. In this case, for example, when the internal resistance becomes larger than a design value, the Hall current I1 is less than a predetermined value, and a magnetic field based on the rotation of the motor 1 cannot be sufficiently detected. On the other hand, when the internal resistance becomes smaller than the design value, the Hall current I1 exceeds a predetermined value, and the Hall element 3 is destroyed by heat generation. Therefore, in the motor drive circuit according to the present embodiment, the Hall current circuit 9 is installed, and the Hall current circuit 9 outputs the optimum Hall current I1 according to the internal resistance of the Hall element 3. . The Hall current circuit 9 is composed of, for example, a low voltage output circuit that outputs a constant voltage Hall bias, and a clip circuit that clips a current output from the low voltage output circuit to a predetermined value.

  The hall amplifier 4 amplifies the detection signal S2 and outputs an amplified detection signal S3. That is, the output of the Hall element 3 is applied to the non-inverting input terminal of the Hall amplifier 4, and the inverted output of the Hall element 3 is applied to the inverting input terminal. The hall amplifier 4 outputs an amplified detection signal S3 having a sine waveform obtained by amplifying the amplitude of the detection signal S2. Here, the voltage amplification factor of the Hall amplifier 4 is set by the amplification factor setting voltage V4 applied to the power supply connection terminal 10.

  The output amplifier 5 amplifies the amplification detection signal S3 according to the applied power supply voltage V1 and outputs a drive signal S1. That is, the value of the power supply voltage V1 is proportional to the amplification degree of the detection signal S2. The power supply voltage V1 defines an input voltage range for the output amplifier 5 to operate normally. That is, when the voltage of the amplification detection signal S3 exceeds the range of the power supply voltage V1, the drive signal S1 output from the output amplifier 5 has a substantially section shape in which the range exceeding the power supply voltage V1 is distorted. .

  Here, the power supply voltage V1 is set by the speed control circuit 6 according to the target rotational speed of the motor. Specifically, when the rotational speed of the motor is made faster than the reference, the power supply voltage V1 is set large, and when it is made slower than the reference, the power supply voltage V1 is set small.

  In the motor drive circuit according to the present invention, the power supply voltage V1 is also applied to the voltage conversion circuit 7. The power supply voltage V1 is converted into a conversion voltage V3 corresponding to the power supply voltage V1 by the voltage conversion circuit 7 and input to the amplification factor setting amplifier 8. The amplification detection signal S3 is also input to the amplification factor setting amplifier 8. The amplification factor setting amplifier 8 compares the conversion voltage V3 with the amplification detection signal S3 and outputs an amplification factor setting voltage V4. The amplification factor setting voltage V4 is applied to the power supply connection terminal 10 of the Hall amplifier 4 to change the voltage amplification factor of the Hall amplifier 4.

  That is, in the motor drive circuit according to the present invention, the voltage amplification factor of the Hall amplifier 4 also changes in accordance with the set power supply voltage V1. For this reason, the amplitude of the amplified detection signal S3 changes according to the power supply voltage V1, and accordingly, the amplitude of the increased drive signal S1 also changes.

  FIG. 2 is a waveform diagram of the drive signal S1 output from the output amplifier 5.

  First, FIG. 2A shows a waveform diagram of the drive signal S1 when the amplitude of the drive signal S1 is appropriate with respect to the power supply voltage V1. In general, the drive signal S1 is designed to be slightly distorted by the power supply voltage V1. This is because when the power supply voltage V1 is larger than the drive signal S1, heat is generated according to the potential difference between the power supply voltage V1 and the drive signal S1. On the other hand, when the power supply voltage V1 is smaller than the drive signal S1, the drive signal S1 is distorted in a range exceeding the power supply voltage V1, and therefore noise is caused by a sharp change in the drive signal S1. Occurs. Here, heat generation is a problem that should be prevented rather than noise because measures for heat dissipation are required. Therefore, emphasis is placed on minimizing heat generation, and the power supply voltage V1 is designed to be slightly smaller than the drive signal S1 so that the balance between heat generation and noise is optimal. Here, in the state where the balance is maintained, the saturation time of the drive voltage is defined as t1, and the non-saturation time is defined as t2.

  FIG. 2B shows a waveform diagram of the drive signal S1 when the power supply voltage V1 is set large so that the rotation speed of the motor 1 is faster than that in FIG. Here, in the motor drive circuit according to the present invention, the voltage amplification factor of the Hall amplifier 4 increases in accordance with the power supply voltage V1. In this case, the amplitude of the amplification detection signal S3 also increases according to the power supply voltage V1. Therefore, the amplitude of the drive signal S1 depending on the amplification detection signal S3 also increases according to the power supply voltage V1. Here, preferably, the ratio between the saturation time t3 and the non-saturation time t4 of the drive signal S1 is set to be equal to the ratio between t1 and t2 in FIG. The change of the amplification factor setting voltage V4 according to the power supply voltage V1 is adjusted by the voltage conversion circuit 7. In this case, the balance between the generation of noise and heat generation according to each power supply voltage V1 can be kept optimal.

  FIG. 2C shows a waveform diagram of the drive signal S1 when the power supply voltage V1 is set smaller so that the rotation speed of the motor 1 is slower than that in FIG. The voltage amplification factor of the Hall amplifier 4 decreases according to the power supply voltage V1. In this case, the amplitude of the amplification detection signal S3 also decreases according to the power supply voltage V1. Therefore, the gain of the drive signal S1 that depends on the amplification detection signal S3 also decreases according to the power supply voltage V1. Here, preferably, similarly to FIG. 2 (b), the ratio of the saturation time t5 and the non-saturation time t6 of the drive signal S1 is t1 and t2 in FIG. 2 (a) and FIG. 2 (b). Is set to be equal to the ratio between t3 and t4.

  FIG. 3 shows an example of the voltage conversion circuit 7.

  The voltage conversion circuit 7 is configured to convert the power supply voltage V1 into the conversion voltage V3 so that the ratio of the saturation time to the non-saturation time is constant. Hereinafter, the circuit will be specifically described.

  A voltage V4 is generated at the base of the transistor Q1. The voltage V4 is set by dividing the power supply voltage V1 between the resistors R1 and R2. Here, the transistor Q1 and the transistor Q2 have the same base-emitter voltage. For this reason, a substantially voltage V4 is also generated at the emitter of the transistor Q2. By the way, the transistor Q3 and the transistor Q4 constitute a mirror circuit. Therefore, a voltage V5 set by the mirror ratio of the transistor Q3 and the transistor Q4 and the resistance ratio of the resistor R3 and the resistor R4 is generated at the collector of the transistor Q4. Transistor Q5 and transistor Q6 have the same base-emitter voltage. For this reason, a substantially voltage V5 is also generated at the emitter of the transistor Q6. Here, a level shift voltage Vr that can be arbitrarily set is applied to the resistor R5. Therefore, the resistor V2 is converted to the converted voltage V3 by the level shift voltage Vr and output from the output section of the voltage conversion circuit 7. That is, the conversion voltage V3 changes according to the power supply voltage V1, and is adjusted so that the ratio between the saturation time and the non-saturation time of the drive signal S1 is satisfied by the level shift voltage Vr. Can do.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the motor drive circuit according to the present invention, the case of a single-phase brushless motor has been described, but the present invention can be similarly applied to a case of a two-phase brushless motor, a three-phase brushless motor, or the like.

  The motor drive circuit according to the present invention is configured such that the voltage change rate of the Hall amplifier 4 changes. However, the present invention is not limited to this embodiment, and for example, an operational amplifier may be separately provided at the subsequent stage of the hall amplifier 4 so that the voltage change rate of the operational amplifier changes.

The circuit diagram of the motor drive circuit which concerns on embodiment of this invention is shown. The wave form diagram of the drive signal which concerns on embodiment of this invention is shown. The circuit diagram of the voltage converter circuit which concerns on embodiment of this invention is shown. The circuit diagram of the motor drive circuit which concerns on a prior art is shown. The wave form diagram of the drive signal which concerns on a prior art is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor 2 Coil 3 Hall element 4 Hall amplifier 5 Output amplifier 6 Speed control circuit 7 Voltage conversion circuit 8 Amplification factor setting amplifier 9 Hall bias circuit 10 Power supply connection terminal S1 Drive signal S2 Detection signal S3 Amplification detection signal V1 Power supply voltage V2 Hall bias V3 conversion voltage V4 gain setting voltage Vr level shift voltage

Claims (4)

A detection circuit that detects the rotational phase of the motor and outputs a detection signal;
An amplification circuit that amplifies the detection signal and outputs an amplified detection signal;
An output amplifier that amplifies the amplification detection signal according to a power supply voltage and outputs a drive signal;
The motor drive circuit, wherein the detection signal is amplified by the amplifier circuit in accordance with the power supply voltage so that a ratio between a saturation time and a non-saturation time of the drive signal is kept constant. A voltage conversion circuit that outputs a conversion voltage according to the power supply voltage;
An amplification factor setting amplifier having the conversion voltage as one input and the amplification detection signal as the other input, and
The motor drive circuit according to claim 1, wherein an output of the amplification factor setting amplifier changes a gain of the amplifier circuit.   The motor driving circuit according to claim 1, wherein the power supply voltage is switched according to a target rotation speed of the motor. The detection signal is detected by a Hall element constituting the detection circuit,
The motor drive circuit according to claim 1, wherein a hall current flowing through the hall element is adjusted so as not to exceed a predetermined value.