JPS6217480B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for a DC motor, and particularly to a control circuit for a DC brushless motor used as a drive source for audio equipment.

In DC brushless motors used as drive sources for audio equipment such as magnetic recording and reproducing devices, it is necessary to minimize unnecessary disturbances such as torque fluctuations, vibrations, and noise. Such disturbances often occur when the drive current supplied to the motor's stator coil is switched, so one effective way to reduce the disturbance is to gradually switch the drive current in a sinusoidal manner. will be adopted. An example of this prior art will be explained with reference to FIG.

In FIG. 1, numerals 1 and 2 are stator coils fixed at positions facing a rotor magnet (not shown), which rotates integrally with the rotating shaft of the motor, with a small gap in between.
Switching of the drive current flowing through the rotor 2 is performed using Hall elements 3 and 4 for rotor position detection. The Hall elements 3 and 4 detect changes in the strength of the magnetic field due to the rotation of the rotor magnet at the mounting positions of each Hall element 3 and 4. A wavy rotor position signal is obtained. The rotor position signal detected by one Hall element 3 is amplified by a differential amplifier formed by resistors 7, 8, 11, 13 and an operational amplifier 15, and is amplified by a differential amplifier formed by power transistors 17, 19. The voltage is applied to the stator coil 1 through a drive circuit. The other Hall element 4 and stator coil 2 are the same as the Hall element 3 and stator coil 1 described above.
Similarly, the rotor position signal detected by the Hall element 4 is detected by the resistors 9, 10, 12,
14 and an operational amplifier 16, and the power transistors 18,
The voltage is applied to the stator coil 2 through a drive circuit formed by 20.

FIG. 2 is a diagram showing the waveforms of drive voltages e ₁ and e 2 applied to each stator coil 1 and ₂ in FIG. 1.
In this way, the stator coils 1 and 2 are
Sinusoidal voltages e ₁ and e ₂ shifted by 90 degrees are applied, respectively. Transistor 5 is for providing a bias current (Hall current) to flow to the Hall elements 3 and 4. When a high voltage is applied to the base potential v _S , the Hall current increases, and the output voltage of the Hall element increases due to the Hall current. Since it is approximately proportional to the current, the amplitude of the driving voltages e ₁ and e ₂ applied to the stator coils increases while maintaining a sinusoidal waveform. Conversely, when the potential of v _S is lowered, the amplitude decreases.

In this way, according to the control circuit shown in Figure 1, no matter what position the rotor is in, the drive current always flows to one of the stator coils to generate torque, there is no so-called blind spot, and the switching of the drive current is sinusoidal. Since it is carried out gradually in a wave-like manner, unnecessary torque fluctuations and noise are less likely to occur, and there is an advantage that the torque and rotational speed of the motor can be freely controlled by adjusting the base potential _VS.

However, in the conventional example shown in FIG.
Since the rotor position signal detected in step 4 is amplified and used directly as the drive voltage for stator coils 1 and 2, it is susceptible to the effects of variations in the sensitivity of the Hall elements and offsets in the output voltage of the Hall elements. To overcome this problem, it is necessary to use Hall elements with well-matched characteristics and adjust the gain and offset of the differential amplifier, resulting in an increase in product cost.

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, and to provide an inexpensive method that is not affected by variations in sensitivity or output voltage offset of a Hall element, and generally a magnetic field detection element for detecting the rotational position of a rotor. , to provide a control circuit for a DC motor.

In order to achieve the above object, the features of the present invention are as follows:
The two reference voltages and the output voltage of the magnetic field detection element are set at the midpoint potential of the two reference voltages.
The control circuit includes an amplifier circuit that draws out an output voltage proportional to the difference between the two reference voltages, and an amplitude limiting circuit that limits the vertical amplitude of the amplified output voltage so that it does not exceed the two reference voltages. .

The present invention will be explained below with reference to the drawings.

FIG. 3 is a circuit diagram of one embodiment of the present invention. In FIG. 3, the transistor 21 is an emitter follower, and the potential V _A at point A can be changed by changing the base potential V _S . The transistor 22 is also an emitter follower, but the base potential is kept constant by the constant voltage diode 23, and the potential V _B at point B is constant.

Hall elements 42, 43, 44 are for detecting the rotational position of the motor rotor, and resistors 27,
Point A and B through 28, 29, 30, 31, 32
Connected to the dots. The resistors 27 and 30 have the same resistance value, and are set to be sufficiently larger than the internal resistance of the input terminal of the Hall element 42. Therefore, the potential V _C at one output end (point C in the figure) of the Hall element 42 is approximately the midpoint potential between V _A and V _B. As a result, the sinusoidal position signal detected by the Hall element 42 is transmitted to the resistors 33 and 36.
and an operational amplifier 45, which amplifies the potential V _C as the center. This amplified rotor position signal is transmitted through a resistor 39 and a diode 4.
The upper and lower amplitudes thereof are limited to two reference potentials V _A and V _B by 8 and 51, respectively, and are applied to stator coil 60 through a coil drive circuit formed by power transistors 54 and 55 in the next stage. As a result, the voltage waveform applied to the stator coil 60 becomes a trapezoidal wave in which the amplitude of the sinusoidal rotor position signal is limited by the two reference potentials _VA and _VB , as shown in FIG.

Since the output voltage _of the Hall element 42 is approximately proportional to the input current, as shown in FIG _.
When the current increases to 1, the input current to the Hall element 42 increases, and the output voltage also increases. In response to the increase to V _A and V _A ', V _C increases to the midpoint V _C ' between V _B and V _A ', and the output voltage of the Hall element 42 is amplified around V _C '. Therefore, the position of point D or D' where the drive current waveform of the stator coil 60 is equal to the midpoint potential V _C or V _C ' is at the center of the upper and lower amplitudes even if V _A changes, and the drive current switching always takes place at this central position. In addition, since the slope of the potential at point D or D' increases or decreases according to changes in V _A , switching of the drive current is always performed at the minimum necessary speed, and no disturbance is generated due to switching of the drive current. .

The Hall elements 42, 43, 44 and the stator coils 60, 61, 62 are arranged at positions shifted by 120 degrees in electrical angle, and the Hall elements 43, 44 are arranged at positions shifted by 120 degrees in electrical angle.
Alternatively, the rotor position signal detected at 44 is also applied to stator coil 61 or 62 in the form of a trapezoidal wave with limited amplitude, as in the case of Hall element 42 described above. 3-phase stator coil 6
Drive voltages e _u , e _v , applied to 0, 61, 62
The waveform and phase relationship of e _w are shown in FIG. The stator coils 60, 61, and 62 are Y-connected, and the current flowing in the coil of one phase is determined by the difference between the terminal voltage of that phase and the terminal voltage of the other two phases, and the voltage induced in the coil of each phase. It is determined by the back electromotive force generated. In Fig. 5, i _u indicates the drive current flowing through the stator coil 60. In this way, the current always flows in both the positive and negative directions, and the current is gradually switched, so that the overall drive current is close to a sine wave. It has a waveform.

The amplitude of the driving voltage of the stator coil is V _A and V _B
V _B is determined by the constant voltage diode 23
is constantized by . V _A can be set to any voltage value by changing the base potential v _S of the transistor 21 . Therefore, by changing v _S , the amplitude of the drive voltage of the stator coil can be adjusted, and the generated torque and rotational speed of the motor can be freely changed. Also, the power supply voltage V
Even if some variation (ripple) occurs in _CC , the drive voltage waveform will not change as long as the variation does not affect the operation of the transistor 21 forming the emitter follower or the power transistor forming the coil drive circuit. The motor continues to rotate stably without any influence.

FIG. 6 is a circuit diagram showing another embodiment of the present invention. Hall elements 42, 43, 44 have a common resistance 6
9 and 70, the two points E giving the reference potential
and F are connected. Since the resistors 69 and 70 have the same resistance value and are selected to have a sufficiently large resistance value compared to the internal resistance of the Hall element,
The potential at point G can be regarded as the midpoint potential between the potentials at points E and F, and operates in the same manner as the embodiment shown in FIG. 3, producing the same effect. The transistor 63 is
The collector is connected to a power supply terminal through a resistor 66, and the emitter is connected to another terminal of the power supply through a resistor 67 having the same resistance value as the resistor 66.
Therefore, if the currents flowing through the bases of transistors 64 and 65 are ignored, the currents flowing through resistors 66 and 67 are equal and the resulting voltage drops are also equal. Transistors 64 and 65 form an emitter follower circuit, and if the difference in potential drop between the base and emitter of transistors 64 and 65 is ignored, the potential V _E at point E and the potential V _F at point F are equal to that of transistor 63. It is determined by the base potential v _S , and when v _S is changed, V _E and V _F simultaneously vary in opposite directions, and their midpoint potential is always equal to 1/2 of the power supply potential V _CC . Therefore, the center of the drive voltage of the stator coil is 1/2 of V _CC , and the NPN transistor groups 54, 56, 58 of the stator coil drive circuit,
The power consumed by the PNP transistor groups 55, 57, and 59 is equal.

FIG. 7 is a circuit diagram showing still another embodiment of the present invention. Hall elements 42, 43, and 44 are connected to points A and B in series through resistors 73 and 74. In this case as well, the resistance values of resistors 73 and 74 are equal and are selected to be sufficiently large compared to the internal resistance of the Hall element, so the potentials at points H, I, and J shown in the figure are all the potential V _A at point A and point B. It can be regarded as the midpoint potential of the potential _VB , and acts in the same manner as the embodiment shown in FIG. 3, producing the same effect. In addition, the resistor 73,
If the resistance value of 74 is not large enough, the 7th
Resistors 71 and 72 with the same resistance value as shown in the figure
, the potential V _K at point K becomes the midpoint potential between V _A and V _B , and the resistors 75, 76, 77, 78, 79,
80, the output voltages of the operational amplifiers 45, 46, and 47 have a sinusoidal waveform centered on the potential _VK , similar to the embodiment in FIG. In this case, either or both of resistors 73 and 74 may be omitted.

In the example circuit described above, the emitter follower circuit for creating the reference potential was replaced with one using an NPN transistor instead of one using a PNP transistor, and one using a PNP transistor instead of one using an NPN transistor. Also, even if the transistor 63 in Fig. 6 is replaced with a PNP transistor, or even if the potential V _A side in Figs. 3 and 7 is fixed and the potential V _B side is made variable, the result will be exactly the same. It goes without saying that they can act and produce the same effect.

As explained above, according to the present invention, the amplitude of the drive voltage of each phase of the stator coil can be made the same with a simple circuit configuration and therefore at low cost, and the variation in characteristics of the rotor position detection element can be reduced. In addition, even though a single power supply is used, the stator coil has power in both positive and negative directions.
It is possible to create a DC motor drive circuit in which a current with a waveform close to a sine wave flows, is efficient, and has little disturbance such as torque fluctuation, vibration, and noise.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a diagram showing a stator coil drive voltage waveform in Fig. 1,
Fig. 3 is a circuit diagram of one embodiment of the present invention, and Fig. 4 is a circuit diagram of an embodiment of the present invention.
Figure 5 is a diagram showing the stator coil drive voltage waveform obtained by the circuit shown in Figure 3. Figure 5 is a diagram showing the three-phase stator coil drive voltage waveform and one-phase current waveform obtained by the circuit shown in Figure 3. 2A and 2B are circuit diagrams showing other embodiments of the present invention, respectively. 21, 22, 63, 64, 65...transistor, 23...constant voltage diode, 48-53...
Diode, 60, 61, 62... Stator coil, 27-32, 69-74... Resistor, 45, 4
6, 47... operational amplifier, 42, 43, 44...
Hall element, 54, 59... power transistor.

Claims (1)

[Claims] 1. A rotor magnet that rotates integrally with the rotating shaft, a stator coil that is fixedly arranged at a position facing the rotor magnet through a small gap, a coil drive circuit that supplies exciting current to the stator coil, and A DC motor comprising a magnetic field detection element that detects the rotational position of a rotor magnet and applies its output voltage to the coil drive circuit,
a reference voltage setting means for setting two reference voltages;
an amplifier circuit that draws out an output voltage proportional to the difference between the two reference voltages by centering the output voltage of the magnetic field detection element on the midpoint potential of the two reference voltages; 1. A control circuit for a DC motor, comprising: an amplitude limiting circuit for limiting two reference voltages so as not to exceed them; and supplying the amplitude limiting output to the coil drive circuit.