JPS6159075B2 - - 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 the 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 the drive circuit. The other Hall element 4 and stator coil 2 are the same as the above-mentioned Hall element 3 and stator coil 1.
The rotor position signal detected by the Hall element 4 is similarly detected by the resistors 9, 10, 12, 1.
4 and an operational amplifier 16, and the power transistors 18, 2
0 is applied to the stator coil 2 through a drive circuit formed by 0.

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 used to supply a bias current (Hall current) to the Hall elements 3 and 4. When a high voltage is applied to the base potential υ _s , the Hall current increases, and the output voltage of the Hall element increases. 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 υ _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 drive current is switched in a sinusoidal manner. Since this is done gradually, unnecessary torque fluctuations and noise are less likely to occur, and the motor torque and rotational speed can be freely controlled by adjusting the base potential υ _s .

However, in the conventional example shown in FIG.
Since the rotor position signal detected by the rotor position signal is amplified and used directly as the driving voltage for the stator coils 1 and 2, it is disadvantageous in that it is easily affected by variations in the sensitivity of the Hall element and offset of the output voltage of the Hall element. To deal with this, it is necessary to use Hall elements with well-matched characteristics and adjust the gain and offset of the differential amplifier, which has the disadvantage of increasing product cost.

It is an object of the present invention to eliminate the above-mentioned disadvantages of the prior art, and to provide a sensor that is not affected by sensitivity variations or output voltage offsets of Hall elements, and in general, magnetic field detection elements for detecting the rotational position of a rotor.
The purpose of the present invention is to provide an inexpensive control circuit for a DC motor.

In order to achieve the above object, the features of the present invention are as follows:
Two reference voltages whose voltage values are set to change vertically in conjunction with the midpoint potential;
Control that includes an amplifier circuit that amplifies the output voltage of the magnetic field detection element around the midpoint potential, and an amplitude limiting circuit that limits the vertical amplitude of this amplified output voltage so that it does not exceed the two reference voltages. There is a circuit.

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

FIG. 3 is a circuit diagram of an embodiment of the present invention. In FIG. 3, a transistor 21 and resistors 24, 2
5 forms an amplifier with a gain of 1, and resistor 2
4 and 25 are resistors having the same resistance value. now,
When the control voltage applied to the base of the transistor 21 is υ _s and the potential drop between the base and emitter is υ _BE , the potential V _B at point B shown in the figure becomes V _B =υ _s −υ _BE . If the current flowing through the bases of transistors 22 and 23 is ignored, the current flowing through resistor 24 and resistor 25 is equal, and the resistance values are also equal, so point A
The potential V _A of is V _A =V _CC −V _B with V _CC as the driving power supply voltage. Therefore, when the control voltage υ _s is changed, the potentials V _A and V _B change vertically in conjunction with each other, and the midpoint potential between V _A and V _B is always equal to 1/2 of the drive power supply voltage V _CC .

The transistors 22 and 23 act as emitter followers, and if the potential drop between the base and emitter of the transistors 22 and 23 is ignored, the point C
The potential V _C at point D is equal to V _A , and the potential V _D at point D is equal to V _B. The resistors 26 and 27 have the same resistance value, and the potential V _E at point E is the midpoint potential between V _C and V _D , and is approximately equal to 1/2 of V _CC .

The Hall elements 30, 31, and 32 are for detecting the rotational position of the rotor magnet, that is, the rotating shaft of the motor. installed in position. The sinusoidal rotor position signal detected by the Hall element 30 is transmitted through the resistors 33, 34, 39, 45.
A differential amplifier formed by a and an operational amplifier 48 amplifies the potential V _E as the center. This amplified rotor position signal is converted to two reference levels V _C and V _D by resistor 40 and diodes 51 and 54.
Its upper and lower amplitude values are limited, and it is applied to the stator coil 63 through a coil drive circuit formed by power transistors 57 and 58. in the end,
As shown in FIG. 4, the voltage waveform applied to the stator coil 63 becomes a trapezoidal wave in which the upper and lower amplitudes of the sinusoidal rotor position signal are limited by two reference voltages V _C and V _D , respectively. .

The Hall elements 30, 31, 32 and the stator coils 63, 64, 65 are respectively arranged at positions shifted by 120 electrical degrees.
Similarly to the case of the Hall element 30 described above, the detected rotor position signal is also applied to the stator coils 64 and 65 in the form of a trapezoidal wave with a limited amplitude. FIG. 5 shows the waveforms and phase relationships of the driving voltages e _u , e _v , e _w applied to the three-phase stator coils. The stator coils 63, 64, and 65 are Y-connected, and the current flowing in one phase is induced by the difference between the terminal voltage of that phase and the terminal voltage of the other two phases and the coil of each phase. Determined by back electromotive force. i _u indicates the current flowing through the stator coil 63. In this way, current always flows in each stator coil in both the positive and negative directions, and the current is switched gradually, resulting in an overall current waveform that is close to a sine wave. ing.

Drive voltage e of stator coils 63, 64, 65
The amplitudes of _u , e _v and e _w , that is, V _C and V _D , are determined by the base potential V _s of the transistor 21, and by changing V _s , the amplitude of the drive voltage is adjusted, and the motor Torque and rotation speed can be changed freely. When v _s is changed, V _C and V _D
changes in conjunction with each other; for example, when v _s increases, V _c
decreases, V _D increases by the same voltage as the change width of V _C , and the driving voltage of the stator coil is V _C and V _D
While the midpoint potential of V _E remains at 1/2 of V _CC ,
Amplitude decreases. Conversely, when v _s is decreased, the amplitude of the drive voltage of the stator coil increases, but even in this case, the midpoint potential V _E does not change. Therefore, it is possible to change the amplitude of the drive voltage from a value close to the drive power supply voltage V _CC to a value close to zero, and the midpoint potential does not change, so the NPN type of the stator coil drive circuit Power transistors 57, 59, 61 and PNP power transistor 5
The power consumed by 8, 60, and 62 is equal.

FIG. 6 is a diagram showing a part of another embodiment of the present invention, in which 66 and 67 are PNP type transistors, and 68 is a diagram showing a part of another embodiment of the present invention.
NPN transistors, 69 and 70 are resistors, v _'s is the control voltage applied to the base of the transistor 66, and A', B', C', D', and E' are A's in the embodiment shown in FIG. , B, C, and DE. In this way, a PNP transistor 66 is used instead of the NPN transistor 21 in FIG. 3, and the transistors 22 and 23 in FIG.
It is also possible to change the emitter follower circuit formed by the emitter follower circuit to the emitter follower circuit as shown in FIG. 6, and the embodiment of FIG. can be caused.

As explained above, according to the present invention, it is possible to make the amplitude of the driving voltage of each phase of the stator coil the same with a simple circuit configuration and therefore at low cost. The influence of variations in the characteristics of the detection element can be removed,
Also, despite using a single power supply,
Current flows in each stator coil in both positive and negative directions with a waveform close to a sine wave, making it possible to create an efficient DC motor control circuit with less disturbances such as torque fluctuations, vibrations, 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 shows the three-phase stator coil drive voltage waveform and one-phase current waveform obtained by the circuit shown in Figure 3. Figure 6 shows the stator coil drive voltage waveform obtained by the circuit shown in Figure 3. FIG. 7 is a circuit diagram showing a part of another embodiment. 21-23, 66-68: transistor, 24
~29,69,70: resistance, 63,64,65:
Stator coil, 30, 31, 32: Hall element, 48, 49, 50: Operational amplifier, 51-5
6: Diode, 57-62: 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 configured to change the values of two reference voltages in conjunction with each other up and down centering on the midpoint potential; and amplifying the output voltage of the magnetic field detection element centering on the midpoint potential. An amplifier circuit and an amplitude limiting circuit that limits the vertical amplitude of the amplified output voltage so as not to exceed the two reference voltages,
A control circuit for a DC motor, characterized in that the amplitude-limited output is supplied to the coil drive circuit.