JPS6321193Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brushless motor drive circuit, and particularly to a drive circuit for a brushless motor with low power consumption.

Although there are various energization methods for driving a brushless motor, the two-phase unidirectional energization method is increasingly used because it provides a compact and simple structure. In this method, the energization of the two-phase stator coils is sequentially switched to allow current to flow in only one direction, and the rotor is rotated using the torque generated by the magnetic flux of the rotor magnet.
The rotor magnet has a plurality of pairs of two adjacent permanent magnets of opposite polarity arranged at intervals.

In the two-phase one-way energization type brushless motor as described above, the energization of the stator coil must be switched depending on the rotational position of the rotor. There are various rotor position detection methods for this switching, but two commonly used methods are an optical method using a photo coupler (photoreflector), and a magnetic method using a Hall element. In the case of an optical type, it transmits or blocks light depending on the rotational position of the rotor.
There are two methods: switching by reflection or absorption. On the other hand, in the magnetic type using a Hall element, switching is performed by changes in voltage caused by the magnetic field of the rotor.

The above two switching methods each have their advantages and disadvantages, but the common problem is that a bias current must be applied to these photocouplers and Hall elements. Particularly in small motors, this accounts for a large proportion of the current consumption.

For example, in the case of a brushless motor that generates a torque of 1.5 to 2.0 g/cm during operation, approximately 10 mA is consumed in the drive electronic circuit. The current consumption of the motor at no load is 20-30 mA, which includes the current of the drive electronics. 60 to 70% of the current of the drive electronic circuit is the current flowing to the position detection element, and this is a current that is consumed without contributing at all to the generation of torque of the brushless motor.
Generally, a current of 5 to 10 mA is required to be passed through a photocoupler or Hall element used in a position detection element.

As mentioned above, the current consumed by the position detection element accounts for a large proportion of the current consumption of the entire brushless motor, so in order to reduce the current consumption of the brushless motor, it is necessary to reduce the current flowing through the position detection element. desirable. However, if the current is simply reduced, the output voltage will decrease and the circuit operation will become unstable. Therefore, it is desirable to reduce the current of the position detection element as much as possible and obtain a large output.

The present invention has been made to achieve the above object, and is intended to obtain a sufficient output of a position detection circuit with less current consumption.

In order to achieve the above object, in the brushless motor drive circuit according to the present invention, a bias current is applied to the position detection element only during startup, and when rotating at a constant speed, the bias current of the position detection element is reduced to zero or very small. That is.

In the brushless motor drive circuit according to the present invention, a coil is connected in series to the position detection element, and the drive coil current is switched by the output of the position detection element during startup, and the bias current of the position detection element is used during constant speed rotation. The switching is performed mainly by the output of the coil.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, and this brushless motor drive circuit includes a servo detection circuit including a comparator CP ₁ , a position detection circuit including a comparator CP ₂ , and a comparator CP ₃ . Equipped with a current limiting circuit. The servo detection circuit detects the back electromotive force generated by the rotation of the rotor and outputs the stator coil L ₁ ,
It supplies the base bias current of transistors Tr ₁ and Tr ₂ that switch L ₂ . Further, the output of the comparator CP ₁ is input to the comparator CP ₃ of the current limiting circuit, and _{the transistors Tr 3 and} Tr ₄ are switched by the output of the comparator CP 3. Thereby, the bias current flowing through the Hall element HE is controlled. In addition, transistor Tr ₄
and the resistor R are added to limit the current flowing through the Hall element HE and protect the Hall element HE.

The output end of the Hall element HE is connected in series with the coil _Ls . Both the Hall element HE and the coil _Ls are placed near the rotor, and input the voltage generated by the magnetic field of the rotor's magnet to the comparator _CP2 . In order to match the phases of the respective generated voltages, the Hall element HE is placed at the midpoint of the two-phase drive coils, and the coil L _s is placed at the same position as the drive coils L ₁ and L ₂ , but the coil L _s is placed at least It is sufficient that only one coil is formed, and the number of turns may be smaller than that of the drive coil. The outputs of the Hall element HE and the coil _Ls are input to the comparator _CP2 , and the drive coils _L1 and _L2 are switched by the output of the comparator _CP2 .

Next, the operation of the brushless motor drive circuit of the above embodiment will be explained.

When the rotor starts rotating, that is, when the back electromotive force of the drive coil L ₁ is zero or very small, the comparator CP ₁ connects the transistors Tr ₁ and Tr ₂
Supply the base bias current so that the maximum current flows through the base. At this time, the output of comparator CP ₁ is
A bias current is input to CP ₃ , and the output of comparator CP ₃ supplies a bias current to the base of transistor Tr ₃ to increase the current flowing through Hall element HE. Therefore, the output voltage of the Hall element HE can also be increased, and the switching signal of the comparator _CP2 is obtained from the output of the Hall element HE.

As the rotational speed of the rotor increases, the back electromotive force also increases, and the output of the comparator _CP1 decreases. Therefore, the output of the comparator CP ₃ of the current limiting circuit becomes smaller, and the bias current at the base of Tr ₃ also becomes smaller, so that the current flowing through the Hall element HE also becomes smaller. Therefore, the output of the Hall element HE becomes smaller, but at this time the output of the coil L _s becomes larger. Therefore, the output of the comparator CP ₂ is obtained by the output of the coil L _s , and this signal is used to control the transistors Tr ₁ , connected to the drive coils L ₁ , L ₂ .
Switching Tr ₂ .

When the rotation speed of the rotor becomes constant or close to it, the Hall element
Reduce the current flowing through HE to zero or to a very small value. Its value is determined by how the reference potential of the comparator is set.

Figure 2 is a graph showing the amount of bias current flowing through the Hall element.The 15mA required at startup gradually decreases as the rotor speed increases, and becomes almost zero when the rotor reaches constant speed. It shows what will happen. This reduction in current occurs because the output of the comparator of the current limiting circuit is gradually reduced by the output of the comparator of the servo detection circuit.

In the brushless motor drive circuit according to the present invention, the output of a position detection element such as a Hall element is used for switching at startup or until a certain number of rotations is reached, and the output of the coil is performed after reaching a certain number of rotations. This allows switching to be performed by As a result, a constant output signal from the position detection circuit can be obtained from the time of startup to the time of constant speed rotation.

Since the coil does not require bias current,
Current consumption when rotating at constant speed can be reduced. That is, since the current consumption of the position detection element of 5 to 15 mA can be reduced, the current consumption of the brushless motor as a whole is also significantly reduced.

In the above example, a case was explained in which a Hall element was used, but even if an optical element such as a photocoupler (photoreflector) is used, the other parts may be the same and the operation will be the same.

Since the back electromotive force generated in the stator coil is proportional to the number of rotations of the rotor, it is also used in a servo circuit for controlling the number of rotations to a constant value, as in the up-voltage embodiment. However, the present invention has no direct relationship with the servo circuit, and the back electromotive voltage for the current limiting circuit may be taken out separately from the servo circuit.

Since it is sufficient for the coil used in the position detection circuit to have about 5 to 10 turns, it may be formed by printing on the stator board, or may be formed integrally with the drive coil.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing its characteristics. CP ₁ , CP ₂ , CP ₃ ... Comparator, HE ... Hall element, L _s (position detection) coil.

Claims (1)

[Scope of utility model registration request] In a brushless motor drive circuit that detects the rotational position of a rotor to which a magnet is attached using a position detection circuit and switches energization between stator coils of different phases, both stator coils are located near the rotor and their output voltages are in the same phase. The position detection circuit includes a position detection element and a coil _Ls connected in series, and a current limiting circuit that controls the bias current flowing to the position detection element according to the magnitude of the back electromotive force generated in the stator coil. A predetermined bias current is applied to the position detection element when the rotor is started, and when the rotational speed of the rotor reaches a predetermined value, the bias current of the position detection element is reduced by the current limiting circuit. A brushless motor drive circuit characterized by: