JPH05236785A - Drive circuit for brushless motor - Google Patents

Abstract

PURPOSE:To provide a drive circuit for brushless motor employing no rotation detector wherein counter-electromotive force can be detected accurately in OFF section of output voltage and the motor can be decelerated forcibly. CONSTITUTION:Zero-cross point of counter-electromotive force is detected and a synthesized driving waveform created utilizing the timing of zero-cross point is inputted to two comparators 5, 6 where it is compared with voltage references 1, 2. Outputs from two comparators are fed to an AND circuit 7 and thus ANDed output is employed as a switching signal for turning an analog switch 8 OFF thereby turning a predetermined section of an output voltage from a power amplifier 4, including the zero-cross point, forcibly OFF to produce a high impedance section. According to the constitution, zero-cross point of counter-electromotive force can be detected easily and a motor can be decelerated forcibly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit using a back electromotive force for phase detection in a brushless motor.

[0002]

2. Description of the Related Art Conventionally, a brushless motor which uses a back electromotive voltage in an off section of a drive waveform for phase detection while the motor is rotating uses a drive transistor in an output stage as a switching element. The current in the ON section of the switching transistor is only inflow on the sink side,
On the source side, only the outflow operation was performed, and the motor deceleration could not be forced. Also, in the drive circuit whose output stage is an amplifier type, there is no section where the output becomes high impedance,
The back electromotive force cannot be detected. Furthermore, it is possible to input and output the current by setting the output stage of the current drive waveform, and it is possible to make it a high impedance, but in reality it is not controlled by a predetermined means when decelerating the motor. There is a problem in that a zero cross point occurs in the output voltage waveform and it becomes impossible to accurately detect the back electromotive force.

FIG. 3 shows a block diagram of a sensorless drive circuit of a three-phase brushless motor in which a drive current switching circuit is constructed by using a transistor switching element in an output stage and a counter electromotive voltage is used for detecting a phase of a rotor. ing.
In the same figure, the brushless motor is driven by a starting circuit 9
Is sent to the output stage 11 under timing control by the timing control circuit 10, and a transistor switching element (not shown) of the output stage 11 is turned on / off to supply a drive current to the drive coil 12 of each phase. At this time, the drive coil 12 of each phase is rotated by the rotation of the rotor magnet of the motor.
, A counter electromotive voltage as indicated by a broken line in FIG. 4 is generated.

While the motor is rotating, the drive coils 12 for the respective phases are
The coil output voltage and the coil common voltage are input to the counter electromotive voltage detection circuit 13 in order to detect the counter electromotive voltage generated in
The zero cross point of the counter electromotive voltage generated in each phase shown in FIG. 4 is detected, and the zero cross point is supplied to the timing control circuit 10. Using this timing, a three-phase drive waveform is created and a composite waveform is obtained. There is. The timing control is performed because the output stage has a low impedance and the output voltage overlaps with the zero-cross point of the back electromotive force and the zero cross point is masked, so that the back electromotive voltage cannot be actually detected. is there. Therefore, for example, in order to detect the zero cross point of the counter electromotive voltage, the supply of the output voltage is stopped for a predetermined period, and the output voltage is supplied from the output stage at a predetermined electrical angle, for example, 30 degrees behind the zero cross point of the counter electromotive voltage. A drive circuit is known in which the timing is controlled to detect a zero cross point (Japanese Patent Laid-Open No. 2-51389).

However, since the drive circuit uses the transistor in the output stage as a switching element, the drive current during the ON period of the transistor is only inflow on the sink side and only outflow on the source side. , The motor cannot be decelerated forcibly.

[0006]

SUMMARY OF THE INVENTION According to the present invention, in a brushless motor drive circuit that does not use a rotation detector, it is possible to accurately detect a back electromotive force in the off section of the output voltage and to forcibly decelerate the motor. It is in the point of providing the drive circuit.

[0007]

According to the present invention, in a drive circuit of a brushless motor using a back electromotive voltage in an off section of a drive output voltage for detecting a phase of a rotor, a drive amplifier connected to each phase drive coil of the motor. And a switching means for forcibly setting a high impedance in a predetermined section including the zero cross point of the output voltage of the drive amplifier on the input side of the drive amplifier.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention proposes a driving circuit as shown in FIG. 1 in order to solve the above problems. In FIG. 1, the drive waveform (composite waveform) created by the timing control is input to the non-inverting input terminal of the buffer circuit 1 through the multiplier 2 controlled by the command voltage of the control circuit 2, and The output voltage of the power amplifier 4 is fed back to its inverting terminal. Then, in order to compare the composite waveform with the two reference voltages 1 and 2, the composite waveform is input to the two comparators 5 and 6 and compared with the respective reference voltages. Obtain the comparator output voltage such as and.

Next, the signals of the comparator output voltage and are input to the AND circuit 7 to take an AND to obtain an AND circuit output voltage waveform as shown in (1). When the analog switch 8 is turned off at the timing of the AND circuit output voltage to forcibly set it to high impedance, the output voltage of the buffer circuit 1 in this section is not transmitted to the power amplifier 4 that drives the motor, and as shown in An output voltage waveform having a high impedance section (off section) is obtained. As shown in FIG. 2, since there is no zero cross point in the output voltage in the high impedance section of the analog switch 8, the zero cross point of the back electromotive force can be easily detected without being masked and the motor is forcibly decelerated. It becomes possible to do. At the time of this deceleration, the output voltage of the drive circuit becomes low, but it does not have the reverse polarity unless the reversal mode is set, and therefore does not affect the detection of the zero cross point of the back electromotive force.

The embodiment shown here is merely an example, and for example, the switching signal of the analog switch may be a rectangular wave as the composite waveform.

[0011]

According to the present invention, the zero cross point of the back electromotive force can be easily detected in the off section of the drive waveform, and the output is forcibly made to have a high impedance in the off section.
With the detection of the counter electromotive voltage, the motor can be forcibly decelerated.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of the embodiment of the present invention.

FIG. 3 is a block diagram of a conventional example.

FIG. 4 is an operation waveform diagram of a conventional example.

[Explanation of symbols]

1 ... Buffer circuit 4 ... Power amplifier 5, 6 ... Comparator 8 ... Analog switch

Claims (1)

[Claims] 1. A drive circuit for a brushless motor using a back electromotive force voltage in an off section of a drive output voltage for detecting a rotor phase, a drive amplifier connected to each phase drive coil of the motor, and an input side of the drive amplifier. And a switching means for forcibly setting a high impedance in a predetermined section including a zero cross point of the output voltage of the drive amplifier.