JP3706440B2 - Motor drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a motor drive circuit that can be used by switching between bipolar drive and unipolar drive.
[0002]
[Prior art]
In order to rotationally drive a motor having a three-phase Y-connection drive coil, a bipolar drive method and a unipolar drive method are conceivable. In the former bipolar driving method, a source-side transistor and a sink-side transistor connected in series between a power supply VCC and a ground VSS are provided for each of the three-phase driving coils, and a predetermined order is set for the three-phase driving coils. In this method, the source-side transistor and the sink-side transistor are controlled to be turned on / off so that current is supplied. On the other hand, in the latter unipolar driving method, instead of the three source side transistors, a common power side transistor is provided in a three-phase driving coil, and the power source side transistor is always turned on. In this method, the sink-side transistor is controlled to be turned on and off for each predetermined electrical angle so that current is supplied in a predetermined order. The former bipolar driving method is a torque-type driving method and is suitable for low-speed rotation. On the other hand, the maximum voltage amplitude of the driving coil is suppressed to VCC / 2 or less, so that high-speed rotation of a predetermined rotation or more is achieved. Can not respond. Specifically, in a motor that uses both high speed and low speed, if the motor for high speed is driven at low speed, torque will not be generated, and if torque can be taken in the low speed area, it will be difficult to rotate in the high speed area. turn into. On the other hand, the latter unipolar driving method is suitable for high-speed rotation because the voltage waveform of the driving coil can swing around the power supply VCC, so that the maximum voltage amplitude of the driving coil can be expanded to VCC.
[0003]
Therefore, recently, taking advantage of both bipolar drive and unipolar drive methods, bipolar drive and unipolar drive, such as bipolar drive at low speed and unipolar drive at high speed, depending on the required number of rotations. There is an increasing demand for motor drive circuits that drive motors by switching between the two.
Hereinafter, a conventional motor driving circuit that switches between bipolar driving and unipolar driving to cope with low speed and high speed rotation will be described with reference to FIG.
[0004]
2, (1), (2), and (3) are U, V, and W phase three-phase drive coils, respectively. For the U-phase drive coil (1), an NPN-type sink-side transistor (4) and source-side transistor (5) connected in series between the power supply VCC and the ground VSS are provided, and both transistors (4 ) The collector-emitter connection point of (5) is connected to one end of the drive coil (1). A resistor (6) for preventing leakage current is connected between the base and emitter of the source side transistor (4), and the base of the source side transistor (4) consists of PNP type transistors (7) and (8). The output of the current mirror circuit is connected. Similarly, for the V-phase drive coil (2), the NPN source side transistor (9) and the sink side transistor (10), the resistor (11), and the PNP type transistors (12) and (13) are used. The output of the current mirror circuit is connected. Similarly, for the W-phase drive coil (3), an NPN source side transistor (14) and a sink side transistor (15), a resistor (16), and a PNP type transistor (17) (18). The output of the current mirror circuit consisting of The other ends of the three-phase drive coils (1), (2) and (3) are connected in common and connected to the power supply VCC via a PNP-type power supply side transistor (19). The base of the power supply side transistor (19) is connected to the power supply VCC through a resistor (20). Reference numeral (21) denotes a switching control circuit for switching between bipolar driving and unipolar driving. The switching control circuit (21) includes transistors (7), (12), (17) which are inputs to a current mirror circuit for three phases. ) Is connected, the bases of the sink side transistors (5), (10), and (15) are connected, and further, the base of the power source side transistor (19) is connected. Thus, the switching control circuit (21) can select bipolar driving or unipolar driving by on / off controlling the transistors connected thereto. A current detection resistor (22) is connected between the emitters of the sink side transistors (5), (10) and (15) and the ground VSS. A voltage corresponding to the rotational state of the motor is generated at both ends of the current detection resistor (22). Specifically, a voltage that increases as the current flowing through the motor drive coils (1), (2), and (3) increases and decreases as the current decreases at both ends of the current detection resistor (22). This voltage is used for motor rotation control and overcurrent protection. That is, it is used in a servo closed loop when it is desired to keep the motor rotation at a predetermined constant rotation speed. The operation of FIG. 2 will be described below.
[0005]
First, when the circuit of FIG. 2 is bipolar driven, the power supply side transistor (19) is always turned off by the output of the switching control circuit (21). In this state, by appropriately controlling the inputs of the current mirror circuit for three phases and the bases of the sink side transistors (5), (10) and (15) by the output of the switching control circuit (21), a source side transistor of a certain phase From the driving coil of the phase and the driving coil of the other phase, the driving current flows to the sink side transistor corresponding to the driving coil of the other phase, and this operation is repeated according to the order of supplying the current to the driving coil. Motor drive is executed.
[0006]
Further, when the circuit of FIG. 2 is unipolar drive, the current mirror circuit for three phases is turned off by the control output of the switching control circuit (21) to turn off all the source side transistors (4), (9) and (14). . Then, the power supply side transistor (19) is always turned on, and for example, the sink side transistors (5), (10), and (15) are successively turned on by energizing 120 degrees. As a result, the motor is unipolarly driven and can be rotated at a higher speed than the bipolar drive.
[0007]
[Problems to be solved by the invention]
However, when the circuit of FIG. 2 is operated by switching to unipolar drive, there are the following problems. As an example, consider a process in which the sink-side transistor (5) in the U-phase drive coil (1) is turned off and then the sink-side transistor (10) in the V-phase drive coil (2) is turned on. . When the sink side transistor (5) is on, a drive current flows from the power source side transistor (19) to the sink side transistor (5) via the drive coil (1). Although the voltage appearing at V is lower than the power supply VCC, when the sink-side transistor (5) is turned off, the voltage at one end A of the drive coil (1) is caused by the counter electromotive voltage generated in the drive coil (1). The voltage is higher than the power supply VCC. As a result, current flows into the base of the source-side transistor (4) that is always turned off via the resistor (6) for preventing leakage current. Since the source side transistor (4) is an NPN type, and a diode is formed between the base and collector in the forward direction, when the one end A of the drive coil (1) becomes a voltage higher than the power supply VCC, The diode between the base collector in the side transistor (4) is turned on, that is, the source side transistor (4) becomes conductive as a reverse transistor. As a result, a current flows from the emitter to the collector of the source side transistor (4), and as a result, the power supply VCC fluctuates.
[0008]
In addition, since the current flows in the opposite direction with respect to the phase where the drive current does not flow, the rotation efficiency of the motor is deteriorated.
Further, the resistors (6), (11), and (16) for preventing leakage are not necessarily provided, but if the resistors (6), (11), and (16) are not provided, the collector side of the source side transistor (4) is provided. When the voltage is VCC but the emitter side voltage becomes much higher than VCC due to the back electromotive voltage generated in the drive coil (1), the source side transistor (4) breaks down, and Similarly, a current flows from the emitter to the collector of the source side transistor (4), causing the power supply VCC to fluctuate. In this case, the source side transistor (4) may be destroyed.
[0009]
Such fluctuations in the power supply VCC have hindered the operation of the motor drive circuit, impairing the drive efficiency of the motor and causing the motor to be unable to rotate normally. In addition, breakdown of the source side transistor (4) and deterioration of the rotation efficiency of the motor are also problems. The same problem occurs when the sink-side transistors (10) and (15) corresponding to the V and W phase drive coils (2) and (3) are turned off from on.
[0010]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a circuit capable of preventing a power supply fluctuation when a unipolar drive is performed and rotating the motor normally in a motor drive circuit capable of switching between a bipolar drive and a unipolar drive.
[0011]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned problems. The feature of the present invention is that the current is supplied to the three-phase drive coils in a predetermined order to drive the motor in a bipolar manner. Since the motor is unipolarly driven by supplying current in the order determined by the source-side and sink-side transistors provided for each of the three-phase drive coils and the three-phase drive coils, the three-phase drive A power supply side transistor provided in common with the coil, and the source side transistor and the power supply side transistor so that when the motor is bipolar driven, the power supply side transistor is turned off and a current flows in the order determined in the three-phase drive coil. When the on-off control of the sink side transistor is performed and the motor is unipolarly driven, the source side transistor is turned off and the three-phase transistor A motor drive circuit comprising: a control circuit that switches on and off the bipolar drive and the unipolar drive of the motor so as to control the on / off of the power supply side transistor and the sink side transistor so that current flows in a predetermined order in the moving coil. When the motor is unipolarly driven, the source-side transistor corresponding to the sink-side transistor is affected by a back electromotive voltage generated in the drive coil when the sink-side transistor is turned off from a predetermined drive coil. Is provided with diode means for preventing current from flowing from the output point of the drive coil toward the power source.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Details of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a circuit block diagram showing a motor drive circuit of the present invention. 1 that are the same as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted.
[0013]
In FIG. 1, (23) is a diode, its anode is connected to the power supply VCC, and its cathode is three source side transistors (3) provided corresponding to the three-phase drive coils (1) (2) (3). 4) Commonly connected to the collectors of (9) and (14).
Consider the case where the circuit of FIG. 1 is used as unipolar drive. In this case, the current supply to the transistors (7), (12) and (17) which are the constituent elements of the current mirror circuit for three phases is stopped by the control output of the switching control circuit (21). As a result, the three source side transistors (4), (9), and (14) are always turned off as the operation of the current mirror circuit stops. Further, the power supply side transistor (19) is always turned on by the output of the switching control circuit (21). In this state, the control output of the switching control circuit (21) is switched by, for example, 120-degree energization to turn on the sink side transistors (5), (10), and (15) sequentially and alternately, thereby driving the drive coil (1 ), (2), and (3) are supplied with current in a predetermined order. Specifically, the sink-side transistor (5) is supplied from the power-supply side transistor (19) through the drive coils (1), (2), and (3). ) (10) Current is supplied to (15), and thus the motor can be driven.
[0014]
Here, in order to rotate the motor, the sink side transistors (5), (10), and (15) are repeatedly turned on and off. For example, the sink side transistor (5) corresponding to the U-phase drive coil (1) is used. ) When the sink-side transistor (5) shifts from on to off, a reverse voltage is generated in the drive coil (1), and the voltage at one end A of the drive coil (1) rises from VCC. Although the source side transistor (4) is off, the voltage at point A rises, so that current flows from the point A through the resistor (6) to the base of the source side transistor (4), and the source side transistor (4) The diode formed between the base collectors can be turned on. However, since the cathode potential of the diode (23) at this time is higher than the anode potential, the source side transistor (4) is turned off by cutting off the path as the reverse transistor, and the fluctuation of the power supply VCC is prevented. .
[0015]
In FIG. 1, resistors (6), (11), and (16) for preventing leakage are connected between the base emitters of the source side transistors (4), (9), and (14). ) (16) compensates for the characteristics. If the satisfactory characteristics can be obtained without connecting the resistors (6), (11), and (16), the resistors (6), (11), and (16) are provided. ) May be deleted from FIG. In this case, the voltage at one end A of the drive coil (1) rises above VCC by the back electromotive voltage generated in the drive coil (1) when the sink-side transistor (5) is turned off from on, and the source-side transistor (4) Even if breakdown occurs, current supply to the power supply VCC side is prevented by the diode (23), and fluctuations in the power supply VCC are prevented.
[0016]
This operation can be applied to the source side transistor (914) corresponding to the drive coils (2) and (3).
Therefore, since the fluctuation of the power supply VCC can be prevented, the motor can be driven normally and efficiently.
[0017]
【The invention's effect】
According to the present invention, in a motor drive circuit that can drive a motor by switching between bipolar drive and unipolar drive, it is possible to reliably prevent power fluctuation caused by a counter electromotive voltage generated in a drive coil during unipolar drive. As a result, there is an advantage that the motor can be driven normally and efficiently.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a motor drive circuit of the present invention.
FIG. 2 is a circuit block diagram showing a conventional motor drive circuit.
[Explanation of symbols]
(1) (2) (3) Drive coil (4) (9) (14) Source side transistor (5) (10) (15) Sink side transistor (19) Power supply side transistor (21) Switching control circuit (23) diode

Claims (2)

A source-side transistor and a sink-side transistor provided for each of the three-phase driving coils, and the three-phase driving coils for supplying a current to the three-phase driving coils in a predetermined order to bipolarly drive the motor. In order to supply the current in the order determined by the unipolar drive of the motor, the power supply side transistor provided in common for the three-phase drive coil and the power supply side transistor are turned off when the motor is bipolar driven. At the same time, the source-side transistor and the sink-side transistor are controlled to be turned on and off so that current flows in the order determined by the three-phase drive coils. When the motor is unipolarly driven, the source-side transistor is turned off and The power supply side transistor and the thin-film transistor are arranged so that current flows in the order determined by the three-phase drive coil. Off controls side transistor, a motor drive circuit and a control circuit for switching the bipolar drive and unipolar driving of the motor,
When the motor is unipolarly driven, the source-side transistor corresponding to the sink-side transistor is affected by a back electromotive voltage generated in the drive coil when the sink-side transistor is turned off from a predetermined drive coil. A motor drive circuit comprising diode means for preventing current from flowing from an output point of the drive coil toward a power source. 2. The motor drive circuit according to claim 1, wherein the diode means is connected between a power source and an input electrode of the source side transistor provided for each of the three-phase drive coils.

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