JPS622960Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a drive circuit for a brushless DC motor, and is particularly designed to prevent differences in characteristics between forward rotation and reverse rotation of the motor.

Figure 1 shows a conventional example of a drive circuit for a brushless motor, in which the rotational angular position of a rotating magnet (hereinafter referred to as rotor magnet) of the motor is detected by a position detection element such as a Hall element 1, and the detected position is detected by a position detection element such as a Hall element 1. Accordingly, for example, the drive currents of the two-phase field coils 2 and 3 are switched and controlled. That is, by sending the two outputs from the Hall element 1, which is a position detection element, to the positive and negative input terminals of the operational amplifier 4 and the negative and positive input terminals of the operational amplifier 5, the outputs of these operational amplifiers 4 and 5 become as follows. They are made to be inverted versions of each other, or have a phase difference of 180° from each other. The outputs from these operational amplifiers 4 and 5 are sent to the bases of switching transistors 8 and 9 via resistors 6 and 7, respectively, and the collector outputs of these switching transistors 8 and 9 are sent via resistors 10 and 11, respectively. and is sent to the bases of driving transistors 12 and 13. These driving transistors 12, 13
Bidirectional transistors are used in
For example, they are connected in series with two-phase field coils 2 and 3, and these driving transistors 1
When field coils 2 and 13 are driven on and off, the drive currents of field coils 2 and 3 are controlled on and off.

In this motor drive circuit, field coil 2,
When the line 14 on the third side is at a positive voltage Vs and the line 15 on the emitter side of the drive transistors 12 and 13 is grounded, for example, when the switching transistor 8 is turned on, the collector potential of the transistor 8 is approximately equal to the circuit power supply. 16, a current flows through the resistor 10, and the base potential of the drive transistor 12 becomes approximately equal to the base-emitter saturation voltage _VBE of this transistor 12. are almost equal, so a voltage of approximately V _CC -V _BE appears across the resistor 10, and if the resistance value of this resistor 10 is selected appropriately, a sufficient base current can be obtained regardless of the value of the drive voltage Vs. can be applied to the driving transistor 12.

By the way, in the drive circuit of such a brushless DC motor, when the direction of the current flowing through the field coils 2 and 3 is reversed to reverse the rotation of the motor, for example, the DC from the drive DC power supply 17 is reversed. The field coils 2 and 3 are supplied to the field coils 2 and 3 through the changeover switch 18.
When switching the line 14 to the switching terminal b side and setting the line 14 to the ground potential and the line 15 to approximately Vs, the following inconvenience occurs.

That is, since the line 14 is at ground potential and the line 15 is at approximately Vs, the driving transistors 11, 1
3 has an emitter drive configuration. Therefore, for example, when the switching transistor 8 is turned on and the drive transistor 12 is about to be turned on, a current flows through the field coil 2 and the transistor 1 is turned on.
The base potential of 2 increases. Here, if the DC resistance of the field coil 2 is R _DC and the current flowing through this coil 2 is L _L , then the base current I _B that can flow through the driving transistor 12 is I _B = V _CC - (R _{DC LL} + _VBE )/R... In this equation, R is the resistance value of the resistor 10, and V _BE is the driving transistor 1 as described above.
This is the base-emitter saturation voltage of 2. As is clear from this equation, the voltage Vs of the drive power supply 17
If you try to increase _L by increasing L, the base current of the drive transistor 12 will decrease, making it impossible to turn on the transistor 12 completely, and for example, the motor torque during reverse rotation will be less than when rotating in the forward direction. Furthermore, there is a difference in characteristics between forward rotation and reverse rotation.

It is an object of the present invention to provide a motor drive circuit that can eliminate such conventional drawbacks and eliminate the difference in characteristics between normal rotation and configuration with a simple circuit configuration.

Another object of the present invention is to provide a motor drive circuit that can reduce torque overlap and depression and obtain smooth torque.

That is, the motor drive circuit according to the present invention is
A bidirectional drive switching means switches and controls the drive power for the multi-phase field coil in accordance with the detected position of the rotor by the position detection element, and the polarity of the power for the field coil is switched to enable forward and reverse rotation. In the drive circuit for the motor, the emitters of the plurality of transistors that turn on and off the bidirectional switching means for driving the multi-phase field coils are connected to the circuit power supply via a resistor, and the collectors are connected to the circuit power supply through the resistor. It is characterized in that it is connected to the control terminal of the directional switching means and supplies a constant voltage to the base of the transistor via the constant voltage means to turn the transistor on.

Therefore, in the conventional technology, the base current of the transistor for driving the coil when the motor is reversed (reverse rotation) decreases when the voltage of the drive power supply increases, and the motor torque decreases. By using this configuration, switching control can be performed by making the base current of the coil drive transistor constant, and even when the drive power supply voltage increases during motor reversal (reverse rotation), it is possible to supply sufficient base current. It is possible to eliminate the difference in characteristics between forward rotation and reverse rotation.

Below, preferred embodiments of the present invention will be described.
This will be explained with reference to the drawings.

FIG. 2 shows a drive circuit for a brushless motor as a first embodiment of the present invention, in which the rotational angular position of a rotating magnet (hereinafter referred to as rotor magnet) of the motor is detected by a position detection element such as a Hall element 20. The driving currents of, for example, two-phase field coils 21 and 22 are switched and controlled depending on the detected position. Here, the Hall element 20 used as a position detection element extracts the strength of a magnetic field as an electric signal using the so-called Hall effect, and outputs a pair of output terminals depending on the direction of the applied magnetic field. The polarity of the voltage is reversed. This Hall element 20
The outputs from the pair of output terminals are sent to the positive and negative input terminals of two differential amplification type operational amplifiers 23 and 24. However, with respect to the pair of output terminals of the Hall element 20, the connection of the positive and negative input terminals of the operational amplifier 23 and the connection of the positive and negative input terminals of the operational amplifier 24 are reversed. , 24 are inverted versions of each other.

Next, the output from the operational amplifier 23 is connected to the resistor 25.
The output from the operational amplifier 24 is sent to the base of the switching transistor 31 via the
switching transistor 32 via resistor 26
is being sent to the base of The emitters of these switching transistors 31 and 32 are connected to the positive terminal of the +V _CC circuit power supply 30 via resistors 27 and 28, respectively, and the bases are connected via resistors 33 and 34 as constant voltage supply elements, respectively. It is connected to the positive terminal of the circuit power supply 30. Constant voltage elements such as Zener diodes may be used instead of these resistors 33 and 34.

Next, drive transistors 41 and 42 switch and control the drive currents of the two-phase field coils 21 and 22.
For example, a bidirectional transistor is used. The bases of these transistors 41 and 42 are connected to the switching transistor 3, respectively.
It is connected to collectors 1 and 32.

Here, direct current from the driving DC power supply 40 is applied to the two-phase field coils 21 and 22, but when the changeover switch 45 is connected to the changeover terminal a side, the line on the field coils 21 and 22 side is 43 becomes a positive voltage (this is referred to as Vs), and when connected to the switching terminal b side, the line 44 on the side of the transistors 41 and 42 becomes a positive voltage Vs.

In such a motor drive circuit, when the changeover switch 45 is connected to the changeover terminal a side,
The line 43 becomes a positive voltage Vs. For example, when the output of the operational amplifier 23 is at ground potential, the base of the switching transistor 31 is connected to the resistors 33 and 25.
A constant voltage V _B1 divided by is applied,
This transistor 31 is turned on. At this time, the emitter potential V _E1 of the transistor 31 is the base-emitter saturation voltage V _BE of this transistor 31.
When it is set to ₁ , it becomes constant as V _E1 = V _B1 + V _BE1 . Furthermore, since a constant voltage of V _CC -V _E1 is applied across the resistor 27, by selecting an appropriate resistance value of the resistor 27,
Even if the voltage V _S of the driving DC power supply 40 changes, a constant and sufficient base current can flow through the base of the driving transistor 41, and this transistor 41 can be completely turned on.

Next, when the changeover switch 45 is connected to the changeover terminal b side, the line 44 side becomes the positive voltage V _S and the line 43 becomes the ground potential. At this time, when the driving transistor 41 is turned on, the base potential of this transistor 41 is approximately V _S as described above.
However, as long as this V _S does not exceed the above V _B , the switching transistors 31 and 32
acts as a constant current source during each ON operation.
Therefore, by appropriately selecting the resistance values of the resistors 27 and 28, even if V _S becomes high, the bases of the driving transistors 41 and 42 can be connected to the switching terminal a side of the changeover switch 45. Sufficient base current can flow in the same way as when Therefore, the same characteristics can be obtained regardless of whether the motor rotates forward or backward.

Next, FIG. 3 shows a second embodiment of the present invention,
The resistors 33 and 34 of the first embodiment are combined into one resistor 35. Since the other configurations are the same as those in the first embodiment, the same reference numerals are given to the same parts in the drawings, and the explanation will be omitted.

In this second embodiment, the operational amplifier 2
Due to variations in the characteristics of transistors 3 and 24, the outputs do not completely invert each other, and even if they slightly overlap and turn on or off, the switching transistors 31 and 32 operate differentially. Drive transistors 41, 42
The overlap or dip in the current flowing through the base of the motor can be reduced, and the overlap or dip in the motor torque can be reduced. In addition,
The forward rotation and reverse rotation operations of the motor when the changeover switch 45 is switched to the changeover terminals a and b are the same as those in the first embodiment described above, and therefore a description thereof will be omitted.

Next, FIG. 4 shows a third embodiment of the present invention.
An example is shown in which a photo interrupter 50 is used as a rotational position detecting element for a rotor magnet of a motor. In the third embodiment shown in FIG. 4, a series circuit consisting of an LED (light emitting diode) 51, which is a light emitting element of a photointerrupter 50, and a resistor 53 is inserted and connected between the positive and negative terminals of the circuit power supply 30. There is. Further, a series circuit including a resistor 33 as a constant voltage element, a phototransistor 52 as a light receiving element of the photointerrupter 50, and a resistor 54 is inserted and connected between both terminals of the circuit power supply 30. LED 51 of this photo interrupter 50
and the phototransistor 52, for example, at an electrical angle along the rotational direction of the rotor magnet.
A shielding plate (not shown) such as a shutter plate arranged over an angular range of 180° passes through and changes the electrical angle according to the rotation of the rotor magnet.
At every 180 degrees, the optical path of the photo interrupter 50 is interrupted and becomes transparent.

Further, the connection point between the resistor 33 and the phototransistor 52 is connected to the base of the switching transistor 31, and the base of the other switching transistor 32 is connected to the divided voltage output terminals of the voltage dividing resistors 34 and 55. ing. This voltage dividing resistor 3
4 and 55 are connected to the positive voltage terminal of the circuit power supply 30 and the connection point between the phototransistor 52 and the resistor 54. This voltage dividing resistor 34 is a constant voltage element for supplying a constant voltage to the base of the switching transistor 32. Further, the emitters of the switching transistors 31 and 32 are commonly connected and connected to the positive voltage terminal of the circuit power supply 30 via a resistor 35. Further, the collectors of the switching transistors 31 and 32 are connected to the bases of the driving transistors 41 and 42, respectively.
2, field coils 21, 22, driving DC power supply 4
0 and the configuration of the changeover switch 45 are as described above.
This is similar to the embodiment.

In such a third embodiment, the resistors 33,
34 acts as a constant voltage element, as in the first embodiment described above, the changeover switch 45
Each drive transistor 41, 42
Sufficient base current can be supplied to the motor, eliminating the difference in characteristics between forward and reverse rotation.

Further, according to the third embodiment, an operational amplifier is not required, the circuit configuration is further simplified, the number of parts is reduced, the number of assembly steps is reduced, and the cost is reduced, and reliability is also improved.

In the third embodiment shown in FIG. 4, the base of the switching transistor 32 is not fixed biased, and the voltage dividing resistors 34 and 55
Since one end is connected to the emitter of the phototransistor 52, the on/off operation is performed normally even if the voltage drop across the resistor 35 changes.

Note that the present invention is not limited to the above-mentioned embodiments; for example, the bidirectional transistor 4
Instead of using 1 or 42, a bidirectional thyristor may be used, or, as shown in FIG. Commonly connected circuits may also be used. Furthermore, instead of these transistors 61 and 62, thyristors or the like may be used. moreover,
Resistor 33 (or 3
Instead of 4), a constant voltage element such as a Zener diode may be used.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a circuit diagram showing a first embodiment of the present invention, Fig. 3 is a circuit diagram showing a second embodiment of the present invention, and Fig. 4 is a circuit diagram showing the present invention. FIG. 5 is a circuit diagram showing the third embodiment of the invention, and is a diagram showing an example of a circuit that can be used in place of the bidirectional transistor 41 (or 42). 20... Hall element, 21, 22... Field coil, 23, 24... Operational amplifier, 31, 32...
Switching transistor, 33, 34... Resistor for constant voltage supply, 41, 42... Drive transistor, 30... Circuit power supply, 40... Drive DC power supply, 45... Changeover switch, 50... Photo interrupter .

Claims (1)

[Claims for Utility Model Registration] Switching control of the driving currents of the multi-phase field coils by a driving bidirectional switching means according to the detected position of the rotor by the position detection element, and the polarity of the power source of the field coils are controlled. In a motor drive circuit configured to be capable of forward and reverse rotation by switching the circuit, the emitters of the plurality of transistors that drive the bidirectional switching means for driving the multi-phase field coils on and off are connected to the circuit power supply via a resistor. and a collector connected to a control terminal of the bidirectional switching means, and supplying a constant voltage to the base of the transistor via a constant voltage means to turn the transistor on. drive circuit.