JPS62221893A - Motor driving apparatus - Google Patents

Abstract

PURPOSE:To ensure limiting of overcurrent without delay in operation, by providing a current control means for preventing overcurrent to a motor, in which an oscillation preventing capacitor is connected between an input and an output and also a current feeding means is connected to the output. CONSTITUTION:At the time of a stop command, a start/stop command means 89 cuts OFF a driving current to a motor on the output signal of the means 89. At the same time, a current from a current feeding means 81 is made to flow to the start/stop command means 89. Thus the charging of an oscillation preventing capacitor 80, which is connected between the input and the output of a current limiting means 82, is prevented. At the time of a start command, the current limiting means 82 passes the current from the current feeding means 81 to the current limiting means 82. The driving current to the motor is limited based on the output signal of the means 82 with the signal from a motor-driving- current detecting means 77 as an input signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a motor drive device used in OA equipment, audio-visual equipment, etc., and particularly relates to a current limiting function for overcurrent protection and a motor start/stop function. It is equipped with functions.

BACKGROUND OF THE INVENTION In recent years, for example, in brushless motor drive circuits used to drive drums in printers, additional functions have been added to limit the current to prevent burnout due to overcurrent to the motor, and to control the start and stop of the motor. It has become necessary to do this in terms of circuits.

An example of a conventional motor drive device will be described below with reference to the drawings.

FIG. 3 shows a circuit diagram of a conventional motor drive device. In FIG. 3, 1, 2.3 are drive coils of the motor. PNP transistor 4.5.6 and NPN) Langstaff, 8°9 is the drive transistor. Diodes 10 to 15 are connected between the emitter and collector of each of the drive transistors 4 to 9. The bases of the drive transistors 4 to 9 are connected to an energization switching circuit 16, and the energization switching circuit 16 is connected to output terminals of position detectors 19, 20, and 21 of a rotor (not shown). The position detectors 19, 20, 21 are connected in series to a positive feed line 18 which is connected to a power supply terminal 17 via a resistor 22, and are also grounded via a resistor 23. One transistor 24 of a current mirror circuit consisting of transistors 24 and 25 is connected to the energization switching circuit 16, and a constant current source 26 is connected to the transistor 25. The drive transistors 7.8 and 9 have their emitters connected in common and are grounded via a current detection resistor 27. One end of the resistor 27 is connected to the base of a transistor 30 via a resistor 28 and grounded via a capacitor 29. The collector of the transistor 30 is connected to the base common connection point of the transistors 24 and 25 constituting the current mirror circuit, and the emitter is grounded. 31 is a frequency generator connected to the rotating shaft of the motor, and 32 is an output signal from the frequency generator 31 (
An amplification circuit for the FG multiplied signal, and a frequency-voltage conversion circuit 33 for converting the frequency of the FG multiplied signal into a DC voltage. A switch 34 is added to the frequency-voltage conversion circuit 33 for instructing the motor to start and stop. Further, the output terminal of the frequency-voltage conversion circuit 33 is connected to a non-inverting input terminal of an error amplifier 35. The inverting input terminal of the error amplifier 35 is grounded via a resistor 37 and a reference voltage source 36, and is connected to the output terminal of the error amplifier 35 via a parallel circuit of a resistor 38 and a capacitor 39 to form a DC amplifier circuit 40. are doing. The output terminal of the DC amplifier circuit 40 is connected to the base of a transistor 41 and grounded via a resistor 42. The emitter of the transistor 41 is grounded, and the collector is connected to the base of the power supply control transistor 43. The emitter of the power supply control transistor 43 is connected to the positive power supply line 18, and the collector thereof is connected to the drive transistor 4.
, 5 and 6 are connected to the emitter common connection point.

The operation of the conventional motor drive device configured as described above will be described below.

First, position detectors 19' and 2 according to the rotational position of the rotor are used.
Based on the signals from 0 and 21, the current switching circuit 16 sequentially switches the drive transistors 4 to 6 and 7 to 9, thereby passing bidirectional current through the drive coils 1 to 3 to generate a rotating magnetic field. Obtains rotational force. The rotational speed of the motor is detected by a frequency generator 31 connected to the motor, and the FG multiplied signal from the frequency generator 31 is amplified to a required voltage by an FG signal amplification circuit 32 and input to a frequency-voltage conversion circuit 33. The frequency voltage conversion circuit 33
is converted into a DC voltage according to the input frequency, that is, a frequency proportional to the rotational speed of the motor, and the voltage is compared with the reference voltage, and the error voltage is detected by the resistor 37.38.
and is amplified by a gain determined by a capacitor 39, further amplified by a transistor 41, and a power supply control transistor 4
3 is applied. The power supply control transistor 43 controls the amount of power supplied to the motor by controlling its emitter-collector voltage, thereby controlling the motor at a constant speed. A switch 34 for instructing the motor to start and stop is added to the frequency-voltage conversion circuit 33, and when the switch 34 is in the ON state, its circuit function is in the operating state, and when it is in the OFF state, its output voltage is is configured to be forced into a LOW state. Therefore, in a state where a voltage is applied to the power supply terminal 17, the switch 3
4 is in the OFF state, the output voltage of the frequency-voltage conversion circuit 33 is forced to a LOW state, that is, it drops to near the ground voltage, so the output voltage of the DC amplifier circuit 40 drops,
In response, the transistor 41 and the power supply control transistor 43 are turned off, so the motor remains stopped. Next, when the switch 34 is turned on, the frequency-voltage conversion circuit 33 is put into operation, but at the moment when the switch 34 is turned on, the motor is not yet rotating, so the FG from the frequency generator 31 is No double signal is generated. Since the frequency-voltage conversion circuit 33 is configured so that its output voltage increases as the input frequency decreases, the moment the switch 34 is turned on as described above, the output of the frequency-voltage conversion circuit 33 changes. Voltage is HI
Becomes GH state. Therefore, the output voltage of the DC amplifier circuit 40 increases, and accordingly, the transistor 41
The power supply control transistor 43 is turned on and the remoter is activated.

Now, the motor drive current flowing through the drive transistors 4 to 6, the drive coils 1 to 3, and the drive transistors 7 to 9 is detected as the terminal voltage of the current detection resistor 27. When the terminal voltage rises to the base-emitter threshold voltage of the transistor 30, the transistor 3o attempts to turn on, so a current mirror circuit of transistors 24 and 25 forming a power supply circuit to the energization switching circuit 16 is activated. transitions to the OFF state. Therefore, the output current of the energization switching circuit 16, that is, the base current of the drive transistors 4 to 9 is reduced, and the
9 to the OFF state, and as a result, the drive current of the motor is limited. By the way, looking at the current limit state, when the current limit is activated, the drive current is cut off, then when the drive current is cut off, the current limit is canceled and the drive current becomes conductive, and then the current limit is activated again. This state is repeated, resulting in an oscillation state. Therefore, conventionally, the detection voltage of the current detection resistor 27 is set to the resistor 2.
The above-mentioned oscillation phenomenon was prevented and alleviated by applying the voltage to the base of the transistor 30 through a low-pass filter consisting of a capacitor 8 and a capacitor 29.

Problems to be Solved by the Invention However, in the above configuration, there is a time delay in the current limiting operation due to the resistor 28 and capacitor 29 connected as a countermeasure against oscillation during current limiting, and the switch 34 is turned ON and the motor is turned off. At the moment when the drive coils 1 to 3 are about to start up, no back electromotive voltage is generated and the impedance is low, so the power supply terminal 17 and the power supply control transistor 43
An excessive current flows to the ground point through the drive transistors 4 to 6, the drive coils 1 to 3, the drive transistors 7 to 9, and the current detection resistor 27. Therefore, there is a problem in that the power supply control transistor 43 and the drive transistors 4 to 9 are destroyed, and the motor is damaged.

In view of the above-mentioned problems, the present invention operates reliably to limit the current even when the motor is started, thereby preventing destruction of the power supply control transistor and drive transistor and damage to the motor due to excessive current, as well as preventing oscillation when limiting the current. The present invention provides a motor drive device that makes it possible.

Means for Solving the Problems In order to solve the above problems, the motor drive device of the present invention includes a motor start/stop command means, an oscillation prevention capacitor connected between the input and output, and a power supply means for the output. current limiting means for preventing excessive current to the connected motor; when a stop command is issued, the start/stop command means cuts off the drive current of the motor based on the output signal thereof, and also cuts off the current from the power supply means; Preventing charging of the oscillation prevention capacitor by flowing the start/stop command means,
Further, when receiving a start command, the current limiting means causes the current from the power supply means to flow through the current limiting means, uses a signal from the motor drive current detection means as an input signal, and limits the motor drive current based on the output signal. It is configured as follows.

Operation The present invention prevents a time delay in the current limiting operation at startup with the above-described configuration, reliably prevents excessive current at startup, and also prevents oscillation during current limiting.

Example Hereinafter, a motor drive device according to an example of the present invention will be described.
This will be explained with reference to the drawings.

FIG. 1 shows a circuit diagram of a motor drive device in an embodiment of the present invention. In Figure 1, 51,5
2.53 is a drive coil of the motor. transistor 5
4,55.56 and transistors 57,58,59 are drive transistors. The transistors 54 to 59
A diode 60 is connected between each emitter and collector of
~65 are connected. The drive transistor 54~
The base of the rotor 59 is connected to an energization switching circuit 66, and the energization switching circuit 66 is connected to an output terminal of a rotor position detector 67°68.69. Said position detector 67.68
．． 69 is connected in series to a constant voltage circuit 73 via a resistor 70.
It is connected to the output line 74 of , and is grounded via a resistor 71 . A capacitor 75 is connected between the positive feed line 72 connected to the power supply terminal 50 and the ground, and a capacitor 76 is connected between the constant voltage line 74 and the ground. Now, the drive transistors 57, 58 and 59
Their emitters are commonly connected and grounded via a current detection resistor 77. One end of the current detection resistor 77 is a resistor 78
is connected to the base of transistor 79 via.

The emitter of the transistor 79 is grounded, and the collector is connected to the base via an oscillation prevention capacitor 80 and to the constant voltage line 74 via a resistor 81. 82 is a current limiting means. Further, resistors 83, 84 and 85 are connected in series between the constant voltage line 74 and the ground, and the connection point between the resistors 83 and 84 is connected to an input terminal 86 of a motor start/stop command means. The connection point between the resistors 84 and 85 is connected to the base of a transistor 87.

The base of the transistor 87 is grounded via a capacitor 88, the emitter is grounded, and the collector is connected to three connection points: one terminal of the capacitor 80, one terminal of the resistor 81, and the collector of the transistor 79. It is connected. 89 is a start/stop command means. 90
is a frequency generator connected to the rotating shaft of the motor, one of its output terminals is connected to the non-inverting input terminal of the differential amplifier 93, and the other is connected to the non-inverting input terminal of the differential amplifier 93 via a capacitor 91 and a resistor 92. It is connected to the inverting input terminal and to the output terminal of the differential amplifier 93 via a parallel circuit of a resistor 94 and a capacitor 95. 96 is an FG signal amplification circuit, the output terminal of which is connected to the input terminal of a frequency-voltage conversion circuit 98 via a coupling capacitor 97. The output terminal of the frequency-voltage conversion circuit 98 is connected to the inverting input terminal of the error amplifier 102 via a resistor 99 and to the output terminal of the error amplifier 102 via a parallel circuit of a resistor 103 and a capacitor 104. . Further, the non-inverting input terminal of the error amplifier 102 is connected to a voltage dividing point of a voltage dividing circuit including resistors 100 and 101 connected between a constant voltage line 74 and ground. Furthermore, the inverting input terminal of the error amplifier 102 is connected to the collector common connection point of the transistor 79 and the transistor 87 via a diode 106 and a resistor 107. 105 is a DC amplifier circuit, the output terminal of which is connected to one input terminal of the comparator 108. The output terminal of a triangular wave generating circuit 109 is connected to the other input terminal of the comparator 108.

Further, the output terminal of the comparator 108 is connected to the transistor 11
0 and the constant voltage line 74 via a resistor 111. The transistor 1
The emitter of the transistor 10 is grounded, and the collector thereof is connected to the base of a transistor 113 and to the constant voltage line 74 via a resistor 112.

The emitter of the transistor 113 is grounded, and the collector is connected to the power supply control transistor 115 via a resistor 114.
connected to the base of. The emitter of the feed control transistor 115 is connected to the positive feed line 72 and its base via a resistor 116, and its collector is grounded via a flywheel diode 117 and connected to one end of a coil 118. ing. The other end of the coil 118 is grounded via a capacitor 119 and connected to a common emitter connection point of drive transistors 54, 55 and 56.

The operation of the motor drive device configured as described above will be described below with reference to FIGS. 1 and 2.

First, position detectors 67 and 68 according to the rotational position of the rotor.
Based on the signals from 69 and 69, the energization switching circuit 66
By sequentially switching drive transistors 54 to 56 and 57 to 59, bidirectional current flows through drive coils 51 to 53 to generate a rotating magnetic field and obtain rotational force. The rotational speed of the motor is detected by a frequency generator 90, and its FG multiplied signal is amplified to a required voltage by an FG signal amplification circuit 96 and input to a frequency-voltage conversion circuit 98 via a coupling capacitor 97. The frequency-voltage conversion circuit 98 converts the input frequency into a DC voltage according to a frequency proportional to the rotational speed of the motor, and the voltage is passed through the DC amplifier circuit 105 with the voltage at the voltage dividing point of the resistors 100 and 101 as a reference. Convert to DC voltage. The DC voltage and the output voltage of the triangular wave generation circuit 109 are connected to the comparator 1.
08, and its output voltage is ON, OF
A so-called pulse width modulation (PWM) signal is generated in which the pulse width of F is modulated by the level of the DC voltage.

The pulse width modulation signal is applied to the base of the power supply control transistor 115 via the transistor 1101 and the transistor 113.

The power supply amount of the power supply control transistor 115 is controlled by controlling the ON/OFF duty ratio. That is, the pulse width modulation signal at the collector of the power supply control transistor 115 is smoothed by the coil 118 and the capacitor 119 and converted into a DC voltage corresponding to the duty ratio of the pulse width modulation signal, so that the voltage applied to the motor is controlled. Therefore, the rotation speed is controlled. Note that the flywheel diode 117 is connected to the coil 1 when the power supply control transistor 115 is OFF.
This is to regenerate the energy stored in 18.

Next, the current limiting operation of the motor drive current will be explained. Current limiting means 82 is added to prevent excessive current from flowing when the motor is started or when an overload is applied to the motor or the motor is forcibly locked for some reason. The operation of the current limiting means 82 is based on the driving transistors 54 to 56 and the driving coils 51 to 56.
53 and the drive transistors 57 to 59 is detected as the terminal voltage of the current detection resistor 77, and when the terminal voltage rises to the base-emitter threshold voltage of the transistor 79, the transistor 79
shifts to the ON state, draws current through the diode 106 and the resistor 107 as part of its collector current, and operates to lower the potential of the inverting input terminal of the error amplifier 102 than the potential of the non-inverting input terminal. The output voltage of DC amplifier circuit 105 increases. Accordingly, the width of the ON period of the pulse width modulation signal at the output terminal of the comparator 108 increases, but the signal is inverted by the transistor 110 and applied to the transistor 113 and the power supply control transistor 115, so that the power supply control transistor 1
As for the collector signal of 15, the width of the OFF period increases,
As a result, the voltage applied to the motor decreases and the drive current of the motor is controlled. Here, the diode 106 is in a reverse bias state in a normal speed control state, so that it is not affected by the current limiting means 82. Note that the capacitor 80 is connected to the transistor 79.
It is connected between the base and collector of the circuit to prevent oscillation during current limit.

Now, with voltage being applied to the power supply terminal 50, the input terminal 86 of the start/stop command means 89 is open or HIGH.
When the voltage is in the state of the stop command, the transistor 87 is turned on, and the diode 106 and the resistor 10 are turned on.
7 to absorb its collector current and saturate it. Therefore, the voltage at the inverting input terminal of the error amplifier 102 is lowered, and the output terminal thereof becomes the upper limit voltage of the output range, so that the output signal of the comparator 108 is maintained at a HIGH state. Accordingly, the transistor 110 is turned on, the transistor 113 is turned off, and the power supply control transistor 115 is maintained in the off state, so that the power supply to the motor is cut off and the motor is stopped. At this time, the motor drive current is cut off, so the transistor 79 is turned off.
It is in F state. By the way, at the time of this stop command, the transistor 87 draws current from the resistor 81 as part of its collector current, thereby preventing the oscillation prevention capacitor 80 from being charged.

Next, when a voltage is applied to the power supply terminal 5o and the input terminal 86 of the start/stop command means 89 is in a LOW voltage state, for example, grounded, and a start command is issued, the transistor 87
is in the OFF state, so when the stop command is issued, the diode 10
The current flowing to the transistor 87 through the transistor 6 and the resistor 107 is cut off, and the voltage at the inverting input terminal of the error amplifier 102 is no longer forcibly lowered. When the input frequency of the frequency-voltage conversion circuit 98 is zero, its output voltage becomes the upper limit voltage of the output range, so the output voltage of the DC amplifier circuit 102 decreases and the comparator 108
The OFF period of the output signal increases, but the signal is inverted by the transistor 110 and applied to the transistor 113 and the power supply control transistor 115, so the ON period of the power supply control transistor 115 increases, and the starting current is applied to the motor. flows. The starting current is detected by the current detection resistor 77.
When the terminal voltage becomes equal to or higher than the base-emitter threshold voltage of the transistor 79, the current is sucked through the diode 106 and the resistor 107 as part of the collector current of the transistor 79, and the inverting input of the error amplifier 102 is detected. Since the terminal voltage is lowered, the starting current is limited to a certain value, which prevents excessive current from flowing. Now, at the time of this activation command, the current flowing through the resistor 81 comes to flow through the transistor 79. This current flows through the transistor 79 and increases the base-emitter threshold voltage of the transistor 79, thereby making the switching operation of the transistor 79 steep. This situation is shown in FIG. 2, where A shows the case where the resistor 81 is not connected, and B shows the case where it is connected. As can be seen from the figure, as the collector current of the transistor 79 increases, its base-emitter voltage increases, and the slope of the change in the collector current with respect to the change in the base-emitter voltage becomes steep. By causing a current to flow from the resistor 81 to the transistor 79 in this manner, the sensitivity of the switch operation can be increased and the current limiting operation can be sharply cut. In addition, by flowing current from the resistor 81, the gain during operation of the transistor 79 increases, and the Miller effect works to a large extent.
This also means that the capacitance value of the capacitor 80 required to prevent oscillation during current limitation can be small.

By the way, suppose that the configuration of the current limiting means 82 is the same as shown in FIG. 1, and the motor start/stop command means is performed by another means, for example, a switch added to the frequency-voltage conversion circuit as shown in FIG. Assuming that the output of the start/stop command means 89, that is, the collector of the transistor 87, is not connected to one end of the capacitor 80 as shown in FIG. state, the collector of the transistor 79 becomes the voltage of the constant voltage line 74. When a startup command is issued in such a state, the value of the startup current that has started flowing is detected by the current detection resistor 77, and the transistor 79 is turned on. However, since the capacitor 80 is charged, the collector of the capacitor 79 immediately turns on. The voltage does not drop to the point where the inverting input terminal of the error tank width divider 102 is lower than the non-inverting input terminal, resulting in a time delay in the current limiting operation, and as a result, an excessive current is generated at the moment the motor starts to start. There is a possibility that it will flow. Therefore, in this embodiment, the transistor 87 of the start/stop command means 89 is turned on when a stop command is issued, and the charge in the capacitor 80 is discharged, thereby eliminating the time delay in the current limiting operation when starting the motor. This can reliably prevent excessive current.

Effects of the Invention As described above, the present invention includes means for commanding a motor to start and stop, and current limiting means for preventing excessive current from flowing to a motor in which an oscillation prevention capacitor is connected between input and output and a power supply means is connected to the output. At the time of a stop command, the start/stop command means cuts off the drive current of the motor based on the output signal thereof, and causes current from the power supply means to flow through the start/stop command means to supply the oscillation prevention capacitor with the current. In addition, when a start command is given, the current limiting means causes the current from the power supply means to flow through the current limiting means, and also uses the signal from the motor drive current detection means as an input signal, and drives the motor based on the output signal. By limiting the current, it is possible to eliminate the time delay in the current limiting operation when starting the motor, and it is possible to reliably prevent excessive current to the motor, so the power supply control transistor,
Destruction of the drive transistor and damage to the motor can be prevented. Furthermore, it is possible to reduce the capacitance of a capacitor added to prevent oscillation during current limiting, which has extremely large effects.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a circuit connection diagram of a motor drive device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of collector current with respect to base-emitter voltage of transistor 79 in FIG. 1,
FIG. 3 is a circuit diagram of a conventional motor drive device. 51-53...Motor drive coil, 54-5
9... Drive transistor, 77... Drive current detection means, 79... Transistor, 80
...Oscillation prevention capacitor, 81...Power supply means, 82...Current limiting means, 87...
...transistor, 89...start/stop command means, 115...power supply control transistor. Name of agent: Patent attorney Toshio Nakao and one other person No. 2 Pace Emmit 9 Seven Swords

Claims (1)

[Claims] A motor start/stop command means, a current limiting means for preventing excessive current to the motor having an oscillation prevention capacitor connected between the input and output and a power supply means connected to the output,
When a stop command is given, the start/stop command means cuts off the drive current of the motor based on the output signal thereof, and prevents charging of the oscillation prevention capacitor by causing current from the power supply means to flow through the start/stop command means. Furthermore, at the time of a start command, the current limiting means causes the current from the power supply means to flow through the current limiting means, uses a signal from the motor drive current detection means as an input signal, and adjusts the motor drive current based on the output signal. A motor drive device designed to limit.