JPH0648397U - Motor drive circuit - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a constant current chopper drive circuit by pulse width modulation control in order to suppress heat loss of a control transistor when a holding current for holding a phase when a motor is stopped is suppressed. It is an object of the present invention to provide an improved motor drive circuit with high efficiency and low heat loss. In a motor drive circuit using a constant current chopper by pulse width modulation control, a high voltage power supply VD1 is connected, a transistor 1 for supplying a drive current to a stepping motor and a low voltage power supply VD2 are connected to drive a stepping motor. A transistor 3 for passing a current and a circuit for switching between the transistor 1 and the transistor 3 depending on whether the stepping motor is rotating or stopped are provided. The transistor 1 is switched when the stepping motor is rotating, and the transistor 3 is switched when the stepping motor is stopped. To control.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a motor drive circuit using a constant current chopper with pulse width modulation control.

[0002]

[Prior art]

 FIG. 4 is a motor drive circuit diagram using a conventional constant current chopper by pulse width modulation control, and shows a circuit for one phase of a two-phase stepping motor. In the conventional drive circuit for a stepping motor, a large current is supplied when the motor is rotated, and a small current (holding current) is supplied so that the phases of the motor are not deviated when the motor is stopped. 101 and 102 are transistors that perform switching operation by pulse width modulation, 103 and 104 are transistors that switch the excitation phase, 111 is a resistor that detects the current flowing in the excitation coil, and 121 is a current that is applied to the excitation coil when the transistor 101 is off. It is a freewheel diode to supply. 131, 132, 133 are buffer circuits, 134 is an inverter circuit, and 135 is a comparator circuit.

DV is a binary signal that switches between rotation and stop of the motor, φA and bar φA are timing signals that switch the excitation phase of the motor, VR is the reference potential of the comparator circuit 135, and resistors 112, 113, It is made by dividing the potential VC at 114. Reference numeral 105 denotes a transistor, which switches the reference potential VR by turning on and off. VS indicates the potential generated by the voltage drop across the resistor 111. S1 indicates a signal source for superimposing a triangular wave on the reference potential VR. I1, I2, and I3 represent currents flowing in the stepping motor.

Next, the operation will be described with reference to the time chart of FIG. First, when the binary signal DV changes from the L level to the H level, the reference potential VR changes from the potential vL to the potential vH. Therefore, the current I1 flowing in the circuit changes from the current value iL to the current value iH. Next, by alternately switching the timing signal φA and the bar φA between the H level and the L level, the transistors 103 and 104 are alternately turned on and off, and the currents I2 and I3 flow in the exciting coil of the stepping motor. Rotate. The transistor 1 repeats switching according to the result of comparison between the reference potential VR and the potential VS by the comparator circuit 135, and operates so as to flow a constant current value iL or iH.

Next, when the binary signal DV changes from the H level to the L level to stop the rotation operation, the reference potential VR changes from the potential vH to the potential vL. Therefore, the current I1 flowing in the circuit changes from the current value iH to the current value iL, and the current I3 changes from the current value iH to the current value iL. At this time, the transistor 101 performs a switching operation as shown in FIG. 6 in order to flow the current value iL. When the transistor 101 is off, the collector-emitter potential Vce is equal to VD1, and when it is on, the collector-emitter saturation voltage Vce s.

In general, a transistor takes longer to turn off than to turn on, t 0 to t 1 indicate a time required to turn on the transistor 101, and t 2 to t 3 indicate a time required to turn off the transistor 101. In the figure, the shaded portion represents heat loss in the transistor 101. In particular, the heat loss during the period from t2 to t3 is large.

[0007]

[Problems to be solved by the device]

 However, in the circuit described above, the constant current chopper drive by pulse width modulation is performed even when the motor is rotating at a high voltage when the motor is rotating at a high speed, so the heat loss associated with the switching operation of the constant current control transistor increases. There was a flaw. Therefore, it is necessary to install a cooling fan and a large radiator.

In order to suppress the heat loss of the control transistor described above, the present invention improves the constant current chopper drive circuit by pulse width modulation control and provides a highly efficient motor drive circuit with less heat loss. With the goal.

[0009]

[Means for Solving the Problems]

 In order to solve the above problems, in the present invention, in a motor drive circuit using a constant current chopper by pulse width modulation control, a first transistor connected to a high voltage power supply and supplying a drive current to the motor, and a low voltage power supply. A second transistor connected to the motor for supplying a drive current to the motor, and a circuit for switching between the first transistor and the second transistor depending on whether the motor is rotating or not. The first transistor is controlled to operate and the second transistor is controlled to stop operation.

[0010]

[Action]

 By switching the power supply voltage of the transistor between when the stepping motor is rotating and when it is stopped, the unnecessary heat loss of the transistor when the motor is stopped is kept small.

[0011]

【Example】

 FIG. 1 is a motor drive circuit diagram showing an embodiment of the present invention and shows a circuit for one phase of a two-phase stepping motor. 1, 2, 3 and 4 are transistors that perform switching operation by pulse width modulation (for example, switching transistors for constant current control), 5 and 6 are transistors for switching the excitation phase of the stepping motor, and 11 is flowing in the excitation coil. A resistor for detecting a current, 21 is a freewheel diode for supplying a current to the excitation coil when the transistor 1 or transistor 3 is off, 22 is a backflow prevention diode when the transistor 3 is off, and 31, 32 are AND gates. Circuits, 33 and 34 are inverter circuits, and 35 and 36 are buffer circuits. Reference numeral 37 indicates a comparator circuit.

DV is a binary signal that switches between rotation and stop of the motor, and φA and bar φA are timing signals that switch the excitation phase of the motor, and are connected to a controller (not shown). VD1 is a power source used when the motor is rotating, VD2 is a power source used when the motor is stopped, and the respective voltages have a relationship of VD1> VD2. VR is a reference potential of the comparator circuit 37, and is created by dividing the potential VC by the resistors 12, 13, and 14. Reference numeral 7 denotes a transistor, which switches the reference potential VR by turning on / off by a binary signal DV. VS indicates an electric potential caused by a voltage drop across the resistor 11. S1 indicates a signal source for superimposing a triangular wave on the reference potential VR. I1, I2, and I3 represent currents flowing in the stepping motor. Vce1 is the collector-emitter voltage of the transistor 1, and IC1 is the collector current of the transistor 1. Vce3 is the collector-emitter voltage of the transistor 3, and IC3 is the collector current of the transistor 3.

Next, the operation will be described with reference to the time chart shown in FIG. First, when the binary signal DV changes from the L level to the H level, the reference potential VR changes from the potential vL to the potential vH. At the same time, the transistor 3 is turned off and the transistor 1 performs a switching operation. Therefore, the current I1 flowing in the circuit changes from the current value iL to the current value iH, and the current I3 changes from the current value iL to the current value iH. Next, the timing signals φA and φA are alternately switched between the H level and the L level, so that the transistors 5 and 6 are alternately turned on / off, and the currents I2 and I3 flow into the exciting coil of the stepping motor to rotate the operation. To do. The transistor 1 repeats the switching operation based on the result of comparison between the reference potential VR and the potential VS by the comparator circuit 37, and operates so as to flow a constant current value iH.

Next, in order to stop the rotation operation, when the binary signal DV changes from the H level to the L level, the reference potential VR changes from the potential vH to the potential vL. At the same time, the transistor 1 is turned off and the transistor 3 performs a switching operation. Therefore, the current I 1 changes from the current value iH to the current value iL, and the current I3 changes from the current value iH to the current value iL.

FIG. 3 shows the switching operation of the transistor 3. When the transistor 3 is off, Vce3 is equal to VD2, and when the transistor 3 is on, it becomes the collector-emitter saturation voltage Vces3. Further, t0 to t1 indicate the time required for the transistor 3 to turn on, and t2 to t3 indicate the time required for the transistor 3 to turn off. The shaded portion in the figure represents heat loss in the transistor 3. Comparing FIG. 3 and FIG. 6, it can be seen that the heat loss (hatched portion) generated in the transistor is changed by setting VD1> VD2. In other words, by lowering the power supply voltage, heat loss during switching operation can be suppressed to a small level.

It should be noted that the present invention provides a further significant effect in a motor that requires high-speed rotation, in a device in which the stop time is longer than the rotation operation time of the motor. Further, as fields to which the present invention is applied, machine tools, robots, medium conveyance, printer head carriage mechanisms, paper feeding mechanisms, and the like are conceivable.

[0017]

[Effect of device]

 As described above in detail, according to the present invention, the power supply voltage of the constant current control switching transistor is switched between the rotation operation and the stop of the stepping motor. Unnecessary heat loss of the control switching transistor can be reduced. Therefore, a cooling fan becomes unnecessary and the radiator can be downsized.

[Brief description of drawings]

FIG. 1 is a motor drive circuit diagram showing an embodiment of the present invention.

FIG. 2 is a time chart of the motor drive circuit shown in FIG.

FIG. 3 is a diagram showing a switching operation of a transistor 3.

FIG. 4 is a conventional motor drive circuit diagram.

5 is a time chart of the motor drive circuit shown in FIG.

FIG. 6 is a diagram showing a switching operation of a transistor 1.

[Explanation of symbols]

 1, 2, 3, 4, 5, 6, 7 Transistor 11, 12, 13, 14 Resistor 21 Freewheel diode 22 Backflow prevention diode 31, 32 AND circuit 33, 34 Inverter 35, 36 Buffer circuit 37 Comparator

Claims (1)

[Scope of utility model registration request] 1. A motor drive circuit using a constant current chopper by pulse width modulation control, comprising: a first transistor connected to a high voltage power supply for supplying a drive current to the motor; and a low voltage power supply connected to the motor. A second transistor for supplying a driving current, and a circuit for switching between the first transistor and the second transistor depending on whether the motor is rotating or not are provided, and the first transistor is rotating when the motor is rotating. In addition, the motor drive circuit is controlled so as to switch to the second transistor when stopped.