JPS58224585A - Speed controller for dc motor - Google Patents

Abstract

PURPOSE:To smoothly control the speed of a DC motor by dividing a reference voltage via resistors. CONSTITUTION:A reference voltage Vref of a reference voltage power source 12 is divided by resistors 16, 17, and the dividing point is connected to a comparator 13. The comparator 13 compares the counterelectromotive force Ea of a DC motor 1 with the reference voltage, and controls the base currents of a transistors 9-11 which form a current mirror in response to the differential voltage of both. Since the transistors 9-11 are not saturated in this manner at the control maximum torque time, the speed control of the DC motor can be smoothly performed, and can be controlled to low rotating speed.

Description

[Detailed Description of the Invention] Page 2 The present invention smoothly controls the speed of a DC motor from when the load on the DC motor is small to the maximum torque (maximum torque or less during rotational speed control, referred to as maximum control torque). The present invention relates to a speed control device for a DC motor that can be implemented.

The speed and control device for DC motors uses transistors.
This so-called electronic governor compares the back electromotive force generated in the drive coil in proportion to the rotational speed of the DC motor with a reference voltage, and controls the control transistor based on the difference voltage between the two to adjust the rotational speed of the DC motor. Executes an action that keeps constant.

By the way, a suitable circuit configuration for implementing such an electronic governor into a semiconductor integrated circuit has already been proposed in Japanese Patent Laid-Open No. 16125/1983.

FIG. 1 shows an example of the circuit configuration of the electronic governor. In FIG. 1, 1 is a controlled DC motor, 2 is a resistor, and 3 is a DC power source. In the figure, each collector is commonly connected to a transistor 5 whose collector is connected to a power supply terminal 3 via a resistor 2 and whose emitter is grounded via a resistor 4. DC motor driving transistors 9, 10.1 connected to terminal 3 and grounded via resistors 6, 7.8 whose respective emitters are set to the same value;
1 and 2 have their bases commonly connected to form a current mirror. Further, the comparator 13 has one input as the other end of the reference voltage source 12, one end of which is connected to the collector of the transistor 5, and the other input as the common collector contact of the transistors 9, 10, and 11. And an output is connected to a common connection point of the transistors 9, 10, and 11. The constant current source 14 is the comparator 13
In addition, the reference voltage source 12 is driven with a constant current. resistance 1
5 is connected between the collector of the transistor 6 and a common connection point of the collectors of the transistors 9, 10, and 11.

In the DC motor speed control device having the above configuration, control is performed to keep the rotational speed of the DC motor 1 constant by comparing the reference voltage Vref of the reference voltage source 12 and the back electromotive force E of the DC motor. Action is performed. for example,
When the rotational speed of the DC motor 1 decreases due to the influence of external load torque, etc., the following circuit operation is performed to control the rotational speed to a constant value.

That is, as the rotational speed of the DC motor 1 decreases, the back electromotive force Ea decreases, and the potential at the common connection point of the collectors of the DC motor drive transistors 9, 10.11 increases. Therefore, the drive transistor 9 of the comparator 13
, 10, 11, the input voltage on the side connected to the collector common connection point becomes high, and the comparator 13 becomes
It works in the direction of increasing the amount of base current supplied to 9, 10, and 11. Therefore, the collector currents of the DC motor drive transistors 9, 10, 11 increase, the armature current Ia increases, and control is performed to increase the rotational speed of the DC motor 1.

In the DC motor speed control device shown in Fig. 1, the back electromotive force of the DC motor 1 is Ea, the armature current is Ia, the internal resistance is R
a, and the reference voltage obtained from the reference voltage source 12 is V.
ref, the constant current of the constant current source, 1 the current ratio of the transistor 6 and the transistor 5 Pagen Lister 9, 10.11 that constitute the current mirror, 1 the resistance value of resistor 2, RT the resistance value of resistor 15 When R8 is assumed, the rotational speed N of the DC motor 1 is expressed as follows. Note that Ka is the power generation constant of the DC motor 1.

Now, the resistance value RT of the resistor 2 corresponding to the internal resistance Ra of the DC motor 1 is R7=K Ra...
... If set to (2), the equation (1) becomes as follows, and the DC motor 1 is not affected by the armature current Ia, that is, the load torque, and has a constant rotation speed.

Page 6 By the way, in a DC motor speed control device having a circuit configuration as shown in FIG. 1, as the load on the DC motor increases, the DC motor drive transistors 9 and 1
The collector voltage of 0.11 becomes lower. The lower the collector voltage of the transistors 9, 10, and 11, the greater the control maximum torque.

The collector voltages of transistors 9, 10, and 11 become low when the transistors are saturated.

By the way, if the offset of the comparator 13 is ignored, the collector voltage of the transistors 9, 10, and 11 is equal to the reference voltage Vr.
The voltage is lower than that of transistor 5 by ef. Therefore, when the motor drive transistors 9, 10, and 11 are saturated, the transistor 5 is not saturated and the current does not have a constant value, but shows an unstable value. Therefore, the rotational speed N of the DC motor shown in equation (3) is not constant and becomes unstable. This characteristic? is shown in Figure A. That is, when the load torque is at a predetermined value, the motor rotation speed increases rapidly.

The present invention aims to eliminate the above-mentioned drawbacks and provide a speed control device for a DC motor that can smoothly control the speed of a DC motor up to a maximum control torque of 7 pages.

FIG. 3 shows an example of a speed control circuit for a DC motor according to the present invention. In FIG. 3, the difference from FIG. 1 is that the reference voltage source 120 and the reference voltage Vref are connected to the resistor 16 and
7 and input the dividing point to the comparator 13. The other configurations are the same as in FIG. 1.

In the configuration of the device according to the embodiment of the present invention shown in FIG. 3, the input voltage VIN of the comparator 130 is expressed by the following equation.

Here, R16 is the resistance value of the base 16, R1□ is the resistance R1□
The voltage of the current source 14 is assumed to be o, 1V. and the input voltage “IN”
10,7 (V) ・・・・・・・・・・
...(5).

Here, even if the saturation voltage of the motor drive transistors 9, 10, 11 at the maximum control torque is o, eV, the collectors of the transistors 9, 10, 11 are connected to the input of the comparator 13, so VIN=0.7 It will not fall below V.

Therefore, the motor drive transistors 9, 10 and 11 are not saturated even at the maximum control torque.

As is clear from equations (4) and (5), the resistance 16.
By freely selecting each resistance value of 17, the value of the comparator input ■■N can be freely set. Since the embodiment device can operate without fully saturating the motor drive transistor 9110111 at the maximum control torque, the rotational speed of the DC motor can be smoothly controlled. The input of the comparator is connected to the motor drive transistors 9 and 10.
．． If you set the voltage slightly higher than the saturation voltage of 11,
Smooth speed control of the DC motor can be performed without reducing the maximum control torque. An example of this characteristic is shown in FIG. 2B. As is clear from the figure, a smooth motor rotation speed can be obtained with respect to the load of the DC motor.

Page 9 Motor rotation speed is normally adjusted by changing the resistor 15. The lowest rotational speed is obtained when resistor 15 is set to infinity. The rotational speed N at this time is expressed by the following formula: N=-(Vrsf+RTIr) ------
-=-(6)a The speed control device for a DC motor of the present invention has a reference voltage Vref.
Therefore, the actual reference voltage Vref is expressed by the following equation.

Substituting equation (7) into equation (6), it is clear from the above equation that the device of the present invention can control the rotation speed down to a lower rotation speed than the conventional example, and can expand the rotation speed adjustment range of the DC motor. Furthermore, since it is possible to control motors with a small power generation constant Ka, it is possible to expand the types of applicable motors.

As described above, according to the present invention, by dividing the reference voltage Vref10 pages by resistors, it is possible to smoothly control the speed of the DC motor, and furthermore, it is possible to control the speed of the DC motor down to a low rotational speed. It is possible to expand the variety of types.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional DC motor speed control device, FIG. 2 is a characteristic diagram showing the relationship between load torque and motor rotation speed, and FIG. 3 is a DC motor speed control device according to the present invention. It is a circuit diagram. 1...DC motor, 2, 4, 6, 7.8...
...Resistance, 9,10.11...Motor drive transistor, 5...Current mirror transistor, 12...Reference voltage, 13...Comparison device, 14...constant current source, 16.17...
...Resistance for reference voltage division, 16...Resistance for adjusting rotation speed. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 1462- Figure 3/

Claims (1)

[Claims] A first transistor for driving the DC motor is provided at the other end of the DC motor connected to the power supply terminal;
A second transistor is provided that has a proportional current relationship with the transistor, and the collector of the second transistor is provided with a value approximately equal to the product of the current proportionality constant of the first transistor and the internal resistance of the DC motor. the other end of the first resistor is connected to a power supply terminal, the bases of the first transistor and the second transistor are connected to the output of the comparator, and the direct current A connection point between the motor and the first transistor is connected to one input terminal of the comparator, and a point at which a predetermined reference voltage is divided by a resistor is connected to the other input terminal of the comparator. DC motor speed control device.