JPS6281987A - Small DC motor speed control device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a small direct current speed control device capable of smooth control over a wide range of load torque fluctuations.

Conventional technology A speed control device for a small DC motor using a transistor is called an electronic governor, which compares the back electromotive force generated in the drive coil in proportion to the rotation speed of the small DC motor with a reference voltage. The control transistor is controlled by the voltage difference between the two to maintain the rotational speed of the DC motor constant.

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

FIG. 3 shows an example of the circuit configuration of the electronic governor. In FIG. 3, 1 is a controlled small DC motor, 2 is a resistor, and 3 is a DC power source. In the same figure, a transistor 2o whose collector is connected to a power supply terminal 3 via a resistor 2 and whose emitter is grounded via a resistor 21 is commonly connected to the transistor 2o, and a small DC motor 1 to be controlled is connected to the power supply terminal 3.
transistors 22, 24, 28 for driving the small DC motor 1, whose respective emitters are grounded via resistors 23, 25, 27 whose respective emitters are set to the same value, connect their bases in common to supply current. It constitutes a mirror.

Further, the comparator 19 has one input as the other end of the reference voltage source 29, one end of which is connected to the collector of the transistor 20, and the other input as the common connection point of the collectors of the transistors 22, 24, and 26. 20 and the base common connection point of the transistors 22, 24, and 26 is connected to the output. A constant current source 28 drives the comparator 19 and the reference voltage source 29 with constant current. A resistor 6 connects the collector of the transistor 20 and the transistor 2.
2, 24, and the collector common connection point of 26.

In the speed control device for a small DC motor having the above configuration, a control operation is performed to keep the rotational speed of the DC motor 1 constant by comparing the reference voltage Vref of the reference voltage source 29 and the back electromotive force ICa of the small DC motor. is executed. For example, when the rotational speed of the small DC motor 1 decreases due to an increase in 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 EIIL decreases, and the potential at the common connection point of the collectors of the DC motor drive transistors 22, 24, and 26 increases. Therefore, the input voltage on the side of the comparator 19 connected to the collector common connection point of the drive transistors 22, 24, 26 increases, and the comparator 19 increases the amount of base current supplied to the transistors 20, 22, 24, 26. works in the direction of increase. Therefore, the collector currents of the drive transistors 22, 24, and 28 of the small DC motor increase, the armature current 1 increases, and control is performed to increase the rotational speed of the small DC motor. Therefore, the input terminal to which the collectors of the transistors 22, 24, and 26 of the comparator 19 are connected is balanced at a slightly higher potential than before with respect to the other input terminal. In the speed control device for a small DC motor shown in Fig. 3, the back electromotive force of the small DC motor 1 is Ea, and the armature current is I! L, the internal resistance is Ra, and the reference voltage obtained from the reference voltage source 29 is V.
r6f, the constant current of the constant current source is Ir, the collector current ratio of transistors 22, 24.28 to the collector current of transistor 2o forming the current mirror is K, the resistance value of resistor 2 is RTs, the resistance value of resistor 6 is Rs Then,
The rotational speed N of the small DC motor 1 is expressed as follows. Note that Ka is the power generation constant of the small DC motor 1.

Now, corresponding to the internal resistance R8- of the small DC motor 1, the resistance value R7 of the resistor 2 is R, = K Ra 0001
0. If set to (2), then equation (1) becomes.

+R, Ir) Concave...(3),
The small DC motor 1 is not affected by the armature current Ia, that is, the load torque, and is controlled to a constant rotation speed.

Problems to be Solved by the Invention By the way, in a DC motor speed control device having a circuit configuration as shown in FIG. 2 also increases, the potential at the power supply side terminal of the reference voltage source 29 decreases, and therefore the potential at the reference voltage input terminal of the comparator 19 decreases, and therefore the small voltage connected to the other input terminal of the comparator 19 decreases. The collector voltage of the DC motor driving transistor 22°24.28 becomes lower. The lower the collector voltage of the transistors 22, 24, and 26, the greater the control maximum torque (maximum load torque that allows speed control). The collector voltage of transistors 22, 24, and 28 becomes low when the transistors are saturated. By the way, if the offset voltage of the comparator 19 is ignored, the collector voltage of the transistor 2o is equal to the reference voltage Yre.
The voltage is higher than that of transistors 22, 24, and 26 by f. Therefore, the small DC motor drive transistor 22
．． When 24.26 is saturated, the transistor 2o is not saturated and the collector current ratio does not have a constant value, but exhibits an unstable value. Unfortunately, the rotational speed N of the small DC motor 1 shown in equation (3) is not constant and becomes unstable. This characteristic is shown in FIG. 2B. 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 small DC motor that can smoothly control the speed of the small DC motor up to the maximum control torque.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a small DC motor whose one end is connected to a power supply terminal, and the other end of which is connected to a collector of a first transistor for driving the small DC motor. , its emitter is grounded via a predetermined resistor, and its base is connected to the base of the second transistor, so that the first
The collector current of the transistor is always approximately K times the collector current of the second transistor, and the collector of the second transistor is set to a value approximately equal to K times the internal resistance of the small DC motor. the other end of the first resistor is connected to a power supply terminal, the emitter of the second transistor is grounded via a predetermined resistor, and the first transistor and the first resistor are connected to each other. Connect the base connection point of transistor 2 to the output terminal of the comparator,
A connection point between the small DC motor and the first transistor is connected to one input terminal of the comparator which has control characteristics in the positive direction for one output current, and a predetermined reference voltage is connected between the ground point and the third transistor. , its emitter is grounded via a predetermined resistor, and its collector and the first
A series load consisting of a fourth transistor whose base and collector are connected and a predetermined resistor is connected between the connection point between the resistor and the second transistor, and a connection point between the collector of the third transistor and the series load. is connected to the other input terminal of the comparator.

Operation As the predetermined reference voltage, a relatively high voltage (for example, 1
．． 2V), the third transistor and a predetermined resistance between its emitter and ground point constitute a constant current source, and from this constant current source, a fourth transistor whose base and collector are connected and a predetermined resistor are connected. By feeding a load in series with the resistor of Above the saturation collector potential of the first transistor for driving the DC motor, (
For example, by holding the voltage at 0, e v ), saturation of the collector voltage of the first transistor is prevented. As a result, the collector current ratio K becomes a constant value, and the rotational speed N of the small DC motor 1 shown in equation (3) also becomes constant.

Example An embodiment of the present invention shown in FIG. 1 will be described.

When a voltage is applied to the power supply terminal 3, a current flows through the resistor 6, voltage is generated across the diode 7.8, and the transistor 9 is turned on.
Transistors 10, 11, and 12 are also turned on, and each enters an operating state. Transistor 10.12 and resistor 13
．． 14 constitutes a reference voltage source.

Here, the emitter current density of transistor 1o is Jl,
If the emitter current density of transistor 12 is J2, then
The reference voltage vre f of the reference voltage source is expressed as follows. Here, q is the electron charge, k is the Boltzmann constant, T is the absolute temperature, 1R43 is the resistance value of the resistor 13, and R14 is the resistance value of the resistor 14*vBll. is the voltage between the base and emitter of the transistor 10.

Here vnx+. If the temperature coefficient of is about -2 mv/°C, the temperature coefficient of the reference voltage Vref can be designed to be zero.

A constant current is generated by connecting a transistor 16 whose base is connected to a reference voltage source and a resistor 17 between the emitter of the transistor 16 and the ground.The base and collector of the transistor 15 are connected, and a resistor 18 is connected to this connection point. The emitter of the connected transistor 16 is connected to the collector of the transistor 16 to generate a constant voltage Vref' across the series load of the transistor 15 and the resistor 18.

Here, if the transistors 16 and 16 are designed to have the same area and the resistors 17 and 18 are designed to have the same value, the same voltage can be obtained. That is, the reference voltage Vref and the constant voltage vrefv
is the same value.

The subsequent configuration and operation are the same as those of the conventional example, and the details will be omitted.

In the configuration of the device according to the embodiment of the present invention shown in FIG.
The input voltage V is expressed by the following equation.

V = Vraf - V + V
-(5)IN BR16
CK + Nico de VB X + 6 is the base of transistor 16, emitter voltage +vCg16 is transistor 16
is the collector-emitter voltage of .

At the maximum control torque, the reference voltage Vref is 1.2V.

The collector-emitter voltage vC1 of the transistor 16 is saturated, 0.1 V, and the base-emitter voltage v
If 111Ef6 is 0.7v, the input voltage vIN is V from equation (5), N = 1.2-0.7 + 0.1vX, = 0
．． 6 V -------・(e
). Here, the motor drive transistor 22°24
．． The saturation voltage of the collector at the maximum control torque of 26 is set to 0.
Even assuming a high voltage of 5V, the transistor 22.24.26
The collector of is connected to the input of the comparator 19, and the input offset voltage is negligible and does not drop below O,SV. Therefore, motor drive transistors 22, 24 .
28 is not saturated even at the maximum control torque, and transistor 2
0 is not saturated, the current ratio is maintained at a constant value, and the speed control of the small DC motor is smoothly executed.

An example of the above characteristics is shown in Figure 2. As is clear from the figure, a smooth motor rotation speed can be obtained with respect to the load torque of the DC motor.

As is clear from the detailed description of the invention, the device of the present invention connects a reference voltage source to the base of a transistor, connects a resistor between the emitter of the transistor and ground, and thereby designs a constant current. Compare the constant voltage caused by passing through a transistor and a resistor. Even when torque is applied, the motor drive transistors 22, 24, and 26 do not saturate, allowing smooth speed control of the small DC motor.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the device of the present invention, Fig. 2 is a characteristic diagram of the motor rotation speed with respect to load torque of the device of the present invention and a characteristic diagram of a conventional device, and Fig. 3 is a circuit diagram of the conventional device. . 1... Small DC motor, 2... Resistor,
3...Power supply, 4...Grounding, 16.16
......Transistor, 17.18...Resistor, 19...Comparator, 20°22.24.26
・・・・・・Transistor, 21.23°26.27・
·····resistance. Name of agent: Patent attorney Toshio Nakao and 1 other person f-
--,J,! Luck) 9℃−ta 2・5・=−Jaa 3−・−4 is source 4−−j

Claims (1)

[Claims] One end is connected to the power terminal, and the other end of the small DC motor is connected to the power terminal.
The collector of the first transistor for driving the small DC motor is connected, its emitter is grounded via a predetermined resistor, and its base is connected to the base of the second transistor, so that the first The collector current of the transistor is always approximately K times the collector current of the second transistor, and the collector of the second transistor has a value approximately equal to K times the internal resistance of the small DC motor. one end of the first resistor is connected, the other end of the first resistor is connected to a power supply terminal, the emitter of the second transistor is grounded via a predetermined resistor, and the first transistor and the second The base connection point of the first transistor is connected to the output terminal of the comparator, and the connection point of the small DC motor and the first transistor is connected to one of the comparator having control characteristics in the positive direction with respect to the output current. A predetermined reference voltage is applied between the ground point and the base of the third transistor, its emitter is grounded via a predetermined resistor, and its collector is connected to the first resistor and the second transistor. A series load consisting of a fourth transistor whose base and collector are connected and a predetermined resistor is connected between the connection points with the transistor, and a connection point between the collector of the third transistor and the series load is connected to the connection point of the comparator. A speed control device for a small direct current motor, characterized in that it is connected to one input terminal of the other.