JPS608559Y2 - Speed control device for small DC motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device in which the speed of a DC motor is controlled using a three-terminal DC motor speed control IC.

A DC motor with a constant magnetic field can be equivalently expressed as an internal resistance and a back electromotive force induced by the rotation of the DC motor connected in series.

Therefore, if the DC motor is driven by a constant voltage source that has an internal resistance (negative internal resistance) whose absolute value is equal to the internal resistance of the DC motor and takes a negative value, the DC motor will always drive in the opposite direction. The motor is driven at a rotational speed at which the electromotive force is equal to that of the constant voltage source, and a constant rotational speed that is independent of load changes and other factors can be obtained.

Although this principle is conventionally known, power supplies with internal resistance as described above have complicated circuit configurations and are expensive.
Only a few were put into practical use.

However, with the recent remarkable progress in IC technology, it has become possible to put the above power supply into practical use as an IC for controlling the speed of a DC motor.

Conventionally, many of these types of DC motor speed control ICs have used inexpensive three-terminal packages for transistors, and have been combined with a few external passive circuit elements to form a DC motor speed control device.

FIG. 1 shows the configuration of this type of DC motor speed control device, where 1 is a DC motor whose speed is to be controlled, 2 is a speed control IC, and terminal pins ① and ② are shown.

■It is equipped with.

3 and 4 are resistors, and 5 is a DC power supply.

In addition, I-=Ill? I? -■2? IK,
I- is the current flowing through each arrow position, R is the equivalent internal resistance value of the DC motor 1, E is its back electromotive force,
,.

f represents a reference voltage, and ■o represents a power supply voltage, respectively.

In the above-mentioned IC, the current distribution circuit is configured such that a current of 1/2 is always flowing through the current distribution circuit (here, K is the current distribution ratio).

), the values of resistor 3 and resistor 4 are RT? R, the voltage Vo applied to the DC motor 1 is given by the following equation.

now, far.

(here, +R Ding I.

) Here, the first and second terms on the right side of the first equation are the resistance Rst
If RT is given, the supply voltage ■.

, takes a constant value regardless of changes in the load torque (i.e., armature current 1.), etc., but the third
The term is armature current 1. changes in proportion to.

If we consider the first term on the right side of the second equation as a voltage source, then the resistance (-
RT/K) is equivalent to connected in series with this voltage source.

On the other hand, considering the DC motor 1, if the terminal voltage of the DC motor 1 is (4) The following relationship is obtained.

The back electromotive force E is Therefore, the DC motor 1 It is expressed as

From this, if we adjust the resistor R7 and select RT = KR, (7), E, = V, and the DC motor 1 is driven at a rotational speed such that its back electromotive force E1 is always a constant voltage. It will be done.

That is, the DC motor 1 is not affected by load torque and maintains a constant rotational speed.

In other words, if the rotational speed of the DC motor 1 is N1 and the power generation constant of the DC motor 1 is, then N is 1 (Ken-R,) 1 RT I r), and the DC motor 1 is Motor, the resistance value RT is RT=KR.

If you choose, Corresponds to internal resistance R of 1 (10) 10 RT I-) becomes.

In other words, the DC motor 1 is driven at a constant rotation speed expressed by Equation 11 without being affected by the load torque.

By the way, in this type of speed control device, the resistor 4 is constituted by a combination of a variable resistor and a fixed resistor, and the speed is usually set by adjusting the variable resistor to an appropriate value. .

In other words, the speed is set by adjusting the resistance value R8 in Equation 11.

Therefore, in this type of conventional speed control device,
The lowest rotational speed that can be set is when Rs becomes infinite, that is, at terminal ■ in FIG.

■When the gap is opened, the minimum rotational speed Nm1n,
Hato becomes.

In other words, it is impossible to set the rotational speed below the rotational speed represented by the 12th &, and there has often been a problem that the required rotational speed cannot be achieved.

The present invention overcomes these drawbacks of the conventional motor by utilizing the forward voltage of the diode, thereby making it possible to set the rotational speed to a lower level without sacrificing controllability.

FIG. 2 shows an electrical connection diagram of an embodiment of the present invention.

That is, a diode 6 is connected between the connection point between the DC motor 1 and the resistor 4 and the terminal 2 in the conventional electrical connection diagram shown in FIG.

The diode 6 has its anode connected to the connection point between the DC motor 1 and the resistor 4, and its cathode connected to the terminal (2).

Now, if the forward voltage of the diode 6 is Vo, then
In the speed control device of the embodiment of the present invention shown in FIG. 2, the DC motor 1 is controlled to a rotational speed N' expressed by the following equation.

In addition, the minimum rotational speed N'min that can be set in this case,
is also obtained when the resistance R3 becomes infinite, that is, when the connection point between the DC motor 1 and the anode of the diode 6 and the terminal (2) are opened in FIG.

According to the formula 1 and formula 14, according to the present invention, Vo/ can be set to a lower rotational speed than the conventional example shown in FIG.

Also, even if diode 6 is added, if the resistance RT is adjusted so that the relationship RT=illustration holds, the rotational speed will be controlled to the value shown in the first trial regardless of the load torque. This is also clear, and therefore, it is natural that controllability is not impaired compared to the conventional example.

As described above, according to the present invention, by adding a diode, which is an inexpensive and simple configuration, it is possible to set a low rotational speed, which was impossible with conventional DC motor speed control devices of this type. The practical range of the DC motor speed control device can be greatly increased.

[Brief explanation of the drawing]

FIG. 1 is an electrical wiring diagram showing a conventional small DC motor speed control device equipped with a 3-terminal DC motor speed control IC;
FIG. 2 is an electrical wiring diagram of a speed control device for a small DC motor according to an embodiment of the present invention. 1... Small DC motor, 2... 3-terminal DC motor speed control IC, 3, 4... Resistor,
5...DC power supply, 6...Diode.

Claims (1)

[Scope of utility model registration request] A three-terminal DC motor that generates a reference voltage between the two terminals (■), grounds the remaining terminal (■), and is configured so that a current proportional to the current flowing through the terminal ■ always flows through the terminal ■. A speed control IC 2 is provided, a resistor 3 is connected between the DC power supply positive terminal and the terminal (2), a series circuit of a controlled DC motor 1 and a diode 6 is connected between the DC power supply positive terminal and the terminal (2), and the The diode has an anode connected to the controlled DC motor, a cathode connected to the terminal (2), a resistor 4 connected between the connection point between the controlled DC motor and the anode of the diode, and the terminal (2), and A speed control device for a small DC motor, characterized in that the terminal (2) is connected to the negative terminal of the DC power source.