JPS58165681A - Speed control circuit for dc motor - Google Patents

Abstract

PURPOSE:To perform a preferable speed control by a DC motor which has small counterelectromotive force characteristic by employing as the control signal of a drive circuit for the DC motor the error detection voltage between a rotating speed proportional voltage and a divided voltage of a reference voltage. CONSTITUTION:A variable resistor 13 provided as voltage dividing means regulates a reference voltage Vref of a reference voltage source 8 in an IC15, thereby freely controlling it from 0V to (1+RD/RC) times even if the reference voltage source in the IC15 is stationary, and thus freely controls the reference voltage Vref =Vref.RA/(RA+RB) from 0V to (1+RD/RC) times. When the reference voltage Vref is set to the prescribed value, the input terminal 6 of an error detector 5 can be set to the Vref, a drive transistor 3 and a shunt transistor 11 can be controlled by the output of the detector 5, thereby obtaining constant rotating speed of a DC motor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to speed control of a DC motor, and particularly to a speed control circuit for a DC motor called an electronic governor, which is most suitable for tape recorders and the like that require constant speed rotation.

In general, motor speed control uses a voltage proportional to the rotation speed,
A reference voltage from a reference voltage source is applied to an error detection circuit for comparison, and a voltage corresponding to the difference is derived by the error detection circuit and applied to the drive means to keep the rotational speed of the DC motor constant. Many configurations have been adopted.

The DC motor has a constant magnetic field, and can be thought of as equivalently connecting an internal resistance Ro and a back electromotive force E induced by the rotation of the DC motor in series. The current flowing through the DC motor is 0, and the rotation speed of the DC motor is N.
Then, . −, Z″h Eo−N/, Zi holds true.

Here, Zi and Zi represent constants related to back electromotive force and torque, respectively.

Conventionally, in order to keep Eo constant, a DC motor (2), drive transistors +31 +31... and emitter resistors +41 +41... were connected between the DC power supply terminal (1) and the ground as shown in Figure 1. A series circuit is connected, and a reference voltage source (8) and one end of an error detection resistor (9) are connected to input terminals +61 and +71 of the error detection circuit (5), respectively.
The drive transistor +31 (3
1... and the shunt transistor 0υ are connected to each other.

In this case, the back electromotive force E0 is established. In the above equation, Vref is the voltage of the reference voltage source (8), R1 is the resistance value of the series resistor (0), and the voltage vm applied to the DC motor (2) is expressed as follows: VIll - IIIRm + EO - (2).

However, E is the motor current, R is the DC resistance of the DC motor (2), and the back electromotive force Eo of the DC motor (2) is as shown in equation (1) above, so that the current 1. Since the speed control is carried out by , there is a drawback that the voltage of the reference voltage source (8) in the second term cannot be varied.
・) (K represents a constant in the system including the error detection circuit (5), the drive transistor (3), and the shunt transistor α) Therefore, the present invention provides a novel DC motor speed control circuit that eliminates the above-mentioned drawbacks. This will be explained below with reference to the drawings.

Fig. 2 shows a speed control circuit for a DC motor according to the present invention, in which the same elements as in Fig. 1 are given the same figure numbers, and αj is a voltage dividing means provided in parallel with the reference voltage source (8). In this embodiment, a variable resistor is used. OIJ is a constant current source, (c) shows the inside of the device when integrated circuit (IC), αIQ
ηα穆αI (社) (社) is an external terminal, and (2) is an emitter resistance of the shunt transistor αυ. In FIG. 2, the following equation holds true.

Vr@f1= N'ref (RA/RA+RB)v
ll-dRT+Vr*flBT=:=KRyuHere, the resistance value Rc of the resistor (9) can be made sufficiently large. (Work S = Vr@f, /RC) The reference voltage ■ of the reference voltage source in the work C internal QS shown by the dashed line in FIG. f and Vr@r are adjusted by the variable resistor provided as the voltage dividing means. Therefore, especially when the necessary parts are integrated into ICs as described above, even though the internal reference voltage source is fixed, any Since it can also be applied to DC motors with back electromotive force, the range of applications is extremely wide. When the reference voltage Vr@f is set to a predetermined value as described above, one input terminal (7) of the error detection circuit (5) and the other input terminal (6
) is also set to Vr@f. The drive transistors 31 (31...) and the shunt transistors are controlled by the output signal of the circuit 2, so that the back electromotive force EO of the DC motor (2) is kept constant and the rotational speed is kept constant.

Next, FIGS. 3(a) to (g) show other embodiments of the voltage dividing means used in the present invention, in which (a) and (b) show a configuration of a semi-fixed resistor @ and a fixed resistor (2), (c)) is fixed resistance CGCS
The structure consists of cn and a changeover switch (E), and the thermistor (E) consists of a thermistor +7:4J and a fixed resistor @.
C) is an example with temperature compensation, (f) and (g) are fixed resistance @
- and a diode (to), the transistor's pace-to-emitter rising voltage ('VBI) can be compensated by the forward direction rising voltage (Vr) of the diode (to).

In the embodiment shown in FIG. 2, if the external terminal is provided, the temperature coefficient of Vr@t will be the resistance value Rm, if the temperature coefficient of the error detection resistor (9) (9) is constant. By inserting a resistor having a temperature coefficient set as above and having a temperature coefficient similar to that of the resistors (9) and (9), control and temperature compensation having various temperature characteristics can be performed.

In addition, in order to achieve multi-stage speed characteristics, the above (c)
The torque characteristics can be kept unchanged by changing the reference voltage itself by changing the changeover switch.

Furthermore, since the voltage vr@f can be controlled by bringing it closer to EO,
Speed adjustment becomes much easier, and reliability is improved accordingly.

As described above, according to the present invention, by dividing the reference voltage, there is an advantage that appropriate control can be achieved in correspondence with various DC motors, that is, DC motors having characteristics of small back electromotive force.

[Brief explanation of drawings]

Fig. 1 shows a conventional speed control circuit for a DC motor, Fig. 2 shows an embodiment of the same speed control circuit according to the present invention, and Figs.
(g) shows an embodiment of the voltage dividing means used in the same speed control circuit of the present invention. Explanation of main drawing numbers (1)...DC power supply terminal, (2)...DC motor,
(3)...Drive transistor, (5)...Error detection circuit, 161 +71...Input terminal, (8)...Reference voltage source, (9)...Error detection resistor, α... ...Output terminal, α℃...Shunt transistor, 0...Voltage dividing means.

Claims (1)

[Scope of Claims] (1) An error detection circuit having first and second input terminals, voltage dividing means connected to a reference voltage source, and an input electrode connected to the output terminal of the error detection circuit; a drive transistor whose output electrode is connected to the DC motor; a shunt transistor whose input electrode is connected to the output terminal of the error detection circuit and whose output electrode is connected to one end of the reference voltage source;
an error detection resistor comprising a DC power supply connected to one end of the DC motor, connecting the voltage division output end of the voltage dividing means to the first input terminal, and detecting voltage fluctuations at both ends of the DC motor; A speed control circuit for a DC motor, characterized in that: is connected to the second input terminal. (21) In claim 1, the speed control circuit for a DC motor is characterized in that a variable resistor is used as the voltage dividing means. (3) In claim 1, A speed control circuit for a DC motor, characterized in that a variable resistor is used as one of a pair of resistors as the voltage dividing means. A speed control circuit for a DC motor, characterized in that a plurality of resistors and changeover switches are provided as pressure means, and are selectively switched to achieve a predetermined voltage division ratio. (5) As set forth in claim 1, , said □ A speed control circuit for a DC motor, characterized in that at least one temperature-dependent resistance element is used as the voltage dividing means. (6) In claim 1, as the voltage dividing means: , a speed control circuit for a DC motor characterized by using a resistor and a diode.・