JPS622958Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a speed control device for a DC motor using a bridge circuit.

This invention relates to a speed control device for a DC motor using a bridge circuit.

A DC motor drive circuit for driving a DC motor used in a small tape recorder or the like is provided with a speed control device so that the DC motor rotates at a constant speed in response to changes in power supply voltage. This DC motor speed control circuit includes, for example, the
There is something disclosed in the issue. Incidentally, recently, tape recorders have appeared in which the tape running speed of the tape recorder can be switched in multiple stages, for example, 1.2 cm/s and 2.4 cm/s. A system has been developed in which the tape running speed is switched by directly changing the rotational speed of a DC motor. It is configured. Therefore, two switching switches are required, one for switching the speed setting circuit and the other for switching the power supply voltage characteristic compensation resistor, which prevents cost reduction and miniaturization of the speed control device.

Therefore, the object of this invention is to provide a speed control device for a DC motor that can reduce the number of changeover switches, thereby reducing cost and size.

Embodiments of this invention will be described below with reference to the drawings.

According to the DC motor speed control device shown in FIG. 1, a bridge circuit 15 is constituted by the DC motor 11 and resistors 12, 13, and 14. A constant current circuit 18 is constituted by a field effect transistor (FET) 16 and a resistor 17 connected between the source or drain and gate of this FET 16. The output end of this constant current circuit 18 is connected to a movable contact of a speed changeover switch 19. A high speed speed setting circuit 23 and a low speed speed setting circuit 27 are connected to fixed contacts A and B of the speed changeover switch 19. The high-speed speed setting circuit 23 includes a series circuit of a variable resistor 20 and a thermistor 21 connected between contacts A and D, and a resistor 22 connected in parallel to the thermistor 21. Similarly,
The low-speed speed setting circuit 27 includes a variable resistor 24, a thermistor 25, and a resistor 26. The movable contact of the changeover switch 19 is connected to the base of a transistor 28 as a comparison element. A DC power supply 33 is connected between power supply terminals of the bridge circuit 15 via a transistor 29 as a variable impedance element. The base of the transistor 29 is connected to the collector of the transistor 28, and the emitter of the transistor 28 is connected to the detection end of the bridge circuit 15, that is, the connection point between the resistors 13 and 14, and is connected to the emitter of the transistor 29 via the resistor 31. Connected. The emitter of this transistor 29 is connected to the source or drain of the FET of the constant current circuit 18. A resistor 32 is connected in parallel to the constant current circuit 18 via a contact B of a changeover switch 19.

According to the above speed control device, when the changeover switch 19 is switched to the low speed speed setting circuit 27 as shown in the figure, the current is determined by the product of the output current of the constant current circuit 18 and the impedance of the low speed speed setting circuit 27. The reference voltage and the back electromotive force of the motor 11 are compared by the transistor 28. Transistor 28 supplies a bias voltage corresponding to the comparison difference to transistor 29 to control the impedance of transistor 29. A current is supplied to the motor 11 according to the impedance of the transistor 29, and the rotational speed of the motor 11 is controlled.

By the way, if the speed control device shown in FIG. 1 is not provided with the resistors 31 and 32, the voltage of the motor 11 is between the upper limit V _MAX and the lower limit V _MIN of the voltage of the power supply 33, as shown by graph I in FIG. 2. The rotation speed changes significantly. A resistor 31 is provided, and this resistor 3
When the resistance value of 1 is arbitrarily set, as shown in the graph, the change in the rotational speed of the motor 11 with respect to the change in the power supply voltage becomes small. In this embodiment, the resistance value of the resistor 31 is set so that when the motor 11 rotates at high speed, it has an appropriate power supply voltage characteristic as shown in graph A of FIG. But in this case,
When the motor 11 rotates at a low speed, the power supply voltage characteristics deteriorate as shown in graph B of FIG. For this reason, in the past, a resistor was provided whose resistance value was set to compensate for the power supply voltage characteristics during low speed rotation.
It was constructed so that two resistors could be switched using a changeover switch. In this invention, a resistor 32 is provided which is connected in parallel to the constant current circuit 18 at low speeds instead of providing a low speed power supply voltage characteristic compensation resistor. When this resistor 32 is connected to the constant current circuit 18, the reference voltage appearing between C and D changes in proportion to the change in the power supply voltage, as shown by graph B in FIG. Since the rotational speed of the motor 11 is proportional to the reference voltage, the power supply voltage characteristic B shown in FIG. 3 and the power supply voltage characteristic corresponding to characteristic B in FIG. can get. Note that when the changeover switch 19 is switched to contact A, a series circuit of the resistor 32 and the speed setting circuit 17 is connected between the positive terminal of the power source 33 and the connection point D. Since the resistor 32 has a relatively high resistance, the high speed is There is almost no effect on the rotation side circuit.

Next, another embodiment will be described with reference to FIG. According to this embodiment, the variable resistor 20 is a resistor 34.
is connected to the thermistor 21 through the variable resistor 2
4 is connected to the thersamistor 25 via a resistor 35. The high-speed setting circuits 23 and 27 are connected to the detection terminal of the bridge circuit 15 via a transistor 40. The movable contact of the changeover switch 19 is connected to the base of the transistor 36.
The emitter 6 is connected to the detection end of the bridge circuit 15 and also connected to the power supply V _CC via a resistor 31 . The collector of transistor 36 is connected to the base of transistor 37, and is also connected to the emitter of transistor 37 and the base of transistor 29 via resistor 38. transistor 29
A capacitor 39 is connected between the base and emitter of. The other circuit configurations are the same as those in the embodiment shown in FIG. 1, so their explanation will be omitted. An experimental example will be described in which the values of each circuit element in the circuit shown in FIG. 5 were set as follows and the power supply voltage characteristics were measured.

Resistor 12... 1.5Ω, Resistor 13..., 680Ω Resistor 14... 220Ω, FET18..., 2sk44 Resistor 20... 300Ω, Resistor 24..., 300Ω Thermistor 21... 90Ω (at room temperature) Thermistor 25... 40Ω (at room temperature) Resistor 22... 390Ω , Resistor 26..., 330Ω Resistor 34... 430Ω, Resistor 35..., 130Ω Resistor 38... 10kΩ, In addition, in the experiment, a test tape with a 3kHz signal recorded was run and the frequency of the playback output was measured, and the resistance 31 (R _A ) , the variable resistor 20 or 24 is adjusted every time the value of the resistor 32 (R _B ) is changed _.
The frequency of test tape playback output when 3V is 3k
Hz. The resistor 20 is used for adjusting high-speed tape running (2.4 cm/s), and the resistor 24 is used for adjusting low-speed tape running (1.2 mm/s).

FIG. 6 shows the characteristics when the resistor R _B is removed and the resistor 32 (R _A =12KΩ) is connected and when it is not connected at a tape running speed of 2.4 cm/s. This graph shows that appropriate power supply voltage characteristics can be obtained when the resistor 32 is provided. FIG. 7 shows the characteristics at a tape running speed of 1.2 cm/s. In this case, resistor 32 is removed, ie R _B =∞ and resistor 31 is set to R _A =27 kΩ or R _A =∞. This graph also shows that good power supply voltage characteristics can be obtained when the resistor 31 is provided.

In FIG. 8, measurements are taken based on the following conditions. That is, tape running speed 1.2cm/s, R _A = 12k
Ω, R _B =56kΩ or ∞. Figure 9 shows tape running speed 2.4 cm/s, R _A = 12 kΩ, R _B = ∞ or R _B
This is the characteristic when = 56kΩ. Note that the graph indicated by △ in the graph shows the characteristics when R _B is added after adjusting the tape speed at R _B =∞. In this case, the influence due to the addition of R _B is only about 1%, which is almost the same as the graph indicated by x, that is, the graph adjusted by the resistor 20.

In the power supply voltage characteristic graphs shown in FIGS. 6 to 9 described above, this is shown as a deviation in tape speed, but this can be considered as a rotational deviation of the motor 11.

As explained above, according to this invention, an appropriate power supply can be maintained even at low speeds and high speeds depending on whether the resistor is connected to or disconnected from the constant current circuit connected to the speed setting circuit via the speed setting circuit changeover switch. The voltage characteristics are obtained by one switch circuit. Thereby, cost reduction and miniaturization of the speed control device can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a speed control device for a DC motor according to an embodiment of the invention, FIGS. 2 to 4 are diagrams showing the power supply voltage characteristics with and without a compensation resistor, FIG. 5 is a circuit diagram of a speed control device for a DC motor according to another embodiment, and FIGS. 6 to 9 are based on actual measured values in the speed control device of FIG. 5 with and without a power supply voltage compensation resistance. FIG. 3 is a diagram showing respective power supply voltage characteristics. 11...DC motor, 15...bridge circuit,
16...FET, 18...constant current circuit, 19...
Selector switch, 23...High speed speed setting circuit, 2
7...Speed setting circuit for low speed, 28, 29...Transistor, 31, 32...Resistor.

Claims (1)

[Claims for Utility Model Registration] (1) A DC motor, a bridge circuit with the DC motor as one side, a variable impedance element connected between the power supply end of the bridge circuit and a power source, and the bridge circuit. between a constant current circuit and a plurality of speed setting circuits each having an impedance set according to a plurality of rotational speeds of the DC motor, and between the constant current circuit and the speed setting circuit; a series circuit comprising a switching means connected to the circuit for selectively switching the speed setting circuit; and a switching means for selectively switching the speed setting circuit; and the selected speed determined by the product of the output current of the constant current circuit and the impedance of the selected speed setting circuit. a comparison circuit element that compares a reference voltage generated at a terminal of a setting circuit with a voltage between detection terminals of the bridge circuit and changes the impedance of the variable impedance element according to the comparison difference; a first one connected between one end of the detection end and the power supply in order to compensate for the characteristics;
an impedance element; and a second impedance element that is connected in parallel to the constant current circuit and changes the power supply voltage characteristics of the reference voltage when another rotational speed is selected by the switching means. DC motor speed control device. (2) The speed control device for a DC motor according to claim 1, wherein the constant current circuit is a constant current circuit using a field effect transistor. (3) The speed control device for a DC motor according to claim 1 or 2, wherein the variable impedance element is a transistor. (4) The speed control device for a DC motor according to any one of claims 1 to 3, wherein the first and second impedance elements are resistance elements.