JPH03212189A - Speed control circuit for dc motor - Google Patents

Abstract

PURPOSE:To protect an IC from breakdown even when a power supply is connected with incorrect polarity by connecting a diode having negative temperature coefficient in forward direction from the source terminal of a motor to the output terminal of the IC. CONSTITUTION:A DC motor M is connected between the source terminal Vo of a motor control IC 1 and a terminal (4), while a torque control resistor Rt and a speed regulation resistor Rs are connected between terminals (1), (3) and (3), (4). A diode 2 having negative temperature coefficient is connected between the source terminal Vo connected with + side of a power supply and the terminal (1) in forward direction toward the terminal (1). When the terminals Vo and (2) are connected with incorrect polarity, the diode 2 blocks excessive current flow to the terminal (1) thus blocking current flow from the terminals (3), (4) to (1). Consequently, the IC is protected and temperature fluctuation of flux of a driving magnet is cancelled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a speed control circuit for a DC motor using a motor speed control IC.

(Prior Art) Generally, speed control of a motor is performed based on a signal obtained by comparing a voltage proportional to the number of rotations with a reference voltage. A DC motor with a constant magnetic field can be equivalently expressed as a series of internal resistance Ro and back electromotive force Eo induced by the rotation of the DC motor, and the load current flowing through the DC motor can be expressed as follows: What is the relationship between the motor rotation speed N and the back electromotive force EO when Ia is Ia?

Eo=N/, ZΦ... (1) However, KIZΦ is a back electromotive force constant, and the relationship between the load torque Td and the DC motor current Ia is Ia=KIZΦ・Td... (2) However, K1ZΦ is a torque constant. Furthermore, the terminal voltage Vm of the DC motor is vm=E
O+RoIa... (3), and the above (3
) can be changed to the relationship E o ” V m - Ro I a to detect a voltage proportional to the rotation speed, and if this voltage is fed back to the control system, the DC motor will not depend on changes in load or other factors. The rotation speed is controlled to a constant speed without any friction.

This principle is well known, and as shown in Figures 2 and 3,
A DC motor speed control circuit is constructed by using an ICI for DC motor speed control and connecting a small number of external passive circuit elements to it. In FIGS. 2 and 3, the DC motor control ICI has four terminals.

The first terminal ■ is a power supply terminal, the second terminal ■ is a ground terminal, the third terminal ■ is a reference terminal, and the fourth terminal ■ is an output terminal. The control ICI has the following internal circuits for each terminal. A plurality of (k) drive transistors Q2 are connected between the fourth terminal ■ and the second terminal ■.
~The collector and emitter of Qn are in the forward direction and the resistor R2
~Rn, respectively. Further, between the third terminal (2) and the second terminal (2), the collector and emitter of a shunt transistor Q are connected in the forward direction via a resistor R0. These drive transistors Q, ~Qn
The control input terminals, that is, the bases of the shunt transistors Q0 and Q0 are commonly connected to the output terminal of the error detection circuit 1a. A current mirror circuit is configured by the drive transistors Q2 to Qn and the shunt transistor Q. The error detection circuit 1a is composed of, for example, a differential amplifier circuit. A reference voltage νref is applied between the third terminal ■ and one input terminal of the error detection circuit 1a, and the other input terminal of the error detection circuit 1a is connected to the fourth terminal ■.

The following external circuits are connected to the DC motor control IC 1 configured as described above. A DC motor M is connected between the power supply terminal vO and the fourth terminal ■. A power supply voltage Vcc is supplied from the power supply terminal Vo to the error detection circuit 1a via the first terminal (2). Resistors Rt and Rs are connected in series between both terminals of the DC motor M.

The resistor Rt is connected as a first resistor between the first terminal (2) and the third terminal (2). The resistor Rs is connected as a second resistor between the third terminal (2) and the fourth terminal (2). The second terminal ■ is grounded. Since the DC motor M generates a back electromotive force in the drive coil due to active rotation, it can be equivalently represented by a series connection of a back electromotive voltage source EO and an internal resistance RΩ. By configuring the circuit in this way, the reference voltage Vref is generated between the third terminal (■) and the fourth terminal (■), and the load current I flowing to the fourth terminal α) is
A current proportional to a flows through the third terminal ■.

Now, if we connect the power terminal vO to the positive side of the power source and the second terminal ■, which is the ground @, to the negative side of the power source, power is supplied to the motor M and its rotor is driven to rotate. A back electromotive force Eo corresponding to the speed is induced between the motor terminals. This back electromotive force EO is the third voltage of the control IC1.
appears between the terminal ■ and the fourth terminal ■. This back electromotive voltage EO is compared with the reference voltage Vref generated between the third terminal (2) and the fourth terminal (2) in the error detection circuit 1a, and the error between the above EO and Vref is detected as a speed error signal. It is output from circuit 1a. Drive transistors Q2 to Qn and shunt transistor Q are driven by this speed error signal, current Ia flowing through motor M is controlled, and the rotational speed of motor M is controlled.

In this way, according to the conventional examples shown in FIGS. 2 and 3, the rotational speed is controlled to a predetermined speed as a so-called electronic governor motor.

(Problems to be Solved by the Invention) A speed control circuit including a control ICI as shown in Figures 2 and 3 is built into the DC motor body, and is connected to the positive side of the power supply from the DC motor body. power supply terminal Vo,
Only the grounding terminal GND (the second terminal ■ of the control ICI) that should be connected to the negative side of the power supply is pulled out. However, when connecting the motor M to the power source, it is possible that the motor M may be connected in the wrong direction by mistake. Figure 2,
In the conventional example shown in FIG. 3, if the terminal Vo and the terminal GND are accidentally connected in opposite directions with respect to the power supply, the current flowing through each terminal ■■ of the control ICI will flow through each resistor Rt, The current flows through Rs, and each of these resistances acts as a limiting resistance, and the current is limited to some extent. However, since the first terminal of the control ICI is directly connected to the positive side of the power supply, the current that flows from the ground terminal GND through the PN junction in the control ICI in the forward direction flows to the first terminal. ,
There is a problem in that this current becomes an excessive current for the PN junction in the control IC 1 and destroys the control ICI.

The present invention has been made to solve the problems of the prior art, and prevents the control IC from being destroyed even if the power supply is connected in the wrong direction in a motor control IC. The purpose of the present invention is to provide a speed control circuit for a DC motor that can control the speed of a DC motor.

Another object of the present invention is to provide a speed control circuit for a DC motor that can correct temperature characteristics of rotation control with a simple circuit configuration.

(Means for Solving the Problem) The present invention supplies a power supply voltage to a first terminal, grounds a second terminal, and generates a base voltage between a third terminal and a fourth terminal. The third terminal is provided with a DC motor control IC configured to allow a current proportional to the load current flowing through the fourth terminal to flow, and the DC motor is connected between the power supply terminal and the fourth terminal. A first resistor is connected between the first terminal and the third terminal, a second resistor is connected between the third terminal and the fourth terminal, and the power supply terminal and A diode is connected between the first terminal and the first terminal.

(Function) Even if the terminal of the motor having the motor control IC is connected to the power supply in the opposite direction by mistake, the first terminal of the motor control IC and the power supply terminal are used to apply the power supply voltage to the motor control IC. A diode connected between the two blocks the current and prevents the motor control IC from being destroyed.

The magnetic flux of the drive magnet of the DC motor changes depending on the temperature change, but this magnetic flux change is caused by the first
This is offset by changes in voltage drop caused by temperature changes in the diode connected between the terminal of the motor and the power supply terminal, and temperature changes in rotational speed are suppressed.

(Example) Hereinafter, an example of a speed control circuit for a DC motor according to the present invention will be described with reference to FIG. However, since the embodiment shown in Fig. 1 has circuit parts added to the conventional example shown in Figs. 2 and 3, the explanation of the configuration will focus on the added parts. , Fig. 2, Fig. 3
Components common to those in the conventional example shown in the drawings are given the same reference numerals to avoid redundant explanation.

In FIG. 1, the motor control ICIs are the first to fourth ICIs.
It has terminals ■■■■. Figure 2.

Similar to the conventional example shown in FIG. 3, the first terminal (2) is a power supply terminal, the second terminal (2) is a ground terminal, the third terminal (2) is a reference terminal, and the fourth terminal (2) is an output terminal.

The circuit configuration inside the control ICI is also the same as that of the conventional example. In addition, the external circuit connected to the control ICI is similar to the conventional example described above, and includes a DC motor M connected between the power supply terminal Vo and the fourth terminal ■ of the control ICI, and a control IC.
The first resistor R connected between the first terminal '1' and the third terminal ■ of I, and the third terminal ■ and fourth terminal σ1 of the control ICI. and a second resistor Rs connected thereto.

The resistance Rt is a torque control resistance, and the resistance Rs is a speed adjustment resistance. As a characteristic component, a diode 2 having a negative temperature coefficient is connected between the negative power supply terminal Vo connected to the positive side of the power supply and the first terminal (2). The diode 2 is directed in the forward direction from the power supply terminal vO to the first terminal ■. Other configurations are in the second
This is the same as the conventional example shown in FIGS.

Now, connect the power terminal ■0 to the positive side of the power supply and the ground terminal GN.
When D is connected to the negative side of the power supply, the rotor of motor M is driven to rotate, similar to the operation explained for the conventional example shown in FIGS. 2 and 3, and motor terminals A to C are A speed control operation is performed based on the back electromotive voltage EO induced during this period, and the rotational speed is controlled to be constant. Here, the load current flowing through the motor M is Ia, the current through the resistor Rt is 1t, the current through the resistor Rs is 15, the current flowing through the shunt transistor Q0 is Ik, and the equivalent internal resistance value of the motor M is R.
O, the back electromotive voltage of the motor M is EO1, the reference voltage of the reference voltage source 1b is Vref, and the terminal voltage of the motor M is Vo. In the motor control ICI, the current Ik is always 1/ of the current 1a due to the current mirror circuit made up of a plurality (k) of drive transistors Q2 to Qn and a shunt transistor Q. However, K is a proportionality constant. Also, I a = K I k, I s = Vref/
Rs, It=Ik+Is. When the voltage Vrn applied to the motor M is found, Vm
=Vx+Rt(Ik+Is)+VrefVm=V
x+Rt (I a/K) 10Rt (Vref/R
s ) +Vref”·(4) where Vx is the voltage drop due to diode 2.

The third term on the right side of the above equation (4) takes a constant value regardless of changes in the power supply voltage ■0 or changes in the load current Ia due to changes in the load torque, if the values of the resistors Rs and Rt are given. The second term on the right side changes in proportion to the load current Ia.

Therefore, V x + Rt (Vref
/Rs) +Vref is regarded as a voltage source and this is V
If we set a, Vm=Va+Rt (Ia/K) '' (5
)It can be expressed as. From this equation (5), the voltage Vm applied to the motor M is determined by the resistance (-Rt/K
) are connected in series.

On the other hand, considering the motor M, if the terminal voltage of the motor M is Vc, then Vc=Eo+RoIa... (6), and Vc=Vm...
(7), so Va+Rt (I a/K)=Eo+Ro I a・
・ ・The relationship is as follows (8). Therefore, the back electromotive force E of the motor M.

is Eo=Va+ ((Rt/K) Ra) I
a・ ・ ・ (9) If the resistance Rt is adjusted and Rt = KR○ (10) is selected, Eo = Va, and the motor M
It is driven at a rotational speed such that O is always at a constant voltage Va. That is, the motor M is controlled to always have a constant rotational speed without being affected by load torque or the like.

In this way, even when the diode 2 is inserted between the power supply terminal 0 and the first terminal 2 of the control ICI, the speed control circuit for the DC motor M can be constructed.

Now, suppose that in the embodiment shown in FIG. 1, the power supply terminal Vo and the terminal GND are mistakenly connected in opposite directions relative to the power supply. For example, if the power supply terminal vO and the first terminal of the control ICI
If diode 2 is not inserted between the Become. However, according to the embodiment shown in FIG.
A diode 2 inserted between the power supply terminal VO and the first terminal of the control ICI prevents excessive current from flowing through the first terminal, and also prevents excessive current from flowing through the third and fourth terminals. (This prevents current from flowing from the neck (2) to the first terminal (2), thereby preventing the control ICI from being destroyed.

Incidentally, as the resistors Rt and Rs, carbon film resistors whose resistance value changes little with respect to temperature changes are usually used, and consideration is given to suppressing changes in the rotational speed of the motor current due to temperature changes as much as possible.

However, the drive magnet of the motor has temperature characteristics, and the magnetic flux changes with temperature changes.

On the other hand, since the reference voltage temperature characteristic of the control ICI is normally set to O, the temperature characteristic of the control ICI can be ignored. Therefore, the temperature characteristics of the drive magnet are the main cause of variations in the rotational speed of the motor.

However, according to the embodiment shown in FIG.
serves to compensate for rotational speed fluctuations due to temperature changes. That is, in the above-mentioned control formula (4), the terminal voltage Vm of the motor M changes by a fraction of the voltage drop Vx across the diode 2.

The voltage drop Vx across diode 2 decreases by approximately -2 as the temperature changes.
(mV/'C) is shown. On the other hand, the temperature change in the magnetic flux of the magnet of the motor M is -0.18 [%/°C] in the case of a commonly used ferrite magnet. Therefore, the temperature change in the voltage drop Vx of the diode 2 and the temperature change in the magnetic flux of the drive magnet cancel each other out, and the temperature change in the rotational speed is suppressed.

Thus, according to the embodiment shown in FIG.
By connecting a diode 2 between 0 and the first terminal 2 for applying power supply voltage to the motor control ICI, even if the power supply is connected in the opposite direction by mistake, the control IC
An excessive current will not flow through I, and the control ICI can be protected. Also, the voltage drop Vx of diode 2
There is also the effect that the temperature change of the magnetic flux of the drive magnet cancels out the temperature change of the magnetic flux of the drive magnet, and the temperature change of the rotation speed is suppressed.

(Effects of the Invention) According to the present invention, by connecting a diode between the power supply terminal and the first terminal for applying power supply voltage within the motor control IC, the power supply may be erroneously reversed. Even if connected, an excessive current will not flow to the control IC, and the control IC can be protected. Furthermore, temperature changes in the voltage drop of the diode and temperature changes in the magnetic flux of the drive magnet are offset, and there is also the effect that temperature changes in the rotational speed are suppressed.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of a speed control circuit for a DC motor according to the present invention, Fig. 2 is a circuit diagram showing an example of a conventional speed control circuit for a DC motor, and Fig. 3 is a circuit diagram showing an example of a conventional speed control circuit for a DC motor. It is a circuit diagram specifically shown.

Claims (1)

[Claims] Supplying a power supply voltage to a first terminal, grounding a second terminal,
generating a reference voltage between the third terminal and the fourth terminal;
The third terminal is equipped with a DC motor control IC configured so that a current proportional to the load current flowing through the fourth terminal flows, and the DC motor is connected between the power supply terminal and the fourth terminal. , a first resistor is connected between the first terminal and the third terminal, a second resistor is connected between the third terminal and the fourth terminal, and the power supply terminal and the above A speed control circuit for a DC motor, characterized in that a diode is connected between the first terminal and the first terminal.