JPS61224892A - Motor drive circuit - Google Patents

Abstract

PURPOSE:To control the voltage between the terminals of a DC motor to become constant by detecting the voltage between the terminals according to the polarity-changing operation of the voltage. CONSTITUTION:A voltage VM between the terminals of a motor 22 is detected, negatively fed back to a drive voltage generator 23 to control the level of the drive voltage Vs of the motor 22 to always hold the voltage VM at constant level. In this case, the voltage VM is detected through an electronic changing switch 24 which uses C-MOS analog switch, and the contacts 241, 242 of the switch 24 are switched in cooperation with the switching of ON and OFF of transistors Q21-Q24. Thus, the polarity of the detected output of the voltage VM is set at one polarity to be fed back as a voltage control, and the input polarity of the detected output for a differential amplifier 25 is always maintained constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a drive circuit for a DC motor that is rotatable in both forward and reverse directions.

[Technical background of the invention]

Conventionally, in a drive circuit for rotating a DC motor in forward and reverse directions, the polarity (+, -) of the voltage between the terminals of the motor is switched using a relay or a transistor switch.

When using a relay, the motor current is switched by mechanical contacts. Therefore, in this case, the performance is inferior to the case of using a transistor switch in terms of contact life, contact resistance, reliability of mechanical parts, switching response speed, etc.

For this reason, if you try to secure the same performance as when using a transistor switch, you will have to use a highly reliable relay, which inevitably increases the cost.

Therefore, in general, the polarity of the voltage between the terminals of the motor is often switched using a transistor switch. FIG. 4 shows a conventional configuration of a motor drive circuit that performs polarity switching using a transistor switch.

In FIG. 4, the DC motor 11 rotates in either the forward direction or the reverse direction depending on whether transistors Q11 #Q14 of the applied voltage polarity switching circuit 12 are turned on or transistors Q12 #Q15 are turned on. Driven.

Voltage vM between the (+) and (-) terminals of the motor 11
This is done by applying negative feedback to the drive voltage generating circuit 13 that outputs the drive voltage V in accordance with the drive voltage v1 of the motor 11. That is, the inverting differential amplifier 14 takes the difference voltage between the detection output of the drive voltage v8 and the predetermined reference voltage v1], and generates the drive voltage of the motor drive voltage generation circuit 13 from this difference voltage DAK. Control behavior. As a result, the inter-terminal voltage vM is controlled to be inversely proportional to the way the drive voltage VB is detected, and is maintained at a predetermined voltage.

In addition, when controlling the terminal voltage vMI to a constant level, the reason why this terminal voltage vM and the potentials of the (hand) terminal and (-) terminal are not directly detected is because the polarity of these voltages is the terminal voltage vM. Because it switches according to the polarity switching of (+)
The terminal (-) is the ninth terminal that floats in potential from the ground point.

[Problems with background technology]

However, as described above, in the case of a configuration in which the inter-terminal voltage vM is controlled to be constant according to the detection output of the drive voltage V,
Even if the drive voltage v8 can be controlled to a constant value, it is not necessarily possible to control the voltage between the terminals vM to a constant value. Transistor Q1 due to changes in current
This is because it changes due to a change in the saturation voltage of Q1 to Q14 or a change in this saturation voltage due to temperature drift.

[Purpose of the invention]

This invention was made to deal with the above circumstances,
It is an object of the present invention to provide a motor drive circuit that can control the voltage itself between the terminals of a DC motor so that it is constant.

[Summary of the invention]

This invention detects the voltage between the terminals according to the polarity switching operation of the voltage between the terminals so that the polarity of the detection output of the voltage between the terminals of the DC motor becomes one polarity, and according to this detection output, the voltage between the terminals of the DC motor is detected. By applying negative feedback to the drive voltage generation operation, the voltage between the terminals is maintained at a predetermined set voltage.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, applied voltage polarity switching circuit 21 is composed of transistors Q21 to Q24. When the DC motor 22 is rotated forward, transistors Q21 #Q24 are turned on, transistors Q22 #Q23 are turned off, and voltage is supplied to the motor 22. When the motor 22 is reversed, the transistor Q
, Q is turned off and transistor Q22 #
Q23 is turned on and voltage is supplied to the motor 22. When rotating the motor 22 forward, the (+) terminal of the motor 22 has a higher stain level than the (-) terminal, and when rotating the motor 22 in the reverse direction, the (+) terminal has a higher stain level than the (-) terminal. The stain level is low. Moreover, since the transistor in the on state has a saturation voltage V, □, the potential va of the higher potential motor terminal is Va-VII-Vsat.
=・”(1). Also, the potential vb of the motor terminal with the lower potential is floating from the ground point of the circuit, and W
b=Vsat=・=<2).

This embodiment detects the voltage vM between the terminals of the motor 22,
By negatively feeding this back to the drive voltage generation circuit 23 to control the level of the drive voltage v8 of the motor 22, the inter-terminal voltage vM is always kept at a constant level.

In this case, the inter-terminal voltage vM is detected through an electronic changeover switch 24 using a C-MOS analog switch or the like. Contacts 241 and 242 of this switch 24 are switched in conjunction with on/off switching of transistors Q21 to Q24.

Accordingly, the polarity of the detection output of the inter-terminal voltage vM is set to one polarity that can be fed back for voltage control, and the input polarity of the detection output to the differential amplifier 25 is always kept constant. ), when the motor 22 is rotated forward, the contacts 241 and 242 of the switch 24 are
Connected to terminals 243 and 245. On the other hand, the motor 22
When reversing the
42 are connected to the terminals 244 and 246, respectively.

As a result, the output polarity of the differential amplifier 25 always matches the input polarity of the differential amplifier 25.

vref is a reference voltage of the differential amplifier 25, and the output voltage of the differential amplifier 25 is vrsf + VM.
“In this case, the amplification factor of the differential amplifier 25 is the resistor R21
~'' is set to 1 by making the resistance values of 24 equal.

The output of the differential amplifier 25 is led to an inverting differential amplifier 26 and has a voltage of V0+V. The difference with f is inverted and amplified.

This differential amplification output vDK is vH−Vref−” (V
MVO)...=<3). Here, -α is the amplification factor of the inverting differential amplifier 26, and α is the resistance R
25# It is expressed as follows using the resistance value of R26.

The differential amplified output VD obtained in this way is supplied to the motor drive voltage generation circuit 23. This motor drive voltage generation circuit 23 is of a switching regulator type. That is, the differential amplification output V□ is the differential amplifier 2
At 31, the level is compared with the output of the toothed wave generating circuit 232 and converted into a rectangular wave pulse. The width of this pulse is
It is modulated in proportion to the differential amplification output VD. Then, according to this square wave curve, the transistor Q25 e
Q26 turns on and off, and transistor Q2 from power supply VD
A pulsed current flows through 6.

This current is smoothed by the coil L21, the diode D21, and the capacitor C2, and is applied to the applied voltage polarity switching circuit 21 as a drive voltage v8.

In the above configuration, when the inter-terminal voltage vM is larger than the voltage vo, an attempt is made to lower the drive voltage vll;
If M<vo, an attempt is made to increase the drive voltage v8. In this way, a negative feedback loop is formed, and the terminal voltage vM
and voltage V. The point where the difference vM-vo becomes O is the stable point.

According to this embodiment, the voltage vM between the terminals of the motor 22 is directly detected, and the voltage vM between the terminals is controlled to be constant according to this detection output.
Transistor Q due to changes in load current and temperature drift
Regardless of changes in the saturation voltage Vsat of Q21 to Q24, the inter-terminal voltage vM can always be maintained at a preset voltage.

In addition, since the voltage V is detected according to the polarity switching operation of the voltage V so that the polarity of the detection output of the voltage vM between the terminals is unipolar, even if the polarity of the voltage vM changes. , the control to keep it constant is not affected in any way.

Moreover, since the changeover switch 24 is an electronic switch, the response speed is fast and reliability is high, and the cost can be reduced compared to using a relay.

FIG. 2 is a circuit diagram showing a second embodiment of the invention.

In this embodiment, two differential amplifiers 31 and 32 with opposite differential input polarities are provided in parallel in place of the changeover switch 24 and differential amplifier 25 shown in FIG. An electronic changeover switch 33 is provided which switches the connection of the contacts to the terminals 332 and 333 in conjunction with rotation and reverse rotation. In this case, the differential amplifier 31
is used to detect the Tanabata voltage during forward rotation, and the differential amplifier f32 is used to detect the motor voltage during reverse rotation. The contact 331 of the switch 33 is connected to the terminal 3 during normal rotation.
32, and is connected to a terminal 333 during reverse rotation.

As a result, the terminal voltage v for the inverting differential amplifier 26
The polarity of the detection output of M is always kept constant regardless of forward or reverse rotation.

In FIG. 2, the resistance values of the resistors R31 to R5B are made equal, and the amplification factors of the differential amplifiers 31 and 32 are both set to l.

FIG. 3 is a circuit diagram showing a third embodiment of the invention.

This embodiment includes an inverting differential amplifier 41 that inverts the output of the differential amplifier f31, and an electronic changeover switch 41 that selectively selects the output of the differential amplifier 7'JJ and the output of the inverting differential amplifier 41. The input polarity of the detection output of the inter-terminal voltage vM to the inverting differential amplifier 26 is made constant. That is, the resistance values of the resistors R41 to R43 are made equal, and the absolute value of the amplification factor of the inverting differential amplifier 41 is set to 1, which is the same as the differential amplifier fsx. In addition, the contact 421 of the switch 42 is connected to the terminal 422 during normal rotation.
and is connected to terminal 423 during reverse rotation. As a result, during forward rotation, the output of the differential amplifier 'f31 is given to the inverting differential amplifier 26, and during reverse rotation, the output of the inverting differential amplifier f41 that inverts the output of the differential amplifier 31 is given to the inverting differential amplifier 26. The signal is applied to the dynamic amplifier 26.

The second point explained above. In the third embodiment as well, the first
The same effects as in the embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a motor drive circuit that can control the voltage itself between the terminals of a DC motor so that it remains constant.

[Brief explanation of drawings]

1 to 3 are circuit diagrams showing the configurations of different embodiments of the present invention, and FIG. 4 is a circuit diagram showing a conventional motor drive circuit. 21... Applied voltage polarity switching circuit, 22... DC motor, 23... Motor drive voltage generation circuit, 24°33.
42...Electronic changeover switch, 25.31...Differential amplifier, 26,32.41...Inverting differential amplifier.

Claims (1)

[Scope of Claims] A DC motor whose rotational direction is switched according to the polarity of the voltage between the terminals, a drive voltage generation means for generating a drive voltage for driving the DC motor, and a drive voltage generated by the drive voltage generation means. a polarity switching means for switching the polarity of the voltage across the terminals applied to the DC motor according to the drive voltage applied to the DC motor; inter-terminal voltage detecting means for detecting the inter-terminal voltage according to the polarity switching operation of the switching means; and generating the driving voltage according to the detection output of the inter-terminal voltage detecting means so that the inter-terminal voltage of the DC motor is constant. A motor drive circuit comprising negative feedback means for applying negative feedback to the means.