JPS5854893A - Control circuit for direct current motor - Google Patents

Abstract

PURPOSE:To improve the efficiency of drive by controlling the magnitude of currents supplied to the base of a transistor for driving the motor from a current power supply circuit in response to currents flowing through the DC motor. CONSTITUTION:An input terminal 1 is supplied with control signals, pulse width thereof is modulated in esponse to the detecting signals of the number of revolution of the motor 2 and mode selective signals and the like, and an input transisitor 21 and the transistor 22 for drive are controlled by the supply. The output of the transistor 22 for drive is supplied to the motor 2 through a low-pass filter formed by a coil 5 and a capacitor 6. A difference amplifier 26 controls the base currents of a transistor 23 for controlling base currents connected in parallel with a resistor 8 through which the base currents of the transistor 22 for drive flow in response to motor currents detected by means of a resistor 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC motor control circuit having a motor drive transistor controlled by a pulse width modulation signal.

FIG. 1 shows a conventional example of a DC motor control circuit in which a motor drive transistor is controlled by a pulse width modulation signal.

In FIG. 1, an input terminal 1 is supplied with a control signal that is pulse width modulated in accordance with the rotational speed detection signal of a motor 2, and is sent via a resistor 3 to transistors 11 and 12 connected to Darlington. is amplified. The common collector output of the Darlington-connected transformers 11 and 12 is converted into DC by a low-pass filter composed of a coil 5 and a capacitor 6, and is supplied to the motor 2ζ.

In the DC motor control circuit of FIG. 1, the voltage applied to the motor 2 is set to cc as the power supply voltage, and
When the voltage between the common collector and emitter of 2 is VCE, it becomes VCC - Vcg. This VcE is
Co1/ctor-emitter voltage of transistor 11 ■cE
1 and the base-emitter voltage VB of transistor 12
Since it is the sum of E2, the minimum value is about 07 to 1■, and the maximum applied voltage to the motor 2 is the value obtained by subtracting about 0.7 to iV from the above VCC. This is because when the above Vcc is relatively low, for example, when it is 5 cm, which is often used in general IC circuits, or about 3 cm, which is equivalent to two dry batteries, the ratio of the above Vcc to vCC becomes large, and 1
-The disadvantage is that the transistor 12 consumes a large amount of power and the motor drive efficiency is low.

Therefore, as in another conventional example shown in FIG.
A configuration in which it is connected to C is being considered.

The other configurations in FIG. 2 are similar to those in FIG. 1, so corresponding parts are given the same reference numerals.

In the DC tape control circuit of FIG. 2, the collector-emitter voltage Vc E 2 of the transistor 12 is
For example, since it can be as small as about 0.2V, the maximum value of the voltage applied to the motor 2 can be reduced to 0.
It can be increased by about 5 to 0.8V.

By the way, when the DC motor control circuit shown in Fig. 2 is applied to, for example, a reel drive motor of a tape recorder, depending on the operation mode of the tape recorder, the motor may rotate at high speed such as in fast forward or rewind mode. , recording, and playback modes, and there are cases where the rotation speed is relatively low, and it is difficult to increase the drive efficiency at each of these different rotation speeds. That is,
Since the base current of the transistor 12 flows through the collector resistor 7 of the transistor 11 in the input stage, it is necessary to set the value of the resistor 7 so that a suitable base current can flow for the tape 2 to rotate at high speed. A lot of power is wasted when the motor 2 rotates at low speed.

The present invention eliminates these conventional drawbacks and provides DC tape control that can increase the drive efficiency at each speed even when the maximum voltage applied to the motor is large and the tape rotation speeds are different. The purpose is to provide circuits.

That is, the characteristics of the DC tape control circuit according to the present invention are as follows.
A morph drive transistor to which a pulse width modulation signal for controlling the rotation of the DC motor is supplied, a current source circuit that supplies current to the L transistor, and a current source circuit that detects the current flowing to the DC tape. A tape current detecting means is provided, and the magnitude of the base current from the current source circuit is controlled in accordance with the output from the tape current detecting means.

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows a first embodiment of the present invention, in which an input terminal 1 is supplied with a control signal whose pulse width is modulated in accordance with a rotational speed detection signal of a motor 2, a mode selection signal, and the like. This input terminal 1 is connected to the base of a 1-transistor 21 in the input stage via a resistor 3, and the collector of this 1-transistor 21 is connected to the +Vcc power supply via a resistor 8, and the emitter is used for driving the next stage. At the base of the transistor 22,
each connected. The emitter of this transistor 22 is grounded, and the collector is connected to the coil 5 and the capacitor 6.
It is connected to the ground side terminal of the motor 2 via a low-pass filter consisting of.

The above configuration is similar to the circuit configuration shown in FIG. 2, but the resistance value of the resistor 8 is different (higher) than that of the resistor 7 shown in FIG.

Further, as a feature of the present invention, a current source circuit is configured by connecting a series circuit of a base current control transistor 23 and a resistor 24 in parallel to the resistor 8 through which the base current of the drive transistor 22 flows; In addition, a resistor 2 for converting the motor current into voltage is connected to the non-grounded terminal of tape 2.
5 is connected, and the voltage between the terminals of this resistor 25 is detected by a differential amplifier 26 such as an operational amplifier and sent to the base of the I/Ransistor 23.

Here, base current control 1-ransistor 2 of this embodiment
Reference numeral 3 operates in a so-called active region, and acts as a variable resistance element whose resistance value between emitter and collector changes approximately linearly depending on the base input. Therefore, transistor 22 for motor current IM flowing through motor 2
The base current In changes approximately linearly as shown in FIG. 4, and as IM increases, IB increases.

According to the first embodiment ζ of the present invention, the minimum value of the collector-emitter voltage VCR2 of the drive transistor 22 is small, about 0.2V, and the maximum voltage applied to the motor 2 is large, about Vcc -0.2V. can.

Further, when the tape current IM is large, the base current In is large, and when the IM is small, the IB is correspondingly small, so that power loss is small and motor drive efficiency can be improved.

Next, FIG. 5 shows a second embodiment of the present invention, and FIG.
Transistors 21, 22, 23, resistor 24,
A motor current detection resistor 25 and a differential amplifier 36 are provided. Here, the Hass current control transistor 33 of the second embodiment performs a switching operation, and the output obtained by dividing the output from the differential amplifier 36 by voltage dividing resistors 37 and 38 is supplied to the base of the transistor 33. ing.

That is, as shown in FIG. 6, depending on whether the current IM flowing through the motor 2 is larger or smaller than the predetermined value IM ref, the transistor 33 performs an on/off switching operation. base current IB
is controlled to be switched to one of two values, In+ and In2. For example, when this embodiment is applied to a reel drive motor of a tape recorder, in the playback and recording modes, IM (IMrct ) is obtained, and the base current In is
IM > IM in old and few, fast forward and rewind modes
ref, and the base current 1n increases to In2.

Therefore, it is possible to eliminate wasteful power consumption and improve motor drive efficiency while maintaining a large maximum voltage applied to the motor 2.

PNP of each transistor of the above eleventh and second embodiments,
For example, in the third embodiment shown in FIG. 7, PNP type transistors are used as the motor drive control transistors 41, 42a, 42b, and NPN type I is used as the base current control transistor 43.・
Each uses a transistor. Further, the trife stage uses a configuration in which the emitters and collectors of two transistors 42 a and 421 are connected in common.

The current flowing through the motor 2 is detected by a resistor 45 and a differential amplifier 46 and sent to the base of a transistor 43. For example, by turning on and off this transistor 43, a resistor 44 is connected in parallel to the resistor 8. Connected or disconnected.

Therefore, the base currents of drive transistors 42a and 42b are controlled.

By the way, the embodiment shown in FIG. 7 shows an example of a circuit configuration that is preferable when applied to, for example, a reel drive motor of a tape recorder. Input terminal 49
For example, the reel control signal supplied to the differential amplifier 47
The pulse width of the pulse signal to the input terminal 1 is changed according to the output level of the amplifier 47. For example, in FIG. 7, a sawtooth wave signal is sent to the non-inverting input terminal of the level-discriminating differential amplifier 48 through the input terminal 50, and the sawtooth wave signal is sent to the inverting input terminal of the differential amplifier 48 from the differential amplifier 47. By sending the output, the level of the sawtooth wave signal is discriminated based on the output level of the differential amplifier 47. Therefore, the switching output pulse width from the differential amplifier 48 changes according to the change in the output level of the differential amplifier 47, and this pulse width modulated pulse signal is applied to the base of the transistor 41 via the input terminal 1. The rotational speed of the motor 2 is controlled by this supply.

If the supply reel and take-up reel of the tape recorder are driven by independent motors, two sets of the circuits shown in FIG. 7 may be provided.

As is clear from the above explanation, according to the DC motor control circuit according to the present invention, the dry nozzle is controlled according to the motor current.
Since the base current of the herange disk is controlled, when the motor current decreases, the base current also decreases, reducing power loss and improving drive efficiency. Moreover, the maximum value of the motor applied voltage is reduced by only about 0.2V from the power supply voltage cc, as in the example shown in Fig. You can also increase the speed.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing different conventional examples, FIG. 3 is a circuit diagram showing a first embodiment of the present invention, and FIG. 4 is a circuit diagram showing a first embodiment of the present invention.
The figure is a graph that explains the operation of the circuit in Figure 3.
The figure is a circuit diagram showing the second embodiment of the present invention, and FIG.
A graph for explaining the operation of the circuit shown in the figure, and FIG. 7 is a circuit diagram showing a third embodiment of the present invention. 1........Pulse modulation signal input terminal 2....More 21.2
2, 31, 32, 41.42 1-run star for motor drive 23.33.43... Transistor for base current control 25.35.45 ...Motor current detection resistor patent applicant Sony Corporation representative Patent attorney Mimi Koike 1) Sakae Mura - 11- Figure 2

Claims (1)

[Claims] A motor drive transistor to which a pulse width modulation signal for controlling the rotation of the DC motor is supplied, a current source circuit to supply a base current to the transistor, and a motor current detection means to detect the current flowing through the DC motor. A DC motor control circuit comprising: a DC motor control circuit for controlling the magnitude of the base current from the current source circuit in accordance with the output from the motor current detection means.