JPH0126277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control circuit for a DC motor, and includes, in an integrated circuit, a control circuit that supplies or cuts off drive current to at least a detection circuit that detects an error voltage. An object of the present invention is to provide a speed control circuit for a DC motor that does not require a switching transistor outside an integrated circuit and can effectively utilize power supply voltage.

Conventionally, there is a speed control circuit that controls the rotational speed of a DC motor to be constant. As shown in FIG. 1, this conventional speed control circuit is supplied with operating power from a DC power supply 1 via a switching transistor 2, and a DC motor connected to this speed control circuit 3 formed into a semiconductor integrated circuit. The rotation speed of the DC motor 4 is controlled to be constant by supplying a drive current corresponding to the rotation speed of the DC motor 4. In this conventional circuit, the DC motor 4 is started and stopped by turning the switching transistor 2 on and off by closing and opening the switch SW. In such a conventional speed control circuit, a high-power switching transistor 2 is required to start and stop the DC motor 4, and even when this switching transistor is on, there is a small amount of voltage between the collector and emitter. Since the motor has a saturation voltage, the voltage applied to the motor decreases accordingly, resulting in a drawback that the voltage of the DC power supply 1 cannot be used effectively. This drawback is particularly noticeable in speed control circuits that use a low power supply voltage; for example, if the battery voltage drops even a little, stable speed control of the motor will be impaired.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to FIG.

FIG. 2 shows a circuit diagram of an embodiment of the circuit of the present invention. In the figure, the same parts as in FIG. 1 are given the same reference numerals. In FIG. 2, 10 is a semiconductor integrated circuit, and 11 to 16 are external terminals thereof. The terminal 11 has one end connected to the grounded switch SW and the other end. This switch SW is DC motor 4
When the switch is used, for example, to run a tape in a tape recorder, it is a switch that is opened when the end of the tape is detected, and that is also manually opened and closed. Terminal 12 is connected to power supply terminal 17, DC motor 4 is connected between terminals 12 and 15, and resistors R ₁ , R ₂ , R ₃ is connected. Further, the terminal 16 is grounded.

Furthermore, within the integrated circuit 10, the terminal 11 is a resistor.
R ₄ and is connected to terminal 12 via diodes D ₁ and D ₂ . The emitter of transistor Q _{1 whose base is connected to the cathode of diode D 1 is} a resistor.
R ₅ is connected to the terminal 12, the collector is connected to the terminal 16 via the diode D ₃ and the base of the transistor Q ₂ and the operational amplifier 18
It is connected to the. Transistor Q ₂ has its emitter connected to terminal 16 and its collector connected to the collector of transistor Q ₃ and the base of transistor Q ₄ . The base of transistor Q ₃ is commonly connected to the bases of transistors Q ₅ , Q ₆ , and Q ₇ and is also connected to the emitter of transistor Q _4. The emitter of transistor Q ₃ is connected to terminal 12, and the emitter of transistor Q ₄ is connected to The collector is connected to terminal 16. these diodes
_D1 to _D3 , transistors _Q1 to _Q4 , and resistors _R4 and _R5 constitute a control circuit. Also, transistor
Q ₅ , Q ₆ , Q ₇ , and Q ₈ constitute a current source circuit with a current mirror configuration, respectively, with resistors R ₆ , R ₇ , R ₈ , R ₉ and transistor Q ₃ connected to their respective emitters. , Siener diode D ₄ , operational amplifier 1
It supplies operating current to each of 9 and 18,
Transistors Q ₃ and Q ₄ are provided because transistor Q ₂ alone cannot supply the base current of these transistors Q ₅ to _{Q 8} .

Here, when the switch SW is closed, the diodes D ₁ and D ₂ of the control circuit become conductive, and the transistor Q ₁
The base of Q1 is biased and transistor _Q1 conducts, allowing a constant current to flow. Therefore, the diode D ₃ becomes conductive and the voltage at the anode of the diode D ₃ is supplied to the operational amplifier 18 as a bias voltage, and the transistor Q ₂ becomes conductive and the transistors Q ₃ ,
Q ₄ conducts. Therefore, the current source circuit constituted by each of the transistors _Q5 to _Q8 generates a constant current and supplies it to the Zener diode _D4 and the operational amplifiers 19 and 18, respectively.

The Zener diode D ₄ is a constant voltage circuit that generates a constant voltage by receiving current from the transistor Q ₅ , and this constant voltage is divided by the resistors R ₁₀ and R ₁₁ and supplied to the non-inverting input terminal of the operational amplifier 19. be done.
The operational amplifier 19 constitutes a constant current circuit together with the transistor Q ₉ and the resistor R ₁₂ , and a current corresponding to the voltage supplied to the non-inverting input terminal, that is, a constant current is outputted from the transistor Q ₉ . This constant current is converted into a constant voltage by the resistor _R13 , and this constant voltage is supplied as a reference signal to the inverting input terminal of the operational amplifier 18 that constitutes the detection circuit. Note that this operational amplifier 18 has a buffer amplifier at its output stage, and the drive current for the main part of this operational amplifier 18 and the drive current for the buffer amplifier are supplied from transistors Q ₇ and Q ₈ , respectively. At this time, since the DC motor 4 is stopped, the non-comparison signal supplied to the non-inverting input terminal of the operational amplifier 18 is the power supply voltage _Vcc , and the error voltage output from the operational amplifier 18 is large. The output terminal of the operational amplifier 18 has an emitter area ratio of 1:K (K is 50, for example).
The bases of transistors Q ₁₀ and Q ₁₁ are connected. The output transistor _Q11 increases its collector current in response to the above large error voltage,
This is supplied as a drive current to the DC motor 4 via the terminal 15, and the DC motor 4 is started.

When the DC motor 4 is rotating steadily, for example, if the load increases and the rotation speed decreases, the back electromotive force of the DC motor 4 decreases and the current flowing through the DC motor 4, that is, the output transistor _Q11 . The collector current increases, and the collector current of transistor _Q10 increases by 1/K times this amount. Therefore,
The voltage drop across the resistor _R1 increases, the potential at the terminal 13 decreases, and the potential at the inverting input terminal of the operational amplifier 18, which is a detection circuit, decreases. Therefore, the error voltage output by the detection circuit increases, the collector current of the output transistor _Q11 , that is, the drive current of the DC motor 4 further increases, and the speed of the DC motor 4 is controlled in the direction of increasing its rotational speed. Furthermore, in the case of fluctuations such as an increase in the rotational speed, the rotational speed of the DC motor 4 is kept constant by an operation opposite to the above.

Next, when the switch SW is opened, the diodes D ₁ to D ₃ and the transistors Q ₁ to _{Q 4} of the control circuit become non-conductive. Therefore, the transistors Q ₅ , Q ₆ , Q ₇ , and Q ₈ constituting the constant current circuit are rendered non-conductive, and the Zener diode D ₄ and the operational amplifiers 19 and 18 stop operating. Therefore, the error voltage output from the operational amplifier 18, which is a detection circuit, disappears, and the output transistor _Q11 stops supplying the drive current to the DC motor 4, and the DC motor 4 stops rotating.

In this way, there is no need to provide a switching transistor or the like outside the integrated circuit as in the past, so the number of parts is reduced, and the power supply voltage V _cc is applied to the DC motor 4 as it is without being dropped. , this voltage can be used effectively.

As described above, the speed control circuit for a DC motor according to the present invention includes a constant voltage circuit in an integrated circuit that generates a constant voltage when supplied with current, and a constant current that is output based on the constant voltage from the constant voltage circuit. A constant current circuit in the integrated circuit, a detection circuit in the integrated circuit that detects an error voltage using the voltage obtained when the constant current flows through a resistor, and a constant current circuit in the constant current circuit and the constant current circuit and the detection circuit, respectively. A current source circuit in an integrated circuit with a current mirror configuration that supplies an operating current of Because it has a control circuit, there is no need to provide a switching transistor outside the integrated circuit as in the past, reducing the number of parts, and the power supply voltage is directly applied to the DC motor, making it possible to use the power supply voltage effectively. In addition, when the switch is open, no current flows through the integrated circuit, allowing efficient use of power, and when the switch is closed, a current source circuit with a current mirror configuration is used to supply the constant voltage circuit, constant current circuit, and detection circuit with optimal current values that differ from each other. It has features such as being able to supply operating current with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an example of a conventional DC motor drive circuit, and FIG. 2 is a circuit diagram of an embodiment of the circuit of the present invention. 4...DC motor, 10...Integrated circuit, 11~
16... terminal, 17... power supply terminal, 18, 19...
…Operation amplifier, D ₁ to D ₃ … Diode, D ₄ …
Zener diode, _Q1 to _Q11 ...transistor, _R1 to _R13 ...resistor.

Claims (1)

[Claims] 1. Detecting the fluctuation of the current flowing through the DC motor in response to the fluctuation of the rotation of the DC motor as an error voltage,
A speed control circuit for a DC motor whose main part is a semiconductor integrated circuit, which controls the rotation speed of the DC motor to be constant by changing the current supplied to the DC motor according to the error voltage, a constant voltage circuit within the integrated circuit that is supplied with current and generates a constant voltage; a constant current circuit within the integrated circuit that outputs a constant current based on the constant voltage from the constant voltage circuit; a detection circuit within the integrated circuit that detects the error voltage using a voltage obtained by flowing through a resistor; and a current mirror configuration that supplies a constant operating current to each of the constant voltage circuit, constant current circuit, and detection circuit. a current source circuit within the integrated circuit; and a control circuit within the integrated circuit that controls operation or stoppage of the current source circuit in response to opening or closing of a switch provided outside the integrated circuit. A speed control circuit for a DC motor, comprising: