JPS6230475Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a DC motor control circuit that controls the speed of a DC motor using a charging/discharging circuit.

Conventionally, this type of DC motor control circuit 1 has a capacitor C of a charging/discharging circuit 2, as shown in FIG.
Since the slice output V'out was taken directly from 1 to the comparator, the output V'out had a gentle integral waveform as shown in Figure 8, making it difficult to control sensitively to motor speed changes. Therefore, when starting up or changing the rotation speed, the fifth
As shown in the figure and the broken line in Figure 6, overshoot, undershoot, etc. of the rotational speed V1 occur,
The drawback was that it took some time to stabilize at a constant speed.

Therefore, in the present invention, a resistor is installed in series on the output side of the charging/discharging capacitor so that both the charging current and the charging current flow through the resistor, and
It is an object of the present invention to provide a control circuit for a DC motor in which a comparator and a charging/discharging capacitor are connected through the resistor, thereby eliminating the above-mentioned drawbacks.

Hereinafter, the present invention will be specifically explained based on an embodiment shown in the drawings.

As shown in FIG. 1, the DC motor control circuit 1 has a speed detection section 5 connected to the DC motor 3, and the detection section 5 is provided with a speed setting section 6. A charging/discharging circuit 2 is connected to the speed setting section 6, and the circuit 2 includes a charging transistor TR1 and a discharging transistor as shown in FIG.
TR2 is connected via resistors R1 and R2. Between the resistors R1 and R2, there is a resistor R3 and a charging/discharging capacitor C1 connected to the ground 7.
3 is connected in series to the output side of the capacitor C1, and one end of the resistor R3, that is, the circuit 2
The output of is connected to comparator 9. Comparator 9 is connected to driver 10, and driver 10 is connected to DC motor 3.

Since the present invention has the above-described configuration, the rotation of the DC motor 3 is converted by the speed detection section 5 into a dot pulse DP having a pulse width T1 corresponding to the rotation speed V1 of the motor 3, and then sent to the speed setting section 6. Output. The speed setting unit 6 receives a speed designation signal S1 corresponding to a predetermined rotational speed V2 of the motor 3.
The pulse width T2 is input in a specified manner, and the speed setting unit 6 compares the pulse widths T1 and T2 to determine if T1<T2, that is, if the rotational speed V1 of the motor 3 is faster than the predetermined speed V2. In this case, the signal S2 is set to "1", and when T1>T2, that is, when the rotation speed V1 of the motor 3 is slower than the predetermined speed V2, the signal S2 is set to "0". When the signal S2 becomes "O", the transistor TR2 of the charging/discharging circuit 2 becomes "ON", and TR1 becomes "OFF", and the charge accumulated in the capacitor C1 is transferred to the resistors R3 and R2.
is discharged to ground 7 via
Then, transistor TR1 becomes “ON” and
TR2 becomes “OFF” and resistor R is connected to the power supply Vcc.
1, capacitor C1 is charged via R3.

Note that when the capacitor C1 is discharged, the discharge current ID flows through the resistors R3 and R2, so the slice output Vout on the side connected to the comparator 9 of the resistor R3 is generated when the transistor TR2 is turned on.
In this state, the terminal voltage Vc of capacitor C1 immediately before discharge is divided by resistors R2 and R3, and Vc
The potential changes to ×R2/(R2+R3). After that, according to the magnitude of the discharge current ID, ID×R2
A voltage of [V] appears at the output Vout, and then gradually decreases as the capacitor C1 discharges.

Also, transistor TR1 is ON, transistor
When TR2 is OFF, capacitor C1
The potential on the resistor R3 side is at 0 [V], so
Vout becomes Vcc×R1/(R1+R2), and the potential changes immediately. After that, the potential of the capacitor C1 rises because the charging current Ic flows into the capacitor C1 via the resistors R1 and R3, and the slice output Vout gradually decreases from the low state immediately before charging as the charging of the capacitor C1 progresses. The waveform gradually increases and eventually becomes a waveform close to a square wave as shown by the solid line a in FIGS. 3 and 4.

Examples will be described below using specific numerical values.
For example, R1=22 [KΩ], R2=56 [KΩ], R
3=10 [KΩ], C1=2.2 [μF], Vcc=3.3
Let it be [V].

When starting the motor, the signal S2 is set to "H" when the motor is stopped in order to suppress overshoot. At this time, the voltage Vc applied to the capacitor C1 is charged and finally becomes the same potential as Vcc, and the current Ic stops flowing VR = R3 × Ic = 10
According to [KΩ]×0=0, Vout=VR+Vcc=0
+3.3=3.3V. From this state, when the signal S2 becomes “L” to rotate the motor, the ID
=Vc/(R2+R3)=3.3/(56[KΩ]×10
[KΩ]) = 50 [μA], Vout = R2 x ID = 56 [K
Ω〕×50〔μA〕=2.8〔V〕, and henceforth R2,
Power is consumed in R3, and the voltage Vc and current ID applied to capacitor C1 decrease, and then gradually CR
It falls down by drawing a discharge curve with a time constant. Next, in this state, for example, the voltage Vc applied to capacitor C1 is
When the signal S2 becomes "H" when the voltage falls to 2.0 [V], a current Ic flows. Therefore, the current
Ic is Ic=(Vcc-Vc)/(R1+R3)=(3.3-
2.0) / (22 [KΩ] + 10 [KΩ]) = 40 [μF],
Vout=R3×Ic+Vc=10[KΩ]×40[μA]+
2.0=2.4 [V], and thereafter the capacitor C1 is charged, and Vc increases following the charging curve of the CR time constant. For reference, when the slice output V'out in the conventional circuit shown in FIG. 7 is shown by a dashed line, the output Vout shows a steeper rise than the output V'out. Note that the slice output Vout is
The signal is input to comparator 9, but comparator 9 receives a sawtooth wave with a constant period, which is an analog wave signal.
SN is input, the comparator 9 compares the sawtooth wave SN and the slice output Vout, and changes the drive signal S3 from "H" to "L" only when the output Vout is a lower voltage than the sawtooth wave SN. As a result, the rotation speed of the motor 3 is high, and the capacitor C
1 is charged, the output Vout rises rapidly as shown in Figure 4C, so the signal S
3 is in the "L" state is extremely narrow, and if the rotation speed of the motor 3 is slow and the capacitor C1 is discharged, the output Vout will fall rapidly, so the width T3 will be extremely narrow. Become. On the other hand, the driver 10 to which the signal S3 is input is
Since power is supplied to the motor 3 to drive the motor 3 only when the signal S3 is "L", if the width T3 is narrow, the driving time of the motor 3 is shortened and the rotational speed of the motor 3 is slowed down. , when the width T3 is wide, the driving time of the motor 3 becomes longer and the rotational speed becomes faster, and as a result, the rotational speed of the motor 3 is maintained at the predetermined rotational speed V2. In addition,
The width T3 of the signal S3 is either extremely narrow or extremely wide due to the rapid rise and fall of the output Vout, and therefore the motor 3 is extremely sensitive to changes in rotational speed. Able to react quickly. In addition, the drive signal S3 of the comparator 9 based on the slice output V'out in the conventional circuit is as shown in FIG.
Since a sudden voltage drop does not occur at V'out, the width T3 of the signal S3 also changes gradually, and even when the motor 3 is decelerated and accelerated, the control is extremely slow compared to the case of the present invention. It is inevitable that this will happen.

As explained above, according to the present invention, the resistor R3 is inserted in series with the charging/discharging capacitor C1 so that the charging current I _c and the discharging current I _D flow through the resistor R3, and the comparator 9 and the capacitor C1 is connected through resistor R3, so resistor R3
Due to the voltage drop VR caused by V _R , the slice output Vout can be rapidly raised or lowered, and therefore the rotational speed of the DC motor 3 can be controlled extremely sharply. Even during startup and when switching the rotational speed V1 shown in FIG. 6, stable speed control is possible without overshoot or undershoot, as shown by the solid line in the figure.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the DC motor control circuit according to the present invention, Fig. 2 is a circuit diagram showing the main parts of the charging/discharging circuit of Fig. 1, and Fig. 3 is a slice of the circuit in Fig. 2. A time chart showing the output, FIG. 4 a time chart showing the operation of the comparator, and FIGS. 5 and 6 showing a comparison with a conventional example when a motor is controlled using the circuit according to the present invention. FIG. 7 is a circuit diagram showing a charging/discharging circuit of a conventional DC motor control circuit, and FIG. 8 is a time chart showing the slice output of the circuit shown in FIG. DESCRIPTION OF SYMBOLS 1...DC motor control circuit, 2...Charging/discharging circuit, 3...DC motor, 5...Speed detection section, 6
...Speed setting section, 9...Comparator, C1...
Charge/discharge capacitor, _Ic ...Charging current, _ID ...Discharge current, R3...Resistance, SN...Analog wave signal (sawtooth wave), S3...Drive signal, Vout...Slice output, V1...Rotation speed.

Claims (1)

[Scope of utility model registration request] It has a speed detection section that detects the rotational speed of the DC motor, and a speed setting section that compares the speed with a predetermined rotational speed, and outputs a slice output by charging and discharging a charging/discharging capacitor according to the output of the speed setting section. In addition to providing a charging/discharging circuit, a comparator capable of comparing the slice output and the analog wave signal and outputting a drive signal is provided, and the driving time of the DC motor is controlled by the drive signal to drive the motor at a constant rotation speed. In a DC motor control circuit configured to rotate, a resistor is installed in series with the charging/discharging capacitor so that charging current and discharging current both flow through the resistor, and the comparator and the charging/discharging capacitor are connected to the resistor. DC motor control circuit connected via.