JPH06335286A - Drive circuit for direct current motor - Google Patents

Abstract

PURPOSE:To provide a drive circuit for a direct current motor that maintains a constant rotational speed even if the applied voltage fluctuates. CONSTITUTION:This drive circuit is provided with an energization control switch 6 that turns on/off the current applied to a direct current motor 3; and a switching control circuit 7 that varies the on-duty ratio of the switch 6 according to the fluctuation of supply voltage so as to keep constant the average of the voltage applied to the direct current motor 3. The switching control circuit 7 consists of an average voltage setter 8 that produces average setting signals Vb, which provides the average of the voltage applied to the motor; a triangular-wave signal generator 9 that produces triangular-wave signals Vc, whose amplitude varies almost in proportion to the applied voltage; and a comparator 10 that compares both signals Vb and Vc, and produces signals to close the energization control switch 6 during a period when the average setting signal Vb is higher than the triangular-wave signal Vc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a DC electric motor in which the average value of the voltage applied to the electric motor is constant even if the power supply voltage fluctuates.

[0002]

2. Description of the Related Art In recent years, in the field of vehicles including automobiles, a DC motor has been widely used as a drive source for driving auxiliary machinery of an internal combustion engine, safety equipment, comfort equipment and the like. There is. A DC motor used for this type of application is driven by a DC power supply including a battery or the like charged by the output of a generator driven by an internal combustion engine.
FIG. 5 shows an outline of a conventional drive circuit for driving a DC motor of this kind. The output voltage of a DC power supply 1 composed of a battery or the like is directly fed to a DC motor 3 via a switch means 2 composed of a relay or the like. The load device 4 is driven by the applied electric motor 3.

[0003]

SUMMARY OF THE INVENTION In a permanent magnet field brush type DC motor mainly used for this type of application,
As is well known, when the load is constant, the rotation speed of the electric motor is almost proportional to the terminal voltage applied to the electric motor. In the conventional drive circuit, the output voltage of the DC power supply 1 is set to the switching means 2
Since the voltage is directly applied to the electric motor via the motor, the rotation speed of the electric motor changes according to the magnitude of the output of the DC power supply. Therefore, when the power supply voltage fluctuates, the driving speed of the load device 4 driven by the electric motor also fluctuates. An object of the present invention is to keep the average value of the voltage applied to the electric motor constant even if the power supply voltage fluctuates so that the driving speed of the load device driven by the electric motor is influenced by the fluctuation of the power supply voltage. Another object of the present invention is to provide a drive circuit for a DC motor that is prevented from receiving the noise.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a drive circuit for a DC motor in which the average voltage applied to the motor is constant even if the power supply voltage fluctuates. In the circuit, the energization control switch provided to turn on and off the drive current to the DC motor and the energization control switch according to the fluctuation of the power supply voltage to keep the average value of the voltage applied to the DC motor constant. A switch control circuit for changing the on-duty ratio (ratio of ON-OFF to one cycle of ON-OFF) is provided.

The switch control circuit includes an average voltage setter for generating an average value setting signal having a magnitude corresponding to the average value of the voltage applied to the DC motor, and a triangular wave signal whose amplitude changes substantially in proportion to the power supply voltage. And a comparator for generating a signal for conducting the energization control switch while comparing the average value setting signal and the triangular wave signal with each other and the average value setting signal is larger than the triangular wave signal. Composed of and.

[0006]

As described above, the energization control switch for turning on / off the energization current to the DC motor is provided, and the energization control is performed according to the fluctuation of the power supply voltage so that the average value of the voltage applied to the DC motor is constant. By changing the on-duty ratio of the power switch, the average value of the voltage applied to the DC voltage can be kept substantially constant even if the power supply voltage changes. Therefore, even if the power supply voltage fluctuates, the rotation speed of the DC motor can be kept constant, and the driving speed of the load can be prevented from changing due to the fluctuation of the power supply voltage.

Further, as described above, when the switch control circuit is composed of the average voltage setting device, the triangular wave signal generator and the comparator, the amplitude of the triangular wave signal becomes large when the power supply voltage becomes high. Is smaller than the triangular wave signal and the on-duty ratio of the energization control switch is reduced. On the contrary, when the power supply voltage becomes low, the amplitude of the triangular wave signal becomes small and the on-duty ratio of the conduction control switch becomes large. Therefore, the average value of the voltage applied to the DC motor via the energization control switch is kept constant even if the power supply voltage changes.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention. In FIG. 1, 1 is a DC power source composed of a battery or the like, 3 is a DC motor using the DC power source 1 as a power source, and 4 is driven by a DC motor 3. Load device 5 is the output voltage VBatt of the DC power supply 1.
C1 is a power supply capacitor connected between the output terminals of the constant voltage power supply 5, and a DC constant voltage VD obtained at both ends of the power supply capacitor C1 is a switch control described later. Used as the power supply voltage for the circuit.

In the present invention, the energization control switch 6 connected in series to the armature winding 3a of the DC motor 3 to turn on / off the energization current to the DC motor 3, and the voltage applied to the DC motor 3 are controlled. There is provided a switch control circuit 7 that changes the on-duty ratio of the energization control switch 6 according to the fluctuation of the voltage of the DC power supply 1 so that the average value is kept constant.

The switch control circuit 7 has an average value setting signal V having a magnitude corresponding to the average value of the voltage applied to the DC motor.
Comparing the average voltage setting device 8 for generating b, the triangular wave signal generator 9 for generating the triangular wave signal Vc whose amplitude changes substantially in proportion to the power supply voltage VBatt, and the average value setting signal Vb and the triangular wave signal Vc. Average value setting signal Vb is triangular wave signal Vc
And a comparator 10 for generating a signal Vq for conducting the energization control switch 6 for a longer period.

The energization control switch 6 is an N-channel field effect transistor N whose source is grounded in this embodiment.
The N-FET is in a conductive state when a voltage higher than a predetermined level is applied to its gate, and a drive current is passed through the armature winding 3a. D1 is a flywheel diode connected between both ends of the armature winding 3a.

The average voltage setting device 8 includes a power source capacitor C1.
It is composed of a voltage divider composed of a series circuit of resistors R1 and R2 connected to both ends of the resistor R1 and R2.
/ (R1 + R2)] is obtained, and the divided voltage Vb is output as an average value setting signal having a magnitude corresponding to the average value of the voltage applied to the DC motor 3.

The triangular wave signal generator 9 includes a voltage comparator CP1.
And operational amplifiers OP1 and OP2 and resistors R3 to R
13 and a capacitor C2 and a diode D2, a triangular wave signal Vc having a constant frequency varying between the voltages VCH and VCL is obtained at the output terminal of the operational amplifier OP2 as shown in FIG.

In the triangular wave signal generator 9, when the potential at the output terminal of the voltage comparator CP1 is at a high level, the voltage V + at the non-inverting input terminal (+ terminal) of the comparator CP1 is the power supply voltage VBatt. Is divided by resistors R3 and R4 to obtain a value V + H [= VBatt.R4 / (R3 + R4)], during which the capacitor C2 is charged through the resistor R5 by the power supply voltage VBatt and the voltage Va across it is constant. It rises with a tilt. When the voltage Va across the capacitor C2 input to the inverting input terminal (-terminal) of the voltage comparator CP1 becomes higher than V + (Va> V +), the output of the voltage comparator CP1 becomes low level. , The comparator CP
The voltage V + at the non-inverting input terminal of 1 is a value obtained by dividing the power supply voltage VBatt by a resistor R3 and a parallel combined resistor of resistors R4 and R6, V + L [= VBatt.R4.R6 / (R3.R4 + R4
.R6 + R6 .R3)], and the charge in the capacitor C2 is discharged through the resistor R7 and the output stage of the voltage comparator CP1. This causes the voltage Va across the capacitor C2
Decreases with a constant slope. When the voltage Va across the capacitor C2 becomes lower than V + L (Va <V + L), the output of the voltage comparator CP1 becomes high level again, so that the voltage Va across the capacitor C2 becomes V + H and V The voltage is a triangular waveform that changes between + L and. Here, when the value of the power supply voltage VBatt changes, the values of V + H and V + L also change in proportion to the value of VBatt, as is clear from the above equation.

The operational amplifier OP1 is composed of a voltage follower circuit and outputs a voltage Va 'at the same level as the voltage Va across the capacitor C2. Therefore, Va 'is V + H and V + L
The voltage has a triangular waveform that changes between and.

The operational amplifier OP2 basically operates as a differential amplifier, and the output voltage Vc is a positive-phase input voltage and a negative-phase input voltage determined by the voltages Va ', VBatt and VD and Vc and the resistors R8 to R13. It is output as the value of Vc when they are equal. The parallel combined resistance of the resistors R8 to R10 is R [1 / R = 1 / R8 + 1 / R9 + 1 / R10], and the parallel combined resistance of the resistors R11 to R13 is R ′ [1 / R ′ = 1 / R11 + 1 / R
12 + 1 / R13], the output voltage V of the operational amplifier OP2
c is expressed by the following equation.

Vc = R13.R / R '{(VD / R8) + (Va' / R10)}-R13. (VBatt / R11) (1) In this embodiment, R = R ' Resistance R8 to R
R13 / is selected so that the value of 13 is R9 = R11, R8 = R12, R10 = R13, and VBatt · R13 / R11 = V + L.
The value of R11 is selected. Therefore, the above equation (1) can be modified as follows. Vc = Va'-VBatt.R13 / R11 + VD.R13 / R8 = Va'-V + L + VD.R13 / R8 (2) In the formula (2), the value of Va 'becomes V + L and V + H. If the values of Vc at this time are VCL and VCH respectively, VCL = VD.R13 / R8 (= constant value), VCH = (V + H-V + L) + VD.R13 / R8 (3) . Therefore, the output voltage Vc of the operational amplifier OP2 is
The voltage of the triangular wave waveform changes between the constant value VCL corresponding to the change of the output voltage Va 'of the operational amplifier OP1 and the value VCH changing according to the magnitude of the power supply voltage VBatt [Fig.
(A)].

The comparator 10 comprises a voltage comparator CP2 and a resistor R14.
In this embodiment, the average value setting signal Vb output from the average voltage setting device 8 is input to the non-inverting input terminal (+ terminal) of the voltage comparator CP2 and the inverting input terminal (-terminal) is connected to the non-inverting input terminal (+ terminal). The triangular wave signal Vc output from the operational amplifier OP2 is input. The comparator 10 compares the average value setting signal Vb with the triangular wave signal Vc, holds the high level state during the period t2 in which Vb> Vc, and Vb≤V.
A rectangular wave signal Vq [FIG. 2 (B)] which holds the low level state during the period t1 when c is output is output. Field Effect Transistor N-FET Constituting Energization Control Switch 6
Is conductive while the square wave signal Vq is at high level,
A drive current is supplied at an on-duty ratio τ [= t2 / (t1 + t2)].

When the power supply voltage VBatt rises, the peak value VCH of the triangular wave signal Vc rises to become VCH ', as shown in FIG.
A waveform Vc 'shown by a broken line in (A) is obtained. Therefore, the rectangular wave signal Vq has a waveform Vq shown by a broken line in FIG.
The period during which the level is high for ??? becomes shorter, and the on-duty ratio τ '[= t2' (t
1 '+ t2')] becomes smaller. Conversely, when the power supply voltage VBatt decreases, the on-duty ratio of the energization control switch 6 increases.

Now, when the DC motor 3 is operated at the rotational speed Nx, the average value of the voltage to be applied to the motor is Vx, and the average value setting signal corresponding to this voltage Vx is Vbx. When the on-duty ratio of the switch 6 is τx, Vx = τx · VBatt. Further, the duty ratio τx is τx = (Vbx−VCL) / (VCH−VCL) = (Vbx−, as can be seen from FIG. 2A and the equation (3).
VCL) / (V + H-V + L). (VCH-VCL) [= V
+ H-V + L] is proportional to the power supply voltage VBatt, the duty ratio τx is inversely proportional to the power supply voltage VBatt. Therefore,
The power supply voltage changes to VBatt → α · VBatt (α is the change rate), and the duty ratio changes accordingly, resulting in τx
→ When τx / α, the average value Vx ′ of the voltage applied to the DC motor 3 is Vx ′ = (τx / α) (α · VBatt) =
τx VBatt = Vx. Therefore, the average value setting signal Vb
If the values are the same, the average value of the voltage applied to the DC motor 3 is always constant even if the power supply voltage varies, and the rotation speed of the motor is kept constant without being affected by the fluctuation of the power supply voltage. can do.

FIG. 3 shows another embodiment of the present invention. In this embodiment, the energization control switch 6 is composed of a P-channel field effect transistor P-FET.
The -FET becomes conductive when a low level voltage below a predetermined level is applied to its gate, and causes a drive current to flow in the armature winding 3a of the DC motor connected in series to the source side. In this embodiment, the triangular wave signal Vc output from the triangular wave signal generator 9 is input to the non-inverting input terminal (+ terminal) of the voltage comparator CP2, and the average voltage is input to the inverting input terminal (-terminal) of the voltage comparator CP2. The average value setting signal Vb output from the setter 8 is input. Further, in this embodiment, the output terminal of the comparator CP2 is connected to the positive terminal of the battery 1 through the resistor R14. Other configurations are shown in FIG.
It is similar to the embodiment of. In FIG. 3, the illustration of the specific circuit configuration of the triangular wave signal generator 9 is omitted.

In the embodiment of FIG. 3, the comparator 10 compares the average value setting signal Vb and the triangular wave signal Vc,
As shown in (A) and (B), a rectangular wave signal Vq that holds a high level state while Vb <Vc is maintained and holds a low level state while Vb ≥ Vc is output. . The energization control switch 6 is turned on while the rectangular wave signal Vq is at a low level, and the on-duty ratio τ [= t2
/ (T1 + t2)], a drive current is passed through the electric motor 3. When the power supply voltage VBatt rises, the triangular wave signal V
c and the rectangular wave signal Vq are shown in FIGS. 4A and 4B, respectively.
Waveforms Vc 'and Vq' shown by broken lines are obtained, and at this time, the on-duty ratio of the energization control switch 6 is τ '.
[= T2 '/ (t1' + t2 ')], and the duty ratio becomes small. The average value V = τ · VBatt of the voltage applied to the DC motor 3 is kept constant even if the value of the power supply voltage VBatt changes, as in the case of the embodiment of FIG.

In the above embodiment, the average value setting signal is generated by using the triangular wave signal generator that outputs the triangular wave signal whose amplitude increases and decreases in proportion to the power supply voltage when the power supply voltage rises and falls, respectively. The switch control circuit was configured to generate a signal for conducting the energization control switch during the period when the voltage is larger than the triangular wave signal.When the power supply voltage rises and falls, the amplitude is inversely proportional to the power supply voltage. Using a triangular wave signal generator that outputs a triangular wave signal that decreases and increases, a switch control circuit that generates a signal for conducting the energization control switch while the triangular wave signal is larger than the average value setting signal With the above configuration, it is possible to obtain the same effect as that of the above embodiment.

[0024]

As described above, according to the present invention, an energization control switch for turning on / off the energization current to the DC motor is provided to keep the average value of the voltage applied to the DC motor constant. Since the on-duty ratio of the energization control switch is changed according to the fluctuation of the voltage, the rotation speed of the DC motor can be kept constant even when the power supply voltage changes, and the fluctuation of the power supply voltage There is an advantage that the driving speed can be prevented from changing.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing signal waveforms of various parts of the embodiment of FIG.

FIG. 3 is a circuit diagram showing a configuration of another embodiment of the present invention.

FIG. 4 is a waveform diagram showing signal waveforms of various parts of the embodiment of FIG.

FIG. 5 is a circuit diagram showing an outline of a drive circuit of a conventional DC motor.

[Explanation of symbols]

 1 DC power supply 3 DC motor 3a Armature winding 5 Constant voltage power supply 6 Energization control switch 7 Switch control circuit 8 Average voltage setting device 9 Triangular wave signal generator 10 Comparator CP2 Voltage comparator

Claims (2)

[Claims] 1. An energization control switch provided to turn on and off an energizing current to a DC motor, and the energization according to a fluctuation of a power supply voltage so that an average value of a voltage applied to the DC motor is constant. A drive circuit for a DC motor, comprising: a switch control circuit that changes an on-duty ratio of a control switch. 2. The switch control circuit includes an average voltage setter that generates an average value setting signal having a magnitude corresponding to the average value of the voltage applied to the DC motor, and the amplitude changes substantially in proportion to the power supply voltage. A triangular wave signal generator for generating a triangular wave signal, and a signal for comparing the average value setting signal with the triangular wave signal to turn on the energization control switch for a period during which the average value setting signal is larger than the triangular wave signal. 2. The drive circuit for a DC motor according to claim 1, wherein the drive circuit comprises a comparator for generating.