JPH0126278B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides speed control for a motor which performs speed control by comparing a sawtooth wave voltage synchronized with the power supply frequency, which is a speed setting signal, and an induced voltage detected in a DC motor to be speed controlled. This is related to the control circuit, which achieves rotational stability with high torque output at low speeds, and
This is intended to eliminate fluctuations in rotational speed due to changes in power supply voltage and ambient temperature.

Conventionally, in the speed control circuit of this type of motor, in order to create a sawtooth wave synchronized with the power supply frequency,
A sawtooth wave was obtained using the configuration shown in Figure 1.
In Figure 1, 1 is an AC power supply, 2, 3, 4, 5
is a motor (not shown) by full-wave rectifying the AC power supply 1.
A diode constituting a phase control power supply for driving the 6
is a DC power supply for speed setting, 7 is a capacitor that forms a time constant circuit with resistor 8, and 9 is resistor 8.
11 is a second transistor whose collector is connected to the base of the first transistor 9, and 12, 13, and 14 are resistors.

In the above configuration, the first transistor 9 is turned on and off in synchronization with the power supply frequency, and when the first transistor 9 is off, the charge that is charged in the capacitor 7 through the resistor 8 is discharged when the first transistor 9 is turned on. A sawtooth wave is taken out from terminal a. Here, the on/off threshold voltage of the second transistor 11 depends on the base saturation voltage of the second transistor 11 of about 0.6V. but,
The base saturation voltage changes depending on the temperature, and the on/off ratio also changes depending on the voltage of the AC full-wave rectified waveform given as the input voltage, that is, the voltage of the AC power supply 1. The slope of the voltage change of the sawtooth wave obtained as a result has temperature characteristics and voltage characteristics. Therefore, if this sawtooth wave is used as a speed setting signal, the rotational speed of the DC motor will fluctuate with changes in temperature and power supply voltage.

Next, the conventional method for detecting induced voltage is the second one.
The configuration shown in the figure served its purpose.

In FIG. 2, Ei is a power supply for driving the phase-controlled DC motor 15, 16 and 17 are diodes,
18, 19, 20, 21, 22 are resistors, 23 is a capacitor, 24 is a transistor, and capacitor 2
3 stores the detected induced voltage of the DC motor 15.

In order to obtain stable rotation especially at low speeds, it is necessary to set the charging time constant of the capacitor 23 short and the discharging time constant long.

Charging time constant is resistor 20 and 21 and capacitor 2
3. The discharge time constant is determined by the resistor 22 and the capacitor 23, and in determining the charge time constant, the capacitor 23's capacity cannot be made too small because it takes a long discharge time constant, so the resistors 20 and 21 are made small. However, in terms of heat generation, this cannot be reduced unnecessarily.

Therefore, in conventional circuits, circuit constants are selected based on contradictory conditions, and there is a problem with rotational stability, especially at low speeds.

The present invention has been made in view of the above-mentioned conventional drawbacks, and one embodiment of the present invention will be described below with reference to FIGS. 3 to 7. In FIG. 3, 25 is a full-wave rectified phase-controlled power supply for driving the DC motor 15, 26 is an induced voltage detection circuit that detects the induced voltage accompanying the rotation of the motor 15, and 27 is a speed setting synchronized with the power supply frequency. A sawtooth wave generation circuit that generates a sawtooth wave as a signal; 28 a comparison circuit (comparator) that compares the speed signal from the sawtooth wave generation circuit 27 and the detection signal from the induced voltage detection circuit 26; 29;
30 is a control circuit including a thyristor that is triggered by a pulse from the pulse generation circuit 29;

FIG. 4 shows a specific configuration of the sawtooth wave generating circuit 27, and the configuration will be explained below based on the drawing. Note that the same numbers are used for the same components as in the conventional structure described above, and the description thereof will be omitted. In the figure 3
1 is a comparator, 32 is a diode that prevents current from flowing back to the power supply side, and 33 and 34 are resistors, which together with the resistors 13 and 14 constitute a bridge circuit. 35 is a first capacitor connected in parallel with the resistor 34 to smooth the full-wave rectified voltage to the inverted input voltage of the comparator 31. Here, the relationship between the potentials of point P, which is the first output, and point Q, which is the second output, of the bridge circuit is such that the resistors 13, 14, 33, 3
If a resistance value of 4 is selected, waveforms at various parts as shown in FIG. 5 will be obtained.

Note that 7 is a second battery charged by the DC power supply 6.
It is a capacitor.

With the above configuration, when the AC power source fluctuates, the inverting and non-inverting input potentials of the comparator 31 change at the same rate according to the AC power source voltage fluctuation, so the time t during which the comparator 31 is on always remains constant. It remains constant, and even with temperature changes,
It is only related to the input offset voltage of the comparator 31 and can be completely ignored in practice, and as a result, the rate of voltage change of the sawtooth wave can be kept constant against fluctuations in power supply voltage and temperature.

This allows stable speed settings.

Next, the specific configuration of the induced voltage detection circuit 26 will be explained with reference to FIG. Note that the same numbers are used for the same components as in the conventional configuration described above, and the description thereof will be omitted.

In FIG. 6, 36 is the first transistor of the emitter follower, and the function of a conventional diode is based on the PN junction between the base and emitter of the emitter follower. 37 is a power supply for the first transistor 36 of the emitter follower.

This configuration replaces the diode with an emitter follower transistor to reduce the output impedance and shorten the charging time constant of the capacitor 23. This allows the capacitance of the capacitor 23 to be increased, and the charging time constant The ratio of the discharge time constant can be made larger than that using conventional diodes.

As is clear from the above description, according to the present invention, it is possible to basically eliminate rotational fluctuations of the DC motor in response to power supply voltage fluctuations and ambient temperature fluctuations. Furthermore, rotational stability at low speeds can be improved compared to conventional ones.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram of a sawtooth wave generation circuit in a conventional motor speed control circuit, Fig. 2 is a wiring diagram of the same induced voltage detection circuit, and Fig. 3 is a motor speed control circuit according to an embodiment of the present invention. 4 is a wiring diagram of the same sawtooth wave generation circuit, Fig. 5 is a waveform diagram of each part in the same circuit, Fig. 6 is a wiring diagram of the same induced voltage detection circuit, and Fig. 7 is a wiring diagram of the same circuit. It is a waveform diagram of each part. 15...Electric motor, 25...Phase control power supply, 26
... induced voltage detection circuit, 27 ... sawtooth generation circuit, 28 ... comparison circuit, 29 ... pulse generation circuit, 30 ... control circuit.

Claims (1)

[Claims] 1 A DC motor driven by a full-wave rectified phase-controlled power source, and a DC motor connected to the phase-controlled power source,
a control circuit including a thyristor that controls energization to the DC motor; a sawtooth wave generation circuit that generates a sawtooth wave voltage synchronized with a power supply frequency serving as a speed setting signal for at least the DC motor; and a rotation of the DC motor. an induced voltage detection circuit that detects the induced voltage caused by the electromotive force; a comparison circuit that compares the speed setting signal from the sawtooth wave generation circuit with the detection signal from the induced voltage detection circuit; The induced voltage detection circuit includes a pulse generation circuit that generates a pulse that triggers a thyristor in the circuit, and the induced voltage detection circuit includes a diode connected between the phase control power source and the motor, and a resistor at the connection point between the diode and the DC motor. a parallel circuit consisting of a capacitor and a resistor connected to the emitter of the first transistor; and a second transistor whose collector is connected to the base of the first transistor.
and a resistor connected between the base of the second transistor and the phase control power supply, an induced voltage detection signal is obtained from the emitter of the first transistor, and the sawtooth wave generation circuit is connected to the AC power supply. a bridge circuit comprising a plurality of resistors that receives a full-wave rectified waveform voltage as an input and obtains waveform voltage signals similar to the full-wave rectified waveform voltage at first and second output terminals; a first capacitor connected to the output terminal of the bridge circuit 2 and smoothing the waveform voltage signal at the second output terminal; and a first capacitor connected to the first output terminal of the bridge circuit and the first capacitor a comparator for comparing the waveform voltage signal at the output end with the smoothed voltage signal; and a second capacitor connected to the output of the comparator and to a DC power supply for speed setting;
A speed control circuit for a motor that controls discharging of a second capacitor charged by the DC power source using on/off outputs of the comparator to generate a sawtooth wave serving as a speed setting signal.