JPH10127073A - Soft starter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To start a load within a time causing no strange feeling in an operator after throwing in a switch by connecting a constant voltage diode between the output end of a diode bridge and a second capacitor, thereby securing the charging current of a first capacitor. SOLUTION: A constant voltage diode 11 is connected between the output end of a diode bridge 8 and a second capacitor 9. Consequently, the charging current of a first capacitor 6 can be secured even immediately after throwing in a trigger switch/of the second capacitor 9 having a low terminal voltage and the time lag corresponding to the time required for charging the second capacitor 9 up to the break voltage of the constant voltage diode 11 can be shortened. According to the arrangement, a load can be started within a time causing no strange feeling in an operator after throwing in a switch even if reaction and power supply voltage drop are suppressed by limiting the starting current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft start device which is gradually started when starting a load having a large starting current, such as a series-wound commutator motor for driving a power tool, an incandescent lamp, and a resistance welding machine. In the following, the load will be described as a series-wound commutator motor for driving a power tool (hereinafter simply referred to as a motor).

[0002]

2. Description of the Related Art A power tool using a motor as a driving source has a disadvantage that a large voltage drop occurs in a wiring path due to a large starting current. The voltage drop of the power supply at the time of starting the power tool causes flicker interference on the lamps connected to the same wiring path. Since the power tool is held by the operator and operated, the operability is deteriorated due to a recoil caused by a rapid increase in the number of revolutions after startup. Conventionally, a power tool equipped with a soft start circuit has been used in order to suppress the starting current having these disadvantages. For example, as described in “6.2.11 Soft Start Circuit” on page 96, “Latest Thyristor Utilization Technology”, edited by Electronic Outlook Editor, August 10, 1974, the first edition was issued. An electronic soft-start circuit has been proposed in which a starting angle is controlled by controlling a control angle so as to be gradually shortened.
This soft start circuit is a circuit used for a dimmer of an incandescent lamp.

FIG. 2 shows an example of a soft start circuit for suppressing a starting current of a motor. The difference between FIG. 2 and the above-described soft start circuit is that FIG. 2 does not show a circuit that functions to advance the conduction angle of the triac to the set phase angle quickly in the above soft start circuit. this is,
In the case of a power tool, even when the soft start circuit is not used, it takes about 0.7 to 1.2 seconds after the trigger switch 1 is turned on to increase the rotation speed to near the maximum rotation speed. When the current peak exceeds 90 degrees and the current peak in the half cycle of the power supply frequency becomes the same as the current peak at the time of the maximum conduction angle, the rotation speed also increases to the same degree. This is because there is no practical problem even if the phase angle is not advanced to the set phase angle, and the circuit configuration is simplified.

The operation of the soft start circuit shown in FIG. 2 will be described. A triac 3 is connected in series with the motor 2 via a trigger switch 1 to a power supply, and a series circuit including a first resistor 4, a second resistor 5, and a first capacitor 6 is connected in parallel with the triac 3, and a second resistor 5 is connected. And the first capacitor 6
Trigger element 7 between the connection point of
Are connected to form a phase control circuit. When the trigger switch 1 is turned on, the phase control circuit charges the first capacitor 6 via the first resistor 4 and the second resistor 5, and the absolute value of the terminal voltage of the first capacitor 6 indicates the breakover of the trigger element 7. If the voltage exceeds the voltage, the charge of the first capacitor 6 is discharged through the trigger element 7 and the gate terminal of the triac 3, and as a result, the triac 3 is turned on,
The triac 3 is turned off when the next half wave of the power supply voltage is reached. The soft start circuit is connected to a diode bridge 8 in parallel with the series circuit of the second resistor 5 and the first capacitor 6 in addition to the phase control circuit, and the second capacitor 9 and the third The circuit configuration is such that the resistors 10 are connected in parallel.

In this soft start circuit, when the trigger switch 1 is turned on, the first capacitor 6 is charged via the first resistor 4 and the second resistor 5 and the second resistor 5
The second capacitor 9 connected in parallel to the series circuit of the first capacitor 6 and the first capacitor 6 is also charged via the first resistor 4 and the diode bridge 8. That is, the charging current to the first capacitor 6 is shunted to the second capacitor 9, and as a result, the charging time of the first capacitor 6 is delayed. Therefore, immediately after the trigger switch 1 is turned on, the conduction angle of the triac 3 is small, and the starting current is suppressed. Since the charging potential of the second capacitor 9 rises with time, the charging current to the second capacitor 9 decreases with time, and the delay of the charging time to the first capacitor 6 gradually decreases, The conduction angle of the triac 3 gradually increases. When the charge potential of the second capacitor 9 has settled to a constant value, the conduction angle becomes the initially set conduction angle.
When the trigger switch 1 is opened, the third resistor 10
It is a discharge resistor for discharging the charge of the capacitor 9.

[0006]

In the soft start circuit of the electric tool, the conduction angle of the triac 3 immediately after the trigger switch 1 is turned on is preferably a conduction angle at which the motor 2 can rotate slowly, and the second capacitor 9 is charged. The conduction angle set at a point where the potential has settled to a constant value is preferably closer to 180 °. If the power supply frequency is 50 Hz, the motor 2
The initial conduction angle at which the motor can rotate slowly is from 36 ° (2 msec) to 72 ° (4 msec), and the maximum conduction angle at the point where the charging potential of the second capacitor 9 has settled to a constant value is the trigger element 7.
From 144 ゜ (8 msec) due to the breakover voltage of the device and restrictions on the gate current when the triac 3 is turned on.
About 2 好 ま し い (9 msec) is preferable. The time during which the phase is controlled from the state of the initial conduction angle to the state close to the maximum conduction angle, that is, the control time, is at least 0.
A time exceeding 1 second is required, and in many cases, the control time is required to be about 0.25 to 0.6 seconds. In the circuit of FIG. 2, the maximum conduction angle is set by the triac 3, the trigger element 7, the first capacitor 6, and the first and second resistors 4, 5, and the control time is set by the capacitance of the second capacitor 9. When the control time is lengthened, the charging current to the second capacitor 9 increases, so that the conduction angle at which the motor 2 can rotate slowly immediately after the trigger switch 1 is turned on cannot be ensured, and the delay time during which the motor 2 does not rotate. Is generated. This delay time is 0.
After about one second, the operator of the power tool turns on the trigger switch 1
Feels that the motor 2 does not rotate even if is input. Since the power tool is often used in a hand, this delay time gives an uncomfortable feeling to the operator. In the conventional soft start circuit of FIG. 2, if the control time is set to about 0.2 second, the delay time exceeds 0.1 second. For this reason, practical use was possible only with a power tool having a relatively small starting current.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to enable the load to be started within a time period in which the operator does not feel uncomfortable after turning on the switch with a simple configuration.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to secure a charging current to the first capacitor which determines the conduction angle of the triac even when the terminal voltage of the second capacitor which determines the control time is small. Thus, this is achieved by connecting a constant voltage diode between the output terminal of the diode bridge and the second capacitor.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to FIG. 1 showing an embodiment. 2 denote the same parts. The constant voltage diode 11 is connected between the output terminal of the diode bridge 8 and the second capacitor 9. Second resistor 5
The voltage across the series circuit of the first capacitor 6 and the terminal voltage of the second capacitor 9 and the voltage of the forward voltage drop of the diode forming the diode bridge 8 and the break voltage of the constant voltage diode 11 are added. So the second
Immediately after the trigger switch 1 having a small terminal voltage of the capacitor 9 is turned on, the voltage at which the charging current to the first capacitor 6 is secured is maintained. Since the break voltage of the constant voltage diode 11 is much smaller than the power supply voltage and exhibits non-linear voltage-current characteristics, the charging time constant of the second capacitor 9 is almost the same as when the constant voltage diode 11 is not inserted. does not change. The constant voltage diode 11 has the same effect on the soft-start circuit as turning on the trigger switch 1 in a state where the second capacitor 9 has already been charged with the same voltage as the break voltage. The delay time corresponding to the charging time of the second capacitor 9 until the voltage becomes the same as the voltage can be reduced.

The determination of the break voltage of the constant voltage diode 11 is performed by first using the conventional circuit shown in FIG. 2 without the constant voltage diode 11, ignoring the delay time during which the motor 2 does not rotate, and reducing flicker disturbance and recoil at the start. Determine the circuit constant,
Next, the voltage of the output terminal of the diode bridge 8 and the trigger switch 1 when the motor 2 starts rotating slowly in the circuit.
The difference between the voltages at the output terminal of the diode bridge 8 immediately after the input is supplied may be used as the break voltage.

By inserting a charging current limiting resistor in the charging circuit of the second capacitor 9, the control time can be extended without increasing the capacitance of the second capacitor 9 too much.

[0012]

As described above, according to the present invention, from the state of the initial conduction angle at which the load can be started gently to the state near the maximum conduction angle at the point where the charging potential of the second capacitor has settled to a constant value. Even if the time during which the phase control is performed, that is, the control time is increased, the delay time from when the switch is turned on to when the load starts can be shortened. Therefore, even if the starting current is suppressed to reduce the recoil and the voltage drop of the power supply, it is possible to start the load within a time period in which the operator does not feel uncomfortable after turning on the switch.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a soft start device of the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional soft start circuit.

[Explanation of symbols]

1 is a trigger switch, 2 is a motor, 3 is a triac,
4 is a first resistor, 5 is a second resistor, 6 is a first capacitor, 7
Is a trigger element, 8 is a diode bridge, 9 is a second capacitor, 10 is a third resistor, and 11 is a constant voltage diode.

Claims (1)

[Claims] 1. A load having a large starting current connected to both ends of a power supply via a switch and a triac;
A series circuit consisting of a second resistor and a first capacitor, connected to both ends of the triac, a trigger element connected between a connection point of the second resistor and the first capacitor and the gate terminal of the triac, and an input terminal A soft start device comprising: a diode bridge connected to both ends of a series circuit of a second resistor and a first capacitor; and a second capacitor connected to an output terminal of the diode bridge. A soft start device comprising a constant voltage diode connected between the second capacitor and the second capacitor.