JP2008043140A - Soft-start circuit for motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soft-start circuit for a motor that allows to respectively optimally set a minimum conduction angle, a maximum conduction angle, and a delay time during starting-up. <P>SOLUTION: When a switch 11 is turned on and if a charging voltage of a capacitor C1 in a phase circuit 21 exceeds a breakover voltage, a silicon bilateral switch (SBS) 16 as a switch element is made conductive so as to turn on a triac 13 at a minimum conduction angle while turning on a thyristor 15. After the soft start and if a voltage of a resistor R5 constituting a firing control circuit 22 becomes a voltage lower than the breakover voltage of the SBS 16 by a forward voltage of a diode D2, the diode 2 is made conductive so as to operate the triac 13 at a maximum conduction angle while controlling a trigger voltage supplied to a gate of the SBS 16. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a soft start circuit which is applied to, for example, an electric tool and reduces a shock at the start of a motor.

  For example, in a relatively large electric tool of 500 W to 2 kW, a large inrush current flows to the motor at the time of startup. For this reason, the voltage of the power supply system to which the electric power tool is connected drops, or the electric power tool suddenly operates, causing an impact on the operator and deteriorating operability. Therefore, various motor soft-start circuits have been developed in order to reduce the voltage drop and impact of the power supply system at startup.

  For example, a trigger element and a first capacitor for controlling a motor, a triac, and a triac gate are connected to an input end of the diode bridge, and a second capacitor for determining a control time is connected to an output end of the diode bridge. The switch is turned on by connecting a Zener diode between the output terminal of the diode bridge and the second capacitor so that the charging current to the first capacitor can be secured even when the terminal voltage of the capacitor is small. Therefore, a soft start circuit for a motor that starts a load within a time when the operator does not feel uncomfortable has been developed (see, for example, Patent Document 1).

Further, for example, a trigger element for controlling a motor, a triac, and a triac gate and a first capacitor are connected to an input terminal of a diode bridge, and a delay circuit connected to an output terminal of the diode bridge and the delay circuit are configured. By using a discharge circuit that controls the discharge of the second capacitor, a motor starter that can generate a rated speed can be soft-started even when the operation is repeated in a cycle shorter than the time required for soft-start. (See, for example, Patent Document 2).
Japanese Patent Laid-Open No. 10-127073 JP-A-10-243671

  By the way, the soft start circuit of the electric tool can reduce the inrush current at the time of start-up and reduce the impact on the operator, but if the time from when the switch is turned on until the maximum torque is generated is long, The user feels uncomfortable and the operability is poor. For this reason, it is necessary to be able to appropriately set the delay time from the minimum conduction angle of the triac at the time of startup to the maximum conduction angle while maintaining the soft start.

  However, in the conventional circuit, it is difficult to optimally set the minimum conduction angle, the maximum conduction angle, and the delay time at startup.

  An object of the present invention is to provide a soft start circuit for a motor that can optimally set a minimum conduction angle, a maximum conduction angle, and a delay time at startup.

  The aspect of the soft start circuit of the motor according to the present invention has first and second terminals and a first gate, and the first terminal is connected to the second terminal via a power source, a switch, and a motor. A bidirectional first switch element having the second terminal and the first gate connected to an input terminal of a full-wave rectifier circuit, an anode, a cathode, and a second gate, and the anode and the cathode Is connected to the output terminal of the full-wave rectifier circuit, is supplied with the output voltage of the full-wave rectifier circuit, generates a constant voltage, and the voltage generated by the Zener diode. A phase circuit having a first capacitor to be charged, an anode, a cathode and a third gate, the anode being connected to the phase circuit, and the cathode being a gate of the second switch element When the switch is turned on, the third switch element that is turned on when the output voltage of the phase circuit reaches the breakover voltage and the anode are connected to the third gate of the third switch element. A second capacitor that has a larger capacity than the first capacitor and is charged by a voltage generated by the Zener diode; and a resistor that divides the charging voltage of the capacitor; The charging voltage divided by the above is supplied to the cathode of the diode, and includes an ignition control circuit for controlling the conduction timing of the diode.

  ADVANTAGE OF THE INVENTION According to this invention, the soft start circuit of the motor which can each set the minimum conduction angle at the time of starting, the maximum conduction angle, and delay time optimal can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a soft start circuit of a motor according to this embodiment. In FIG. 1, for example, one end of the trigger switch 11 is connected to the other end of the switch 11 via, for example, an AC commutator motor AC power supply 12, a bidirectional thyristor such as a triac 13, and an AC power supply 14. The terminal T2 of the triac 13 and the gate G of the triac 13 are connected to the input terminal of the diode bridge DB.

  One output terminal of the diode bridge DB is connected to, for example, the anode A of the thyristor 15, and the cathode K of the thyristor 15 is connected to the other output terminal of the diode bridge DB. Furthermore, a resistor R1 and a Zener diode ZD for generating a constant voltage are connected in series between one and the other output terminals of the diode bridge DB.

  A connection node between the resistor R1 and the cathode of the Zener diode ZD is connected to the anode A of the trigger element 16 via the resistor R2. The trigger element 16 is, for example, a silicon bilateral switch (SBS). The trigger element 16 can be replaced with a circuit including a plurality of transistors and a Zener diode, as shown in a broken line in FIG. The cathode K of the trigger element 16 is connected to the gate G of the thyristor 15.

  Further, the connection node between the resistor R1 and the cathode of the Zener diode ZD is connected to the anode of the diode D1, and the cathode of the diode D1 is connected to the cathode of the diode D2 via the resistors R3 and R4. The anode of the diode D2 is connected to the gate G of the trigger element 16.

  A capacitor C1 is connected between the connection node of the resistor R2 and the anode A of the trigger element 16 and the other output terminal of the diode bridge DB. A capacitor C2 is connected between the connection node of the resistors R3 and R4 and the other output terminal of the diode bridge DB. A resistor R5 is connected between a connection node between the resistor R4 and the cathode of the diode D2 and the other output terminal of the diode bridge DB. A series circuit of a resistor R6 and a capacitor C3 is connected in parallel to the resistors R3 and R4.

  The resistor R2 and the capacitor C1 constitute a phase circuit 21. The phase circuit 21 and the trigger element 16 are circuits that determine the initial conduction angle of the triac 13, and the initial conduction angle of the triac 13 is determined by the voltage of the capacitor C 1 and the breakover voltage Vs 1 of the trigger element 16.

  The capacitor C2 and the resistors R4 and R5 constitute an ignition control circuit 22 that controls the ignition timing of the trigger element 16. The ignition control circuit 22 determines the maximum conduction angle of the triac 13 and the delay time from the initial conduction angle to the maximum conduction angle. That is, the maximum conduction angle is determined by the voltage of the capacitor C2, that is, the divided voltage of R4 / (R4 + R5), and this divided voltage is smaller than the breakover voltage Vs1 of the trigger element 16 by the forward voltage of the diode D2. When the voltage is reached, the diode D2 becomes conductive. Therefore, the trigger element 16 is controlled by the trigger voltage Vs2 supplied to the gate G. Further, the delay time from the initial conduction angle to the maximum conduction angle of the triac 13 is determined by the time constant C2R4R5 of the capacitor C2, resistors R4 and R5.

  The capacitance relationship between the capacitors C1, C2, and C3 is set to C1 <C2 <C3 (for example, C1: 0.1 μF, C2: 22 μF, C3: 100 μF), and the relationship between the resistors R2 to R6 is, for example, R3 = R6 <R5 <R4 = R2 is set.

  1 will be described with reference to FIGS. 2 and 3. FIG.

  When the switch 11 is turned on, power is applied to the traac 13 from the AC power supply 14. A full-wave rectified voltage is output from the output terminal of the diode bridge DB as shown by a broken line in FIG. This voltage is supplied to the Zener diode ZD through the resistor R1. In response to the half wave of the AC voltage, the Zener diode ZD generates a trapezoidal constant voltage (Zener voltage) Vz as shown in FIG. This voltage Vz is not affected by voltage fluctuations of the AC power supply, and stably operates the circuit.

  The initial conduction angle when the switch 11 is turned on is determined by the breakover voltage Vs1 of the trigger element 16, the resistor R2 as the phase circuit 21, and the time constant R2C1 of the capacitor C1. That is, when the switch 11 is turned on, the capacitor C1 is charged by the Zener voltage Vz. In FIG. 2B, Vc1 indicates the charging voltage of the capacitor C1.

  When the charging voltage of the capacitor C1 reaches the breakover voltage Vs1 (for example, 8V) of the trigger element 16, the trigger element 16 is turned on, and the trigger voltage is supplied to the gate G of the thyristor 15. For this reason, the thyristor 15 becomes conductive. Along with this, the triac 13 is turned on at the minimum conduction angle as shown in FIG. Therefore, the motor 12 is activated softly.

  The gate G of the trigger element 16 is controlled by a diode D2 whose on / off is controlled by the voltage across the resistor R5. However, when the switch 11 is turned on, the voltage supplied to the cathode of the diode D2 through the diode D1, the resistor R6, and the capacitor C3 is superposed on the voltage charged to the capacitor C2 through the resistor R3 and discharged to the resistor R5 through the resistor R4. The For this reason, the voltage supplied to the cathode of the diode D2 is sufficiently higher than the breakover voltage Vs1 of the trigger element 16, as shown in FIG. Therefore, since the diode D2 is biased in the reverse direction and is turned off, the trigger voltage (Vs1) does not change. Thus, when the switch 11 is turned on, the trigger element 16 is controlled by the phase circuit 21.

  On the other hand, after the switch 11 is turned on, when the triac 13 operates at the minimum conduction angle, the time for generating the zener voltage (triac off time) is shortened as shown by the left-pointing arrow in FIG. Along with this, the voltage generated at both ends of the resistor R5 gradually decreases as shown in FIG.

  When the voltage across the resistor R5 is lower than the breakover voltage Vs1 of the trigger element 16 by a forward voltage of the diode D2, for example, 0.6V, the diode D2 is turned on. For this reason, the trigger element 16 is conductively controlled by the voltage of the gate G, and is conductive at a voltage lower than the breakover voltage Vs1, and the trigger element 16 discharges the capacitor C1 at a voltage lower than the breakover voltage Vs1. . Therefore, the conduction angle of the thyristor 15 and the triac 13 is increased.

  The speed (delay time) at which the breakover voltage reaches from Vs1 to Vs2 is matched with the inertial force of the load of the electric power tool used and is determined by the values of the capacitor C2 and the resistors R4 and R5. For this reason, the operator does not feel uncomfortable.

  As described above, the conduction angle gradually increases, and when the steady state (at the maximum conduction angle) is reached, the voltage charged to the capacitor C2 through the diode D1 and the resistor R3 is divided into R4 / (R4 + R5) to a DC voltage. The trigger voltage Vs2 supplied to the gate of the trigger element 16 is determined by the maximum value of the voltage on which the pulse-like voltage generated by R6 and the capacitor C3 is superimposed. Thus, the ignition voltage of the trigger element 16 is gradually lowered from the breakover voltage Vs1 to the trigger voltage Vs2, and finally the maximum conduction angle of the triac 13 shown in FIG. 2C is held by the trigger voltage Vs2. The

  FIG. 3A shows the relationship between the voltage applied to the motor after startup and the rotational speed of the motor, and FIG. 3B shows the relationship between the current supplied to the motor and time. As shown in FIGS. 3A and 3B, after the switch 11 is turned on, the triac 13 starts the motor with the minimum conduction angle. For this reason, the inrush current as shown by the broken line in FIG. 3B is suppressed, and the motor is soft-started. After the switch 11 is turned on, when 2 to 3 seconds, for example, set by the time constant of the capacitor C2 and the resistors R4 and R5 have elapsed, the triac 13 reaches the maximum conduction angle, and a steady current is applied to the motor.

  According to the above embodiment, at the time of start-up, the motor can be soft-started by the initial conduction angle determined by the breakover voltage Vs1 of the trigger element 16, the resistor R2, and the capacitor C1. For this reason, there is no impact on the operator, and a voltage drop in the same power supply system as the power tool can be prevented.

  In addition, after starting, the trigger voltage Vs2 supplied to the gate G of the trigger element 16 is controlled by the voltage across the resistor R5 obtained by dividing the charging voltage of the capacitor C2 by the resistors R4 and R5, and the maximum conduction of the triac 13 is achieved. Holding the corner. Moreover, the delay time from startup to the maximum conduction angle can be easily set by the time constants of the capacitor C2 and the resistors R4 and R5. For this reason, by setting the time constants of the capacitor C2 and the resistors R4 and R5 as appropriate, the maximum conduction angle of the triac 13 can be set without giving a sense of incongruity to the operator after the soft start.

  Furthermore, the trigger voltage Vs2 supplied to the gate G of the trigger element 16 can be easily and accurately controlled by the capacitor C2, the resistors R4 and R5, the capacitor C3, the resistor R3, and the diode D2. For this reason, the delay time from the minimum conduction angle to the maximum conduction angle can be easily set according to the inertial force of the motor load.

  In addition, this invention is not limited to the said embodiment, Of course, various deformation | transformation implementation is possible in the range which does not change the summary of invention.

The circuit diagram which shows the soft start circuit of the motor which concerns on embodiment of this invention. FIG. 2 is a waveform diagram showing the operation of the circuit shown in FIG. 1. FIG. 2 is a waveform diagram showing the operation of the circuit shown in FIG. 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 12 ... Motor, 13 ... Triac, DB ... Diode bridge, 15 ... Thyristor, 16 ... Trigger element, ZD ... Zener diode, 21 ... Phase circuit, 22 ... Firing control circuit, R1-R6 ... Resistance, C1-C3 ... Capacitor , D1, D2... Diodes.

Claims (2)

First and second terminals and a first gate, wherein the first terminal is connected to the second terminal via a power source, a switch and a motor, and the second terminal and the first gate A bidirectional first switch element connected to the input end of the full-wave rectifier circuit;
A second switch element having an anode, a cathode, and a second gate, wherein the anode and the cathode are connected to an output terminal of the full-wave rectifier circuit;
A Zener diode that is supplied with an output voltage of the full-wave rectifier circuit and generates a constant voltage;
A phase circuit having a first capacitor charged by a voltage generated by the zener diode;
An anode, a cathode, and a third gate, the anode is connected to the phase circuit, the cathode is connected to the gate of the second switch element, and the output voltage of the phase circuit breaks over when the switch is turned on A third switch element that is conductive when the voltage is reached;
A diode having an anode connected to the third gate of the third switch element;
A second capacitor that has a larger capacity than the first capacitor and is charged by a voltage generated by the Zener diode; and a resistor that divides the charging voltage of the capacitor, and is divided by the resistor. And a starting control circuit for supplying a charging voltage to the cathode of the diode and controlling a conduction timing of the diode. The diode conducts when the charging voltage divided by the resistor is lower than the breakover voltage of the third switch element by the forward voltage of the diode, and is supplied to the gate of the third switch element. 2. The motor soft start circuit according to claim 1, wherein the trigger voltage is controlled.

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