JP2010088199A - Motor control circuit with built-in trigger switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor control circuit with a built-in trigger switch, capable of securing the stop and control of a motor by preventing an increase in a switch form. <P>SOLUTION: A first MOS transistor F1 supplies power to the motor M from a power supply EB. A signal generating circuit 12 generates a pulse signal in response to the operation amount of a trigger TR and supplies the pulse signal to the gate electrode of the first transistor F1. A second transistor F2 is connected in parallel with the motor M. A voltage generating circuit 13 generates a first voltage for turning on the second transistor from the power supply EB with a switch S1 being turned on. A switching means S3, while the switch S1 is turned on, sets the gate electrode of the second transistor F2 to the second voltage having the second transistor F2 turned off state, and after the switch S1 is turned off, the switching means supplies the first voltage to the gate electrode of the second transistor F2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a motor control circuit that controls a motor used in an electric tool, for example, built in a trigger switch.

  As a trigger switch for controlling a motor of an electric tool, a trigger switch having a built-in speed control circuit capable of controlling the rotation speed of the motor has been developed. The trigger switch incorporating this speed control circuit is configured to increase the power supplied to the motor as the trigger is pulled in, and to reduce the power supplied to the motor as the trigger is returned (for example, Patent Document 1). reference).

  The trigger switch incorporating this speed control circuit has a mechanism for shortening the motor stop time in order to improve workability. This mechanism uses a separate switch to short-circuit both ends of the motor when the supply of power to the motor is interrupted in response to a trigger return operation, and the electromotive force generated by inertial rotation of the motor is caused to flow through the armature winding. The motor stop time is shortened.

  However, the motor stop mechanism built in the trigger switch is constituted by a contact switch. For this reason, when the switch of the stop mechanism is turned on in response to the trigger return operation during the stop operation, an arc is generated at the contact point due to the large electromotive force of the motor. Therefore, there is a problem that the contact point is deteriorated, the life of the trigger switch is shortened, and further, the life of the power tool itself is shortened.

Therefore, it is conceivable to use a switch having a large current capacity. However, in this case, since the switch is enlarged, there is a problem that the shape of the trigger switch is enlarged. It is also conceivable to replace the mechanism using a contact switch with a circuit of a contactless switch using a transistor (see, for example, Patent Document 2). However, a motor control circuit using this type of transistor has a large circuit scale, and the motor control circuit is often configured separately from the trigger switch and is assumed to be housed in an electric tool together with the trigger switch. It was not suitable for incorporation in a single trigger switch.
JP-A-10-243671 JP 2007-236029 A

  An object of the present invention is to provide a motor control circuit with a built-in trigger switch that can prevent the switch shape from becoming large and can reliably stop and control the motor.

  An embodiment of a motor control circuit with a built-in trigger switch according to the present invention includes: a switch that switches power on and off according to a trigger operation; and a first transistor that supplies power to the motor from the power source when the switch is on. A signal generation circuit for generating a pulse signal corresponding to the operation amount of the trigger and supplying the pulse signal to the gate electrode of the first transistor, a second transistor connected in parallel to the motor, and the switch being in an ON state A voltage generating circuit for generating a first voltage for turning on the second transistor from the power source, and when the switch is in an ON state, the gate electrode of the second transistor is used as the second transistor. Is set to a second voltage that is turned off, and is generated by the voltage generation circuit after the switch is turned off. Characterized by comprising a switching means for supplying to the gate electrode of the first voltage and the second transistor.

  According to the present invention, it is possible to provide a motor control circuit with a built-in trigger switch that can prevent the switch shape from being enlarged and can reliably stop and control the motor.

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

(First embodiment)
FIG. 1 shows a motor control circuit 11 with a built-in trigger switch according to the first embodiment. In FIG. 1, switches S1, S2, and S3 are switches that are linked by a trigger TR of a trigger switch. The switch S1 is a power switch, and is a switch that is turned on in response to the pull-in operation of the trigger TR. The switch S2 is a switch that is turned on when the trigger TR is pulled to the maximum and supplies the motor with the maximum power. The switch S3 is turned on when the trigger TR is turned on in the non-operation state and turned off, and is turned on when the trigger TR returns from the operation state to the non-operation state, that is, when the motor is stopped. It is.

  One end of the switch S1 is connected to the negative electrode of the battery EB. The positive electrode of the battery EB is connected to one end of the motor M. The motor M is, for example, a direct-current motor, and the other end of the motor M is connected to the other end of the switch S1 via the switch S2. Both ends of the current path of the MOS transistor F1 are connected in parallel to the switch S2, and both ends of the current path of the MOS transistor F2 are connected in parallel to the motor M. The MOS transistors F1 and F2 include a flywheel diode between the drain and the source. The gate electrode of the transistor F1 is connected to a PWM (Pulse Width Modulation) generation circuit 12. The PWM generation circuit 12 is connected between the connection node of the switches S1 and S2 and the positive electrode of the battery EB. The PWM generation circuit 12 has a variable resistance VR whose resistance value is changed in conjunction with the operation of the trigger TR, and generates a pulse signal having a different duty ratio according to the operation of the trigger TR, as will be described later.

  A resistor R1 and a Zener diode Z1 are connected in parallel between the gate electrode and the source electrode of the transistor F2. Further, a series circuit of a diode D1 and a capacitor C1 is connected in parallel between the drain and source of the transistor. The diode D1 and the capacitor C1 constitute a voltage generation circuit 13. The switch S3 is connected between the connection node of the diode D1 and the capacitor C1 and the gate electrode of the transistor F2.

  FIG. 2A schematically shows the relationship between the switches S1, S2, S3, the variable resistor VR, and the trigger TR. The switches S1, S2, S3 are constituted by, for example, slide type switches. That is, the switch S1 is composed of fixed contact pieces S1a and S1b and a movable contact piece S1c, and the switch S2 is composed of a fixed contact piece S2a, a fixed contact piece S2b, and a movable contact piece S2c. The switch S3 includes fixed contact pieces S3a and S3b and a movable contact piece S3c. The variable resistor VR is composed of a resistor VRa, a fixed contact VRb, and a movable contact VRc. The movable contact pieces S1c, S2c, S3c, and VRc are connected to the trigger TR. The movable contact piece VRa is insulated from the movable contact pieces S1c, S2c, and S3c.

  FIG. 2B shows the relationship between the pull-in position of the trigger TR, the on / off states of the switches S1, S2, and S3 and the rotational speed of the motor M. The operation of the circuit shown in FIG. 1 will be described with reference to FIGS.

  When the trigger TR is in a non-operating state, the movable contact pieces S1c, S2c, S3c, and VRc of the switches S1, S2, and S3 and the variable resistor VR are at positions indicated by solid lines in FIG. That is, the movable contact piece S1c of the switch S1 is not in contact with the fixed contact piece S1a, and the movable contact piece S2c of the switch S2 is also not in contact with the fixed contact piece S2a. Further, the movable contact piece S3c of the switch S3 is in contact with the fixed contact pieces S3a and S3b. For this reason, the switches S1 and S2 are in an off state and the switch S3 is in an on state. Furthermore, the movable contact piece VRa of the variable resistor VR is located on one end side of the resistor VRa and has, for example, the maximum resistance value.

  When the trigger TR is pulled in the direction of the arrow A from the above state, the movable contact pieces S1c, S2c, S3c, VRc move in the direction of the arrow A in conjunction with this. First, the movable contact piece S3c of the switch S3 is not in contact with the fixed contact piece S3a, and the switch S3 is turned off. Thereafter, the movable contact piece S1c of the switch S1 comes into contact with the fixed contact piece S1a, and the switch S1 is turned on. At this time, the switch S2 remains off.

  When the switch S1 is turned on, power is supplied from the battery EB to the motor M. At the same time, the PWM generation circuit 12 operates, and a pulse signal is supplied from the PWM generation circuit 12 to the gate electrode of the transistor F1. At this time, the resistance value of the variable resistor VR is a large value, and the duty ratio of the pulse signal generated from the PWM generation circuit 12 is set small. For this reason, there is little electric power supplied to the motor M, and the motor M is started at low speed.

  When the switch S3 is turned off, charging of the capacitor C1 is started via the diode D1 of the voltage generation circuit 12. The capacitor C1 is charged when the transistor F1 is turned on.

  Thereafter, when the trigger TR is further pulled, the resistance value of the variable resistor VR is gradually lowered while the switch S1 is in the on state and the switches S2 and S3 are in the off state. For this reason, the duty ratio of the pulse signal output from the PWM generation circuit 12 is increased, and the power supplied to the motor M is increased. Therefore, the rotation speed of the motor M is increased.

  Next, when the trigger TR is pulled in as much as possible, the fixed contact piece S2a and the fixed contact piece S2b are connected by the movable contact piece S2c of the switch S2, as indicated by a broken line in FIG. When the switch S2 is turned on, the drain and source of the transistor F1 are short-circuited, so that the maximum power is supplied to the motor M regardless of the output signal of the PWM generation circuit 12, and the motor M has the highest rotation speed.

  Thereafter, when the pulling operation force of the trigger TR is released, the trigger TR is moved in the direction of the arrow B shown in FIG. 2A by the urging force of a return spring (not shown) housed in the trigger switch. . At this time, first, the switch S2 is turned off, and the motor M is controlled again by the output signal of the PWM generation circuit 12. As the trigger TR is moved in the direction of the arrow B in the figure, the resistance value of the variable resistor VR increases and the duty ratio of the pulse signal output from the PWM generation circuit 12 decreases, so the power supply to the motor M is reduced. The rotational speed of the motor M is reduced.

  Furthermore, when the trigger TR approaches the initial position, the switch S1 is turned off, the supply of power to the motor M is stopped, and the motor M rotates by inertial force. Thereafter, when the switch S3 is turned on, the charging voltage of the capacitor C1 constituting the voltage generation circuit 13 is supplied to the gate electrode of the transistor F2 via the switch S3. For this reason, the transistor F2 is turned on, and both ends of the motor M are short-circuited. For this reason, the motor M is braked and the motor M is stopped. In the state where the switch S1 is turned off, the voltage generated by the rotation of the motor M due to the inertial force has the same polarity as the polarity of the battery EB. For this reason, when the switch S3 is turned on and the transistor F2 is turned on, the electromotive force of the motor M can be rapidly reduced and the motor M can be stopped. That is, as shown in FIG. 2B, the rotational speed of the motor M can be rapidly reduced and stopped by turning on the switch S3 as shown by the solid line. Therefore, as shown by a broken line in FIG. 2B, the motor stop time can be shortened compared with the case where there is no motor M stop circuit.

  According to the first embodiment, when the MOS transistor F2 is connected in parallel to the motor M, and the switch S1 is in the off state, the voltage generation circuit 13 turns on the MOS transistor F2 and the current generated from the motor M is reduced. The motor M is stopped by flowing through the MOS transistor F2. Since the transistor F2 can withstand a current that is about three times the normal rated current, a larger current can flow than the conventional contact switch. Therefore, it is possible to avoid malfunction due to melting of the contacts as in the case of the contact switch, and it is possible to maintain stable operation for a long time. Further, since the switch S3 only opens and closes the voltage supplied to the gate electrode of the transistor F2, the contact is unlikely to melt or break, and can be constituted by a small switch.

  Further, the transistor F2 is smaller than the contact switch, the switch S3 for controlling the transistor F2 is also small, and the motor control circuit 11 itself includes only the voltage generation circuit 13 composed of few components. An increase in scale is prevented. For this reason, the entire motor control circuit 11 shown in FIG. 1 can be placed on a printed circuit board, for example, and accommodated in a Trigasucci housing. Therefore, since the motor control circuit can be provided in the trigger switch alone, it is possible to prevent the size of the trigger switch from being increased and the size of the electric tool from being increased.

(Second Embodiment)
FIG. 3 shows a second embodiment. 3, the same parts as those in FIG. 1 are denoted by the same reference numerals, and only different parts will be described.

  In the first embodiment, the switch S3 is a contact switch. On the other hand, 2nd Embodiment is comprised by the non-contact switch. That is, in FIG. 3, the resistor R30 is connected between the gate electrode of the transistor F2 and the voltage generation circuit 13, and the switch circuit S31 is connected between the gate electrode of the transistor F2 and the resistor R30. The switch circuit S31 includes, for example, a PNP transistor Q1, a diode D2, and resistors R31 and R32. The emitter of the transistor Q1 is connected to the gate electrode of the transistor F2, and is connected to the base of the transistor Q1 via the resistor R31. The collector of the transistor Q1 is connected to the anode of the diode D2, and the cathode of the diode D2 is connected to the source of the transistor F2. The base of the transistor Q1 is connected to the anode of the diode D3 constituting the backflow prevention circuit 14 via the resistor R32. The cathode of the diode D3 is connected to the switch control circuit 15.

  The switch control circuit 14 is composed of, for example, an NPN transistor Q2 and resistors R33 and R34. The collector of the transistor Q2 is connected to the cathode of the diode D3, and the base is connected to the positive electrode of the battery EB via the resistor R33. Further, the emitter of the transistor Q2 is connected to the connection node of the switches S1 and S2, and is connected to the base of the transistor Q2 via the resistor R34.

  On the other hand, a battery overdischarge prevention circuit 16 is connected to the positive electrode of the battery EB. The overdischarge prevention circuit 16 is composed of, for example, a PNP transistor Q3 and a resistor R35. The emitter of the transistor Q3 is connected to the positive electrode of the battery EB, and is connected to the base of the transistor Q3 via the resistor R35. The collector of the transistor Q3 is connected to the PWM generation circuit 12 via a resistor R36. Further, the base of the transistor Q3 is connected to the anode of the diode D4 constituting the backflow prevention circuit 14 through the resistor R37. The cathode of the diode D4 is connected to the collector of the transistor Q2 constituting the switch control circuit 15.

  The PWM generation circuit 12 includes, for example, operational amplifiers OP1 and OP2, a variable resistor VR, capacitors C2 and C3, a Zener diode D5, a diode D6, and resistors 38 to R48. The configuration of the PWM generation circuit 12 is not limited to this.

FIG. 4 shows the relationship between the switch S1, the drain of the transistor F1, the source voltage F1V _DS , the voltage of the capacitor C1, the gate of the transistor F2, the source voltage F2V _GS , and the rotational speed of the motor M shown in FIG. Yes.

  The operation of the circuit shown in FIG. 3 is almost the same as the operation of the circuit shown in FIG. 1, so only the parts different from the circuit shown in FIG.

  When the trigger TR is in a non-operation state, the switches S1 and S2 are in an off state. At this time, since the transistor Q2 constituting the switch control circuit 15 is in the off state, the transistor Q1 constituting the switch circuit S3 is also in the off state.

  From this state, when the trigger TR is drawn and the switch S1 is turned on, the transistor Q2 of the switch control circuit 15 is turned on and the transistor Q1 of the switch circuit S31 is turned on. For this reason, the voltage between the gate and the source of the transistor F2 is lowered, and the transistor F2 is held in the off state. At the same time, when the transistor Q2 of the switch control circuit 15 is turned on, the transistor Q3 constituting the battery overdischarge prevention circuit 16 is also turned on, and the PWM generation circuit 12 is operated. Therefore, the transistor F1 is on / off controlled according to the pulse signal output from the PWM generation circuit 12, and the motor M is driven. Thereafter, as the trigger TR is pulled, the rotational speed of the motor is increased.

  As shown in FIG. 4, the capacitor C1 of the voltage generation circuit 13 is charged when the transistor F1 is turned on and discharged through the resistor R30, the transistor Q1, and the diode D2, and the resistor R30, transistor Q1, resistor R32, The control current of the switch circuit S31 flows through the diode D3 and the diodes of the transistors Q2 and F1. Here, in order to perform the on / off control of the transistor F2 with certainty, the discharge time of the capacitor C1 needs to be set longer than the charge time. For this reason, the resistance value of the resistor R30 is set to an optimum value.

  On the other hand, when the operating force of the trigger TR is released and the switch S1 is turned off, the transistor Q2 of the switch control circuit 15 is turned off. Accordingly, the transistor Q3 of the overdischarge prevention circuit 16 and the transistor Q1 of the switch circuit S3 are also turned off. When the transistor Q1 is turned off, the voltage charged in the capacitor C1 is supplied to the gate electrode of the transistor F2 via the resistor R30. For this reason, the transistor F2 is turned on, and both ends of the motor M are short-circuited by the transistor F2. Accordingly, the motor M is rapidly stopped.

  FIG. 5 shows the relationship between the electromotive force of the motor and the motor stop time. In the second embodiment, the brake operation start voltage of the motor M is set to a voltage equivalent to the discharge end voltage of the battery EB, for example. For this reason, the resistance values of the resistors R33 and R34 are determined so that the transistor Q2 of the switch control circuit 15 is turned on above the end voltage of the battery EB. When the voltage of the battery EB becomes equal to or lower than the discharge end voltage while driving the motor M, the switch control circuit 15 is turned off, the transistor Q3 of the overdischarge prevention circuit 16 is turned off, and the transistor Q1 of the switch circuit S1 is also turned on. Turned off. As described above, when the voltage of the battery EB decreases, the number of rotations of the motor is also low, so that the transistor F2 is easily stopped by being turned on by the output voltage of the voltage generation circuit 13.

  Also in the second embodiment, as in the first embodiment, the motor M can be stopped reliably and in a short time. Moreover, in the case of the second embodiment, by using the switch circuit S1, the number of contact switches can be reduced, and the circuit configuration can be further reduced in size as compared with the first embodiment. Yes.

  In addition, the operation reference of the switch control circuit 15 is set to be equal to the discharge end voltage of the battery EB. Therefore, when the voltage of the battery EB is reduced to the end voltage, the transistor Q2 of the switch control circuit 15 is not turned on in the state where the switch S1 is turned on, and the transistor Q3 constituting the overdischarge prevention circuit 16 is also turned off. Retained. For this reason, since no power is supplied to the PWM control circuit 12, the transistor F2 is also held in the OFF state, and the motor M is not operated. Therefore, overdischarge of the battery EB can be prevented.

  In the second embodiment, the overdischarge prevention circuit 16 is provided to reliably prevent overdischarge of the battery EB. However, the overdischarge prevention circuit 16, the resistor R37, and the diode D4 are omitted, and the positive electrode of the battery EB is omitted. Can be directly connected to the PWM generation circuit 12. That is, when the transistor Q2 of the switch control circuit 15 is not turned on, the switch circuit S1 is also turned off. Therefore, even when the switch S1 is turned on and the PWM generation circuit 12 is operated and the motor M is operated via the transistor F1, when the capacitor C1 of the voltage generation circuit 13 is charged, the transistor F2 is turned on. The motor M is stopped. Therefore, it is possible to prevent the battery EB from being overdischarged.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

The circuit block diagram which shows an example of the motor control circuit with a built-in trigger switch which concerns on 1st Embodiment. 2A is a schematic diagram showing the relationship between the trigger and the switch of the motor control circuit with built-in trigger switch shown in FIG. 1, and FIG. 2B is the relationship between the operation of the switch shown in FIG. 1 and the rotational speed of the motor. FIG. The circuit block diagram which shows an example of the motor control circuit with a built-in trigger switch concerning 2nd Embodiment. FIG. 4 is a waveform diagram showing the operation of the circuit shown in FIG. 3. The figure shown in order to demonstrate the stop operation | movement of the circuit shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Motor control circuit, 12 ... PWM generation circuit, 13 ... Voltage generation circuit, S1, S2, S3 ... Switch, F1, F2 ... Transistor, TR ... Trigger, Q1 ... Transistor, 16 ... Overdischarge prevention circuit

Claims (4)

A switch that switches the power on and off according to the trigger operation,
A first transistor for supplying power from the power source to the motor in an on state of the switch;
A signal generation circuit that generates a pulse signal corresponding to the operation amount of the trigger and supplies the pulse signal to the gate electrode of the first transistor;
A second transistor connected in parallel to the motor;
A voltage generation circuit configured to generate a first voltage for turning on the second transistor from the power source when the switch is in an on state;
When the switch is in an on state, the gate electrode of the second transistor is set to a second voltage at which the second transistor is in an off state, and after the switch is in an off state, the voltage generation circuit And a switch means for supplying the first voltage generated by the above to the gate electrode of the second transistor. 2. The motor control circuit with a built-in trigger switch according to claim 1, wherein the switch means is a switch linked to the switch, and supplies an output voltage of the voltage generation circuit to a gate electrode of the second transistor. . 2. The trigger switch according to claim 1, wherein the switch means is a third transistor that is set to an off state when the switch is in an off state and is set to an on state when the switch is in an on state. Motor control circuit. The power source is a battery, and further includes a detection circuit that detects a discharge end voltage of the battery, and the detection circuit cuts off the power supply to the signal generation circuit when the voltage of the battery is equal to or lower than the discharge end voltage. The motor control circuit with a built-in trigger switch according to claim 1.

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