JP2007236043A - Dc motor control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive DC motor control circuit in which variation among products is eliminated. <P>SOLUTION: A DC motor 2 and a switching element 3 are connected in series with a DC power supply 1, the voltage En across the switching element 3 is divided by a voltage division circuit 4, and the switching element 3 is switched with the output from a hysteresis circuit 6 configured by connecting a plurality of transistors TR1 and TR2 such that the voltage output V8 transits between two values with hysteresis characteristics for the output voltage V5 from the voltage division circuit 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a DC motor control circuit, and more particularly to a DC motor control circuit used for a trigger switch of a rechargeable electric tool.

  As described in Patent Document 1, the DC motor control circuit for the trigger switch is provided with a transmission circuit, and a switching element connected in series with the DC motor is turned on / off (switching) at high speed, and transmitted by a volume. Some change the duty ratio of switching by changing the bias voltage of the circuit.

  Also, when the switching element is turned off, the DC motor generates a counter electromotive force due to its rotation, so the comparator compares the voltage across the switching element with the threshold voltage set by the volume to turn the switching element on / off. There is a known DC motor control circuit that turns on a switching element when the voltage across the switching element drops below a threshold voltage and maintains the switching element on to some extent by changing the threshold voltage higher. ing.

  In Patent Document 2, the voltage across the switching element is compared with the first threshold voltage set by the volume by the first comparator, the switching element is turned on, and the ON state of the switching element is continued by the second comparator. A DC motor control circuit that defines the time is described.

  The DC motor control circuit as described above has a problem of high cost because it controls the DC motor using an IC such as a comparator.

Furthermore, the variable resistor used in the DC motor control circuit is an inexpensive variable resistor of the type in which a resistor layer is formed on the substrate and the movable terminal is slid on the resistor to divide the resistor. Often. Such a variable resistor has a large variation of about ± 30% in resistance value, and the conventional DC motor control circuit has a problem that there is a variation for each product in a controllable range of the rotational speed of the DC motor. .
JP-A-8-66084 Japanese Patent Laid-Open No. 11-168893

  In view of the above problems, an object of the present invention is to provide a DC motor control circuit that is inexpensive and does not vary from product to product.

  In order to solve the above problems, a DC motor control circuit according to the present invention includes a switching element connected in series with a DC motor with respect to a DC power source, a voltage dividing circuit that divides a voltage across the switching element, A hysteresis circuit configured by connecting a plurality of transistors so as to have a voltage output that transitions between two values with a hysteresis characteristic with respect to the output voltage of the voltage dividing circuit, and switching the switching element by the output of the hysteresis circuit It shall be.

  According to this configuration, the voltage across the switching element due to the counter electromotive force is divided and the voltage dividing ratio is changed without changing the reference voltage to be compared with the counter electromotive force of the DC motor when the switching element is turned off. When the rotational speed setting value is changed by changing the voltage dividing ratio, the output voltage characteristic does not change even in the case of a hysteresis circuit composed of transistors without using an IC such as a comparator. Thus, an inexpensive control circuit can be manufactured while the DC motor can be stably controlled.

  Further, in the DC motor control circuit of the present invention, the hysteresis circuit is turned on when a first transistor to which an output voltage of the voltage dividing circuit is inputted to a base, and the first transistor is turned off, A first transistor that is turned off when the first transistor is turned on, and the first transistor and the second transistor have emitters connected to each other and share an emitter resistance. The emitter current of the second transistor may be larger than the emitter current of the transistor.

  According to this configuration, the hysteresis circuit can be easily configured, and the manufacturing cost is reduced.

  Further, in the DC motor control circuit of the present invention, the voltage dividing circuit includes two voltage dividing resistors composed of fixed resistors connected in series to both ends of the switching element, and a resistor between the two fixed electrodes. The variable resistor is divided into an arbitrary ratio from 0: 1 to 1: 0. The variable resistor has both the fixed electrodes connected to both ends of the switching element, and the movable electrode between the voltage dividing resistors. It may be connected to a connection point.

  According to this configuration, when the voltage dividing ratio of the variable resistor is 1: 0 and 0: 1, the resistance value of the variable resistor is not reflected in the output voltage of the voltage dividing circuit. That is, even if the resistance value of the variable resistor varies, the control range of the DC motor is kept constant. The two threshold values of the hysteresis circuit composed of transistors are intermediate between the potentials at both ends of the power supply. However, if a bypass resistor is provided, the voltage dividing ratio of the voltage dividing circuit can be set to a limited range that does not become 0 or 1. The output of the voltage dividing circuit can be changed in a wide range including two threshold values according to the rotational speed of the DC motor. That is, the hysteresis circuit can transition between the two output states, and the rotational speed of the DC motor can be controlled by switching the switching element on / off regardless of the position of the fixed electrode.

  The DC motor control circuit of the present invention may further include a matching circuit that matches the output of the hysteresis circuit with the input characteristics of the switching element.

  According to this configuration, the two outputs of the hysteresis circuit constituted by the transistors are voltage outputs, and at least one of them is an intermediate potential of the power supply voltage, but the two outputs of the hysteresis circuit are switched by the matching circuit. Can be matched to the input characteristics. As a result, the hysteresis circuit can be designed without considering the input characteristics of the switching element, so that the control of the DC motor can be made stable and highly operable.

  In the DC motor control circuit of the present invention, the matching circuit may be a circuit including a transistor capable of outputting a voltage on the lower side of the DC power supply.

  According to this configuration, a switching element having a low turn-on voltage can be driven.

  As described above, according to the present invention, the potential at both ends of the switching element is divided, so that a hysteresis output corresponding to the back electromotive force of the DC motor can be obtained with a circuit constituted by a transistor, and inexpensive DC motor control is achieved. A circuit can be provided.

Embodiments of the present invention will now be described with reference to the accompanying drawings.
FIG. 1 shows an embodiment of the present invention and shows a DC motor control circuit used for rotation control of an electric drill. In this DC motor control circuit, a DC motor 2 for rotating a drill and a switching element 3 made of an FET are connected in series to a DC power source (storage battery) 1 whose voltage at both ends P1 and P2 is E (V). .

  Further, the DC motor control circuit is connected to both ends P1 and P3 of the switching element 3, and a voltage dividing circuit 4 that divides the voltage between P1 and P3, and a smoothing circuit 5 that smoothes the output of the voltage dividing circuit 4. A hysteresis circuit 6 whose output transitions between two voltages according to the output of the smoothing circuit 5 and a matching circuit 7 that switches the switching element 3 according to the output of the hysteresis circuit 6 are provided. In this DC motor control circuit, the minus side P1 of the DC power supply is shared by the inputs and outputs of the circuits 4, 5, 6, and 7, and is used as a reference for the potential at each point in the following description.

  The voltage dividing circuit 4 has two voltage dividing resistors R1 and R2 composed of fixed resistors connected in series between P1 and P3, and the potential V4 of the connection point P4 between the voltage dividing resistor R1 and the voltage dividing resistor R2 is This is the output of the voltage dividing circuit 4. Further, the voltage dividing circuit 4 includes a variable resistor VR and a bypass resistor R3 including a fixed resistor. In the variable resistor VR, the fixed electrodes T1 and T2 are connected to both ends P1 and P3 of the switching element 3, and the movable electrode T3 is connected to a connection point P4 of the voltage dividing resistors R1 and R2 via the bypass resistor R3. Yes. In the variable resistor VR, a layer of a resistor is formed between two fixed electrodes T1 and T2, and the movable electrode T3 is in sliding contact with the resistor, and the resistance between T1 and T2 is arbitrarily set from 0: 1 to 1: 0. It is a slide-type volume that can be divided into ratios.

  The smoothing circuit 5 includes a resistor R4 and a capacitor C1, and is a low-pass filter that smoothes the waveform by smoothing the output V4 of the voltage dividing circuit 4 (cutting high-frequency components of MHz or higher). The potential V5 at the output point P5 of the smoothing circuit 5 is an input to the hysteresis circuit 5.

  The hysteresis circuit 6 includes two junction type transistors TR1 and TR2 and a plurality of resistors R5, R6, R7, R8, R9, and R10, and outputs V5 from the smoothing circuit 5 (output V4 from the smoothed voltage dividing circuit 4). ) Is input to the base of the transistor TR1. The emitters of the transistors TR1 and TR2 are connected to each other at a point P6, and are connected to the negative side P1 of the DC power supply 1 through an emitter resistor R5. The collector of the transistor TR1 is connected to the positive side P2 of the DC power source 1 via a resistor R6, and is also connected to the negative side P1 of the DC power source 1 via a resistor R7 and a resistor R8 connected in series. On the other hand, a connection point P7 between the resistor R7 and the resistor R8 is connected to the base of the transistor TR2, and a resistor R9 and a resistor R10 connected in series are connected to the collector of the transistor TR2, and the resistor R9 and the resistor R10 Is the output terminal of the hysteresis circuit 6.

  In the matching circuit 7, the potential V8 at the point P8 of the hysteresis circuit 6 is input to the base, the emitter is connected to the positive side P2 of the DC power source 1, and the DC power source is connected through the resistors R11 and R12 connected in series. 1 has a base connected to a connection point P9 between the transistor TR3 connected to the negative side P1 of the first resistor R11 and the resistor R12, a collector connected to the positive side P2 of the DC power source 1 through the resistor R13, and a resistor R14. The transistor TR4 is connected to the gate of the switching element 3 through the base, and the emitter is directly connected to the negative side P1 of the DC power source 1.

Next, the operation of the DC motor control circuit having the above configuration will be described.
Since the DC motor 2 generates the counter electromotive force Vn (V), the voltage between both ends P1 to P3 of the switching element 3 (the potential of P3 with reference to P1) is given by En = E−Vn. En is in a negative proportional relationship with the rotational speed. When the switching element 3 is turned off, the DC motor 2 tries to maintain the rotation due to inertia, but the rotation speed decreases due to rotation resistance or the like, and the voltage En increases.

  The voltage dividing circuit 4 outputs a voltage V4 obtained by dividing the voltage between P1 and P3 between P1 and P4. This voltage V4 is divided by the dividing ratio (resistance between T1 and T3) by the movable terminal T3 of the variable resistor VR. And the ratio of resistance between T3 and T2). When the dividing ratio of the variable resistor VR is 1: 0, the output voltage V4 = En × R2 / (R2 + R1 // R3), and when the dividing ratio of the variable resistor VR is 0: 1, the output voltage V4 = En × ( R1 // R3) / (R1 + R2 // R3). However, “//” is an operator representing the combined resistance of the parallel resistors. Thus, the maximum value and the minimum value of the output voltage V4 of the voltage dividing circuit 4 are determined regardless of the resistance value of the variable resistor VR. This means that the control range of the DC motor 2 by the DC motor control circuit does not fluctuate due to variations in the variable resistance VR.

  Further, since the bypass resistor R3 is present, the point P4 is not short-circuited to the point P1 or the point P3 even when the dividing ratio of the variable resistor VR is 1: 0 or 0: 1. Regardless of the ratio, it is possible to configure a circuit that maintains the output voltage V4 of the voltage dividing circuit 4 in an appropriate range as an input to the hysteresis circuit 6 described later.

  When the potential V5 at the point P5 (the output V4 of the smoothed voltage dividing circuit 4) becomes equal to or lower than the first potential VD (V), the hysteresis circuit 6 turns off the first transistor TR1 and turns on the second transistor TR2. When the potential V5 at the point P5 becomes equal to or higher than the second potential VU (V), the transistor TR1 is turned on and the transistor TR2 is turned off.

  More specifically, first, immediately after the DC motor 2 is started, the rotational speed is low and the potential V5 at the point P5 is high, so the transistor TR1 is turned on. Then, the collector current of the transistor TR1 flows through the resistor R6, and the potential V7 at the point P7 is lowered by the voltage drop at the resistor R6. Accordingly, the resistors R5, R6, R7, R8, R9, and R10 are set so that the voltage between the base and the emitter of the transistor TR2 is equal to or lower than the turn-on voltage of the transistor TR2. When the transistor TR2 is off, no current flows through the resistor R9. Therefore, the potential V8 at the point P8, which is the output of the hysteresis circuit 6, becomes the same potential E (V) as the positive point P2 of the DC power supply.

  When the rotational speed of the DC motor 2 is increased and the potential V5 at the point P5 is decreased and the transistor TR1 is turned off, the collector current of the transistor TR1 is eliminated, so that the voltage drop of the resistor R6 is decreased and the potential V7 at the point P7 is increased. . As a result, the voltage between the base and the emitter of the transistor TR2 rises to turn on the transistor TR2. Then, since a current flows between the collector and emitter of the transistor TR2, the potential at the point P8 falls below E (V) due to a voltage drop at the resistor R9. The potential V8 at the point P8, which is the output of the hysteresis circuit 6, becomes EV (BE) (V).

  The transistors TR1 and TR2 have their emitters connected to each other and share an emitter resistor R5. The potential V6 of the emitters of the transistors TR1 and TR2 and the point P6 is higher when the transistor TR1 is off and the transistor TR2 is on than when the transistor TR1 is on and the transistor TR2 is off. The resistance values of the resistors R5, R6, R7, R8, R9, and R10 are set so that the emitter current of the transistor TR2 is larger than the emitter current of TR1.

  Due to the change in the potential V6 at the point P6, the potential VU at the point P5 necessary for turning on the transistor TR1 becomes higher than the potential VD when the transistor TR1 is turned off. As a result, the hysteresis circuit 6 makes transition between the two output states of the output V8 with respect to the input V5 with hysteresis characteristics.

  The transistor TR3 of the matching circuit 7 is turned off when the output V8 of the hysteresis circuit 6 becomes E (V), and when the output V8 of the hysteresis circuit 6 falls below E (V), a potential difference is generated between the base and the emitter. Turns on when current flows. As a result, the potential V8 at the point P8 is lower than the potential at the point P2 by a base-emitter voltage (generally 0.6 V) of the transistor TR3. When the transistor TR3 is turned on, the potential at the connection point P9 between the resistor R11 and the resistor R12 rises, and the transistor TR4 is turned on. The potential at the point P10 is E (V) when the transistor TR4 is off, but is 0 (V) because it is connected to the negative side P1 of the DC power source 1 when the transistor TR4 is on. Since the potential of the point P10 is applied to the gate of the switching element 3, when the transistor TR4 is off, the switching element 3 is turned on and the power supply voltage E (V) is applied to the DC motor 2.

  FIG. 2 shows how the potential V5 at the point P5, which is the input of the hysteresis circuit 6, the potential V6 at the junction point P6 of the emitter of the hysteresis circuit 6, the potential V8 at the output point P8, and the gate voltage of the switching element 3. Indicates how it will change. In this figure, the division ratio (position of the movable electrode T3) of the variable resistor VR of the voltage dividing circuit 4 is kept constant, and the potential V5 at the point P5 obtained by smoothing the potential V4 at the point P4 becomes the potential En at the point P3. It is proportional.

  The potential V5 at the point P5 decreases in proportion to the increase in the rotational speed of the DC motor 2. When the potential V5 becomes equal to or lower than the first potential VD, the output voltage V8 of the hysteresis circuit 6 becomes low, so that the switching element 3 is turned off. Then, since the rotational speed of the DC motor 2 decreases, En increases and increases the potential V5. When the potential V5 becomes equal to or higher than the second potential VU, the output voltage V8 becomes E (V) again, and the switching element 3 is turned on.

  In other words, the DC motor control circuit maintains the potential V5 at the point P5 at the first potential VD or more and the second potential VU or less, thereby changing the potential V3 at the point P3 to the first potential VD and the second potential VU. The switching element 3 is switched so as to maintain a certain range determined by the voltage dividing ratio of the voltage dividing circuit 4.

  In the hysteresis circuit 6, the potential V6 of the emitter P6 also changes in accordance with the change in the potential V5. The value obtained by adding the turn-on voltage (base-emitter voltage) of the transistor TR1 to the two values of the potential V6 is VU. And VD.

  If the voltage dividing ratio of the voltage dividing circuit 4 is changed by moving the movable electrode T3 of the variable resistor VR, the ratio between the potential V5 of P5 and the potential En of the point P3 changes, and the rate of increase / decrease of the potential V5 changes. The on / off time of the switching element 3 changes. In the present embodiment, the ON / OFF cycle of the switching element 3 varies depending on the load of the drill, but is in the range of approximately 100 Hz to several kHz.

  In this embodiment, since the switching element 3 composed of an FET that is turned on with a low gate voltage is used, the matching circuit 7 changes the output voltage V8 of the hysteresis circuit 6 to a voltage that transitions between 0 (V) and E (V). Conversion is made to match the input characteristics of the switching element 3. However, in the present invention, the hysteresis circuit 6 can also output potentials at other points such as the point P6 and the point P7, and can set the resistance values of the resistors R5, R6, R7, R8, R9, and R10. Depending on the selection of the switching element 3, the switching element 3 can be directly turned on / off by the output of the hysteresis circuit 6.

The circuit diagram of the DC motor control circuit of one embodiment of the present invention. The graph which shows the electric potential change of each part of the direct-current motor control circuit of FIG.

Explanation of symbols

1 DC power supply 2 DC motor 3 Switching element (FET)
4 voltage divider circuit 5 smoothing circuit 6 hysteresis circuit 7 matching circuit R1 voltage dividing resistor R2 voltage dividing resistor R3 bypass resistor R5 emitter resistor VR variable resistor T1 fixed electrode T2 fixed electrode T3 movable electrode TR1 first transistor TR2 second transistor

Claims (6)

A switching element connected in series with a DC motor to a DC power supply;
A voltage dividing circuit for dividing the voltage across the switching element;
A hysteresis circuit configured by connecting a plurality of transistors so as to have a voltage output that transitions between two values with hysteresis characteristics with respect to the output voltage of the voltage divider circuit;
A DC motor control circuit, wherein the switching element is switched by an output of the hysteresis circuit. The hysteresis circuit includes a first transistor having a base to which an output voltage of the voltage dividing circuit is input;
A second transistor that is turned on when the first transistor is off and turned off when the first transistor is on;
The first transistor and the second transistor have their emitters connected to each other and share an emitter resistance,
2. The DC motor control circuit according to claim 1, wherein the emitter current of the second transistor is larger than the emitter current of the first transistor. The voltage dividing circuit includes two voltage dividing resistors composed of fixed resistors connected in series to both ends of the switching element,
A variable resistor that divides a resistor between two fixed electrodes into an arbitrary ratio from 0: 1 to 1: 0 with a movable electrode;
3. The direct current according to claim 1, wherein the variable resistor has the two fixed electrodes connected to both ends of the switching element, and the movable electrode is connected to a connection point between the voltage dividing resistors. Motor control circuit.   The DC motor control circuit according to claim 3, wherein a connection point between the voltage dividing resistors and the movable electrode are connected via a bypass resistor formed of a fixed resistor.   5. The DC motor control circuit according to claim 1, further comprising a matching circuit that matches an output of the hysteresis circuit with an input characteristic of the switching element.   The DC motor control circuit according to claim 5, wherein the matching circuit includes a transistor capable of outputting a voltage on a lower side of the DC power supply.

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