JPH11220897A - Motor driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To absorb a voltage decline caused by a counter-electromotive force with a small device size. SOLUTION: A 1st driving transistor Q1 which controls a driving current supplied to the 1st terminal Tm1 of a motor 3 from a DC power supply 2, a 2nd driving transistor Q2 through which a current from the 1st terminal Tm1 of the motor 3 is supplied to the ground, a 3rd driving transistor Q3 which controls a driving current supplied to the 2nd terminal Tm2 of the motor 3 from the DC power supply 2, a 4th driving transistor Q4 which receives a current from the 2nd terminal Tm2 of the motor 3 and a driving control circuit 4 which controls the 1st-4th driving transistors Q1-Q4 in accordance with 1st and 2nd control signals supplied to 1st and 2nd control terminals Tc1 and Tc2 to control the operation of the motor 3 are provided. A swing to a load side which is caused by a counter-electromotive force generated in the motor 3 is detected and the 1st and 3rd driving transistors Q1 and Q3 are turned on to absorb the swing to the load side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive circuit, and more particularly to a motor drive circuit capable of driving a DC motor to rotate forward and backward.

[0002]

2. Description of the Related Art FIG. 6 is a circuit diagram showing an example of a conventional motor drive circuit. The conventional motor drive circuit 300
Driven by a DC power supply 301 connected to the power supply terminals Tv11 and Tv12,
A first driving transistor QA for controlling a driving current supplied to a terminal Tm11 of the motor 302; a second driving transistor QB for drawing a current from the first terminal Tm11 of the motor 302 and supplying the current to the ground; A third driving transistor QC for controlling the driving current supplied to the terminal Tm12 of the motor 302; a fourth driving transistor QD for drawing a current from the second terminal Tm12 of the motor 302;
Of the first to fourth driving transistors QA to QA according to the first and second control signals supplied to the control terminals Tc11 and Tc12 of
The drive control circuit 303 controls the QD and controls the operation of the motor 302, and includes diodes D11 to D14 for absorbing the positive-side swing caused by the back electromotive force generated in the motor 302.

The first driving transistor QA is composed of a PNP transistor, the emitter is connected to the positive terminal of the DC power supply 301, the collector is connected to the first terminal Tm11 of the motor 302, and the base is supplied from the driving control circuit 303 to the first driving terminal Tm11. A control signal is provided. The second driving transistor QB is
An NPN transistor, the emitter is the negative terminal of the DC power supply 301, and the collector is the first terminal T of the motor 302.
m11 and the second from the drive control circuit 303 to the base.
Are supplied.

The third drive transistor QC is formed of a PNP transistor, the emitter is connected to the positive terminal of the DC power supply 301, the collector is connected to the second terminal Tm12 of the motor 302, and the base is connected to the drive control circuit 303 from the third drive circuit 303. A control signal is provided. The fourth drive transistor QD is
An NPN transistor, the emitter is the negative terminal of the DC power supply 301, and the collector is the second terminal T of the motor 302.
m2, and a fourth drive control signal is supplied to the base from the drive control circuit 303.

The second drive control signal supplied to the base of the second drive transistor QB is a signal obtained by inverting the third drive control signal supplied to the base of the third drive transistor QC. The fourth drive control signal supplied to the base of the fourth drive transistor QD is the first drive control signal.
Is a signal obtained by inverting the first drive control signal supplied to the drive transistor QA.

The first to fourth drive control signals are supplied to first and second control terminals Tc11 and Tc12 by a drive control circuit 303.
Are generated in response to the first and second control signals supplied to the first and second control signals. In the conventional motor drive circuit 300, for example, if the first control signal supplied to the first control terminal Tc11 is at a high level and the second control signal supplied to the second control terminal Tc12 is at a low level, , The first driving transistor Q
A and the fourth drive transistor QD are turned on, the second drive transistor QB and the third drive transistor QC are turned off, and the motor 302 is driven in the direction from the first terminal Tm11 to the second terminal Tm12. Electric current flows and motor 3
02 rotates forward.

If the first control signal supplied to the first control terminal Tc11 is at a low level and the second control signal supplied to the second control terminal Tc12 is at a high level, the first
, The fourth driving transistor QD is turned off, the second driving transistor QB and the third driving transistor QC are turned on, and the motor 302
Then, a drive current flows from the second terminal Tm12 to the second terminal Tm11, and the motor 302 rotates in the reverse direction.

Further, the first and second control terminals Tc11,
When both the first and second control signals supplied to Tc12 become high level, the first to fourth driving transistors QA to QA are output.
The first and third transistors QA and QC of QD are turned off, and the motor 302 is braked. Motor 30
In No. 2, a back electromotive force is generated by the brake. FIG. 7 shows an equivalent circuit diagram of the motor.

Since the motor 302 has a built-in coil,
Generally, as shown in FIG. 7, it is represented by an equivalent circuit in which an inductance ML and a load resistance RL are connected in series. Therefore,
When the drive current Im is supplied to the motor 302, a back electromotive force is generated by the inductance ML. In particular, since the rotor of the motor 302 rotates due to inertia during braking, a voltage is generated in the opposite direction by the rotation of the rotor, resulting in a back electromotive force.

At this time, the motor drive circuit 300
Assuming that C is used, the back electromotive force at the time of braking
First and second terminals Tm11, Tm1 for connecting the motor 302
2 generates a negative voltage. In an IC, each element such as a transistor is formed by diffusing an impurity into a semiconductor substrate, and the polarity of the semiconductor layer is set to be reverse between adjacent elements. Because of this,
It operates normally with a bias voltage in a predetermined direction.

When a negative voltage is generated at the first and second terminals Tm11 and Tm12 and the bias state of the substrate is broken, the semiconductor layer between the elements operates as a parasitic element and abnormal operation such as latch-up occurs. I do. Therefore, when a negative voltage is generated at both ends of the motor 302 due to a braking operation or the like,
In order to absorb this, diodes D11 to D14 are provided.

In particular, the diodes D12 and D14 prevent voltage swing to the minus side of the terminals Tm11 and Tm12 during the braking operation, and prevent abnormal operations such as latch-up. The first and second terminals Tm1 of the motor 302 are generated by the back electromotive force generated by the motor 302 during the braking operation of the motor 302.
1, when the Tm12 side swings to the negative side, the diodes D12 and D12
When the switch 14 is turned on, a current is supplied from the ground side, and the voltage of the first and second terminals Tm11 and Tm12 of the motor 302 is prevented from swinging to the negative side. Abnormal operation was prevented.

FIG. 8 shows an operation waveform diagram of an example of the related art. 8A shows the operation mode of the motor 302, and FIG. 8B shows the voltage of the first terminal Tm11 of the motor 302. FIG. 8 (A)
As shown in FIG. 8, when the operation state of the motor 302 shifts from the normal rotation state to the braking state, a negative voltage is generated at the first terminal Tm11 as shown in FIG. When a negative voltage is generated by the back electromotive force of the motor 302, the motor drive circuit 300 is clamped by the diodes D12 and D14 at the forward voltage VF of the diodes D12 and D14 and does not decrease any more. At this time, the negative voltage is about 1.2 [V] at the maximum due to the back electromotive force of the motor 302.

[0014]

However, in the conventional motor drive circuit, the current caused by the back electromotive force is bypassed to ground by the diodes D12 and D14, so that a large current flows through the diodes D12 and D14. Therefore, it was necessary to make the element size of the diodes D12 and D14 relatively large. Therefore, when the motor drive circuit is formed into an IC, there is a problem that the chip area increases.

In addition, there is a problem that the diodes D12 and D14 alone cannot sufficiently absorb the negative current due to the back electromotive force due to variations in element characteristics in the manufacturing process.
The present invention has been made in view of the above points, and has as its object to provide a motor drive circuit having a small element size and capable of absorbing a voltage drop due to back electromotive force.

[0016]

According to a first aspect of the present invention, there is provided a first drive transistor for controlling a current supplied to a first terminal of a motor in response to a control signal; A second drive transistor for drawing a current from a first terminal of the motor, a third drive transistor for controlling a current supplied to a second terminal of the motor in accordance with the control signal, and a third drive transistor in accordance with the control signal. A fourth drive transistor for drawing a current from a second terminal of the motor, wherein when the voltage of the first terminal of the motor falls below a predetermined voltage, the first drive transistor is turned off. And a control unit for turning on the third drive transistor when the voltage of the second terminal of the motor is lower than a predetermined voltage.

According to the first aspect, when the voltage of the first terminal of the motor is lower than the predetermined voltage, the first drive transistor is turned on, and the voltage of the second terminal of the motor is lower than the predetermined voltage. When the voltage drops, the third drive transistor is turned on, so that the current is supplied by the first and second drive transistors even if the voltage at the first and second terminals of the motor drops due to the back electromotive force. Accordingly, it is possible to suppress a decrease in the voltage of the first and second terminals of the motor. At this time, since the first and third drive transistors that supply current to the motor are controlled to suppress a decrease in the voltage of the first and second terminals of the motor, the first and second terminals of the motor are connected to the first and second terminals. An element such as a diode for supplying a current is not required, and the chip area can be reduced.

According to a second aspect of the present invention, in the first aspect, the control means includes: a first control transistor having a collector connected to a base of the first drive transistor and an emitter connected to one end of the motor; Has a second control transistor whose emitter is connected to the base of the third drive transistor and whose emitter is connected to the other end of the motor, and bias means for biasing the bases of the first and second control transistors. It is characterized by the following.

According to the second aspect, the first and second control transistors are biased by the bias means, so that when the voltage of the first or second terminal of the motor decreases, the first or second control transistor is biased. Current is drawn from the emitter of the first control transistor, the first or third drive transistor whose base is connected to the collector of the first or second control transistor is turned on, and the first or second terminal of the motor is connected to the first or second terminal of the motor. A current is supplied from the first or third drive transistor. The first and second control transistors need only control the base potential of the first or third drive transistor in accordance with the voltages of the first and second terminals of the motor, so that a relatively small withstand voltage structure is sufficient. In addition, since a current is supplied to the first and second terminals of the motor, an element such as a diode having a large-capacity withstand voltage structure becomes unnecessary, and the chip area can be reduced.

According to a third aspect, in the second aspect, the bias means generates a constant current in response to the control signal and the second current in response to the constant current generated by the constant current circuit. A constant voltage circuit that generates a bias voltage to be applied to the bases of the first and second control transistors.

According to the third aspect, a constant current is generated according to the control signal, and a bias voltage to be applied to the bases of the first and second control transistors is generated according to the generated constant current. The first and second control transistors operate when the control signal causes a back electromotive force to be generated in the motor. According to a fourth aspect, in the second or third aspect, the first control transistor is provided between an emitter of the first control transistor and one end of the motor, and reduces a voltage between an emitter and a collector of the first control transistor. And a second voltage reducing means provided between the emitter of the second control transistor and the other end of the motor for reducing a voltage between the emitter and the collector of the second control transistor. It is characterized by having.

According to the fourth aspect, the voltage applied to the first and second control transistors can be reduced by the first and second voltage reducing means, so that a high voltage operation can be supported.

[0023]

FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG. 2 is a circuit diagram of the first embodiment of the present invention. The motor drive circuit 1 of the present embodiment has a power supply terminal T
a first driving transistor Q1 which is driven by a DC power supply 2 connected to v1 and Tv2 and controls a driving current supplied from the DC power supply 2 to a first terminal Tm1 of the motor 3, from a first terminal Tm1 of the motor 3 Second to supply current to ground
, A third driving transistor Q3 for controlling the driving current supplied from the DC power supply 2 to the second terminal Tm2 of the motor 3, and a fourth driving transistor Q4 for drawing the current from the second terminal Tm2 of the motor 3. , First and second
In response to the first and second control signals supplied to the first and second control terminals Tc1 and Tc2.
A drive control circuit 4 for controlling the operation of the motor 3
A noise swing control circuit 5, which detects a swing to the negative side due to a back electromotive force generated in the motor 3, turns on the first and third drive transistors Q1, Q3, and absorbs the swing to the negative side.
It comprises diodes D1, D2 and capacitors C1, C2 for absorbing positive-side deflection due to back electromotive force generated in the motor 3.

The first drive transistor Q1 is composed of a PNP transistor, the emitter is connected to the positive terminal of the DC power supply 2, the collector is connected to the first terminal Tm1 of the motor 3,
The first drive control signal is supplied from the drive control circuit 4 to the base. The second drive transistor Q2 is composed of an NPN transistor, the emitter is connected to the negative electrode of the DC power supply 2, the collector is connected to the first terminal Tm1 of the motor 3, and the base receives the second drive control signal from the drive control circuit 4. Supplied.

The third drive transistor Q3 is composed of a PNP transistor, the emitter is connected to the positive electrode of the DC power supply 2, the collector is connected to the second terminal Tm2 of the motor 3,
A third drive control signal is supplied from the drive control circuit 4 to the base. The fourth drive transistor Q4 is composed of an NPN transistor, the emitter is connected to the negative electrode of the DC power supply 2, the collector is connected to the second terminal Tm2 of the motor 3, and the base receives the fourth drive control signal from the drive control circuit 4. Supplied.

The second drive control signal supplied to the base of the second drive transistor Q2 is a signal obtained by inverting the third drive control signal supplied to the base of the third drive transistor Q3. The fourth drive control signal supplied to the base of the fourth drive transistor Q4 is the first drive control signal.
Is a signal obtained by inverting the first drive control signal supplied to the drive transistor Q1.

The first to fourth drive control signals are generated by the drive control circuit 4 in accordance with the first and second control signals supplied to the first and second control terminals Tc1 and Tc2. The drive control circuit 4 includes an NPN transistor Q11 as shown in FIG.
To Q30, PNP transistors Q31 to Q41, resistors R1 to R
Consists of 27. Here, the operation of the drive control circuit 4 will be described.

FIG. 3 shows an operation waveform diagram of a main part of the first embodiment of the present invention. FIG. 3A shows the operation mode of the motor 3 and FIG.
(B) is a current flowing through the motor 3, and FIG.
Shows the waveform of the voltage at both ends. FIG. 3 for rotating the motor 3 forward
When operating in the normal rotation mode of (A), the first control terminal Tc1 of the drive control circuit 4 is at a high level, and the second control terminal Tc2 is at a low level. When the first control terminal Tc1 of the drive control circuit 4 is at a high level and the second control terminal Tc2 is at a low level, the transistor Q11 turns on and the transistor Q14 turns off. When the transistor Q11 turns on, the transistor Q31 turns on.
Q33 and Q40 are turned on. When the transistors Q32 and Q33 turn on, the transistors Q12 and Q13 turn on.

On the other hand, since the transistor Q14 is turned off, the transistor Q34 is turned off, thereby turning off the transistors Q35, Q36 and Q39. Transistor Q3
5. When Q36 turns off, transistors Q15 and Q18 turn off. When the transistor Q12 turns on, the transistor Q24 turns off. At this time, the base potential of the transistor Q29 becomes low level, and the transistor Q29 is turned off. When the transistor Q29 is turned off, the base potential of the third drive transistor Q3, that is, the third drive control signal goes high, and the third drive transistor Q3
Turn off. When the transistor Q29 is turned off,
The base potential of the second driving transistor Q2, that is,
The second drive control signal goes low, turning off the second drive transistor Q2.

When the transistor Q18 is turned off, the transistors Q37 and Q38 are turned off. When the transistors Q37 and Q38 turn off, the transistor Q19 turns off, and the transistors Q22, Q23 and Q41 turn off.
At this time, the transistor Q40 is on and the transistor Q15
Is off, the collector current of transistor Q40 is supplied to the base of transistor Q27. Therefore, the transistor Q27 turns on.

When the transistor Q27 turns on, the base potential of the first drive transistor Q1, that is, the first drive control signal becomes low level, and the first drive transistor Q1 turns on. When the transistor Q27 is turned on, the base potential of the fourth drive transistor Q4, that is, the fourth drive control signal goes high, so that the fourth drive transistor Q4 is turned on.

As described above, by setting the first control signal supplied to the first control terminal Tc1 to high level and the second control signal supplied to the second control terminal Tc2 to low level, the first When the driving transistor Q1 is turned on, the second driving transistor Q2 is turned off, the third driving transistor Q3 is turned off, and the fourth driving transistor Q4 is turned on, the first terminal Tm1 of the motor 3 is connected to the positive terminal of the DC power source 2. And the second terminal Tm2 is connected to the negative electrode of the DC power supply 2. Therefore, a current flows through the motor 3 from the first terminal Tm1 to the second terminal Tm2, and the motor 3 rotates forward.

Next, when the first control terminal Tc1 is at the high level and the second control terminal Tc2 is changed from the low level to the high level, the motor 3 is braked. When the second control terminal Tc2 changes from low level to high level, the transistor Q14 turns on. When the transistor Q14 turns on, the transistor Q34 turns on.
5, Q36 and Q39 are turned on. When the transistors Q35 and Q36 turn on, the transistors Q15 and Q18 turn on.

When the transistor Q15 turns on, the transistors Q27 and Q25 turn off. When the transistor Q27 turns off, the base potential of the first drive transistor Q1, that is, the first drive control signal becomes high level, and the first drive transistor Q1 turns off. When the transistor Q27 is turned off, the base potential of the fourth drive transistor Q4, that is, the fourth drive control signal becomes low level, so that the fourth drive transistor Q4 is also turned off. Therefore, the first terminal Tm1 of the motor 3 is disconnected from the DC power supply 2.

At this time, the third driving transistor Q3,
Since the second driving transistor Q2 remains off,
Both the first terminal Tm1 and the second terminal Tm2 of the motor 3 are disconnected from the DC power supply 2, and the motor 3 is braked. Next, when the first control signal supplied to the first control terminal Tc1 is changed from the high level to the low level, the motor 3 rotates in the reverse direction. When the first control signal supplied to the first control terminal Tc1 changes from high level to low level, the transistor Q11 turns off. When the transistor Q11 turns off, the transistors Q31, Q32, Q33, Q40 turn off.

When the transistor Q32 turns off, the transistor Q12 turns off. When transistor Q12 turns off,
The transistor Q24 turns on. At this time, since the transistor Q18 is on, the transistors Q22 and Q2
3, Q26 and Q41 are turned on, the base potential of the transistor Q29 becomes high level, and the transistor Q29 is turned on.
When the transistor Q29 turns on, the base potential of the third drive transistor Q3, that is, the third drive control signal goes low, so that the third drive transistor Q3 turns on. When the third drive transistor Q3 turns on,
A current is supplied from the DC power supply 2 to the second terminal Tm2 of the motor 3.

When the transistor Q29 turns on, the base potential of the second drive transistor Q2, that is, the second drive control signal goes high, turning on the second drive transistor Q2. At this time, since the first drive transistor Q1 and the fourth drive transistor Q4 remain off, the motor 3 is connected to the first terminal from the second terminal Tm2.
Current flows in the direction of the terminal Tm1, and the motor 3 rotates in the reverse direction.

The noise absorption control circuit 5 comprises NPN transistors Q42 to Q47, PNP transistors Q48 and Q49, and resistors R28 to R30 as shown in FIG. The transistors Q42, Q44, Q48, Q49 and the resistors R28, R29 constitute a constant current circuit, the second control signal is at a high level, and the first and second terminals Tm1, Tm2 of the motor 3
, A constant current is generated when the motor 3 brakes. The transistor Q45 and the resistor R30 form a constant voltage circuit, and generate a predetermined voltage according to the constant current generated by the constant current circuit. The transistor Q46 has a collector connected to the base of the first driving transistor Q1, and an emitter connected to the first terminal T1 of the motor 3.
Connected to m1, the base is biased by the constant voltage generated by the constant voltage circuit. The transistor Q47 has a collector connected to the base of the third drive transistor Q3, an emitter connected to the second terminal Tm2 of the motor 3,
The base is biased by the constant voltage generated by the constant voltage circuit.

When the transistor Q46 is biased by the constant voltage generated by the constant voltage circuit,
When the motor 3 brakes, the first terminal Tm1 of the motor 3
When the potential of the first drive transistor Q1 becomes negative, it turns on, and draws current from the base of the first drive transistor Q1. When the transistor Q46 is turned on and a current is drawn, the first drive transistor Q1 is turned on because the base potential decreases.

When the first drive transistor Q1 is turned on, a current is supplied from the DC power supply 2 to the first terminal Tm1 of the motor 3, so that a decrease in the first terminal Tm1 of the motor 3 can be prevented. When the transistor Q47 is biased by the constant voltage generated by the constant voltage circuit, that is, when the potential of the second terminal Tm2 of the motor 3 becomes negative during the braking operation of the motor 3, the transistor Q47 turns on. Current is drawn from the base of the driving transistor Q3. When the transistor Q47 is turned on and the current is drawn, the third drive transistor Q3 is turned on because the base potential decreases.

When the third drive transistor Q3 is turned on, a current is supplied from the DC power supply 2 to the third terminal Tm2 of the motor 3, so that a decrease in the second terminal Tm2 of the motor 3 can be prevented. At this time, the collector potential of the transistors Q46 and Q47 is Vcv, and the base potential of the transistors Q46 and Q47 is minus.
Assuming that the voltage between the emitters is VBE, the first and second
Potential Vm of the terminals Tm1 and Tm2 is Vm = (Vcv-VBE)
Is clamped to.

For example, the first and second terminals Tm of the motor 3
1. The potential Vm of Tm2 can be suppressed to a maximum of 0.2 to 4 [V]. According to the present embodiment, even if the voltage of the first and second terminals Tm1 and Tm2 connecting the motor 3 decreases due to the back electromotive force generated in the motor 3 during the braking operation of the motor 3, the transistors Q46 and Q47 control the voltage. And turning on the first and third drive transistors Q1 and Q3, it is possible to prevent the voltage at the first and second terminals Tm1 and Tm2 of the motor 3 from decreasing.

Therefore, when the motor drive circuit 1 is formed into an IC, it is possible to prevent occurrence of an abnormal state such as so-called latch-up in which a parasitic transistor is turned on. In this embodiment, the transistors Q46 and Q47
Directly detects the potentials of the first and second terminals Tm1 and Tm2 of the motor 2, but if the transistors Q46 and Q47 require a withstand voltage, insert a withstand voltage adjusting means into the collectors of the transistors Q46 and Q47. Is also good.

FIG. 4 is a circuit diagram of a second embodiment of the present invention. 2, the same components as those of FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. The motor drive circuit 100 according to the present embodiment includes the transistors Q46 and Q47, the collector and the motor 3 in order to provide the transistors Q46 and Q47 with a withstand voltage.
And NPN transistors Q50 and Q51 diode-connected between the first and second terminals Tm1 and Tm2.
The transistor Q50 corresponds to a first voltage reducing unit in the claims, and the transistor Q51 corresponds to a second voltage reducing unit in the claims.

The diode-connected transistor Q50,
By connecting Q51, the voltage between the collector and the emitter of the transistors Q46 and Q47 can be set small, so that the withstand voltage of the transistors Q46 and Q47 can be improved. Further, the circuit configuration for driving the first to fourth drive transistors Q1 to Q4 is not limited to the configuration of the first or second embodiment.

FIG. 5 is a circuit diagram of a third embodiment of the present invention. 2, the same components as those of FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. The motor drive circuit 200 of the present embodiment integrates the resistors R21, R22 and R28 into a resistor R31.
And the resistors R24, R25 and R29 are put together to form a resistor R32
A resistor R33 is connected to the bases of the transistors Q28 and Q42, a resistor R34 is connected to the bases of the transistors Q30 and Q44, and the levels of the first to fourth drive control signals are adjusted.
The resistance is reduced.

It should be noted that the present invention is not limited to the circuit configurations of the above-described first to third embodiments, but the point is that the first to fourth drive transistors are controlled in accordance with the voltage across the motor 3. Therefore, any configuration may be used as long as it can absorb unnecessary components and prevent abnormal operation such as latch-up.

[0048]

As described above, according to the first aspect of the present invention, when the voltage of the first terminal of the motor falls below a predetermined voltage, the first drive transistor is turned on, and the second drive transistor of the motor is turned on. When the voltage at the terminal of
By turning on the third drive transistor, even if the voltage of the first and second terminals of the motor decreases due to the back electromotive force, current is supplied by the first and second drive transistors and the first In addition, a decrease in the voltage of the second terminal can be suppressed. At this time, since the first and third drive transistors that supply current to the motor are controlled to suppress a decrease in the voltage of the first and second terminals of the motor, the first and second terminals of the motor are connected to the first and second terminals. There is an advantage that an element such as a diode for supplying a current is not required, and a chip area can be reduced.

According to the second aspect, the first and second control transistors are biased by the bias means, so that when the voltage at the first or second terminal of the motor decreases, the first or second control transistor is biased. Current is drawn from the emitter of the first control transistor, the first or third drive transistor whose base is connected to the collector of the first or second control transistor is turned on, and the first or second terminal of the motor is connected to the first or second terminal of the motor. A current is supplied from the first or third drive transistor. Since the first and second control transistors need only control the base potential of the first or third drive transistor in accordance with the voltages of the first and second terminals of the motor, a relatively small withstand voltage structure is sufficient. In addition, since a current is supplied to the first and second terminals of the motor, elements such as a diode having a large-capacity withstand voltage structure are not required, and the chip area can be reduced.

According to the third aspect, a constant current is generated according to the control signal, and a bias voltage to be applied to the bases of the first and second control transistors is generated according to the generated constant current. When a control signal generates back electromotive force to the motor, the first and second control transistors can be operated. According to the fourth aspect, the voltages applied to the first and second control transistors can be reduced by the first and second voltage reducing means.
It has such features that the breakdown voltage of the first and second control transistors can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a first embodiment of the present invention.

FIG. 3 is an operation waveform diagram of a main part of the first embodiment of the present invention.

FIG. 4 is a circuit configuration diagram of a second embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of a third embodiment of the present invention.

FIG. 6 is a circuit configuration diagram of an example of the related art.

FIG. 7 is an equivalent circuit diagram of the motor.

FIG. 8 is an operation waveform diagram of a main part of a conventional example.

[Explanation of symbols]

 Reference Signs List 1 motor drive circuit 2 DC power supply 3 motor 4 drive control circuit 5 noise absorption control circuit Q1 first drive transistor Q2 second drive transistor Q3 third drive transistor Q4 fourth drive transistor

Claims (4)

[Claims] A first drive transistor for controlling a current supplied to a first terminal of the motor in response to a control signal; and a second drive transistor for drawing a current from the first terminal of the motor in response to the control signal. A driving transistor, a third driving transistor for controlling a current supplied to a second terminal of the motor in accordance with the control signal, and a second driving transistor of the motor in response to the control signal.
A fourth drive transistor that draws current from the terminal of the motor, when the voltage of the first terminal of the motor drops below a predetermined voltage, the first drive transistor is turned on, A motor drive circuit, comprising: control means for turning on the third drive transistor when the voltage of the second terminal of the motor falls below a predetermined voltage. 2. The control means includes: a first control transistor having a collector connected to a base of the first drive transistor and an emitter connected to one end of the motor; and a collector having a collector connected to the third drive transistor. 2. A motor control device comprising: a second control transistor connected to a base and having an emitter connected to the other end of the motor; and bias means for biasing the bases of the first and second control transistors. Motor drive circuit as described. 3. The constant current circuit for generating a constant current in accordance with the control signal, and the bias means includes a first and a second control transistors for controlling the first and second control transistors in accordance with the constant current generated by the constant current circuit. 3. The motor drive circuit according to claim 2, further comprising: a constant voltage circuit that generates a bias voltage applied to the base. 4. A first voltage reducing means provided between an emitter of the first control transistor and one end of the motor and configured to reduce a voltage between an emitter and a collector of the first control transistor; And a second voltage reducing means provided between the emitter of the second control transistor and the other end of the motor and configured to reduce a voltage between the emitter and the collector of the second control transistor. The motor drive circuit according to claim 2.