JP2004254391A - Motor drive circuit and driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive circuit which drives a motor within its rating. <P>SOLUTION: A voltage detection circuit 7 detects a voltage value supplied from a battery 1 to the motor drive circuit through a signal line 22. A calculation circuit 8 calculates a duty so as to switch an H level and an L level alternately corresponding to an excessive voltage when a voltage detection value from the voltage detection circuit 7 is in excess of rated voltage. An output control circuit 9 generates a control signal corresponding to a control command by the calculation circuit 8. A predriver 10 turns on/off a P channel MOS-FET 11 with the duty to output a drive signal turning off an N channel MOS-FET 12. Thus, an effective voltage supplied to the motor 13 is restrained to the rated voltage of the motor 13. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a driving circuit and a driving method for a DC motor.
[0002]
[Prior art]
2. Description of the Related Art A technique for applying a pulse current to a motor driven by a battery is known (for example, see Patent Document 1). Patent Literature 1 discloses a camera in which a photographing lens is driven forward and backward in an optical axis direction by a motor. The motor for driving the photographing lens of the camera is controlled so that the motor is energized for a predetermined time at the time of starting and the starting torque rises, and starts driving the lens. This motor is controlled to be switched to pulsed current after starting and decelerated, so that a shock generated in the lens and the power transmission system at the time of mechanical collision is suppressed.
[0003]
[Patent Document 1]
JP-A-63-113431
[Problems to be solved by the invention]
In the driving of the motor according to Patent Literature 1, when the motor is started, the motor is switched to pulse energization, so that the power supplied to the motor after the start is lower than at the time of the start, and the torque after the start is reduced. In addition, since the motor is continuously energized for a predetermined time regardless of the battery voltage when starting the motor, if the battery voltage is too high, the voltage supplied to the motor exceeds the motor rating or the starting current becomes several times the motor rating. There is a risk.
[0005]
The present invention provides a motor drive circuit and a drive method for driving a motor within a rating.
[0006]
[Means for Solving the Problems]
A motor drive circuit according to a first aspect of the present invention includes a voltage detection unit that detects a voltage supplied from a power supply, a calculation unit that calculates a duty in accordance with a voltage detection value obtained by the voltage detection unit, And a motor driving means for applying the supply voltage to the DC motor, wherein the calculation means is configured to calculate the duty so that the effective voltage applied to the DC motor does not exceed a predetermined value.
The calculating means may reduce the duty so that the effective voltage applied to the DC motor does not exceed the rated value of the DC motor.
A motor drive circuit according to a third aspect of the present invention is a motor drive circuit, comprising: a voltage detection means for detecting a voltage supplied from a power supply; a calculation means for calculating a duty in accordance with a voltage detection value by the voltage detection means; Motor driving means for applying the supply voltage to the DC motor, and controlling the motor driving means to apply the supply voltage to the DC motor by gradually increasing the duty up to the operation value calculated by the operation means when the DC motor is started. And control means.
A motor drive circuit according to a fourth aspect of the present invention is a motor drive circuit, comprising: a voltage detection means for detecting a voltage supplied from a power supply; a calculation means for calculating a duty in accordance with a voltage detection value by the voltage detection means; And (1) when the DC motor is started, gradually increase the duty to a predetermined value, and after starting, supply the supply voltage to the DC motor with the duty according to the predetermined value. The first drive to be applied and (2) when the DC motor is started, the duty is gradually increased to the calculated value calculated by the calculating means, and after the start, the supply voltage is applied to the DC motor with the duty based on the calculated value. Control means for instructing the motor drive means on the second drive to be applied; and a determination means for determining whether the power supply is a battery or an external power supply. Control means for instructing the second drive when the battery is judged by the judging means, and instructing the first drive when the external power source is judged by the judging means. It is.
The calculating means reduces the duty so that the effective voltage applied to the DC motor does not exceed the rated value of the DC motor, and a range in which the effective voltage does not exceed the rated value when the voltage detected by the voltage detecting means decreases. And if the detected voltage value is equal to or lower than a predetermined voltage, the duty can be limited to a predetermined value lower than 100%.
The motor drive circuit may further include temperature detecting means for detecting the temperature of the battery. In this case, the calculating means may set the duty to a predetermined value lower than 100% when the battery is determined by the determining means and the temperature detected by the temperature detecting means is equal to or lower than a predetermined temperature.
The external power supply may be constituted by an AC / DC adapter.
The DC motor may repeat a drive state and a stop state at the duty.
A motor driving method according to a ninth aspect of the present invention detects a voltage supplied from a power supply and calculates a duty according to the detected voltage value so that an effective voltage applied to the DC motor does not exceed a predetermined value. The supply voltage is applied to the DC motor at the calculated duty.
A motor driving method according to a tenth aspect of the present invention detects a voltage supplied from a power supply, calculates a duty according to the detected voltage value, and gradually starts the duty up to the calculated value when the DC motor is started. It is characterized in that the supply voltage is increased and applied to the DC motor.
According to the motor driving method of the present invention, a voltage supplied from a power supply is detected, a duty is calculated according to the detected voltage value, and (1) when starting the DC motor, up to a predetermined value. The first drive in which the duty is gradually increased and the supply voltage is applied to the DC motor at a duty according to a predetermined value after the start, and (2) the operation value calculated by the operation means when the DC motor is started. A second drive for gradually increasing the duty and applying a supply voltage to the DC motor at a duty according to the calculated value after the start, and determining whether the power source is a battery or an external power source. At this time, the second drive is performed, and when the external power supply is determined, the first drive is performed.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing an outline of a motor control circuit according to a first embodiment of the present invention. In FIG. 1, the motor control circuit includes diodes 4 and 4 ', a stabilization circuit 5, a control circuit 6, a pre-driver 10, a P-channel MOS-FET 11, and an N-channel MOS-FET 12. The motor control circuit drives the DC motor 13 using electric power from a DC voltage source connected between the terminal 2 and the terminal 2 ′ or between the terminal 3 and the terminal 3 ′. In the example of FIG. 1, the battery 1 is connected between the terminal 2 and the terminal 2 '. Terminals 3 and 3 'are used to connect an external power supply (not shown).
[0008]
The voltage of the battery 1 is applied via the diode 4 between the stabilizing circuit 5, the pre-driver 10, the source terminal of the P-channel MOS-FET 11, and the drain terminal of the N-channel MOS-FET 12, respectively. Here, the P-channel MOS-FET 11 and the N-channel MOS-FET 12 are connected in series. That is, the drain terminal of the P-channel MOS-FET 11 and the source terminal of the N-channel MOS-FET 12 are connected. The stabilizing circuit 5 DC / DC converts a voltage from a DC voltage source (the battery 1 in this case) into a predetermined voltage required by the control circuit 6 and supplies the voltage to the control circuit 6. The control circuit 6 includes a voltage detection circuit 7, an arithmetic circuit 8, and an output control circuit 9.
[0009]
The voltage detection circuit 7 detects a voltage value of an external power supply (not shown) connected between the terminal 3 and the terminal 3 ′ via the signal line 21 and detects a voltage value supplied to the motor drive circuit on the signal line 22. To detect through. In the present embodiment, the voltage applied between P-channel MOS-FET 11 and N-channel MOS-FET 12 corresponds to the voltage supplied to motor 13. The detection result by the voltage detection circuit 7 is output to the arithmetic circuit 8 via the signal line 23. The calculation circuit 8 performs a predetermined calculation based on the voltage detection value by the voltage detection circuit 7 and outputs a motor control command to the output control circuit 9 via the signal line 24. The output control circuit 9 generates a control signal according to a control command from the arithmetic circuit 8. The control signal is constituted by two signals having H level or L level, and these two control signals are output to the pre-driver 10 via the signal lines 25 and 26, respectively.
[0010]
The pre-driver 10 generates a drive signal for turning on / off the P-channel MOS-FET 11 and a drive signal for turning on / off the N-channel MOS-FET 12 in response to the two control signals from the output control circuit 9. , And output to the gate terminal of the P-channel MOS-FET 11 and the gate terminal of the N-channel MOS-FET 12 via the signal lines 27 and 28, respectively. The motor 13 is connected between the source terminal and the drain terminal of the N-channel MOS-FET 12. The motor 13 is controlled to one of the driving (rotation), stop, and braking (brake) states according to ON / OFF of the P-channel MOS-FET 11 and the N-channel MOS-FET 12.
[0011]
FIG. 2 shows a control signal (control input) level input to the pre-driver 10, a drive signal (control output) level output by the pre-driver 10, a state of the P-channel MOS-FET 11 and an N-channel MOS-FET 12, FIG. 4 is a diagram illustrating a relationship with an operation state of a motor 13. In FIG. 2, when both the P-channel MOS-FET 11 and the N-channel MOS-FET 12 are off, the winding (not shown) of the motor 13 is opened, so that the motor 13 is stopped. Here, the stopped state is a state in which no torque is generated in the rotor (not shown) of the motor 13.
[0012]
When the P-channel MOS-FET 11 is off and the N-channel MOS-FET 12 is on, the winding (not shown) of the motor 13 is short-circuited, so that the motor 13 enters a braking state. Here, the braking state is a state in which no torque is generated in the rotor (not shown) of the motor 13 and the brake is electromagnetically applied.
[0013]
When the P-channel MOS-FET 11 is on and the N-channel MOS-FET 12 is off, a current flows through the winding (not shown) of the motor 13 via the P-channel MOS-FET 11, so that the motor 13 is driven. Here, the drive state is a state in which torque is generated in a rotor (not shown) of the motor 13. The pre-driver 10 drives the motor 13 when (1) the control input 25 is H and the control input 26 is L, and (2) the control input 25 and the control input 26 are both H. Is configured.
[0014]
According to the present invention, the drive state and the stop state are alternately switched when the motor 13 is driven by the motor control circuit described above. In the first embodiment, the duty in the drive state and the duty in the stop state are changed according to the voltage supplied to the motor 13.
[0015]
The arithmetic circuit 8 outputs a motor control command to the output control circuit 9 as follows.
1. When the motor 13 is stopped, the stop state calculation circuit 8 outputs a motor control command so that the control signal corresponding to the signal line 25 and the control signal corresponding to the signal line 26 are respectively set to L level.
[0016]
2. When braking the motor 13, the braking state calculation circuit 8 outputs a motor control command so that the control signal corresponding to the signal line 25 is set to L level and the control signal corresponding to the signal line 26 is set to H level.
[0017]
3. When driving the motor 13, the drive state calculation circuit 8 outputs a motor control command so that the control signal corresponding to the signal line 25 is at H level and the control signal corresponding to the signal line 26 is at L level. The arithmetic circuit 8 further controls the ratio (duty) between the H level and the L level of the control signal corresponding to the signal line 25 according to the voltage so that the voltage supplied to the motor 13 does not exceed the rated voltage of the motor 13. The control command is output so as to change. Note that the control signal corresponding to the signal line 26 keeps the L level.
[0018]
FIG. 3 is a diagram illustrating a waveform example of the control signal (signal line 25) when the voltage supplied to the motor 13 exceeds the rated voltage of the motor 13. For example, when the rated voltage of the motor 13 is 6 V and the voltage detected by the voltage detection circuit 7 via the signal line 22 is 9 V, the arithmetic circuit 8 calculates the duty by the following equation (1), and obtains the duty. Outputs control commands.
(Equation 1)
(6/9) × 100 = 67% (1)
[0019]
In the control signal (signal line 25) of FIG. 3, the H state is set to 67% in one cycle and the L level is set to the remaining 33%, so that the motor 13 alternately repeats the drive state and the stop state. Actually, the rotor of the motor 13 keeps rotating even in the above-mentioned stopped state due to the moment of inertia. Therefore, while controlling the voltage so that the average value (effective voltage) of the voltage supplied to the motor 13 does not exceed the rated voltage, 13 can be continued. The frequency at which the control signal repeats the H level and the L level is preferably several tens KHz.
[0020]
When the voltage supplied to the motor 13 is equal to or lower than the rated voltage of the motor 13, the arithmetic circuit 8 outputs a control command to obtain a duty of 100%. The duty of 100% is a state where the control signal (signal line 25) is always set to the H level when the motor 13 is driven. Note that the control signal corresponding to the signal line 26 keeps the L level.
[0021]
The first embodiment described above will be summarized. The arithmetic circuit 8 performs an arithmetic operation using the above equation (1) so that the voltage supplied to the motor 13 does not exceed the rated voltage of the motor 13. The arithmetic circuit 8 further outputs a control command to the output control circuit 9 so that the control signal corresponding to the signal line 25 is alternately switched between the H level and the L level according to the voltage exceeding the rated voltage. The control signal corresponding to the signal line 26 is kept at the L level. As a result, the driving state and the stopped state of the motor 13 are alternately repeated with the duty obtained by the above calculation (67% in the above example), and the effective voltage supplied to the motor 13 is suppressed to the rated voltage of the motor 13 or less. be able to. As a result, since the motor 13 is always used within the rating, the life of the motor 13 is not adversely affected. Further, since the rated effective voltage is applied during the duty driving, the motor 13 can be stably operated continuously without causing a decrease in the torque of the motor 13.
[0022]
In the driving state of the motor 13, instead of keeping the control signal corresponding to the signal line 26 at the L level, the signal level may be changed similarly to the control signal corresponding to the signal line 25.
[0023]
Although the driving state and the stop state of the motor 13 are alternately repeated during the duty driving, the driving state and the braking state may be alternately repeated. In this case, the control signal corresponding to the signal line 25 is alternately switched between the H level (driving state) and the L level (braking state) according to the voltage exceeding the rated voltage, and the control signal corresponding to the signal line 26 is also provided. The control signal is kept at the H level.
[0024]
(Second embodiment)
In general, at the initial stage of starting (starting) the motor 13, a current approximately calculated from a winding (not shown) resistance of the motor 13 and a voltage applied to the winding flows to the motor 13. This current gradually decreases due to the back electromotive force generated by the rotation of the motor 13, and converges to a value determined by the load of the motor 13 in a steady state. In the second embodiment, when the motor is started, the duty for repeating the drive state and the stop state is changed so as to gradually increase.
[0025]
FIG. 4 is a diagram illustrating the duty of the control signal (signal line 25) when the motor 13 is started. In FIG. 4, the horizontal axis represents time, and the vertical axis represents duty. The arithmetic circuit 8 sets the duty to 20% from the start time t0 to the time t1, the duty to 40% from the time t1 to the time t2, the duty to 60% from the time t2 to the time t3, and after the time t3 (the steady state). ) Outputs a control command to set the duty to 67%. The duty of 67% is based on the assumption that the rated voltage of the motor 13 is 6 V and the voltage detected by the voltage detection circuit 7 is 9 V, as in the first embodiment.
[0026]
FIG. 5 is a diagram illustrating a waveform example of a control signal (signal line 25) having a duty of 20%. The motor 13 alternates between a driving state and a stopped state by setting the H level for 20% of one cycle and the L level for the remaining 80%. FIG. 6 is a diagram illustrating a waveform example of a control signal (signal line 25) with a duty of 40%. The motor 13 alternates between a driving state and a stopped state by setting the H level for 40% of one cycle and the L level for the remaining 60%. By gradually increasing the duty, the driving torque of the motor 13 is gradually increased.
[0027]
A period in which the duty is lower than that in the steady state (time t0 to time t3 in the above example), the number of steps in which the duty is gradually changed (three in the above example), and the value of the duty in each step (20 in the above example) %, 40%, and 60%) are determined in advance in accordance with the starting characteristics of the motor 13, and these values are stored in a memory (not shown) in the arithmetic circuit 8 in advance.
[0028]
The output control circuit 9 changes the duty of the control signal according to the control command sent from the arithmetic circuit 8. More specifically, a timer circuit (not shown) starts measuring time at the start time t0, and every time a predetermined time is measured by the timer circuit, the duty of the control signal is changed as described above.
[0029]
FIG. 7 is a diagram showing a waveform of a current flowing through the motor 13 during the control according to FIG. 7, the horizontal axis represents time, and the vertical axis represents the magnitude of current. When the motor 13 is started at time t0, a current starts to flow through the motor 13. Since the duty is set to 20% from time t0 to time t1, the maximum value of the current is suppressed to be smaller than the current waveform (FIG. 8) when starting the motor 13 with the duty of 100% after the start time t0. Can be The duty 20% is determined so that the maximum value of the current does not exceed the current limit target value of the motor 13 at times t0 to t1.
[0030]
The current flowing through the motor 13 starts to decrease due to the back electromotive force generated by the rotation of the motor 13. When the duty is set to 40% at time t1 after the current has turned from increasing to decreasing, the current flowing through the motor 13 starts increasing again. Thereafter, similarly, by increasing the duty of the control signal each time the current changes from increasing to decreasing, the current waveform flowing through the motor 13 has a sawtooth waveform that alternately rises and falls. Thus, the motor 13 is started so that the maximum value of the current flowing through the motor 13 does not exceed the current limit target value.
[0031]
The second embodiment described above will be summarized. The arithmetic circuit 8 sets the duty to 20% from the start time t0 to the time t1, the duty to 40% from the time t1 to the time t2, the duty to 60% from the time t2 to the time t3, and after the time t3 (the steady state). ) Outputs a control command to set the duty to 67%. As a result, the waveform of the current flowing through the motor 13 is controlled in a sawtooth waveform that alternates between rising and falling, and the current at the time of starting the motor 13 can be suppressed to a current limit target value or less. As a result, a voltage drop due to overload of the battery 1 does not occur, so that the motor 13 can be started stably by a battery-driven device.
[0032]
In the first and second embodiments described above, the case where the rated voltage of the motor 13 is 6 V and the voltage detected by the voltage detection circuit 7 is 9 V has been described. The duty of the control signal for driving was set to 67%. When the voltage of the battery 1 decreases and the voltage detected by the voltage detection circuit 7 decreases, the duty is gradually increased. When the detection voltage reaches 6 V, the duty of the control signal is set to 100%.
[0033]
When the battery 1 is exhausted, the duty of the control signal does not have to be 100% even when the voltage detected by the voltage detection circuit 7 falls below the rated voltage of the motor 13. For example, when the battery 1 is exhausted and the voltage of the battery 1 is lower than a predetermined voltage (for example, 5 V), the upper limit of the duty of the control signal is limited to, for example, 80%. This limits the discharge power of the battery 1 when the battery 1 is depleted, so that an overload on the battery 1 is prevented and the battery 1 can be protected.
[0034]
The temperature of the battery 1 may be detected, and the upper limit of the duty of the control signal may be limited when the detected temperature falls below a predetermined temperature. In this case, a temperature sensor is provided near the battery 1 and this temperature detection signal is input to the arithmetic circuit 8. Accordingly, the discharge power of the battery 1 is limited in a state where the performance of the battery 1 is reduced at a low temperature (for example, 0 ° C. or lower), so that the overload on the battery 1 is prevented and the battery 1 can be protected. .
[0035]
The operation of changing the duty of the control signal in accordance with the voltage detected by the voltage detection circuit 7 or limiting the upper limit of the duty of the control signal is performed only when there is no power supply from an external power supply (not shown). It may be. The external power supply is an AC / DC adapter or the like. As described above, when an external power supply (not shown) is connected to the terminals 3 and 3 ′ of FIG. 1 and the power is supplied from the external power supply, the voltage from the external power supply is applied via the signal line 21 to the voltage detection circuit. 7 is detected. Generally, since the external power supply is configured to generate a constant voltage, it is considered that the voltage fluctuation accompanying the driving of the motor 13 occurs when the power is supplied from the battery 1. Therefore, the arithmetic circuit 8 changes or restricts the duty of the control signal only when the voltage via the signal line 21 is not detected by the voltage detection circuit 7, that is, when the power is supplied by the battery 1. . As a result, the load on the arithmetic circuit 8 can be reduced by eliminating unnecessary processing by the arithmetic circuit 8.
[0036]
The arithmetic circuit 8 sets the duty of the control signal to a fixed value when the voltage detection circuit 7 detects the voltage via the signal line 21, that is, when the voltage is supplied from an external power supply (not shown). You may. As described above, since it is considered that the external power supply does not cause a voltage change due to the driving of the motor 13, the arithmetic circuit 8 changes the duty of the control signal to a fixed value when the power is supplied by the external power supply. The fixed value in this case may be determined in advance in accordance with the supply voltage from the external power supply and stored in a memory (not shown) in the arithmetic circuit 8.
[0037]
INDUSTRIAL APPLICABILITY The present invention can be applied to devices including a battery-driven motor, such as cameras, toys, and peripheral devices for personal computers.
[0038]
Correspondence between each component in the claims and each component in the embodiment of the invention will be described. The power supply is constituted by, for example, a battery 1. The voltage detecting means is constituted by, for example, a voltage detecting circuit 7. The motor driving means includes, for example, a pre-driver 10, a P-channel MOS-FET 11, and an N-channel MOS-FET 12. The calculation means and the determination means are constituted by, for example, a calculation circuit 8. The control means includes, for example, an arithmetic circuit 8 and an output control circuit 9. Note that each component is not limited to the above configuration as long as the characteristic functions of the present invention are not impaired.
[0039]
【The invention's effect】
According to the first and ninth aspects of the invention, the duty of the supply voltage is calculated so that the effective voltage applied to the motor does not exceed a predetermined value (for example, the rating of the motor). Can be driven.
According to the third and tenth aspects of the present invention, at the time of starting the motor, the supply voltage is applied to the motor while gradually increasing the duty to an operation value calculated in accordance with the supply voltage. And the load on the power supply can be reduced.
According to the fourth and eleventh aspects of the invention, it is determined whether the power supply is a battery or an external power supply, and when the battery is determined, the motor is changed while changing the maximum duty according to the supply voltage (battery voltage). Was started. Further, when the external power source is determined, the motor is started while changing the duty to a predetermined value. As a result, the motor can be driven within the rating when using the battery, and the duty change process according to the supply voltage can be omitted when using an external power supply that does not cause voltage fluctuation unlike a battery.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of a motor control circuit according to a first embodiment of the present invention.
FIG. 2 illustrates a relationship among a control signal level input to a pre-driver, a drive signal level output from the pre-driver, states of a P-channel MOS-FET and an N-channel MOS-FET, and an operation state of a motor. FIG.
FIG. 3 is a diagram illustrating a waveform example of a control signal when a voltage supplied to a motor exceeds a rated voltage of the motor.
FIG. 4 is a diagram showing a duty of a control signal when starting a motor.
FIG. 5 is a diagram illustrating a waveform example of a control signal having a duty of 20%.
FIG. 6 is a diagram illustrating a waveform example of a control signal having a duty of 40%.
FIG. 7 is a diagram showing a waveform of a current flowing to a motor during control according to FIG. 4;
FIG. 8 is a diagram showing a current waveform when a motor is driven at a duty of 100%.
[Explanation of symbols]
1 ... battery 5 ... stabilization circuit
7: voltage detection circuit, 8: arithmetic circuit,
9: output control circuit, 10: pre-driver,
11 ... P-channel MOS-FET, 12 ... N-channel MOS-FET,
13 ... Motor

Claims (11)

Voltage detection means for detecting a voltage supplied from a power supply,
Calculating means for calculating the duty according to the voltage detection value by the voltage detecting means,
Motor driving means for applying the supply voltage to the DC motor at the calculated duty,
The motor drive circuit, wherein the calculating means calculates the duty so that the effective voltage applied to the DC motor does not exceed a predetermined value. The motor drive circuit according to claim 1,
The motor drive circuit according to claim 1, wherein the calculating unit reduces the duty so that an effective voltage applied to the DC motor does not exceed a rated value of the DC motor. Voltage detection means for detecting a voltage supplied from a power supply,
Calculating means for calculating the duty according to the voltage detection value by the voltage detecting means,
Motor driving means for applying the supply voltage to the DC motor at the calculated duty,
Control means for controlling the motor driving means so as to apply a supply voltage to the DC motor by gradually increasing a duty to an operation value calculated by the operation means when the DC motor is started. Motor drive circuit. Voltage detection means for detecting a voltage supplied from a power supply,
Calculating means for calculating the duty according to the voltage detection value by the voltage detecting means,
Motor driving means for driving a DC motor with a supply voltage from the power supply,
(1) When the DC motor is started, the duty is gradually increased to a predetermined value, and after the start, the first drive for applying the supply voltage to the DC motor at a duty according to the predetermined value is performed. (2) When the DC motor is started, the duty is gradually increased to a calculated value calculated by the calculating means, and after the start, the supply voltage is applied to the DC motor with a duty based on the calculated value. Control means for instructing the motor drive means to perform a second drive;
Determining means for determining whether the power supply is a battery or an external power supply,
The control means instructs the second drive when the battery is judged by the judgment means, and instructs the first drive when the external power supply is judged by the judgment means. A motor drive circuit characterized by the above-mentioned. The motor drive circuit according to claim 4,
The calculating means reduces the duty so that the effective voltage applied to the DC motor does not exceed the rated value of the DC motor, and when the voltage detected by the voltage detecting means decreases, the effective voltage becomes the rated value. A motor drive circuit wherein the duty is increased within a range not exceeding a predetermined value, and the duty is limited to a predetermined value lower than 100% when the detected voltage value is equal to or lower than a predetermined voltage. The motor drive circuit according to claim 4, wherein
Further comprising a temperature detecting means for detecting the temperature of the battery,
The motor drive circuit, wherein the calculating means sets the duty to a predetermined value lower than 100% when the battery is determined by the determining means and the temperature detected by the temperature detecting means is equal to or lower than a predetermined temperature. . The motor drive circuit according to any one of claims 4 to 6,
The motor drive circuit, wherein the external power supply is configured by an AC / DC adapter. The motor drive circuit according to any one of claims 1 to 7,
A motor drive circuit, wherein the DC motor repeats a drive state and a stop state at the duty. Detect the voltage supplied from the power supply,
According to the detected voltage value, calculate the duty so that the effective voltage applied to the DC motor does not exceed a predetermined value,
A motor driving method, wherein the supply voltage is applied to the DC motor at the calculated duty. Detect the voltage supplied from the power supply,
Calculate the duty according to the detected voltage value,
When the DC motor is started, a duty is gradually increased to the calculated value to apply the supply voltage to the DC motor. Detect the voltage supplied from the power supply,
Calculate the duty according to the detected voltage value,
(1) a first drive for gradually increasing the duty to a predetermined value when the DC motor is started, and applying the supply voltage to the DC motor at a duty according to the predetermined value after the start; (2) When the DC motor is started, the duty is gradually increased to a calculated value calculated by the calculating means, and after the start, the supply voltage is applied to the DC motor at a duty based on the calculated value. 2 drives,
Determine whether the power supply is a battery or an external power supply,
A motor driving method, wherein the second drive is performed when the battery is determined, and the first drive is performed when the external power supply is determined.

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