JPH04368490A - Motor driving circuit - Google Patents

Abstract

PURPOSE:To realize linear detection of coil current. CONSTITUTION:MOSFETs Q1-Q6, comprising circulation diodes D1-D6 connected in reverse parallel, are connected in bridge thus constituting a power converting section 2. A resistor RS detects current flowing through coils LU, LV, LW based on the total current flowing through the power converting section 2. An error amplifier 25 extracts the error component between the voltage across the resistor RS and a reference voltage for setting current. A constant current control section 4 controls the current flowing through the coils LU, LV, LW, at a constant level through PWM control according to the output from the error amplifier 25. A sample & hold circuit 36 samples and holds the peak value of the voltage across the resistor RS. A timing circuit 37 provides the sample & hold circuit 36 with a timing signal according to the output from the constant current control section 4.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention comprises a power converter formed by connecting switching elements in which freewheeling diodes are connected in antiparallel to each other in a bridge structure, and a current flowing through the entire power converter. The current flowing into the coil is detected by a current detection resistor, and the coil is detected by PWM control according to the output of an error amplifier that extracts the error between the voltage generated across the current detection resistor and the reference voltage for current setting. The present invention relates to a motor drive circuit that controls the current flowing through the motor to a constant value.

0002

2. Description of the Related Art A three-phase brushless motor has a structure shown in FIG. The rotor 40 of this three-phase brushless motor includes a rotor shaft 41, a rotor core 42 made of a cylindrical magnetic material through which the rotor shaft 41 is inserted, and a permanent magnet fixed to the rotor core 42. 43, the stator 50 includes a cylindrical stator core 51 that surrounds the rotor 40 and has a plurality of magnetic pole teeth 51a facing the rotor 40 with a small gap therebetween, and an insulated stator core 51 that surrounds the rotor 40. It consists of a coil 52 wound around the coil 52. And these rotors 4
0 and the stator 50 are housed in a case 60 consisting of a cylindrical case body 61 with one side closed and a back cover 62 that closes the other open side of the case body 61. The child shaft 41 is rotatably fitted into a bearing 63 fixed to the case 60. In this three-phase brushless motor, a position detection magnet 70 separate from the rotor 40 is fixed to the rotor shaft 41.
For example, the position of the magnetically sensitive element 8 consisting of a Hall element, etc.
0 to detect the position of the rotor 40. When a Hall element is used as the magnetic sensing element 80, the Hall element generates an output voltage proportional to the amount of magnetic flux from the position detection magnet 70, and receives the output voltage of the Hall element and fixes it in a motor drive circuit. Excitation current is passed through the three-phase coil 52 of the child 50.

The coils (in the following explanation, the coils are connected to each other for each phase as LU, LV, LW) according to the output voltage of the Hall element.
FIG. 11 shows an example of a motor drive circuit that causes an excitation current to flow through the motor. The power converter 2 converts the DC power of this motor drive circuit into AC power and supplies excitation current to the coils LU, LV, LW.
It has a so-called bridge configuration in which MOSFETs Q3 and Q6 are connected in series, and a three-phase coil L is connected to the connection point of each of the series-connected FETs Q1 to Q6.
One ends of U, LV, and LW are connected. and,
The other ends of the coils LU, LV, and LW are commonly connected via a resistor RS for coil current detection. Note that diodes D1 to D6 are connected in antiparallel to each of the FETs Q1 to Q6. The signal processing section 3 is a Hall element HU
, HV, and HW are binarized into 0 and 1 as shown in FIGS. 12(a) to 12(c), and based on this binarized signal, FETQ1 to 1 shown in FIGS. 12(d) to 12(i) are Create a gate signal to drive Q6. Note that (j) to (l) in FIG.
) indicate the currents flowing through the coils LU, LV, and LW, respectively. The current detection unit 12 includes the coils LU, LV, LW.
This current detection section 12
In response to the output, the constant current control unit 4 provides the signal processing unit 3 with a PWM signal for controlling the current flowing through the coils LU, LV, and LW to a constant value. Note that the right half of FIG. 12 shows a case where the lower FETs Q4 to Q6 in FIG. 11 are subjected to PWM control.

By the way, during servo driving, as shown in FIG. A method is adopted in which only the phase components are detected and the currents of the remaining phases are calculated vectorially. For example, these methods are employed in AC servo motors for robots, industrial inverters, and the like. However, this method requires a high-speed CPU, and since the detected waveform is in both positive and negative directions, there are problems such as a complicated circuit configuration. This becomes a problem. Moreover, when driving a 3-phase brushless motor simply by a 120° energization method without performing sine wave driving, the coils LU, LV, and LW are energized only to two of the three phases. Therefore, sufficient current information can be obtained with one current detection resistor.

FIG. 13 shows a motor drive circuit in which the coil current is detected using one resistor RS. In this motor drive circuit, resistor RS is replaced by FETQ4
~Q6 between the commonly connected sources and ground. FIG. 14 shows an example of a specific configuration of the constant current control section 4 in FIG. 13. In FIG. 14, the output of the current detection signal passed through the low-pass filter 24 and the variable resistor 28 are shown.
The error amplifier 25 calculates the error from the current setting value set by
This error output is compared with the output of the triangular wave generator 27 by the comparator 26 to create the PWM signal shown in FIG. 15(b). The PWM signal is passed through the signal processing section 3 to the FE.
This is applied to TQ1 to Q6, thereby controlling the coil current to a constant value (controlling the speed of the motor to a constant value). Here, when the pulse width of the PWM signal becomes narrower, the coil current decreases, and when the pulse width of the PWM signal becomes wider, the coil current increases. Note that such a PWM control function is a function that is always built into commercially available switching power supply ICs.

[0006]

[Problem to be solved by the invention] By the way, the above PWM
Current control using this method had the following problems. Figure 1
When the coil current is detected by one resistor RS shown in Fig. 3, the current value detected by the resistor RS is as shown in Fig. 16(a) to (
It is the sum of the absolute values of the currents flowing through the three coils LU, LV, and LW shown in c). The current value detected by the resistor RS is shown in (d) of the same figure.

Here, when the FETs Q1 to Q6 are turned on and off relatively faster than the switching cycle of the current flowing through the coils LU, LV, LW, that is, the switching of the current flowing through the coils LU, LV, LW. FET Q1 ~ Q6 only for a period shorter than the cycle of
When the resistor RS is turned on, the resistance RS
In this case, the current is detected only during the period when FETs Q1 to Q6 are on, and no current is detected during the period when FETs Q1 to Q6 are off.

[0008] As mentioned above, this applies to FETQ1 to Q6
When the on-period of FETQ1-Q6 is short, a freewheeling current flows through the diodes D1-D6 connected in antiparallel to each FETQ1-Q6 during the off-period of FETQ1-Q6.
This is because the current flowing through the actual coils LU, LV, and LW has the waveform shown in FIG. 17(a), but the above-mentioned return current does not flow through the resistor RS.

This point will be explained in detail regarding the case where PWM control is performed by controlling the lower FETs Q4 to Q6 in FIG. 11, as shown in the right half of FIG. For example, if gate signals are applied to FETs Q1 and Q5, as shown in FIG. 18(a), the DC power supply E→FE
TQ1 → Coil LU → Coil LV → FETQ5
Current flows through the path. Then, when the gate signal is no longer applied to FETQ5, the energy stored in the coils LU and LV acts to cause current to flow in the same direction as when FETQ1 and Q5 are turned on, as shown in FIG. 18(b). , a current flows through the path of coil LU → coil LV → diode D2 → FET Q1. Therefore,
As shown in FIG. 18(c), a resistor R is connected between the commonly connected sources of FETs Q4 to Q6 and the ground.
No current flows through S when FETQ5 is off. Figure 19 shows the detected current waveform (VRS) by resistor RS.
shows.

The problem in this case is that the input to the error amplifier 25 must be direct current, and if the input is intermittent as described above, accurate error extraction cannot be performed. Therefore, in the circuit shown in FIG. 14, a low-pass filter 24 is provided on the input side of the error amplifier 25 to shape the intermittent input waveform into a continuous waveform. However, when the coil current is controlled by PWM control, the coil current detected by the resistor RS is as shown in Figure 2.
0, not only the peak value P but also the pulse width W changes. Therefore, if you simply shape the DC waveform into a continuous DC waveform using the low-pass filter 24 (in this case, the average value of the current value will be determined using the low-pass filter 24), the current value will double (n = 2). Then, the average value becomes 4 times,
Unable to detect linear coil current.

The present invention has been made in view of the above points, and its purpose is to provide a motor drive circuit that can linearly detect a coil current even by detection using a single resistor. be.

0012

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a sample hold circuit that samples and holds the peak value of the voltage across the current detection resistor, and an output of the constant current control section. Accordingly, a timing circuit is provided for creating a timing signal for sample-holding the peak value of the voltage across the current detection resistor using the sample-and-hold circuit.

[0013] Furthermore, there is a switch that controls the input of the voltage across the current detection resistor to the constant current control section, and a gate signal of a constant width is created according to the output of the constant current control section to control the opening and closing of the switch. The same objective can also be achieved by providing a gate circuit that performs the following steps. The same objective can also be achieved by providing an integrator that integrates the voltage across the current detection resistor and a square root calculation circuit that calculates the square root of the output of the integrator and inputs it to the constant current control section. can.

[0014]

[Operation] By configuring the present invention as described above,
By using PWM control, only the increase in current can be detected while ignoring changes in the pulse width that appear in the voltage across the current detection resistor, and linear coil current detection is possible even with a single resistor. It was designed so that

[0015]

[Embodiment] (Embodiment 1) An embodiment of the present invention is shown in FIGS. 1 and 2. In this embodiment, a sample-and-hold circuit 36 samples and holds the peak value of the voltage across the resistor RS, and the sample-and-hold circuit 36 samples the peak value of the voltage across the resistor RS according to the output of the constant current control section 4. A timing circuit 37 for creating a timing signal to be held is provided.

In this embodiment, a sample and hold circuit 36 extracts the peak value of the current value output as the voltage across the resistor RS. Therefore, the current value can be detected linearly without being affected by the pulse width that changes due to PWM control that appears in the voltage waveform across the resistor RS. Note that since the output of the constant current control section 4 determines the point in time at which the current value is detected by the resistor RS, the timing circuit 37 controls the sample and hold circuit 36 according to the output of the constant current control section 4.
It can be operated to sample and hold the peak value. FIG. 2(a) shows the detected waveform of the current value detected by the resistor RS, and FIG. 2(b) shows the waveform of the current value detected by the resistor RS.
The waveform of the timing signal output from is shown.

By the way, the current detecting section 12 may have the configuration shown in FIG. 3. In FIG. 3, an analog switch 38 is used as a switch for controlling the input of the voltage across the resistor RS to the constant current control unit 4, and a gate signal of a constant width is created according to the output of the constant current control unit 4 to It is composed of a gate circuit 39 that controls opening and closing of the switch 38. In this case, the voltage across the resistor RS is input to the current controller 4 only during the period when the gate signal from the gate circuit 39 is applied to the analog switch 38. In this way, even if the pulse width of the detection signal changes due to PWM control as shown in FIG. can be sliced into constant pulse widths as shown in FIG. Therefore, as in the case of the circuit shown in FIG. 1, the current value can be linearly detected without being affected by changes in the pulse width of the voltage signal generated across the resistor RS.

Furthermore, as shown in FIG. 5, an integrator 91 and a square root calculation circuit 92 are connected between the resistor RS and the current control section.
By providing this, it is possible to linearly detect the current value without being affected by the pulse width of the detection signal. In the case of FIG. 5, the detected voltage of the resistor RS is
Integrate by 1. The output of the integrator 91 at this time is current peak value P×pulse width W. Here, if the current peak value P increases by n times, the pulse width W also increases by n times, and the output of the integrator 91 becomes n2×current peak value P×pulse width W. Then, when the square root of the output of the integrator 91 is determined by the square root calculation circuit 92, the output of the square root calculation circuit 92 becomes n×√current peak value P×pulse width W. Here, √current peak value P x pulse width W indicates the square root of current peak value P x pulse width W, and is constant, so it is not affected by changes in pulse width and linear current value detection is possible. I can do it.

(Embodiment 2) FIGS. 6 to 9 show an embodiment in which the above motor drive circuit is applied to an actual power tool. First, before explaining the main parts of this embodiment, a power tool to which this embodiment is applied will be explained. Examples of power tools include electric screwdrivers, which conventionally use mechanical clutches to control screw tightening torque.

An example is shown in FIG. In this electric screwdriver, the motor and the output shaft 30 of the electric screwdriver are connected through a reduction mechanism A consisting of a plurality of gears, and the transmission of power from the motor to the output shaft 30 is controlled by a clutch 31. There is. Here, the clutch 31 engages a clutch plate 32 into which the output shaft 30 is inserted, and a locking portion 33a formed on the front end surface of an internal gear 33 that constitutes the reduction mechanism A and meshes with a planetary gear (not shown). A ball 34 to be stopped;
The ball 3 is disposed between the clutch plate 32 and the ball 34.
4 in the direction of locking the locking portion 33a of the internal gear 33.

In this electric screwdriver, when the load torque is less than a predetermined value, the ball 34 is locked to the locking portion 33a of the internal gear 33, thereby preventing the internal gear 33 from rotating. Power is transmitted to the output shaft 30 via the speed reduction mechanism A. Now, if the screw is completely tightened and the load torque reaches a predetermined value, the internal gear 33 will push back the ball 34 against the spring 35 and start rotating, causing the reduction mechanism A to idle. As a result, power transmission from the motor to the output shaft 30 is cut off, and the screw is tightened with a predetermined torque. The tightening torque of the screw is adjusted by changing the amount of compression of the spring 35 using the clutch plate 32.

However, in the case of the above-mentioned mechanical clutch, there are problems in that it generates large noise and vibration during operation and has a short lifespan. Therefore, as a torque control method to eliminate the above drawbacks, for example, the current supplied to the motor is limited to a predetermined value or less using a circuit, and the tightening torque is limited to a predetermined value or less. One possibility is to limit the torque.

However, with this method, when the head of the screw comes into contact with the member to be screwed (hereinafter, this state is referred to as seating), the load increases instantaneously and the motor stops. In addition, extra force is applied to the screw due to the inertial torque of the motor's rotor, gears, etc., and this force causes an uncontrollable error when limiting the torque generated by the motor to a predetermined value or less to achieve the desired tightening force, resulting in extreme In some cases, the threads could be damaged.

[0024] In principle, inertial torque is proportional to inertia force and change in rotational speed (acceleration), and can be reduced by slowing down the rotational speed of the motor, etc., so it is a good idea to reduce the rotational speed of the motor, etc. It will be done. However, in this case, there is a problem in that it takes time to tighten the screws, reducing work efficiency. Figure 2 shows the circuit configuration of a conventional power tool that has improved this point.
Shown in 2. Note that a case where the power tool is an electric screwdriver will be described below.

In this electric driver, a DC brushless motor is used as the motor 1 having DC motor characteristics. This motor 1 is driven by a power converter 2 consisting of a bridge circuit configured using six FETs. The signal processing unit 3 includes a Hall element 11 that detects the position of the rotor.
The FETs of the power conversion section 2 are driven and controlled according to the output of the signal processing section 3, and the drive signal outputted from the signal processing section 3 is created based on the PWM signal given from the PWM type constant current control section 4. .

The constant current control unit 4 creates a PWM signal in accordance with the output of the oscillator 5 which determines the frequency of the PWM signal. This constant current control section 4 includes a detection resistor RS.
Data corresponding to the motor current detected by the current detection section 12 is inputted from the voltage across the motor, and the motor speed is controlled to a constant speed by feedback control. Further, the command data indicating the current setting value from the arithmetic processing section 7 is converted into an analog value by the D/A converter 6 and is given to the constant current control section 4.

[0027] The arithmetic processing unit 7 is composed of a CPU having a built-in ROM and RAM, and an I/O interface, and controls the entire operation sequence of the electric screwdriver. The arithmetic processing unit 7 is supplied with torque setting data for determining the tightening torque from the torque setting volume 10 via the A/D converter 8. Further, a control command is given to the arithmetic processing unit 7 via the switch interface 13 from an operation switch 18 such as a switch for setting an operation mode.

In this electric screwdriver, the seating point of the screw is detected by constantly sensing it using a sensor or the like, or by storing the rotational speed of the screw in advance through learning. However, when detecting the seating point by learning, seating detection means for detecting that the screw is seated and rotation speed detection means for detecting the rotation speed of the output shaft are required, and the arithmetic processing section 7 performs the screw tightening work. Before starting, it is first necessary to provide a function to set the operating mode to learning mode.

[0029]Then, until the screw is seated, the screw is tightened at high speed as shown in A (however, speed (1)) in Fig. 7, and the rotational speed is lowered just before the seat is seated to eliminate the influence of inertial force. . Furthermore, specifically, when the screw is tightened just before seating, the rotation of the motor 1 is abruptly braked and stopped as shown in FIG. 7B. Note that the number of rotations that the output shaft of the electric screwdriver rotates due to inertia is also taken into consideration when applying the brake. C in FIG. 7 shows a certain period when the motor 1 is stopped. Then, restart the motor 1 and completely tighten the screws. After this restart, as shown in FIG. 7D, the current of the motor 1 is slowly increased until it reaches a predetermined current value, and the screws are tightened. Note that it is preferable to tighten the screws with constant acceleration rotation at least until the person is seated. Here, the arithmetic processing section 7 gives the current set value to the constant current control section 4, and the constant current control section 4 detects from the output of the current detection section 12 that the motor current has reached the current set value. After the current value corresponding to the set current value is maintained for a predetermined short time, the supply of current to the motor 1 is stopped, and the screw tightening is completed. In this way, by finally making the motor current constant, the torque generated by the motor is kept constant, and constant torque control is realized. In the above case, the motor 1 was completely stopped before the seat was seated, but the rotational speed of the motor 1 may be reduced to a state just before stopping.

However, the conventional electric screwdriver described above has a problem in that it is not possible to arbitrarily set the speed until the screw is seated. Therefore, this embodiment is characterized in that by adopting the configuration shown in FIG. 6, the speed up to just before seating can be arbitrarily set. In FIG. 6, a volume 20 that sets the speed of the motor 1, a speed detection circuit 23 that detects the speed of the motor 1 from the output of the Hall element 11, and command data of the arithmetic processing unit 7 via the D/A converter 6 are shown. and an analog switch 21 for selecting one of the speed command data from the speed setting volume 20;
An analog switch 22 is provided to select which of the outputs of the current detection section 12 and the speed detection circuit 23 is input to the constant current control section 4.

[0031] In this embodiment, up to just before seating ((a in Fig. 9)
) to (b)), the analog switch 21 is switched to the speed setting volume 20 side, and the arithmetic processing unit 7 is switched to switch the analog switch 22 so that the speed detection circuit 23 is input to the constant current control unit 4. Control. Therefore, the rotation of the motor 1 can be controlled at the speed set by the speed setting volume 21. That is, in the case of this embodiment, the PWM control function provided in the constant current control section 4 is used to perform speed control. The broken line shows the case where the speed is varied in A of FIG. This state is shown in FIG. 8 in terms of the relationship between the speed and torque of the motor 1. Note that the set speeds in each figure are indicated by (1) to (4), and the smaller the number, the faster the speed. In this way, the rotational speed of the power tool can be set to an arbitrary speed. Further, FIG. 9 shows a state in which a pit 94 attached to the tip of an electric screwdriver is fitted into a screw 93 and tightened to a member 95 to be screwed.

Then, when the state shown in FIG. 9(b) is reached, the rotation of the motor 1 is temporarily stopped by rapidly applying the brake as in the conventional example. At this time, the analog switch 21 is switched to input the output of the D/A converter 6, and the output of the current detection section 12 is switched to the constant current control section 4. Note that this switching control is automatically performed by the arithmetic processing circuit 7. Thereafter, the screws are completely tightened without being affected by inertial force in the same manner as in the conventional example described above.

Note that the current detecting section 12 has a function of linearly detecting the current flowing through the three types of coils LU, LV, LW such as the sample hold circuit 36 and the timing circuit 37 in the first embodiment. The specific configuration of the constant current control section 4 is shown in FIG. 1, and the current setting value of the error amplifier 25 is given from the arithmetic processing section 7.
The triangular wave will be given from the oscillator 5.

[0034]

Effects of the Invention As described above, the present invention includes a sample and hold circuit that samples and holds the peak value of the voltage across the current detection resistor, and a sample and hold circuit that detects current according to the output of the constant current control section. Since a timing circuit is provided to create a timing signal to sample and hold the peak value of the voltage across the current detection resistor, PWM control is used to ignore changes in the pulse width that appear in the voltage across the current detection resistor. Only the increase in current can be detected, and linear coil current detection is also possible by detection using a single resistor.

In addition, a switch is provided to control the input of the voltage across the current detection resistor to the constant current control section, and a gate signal of a constant width is created in accordance with the output of the constant current control section to control the opening/closing of the switch. By providing a gate circuit to perform PWM control, even if the pulse width appearing in the voltage across the current detection resistor changes due to PWM control, the pulse width of the waveform at both ends of the current detection resistor input to the constant current control section can be kept constant. Therefore, the constant current control section is not affected by changes in the pulse width, making it possible to linearly detect the coil current.

Furthermore, even if an integrator that integrates the voltage across the current detection resistor and a square root calculation circuit that calculates the square root of the output of the integrator and inputs it to the constant current control section are provided, By taking the square root of the output using the square root arithmetic circuit, only the values related to the current value flowing through the coil can be extracted and given to the constant current control section, making it possible to linearly detect the coil current.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the same operation as above.

FIG. 3 is a circuit diagram of another embodiment.

FIG. 4 is an explanatory diagram of the same operation as above.

FIG. 5 is a circuit diagram of yet another embodiment.

FIG. 6 is a block diagram showing a circuit configuration of an embodiment in which the idea of each embodiment described above is applied to a power tool.

FIG. 7 is an explanatory diagram of the same operation as above.

FIG. 8 is a speed-torque characteristic diagram during speed control same as above.

FIG. 9 is an explanatory diagram of the screw tightening method according to the above.

FIG. 10 is an exploded perspective view showing the structure of a three-phase brushless motor.

FIG. 11 is a circuit diagram of a conventional motor drive circuit.

FIG. 12 is a signal waveform diagram showing the same operation as above.

FIG. 13 is a circuit diagram of another motor drive circuit.

FIG. 14 is a specific circuit diagram of the main parts of the same as above.

FIG. 15 is an explanatory diagram of the same operation as above.

FIG. 16 is an explanatory diagram showing the relationship between a coil current and a detection signal of a current detection resistor.

FIG. 17 is an explanatory diagram showing a coil current and a detection state of the coil current by a current detection resistor.

18 is an explanatory diagram of the operation showing the reason why the coil current detection state by the current detection resistor is as shown in FIG. 17. FIG.

FIG. 19 is an explanatory diagram showing an actually measured detected current waveform.

FIG. 20 is an explanatory diagram of a problem that occurs due to the state of coil current detection by the current detection resistor in FIG. 17;

FIG. 21 is an explanatory diagram of a conventional torque control mechanism.

FIG. 22 is a block diagram showing the circuit configuration of a conventional power tool.

[Explanation of symbols]

1 Motor 2 Power conversion section 3 Signal processing section 4 Constant current control section 25 Error amplifier 36 Sample and hold circuit 37 Timing circuit 38 Analog switch 91 Integrator 92 Square root calculation circuit Q1 ~ Q6 MOSFET D1 ~ D6 Diode LU, LV, LW coil RS resistance

Claims (3)

[Claims] 1. A brushless motor having DC motor characteristics and a switching element in which reflux diodes are connected in antiparallel to each other are connected in a bridge structure to convert DC power into AC power. A power conversion unit that supplies excitation current to the coil, a current detection resistor that detects the current flowing to the coil from the current flowing throughout the power conversion unit, and a voltage and current setting resistor that are generated across the current detection resistor. A constant current control section that creates a PWM signal to control the current flowing through the coil at a constant level according to the output of an error amplifier that extracts the error with respect to the reference voltage, and a power conversion section that generates a PWM signal for controlling the current flowing through the coil to a constant value according to the output of the constant current control section. In a motor drive circuit that includes a signal processing section that creates drive signals for the switching elements constituting the 1. A motor drive circuit comprising: a timing circuit for creating a timing signal for sample-holding a peak value of a voltage across a current detection resistor in a sample-and-hold circuit in response to the current detection resistor. 2. A switch that controls the input of the voltage across the current detection resistor to the constant current control section, and a gate signal of a constant width according to the output of the constant current control section to control the opening and closing of the switch. 2. The motor drive circuit according to claim 1, further comprising a gate circuit for controlling the motor drive circuit. [Claim 3] A claim comprising: an integrator that integrates the voltage across the current detection resistor; and a square root calculation circuit that calculates the square root of the output of the integrator and inputs it to the constant current control section. The motor drive circuit according to item 1.