JP2000278986A - Motor drive circuit - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize high-precision motor control and driving with the maximum use of the power supply capability, and further enhance the protection capability of the drive circuit. SOLUTION: The motor drive circuit 1 is provided with a current detection resistor R2 for driving a motor 3 by a PWM drive signal and detecting a current flowing into or out of the coil of the motor 3; A sample and hold circuit 17 for holding a value approximating a flowing current;
A comparator 15 and a PWM circuit 16 for controlling the driving of the motor based on the output of the hold circuit 17; a primary CR filter composed of C1 and R1 for calculating the average value of the current flowing from the outside; , A current limiting circuit 19 for limiting the current flowing from the outside or the current flowing into the coil of the motor 3 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a motor drive circuit suitable for, for example, a brushless motor.

[0002]

2. Description of the Related Art Conventionally, in a brushless motor driven by a so-called direct pulse width (PWM) control, a current flowing out of a motor driving circuit or flowing into a motor driving circuit is measured by using a detection resistor. Has been done.

As a method of detecting a current of the brushless motor, there are a detection method of integrating a voltage drop of a detection resistor by a CR filter and a detection method of detecting a voltage drop of a detection resistor by a peak value.

[0004]

However, these current detection methods have the following problems.

In the case of the current detection method in which the voltage drop of the detection resistor is integrated by the CR filter, the current value actually flowing in the motor coil and the detection value greatly differ depending on the PWM duty. The drive current does not correspond at a ratio of 1: 1. As a result, highly accurate motor control cannot be performed. Further, even if an attempt is made to protect the drive circuit from an instantaneous overcurrent, the current detection value is integrated by the filter, which is not possible.

In the case of the current detection method for detecting the voltage drop of the detection resistor by a peak value, the actual current supply capability of the power supply is problematic even if the motor is operated by using the power supply at its maximum. Since the average input current value cannot be grasped, the limiter operates with the instantaneous peak current, and it becomes impossible to perform sharp acceleration / deceleration. For example, even if there is a power supply capable of flowing 2 A (ampere) as an average current, if the current value becomes 2 A at the point where the PWM duty becomes 50%, the peak value is detected. In the current detection method, an external current is cut off at the point where the PWM duty is 50%, so that the current supply from the power supply is only 1 A or less on average. As a result, the torque of the motor is reduced to less than half.

Therefore, the present invention has been made in view of such a situation, and realizes highly accurate motor control.
In addition, it is possible to drive with the maximum use of the power supply capability, and to further enhance the protection capability of the drive circuit.
It is an object to provide a motor drive circuit.

[0008]

A motor driving circuit according to the present invention drives a motor by a pulse width modulation signal,
An approximate value calculating means for calculating a value approximating the current flowing through the coil, comprising a current detecting resistor for detecting a current flowing into or out of the coil of the motor; and driving the motor based on the approximate value. The above-mentioned problem is solved by having control means for controlling the above.

Further, the motor drive circuit of the present invention comprises an average value calculating means for calculating an average value of a current flowing from the outside,
The above-mentioned problem is solved by providing a current limiting means for limiting the current flowing from the outside to within a predetermined value based on the average value.

Further, the motor drive circuit according to the present invention comprises: an approximate value calculating means for calculating a value approximating a current flowing through a coil of the motor; a control means for controlling the driving of the motor based on the approximate value; Means calculating means for calculating the average value of the inflowing current, and current limiting means for limiting the current flowing from the outside or the current flowing into the coil of the motor to a predetermined value or less based on the average value or the approximate value. This solves the above-mentioned problem.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a basic configuration of a motor drive circuit 1 of a direct type PWM drive as an embodiment of a motor control circuit of the present invention.

In the motor drive circuit shown in FIG. 1, a control signal for controlling the rotation of the motor 3 is output from the control signal generator 2, and the control signal is transmitted to the forward / reverse control circuit 12 via the amplifier 11. It is sent to the absolute value circuit 13.

The forward / reverse control circuit 12 generates a forward / reverse control signal for controlling the rotation of the motor in either the forward direction or the reverse direction, and sends it to the logic synthesis circuit 14.

The absolute value circuit 13 generates an absolute value signal of the control signal and sends it to the PWM circuit 16 via the comparator 15.

The PWM circuit 16 generates a PWM drive signal (PWM drive timing signal) as shown in FIG. 2A based on an absolute value signal of a control signal via a comparator 15 described later.

The logic synthesizing circuit 14 converts a signal from the Hall element 4 as a position detecting means into U, V, W signals of the motor.
The output signal is distributed to the output circuit 18.

The output circuit 18 outputs the P signal from the PWM circuit 16.
The WM drive signal is distributed according to the distribution signal to drive the motor 3.

The resistor R2 is a detection resistor for detecting the value of the current flowing through the motor 3.

In general, the detection of the current flowing through the motor is performed for the purpose of controlling the motor output and the purpose of protecting the drive circuit or the power supply circuit, or both. In general, the current flowing through the motor is
A detection resistor is inserted between the power supply and the drive circuit, or between the drive circuit and the ground, and the current flowing through the detection resistor is converted into a voltage value for detection.

However, in the case of the direct PWM drive, since the motor is driven while performing voltage-current conversion, the current value input to the drive circuit and the current value flowing through the coil of the motor differ. Therefore, one of the input current value of the drive circuit and the current value flowing through the motor coil is detected, and the detected current value is used for both the motor output control and the protection of the drive circuit or the power supply circuit. If they do, their control and protection will be very inaccurate.

Therefore, in the motor drive circuit 1 according to the embodiment of the present invention, as shown in FIG. 1, in order to be able to detect the respective values of the input current value to the drive circuit 1 and the current value flowing through the motor coil. And a coil current detection circuit 30 and an average current detection circuit 31. The coil current detection circuit 30 is provided with a sample and hold circuit 17 for sampling and holding a voltage value appearing in the detection resistor R2 when the PWM is turned on. The circuit 31 is provided with a CR filter (averaging circuit) including a capacitor C1 and a resistor R1 for averaging the voltage value appearing at the detection resistor R2.

In the motor drive circuit 1 having the above-described configuration, the current flowing from the Vs terminal 6 passes through the motor coil of the motor 3 through the output circuit 18 and
It returns to the output circuit 18 and flows out to the ground (GND) through the detection resistor R2. At this time, the motor drive circuit 1
Performs direct PWM drive by the PWM drive signal shown in FIG. 2A, the current flowing in the motor coil has a waveform as shown in FIG. 2B and is generated in the detection resistor R2. The voltage appears as an intermittent waveform as shown in FIG.

Here, in the present embodiment, the output circuit 18
The input terminal of the sample-and-hold circuit 17 is connected between the input terminal and the detection resistor R2. The sample and hold circuit 17
Fetches the voltage value of the detection resistor R2 only when the PWM drive signal is on (ON) based on the voltage waveform of (c) of FIG. 2, and when the PWM drive signal is off (OFF), the above ON current It is made to hold the value. Therefore, the output waveform of the sample hold circuit 17 is as shown in FIG. That is, FIG.
2 is a waveform similar to the current waveform shown in FIG. 2B flowing through the motor coil.

Further, in this embodiment, a CR filter including a capacitor C3 and a resistor R3 is provided on the output terminal side of the sample and hold circuit 17, and the CR filter is provided.
The time constant of the filter is set according to the time constant of the motor coil. According to this CR filter, the charge held by the sample hold circuit 17 is discharged to change the output waveform of the server hold circuit 17 into the motor coil current waveform (FIG. 2) as shown in FIG.
(B)).

In the present embodiment, the output of the coil current detecting circuit 30 composed of the sample and hold circuit 17 and the CR filter including the capacitor C3 and the resistor R3 is supplied to the comparator 15. That is, in the motor drive circuit 1 of the present embodiment, the output signal of the coil current detection circuit 30 is fed back to the comparator 15, so that the current value flowing in the motor coil can be accurately grasped, and Motor control is possible.

FIG. 3 shows the sample hold circuit 17
5 shows a simple circuit example of the coil current detection circuit 30 including the CR filter. That is, the coil current detection circuit 30 shown in FIG. 3 includes the comparator 41 and the transistor Tr forming the sample-and-hold circuit 17, and the capacitor C3 and the resistor R3 forming the CR filter. FIG. 3 also shows the detection resistor R2.

In the configuration shown in FIG. 3, for example, the PWM drive signal is turned on (ON), and
When a voltage is applied to the detection resistor R2 via 0, the comparator 41 turns on the transistor Tr. As a result, while the PWM drive signal is on (ON), the current through the transistor Tr continues to flow to the terminal 42, and CR
Charge is accumulated in the capacitor C3 of the filter. On the other hand, for example, when the PWM drive signal is turned off (OFF),
The comparator 41 turns off the transistor Tr. As a result, the charge stored in the capacitor C3 of the CR filter is discharged, and the current flows to the terminal 42. By repeating the operation according to the ON / OFF of the PWM drive signal as described above, the output waveform of the terminal 42 becomes as shown in FIG.

In the motor drive circuit 1 of the present embodiment, the average current detection circuit 31 includes a capacitor C in addition to the detection resistor R2 for detecting the current flowing through the motor 3.
1 and a primary CR filter composed of a resistor R1. Therefore, the output of the average current detection circuit 31 is
A voltage waveform generated in the detection resistor R2 is integrated by the primary CR filter to be a waveform as shown in FIG.

Here, in the average current detecting circuit 31,
In order to integrate the voltage waveform generated in the detection resistor R2 by the primary CR filter, the larger the duty ratio of the PWM drive signal, the larger the detected value than the current value actually flowing through the motor coil. Value (input value to the current limiting circuit 19) becomes small.

However, since an external power supply for driving the motor is usually provided with a large-capacity output capacitor, it is necessary to limit the current to protect the power supply only by the current value flowing through the motor coil (= peak current value). Instead, the average current value flows into the drive circuit from the outside. Therefore, according to the present embodiment, the current limiting circuit 19 controls the on / off of the output circuit 18 based on the output of the average current detection circuit 31, so that the power supply can be protected. The motor drive using the maximum can be performed.

FIG. 4 shows a simple circuit example of the average current detecting circuit 31 and the current limiting circuit 19. That is, the circuit shown in FIG. 4 includes a detection resistor R2, a capacitor C1, and a resistor R1 which constitute the average current detection circuit 31.
It comprises a next CR filter, a comparator 50 and a reference voltage generation source 51 which constitute the power supply limiting circuit 19.

In the configuration of FIG. 4, for example, the PWM drive signal is turned on (ON), and the output circuit 18
0, a voltage is applied to the detection resistor R2 through the primary C.
An electric charge is accumulated in the capacitor C1 of the R filter, and the output side (terminal 52 side) of the comparator 50 outputs the voltage integrated value by the primary CR filter to the reference voltage generation source 5.
When the reference voltage value Vref exceeds the reference voltage value Vref, the signal goes to the H (high) level. On the other hand, for example, the PWM drive signal is off (OFF).
, The electric charge accumulated in the capacitor C1 is discharged, and the output side of the comparator 50 (terminal 52 side)
Becomes L (low) level when the voltage integral value of the primary CR filter falls below the reference voltage value Vref of the reference voltage generation source 51. That is, according to the configuration of FIG. 4, the output of the comparator 50 of the current limiting circuit 19 is at the H level or the L level according to the voltage integrated value of the primary CR filter.
Change to a level. H / L from the current limiting circuit 19
When the signal indicates the H level, the output circuit 18 is turned off,
When the H / L signal from the power supply limiting circuit 19 indicates the L level, the output circuit 18 is turned on.

Here, the current limiting circuit 19 as described above
Is performed based on a signal indicating a value approximately twice as large as that shown in FIG. 2 (f), for example, the motor coil has half the current if the same limiting current value is used. That is, the motor can output only half the torque. On the other hand, in order to protect the motor drive circuit 1 itself from overcurrent, the peak current flowing in the drive circuit 1 becomes a problem.
It becomes necessary to limit the current according to the value of the current flowing through the motor coil.

From the above, in the motor drive circuit 1 of the present embodiment, as shown by the broken line in FIG. 1, (e) in FIG. The output signal of the sample-and-hold circuit 17 as shown in FIG.
9 is supplied.

That is, the power supply limiting circuit 1 of the present embodiment
In No. 9, the external power supply is protected by the current limitation based on the output signal of the average current detection circuit 31 described above, and the protection of the motor drive circuit is realized by the current limitation based on the output signal of the sample and hold circuit 17. In other words, according to the power supply control circuit 19 of the present embodiment, the protection of the power supply and the protection of the drive circuit are made compatible by performing the double current limitation on the output circuit 18.

If only protection of the motor drive circuit 1 itself is required and protection of the external power supply is not required, the output signal of the sample hold circuit 17 is supplied to the current limiting circuit 19 as described above, The CR filter composed of the resistor R1 may be left unconnected.
Thus, the motor drive circuit 1 itself can be protected without providing a new configuration.

As described above, according to the motor drive circuit of the embodiment of the present invention, the current value flowing through the motor coil can be accurately grasped, so that the motor can be controlled with high accuracy, and the capability of the power supply can be maximized. Can be used to drive the motor,
Further, when the current limit is applied at the peak current value for protecting the drive circuit, the current limit can be applied twice as well as the current limit at the average current value.

[0039]

As apparent from the above description, in the motor drive circuit of the present invention, a value approximating the current flowing through the coil is calculated, and the driving of the motor is controlled based on the approximate value. Highly accurate motor control that accurately grasps the current value flowing through the motor coil can be realized.

Further, the motor drive circuit of the present invention calculates the average value of the current flowing from the outside and limits the current flowing from the outside to a predetermined value based on the average value, thereby protecting the power supply. It is possible to drive with the maximum power supply capability.

Further, the motor drive circuit of the present invention calculates a value approximating the current flowing through the coil of the motor, controls the driving of the motor based on the approximate value, and calculates the average value of the current flowing from the outside. By limiting the current flowing from the outside or the current flowing into the coil of the motor to within a predetermined value based on the average value or the approximate value, the accuracy of accurately grasping the current value flowing in the motor coil is improved. It is possible to realize high motor control, protect the power supply, drive with the maximum use of the power supply capability, and further enhance the protection capability of the drive circuit.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a basic configuration of a motor drive circuit according to an embodiment of the present invention.

FIG. 2 is a waveform chart showing waveforms at various parts of the motor drive circuit according to the embodiment.

FIG. 3 is a circuit diagram illustrating a simple configuration example of a coil current detection circuit including a sample and hold circuit and a CR filter of the motor drive circuit according to the present embodiment.

FIG. 4 is a circuit diagram illustrating a simple configuration example of an average current detection circuit and a current limiting circuit of the motor drive circuit according to the present embodiment.

[Explanation of symbols]

1 motor drive circuit, 2 control signal generator, 3 motor, 4 Hall element, 6 Vs terminal, 11 amplifier, 12 forward / reverse control circuit, 13 absolute value circuit,
14 logic synthesis circuit, 15 amplifier, 16P
WM circuit, 17 sample hold circuit, 18 output circuit, 19 current limit circuit, 30 coil current detection circuit, 31 average current detection circuit

Claims (6)

[Claims] 1. A motor drive circuit comprising a current detection resistor for driving a motor by a pulse width modulation signal and detecting a current flowing into or out of the motor coil, the current flowing in the motor coil. A motor drive circuit comprising: an approximate value calculating means for calculating a value approximating the above; and a control means for controlling driving of the motor based on the approximate value calculated by the approximate value calculating means. 2. The motor according to claim 1, further comprising current limiting means for limiting a current flowing into a coil of the motor to within a predetermined value based on the approximate value calculated by the approximate value calculating means. Drive circuit. 3. An average value calculating means for calculating an average value of the current flowing from the outside, and limiting the current flowing from the outside to within a predetermined value based on the average value calculated by the average value calculating means. 2. The motor drive circuit according to claim 1, further comprising current limiting means. 4. The method according to claim 1, wherein the current limiting means limits the current flowing into the coil of the motor within a predetermined value based on the approximate value calculated by the approximate value calculating means. Item 3. A motor drive circuit according to item 3. 5. A motor drive circuit having a current detection resistor for driving a motor by a pulse width modulation signal and detecting a current flowing into or out of the coil of the motor, comprising: An average value calculating means for calculating a value, and a current limiting means for limiting the current flowing from the outside to within a predetermined value based on the average value calculated by the average value calculating means. Drive circuit. 6. An approximation value calculating means for calculating a value approximating a current flowing through a coil of the motor, wherein the current limiting means calculates a value of the coil of the motor based on the approximation value calculated by the approximation value calculating means. 6. The motor drive circuit according to claim 5, wherein the current flowing into the motor is also limited to within a predetermined value.