JP2002010673A - Silent spin sine wave generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce acoustic noise by smoothing a rotation of a multi-phase DC motor. SOLUTION: Three waves (45, 46 and 47) for applying a driving voltage to each winding of the motor shall be generated in one combination. Each wave has a 360 deg. cycle and a first segment (43) having a 0 value within the range of 120 deg.. A second segment (50) follows to the first segment within the range of 60 deg., and a third segments (67, 68) follow thereto having two consecutive 'cap' shapes within the range of 120 deg.. Next to the third segment, a fourth segment (52) follows having a 'down slope' shape within the range of 60 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improved method and circuit for driving a DC brushless polyphase motor, such as a spindle motor, such as a hard disk drive, and more particularly, to reducing acoustic noise in this type of motor. Such motors are improved using at least reduced improvements in such driving methods and circuits and approximations of waveforms composed of approximately sine waveform segments, and in particular, using a drive voltage composed of a substantially linear approximation waveform that approximates such waveforms. The present invention relates to an improvement in a driving method and a circuit for driving.

[0002]

BACKGROUND OF THE INVENTION To operate a DC brushless multi-phase motor of the type to which the present invention relates, in order to drive the motor efficiently, the excitation current applied to the motor phases is generated by the individual phases. It is necessary to match with the back electromotive force (bemf). One of the best ways to achieve such matching is to adjust the phase and frequency of the commutation such that the back EMF of the undriven winding passes through a zero point approximately at the center of the commutation state. The use of a phase locked loop (PLL). This scheme works well when the shape of the rectified waveform includes regions that are not driven, such as the conventional six-state, +1, +1, 0, -1, -1, 0 sequence.

[0003]

Problems to be Solved by the Invention +1, +1, 0,-
Since the sequence of 1, -1, 0 transitions sharply between drive states, this sequence has many high frequency components. These conditions tend to excite mechanical resonance in the motor, resulting in undesirable acoustic noise. In addition, the three state changes of the step function of the undriven motor phase, along with the step function drive waveform itself, cause some torque ripple in the motor. As a result of the occurrence of torque ripples, the rotation of the motor becomes uneven, that is, a jerky rotation occurs, which also excites the resonance of the motor and further generates undesirable acoustic noise.

Therefore, when it is desired to reduce acoustic noise, a sine-wave excitation signal is more appropriate than a six-state sequence. If the motor driver consists of a sine waveform current source, the same voltage detection P
LL can be used. However, if the duty cycle of the driver changes in a sign-like manner, the driver I
To minimize power consumption at C, the motor driver excitation is pulse width modulated (PWM). This allows for lower cost packaging and overall savings in system cost. However, it has been difficult in the past to generate a current having a pure sine waveform, especially when the current is relatively large and it is desirable to use a PWM scheme.

In US patent application Ser. No. 09 / 300,754, described below, after canceling the initial baseline, the concatenation of 120 ° of zero, followed by 120 ° of “up hook” and 120 ° of “down hook” is described. The drive waveform is composed of the segments that have been generated, and the up-hook waveform and the down-hook waveform have been generated by two MDACs. MDAC operation has certain problems that make it difficult to generate the desired drive waveform. In particular, circuit compromises must be made to ensure proper operation of the waveforms in a multi-phase DC motor environment.

Further, in order to form a self-formed waveform segment from a combination of sine waveform segments, M
To use a DAC, the structure and operation of a special MDAC must be considered. In order to approximate a combination of sine waveform segments, if the drive waveform is designed to be composed of linear waveform segments, such an MDA
Realization and operation of C are greatly facilitated.

Accordingly, there is a need for a method of operating a disk drive that reduces or eliminates noise associated with the disk drive and the operating disk drive. There is a further need for a disk drive and method that uses drive signals generated from sine waveform signal segments that can be easily approximated and generated by concatenated linear signal segments.

In view of the above, it is therefore an object of the present invention to provide an improved disk drive and a method of operating a disk drive that reduces or eliminates noise associated with the operating disk drive.

Yet another object of the present invention is to use a segment having a substantially continuous concatenated waveform composed of segments of a sine waveform signal, or a number of drive signals approximating a segment of a sine waveform signal. Disc drive and method are provided.

[0010] These and other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the invention when read in conjunction with the accompanying drawings and claims.

[0011]

Accordingly, in accordance with a broad aspect of the present invention, there is provided a method for operating a three-phase DC motor. The method includes generating a set of three waveforms to provide a drive current to each winding of the motor. Each waveform has a period of 360 ° and 120
Between 0 ° and a first segment (portion) having a value of 0, followed by a first segment between 60 ° followed by a second segment having an “up slope” shape, A second segment is followed by a third segment having two successive “cap” shapes between 120 ° followed by a “down slope” between 60 ° following the third segment. A fourth segment having a shape follows. Each waveform in the set is 12
Offset by 0 °, these waveforms are applied to the respective windings of the motor. Each of the segments is a VMAG
(Sin (ωt−φ) −min ｛sin (ωt), si
n (ωt−120 °), sin (ωt−240 °)｝
(Where VMAG is the maximum amplitude of each waveform, ωt is the phase angle of the waveform, and φ is the initial phase angle). However, in the preferred embodiment, these waveform segments have at least one linear waveform. Preferably, the corrugated segments have two straight sections and a break in the middle of the straight sections.

According to another broad aspect of the present invention, there is provided a method for reducing acoustic noise generated when operating a polyphase DC motor. The method generates a set of n waveforms to apply a drive voltage to each winding of the motor. Here, n is the number of phases of the polyphase DC motor, each waveform has a cycle of 360 °, and (360 /
n) between 0 °, a first segment having a value of 0,
The first segment is followed by (360 / 2n) ° followed by a second segment having a “rising slope” shape, and the second segment is followed by (360 / n) ° and two consecutive “360 / n” degrees. Followed by a third segment having a “cap” shape,
The segment is followed by a fourth segment having a “down slope” shape between (360 / 2n) °. Each waveform in the set is offset by (360 / n) ° from each other.
These waveforms are applied to respective windings of the motor to energize the motor. These waveforms can be pulse width modulated before being applied to the driver.

Each of the segments is a VMAG (si
n (ωt−φ) −min ｛sin (ωt−0 × 360 /
n) °, sin (ωt−1 × 360 / n) °,. . . .
sin (ωt− (n−1) × 360 / n) °) (where VMAG is the peak amplitude of each waveform, n is the number of motor phases, ωt is the phase angle of the waveform, φ Is the initial phase angle). These waveform segments are
It may have at least one linear waveform, in particular two linear sections, and have a break in the middle of these linear sections.

According to yet another broad aspect of the invention, n
A circuit is provided for operating a phase DC motor.
This circuit has a driver for applying n signal waveforms to the motor, and provides a source of drive signal waveforms. Each of the drive signal waveforms has a period of 360 °,
Between (360 / n) ° has a first segment with a value of 0, followed by a second segment having a “rising slope” shape between (360 / 2n) °. , After the second segment, between (360 / n) °, 2
A third segment having two consecutive “cap” shapes follows, followed by a fourth segment having a “down-tilt” shape between (360 / 2n) °. Each waveform in the set is (360 / n) °
It is out of alignment. These drive signal waveforms may have substantially linear segments, in particular two linear portions, and have a break in the middle of these linear portions. Before applying the drive signal waveform to the driver, a circuit for pulse width modulation of the drive signal waveform can be provided.

Each of the segments is a VMAG (si
n (ωt−φ) −min ｛sin (ωt−0 × 360 /
n) °, sin (ωt-1 × 360 / n)
°,. . . . . sin (ωt− (n−1) × 360 /
n) °｝) (where VMAG is the peak amplitude of each waveform, ωt is the phase angle of the waveform, and φ is the initial phase angle).

According to still another aspect of the present invention, there is provided a disk drive product having a DC brushless, Hall-less type three-phase motor for rotating media containing data. . The product includes three driver circuits for applying drive signals to a selected respective set of windings in the motor, and three sources of motor drive voltage waveforms provide the drive signals. Each waveform has a 360 ° period and the first
The segment has a value of 0 between 120 °, the second segment has a “climb” shape between 60 °,
The third segment has two successive “cap” shapes between 120 °, and the fourth segment has a “down-tilt” shape between 60 °. Each waveform in the set is offset from each other by 120 °. Each of the drive signal waveforms can be formed from substantially straight segments, and in particular can be formed from two substantially straight portions, with a break in the middle of the portions. These segments are VMAG (si
n (ωt−φ) −min ｛sin (ωt−0 × 360 /
n) °, sin (ωt-1 × 360 / n)
°,. . . . . sin (ωt− (n−1) × 360 /
n) °｝) (where VMAG is the peak amplitude of each waveform, ωt is the phase angle of the waveform, and φ is the initial phase angle).

The present invention will be described with reference to the accompanying drawings.

In the various accompanying drawings, like reference numerals are used to indicate identical or similar parts.

[0019]

According to a preferred embodiment of the present invention, the drive waveform applied to the windings of the motor to be driven is:
As described in U.S. Patent Application No. 09 / 300,754,
Derived from the sine waveform. This motor may be of the type described above, in particular a polyphase DC motor of the type described in US patent application Ser. No. 09 / 300,754. In the embodiment shown, this motor is preferably a three-phase DC motor.

In the illustrated embodiment, three signals are shown. The signals are 120 ° out of phase with each other to drive each phase of the motor. The motor winding drives each node with a pure sine waveform, as two of the nodes of the three coil windings of the Y-shaped coil structure are typically driven such that one is used as a sink. No need. It is sufficient if the voltage difference between the two driven nodes is approximately a sine waveform. FIG. 1 shows three consecutive drive waveforms 4 according to a preferred embodiment of the present invention.
Graphs showing 5, 46 and 47 are shown. Each of the waveforms 45, 46, 47 is applied to each interchangeably determined pair of input terminals of the motor to be driven.

To form the drive waveforms 45, 46 and 47, the value of the sine waveform having the instantaneous minimum of one set of sine waveforms that are 120 ° out of phase with each other is subtracted from the other waveforms. This results in the set of waveforms shown in FIG. 1, which are similar to the waveforms described in US patent application Ser. No. 09 / 300,754. Therefore, each of the segments is
(Sin (ωt−φ) −min ｛sin (ωt−0 × 3
60 / n) °, sin (ωt-1 × 360 / n)
°,... Sin (ωt− (n−1) × 360 / n)
°｝). Here, VMAG is the maximum amplitude of each waveform, n is the number of motor phases, ωt is the phase angle of the waveform, and φ is the initial phase angle. Each of the corrugations has an uphook portion 40 and a downhook portion 42. Thus, the drive waveform segment occurs in the same manner as the sine waveform segment, but is not actually a sine waveform segment. Further, since each motor phase is in three states during 120 ° of the commutation cycle, each waveform is 120 °.
Has a segment 43 that is zero between the two.

FIG. 2 shows a portion 10 of a circuit for providing drive signals to a polyphase DC motor according to a preferred embodiment of the present invention. This circuit includes a “cap” generating MDAC 12 and a “tilt” generating MD which will be described in detail below.
AC14. 1 for every PWM CLK cycle
Times, "cap" MDAC12 and "tilt" MDAC
14 are updated and these MDACs are
Generates a shaping signal selectable by the multiplexer 16 for application to The DC motor 18 rotates a spindle of a disk 19 used in a mass data storage device, for example. If desired, the output signals of MDACs 12 and 14 may be controlled by PWM modulators 36 and 3 as shown to control the power applied to motor 18.
8 allows pulse width modulation in a known manner.

MDAC 14 is a segment of a sine wave,
More specifically, a signal having a “slope” waveform that can be generated to approximate a 60 ° segment of a sine wave is generated at its output. The MDAC 14 determines whether the ascending waveform substantially follows the “rising slope” segment 50 shown in FIG.
The descending waveform is the “down slope” segment 52 shown in FIG.
Can be generated in ascending or descending order to substantially follow. Assuming that the waveform period is 360 °, the “up slope” segment 50 or the “down slope”
The segment 52 has a length of (360 / 2n) °. Here, n is the number of phases of the motor.

The waveform generated by the "slope" MDAC 14 is preferably a linear waveform, shown for example as waveform 60 in FIG. Waveform 6 as shown
The overall shape of each half of the "0" is the "up slope" segment 50 or the "down slope" segment 52 shown in FIG.
A break point 62 is included substantially halfway between the top and bottom of the waveform so that the curve is approximately the same as One of the benefits obtained from using a linear waveform in the operation of MDAC 14
One is that a linear waveform can be easily generated by providing a linear counter that selectively counts up or down at a predetermined rate.

If desired, MDAC 14 may include scaling circuitry to determine the overall amplitude of generated waveform 60. This scaling circuit
For example, a plurality of current generators, individually addressable and selectable to generate the bias current needed to generate the desired waveform, can be included. Further, the waveform 60 can be generated by subtracting the count value from a predetermined bias value.

Similarly, the "cap" MDAC 12 can be configured to generate two consecutive "cap waveforms" 65 and 66, as shown in FIG. Each of the "cap" waveforms 65 and 66 is formed by a linear upcount up to a break 68 followed by a linear downcount up to the first start value. The resulting waveforms 65 and 66 correspond to waveforms 67 and 68 in FIG. Again, by using a linear waveform technique using, for example, a linear up counter and a down counter, the sine waveform segment 6
7 and 68 can be easily approximated. Furthermore, a scaling circuit can be provided in the MDAC 12 so that the entire scale of the waveform can be determined by, for example, an addressing circuit. If the period of the waveform is 360 °, each of the cap segments can be (360 / 2n) ° long for a total length of (360 / n) ° (n
Is the number of motor phases).

The output signals from the respective MDACs 12 and 14 are selectively applied by a multiplexer circuit 16 to motor control lines 30-32 for application to a three-phase motor 18. The multiplexer circuit 16 is controlled by a multiplexer controller 21, and the multiplexer controller 21 receives a clock pulse from a clock generator 22 divided by a frequency dividing circuit 24. The multiplexer controller 21 can be an address circuit that repeatedly applies an address to the multiplexer 16 so as to generate, for example, the repetitive waveforms 45 to 47 shown in FIG.

If desired, as shown, the MDA
The output signals from C12 and C14 may be pulse width modulated by, for example, respective PWM modulators 36 and 38 as shown. This pulse width modulation can be performed by a known method. Generally, a triangular wave is used as a passing waveform for allowing a modulated signal to pass only when the value becomes greater than the instantaneous triangular waveform value. One of the advantages obtained by using the circuit of FIG. 2 is as follows. That is, the MDAC circuits 12 and 14 can use the common clock signal derived from the clock generator 22 to generate the linear waveform segment as described above, and control the timing of the pulse width modulators 36 and 38. Since the same clock signal can be used to adjust the timing between the pulse width modulation and the respective waveforms generated by the MDAC, the delay and discontinuity of the signal applied to the three-phase motor 18 can be easily adjusted. Can be prevented.

While the present invention has been described and illustrated in some detail, this disclosure is merely illustrative.
It will be understood by those skilled in the art that various combinations and arrangements of components can be made without departing from the spirit and scope of the invention as set forth in the appended claims.

In view of the above description, the following items are further disclosed. (1) generating a set of three waveforms and applying a drive voltage to each winding of the motor, each waveform having a 360 ° period and a value of 0 between 120 °; With a first segment having the following:
, Followed by a second segment having an “up-tilt” shape, followed by a second segment between 120 ° followed by a third segment having two consecutive “cap” shapes;
The third segment is followed by a fourth segment having a “downslope” shape between 60 °, wherein the respective waveforms of the set are offset by 120 ° from each other; Applying a waveform to operate the multi-phase DC motor.

(2) The method according to claim 1, further comprising, before applying the drive voltage to the motor winding, pulse width modulating the drive voltage. (3) Each of the segments is VMAG (sin (ω
t−φ) −min ｛sin (ωt), sin (ωt−1)
20 °), sin (ωt−240 °)｝ (where VMA
G is the maximum amplitude of each waveform, ωt is the phase angle of the waveform, and φ is the initial phase angle). 4. The method of claim 1, wherein each of said waveform segments comprises at least one linear waveform. (5) The method according to (4), wherein each of the waveform segments has two linear portions, and has a break point at an intermediate portion between the linear portions.

(6) A method for reducing acoustic noise in the operation of a polyphase DC motor, comprising the step of generating a set of n waveforms for applying a drive voltage to each winding of the motor. Wherein n is the number of phases of the polyphase DC motor, each waveform having a 360 ° period,
Between (360 / n) ° has a first segment with a value of 0, followed by a second segment having a “rising slope” shape between (360 / 2n) °. , After the second segment, between (360 / n) °, 2
A third segment having two consecutive "cap" shapes, followed by a fourth segment having a "falling down" shape between (360 / 2n) °,
Each waveform of the set is offset by (360 / n) ° from each other,
Applying the waveform to the respective windings of the motor.

(7) The method according to the above (6), further comprising pulse width modulating the drive voltage before applying the drive voltage to the motor winding. (8) Each of the segments is VMAG (sin
(Ωt−φ) −min ｛sin (ωt−0 × 360 /
n) °, sin (ωt−1 × 360 / n) °,. . . .
sin (ωt− (n−1) × 360 / n) °｝) (where VMAG is the maximum amplitude of each waveform, n is the number of phases of the motor, ωt is the phase angle of the waveform, 7. The method of claim 6, wherein φ is the initial phase angle. 9. The method of claim 6, wherein each of said waveform segments comprises at least one linear waveform. (10) The method according to (9), wherein each of the waveform segments has two linear portions, and has a break point at an intermediate portion between the linear portions.

(11) A driver for applying n drive signal waveforms to the motor, and a source of the drive signal waveforms, each waveform having a period of 360 °, (36)
0 / n) °, having a first segment with a value of 0, followed by a first segment between (360 / 2n) °,
Followed by a second segment having an “up-tilt” shape,
The segment is followed by (360 / n) ° a third segment having two consecutive “cap” shapes,
A third segment is followed by a (360 / 2n) ° fourth segment having a “downslope” shape, where each waveform in the set is offset by (360 / n) ° from each other, n
Circuit for operating a phase DC motor.

(12) The source of the drive signal waveform is:
12. The circuit of claim 11, wherein the circuit is a first MDAC for generating the "rising slope" and "down slope" waveforms and a second MDAC for generating the "cap" shaped waveform. (13) The circuit according to (12), wherein the drive signal waveform includes a substantially linear segment. (14) each of the waveforms has two linear portions;
14. The circuit of claim 13 having a break in the middle of these parts. The circuit of claim 11, further comprising a multiplexer connected to receive the output signal of the MDAC, wherein the multiplexer is operative to selectively apply the output signal of the MDAC to the driver. . (16) Before applying a drive signal to the driver,
12. The circuit according to claim 11, further comprising a circuit for pulse width modulating a waveform of the drive signal. (17) The circuit according to (11), wherein n is 3. (18) Each of the segments is VMAG (sin
(Ωt−φ) −min ｛sin (ωt−0 × 360 /
n) °, sin (ωt−1 × 360 / n) °,. . . .
sin (ωt− (n−1) × 360 / n) °) (where VMAG is the maximum amplitude of each waveform, ωt is the phase angle of the waveform, and φ is the initial phase angle). ing,
12. The method according to claim 11.

(19) Three driver circuits for applying drive signals to selected sets of windings in the motor, and three motor drive voltage waveform sources for applying the drive signals And each waveform is 36
A first segment having a period of 0 ° and having a value of 0 between 120 °, followed by a second segment having a “rising slope” shape between 60 ° and the first segment. ,
A second segment is followed by a third segment having two successive “cap” shapes, between 120 °,
The segment is followed by a fourth segment having a “down slope” shape between 60 ° and each waveform in the set is 1
DC brushless, Hall-less effect (Hall-le) for rotating media containing data that is shifted by 20 °
ss) A disk drive product having a three-phase motor. (20) The driver circuit according to (19), wherein each of the driver circuits includes a pair of FETs, the FETs being connected together at a drive signal node, and further being connected in series between a voltage power supply and a reference potential. Disk drive products. 21. The disk drive product of claim 19, further comprising a multiplexer connected to receive the motor drive voltage waveform and selectively apply the motor drive voltage waveform to the driver circuit. (22) The disk drive product according to (19), further comprising a circuit for pulse width modulating the motor drive voltage waveform before applying the motor drive voltage to the driver circuit. (23) The disk drive product according to (19), wherein the drive signal voltage waveform includes a substantially linear segment. (24) each of the waveforms has two linear portions;
24. The disk drive product of claim 23, wherein the product has a break in the middle of these portions. (25) Each of the segments is VMAG (sin
(Ωt−φ) −min ｛sin (ωt−0 × 360 /
n) °, sin (ωt−1 × 360 / n) °,. . . .
sin (ωt− (n−1) × 360 / n) °) (where VMAG is the maximum amplitude of each waveform, ωt is the phase angle of the waveform, and φ is the initial phase angle). ing,
Item 25. The disk drive product according to item 24. (26) The disk drive product according to item 19, wherein the medium containing the data is a magnetic medium of a hard disk drive.

(27) A method and circuit for operating a polyphase DC motor that applies a drive voltage to a winding in a predetermined phase is described. A zero-cross point of the current flowing through each winding of the motor is detected, and the phase of the drive voltage is adjusted so as to have a zero-cross point almost simultaneously with the detected zero-cross point of the current flowing through each winding of the motor.
The method includes generating a set of three waveforms (45, 46, 47) for applying a drive voltage to each winding of the motor, each waveform having a 360 ° period, 12
Between 0 °, there is a first segment (43) with a value of 0, followed by a first segment between 60 ° with a second segment (50) having a “rising slope” shape, and Followed by a third segment (67, 68) having two consecutive "cap" shapes between 120 ° and a fourth segment having a “down-tilt” shape between 60 ° following the third segment.
A segment (52) follows. The waveforms in the set are 120 ° apart from each other, resulting in reduced acoustic noise of the motor.

REFERENCE TO PRIORITY Priority Application This application claims the benefit of US Provisional Patent Application No. 60 / 083,156, filed Apr. 27, 1998.
Pending US Patent Application No. 09, filed April 26, 9
/ 300,754 is a continuation-in-part application and 1999 November
US Patent Application Serial No. 09 / 448,5, filed on March 23
This is a continuation-in-part application of No. 71. All of the above U.S. patent applications are incorporated herein by reference. The application is 2000
It also claims priority from US Provisional Patent Application No. 60 / 203,129, filed May 8, 2010, which is also incorporated by reference.

[Brief description of the drawings]

FIG. 1 shows an ideal drive signal waveform to be applied to a three-phase DC motor.

FIG. 2 is a block diagram of a portion of a circuit for providing a drive signal to a polyphase DC motor according to a preferred embodiment of the present invention.

FIG. 3 illustrates one of the MDAC circuits of FIG. 2 in accordance with a preferred embodiment of the present invention to approximate the ideal waveform of FIG.
3 shows a “rising slope” waveform segment generated at two outputs.

FIG. 4 shows a "cap" waveform segment generated at the output of another circuit of the MDAC circuit of FIG. 1 to approximate the ideal waveform of FIG. 1, according to a preferred embodiment of the present invention.

[Explanation of symbols]

 12 Cap waveform MDAC 14 “Slope” MDAC 16 Multiplexer 18 DC motor 19 Disk 21 Multiplexer controller 36, 38 PWM modulator 45, 46, 47 Drive waveform

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Burt White United States of America California, Irvine, Cedar Ridge 5F term (reference) 5H560 BB04 DC01 EC05 GG04 JJ13 RR01 TT11 XA12

Claims (2)

[Claims] 1. A method for generating a set of three waveforms and applying a drive voltage to respective windings of a motor, wherein each waveform has a period of 360 ° and a 0 ° between 120 °. A first segment having a value of ???, followed by a second segment having an "up-tilt" shape between 60 [deg.] Followed by a second segment between 120 [deg.] And then 120 [deg.] A third segment having a continuous “cap” shape follows, followed by a third segment having a “downhill” shape between 60 ° followed by a fourth segment having a “downslope” shape, wherein each waveform in the set is 120 ° relative to each other. A method for operating a multi-phase DC motor, comprising: offset; and applying the waveform to the respective windings of the motor. 2. A driver for applying n drive signal waveforms to a motor, and a source of the drive signal waveforms, wherein each of the waveforms is 360
And a first segment having a value of 0 between (360 / n) °, followed by (3
60 / 2n) °, the second having an “ascending slope” shape
Segment followed by a second segment (360 /
n) ° followed by a third segment with two consecutive “cap” shapes, followed by (36)
0 / 2n) °, followed by a fourth segment having a “downslope” shape, and each waveform in the set is (36
A circuit for operating an n-phase DC motor that is offset by 0 / n) °.