Abstract: A data storage device that can perform a track following process even when vibrations are produced by a wide range of frequencies.

Abstract: In a flexible disk drive for driving a flexible disk (40) inserted in the flexible disk drive, when a power supply is turned on (step S1) and when the flexible disk drive is not inserted in the flexible disk drive (N of a step S7, N of a step S12), a seek operation is inhibited and a track 00 signal (TKO) is supplied to a host system just as if the flexible disk drive normally operate (step S8, step S14).

Abstract: A rotational recording apparatus that comprises a shock sensor and that adaptively processes the output of the shock sensor to obtain a feed forward signal, so as to implement a stable operation within a practical range.

Abstract: Apparatus and method for compensating for position signal distortion during a disc drive seek. A disc drive has first and second data recording surfaces on which tracks are defined, a moveable actuator which supports first and second magneto-resistive heads, and a servo circuit which applies current to an actuator motor to position the heads. During a seek in which the first head is moved from an initial track to a first destination track, upon loss of transduced servo data from the first data recording surface indicative of radial position of the head, the servo circuit switches from the first head to the second head and applies current to the actuator motor to move the second head to a known radial position with respect to the first destination track while transducing servo data from the second data recording surface. The servo circuit subsequently switches back to the first head to position the first head over the first destination track.

Abstract: A magnetic storage medium is configured to store data along tracks on a disk-shaped storage medium. A distance between the tracks adjacent to each other in a radius direction of the storage medium is different depending on each position in a radius direction of the storage medium.

Abstract: In a magnetic disk drive that performs the seek operation of a magnetic head by a VCM, a characteristic that is excellent in fault tolerance that will not generate a fault in severe environment, such as a high temperature and the issue of high frequency command without requiring a special device and special operation and without deteriorating access performance.

Abstract: A new synchronous Partial Response Maximum Likelihood (PRML) servo is provided for a high track-per-inch disk-drive system. To increase the data capacity in hard disk drives (HDD), one can shorten the servo format and/or increase the track density. The new servo system has circuits that allow a high-performance and accurate system for positioning the read-write heads. The major circuits include burst demodulation, Viterbi detection, timing synchronization, and spin-up search. A highly linear discrete-fourier-transform (DFT) burst-demodulation circuit can demodulate high-density and low-signal-to-noise-ratio (SNR) position bursts. The Viterbi detection circuit includes a sync-mark detector and a Viterbi detector that are matched to at least two sets of Gray code ( e.g., ¼ rate and {fraction (4/12)} rate) and pruned accordingly. The timing synchronization circuit includes phase restart and interpolating timing recovery (ITR) circuits to implement a fully digital timing recovery.

Abstract: An attenuating filter for the servo control processor of a disc drive data storage device. The filter is constructed by determining the peak resonance in the structure frequency response above a preselected magnitude and computing a digital notch filter to attenuate that peak resonance. The notch filter domain is then summed with the structure frequency response to derive a modified structure frequency response. The modified structure frequency response is substituted for the unfiltered structure frequency response and again the peak resonance in the modified structure frequency response above a preselected magnitude is determined and a notch filter is computed as necessary. This process of summing the structure frequency response with the latest computed notch filter domain to derive a modified structure frequency response continues until the peak resonance of the latest modified structure frequency response is less than the preselected magnitude.

Abstract: It is an object of the present invention to provide a magnetic disk apparatus capable of recording a servo signal onto the surface of a magnetic disk with a high degree of reliability and a high degree of efficiency without using an external write apparatus and capable of recording a predetermined servo signal onto the surface of a magnetic disk even if dimensional variations of a recording/reproducing device of a head exist.

Abstract: A disk drive is provided which uses a disk having a maximal limit cylinder group formed based on an initially recorded servo data before being assembled in a drive body. A CPU sets an actually usable data recording area on the disk by seeking the head in a radial direction over the disk. Further, the CPU allows the generation of a translation table for obtaining a correspondence between inherent physical cylinder address information of an effective cylinder group contained in the set data recording area and logical cylinder address information set to identify the effective cylinder group and allows the translation table to be stored in a memory. The CPU refers to the translation table when, in response to an access request from a host system, control is made to position a head to a target position, and finds-physical cylinder address information corresponding to the target cylinder.

Abstract: This invention intends to provide a storage unit capable of improving data transmission efficiency and reducing a seek time. The storage unit of this invention comprises a read/write head for carrying out read/write with respect to a recording medium, a VCM for moving the read/write head during seek operation, and a seek command executing section for outputting a VCM voltage when a seek start permission signal is inputted from a seek timing issuing section. The seek timing issuing section outputs a seek start permission signal in order to start the seek operation to the seek command executing section at a timing at which the read/write operation ends.

Abstract: A detector recovers servo data from a servo signal generated by a read-write head, and determines the head-connection polarity from the recovered servo data. Such a detector allows a servo circuit to compensate for a reversed-connected read-write head, and thus allows a manufacturer to forego time-consuming and costly testing to determine whether the head is correctly connected to the servo circuit.

Abstract: A magnetic disk drive has a low power consumption state in which the spindle motor is stopped for reducing the average power consumption when no read or write commands have been received. When a read or write command is received, the spindle motor is started. The time it takes to complete a read command is shorter than that for a write command as measured from the receipt of the read command or write command with the spindle motor stopped in the low power consumption state.

Abstract: Methods and apparatus for processing a seek request on a disk drive apparatus having a disk drive head is disclosed. The seek request is processed. During the seek request, the disk drive head is traversed across an actual distance. At least one expected seek time associated with the actual distance is obtained from a set of seek time data. One or more measurements are performed on the disk drive apparatus to obtain an update value. At least one expected seek time is then updated such that at least part of the update value is included in the at least one expected seek time.

Abstract: A power driver for driving a signal on a load using voltage-mode driver. A system processor generates commands indicating a programmed drive signal desired from the voltage-mode driver. A VBEMF compensator determines a compensated command to compensate for the back electromotive force voltage produced by the load. The compensated commands are coupled to the voltage-mode driver, such that the voltage-mode driver generates a voltage output based upon the compensated command.

Abstract: A new technique incorporates a 1/4-rate Hard Disk Drive (HDD) servo-data encoding into a Partial Response Maximum Likelihood (PRML) read channel. The limitation of the HDD servo-track writer is the maximum frequency associated with writing the servo data while maintaining a level of data alignment between the data in the adjacent tracks (coherency). The 1/4 code allows the servo data to be written at the maximum coherency bandwidth. Specifically, the data is read back (or sampled) at twice the write frequency. This increases the data redundancy while also increasing the data density and the disk storage capacity. The 1/4 coding can also be applied to conventional HDD dibit coding. Specifically, the 1/4-coding scheme reads each dibit-coded servo-data transition 01 as 0011, and reads each non-transition 00 (or 0) as 0000. The 1/4 coding and its matched Viterbi detector can also increase the data detection in comparison to conventional peak-detection schemes.

Abstract: Disk drive access times are reduced by including at least one cancellation impulse in a voice coil motor input signal to effectively cancel oscillations caused by natural resonances in an actuator assembly during a seek operation. Each cancellation impulse has an amplitude and application time that is tailored for optimal cancellation of oscillations. The amplitude and application time are calculated based upon known or estimated characteristics of the natural resonance within the actuator assembly.

Abstract: A servo circuit includes a servo channel and a processor. The servo channel recovers servo data from servo wedges that identify respective data sectors on a data-storage disk. On spin up of the disk, the processor detects a spin-up wedge associated with one of the servo wedges and then detects the servo wedge. Once the servo wedge is detected, a head-position circuit can read the location data from the servo wedge to determine an initial position of the read-write head. By detecting a both a spin-up wedge and a servo wedge to determine an initial head position on disk spin up, such a servo circuit often allows one to increase the disk's storage capacity by reducing the lengths of the spin-up wedges.

Abstract: An actuator driving method and an actuator driving device for PWM-driving an actuator of a storage disk device are disclosed. This method and device prevent a servo signal from being overlapped with switching noises. The storage disk device includes a head for reading information from a storage disk, a PWM driver for generating a drive current having a pulse width corresponding to a current indication value, a linear driver for generating a drive current of which a magnitude corresponds to the current indication value, an actuator, driven by the drive current, for moving the head, and a control circuit for generating the current indication value for positioning the head from the servo information read by the head from the storage disk. The driving method includes a step of PWM-driving the actuator by the PWM driver, and a step of effecting a switchover from the PWM drive to a linear drive by the linear driver during a period for which the control circuit reads the servo information.

Abstract: A method and system for servo error integration in read-channel equalization are described. In the present invention servo error is integrated into an equalizer. Also described in the present invention are methods and systems for determining the servo error.

Abstract: A magnetic recording system is provided having a write head employing a combination of magnetic write field gradient and thermal gradient to write data on a ‘thermal spring’ magnetic recording media. The write head comprises a magnetic element using a write current to induce a magnetic write field at the magnetic media and a thermal element using a very small aperture laser to heat a portion of the media. The thermal spring magnetic media comprises comprises first and second stacks providing two exchange coupled ferromagnetic layers having different Curie temperatures. The first stack has a high magneto-crystalline anisotropy, a relatively low saturation magnetization and a low Curie temperature. The second stack has a relatively low magneto-crystalline anisotropy, a high saturation magnetization and a high Curie temperature.

Abstract: A magnetic disk drive has a low power consumption state in which the spindle motor is stopped for reducing the average power consumption when no read or write commands have been received. When a read or write command is received, the spindle motor is started. The time it takes to complete a read command is shorter than that for a write command as measured from the receipt of the read command or write command with the spindle motor stopped in the low power consumption state.

Abstract: A method of manufacturing a disk drive (10) including determining and implementing skew values for each head (12a-12d) of the disk drive (10) during a production test phase is provided herein. The method for each head (12a-12d) includes initiating a head switch test series, measuring a head switch time, computing an average head switch time, computing a standard deviation of the head switch times, and computing a head skew based on the average and the standard deviation of the head switch times. The method for each head (12a-12d) further includes initiating a single-cylinder seek test, measuring a single-cylinder seek time, computing an average single-cylinder seek time, computing a standard deviation of the single-cylinder seek times, and computing a cylinder skew based on the average and the standard deviation of the single cylinder seek times.

Abstract: A disk drive system corrects run-out errors without substantial PES transients and without significant response time. The disk drive system includes a servo compensation system coupled to a read/write head. The servo compensation system is adapted to generate a run-out correction waveform for a track in a disk. The run-out correction waveform includes one or more sinusoidal component waveforms, each of which is defined by a phase and an amplitude. The method includes measuring an amplitude and a phase of one or more sinusoidal component waveforms for a set of specified tracks in a disk. The method also includes determining a phase and an amplitude of one or more sinusoidal component waveforms for a destination track based on a measured amplitude and a measured phase of the one or more measured sinusoidal component waveforms. The sinusoidal component waveforms for the destination track are adapted to substantially correct a run-out error in the destination track.

Abstract: In a magnetic disk storage apparatus, when a drive current of the voice coil motor is small, the head drive control means executes the linear drive mode under which the voice coil motor is driven in a linear control manner, whereas when the drive current is large, the head drive control means executes the pulse drive mode under which the voice coil motor is driven in a pulse width control manner. Both modes are carried out by employing a commonly-used output amplifier that is arranged as a push-pull type output circuit made of both a push-driving output transistor and a pull-driving output transistor. An operation mode of this output amplifier is set to an AB-class operation during the linear drive mode, whereas the operation mode of this output amplifier is set to a B-class operation during the pulse drive mode.

Abstract: A disk drive includes at least one disk having a disk surface and at least one transducer head for writing and/or reading data from the disk surface. The disk drive performs a power-saving idle operation including reducing a rotational speed of the disk, and continuously moving the transducer head at varying radial velocity components relative to the disk surface in a repeating sweeping pattern between a selected inner disk diameter and a selected outer disk diameter. The radial velocity components are varied as a function of the transducer head's radial position in relation to the disk surface, such as with a radial velocity idle sweep profile representing a relationship between the radial velocity component of the transducer head and its radial location relative to the disk surface that optimizes head-disk interaction (HDI) when the disk is rotating at a given reduced rotational speed.

Abstract: A disk drive capable of controlling two or more high-response small-stroke precise-movement actuators and a low-response large-stroke rough-movement actuator to be operated in cooperation with each other so that two or more heads can be fast and precisely positioned at a time by those actuators. The disk drive includes a rough-movement actuator having a stroke enough to cover all disk, a first precise-movement actuator having a small stroke, and a second precise-movement actuator having a small stroke, wherein a head is positioned at a track on a disk surface by the first precise-movement actuator, at the same time a head is positioned at a track on a second disk surface by the second precise-movement actuator, and the rough-movement actuator is operated to follow and to be brought to a center position between the located heads.

Abstract: A disk drive recording apparatus includes an actuator arm with first and second heads extending from the actuator arm for writing and reading data to and from a first surface of a disk recording medium. The first and second heads are spaced apart from each other in a circumferential direction along the first surface of the disk recording medium. A switching device switches a data input/output path between the first head and the second head in response to a control signal. A microprocessor identifies a target position on the first surface of the disk recording medium and determines which one of the first and second heads is closer to the target position. The microprocessor then generates the control signal to switch the data input/output path to the first head when the first head is closer to the target position, and generates the control signal to switch the data input/output path to the second head when the second head is closer to the target position.

Abstract: By dynamically adjusting the maximum voice coil motor driving current produced by an amplifier in a disc drive, amplifier saturation may be reduced, while still maintaining optimal current to quickly drive the voice coil motor during seek operations. Reducing disc drive saturation, and thus non-linearities in the driving current, increases notch filter performance. As the notch filter is used in the disc drive to remove frequencies from the driving current that tend to cause or excite the mechanical oscillations in the disc drive, increased notch filter performance reduces mechanical oscillations and improves disc drive noise characteristics.

Abstract: A method for improving servo seek settling performance by selectively activating a gain enhancement control signal during settling. As an actuator approaches a target location, absolute position and velocity of the read/write transducer head are monitored. If the absolute position changes absolute values (positive to negative or vice-versa) or the velocity approaches zero, the gain enhancement control signal is activated and combined with a nominal actuator control signal to further urge the actuator towards the target location. The gain enhancement control signal decays exponentially so as not to excite mechanical resonance of the actuator arms.

Abstract: An HDA includes a base, a disc stack coupled to a spindle rotatably attached to the base by a spindle shaft and spindle bearing. An actuator assembly is pivotally attached to the base at a pivot shaft. Attached to one end of the actuator assembly proximal the disc stack is one or more transducers for reading/writing information from/to the discs. A servo writer includes a controller for moving the actuator during the servo writing process. The controller moves the servo writer at the cage frequency of the spindle bearing to lessen the relative motion between the transducer head and the disc as the servo information is written to the disc. The controller also may be programmed to move the transducer at both the spindle rotation frequency and the cage frequency of the spindle bearing to lessen the relative motion between the transducer and the disc during the servo writing process.

Abstract: In control means having a feedforward system and a feedback system, a control model for generating reference position data yr from feedforward control signal Uff0 is separated into an original control model 22 and a compensation filter 23. Gain of feedforward control signal Uff0 is compensated by gain compensation means 24 to form feedforward control signal Uff after compensation. Data yr is input to a feedback controller 25, and feedback control signal Ufb and Uff are input to a control object 26. Coefficients of the compensation filter 23 and the gain compensation means 24 are compensated on the basis of a head position trajectory obtained by actual seek operation.

Abstract: A transducing head positioning system for use with patterned media. The patterned media comprises a plurality of data tracks and grooves. The grooved tracks can be used in connection with electrodes on a slider to create an electrostatic motor for microactuation of the slider.

Abstract: Apparatus and method for enhancing disc drive reliability by applying reduced read bias levels to read elements of a disc drive during an idle mode of operation. A preamplifier driver circuit applies an operational read bias signal of selected, nonzero magnitude to the read element to transduce data from a recording surface during an active mode. Once a predetermined period of inactivity occurs during which host data transfer commands are not processed, the disc drive enters the idle mode and the preamplifier reduces the read bias signal magnitude. The reduced bias level during the idle mode reduces thermal stress and electromigration within the read element while still allowing data to be transduced from the recording surface as the drive performs a dithering operation to move the head to different tracks on the recording surface.

Abstract: The A burst and B burst for tracking are recorded with the width of track pitch, the address signal is recorded as the same signal with the interval equal to two track pitches (2×Tp) and B1 bit is also recorded with deviation of one track pitch from the address signal with the interval equal to two track pitches (2×Tp). Therefore, the servo pattern of one track can be written as much as one track pitch and thereby the recording time can be shortened. Moreover, accurate track address can be calculated by the correcting process using the B1 bit.

Abstract: A disk drive and a disk drive control method is described which reduces the number of one track seeks a drive performs. The one track seeks can operate the actuator bearing in a non-linear mode or can increase in the friction of the actuator bearing which leads to servo positioning inaccuracies. In the disk drive the logical block address (LBA) assignments are made so that when sequential addresses are allocated to two different tracks, the tracks are physically non-adjacent. Thus, when a sequential LBAs are read across a track boundary, the actuator is moved farther than would be required if the LBAs were assigned the adjacent tracks.

Abstract: Apparatus and method for improved servo control in a disc drive. The disc drive includes a rotatable disc, a moveable actuator which supports a head adjacent the disc, and a stationary active magnetic bearing assembly which uses bearing coils to levitate the actuator. An active magnetic bearing control circuit applies currents to the bearing coils, and a servo control circuit applies current to an actuator motor to position the head with respect to the disc. The active magnetic bearing control circuit outputs a disturbance signal when a disturbance affects the relative positioning of the actuator and the bearing assembly, and this disturbance signal is fed forward into the servo control circuit. Conversely, the servo control circuit provides a seek expectancy signal to the bearing control circuit to enable the bearing control circuit to compensate for torque forces applied by the actuator motor.

Abstract: A circuit estimates speed of an electromagnetic actuator associated with a reading head of a disk storage unit and a digital controller. The circuit includes first and second supply terminals and an output terminal, with the first supply terminal being connected to the electromagnetic actuator. A measuring resistor is connected to the second supply terminal, and is connected in series with the electromagnetic actuator for measuring a current which passes therethrough when a supply voltage is applied between the first and second supply terminals. An adder has an output connected to the output terminal for providing an output voltage, a first input is connected to the first supply terminal, and a second input is connected to the second supply terminal. An adjustable-gain amplifier is connected between the measuring resistor and the second input of the adder for transferring the supply voltage and a voltage across the measuring resistor to the adder.

Abstract: An error amplifier for use in a disk drive actuator system having an actuator motor for radially positioning a transducing head with respect to a rotatable disk is newly designed to enable full implementation as an integrated circuit. The error amplifier includes a switched-capacitor proportional-integral controller for comparing first and second differential input signals representing a respective actual current and commanded current for driving the actuator motor, and providing a differential output signal. A transconductor-capacitor filter is connected to filter the differential output signal of the switched-capacitor integrator, and provides a motor control signal to control the actuator motor.

Abstract: A method and apparatus are provided for positioning a head over a disc in a disc drive while maintaining servo loop stability. The apparatus includes an actuator-head assembly having a large-scale actuator and a micro-actuator that are both able to move the head over the disc. A saturation adjustment component detects when a micro-actuator controller is producing a micro-actuator control value that will saturate the micro-actuator. Using the micro-actuator control value, the saturation adjustment component generates a saturation error value. An adaptive anti-windup circuit transfers control to the large-scale actuator when the saturation error value is generated by the saturation adjustment component.

Abstract: A servo track writer for writing a servo track signal to a disk medium in a disk drive including the disk medium, a head for reading/writing information from/to the disk medium, and an internal actuator for moving the head across tracks formed on the disk medium. The internal actuator has a rotatable carriage for supporting the head. The servo track writer includes an external actuator having an arm, a solid deformation element provided in relation to the arm, and an effector mounted on the arm; an internal actuator control unit for controlling the internal actuator; an external actuator control unit for controlling the external actuator; a solid deformation element control unit for controlling the solid deformation element; and an arm position detecting device for detecting a position of the arm. The solid deformation element is divided into a first segment functioning as an actuator for minutely displacing the carriage, and a second segment functioning as a sensor for detecting a position of the effector.

Abstract: A method and apparatus are provided for determining the tribology for a head/disk interface in a direct access storage device (DASD). A readback signal is obtained from a predetermined cylinder. The readback signal is sampled to provide a readback sampled sequence. The readback sampled sequence is summed to store a sum for each data sector of a plurality of data sectors in said predetermined cylinder. Predetermined discrete Fourier transform (DFT) magnitude components are calculated for the data sector sums. A harmonic ratio is calculated utilizing the calculated predetermined DFT magnitude components. The calculated harmonic ratio is compared with a predefined threshold value to identify the tribology for a head/disk interface.

Abstract: An actuator retract system and method for moving read/write heads from data regions on discs to non-data locations in a disc drive is disclosed. The non-data locations may be on or in close proximity to the discs. The non-data locations may be a landing zone or a load/unload ramp. At disc drive power-down, power generated from the rotational inertia in rotating discs is used to supply a current to a coil of a voice coil motor operably coupled to the actuator. The current generates an electric field around the coil that interacts with a magnetic field in the voice coil motor to move the actuator such that the read/write heads are retracted to the non-data location.

Abstract: A hard disc drive employs the self-servo-writing technique that writes practical servo signals on a hard disc based on the temporary servo signals written on the hard disc in advance, includes a holding mechanism that mechanically holds a rotary positioner, a memory which stores an eccentricity signal obtained while the holding mechanism is holding the rotary positioner, and a feedback compensator. The hard disc drive uses the stored eccentricity signal for a reference signal d*, calculates the difference between the reference signal d* and a head position signal x+d, obtains a positioner drive signal in the feedback compensator from the positional error based on the difference, and positions the magnetic head based on the positioner drive signal.

Abstract: In a tunnel junction sensor a free layer structure has a cobalt iron (Co90Fe10) layer and a half metallic iron oxide (Fe3O4) layer and a pinned layer structure has a cobalt iron (Co50Fe50) layer and a half metallic iron oxide (Fe3O4) layer. Each of the iron oxide layers interfaces a barrier layer which is compatible therewith. The thicknesses of the iron oxide (Fe3O4) layers are less than the thicknesses of the other layers of the free and pinned layer structures.

Abstract: A disk drive seek control system device to reduce track pitch. When data is recorded, an offset value is added to the position of a read head element along the width of a track corresponding to an offset &Dgr;w between the read head element and a write head element. The value of the offset depends on the yaw angle &thgr; of the head. When data is read, the position of the read head element is chosen to be either the position of the write head element during write operations, or the midpoint between the position of the write head element and the read head element during write operations, or the center of a track.

Abstract: A memory section stores values of the runout component, which are obtained in respective predetermined radial positions on the disk. A determining section selects, from the memory section, a value of the runout component corresponding to a target position. A runout detector uses, as an initial value for adaptive learning, the value of the runout component selected by the determining section, and calculates, by the adaptive learning, a value of the runout component contained in a position error between a head position and the target position. A feedforward controller calculates a feedforward value used to suppress the runout component calculated by the runout detector. A feedback controller calculates a feedback value from the position error. An adder generates, from the feedback value and the feedforward value, a control amount used to position the head in the target position.

Abstract: A head positioning control apparatus and a method therefor are capable of significantly improving the head positioning accuracy in a simple configuration. Head moving means moves a head from a first target track on a disc recording medium, on which the head is now positioned as a result of a tracking control, to a neighboring position of the next second target track based on frequency correction coefficients derived from frequency correcting means when the tracking control was performed based on a position error signal, so that a disturbance frequency occurring in synchronism with the rotational frequency of the disc recording medium can be corrected even in an operation in which the head moving means causes the head to travel over a large amount, thereby making it possible to realize a head positioning control apparatus and a method therefor which are capable of significantly improving the head positioning accuracy in a simple configuration.

Abstract: A signal processing device for analog-to-digital converting a burst signal has a feature of selecting a data bus to notify a disk control device of a conversion result via an NRZ data bus. The disk control device stores the result of the analog-to-digital conversion of the servo positional signal. The positional signal of a head of the disk device is digitalized in a R/W channel. Sampling for digital conversion is performed in only a window which is defined only in the vicinity of peaks of the positional signal. The values of peaks which are obtained by sampling are averaged by an averaging circuit. This enables the influence of noise occurred outside of the window to be eliminated. Although the noise in the window is sampled, its adverse influence is suppressed by the averaging processing.

Abstract: An apparatus and method for supplying bi-directional load current to a load device. Four current sensing metal oxide semiconductor field effect transistors are operably configured to form an H-bridge with the load device, each transistor having separately insulated gate, source and drain and sense terminals with a source to drain conductivity determined in relation to a voltage applied to the gate terminal and a sense current from the sense terminal determined in relation to a magnitude of source to drain current. Drive voltages are applied to the gate terminals of alternating pairs of the transistors to apply the load current to the load device. The sense currents are used to provide adaptive, closed-loop clamping of the drive voltages at levels sufficient to maintain the non-load current conducting transistors in a quiescent state.