Abstract:
A method is disclosed for controlling the voltage applied to a voice coil motor coil during the retract operations of a mass storage device, comprising a combination of three different voltage regulator stages. This method includes providing a first circuitry stage adapted to source current to a voice coil motor apparatus, raising the voltage across the voice coil motor to a desired level, providing a second circuitry stage adapted to draw current from the voice coil motor effecting a desired voltage across the voice coil motor, and providing a third circuitry stage adapted to raise the voltage of the voice coil motor to ground by effectively shorting the voice coil motor to ground.

Description:
This application claims priority under 35 U.S.C. §119(e)(1) of provisional patent application No. 60/083,364 filed Apr. 28, 1998. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to circuitry for voltage regulation within mass storage devices and, more particularly, to a multi-zone voltage regulation system for voice coil motor operation. 
     BACKGROUND OF THE INVENTION 
     Circuitry performing voltage regulation is used extensively in modern electronics. Within mass storage devices and electronics, voltage regulation circuitry is commonly used in conjunction with voice coil motors to regulate actuation and retract operations within the storage device. A primary benefit of using voltage regulation during retract operations is that it enables a relatively constant rate of retract to be accomplished. 
     Conventional methods of regulating voltage during retract operations typically employs circuitry to source current into a voice coil motor. Various complex methods are employed to compensate for existing voltage across the voice coil, which indicates movement of an associated actuator either in or against a desired direction. 
     As performance and efficiency demands of mass storage devices are increased, voltage regulation associated with retract operations can be optimized to perform with desired operational characteristics. Highly effective and efficient retract operations, capable of operation with low supply voltages, are desirable characteristics of modern storage devices. The effectiveness of retract operations within a storage device is directly related to the efficiency with which current is moved across the voice coil motor, and the ability to move that current in either direction across the voice coil motor. Voltage regulation circuitry can provide these desired operational characteristics. 
     SUMMARY OF THE INVENTION 
     Within modern storage devices, voice coil motor circuitry often controls actuator assemblies, used to move signal read/write components across a storage media. As a storage device powers down, retracting the actuator to a fixed position is necessary to prevent damage to the storage media by the read/write components. Because the system is powering down, it is important that retract is operable down to very low voltages. Actuation and retract is most often controlled by a voice coil motor. Voltage across the voice coil is directly related to the direction and magnitude of movement by the actuator. It is possible that once a system power down is signaled within the storage device, the actuator may be moving either in a retract direction or in an opposite actuate direction. Retract operation may be controlled using voltage regulation circuitry to either source or sink current across the voice coil motor, depending on the voltage already present on the voice coil. 
     In the past, voltage regulators have been used in conjunction with voice coil motors to source current across the voice coil motors. A major problem faced by designers utilizing such voltage regulator configurations was the possibility of an existing voltage across the voice coil motor. If this voltage was such that the actuator was moving in a retract direction, then the voltage regulator circuitry could source current to complete the retract operation. If the actuator was moving in the direction opposite (actuating), having only the ability to source current with the voltage regulator circuitry, the system would have to wait for the existing voltage across the coil to dissipate—indicating the actuator slowed down and stopped—before supplying current to the coil to begin retract operation. This methodology results in differing degrees of ability to regulate the voltage across a coil, in order to get it to move at a fixed rate. This methodology is also inefficient. 
     Other methods have provided additional voltage regulator circuitry capable of sinking current from the voice coil motor, distinct from the current sourcing circuitry. While this has addressed the ability to alter the voltage across the coil and move the actuator in both directions, it has presented other problems in terms of design overhead and system timing. Such methods present problems and limitations to designers in optimizing system performance, especially during low voltage retract operations. These conventional methods for regulating voltage across the voice coil motor require extra circuitry, are not time efficient, and are not capable of operating at low system voltages. 
     Further existing methods attempt make no assumptions about the movement of the actuator. These methods stop the actuator regardless of which direction it is moving in, and begin sourcing current to move it in the desired direction. Obviously, a degree of system efficiency is lost when the actuator was already moving in the desired direction before being stopped. 
     The present invention overcomes the aforementioned limitations of current methods by a system that utilizes existing circuitry within the storage device to perform voltage regulation and provides the ability to source and sink current across the voice coil motor. Additionally the present invention provides the ability to operate at a low system voltage, which is especially important during final retract operation. 
     The invention provides a method of multi-zone voltage regulation for a voice coil motor during retract operation. Voltage regulator circuitry is provided, comprising three operational systems. Current sourcing circuitry is coupled together with current sinking circuitry and dynamic rectification circuitry to regulate voltage across a voice coil motor. This combination of regulation circuitry provides continuous and optimal regulation the voice coil motor, even during low voltage final retract operations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention, along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts, and in which: 
     FIG. 1 is an illustrative embodiment of voltage regulation system in combination with a voice coil motor assembly; 
     FIG. 2 is an illustrative embodiment of a current sourcing stage of the voltage regulation system depicted in FIG. 1; 
     FIG. 3 is an illustrative embodiment of a current sinking stage of the voltage regulator system as depicted in FIG. 1; 
     FIG. 4 is an illustrative embodiment of a dynamic rectification stage of the voltage regulator system as depicted in FIG. 1; and 
     FIG. 5 is an illustrative embodiment of a voltage regulator system in combination with voice coil motor circuitry. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. 
     The present invention allows a user to control the voltage applied to a voice coil motor coil, providing optimal performance during a retract operation. Three voltage regulator circuitry systems are employed. These systems utilize existing MOS circuitry within a mass storage device in conjunction with a linear regulator, providing efficient control of a voice coil voltage independent of actual voltage at the coil. 
     As will be apparent to one skilled in the art, the present invention may be employed with various voltage regulator circuitry. The underlying principle of this invention is applicable, and its implementation readily adaptable, in a wide range of voltage regulation applications. All such embodiments are comprehended by the present invention. 
     Referring now to FIG. 1, an illustrative combination of voice coil motor circuitry and a voltage regulator circuitry  100  is depicted. Supply voltage is coupled by lead  102  to current sourcing stage  104 . The supply voltage may be provided by a number of user selectable means. For purposes of illustration, the supply voltage here is provided by a spindle motor within a mass storage device—usually employed to manipulate storage media. A user provided retract voltage signal is coupled by lead  106  to current sourcing stage  104 , and to current sinking stage  108 . Lead  110  couples current sinking stage  108  and dynamic rectification stage  112  jointly to ground. Stage  104  is coupled to node  114  by lead  116 . Similarly, stages  108  and  112  are coupled to node  114  by leads  118  and  120 , respectively. Lead  122  connects node  114  to voice coil assembly  124 . Assembly  124  is also coupled to ground by lead  126 . For purposes of this illustration, the voltage across the voice coil assembly is represented by the voltage as measured at node  114 . 
     As retract operation is initiated, system power within the mass storage device will power down. Supply voltage will be provided from the spindle motor as it spins down. This voltage will obviously continue to decrease over a period of time as the motor comes to a stop. A user provided signal will supply the retract voltage as a reference. 
     Referring now to FIG. 2, an illustrative embodiment of current sourcing stage  104  is depicted. Lead  106  is coupled to one input of amplifier stage  200 . The other input of stage  200  is coupled to lead  116 . The output of amplifier  200  is coupled to the base of transistor  202 . The collector of transistor  202  is coupled to lead  116 , and the emitter of transistor  202  is coupled to lead  102 . The source of transistor  204  is coupled to lead  116  and the drain of transistor  204  is connected to lead  102 . 
     Referring now to FIG. 3, an illustrative embodiment of current sinking stage  108  is depicted. Leads  118  and  106  couple to the inputs of amplifier stage  300 . The output of amplifier  300  is coupled to the gate of transistor  302 . The drain of transistor  302  is coupled to lead  118 , and the source of transistor  302  is coupled to lead  110 . 
     Referring now to FIG. 4, an illustrative of dynamic rectification stage  112  is depicted. Leads  110  and  118  are coupled to the inputs of amplifier stage  400 . The output of amplifier  400  is coupled to the gate of transistor  402 . The source and the gate of transistor  402  are coupled to leads  110  and  118 , respectively. 
     Referring now to FIG. 5, an illustrative embodiment of the system  500  of voltage regulator circuitry previously depicted in FIGS. 1 through 4 in combination with voice coil motor circuitry is depicted. Amplifier stage  502  has a first input coupled to lead  106 . A second input of amplifier  502  is coupled to node  504 . The output of amplifier  502  is connected to the base of transistor  506 . The emitter of transistor  506  is coupled to lead  102 , while the collector of transistor  506  is coupled to node  504 . Transistor  508  has its source coupled to node  504 , while its drain is coupled to lead  102 . A first end of diode  510  is coupled to the source of transistor  508 , while a second end of diode  510  is coupled to the drain of transistor  508 . This diode is merely representative of existing circuitry within a mass storage device and is not critical to the functionality of the present invention. A first input of amplifier stage  512  is coupled to lead  106 . A second input of amplifier  512  is coupled to node  504 . The output of amplifier  512  is coupled to a first input of OR-gate  514 . The output of OR-gate  514  is coupled to the gate of transistor  516 . The source of transistor  516  is coupled jointly to lead  110 , and to a first end of diode  518 . The drain of transistor  516  is coupled jointly to lead  514 , and to a second end of diode  518 . Again, diode  518  is representative of existing system circuitry and is not critical to functionality. Amplifier stage  520  has a first input coupled to node  504 , and a second input coupled to lead  110 . The output of amplifier  520  is coupled to a second input of gate  514 . Coupled serially between node  504  and node  522  are inductive element  524  and resistive element  526 . Transistor  528  has its source coupled jointly to node  522  and to a first end of diode  530 . The drain of transistor  528  is coupled jointly to lead  102 , and a second end of diode  530 . Transistor  532  has its source coupled jointly to lead  110 , and a first end of diode  534 . The drain of transistor  532  is coupled jointly to node  522  and to a second end of diode  534 . The gate of transistor  532  is coupled to lead  536 . Transistor  538  has its base coupled to lead  536 . The emitter of transistor  538  is coupled to lead  110 , and the collector of transistor  538  is coupled to node  522 . For purposes of illustration, node  522  is effectively coupled to ground, indicating that the voltage across the voice coil assembly—elements  524  and  526 —can be represented as the voltage at node  504 . 
     Functionally, circuit  500  represents one implementation of the voltage regulator system  100  depicted in FIG.  1 . Referring again to FIG. 1, if the voltage across the voice coil motor  124 , as measured at node  114 , is too low, then stage  104  will be operational. Stage  104  will operate to source current through stage  124  to raise the voltage as measured at node  114  to the desired level as supplied on lead  106 . If the voltage as measured at node  114  is greater than the desired level, then stage  108  will become operational. Stage  108  will operate to sink current from stage  124 , pulling the voltage at node  114  down to a desired level as provided on lead  106 . If the voltage at node  114  is lower than ground, then stage  112  will become operational. Stage  112  will operate to short node  114  to ground, pulling the voltage at node  114  up to ground. 
     Referring back to FIG. 5 now, operation of the voltage regulator system is discussed in greater detail. The first mode of operation assumes that the voltage measured between nodes  504  and  522  is greater than zero but less than the retract voltage signaled on lead  106 . During this mode of operation, the voltage regulator system will operate to source current from transistors  506  and  508  through node  504  to raise the voltage across elements  524  and  526  up to the level on lead  106 . During this mode of operation, a loop is formed amongst amplifier  502 , node  504  and transistors  506  and  508  that effects a voltage regulator providing desired voltage to the voice coil motor stage. 
     A second mode of operation assumes that the voltage measured between nodes  504  and  522  is greater than the voltage signaled on lead  106 . During this mode of operation, amplifier  512  and transistor  516  act to sink current from node  504  through transistor  516 —drawing the voltage across the voice coil motor stage down to the desired voltage as signaled on lead  106 . In this illustration, amplifier  512  employs switching regulation, reducing the complexity of the required circuitry and improving its efficiency. Because any oscillation associated with the switching of amplifier  512  would be at a very high frequency, such oscillation will not affect system functionality while the system is in final retract operation. During retract operation, the rest of the system components are powered off and noise is not a concern. Node  106  provides a signal to amplifier  512  which turns transistor  516  on. Transistor  516  draws current from node  504 , effectively pulling the voltage at node  504  down to a desired voltage level. 
     A third mode of operation is assumed when the voltage measured between nodes  504  and  522  is lower than ground. During this mode of operation, amplifier  520  and transistor  516  are active, effectively forming an operational amplifier follower circuit with the reference voltage of amplifier  520  tied to ground. This circuitry will then regulate the voltage at node  504 , pulling it up to ground. This provides a quick and efficient way to raise the voice coil motor voltage between nodes  504  and  522 . 
     Functionally, the voltage across the voice coil motor stage, as represented between nodes  504  and  522  by elements  524  and  526 , will vary with operation of the mass storage device. The voltage on the coil, that is measured at node  504 , is proportional to the rate at which voice coil motor is moving the associated actuator. The effectiveness of any retract scheme concerns being able to move currents in either direction, either into or out of the coil, to achieve the desired voltage level across the coil. 
     The present invention utilizes existing circuitry within mass storage device designs to provide an effective voltage regulation scheme. Further, the method of the present invention provides the ability to operate the voltage regulator circuitry down to a very low supply voltage. As previously noted, during retract operations the supply voltage on lead  102  consistently diminishes. 
     As will be apparent to those skilled in the art, the embodiments of the voltage regulator system depicted are not exclusive and can be effected using other suitable combinations and elements. While this invention has been described in reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.