Abstract:
A liquid crystal display television receiver projection system uses a controller responsive to a first signal by providing power to a first set of circuits of the system. The controller is responsive to a second signal by removing power from a second set of circuits of the system; A timer defines a time interval between an instance of a power off signal and an instance of a power on signal. In the event a user issues a power on command before the first interval has elapsed, power will be applied to circuits other than the lamp. The lamp will remain de-energized until the first interval has elapsed. Therefore, a user is prevented from re-striking the lamp.

Description:
BACKGROUND OF TH INVENTION  
       [0001]     This invention relates to a power control circuit for a high intensity discharge lamp, for example of the type used in video displays. Typical liquid crystal display (LCD) and liquid crystal on silicon (LCOS) television (TV) projection systems utilize high-intensity discharge lamps (also referred to as bulbs) as image back lighting sources. High intensity discharge lamps typically operate with mercury vapor. Applying power to a partially energized mercury vapor lamp is to be avoided. Applying power to the lamp before the mercury vapor de-energizes, i.e., re-striking the lamp, shortens the lamp&#39;s life. To avoid this problem, some projection systems introduce a delay between power off and power on. This delay is sometimes referred to as a “restart” delay. The restart delay prevents a user from applying power to the television receiver until the mercury vapor lamp is substantially fully de-energized. An example of a typical restart delay time is approximately 30 seconds. Introducing a restart delay in this manner can be annoying to a user. Users have come to expect instant restart of their television sets since instant response is typical with television receivers that do not employ high-intensity discharge lamps. A typical high intensity discharge lamp can take approximately 30 seconds for the bulb to cool down and approximately another 30 seconds for the bulb to reheat.  
         [0002]     Therefore a need exists for circuits and methods for applying power to such systems in a way that minimizes user perception of delay while preserving the life of the mercury vapor lamp.  
       SUMMARY OF THE INVENTION  
       [0003]     The invention provides a video display apparatus comprising an image lighting lamp; a power on control circuit, a power off control circuit and a timer. The power on control circuit energizes selected circuits of the video display in response to a power on control signal. The power off control circuit de-energizes circuits of the video display in response to a power off control signal. The timer is coupled to the image lighting lamp so as to maintain the lamp in a de-energized state during a time interval that follows the occurrence of the power-off control signal. The power on control circuit selects circuits for energizing in response to a power on control signal based upon a condition of the timer.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1 : is a block diagram of a system for applying power to a high intensity discharge lamp according to an embodiment of the invention.  
         [0005]      FIG. 2 : is a flow chart illustrating the steps of a method for processing user commands for the system illustrated in  FIG. 1  according to an embodiment of the invention.  
         [0006]      FIG. 3 : is a flow chart illustrating the steps of a method for applying power to the system illustrated in  FIG. 1  according to an embodiment of the invention.  
         [0007]      FIG. 4 : is a flow chart illustrating the steps of a method for timing a cool down interval according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0008]     With the introduction of micro display systems for consumer televisions, efficient handling of the transition between a “power off” state and a “power on” state for the system is desirable. After powering a micro display system off, the power to the lamp typically remains off, and cannot be re-applied for a length of time. This time period allows the lamp to cool down before being powered back on. The time period sufficient for a given device depends upon the type of lamp and its associated electronics. In an embodiment of the invention, a sufficient time period is about 30 seconds. Time periods of more than, and less than about 30 seconds are appropriate depending on the device. Appropriate time periods include those determined and recommended by the lamp manufacturer. In any case, failure to enforce a sufficient cool down period sometimes results in reduced lifetime of the lamp. Therefore, systems and methods to extend the lifetime of the lamp while responding to user commands are needed.  
         [0009]     As used herein, the term “power on state” refers to an operationally ready state wherein operating power is applied to circuits and subsystems, including a lamp subsystem, such that the system is capable of near real time response to at least one user command to perform a function corresponding to the command. The term “partial power on” and “partial power on state” refer to operationally ready states wherein operating power is applied to circuits other than a lamp power circuit. The term “power off state” refers to a state in which a system is not operable to perform common userfunctions such as tuning. In one embodiment of the invention, a power off state is a state wherein substantially all of the power is absent from a plurality of circuits and sub systems of a system. However, in a power off state according to one embodiment of the invention, at least one circuit is provided with power for responding to “power on” commands from a user while the system is in a power off state. This at least one circuit maintains a power level sufficient to enable the system to receive, interpret and respond to the “power on” command from a user in accordance with the steps of the methods of the invention described herein.  
         [0010]     Commands for energizing a system are generally referred to herein as “Power on” commands. Such commands provide a first signal to the system to remove power. Those of ordinary skill in the art will recognize “Power on ” as a general type of command capable of representation by a number of names and symbols, all of which have the same meaning. For example, the words “Power” and “On” as well as a variety of symbols and other graphical indications such as light bulbs, a green color, etc are commonly employed to indicate a power on function. Likewise, the power off command has a variety of corresponding indications and representations to indicate that power is removed from a system.  
         [0011]     A wide variety of user operable devices exist for communicating signals, representing commands from a user to a system. Suitable user operable devices include those capable of providing at least a first and a second signal to a system. A first signal represents a power on command. A second signal represents a power off command. Conventional power on and power off signals are relayed from a user operable device to a system by a wide variety of known user operable devices including buttons, switches, voice activation, relays, software switches, vibration activation, touch screen activation, and others too numerous to mention. Similarly, a wide variety of communication links are in use to transmit first and second signals from a user operable device to a system. These include, but are not limited to front hardware and software implemented switches and actuators, as well as remote controllers relaying signals by electromagnetic, infrared, wired or wireless means.  
         [0012]     Without power, systems, circuits and subsystems are typically not operable to perform all of their designated functions. Consumers are accustomed to an immediate response to power on commands initiated either by remote control or the front panel. However, as discussed above the characteristics of the lamps typically utilized in micro display systems often preclude an immediate response to a user command to apply power to a system. One example is a command to apply power to a system including a mercury vapor lamp, when the power on command is received before the vapor has substantially de-energized. In that case, power on is typically delayed until after a lamp cool down period has expired. A lamp cool down period allows mercury vapor to substantially de-energize before power is again applied to a lamp.  
         [0013]     This invention outlines a method and system by which a system transition from a power off state to a power on state during a lamp cool down period is implemented efficiently. This is done by enabling power to be applied to circuits and systems other than Light Engine circuits, during the lamp cool down period. Light engine circuits are circuits involved in energizing a high intensity discharge lamp such as a mercury vapor bulb.  
         [0014]      FIG. 1  is a block diagram illustrating an embodiment of the invention. Display system  100  comprises a plurality of television circuits and subsystems as represented by indicators  105 - 199 . Circuits  161 - 199  perform typical television functions such as tuning (tuner circuit  161 ), speaker control (circuit  162 ), Audio Video (A/V) input output functions (A/V circuits  163 ), and the like.  
         [0015]     In one embodiment of the invention, system  100  utilizes a high-intensity discharge lamp  107  to form a back light source for a light valve of an LCOS display. In an embodiment of the invention, high intensity discharge lamp  107  is a mercury vapor lamp and power circuits  105  comprise power circuits for high-intensity discharge lamp  107  (also referred to herein as a light engine). In addition to high-intensity discharge lamp  107 , system  100  further comprises a power controller  130  including at least a timer  135 ; at least one processor  131 ; a power indicator circuit  115  including a power indicator  114 ; a partial power on flag circuit  120 ; and a user operable control device  150 . User operable control device  150  is capable of communicating commands, including power on and power off commands from a user to processor  131 . In one embodiment of the invention power indicator  114  is a light emitting diode (LED). However, as those of ordinary skill in the art will readily appreciate upon reading this specification, there are a great number of known visual indicators available in the art and suitable for use in the invention to signal system conditions to a user.  
         [0016]     In one embodiment of the invention, processor  131  includes a memory  132  for storing user commands. Processor  131  receives user commands from user operable control device  150 . In response to user commands, processor  131  provides control signals to circuits  105 - 199  of system  100 . Processor  131  is capable of independently controlling circuits and subsystems  105 - 199  of system  100  according to one embodiment of a method of the invention. In one embodiment of the invention, processor  131  is capable of selecting and controlling a first set of circuits, for example, the set comprising circuits  161 ,  162  and  163 , independently of a second set of circuits for example the set comprising lamp subsystem  105 . In one embodiment of the invention, processor  131  is capable of controlling lamp subsystem  105  independently of all other subsystems.  
         [0017]      FIG. 2  is a flow chart outlining steps of a method  200  for processing user commands according to an embodiment of the invention. In an embodiment of the invention, processor  131  executes a program to carry out the steps of the method. A program in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a device having processing capability to perform a particular function either directly or after either or both of the following a) conversion to another language, code or notation; b) reproduction in a different material form. In one embodiment of the invention, the method of  FIG. 2  is used with system  100  of  FIG. 1  and is implemented by processor  131  of system  100 . Therefore, reference is made below to  FIG. 1  and  FIG. 2 .  
         [0018]     Process  200  starts as indicated at  205 , wherein processor  131  waits until a command is received from user operable control device  150  according to step  210 . Upon receipt of a user command, processor  131  checks the state of power to high intensity discharge lamp  107  (hereinafter, lamp  107 ). If power is applied to lamp  107 , processor  131  processes the user command as illustrated in step  216 . Then, processor  131  returns to the wait state of step  210 .  
         [0019]     If processor  131  determines power is not applied to lamp  107 , processor  131  determines if the command received from user operable control device  150  is a power on command as indicated at step  220 . If the command is not a power on command, for example, if the command is a tuning command, processor  131  discards the command as illustrated in step  221 . Then, processor  131  returns to the wait state as shown in step  210 .  
         [0020]     On the other hand, if processor  131  determines in step  220  the command is a power on command, further processing is carried out. In one embodiment of the invention, processor  131  checks the state of timer  135  to determine if a cool down interval is in progress as indicated at step  225 . If timer  135  is timing a cool down interval, it is not desirable to apply power to lamp  107 . However, circuits other than lamp power circuits can safely be powered on. In that case processor  131  sets partial power flag  120  and causes power on LED  114  to blink. Processor  131  then processes the command, and waits for the next command. In one embodiment of the invention, if the command is a power on command, processor  131  processes the command according to the method illustrated in  FIG. 3 . In an embodiment of the invention, this step occurs without intervention from the user. To the user, execution of the forgoing steps may be indistinguishable from a lamp error, for example the error that occurs when restriking lamp  107 . However, in one embodiment of the invention, an LED indicator  114  blink sequence is implemented such that a user can differentiate between a partial power on condition and an lamp error condition of system  100 .  
         [0021]      FIG. 3  illustrates steps of a method for processing a power on command such as indicated in step  216  of  FIG. 2 . For purposes of explanation reference will be made below to  FIGS. 1 and 3 . When a power on command is to be processed (for example as per step  216  of  FIG. 2 ) the method starts as indicated at start step  305 . At step  310 , processor  131  enables power to circuits selected from the group comprising circuits  106 - 199 , not including lamp power circuits  105 . In one embodiment of the invention, processor  131  enables power to a first subset of circuits  106 - 199  at step  310 . The first subset excludes lamp power circuit  105 . In one embodiment of the invention, the first subset comprises tuner power circuit  161 , speaker power circuit  162  and Audio Visual (A/V) input circuits  163 . In another embodiment of the invention, the first subset includes, but is not limited to, tuner power circuit  161 , speaker power circuit  162  and Audio Visual (A/V) input circuits  163 .  
         [0022]     According to one embodiment of the invention, at step  315  processor  131  waits for power supplies of the circuits enabled in the previous step  310  to stabilize, e.g, to reach a quiescent state. Next, in step  320 , processor  131  determines if a cool down interval is in progress. In one embodiment of the invention, processor  131  checks timer  135  to determine if a cool down interval is in progress. In an alternative embodiment of the invention, processor  131  checks partial power on flag  120  to determine if a cool down interval is in progress. If a cool down interval is not in progress, processor  131  enables power to lamp circuit  105  as indicated at step  325 . On the other hand, if a cool down interval is in progress, processor  131  initializes the first subset of circuits selected in step  310  and waits for the next command. This step is indicated at  330 . In other words, processor  131  prepares the first subset of circuits for operation and response to user commands, but does not apply power to the high intensity lamp  107 , if lamp cool down is in progress.  
         [0023]     Once the first subset of circuits are initialized system  100  can operate substantially fully, excepting any on screen functions. In one example, the appropriate channel will be tuned and the correct input will be selected in response to user commands. Audio commands will be enabled. The command processing that is available when system  100  is powered on is enabled. This allows a user to change channels or inputs and adjust the volume when the cool down interval is in progress. Next, according to one embodiment of the invention, processor  131  stops until the next power on command is received as indicated at step  335 .  
         [0024]      FIG. 4  illustrates one method  400  for operating timer  135  of system  100  according to an embodiment of the invention. As those of ordinary skill in the art will recognize, the specific implementation of timer  135  will vary depending on the software and hardware architecture of system  100 . According to one embodiment, timer  135  is started when system  100  receives a power off command from a user. Timer  135  is then checked periodically to determine whether the cool down interval has expired. In one embodiment of the invention, a simple counter is used to implement timer  135 .  
         [0025]     In one embodiment of the invention lamp cool down timer  135  begins timing a cool down interval when processor  131  receives a power off command as indicated at  410 . In step  420 , timer  135  times the time interval. In one embodiment of the invention the interval is about 30 seconds. In another embodiment of the invention, the interval is about 60 seconds. However, those of ordinary skill in the art will recognize that any desired time interval for allowing discharge of lamp  107  is suitable for use in the timer  135  of the invention. Sufficient time intervals include those determined and recommended by the manufacturer of lamp  107  and are readily determined. In one embodiment of the invention timer  135  is set as per manufacturer recommendations and is factory adjustable.  
         [0026]     At step  430  processor  131  determines if the time interval has expired. If the time interval is not expired, timer  135  continues to time the interval until the interval expires. Upon expiration of the interval, partial power on flag  120  is tested, as illustrated in step  440 . If partial power on flag  120  is set, power will be applied to lamp  107  according to step  450 .  
         [0027]     When processor  131  determines the time interval has expired, processor  131  checks the status of partial power on flag  120 , as indicated in step  440 . If partial power on flag  120  is set (for example as by step  230  illustrated in  FIG. 2 ) processor  131  enables power to lamp  107  as indicated at step  450 . In an embodiment of the invention, a set partial power flag indicates receipt of a power on command during a cool down interval. At step  452 , processor  131  clears partial power on flag  120  and the process  400  ends. If partial power on flag  120  is not set, processor  131  proceeds by placing system  100  in a power off state.  
         [0028]     In light of the foregoing description of the invention, it will be recognized that the present invention can be realized in hardware, software, or a combination of hardware and software. The system and method according to the present invention is capable of realization in a centralized fashion, or in a distributed fashion where different elements are spread across several interconnected circuits. The description above is intended by way of example only and is not intended to limit the present invention in any way, except as set forth in the following claims.