Patent Publication Number: US-2003234780-A1

Title: Power management system for liquid crystal displays

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The invention relates to a power management system. In particular, the invention relates to a power management system for a liquid crystal power supply, which cuts off the LCD power supply that has entered a power-down mode, thereby saving power.  
       [0003] 2. Description of the Prior Art  
       [0004] For power saving requirement, a lot of hardware and software of a computer system are designed with power management functions. Major computer systems are powered by power supply that is powered by an external power source. Some peripherals such as Compact Disc Read-Only Memory (CD_ROM) drives, LCD displays can be powered by computer system itself because of low power consumption. Generally, power management system for a computer system can be divided into two types as below. One type uses Operating System (OS) or Power Management software to detect operating states of current peripherals. For example, current drive may switch from a normal mode to a power-down mode under the conditions of no disc in a CD_ROM drive or no fetch to a CD disk for a long time. The switching method is to output a standby signal to drive&#39;s power supply. After the standby signal is received, the power supply will change the supplied voltage from normal level to power-down level. The second type of a power management system uses switching devices that located on the case or any obvious location of the computer system or its peripherals, to switch the supplied voltage from normal to power-down. The above two types of power management systems can both achieve the power save purpose. FIG. 1 is a block diagram of a typical power management system. The system adapts to a display devise and uses an external power source to provide line voltage S 6  to a power supply  14  first and then to display  16  by an operating power S 2 . The operating power S 2  can be a normal power level or a power-down power level. The power supply  14  receives a synchronization signal S 0  from the computer system  10 . When the computer system is operating at normal, the signal S 0  is in an enable state and so the power supply  14  provides the display  16  with a normal power level. When the computer system enters a power-down state or a power off state, the signal S 0  is disable, the power supply  14  powers the LCD  16  with the power-down power. However, when the computer system  10  output the signal S 0  with the disable state, the power supply  14  still provides a power-down power to the display  16  and so the display  16  continues to consume the power so that the power save performance is reduced.  
       SUMMARY OF THE INVENTION  
       [0005] Accordingly, an object of the invention is to provide a power management system for a display, which uses a power input switching device and a detecting device to cut off the power supply when the power supply enters a power-down mode. The power management system can be installed in the internal power system or in an external power adaptor of a display.  
       [0006] The invention provides a power management system suitable for a display, i.e. a liquid crystal display (LCD), where the LCD enters an operation of normal mode or power-down mode according to a synchronization signal being enable or disable states. The system includes a power supply to convert line voltage of a power source and thus provides a converted voltage to the LCD; a power input switching device implemented between the power supply and the power source; and a detecting device detected the synchronization signal if the synchronization signal is changed from the enable to disable states, the detecting device waiting a predetermined time then turning the power input switching device off and thus the line voltage does not input into the power supply. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0007] The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
     [0008]FIG. 1 is a block diagram of a typical computer power management system;  
     [0009]FIG. 2 is a block diagram of an embodiment of a display power management system according to the invention;  
     [0010]FIG. 3 is a diagram of a detecting device of FIG. 2 according to the invention; and  
     [0011]FIG. 4 is a diagram of a power input switching device of FIG. 2 according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0012] The same element function denotes the same reference number throughout the description.  
     [0013]FIG. 2 is a block diagram of an embodiment of a display, i.e. a liquid crystal display, power management system according to the invention. The embodiment includes devices as below.  
     [0014] A detecting device  22  receives a synchronization signal S 0  and outputs a switching signal s 3 . When a synchronization signal S 0  changes from an enable state to a disable state for a predetermined time, the switching signal S 3  is changed from the enable state to the disable state. The synchronization signal S 0  is provided by the computer system  20  or the other switching device (not shown). An example of the detecting device  22  is shown in FIG. 3. The detecting device  22  includes a diode  32  and a capacitor  34 . When the synchronization signal S 0  is in the enable state, the diode  32  detects the peak voltage of the synchronization signal S 0  and stores to the capacitor  34  in order to produce a high-level switching signal S 3  through the peak voltage. When the synchronization signal S 0  changes to the disable state, the capacitor discharges for a predetermined time until the peak voltage is down to be a cutoff voltage and thus output a low-level switching signal S 3 , wherein the determined time depends on the capacitance of the capacitor  34 .  
     [0015] A power input switching device  24  is input an external power provided by a line voltage S 6  and provides the line voltage S 6  to a liquid crystal power supply  26  according to the switching signal S 3 . When the switching signal S 3  is enabled, the line voltage S 6  is provided to the power supply  26 . When the switching signal S 3  is disabled, the line voltage S 6  provided to the power supply  26  is stopped. An example of the power input switching device  24  is shown in FIG. 4. The example can be a triple-state alternating current (TRIAC) diode. That is, when the switching signal S 3  is enabled, the line voltage S 6  is sent to the power input switching device  24  to provide the line voltage S 6  to the power supply  26 . When the switching signal S 3  is disabled, the line voltage S 6  cannot be sent to the power input switching device  24  so that the device  24  cannot provide the line voltage S 6  to the power supply  26 . Therefore, since no line voltage is provided to the power supply  26 , the power supply consumes no power and thus the power save purpose is achieved.  
     [0016] The power supply  26  inputs the line voltage S 6  provided by the power input switching device  24  and provides required power to the display  28 . When the synchronization signal S 0  is enabled, the power supply  26  provides required voltage to the display  28 . When the synchronization signal S 0  is disabled, the power supply  26  does not provide required voltage to the display  28  and so the power supply  26  does not provide any power to the display  28 . Therefore, the power supply  26  and the display  28  do not consume any power as the synchronization signal S 0  is in the disable state. Thus, the inventive power save purpose is achieved.  
     [0017] Additionally, the computer system  20  also includes a power required by the power supply  26  to provide the display  28  respectively to the normal or power-down mode according to the synchronization signal S 0 , when the synchronization signal S 0  is input and a switching signal is output to the power supply. When the synchronization signal S 0  is in the enable state, the power supply  26  provides required power by the display  28  with the normal mode. When the synchronization signal S 0  is in the disable state, the power supply  26  provides required power by the display  28  with the power-down mode.  
     [0018] While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.