Abstract:
Disclosed are a power supply circuit and method for mobile communication terminals, such as PDAs and portable phones. When a main power source such as a battery is abruptly detached from a system, the abrupt detachment of the main power source is detected and the system is stably turned off only with a backup power source. The power supply circuit includes a first switch for providing a driving voltage from the main power source to the system, a second switch for providing a driving voltage from the backup power source to the system when the main power source is detached from the system, a controller for generating a control signal for opening the first switch and closing the second switch when the main power source is detached from the system, and a memory for storing user data.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Power Supply Circuit And Method For Stable System Turn-Off” filed in the Korean Intellectual Property Office on Oct. 6, 2004 and assigned Ser. No. 2004-0079312, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to mobile communication terminals, such as Personal Digital Assistants (PDAs) and portable phones, and more particularly to a power supply circuit and method which, when a main power source such as a battery is abruptly detached from a system, detects the abrupt detachment of the main power source and enables stable system turn-off only by a residual power source.  
         [0004]     2. Background of the Prior Art  
         [0005]     Recently, with development of telecommunication technology, mobile communication terminals are being widely used. Typical examples of mobile communication terminals include portable phones and Personal Digital Assistants (PDAs).  
         [0006]     The PDA is a next generation personal portable device combining a wireless communication function and an information processing function, which is also called a personal information processor or a personal portable communication terminal. A PDA typically provides functions, of a secretarial function enabling management of a personal schedule program; a function for managing personal information by using an electronic pen or hand-writing recognition technology; a reference data source function enabling a simple search of reference data by a built-in dictionary or manual; and a communication function enabling an exchange of e-mail, fax, paging messages and portable phone messages.  
         [0007]     An initial PDA product is a Newton developed by the Apple Computer Corporation, which is a handheld-sized portable terminal combining an information processing function and a wireless communication function. Recently, various PDA products have been developed, and a wireless communication service using the same is provided.  
         [0008]     Meanwhile, various mobile terminals such as PDAs and portable phones employ a battery as a main power source. However, problems arise when a user abruptly detaches the battery from the mobile terminal or the battery is detached from the mobile terminal by the user&#39;s carelessness during the operation of the mobile terminal. Specifically, the mobile terminal cannot detect the detachment of the battery, resulting in the mobile terminal being abruptly turned off, without performing a normal turn-off procedure.  
         [0009]     Further a PDA may employ a POCKET PC or similar Operating System (OS), which stores user data in a volatile memory, rather than in nonvolatile memory, such as a Synchronous Dynamic Random Access Memory (SDRAM). Accordingly, if the PDA is abnormally turned off without performing a normal turn-off procedure, the SDRAM cannot perform a self-refresh operation.  
         [0010]     When the PDA is normally turned off, a Central Processing Unit (CPU) of the PDA commands the SDRAM to perform a self-refresh operation. In response to the command, the SDRAM performs the self-refresh operation to thereby prevent a loss of user data, which may be caused by abrupt turn-off of the PDA.  
         [0011]     However, when the conventional PDA is abnormally turned off, the SDRAM cannot perform the self-refresh operation, thereby causing loss of user data.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention provides a power supply circuit and method which, when a main power source is abruptly detached from a system, detects the abrupt detachment of the main power source and performs a stable system turn-off only by a backup power source, thereby preserving user data and preventing malfunction of the system.  
         [0013]     According to an aspect of the present invention, a power supply circuit equipped with a main power source and a backup power source for stably turning off a system includes a first switch for providing a driving voltage from the main power source to the system; a second switch for providing a driving voltage from the backup power source to the system when the main power source is detached from the system; a controller for generating a control signal for opening the first switch and closing the second switch when the main power source is detached from the system; and a memory for storing user data.  
         [0014]     The power supply circuit may further include a capacitor for providing a driving voltage to the controller when the main power source is detached from the system.  
         [0015]     The capacitor may be charged by the main power source. The capacitor may be connected in parallel to the main power source.  
         [0016]     The memory may be an SDRAM and receive power from the backup power source when the main power source is detached from the system.  
         [0017]     The controller may receive power from the backup power source when the main power source is detached from the system.  
         [0018]     The power supply circuit may further include a main power source detection switch for transmitting a detection signal to the controller when the main power source is detached from the system.  
         [0019]     According to another aspect of the present invention, a power supply method for stably turning off a system includes providing a driving voltage charged in a capacitor to a controller when a main power source is detached from the system; providing a driving voltage from a backup power source to the system when the main power source is detached from the system; and performing a refresh command for a memory and then performing a system turn-off operation at the controller.  
         [0020]     The driving voltage from the backup power source may be provided to the system by opening a first switch for supplying main power and closing a second switch for supplying backup power.  
         [0021]     The capacitor may be charged by the main power source. The capacitor may be connected in parallel to the main power source. Also, the memory may be an SDRAM. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0023]      FIG. 1  is a block diagram of a power supply circuit according to an embodiment of the present invention;  
         [0024]      FIG. 2  is a block diagram of a power supply circuit for stably supplying power to the system according to an embodiment of the present invention;  
         [0025]      FIG. 3  is a block diagram of a power supply circuit for enabling a stable system turn-off when a main battery is abruptly detached from a system, according to an embodiment of the present invention; and  
         [0026]      FIG. 4  is a flow diagram illustrating a method for performing a stable system turn-off when the main battery is abruptly detached from a system, according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In the drawings, like reference numerals in the drawings denote like elements, and thus their description is not repeated. A detailed description of the related well-known functions and constructions will be omitted for conciseness.  
         [0028]      FIG. 1  is a block diagram of a power supply circuit according to an embodiment of the present invention.  
         [0029]     Referring to  FIG. 1 , a battery detection switch  100  detects whether a main battery  110  is detached from a PDA system and then informs a CPU  102  of a detection result. That is, if the main battery  110  is attached to the PDA system, the battery detection switch  100  transmits a signal ‘ATTACHED’ to the CPU  102 . If the main battery  110  is detached from the system, the battery detection switch  100  transmits a signal ‘DETACHED’ to the CPU  102 .  
         [0030]     When the main battery  110  is detached from the system, the CPU  102  transmits a refresh command to a device for maintaining data, such as an SDRAM  104 . The SDRAM  104  then stores data that is to be preserved, such as user data, and performs a refresh operation for maintaining such necessary or required data.  
         [0031]     A main power circuit  106  maintains a voltage of the main battery  110  to a regular voltage so as to enable the PDA system to operate stably. A large capacitor  108  is provided to temporarily supply backup power to the CPU  102  when the main battery  110  is detached from the system, and generally maintains a voltage higher than a driving voltage Vcc. The large capacitor  108  is available to supply voltage until completion of its discharge.  
         [0032]     The main battery  110  is the primary power source device, which supplies a driving voltage to the system through the main power circuit  106 . A backup battery  116  is a backup power source device, which supplies power to the CPU  102  and the SDRAM  104  when the main battery  110  is detached from the system.  
         [0033]     When the main battery  110  is detached from the system, the present invention enables the system to be stably turned off according to the CPU  102 &#39;s control signals for operation of a first switch  112  and a second switch  114 .  
         [0034]      FIG. 2  is a block diagram of a power supply circuit for stably supplying power to the system according to an embodiment of the present invention.  
         [0035]     Referring to  FIG. 2 , the PDA system performs a stable operation while the main battery  110  is normally maintained. The battery detection switch  100  transmits a battery detection signal to the CPU  102  when the main battery  110  is normally maintained. The battery detection switch  100  is constructed to be physically pressed when a user moves, i.e. unlocks, a lock device for the main battery  110 , to thereby be able to sense that the main battery is about to be attached to or detached from the system.  
         [0036]     Upon reception of the battery detection signal from the battery detection switch  100 , the CPU  102  closes the first switch  112  and opens the second switch  114 . Accordingly, the main battery  110  supplies power to the system. In detail, the main battery  110  supplies power to the CPU  102  and the SDRAM  104  through the main power circuit  106  and the first switch  112 . The main power circuit  106  maintains a voltage of the main battery  110  regularly to thereby supply power to the system.  
         [0037]     In the meanwhile, the large capacitor  108  is connected in parallel to the main battery  110  to thereby be charged by the main battery  110 . The backup battery  116  cannot supply power to the system according due to the second switch  114  being in an open position.  
         [0038]     Consequently, when stably supplying power to the system, the power supply circuit maintains the first switch  112  in a closed position and the second switch  114  in an opened position.  
         [0039]      FIG. 3  is a block diagram of a power supply circuit for enabling a stable system turn-off when a main battery is abruptly detached, according to an embodiment of the present invention.  
         [0040]     Referring to  FIG. 3 , the power supply circuit of the present invention enables the PDA system to be stably turned off when the main battery  110  is abruptly detached from the system. For this, when a user abruptly detaches the main battery  110  from the system (or when the main battery  110  is detached from the system by the user&#39;s carelessness) during the operation of the system, the battery detection switch  100  detects the abrupt detachment of the main battery  110  to then transmit a signal ‘ABRUPTLY DETACHED’ to the CPU  102 .  
         [0041]     Upon receiving the signal ‘ABRUPTLY DETACHED’ from the battery detection switch  100 , the CPU  102  performs a command for opening the first switch  112  and closing the second switch  114 .  
         [0042]     Accordingly, the first switch  112  is opened and the second switch  114  is closed, whereby the main power circuit  106  does not operate and the backup battery  116  supplies power to the CPU  102  and the SDRAM  104 .  
         [0043]     Accordingly, the CPU  102  can operate continuously and user data stored in the SDRAM  104  can be preserved. That is, the CPU  102  performs a refresh command for the SDRAM  104  to store necessary data, and the SDRAM  104  stores the necessary data according to the refresh command.  
         [0044]     However, if the refresh command is performed only by the backup battery  116 , the power consumption of the backup battery  116  becomes great, and, in some cases, the CPU  102  cannot perform the refresh command owing to time consumption caused by the switching operations of the first and second switch  112  and  114 .  
         [0045]     To prevent this problem, the power supply circuit of the present invention also includes the separate large capacitor  108 . As described previously, the large capacitor  108  is connected in parallel to the main battery  110  and is charged by the main battery  100 .  
         [0046]     When the main battery  110  is detached from the system and the first switch  112  is opened, the large capacitor  108  provides a driving voltage Vcc to the CPU  102  through the main power circuit  106 . Here, when the main battery is detached from the system, the provision of the driving voltage Vcc by the large capacitor  108  is instantaneously performed.  
         [0047]     Accordingly, even if the backup battery  116  cannot provide a driving voltage Vcc to the CPU  102  owing to the switching time, the large capacitor  108  can provide a driving voltage Vcc to the CPU  102 . Upon reception of the driving voltage from the large capacitor  108 , the CPU  102  performs a refresh command for the SDRAM  104  to store necessary data. Accordingly, the SDRAM  104  stores important data such as user data, whereby the CPU  102  can perform a stable system turn-off.  
         [0048]     In brief, even when the main battery  110  is abruptly detached from the system, the power supply circuit of the present invention provides a driving voltage to the system through the backup battery  116  and the large capacitor  108  by opening the first switch  112  and closing the second switch  114 , thereby enabling a stable system turn-off.  
         [0049]      FIG. 4  is a flow diagram illustrating a method for performing a stable system turn-off when the main battery is abruptly detached from the system, according to an embodiment of the present invention.  
         [0050]     Referring to  FIGS. 3 and 4 , while the system operates, a user desiring to turn off the system can turn off the system through a normal system turn-off procedure (S 100 ). At this time, the CPU  102  performs a refresh command for the SDRAM  104  to store data. Upon completion of the data storage by the SDRAM  104 , the system performs a stable system turn-off.  
         [0051]     The present invention also enables a stable system turn-off by using the backup battery  116  and the large capacitor  108  even when the main battery  110  is abruptly detached from the system irrespective of the user&#39;s intention.  
         [0052]     Accordingly, if the main battery  110  is abruptly detached from the system irrespective of the user&#39;s intention during the operation of the system (S 110 ), the CPU  102  receives a signal ‘DETACHED’ from the battery detection switch  100 , and then opens the first switch  112  and closes the second switch  114 .  
         [0053]     At this time, the large capacitor  108  provides a driving voltage Vcc to the CPU  102  through the main power circuit  106 . If the main battery  110  is detached from the system, the provision of a driving voltage Vcc by the large capacitor  108  is instantaneous (S 120 ).  
         [0054]     Accordingly, even if the backup battery  116  cannot provide a driving voltage Vcc to the CPU  102  owing to a switching time, the large capacitor  108  provides a driving voltage to the CPU  102 . Accordingly, as the second switch is closed, the backup battery  116  provides power to the CPU  102  and the SDRAM  104  (S 130 ).  
         [0055]     Accordingly, the CPU  102  can operate continuously and user data stored in the SDRAM  104  can be preserved. That is, the CPU  102  issues a refresh command for the SDRAM  104  to store necessary data, and the SDRAM  104  stores the necessary data according to the refresh command, whereby a stable system turn-off is successfully performed (S 140 ).  
         [0056]     As described above, when the main battery is abruptly detached from the system, the power supply circuit and method of the present invention detects the abrupt detachment of the main battery in advance and performs a stable system turn-off only by a backup power source, thereby making it possible to prevent the loss of user data and the malfunction of the system that may be caused by the abrupt detachment of the main battery.  
         [0057]     The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatus. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.