Abstract:
An electronic device including a voltage supply source is presented. Included in the electronic device is a low voltage detection circuit that is connected to the voltage supply source. Also, a voltage offset circuit is connected to the low voltage detection circuit. The voltage offset circuit offsets a voltage drop in the low voltage detection circuit that is caused by a voltage transient. Therefore, a false reading is prevented in the low voltage detection circuit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to battery protection circuitry, and more particularly to a method and apparatus of preventing early shutdown of computer systems due to a power demand change.  
           [0003]    2. Background Information  
           [0004]    Computer systems that are capable to be powered by battery or a direct current (DC) source that is supplied through an alternating current (AC) adapter typically have mechanisms to protect batteries from damage and to allow the system to switch between the two types of power sources. The main purpose of these battery protection circuits are to detect: whether the battery has enough energy to run the system, i.e. the battery is good, the battery is low, or the battery is critically low. This information is used by the system power management controller to determine if a power failure is about to occur, or to shutdown the whole system itself. This is done to prevent deep charging of the battery which can cause irreversible damage to the battery.  
           [0005]    Many computer systems that are powered by either battery or DC sources through an AC adapter, such as notebook computer systems, have different processing speeds depending on the power source. Some of these notebook computer systems will run at a higher processing frequency when powered by an DC supply through an AC adapter as opposed to battery power. When the power source switches between the DC source and battery, a transient may occur. This transient can lead to a false reading by the power management system, thus causing the computer system to prematurely shutdown. As the batteries in computer systems become smaller, i.e. less battery cells, (which reduces the weight and can also reduce the size of the system) the transient becomes greater and the reliability of the power management system becomes a greater issue. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.  
         [0007]    [0007]FIG. 1 illustrates a battery detection circuit.  
         [0008]    [0008]FIG. 2 illustrates an embodiment of the invention having a voltage offset circuit.  
         [0009]    [0009]FIG. 3 illustrates an example of a timing of processing signals for computer system mode detection.  
         [0010]    [0010]FIG. 4 illustrates an embodiment of the invention having a current monitor circuit.  
         [0011]    [0011]FIG. 5 illustrates an embodiment of the invention having a voltage monitor circuit. 
     
    
     DETAILED DESCRIPTION  
       [0012]    The invention generally relates to a method and apparatus for offsetting computer system transients that occur due to switching of supply sources. Referring to the figures, exemplary embodiments of the invention will now be described. The exemplary embodiments are provided to illustrate the invention and should not be construed as limiting the scope of the invention.  
         [0013]    [0013]FIG. 1 illustrates a typical computer system  100  that is powered by battery  110  or a direct current (DC) supply through an alternating current (AC) adapter (not shown). Computer system  100  may be a notebook style computer system or any portable processing device. Computer system  100  also contains main voltage regulator  120  for regulating voltage supply to chipset  170  and memory  180 . Also, central processing unit (CPU)  190  voltage comparator  140 , voltage divider  150 , and hysteresis feedback  160  are included. CPU  190  may be a dual processing speed CPU. That is, CPU  190  may run at one processing frequency when computer system  100  is powered by battery, and another processing frequency when powered by a DC supply through an AC adapter.  
         [0014]    Computer system  100  has an accurate reference voltage  111 , such as 1.225 V or a 2.45V band gap type reference with a ±1% tolerance. Power to voltage reference  111  is provided by series resistor  195  and is decoupled by capacitor  196  to filter out unwanted noise. Voltage divider network  150  is comprised of resistor  151  and resistor  152 . Resistors  151  and  152  are used to divide the critical supplied voltage down to the same level as reference voltage  111 . Voltage comparator  140  is used to compare reference voltage  111  to that of the voltage at voltage divider  150 . The output voltage of comparator  140 , indicated by LOW_BATT signal  199 , is low (where “low” is a determined voltage level equated to a low state) which indicates that the battery voltage level is normal for operating levels. When the battery voltage level becomes low or critically low, the voltage level at voltage divider  150  will be lower than voltage reference  111 . Therefore, LOW_BATT signal  199  will be high (where “high” is a determined voltage level equated to a high state), which indicates that battery  110  is running low. Hysterisis feedback  160  is comprised of resistors  161  and  162 . Hysterisis feedback  160  is used to from DC supplied voltage to battery, or vice versa. A single signal, or combination of signals can be used with compensation circuit  210  to offset the voltage drop caused by changed current demand. The offset changes the voltage at comparator  140  so a comparison of voltages will not result in a false trigger of LOW_BATT signal  199 . Therefore, a false reading is prevented and the system is prevented from shutting down prematurely. Also, battery life is increased by preventing the premature shutdown, where computer system  100  would need to be restarted.  
         [0015]    [0015]FIG. 3 illustrates examples of signals produced by CPU  190  and timing of the signals upon switching of supplied voltage sources. It can be seen that a slight delay occurs before the signals respond to the change of voltage source. The signals illustrated in FIG. 3 represent possible timing due to switching from a DC supplied voltage to battery  110 .  
         [0016]    In another embodiment, reference voltage  111  can be modified upon a change DC supplied voltage to battery, or vice versa. This can be accomplished by using the signals produced by CPU  190  and by modifying variable circuit elements. Digital to analog (D/A) or analog to digital (A/D) devices can be used along with variable elements. An D/A device converts a digital signal to an analog voltage. For example, a stop clock signal can be converted by a D/A device to a voltage for offsetting the voltage drop caused by a voltage source switching transient. An A/D device converts an analog voltage to a digital signal. For example, a voltage can be converted by an A/D device to a signal that can be used by other components to offset the voltage drop caused by a voltage source switching transient. Also, the modification can be accomplished by using potentiometers that replace resistors.  
         [0017]    [0017]FIG. 4 illustrates another embodiment of the invention that accomplishes compensation for voltage drops caused by transients. This embodiment does not depend on processing signals from CPU  190 . Current monitor circuit  410  is used to monitor the current from voltage supply source  420 . Voltage supply source  420  can be DC supplied voltage or battery  110 . If the current from voltage supply source  420  is high (based on a predetermined reference current), then the reference voltage is adjusted down to compensate for the voltage drop. The higher the current from voltage supply source  420 , the larger the voltage drop caused by a transient. The adjustment may be accomplished as is presented in previous embodiments, without relying on CPU signals.  
         [0018]    [0018]FIG. 5 illustrates another embodiment of the invention that accomplishes compensation for voltage drops caused by transients. This embodiment does not depend on processing signals from CPU  190 . Voltage monitor circuit  510  is used to monitor the voltage at voltage supply source  420 . Voltage supply source  420  can be DC supplied voltage or battery  110 . If the voltage from voltage supply source  420  changes abruptly (from a predetermined reference voltage), then the reference voltage is adjusted up to compensate for the transient voltage drop. The adjustment may be accomplished as is presented in previous embodiments, without relying on CPU signals.  
         [0019]    The above embodiments can also be stored on a device or medium and read by a machine to perform instructions. The device or medium may include a solid state memory device and/or a rotating magnetic or optical disk. The device or medium may be distributed when partitions of instructions have been separated into different machines, such as across an interconnection of computers.  
         [0020]    While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.