Abstract:
A power distribution system is provided for distributing power in a portable device being coupable to a charging system and including a main battery power and a bridge battery power. The charging system is coupled to a power bus through a diode. The main battery power system and the bridge battery system are also both coupled to the power bus through diodes. The predetermined voltage level is set with respect to the charging system, the main battery and the bridge battery, such that if all three are coupled to the bus, the recharging system both powers the unit and recharges the main battery. If the recharging system is removed, the main battery power system powers the portable device, and if the main battery power system is removed the bridge battery will provide power to the portable device. The distribution system also includes a monitoring system for measuring the predetermined charge level on the battery and disabling a FET switch, so that the main battery stops charging to protect the main battery against overcharging. A monitoring system is also provided for monitoring the voltage level of the main battery utilizing a comparator system.

Description:
TECHNICAL FIELD 
     The present invention relates to a portable devices and more particularly to a low cost power distribution system and method for a portable device that is powered by a recharger unit or alternatively a rechargeable battery. The portable device includes a bridge battery for powering the portable device in the event the rechargeable battery is removed. 
     BACKGROUND OF THE INVENTION 
     Portable electronic devices (e.g. notebook computers, cellular telephone, cordless telephones mobile data terminals, radio frequency portable communication devices, etc.) typically include a rechargeable battery that is charged by a recharging unit plugged into an AC power source, such as that found in conventional 115 VAC lines. The recharging unit powers the portable device, while simultaneously charging the rechargeable battery. The portable device switches over to battery power upon removal of the portable device from the charging unit or the power source. Most intelligent portable devices employ a bridge battery that is utilized during the removable of the main rechargeable battery when it powers the portable device. The main function of the bridge battery is to insure that data stored in a Random Access Memory (RAM) device is not lost during swapping of the rechargeable battery. The bridge battery is usually a much smaller battery because during a battery swap, the portable device normally will enter a low current or suspend mode, so that most current drawn from the bridge battery is used to refresh the RAM device, until a new main battery is installed into the device. 
     Many portable devices employ complicated switching or logic circuitry when changing from the rechargeable device power to the main battery power, and from the main battery power to the bridge battery power. The switching or logic circuitry takes up valuable space on a circuit board that could be utilized to perform the functions of the portable device. In some cases, additional circuit boards are necessary to house the switching or logic circuitry. This increases the size and cost of the portable device. Furthermore, some of these portable devices employ expensive power management and supervisory circuitry to cause the functional components in the portable device to enter different modes, depending on the type of unit powering the portable device or the current status of the unit powering the portable device. The additional power management and supervisory circuitry adds to the size, the cost and also to the complexity of the portable device. 
     Accordingly, there is a strong need in the art for a system and/or method that can provide power distribution for a portable electronic device at low cost, while reducing space utilized in employing such a system. 
     SUMMARY OF THE INVENTION 
     According to a preferred embodiment of the present invention, a power distribution system is provided for distributing power in a portable device being coupable to a charging system and including a main battery power system and a bridge battery power system. The charge system is coupled to a power bus through a diode. The main battery power system and the bridge battery system are also both coupled to the power bus through diodes. A predetermined voltage level is set with respect to the charging system, the main battery and the bridge battery such that if all three are coupled to the bus, the recharging system both powers the unit and recharges the main battery. If the recharging system is removed, the main battery power system powers the portable device, and if the main battery power system is removed, the bridge battery will provide power to the portable device. The distribution system also includes a monitoring system for measuring a predetermined charge level on the battery and disabling a FET switch, so that the main battery stops charging to protect the main battery against overcharging. A monitoring system is also provided for monitoring the voltage level of the main battery utilizing a comparator system. Accordingly, the present invention provides for a very low cost power distribution system for portable devices. 
     Thus, according to one aspect of the present invention, a power distribution system is provided that provides power to functional and power circuitry on a portable device. The system includes a main battery system coupled to a power bus through a first switch system and a charging system coupled to the power bus through a second switch system. The charging system provides power to the power bus through the second switch system while the charging system is coupled to the second switch system and the main battery system provides power to the power bus through the first switch system upon removal of the charging system. 
     In accordance with another aspect of the present invention a power distribution system is provided that provides power to functional and power circuitry on a portable device. The system includes a main battery system coupled to a power bus through a main battery diode and a bridge battery system coupled to the power bus through a bridge battery diode. The voltage level of the bridge battery is lower than the voltage level of the main battery and removal of the main battery system causes the second switch system to allow the bridge battery system to provide power to the power bus. 
     In accordance with yet another aspect of the present invention, a method is provided for power distribution in a portable device including a power bus coupled to a device power and functional circuitry. The method includes the steps of providing a main battery system coupled to a power bus through a main battery diode, providing a charging system coupled to the power bus through a charger diode and providing a bridge battery system coupled to the power bus through a bridge battery diode wherein the charging system has a voltage level above the main battery voltage level and the main battery has a voltage level above the bridge battery, such that the charger powers the power bus if the charger is present, the main battery powers the power bus if the charger is not present and the bridge battery powers the bus if the charger and the main battery are not present. 
     In accordance with another aspect of the present invention, a power distribution system is provided that provides power to functional and power circuitry on a portable device. The system includes means for providing main battery power. The means for providing main battery power includes means for coupling the means for providing main battery power to a power bus. The system also includes means for recharging the means for providing main battery power. The means for recharging the means for providing main battery power includes means for coupling the means for recharging to the power bus. The means for charging having a voltage level that is at a predetermined level above a voltage level of the means for providing main battery power causing the means for charging to simultaneously provide power to the power bus and recharge the means for providing main battery power. 
     In accordance with yet another aspect of the present invention, a power distribution system for a providing power to functional and power circuitry on a portable device is provided. The system includes a main battery system coupled to a power bus through a main battery diode, a charging system coupled to the power bus through a charger diode and a bridge battery system coupled to the power bus through a bridge battery diode. The charging system has a voltage level that is at a predetermined level above a voltage level of the main battery system and the voltage level of the bridge battery system is lower than the voltage level of the main battery system. If the charging system is present, the charger diode is forward biased and the charging system provides power to the power bus. If the charging system is not present, the main battery diode becomes forward biased and the main battery system provides power to the power bus. If the charging system and the main battery system are not present, the bridge battery diode becomes forward biased and the bridge battery system provides power to the power bus. 
     To the accomplishment of the foregoing and related ends, the invention then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such embodiments and their equivalents. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1   a  illustrates a block diagram of a portable device coupled to a power source in accordance with one aspect of the present invention; 
     FIG.  1   b  illustrates a block diagram of a portable device coupled to a power source in accordance with another aspect of the present invention; 
     FIG. 2 illustrates a block diagram of a portable device coupled to a charger in accordance with another aspect of the present invention; 
     FIG. 3 illustrates a block diagram of a portable device including a low battery voltage monitor in accordance with the present invention; 
     FIG. 4 illustrates a flow diagram for providing power to the portable device and the rechargeable main battery in accordance with the present invention; 
     FIG. 5 illustrates a flow diagram for providing bridge battery power to the portable device in the event of removal of the main battery power in accordance with the present invention; and 
     FIG. 6 illustrates a flow diagram for providing a low battery power warning signal to the portable device in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described with respect to the accompanying drawings in which like numbered elements represent like parts. 
     Referring initially to FIG.  1   a , a portable device  10  is provided with a charger  40  coupled to a power source  30 . The source  30  is preferably AC power and operates at an AC power line frequency of 60 Hz. However, it is appreciated that in other countries different line frequencies (e.g., 50 Hz) may be employed. The charger  40  provides power to a power bus  90  for use with powering device power and functional circuitry  55  and recharging a main battery  65 . The charger  30  is coupled to the power bus  90  through a first switch system  50 . A bridge battery  95  is provided coupled to the power bus  90  through a second switch system  60 . The main battery  65  is coupled to the power bus  90  through a second switch system  70 . The charging system  40  powers the portable device  10  while the power source  30  is connected to the charger  40 . The first switch system  50  provides power to the power bus  50 , when the power source  30  is connected. After the power source  30  is removed, the first switch system  50  disables and the third switch system  70  allows power to be provided to the power bus  90  from the main battery  65 . If the main battery is disabled, the third switch system  60  disables and the second switch system  60  allows power to be provided to the power bus  90  from the bridge battery  70 . 
     In a preferred aspect of the invention, the first switch system  50  and the second system  60  are replaced with diodes and the third switch system is replaced with a diode and FET combination. Referring now to FIG.  1   a b , the portable device  10  is provided with the charger  40  coupled to the power source  30 . The charger  40  provides power to the power bus  90  for use with powering device power and functional circuitry  55  and recharging the main battery  65 . The charger  30  is coupled to the power bus  90  through a charger diode  51 . The charger diode  51  begins conducting when the power source  30  is connected to the charger  40 . Preferably, the charger is a lithium ion charger. However, it should be appreciated that the charger could be other types of chargers beside lithium, depending on the type of battery being recharged. The main battery  65  is coupled to the power bus  90  through a main battery diode  75 . The main battery diode  75  is connected to a Field Effect Transistor (FET) switch  71  in a parallel relationship. The opening and closing of the FET switch  71  is controlled by a charge status monitor  45 . The charge status monitor  45  could include a timer circuit that begins counting when the charger  40  begins operation by being connected to the power source  30 . The timing circuit could include a processor (not shown), such as Intel&#39;s 8 bit microcontroller, the 8031, 8051 or 8052. Furthermore, the manner in programming the processor to operate the invention according to the description herein will be apparent to those skilled in the art of computer programming. The FET switch  71  is closed upon detection of the charger  40  allowing the charger  40  to charge the main battery  65 . After a predetermined amount of time, the charge status monitor  45  changes the state of the FET switch  71 , so that the FET switch  71  enters an open state and stops charging the main battery  65 . 
     The removal of power source  30  causes the charger diode  51  to stop conducting. This causes the charger  40  to stop charging the main battery  65  and to stop providing power to the device power and functional circuitry  55 . Turning off the lithium charger  40  results in a voltage drop on the power bus  90 . The positive voltage drop between the main battery  65  and the power bus  90  causes the main battery diode  75  to begin conducting, such that the device power and functional circuitry  55  are powered by the main battery  65 . It is well known in the art that a diode becomes forward biased when a voltage drop of about 0.6-1.0 volts, depending on the type of diode, is provided from a cathode side to an anode side causing the diode to conduct and resemble a short circuit. Furthermore, the diode resembles an open circuit if the voltage drop is less than 0.6-1.0 volts or is a positive voltage drop from the anode to the cathode. 
     The bridge battery  95  is provided coupled to the power bus  90  through a bridge battery diode  61 . The bridge battery  95  is provided to supply power to the portable device  10  in the event that the main battery  65  fails or is being replaced. The bridge battery  95  is a much smaller battery than the main battery  65  and functions to provide current mostly to a RAM device within the device power and functional circuitry  55 . The other circuitry utilized in the portable device  10  operates in the suspend or low current mode, so that only a small amount of current is necessary to continue operation of the portable device  10 . For example, the bridge battery  95  typically may provide 1-1.2 millamps of current to the portable device  10  when it operates in the suspend mode, while the main battery  65  may be supplying 1-1.2 amps during normal operation of the portable device  10 . 
     The main battery  65  is preferably at a voltage range of between 3-4.2 volts with a nominal voltage of 3.6 volts, while the voltage range of the bridge battery is preferably at 2-3.2 volts with a nominal voltage of 2.4 volts. In the event that the main battery  65  is removed or malfunctions, the main battery diode  75  stops conducting. This results in a voltage drop on the power bus  90 . The positive voltage drop between the bridge battery  65  and the power bus  90  causes the bridge battery diode  61  to begin conducting, such that the device power and functional circuitry  55  are powered by the bridge battery  65 . If the main battery  65  is replaced, the voltage level on the bus rises above the voltage of the bridge battery and causes the bridge battery diode  61  to stop conducting. Thus, by utilizing diode coupling to the power bus  90 , a power distribution system is provided that is inexpensive, takes up very little room on a circuit board, and is simple to fabricate. 
     It should be appreciated that the lithium charger  40  could be a separate unit from the portable device  10 . For example, FIG. 2 illustrates a system where the charger  40  is a separate device coupled to the portable device  10  via a charge status circuit  80 . In this embodiment of the invention, the charge status circuit  80  monitors the charge current of the battery utilizing conventional current sensing techniques. If the charge current drops to a certain level indicating that the main battery  65  has become fully charged, the charge status  80  will alternate the state of FET switch  71  causing the switch to open. The charge status circuit  80  could monitor the temperature of the main battery  65  to determine if it has reached full charge capability. It should be noted that the charger  40  could take the form of a conventional cradle device that the portable device  10  rests in, as it recharges. 
     Referring to FIG. 3, the portable device  10  could include a low main battery power warning system. The portable device  10  could utilize a comparator  85  to monitor the voltage level of the power bus  90 . In the embodiment shown in FIG. 3, the positive terminal of the comparator is connected to the power bus  90 , while the negative terminal of the comparator  85  is connected to a reference voltage labeled as V BatLow . The output of the comparator  85  labeled as “Low Main Battery” changes state when the voltage level on the power bus  90  drops below the reference signal. The output signal can be coupled to the unit power and functional circuitry  55  to perform a power down routine on the portable device  10  or cause the portable device to enter the suspend mode. The output signal can also be coupled to a display or a Light Emitting Diode (LED) to provide a visual warning to the user. 
     FIG. 4 illustrates the steps taken by the present invention to ensure that the charger  40  provides power to the unit power and functional circuitry  55 , and also performs the function of recharging the main battery  65  when the charger  40  is operably coupled to the power bus  90  via the diode  51 . Beginning in step  120 , the potable device  10  is coupled to the charger  40  and the charger  40  is powered up. This may be accomplished by coupling the portable device  10  to the power source  30 , as shown in FIG. 1, or by coupling the portable device  10  to the charger  40 , as shown in FIGS.  2 - 3 . This depends on whether or not the charger  40  is a separate unit from the portable device  10  or is part of portable device  10 . In step  130 , the charger diode  51  begins conducting because the voltage level produced by the charger is above the voltage level of the main battery  65  and the bridge battery  95  causing the charger diode  51  to become forward biased and begin conducting. In step  140 , the charger provides power to the power bus  60  and runs the portable device  10 . In step  160  the FET switch  71  is turned on, which allows the charger  40  via the power bus  90  to provide current to the main battery  65 , thus recharging the main battery  65 . The charge status monitor  80  monitors the charge provided to the main battery  65  from the charger  40 . As previously discussed, the charge status monitor  80  could monitor the charge by utilizing a timer device or monitor the current draw utilizing conventional current measurement techniques. The charge status monitor  80  determines if the main battery  65  has met a predetermined charge level. If no, the charger  40  continues charging the main battery  65 . If yes, the charge status monitor turns the FET switch  71  off in step  180 , such that the main battery  65  stops charging in step  190 . 
     FIG. 5 illustrates the steps taken by the present invention to ensure that the main battery  65  provides power to the unit power and functional circuitry  55  if the charger  40  is removed, and also that the bridge battery provides power to the unit power and functional circuitry  55  if the charger  40  and the main battery  65  is removed. Beginning in step  230 , the charger  40  is powered off. In step  240 , the charger diode  51  becomes inactive and the FET switch  71  turns off. This causes a voltage drop across the main battery diode  75 , causing the main battery diode  75  to begin conducting and become active in step  250 . Since the voltage level provided to the power bus  90  from the main battery  65  is higher than the bridge battery voltage  95 , the bridge battery  60  does not conduct. The main battery then provides power to the power bus  90 , so that the portable device can run. The portable device  10  continues to be powered by main battery  65 , until the main battery  65  is disconnected form the portable device in step  270 . Once the main battery  65  is disconnected, the main battery diode  75  becomes inactive and the bridge battery diode  61  becomes active in step  280 . This is because the voltage level on the power bus  90  falls below the voltage level of the bridge battery  95 . In step  290 , the device  10  enters the low power mode or suspend state, and the bridge battery  95  powers the device  10 . 
     FIG. 6 illustrates the steps taken by the present invention to insure that the main battery  65  provides the proper level of voltage to power the unit power and functional circuitry  55 , if the charger  40  is removed. Beginning in step  330 , the charger  40  is powered off. In step  340 , the charger diode  50  becomes inactive and the FET switch  71  turns off. This causes a voltage drop across the main battery diode  75 , causing the main battery diode  75  to begin conducting and become active in step  350 . Since the voltage level provided to the power bus  90  from the main battery  65  is higher than the bridge battery voltage  95 , the bridge battery diode  61  does not conduct. The main battery  65  then provides power to the power bus  90 , so that the portable device can run in step  360 . The comparator  85  monitors the voltage level of the power bus  90  to insure that it stays above a predetermined level in step  370 . If the voltage is low on the power bus  90 , the comparator  85  transmits an output low main battery signal, in step  380 , to the device power and functional circuitry  55 , so that the device  10  can enter the low power mode in step  390 . It should be appreciated that the signal may be coupled to an LED or a display to provide a visual warning to the user of device  10 . It should also be appreciated that the device  10  could power down upon detection of a low battery voltage level. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications alterations, and equivalents thereof.