Abstract:
The present invention comprises a combination of a new circuit topology utilizing microcontroller ( 202, 302 ) and a modified logic control circuit which enables the replacement of a Schottky diode, commonly used in series with AC adapter, by a MOS transistor switch ( 212, 312 ) to implement airline mode operation of a system, with the added benefits of more efficient power dissipation and minimization of sparking or arcing at the power input terminal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field of the Invention  
         [0002]     The present invention generally relates to power management sections comprising methods of monitoring and switching between external and internal power sources in a system, and means of facilitating the recharge of rechargeable internal power sources such as battery packs. These power management sections are adapted to sense when a source has been coupled to an input terminal and also to recharge, when appropriate, said internal power sources. Such power management systems are typically used in electronic devices, such as notebook computers.  
         [0003]     2. Description of Related Art  
         [0004]     Power management sections facilitate the powering of systems and devices that require a stable output voltage from one of a plurality of power sources. Many electronic device applications require these power management sections as they are adapted to receive power, for example, from an AC wall source or an external or internal DC source. Power management sections have been developed to control and regulate power to a system from several sources. Often, these systems can be powered from one of several sources, including an AC source, an internal DC source, such as a battery, or an external DC power source such as a car or airline adapter. The battery packs used in these systems are usually rechargeable types, such as NiCd, NiMH, Li-Ion, and Li-Pol battery packs. In addition to powering the system, AC or wall sources or external DC sources also are used to recharge these battery packs.  
         [0005]     In notebook computer systems, the primary function of the power management section is to charge the battery pack and guarantee power continuity to the system. These functions are often implemented with the use of dedicated integrated logic circuits (“ICs”) or a combination of micro-controller and discrete analog and digital components such as oscillators, comparators and logic gates. In order to perform the power switch and battery pack recharging functions, conventional circuit topologies use a set of power switches (usually MOS transistors) and discrete diodes. Typically a power diode is required to isolate the adapter from internal nodes, and the MOS transistors are controlled to isolate the AC adapter from the battery or load. A buck converter uses the adapter power to recharge the battery.  
         [0006]     Usually the input power is switched to the system when the AC adapter voltage is above the target charge voltage. There are some instances, however, when the AC adapter voltage must be switched to the system even if it is lower than the battery voltage. This condition is normally referred to as “airline” mode operation and is required when the end equipment must be powered from an external supply which voltage is lower than the pack voltage. Disadvantageously, conventional topologies are unable to implement airline mode. In such cases, the system continues to run off the higher voltage battery pack even with the external DC source or AC adapter wall source connected to the device, thus discharging the battery pack until the pack voltage matches the external supply voltage. To implement airline mode using conventional topologies at least 2 additional switches and external control logic must be added to block the conduction path from battery to system. This increases the system cost and decreases overall system efficiency, as the series resistance from the battery pack to the system is increased.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention comprises a combination of a new circuit topology and a modified logic control circuit which enables bypassing the Schottky diode commonly used in series with AC adapter with a MOS transistor switch. This new topology effectively, reduces the overall power dissipation for the system when operating from adapter power. In addition, a new configuration for the power switches is introduced which enables the implementation of airline mode with fewer switches, when compared to conventional topologies. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Other aspects and features of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof. For a more complete understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings wherein:  
         [0009]      FIG. 1  illustrates a conventional power supply regulation and switching circuit.  
         [0010]      FIG. 2  illustrates one embodiment of the present invention wherein component count is minimized at the expense of higher series resistance on the current charge path, as compared to the conventional topology presented in  FIG. 1 .  
         [0011]      FIG. 3  illustrates an alternative embodiment of the present invention with lower series resistance on current charge path, when compared to the embodiment presented in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     While the invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. For example, the illustrative embodiments are implemented using single gate, enhancement mode PMOS transistors. Various other embodiments, for example, using transistors with opposite polarities and modes, or multiple gates, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the disclosed and appended claims will cover any such modifications of the embodiments as fall within the true scope and spirit of the invention. Throughout the drawings, it is noted that the same reference numerals will be used to designate like or equivalent elements having the same function. Detailed descriptions of known functions and constructions unnecessarily obscuring the subject matter of the present invention have been omitted for clarity.  
         [0013]     In systems such as notebook computers, the primary function of the power management section is to recharge the battery pack and guarantee power continuity to the system. These functions are often implemented with use of dedicated integrated circuits (“ICs”) or a combination of micro-controller and discrete components. The power into the power management section is either from an external source such as an AC adapter or DC source or an internal power source such as a battery pack. In order to perform the power switching and battery recharging functions, conventional circuit topologies use a set of power switches, typically MOS transistors, that can be controlled to isolate the adapter from the battery or load and a buck converter that can be switched in series from the adapter terminal to the battery. A commonly used topology used in notebook computers to implement power switching to the system and battery recharging is seen in  FIG. 1 .  
         [0014]      FIG. 1  illustrates a conventional power supply regulation and switching circuit. As seen therein, power for the system derives either from an external power source, e.g., an AC wall source, introduced at adapter terminal  101 , or from an internal source, such as a battery  103 , introduced at terminal  111 . Power is output to the system at system terminal  110 . Controller  102  drives transistors  104  and  106  to switch between adapter terminal  101  and battery terminal  111 , and further, as seen therein, regulates power from the adapter terminal  101  to the battery  103  for recharge by controlling buck converter  107 . A Schottky diode  108  is added to isolate the adapter voltage  101  from system terminal  110 , thus preventing current flow from system terminal  110  to adapter  101  via the backgate diode of switch  104  or from the battery  103  to the adapter terminal  101  via the backgate diode of switch  106  and backgate diode of switch  104 . The buck converter circuit  107  facilitates use of power from the external source at the adapter terminal  101  when the voltage from that source is higher than the battery  103  voltage. The buck converter  107  duty cycle is set by the controller  102  to achieve the desired charge current and charge voltage. The charge current information is fed back to the controller  102  through pins  126  SRP and  127  SRN. The battery  103  voltage is attenuated via an external resistive divider and fed back to the controller via pin BATP  140 . In addition to that the duty cycle signal  125  /PWM is level shifted to provide the necessary gate voltage levels for the external PMOS transistor  105 . The diagram of  FIG. 1  displays a non-synchronous converter, however it should be noted that a synchronous converter can also be used without affecting the implementation of the present invention.  
         [0015]     Controller  102  is a typical battery charge controller and selector, such as the Texas Instruments bq24701, that contains the logic and drivers that control the plurality of transistors in the power management section. When power is attached to the adapter terminal  101 , it is detected at ACDET pin  128 , through the resistor divider circuit of resistor  112  and resistor  113 . The controller  102  connects either the AC adapter terminal  101  or battery terminal  111  to the system terminal  110  by controlling switches  104  and  106 , respectively. Transistor  106 , driven by /BATDRV pin  124  of controller  102 , switches power from the battery  103  to the system terminal  110 . /ACDRV pin  123  drives the external PMOS transistor  104  used to switch to the external power supply, such as an adapter, as the power source. /PWM pin  125  is a gate drive output pin that drives the PMOS transistor  105  for PWM control. The functions provided by controller  102  can also be performed by a micro-controller and/or discrete circuit elements such as oscillators, comparators and logic circuits.  
         [0016]     There are several disadvantages with this conventional circuit. First, adapter diode  108  is required to isolate the adapter at adapter terminal  101  from the system  110  and battery  111  terminals. New systems have loads ranging from 3 amperes to 10 amperes or higher. As a result, the power dissipation generated by diode  108  is significant and it contributes to increase the internal temperature of the end equipment. It is not possible to simply replace diode  108  with a transistor or other switch, using the AC switch control signal from controller  102 , as capacitor  109  will hold the adapter voltage high if the adapter is removed from adapter terminal  101  when such an AC switch is on. Secondly, the topology shown in  FIG. 1  cannot be used to implement airline mode, as the intrinsic backgate diode in transistor  106  will power the system terminal  110  from battery terminal  103  if the battery terminal voltage is above the adapter terminal  101  voltage. Finally, connecting the buck converter switch source to capacitor  109 , as shown in  FIG. 1 , results in increased capacitance at node  150 , as the capacitor  109  filters the ripple current required by the buck converter  107  when a battery pack is being charged. Upon connection of an external supply to adapter terminal  101  this capacitive load is charged with inrush current being limited by diode  108  impedance. Usually this impedance is very small, resulting in very high inrush peak currents at adapter terminal  101 . This generates sparks at the adapter terminal during adapter insertion with possible oxidation of contacts and long term reliability issues.  
         [0017]     Therefore, a circuit topology is desired which is able to (i) reduce the amount of power through the adapter diode  108 , (ii) open the discharge path from the battery pack  103  to system terminal  110  when the voltage at terminal  101  is below the battery voltage  103  and (iii) reduce the capacitive load responsible for inrush current during adapter connector insertion. The present invention accomplishes these objectives with a combination of a new circuit topology and new control logic functions. Advantages of the present invention include more efficient power dissipation when the external power source is recharging the battery and powering the system. The present invention advantageously enables the implementation of airline mode with minimum external switch count, thus reducing power management section cost when implementing airline mode.  
         [0018]      FIG. 2  illustrates one embodiment of the present invention wherein component count is minimized at the expense of higher series resistance on the current charge path, as compared to the conventional topology presented in  FIG. 1 .  
         [0019]     As seen in  FIG. 2 , power for the system derives either from an external power source, e.g., an AC wall source, introduced at adapter terminal  201 , or from an internal source, such as a battery  203 , introduced at terminal  211 . Power is output to the system at system terminal  210 . Controller  202  drives transistors  204  and  213  to switch between adapter terminal  201  and battery terminal  211 , and further, as seen therein, regulates power from the adapter terminal  201  to the battery  203  for recharge by controlling buck converter  207 . A Schottky diode  208  is added to isolate the adapter voltage  201  from system terminal  210 , thus preventing current flow from system terminal  210  to adapter  201  via the backgate diode of switch  204  or from the battery  203  to the adapter terminal  201  via the backgate diode of switch  213  and backgate diode of switch  204 . The buck converter circuit  207  facilitates use of power from the external source at the adapter terminal  201  when the voltage from that source is higher than the battery  203  voltage. The buck converter  207  duty cycle is set by the controller  202  to achieve the desired charge current and charge voltage. The charge current information is fed back to the controller  202  through pins  226  SRP and  227  SRN. The battery  203  voltage is fed back to the controller via pin VPACK  241 , the voltage at pin VPACK is compared to the voltage at pin VCC; if VPACK is greater than VCC a battery greater than adapter condition (VPACK&gt;VCC) is detected. In addition to that the duty cycle signal at /PWM pin  225  is level shifted to provide the necessary gate voltage levels for the external PMOS transistor  205 . Current through diode  208  is bypassed through transistor  212 , thus reducing power dissipation in diode  208  when adapter power is used to power the system and charge the battery pack. Switch  212  is never turned on with a 100% duty cycle. The controller  202  applies a duty cycle smaller than 100% to /ACDRV 1  pin  230 , effectively turning switch  212  on for a very short time and allowing detection of the removal of an external supply connected to terminal  201 . During the time that switch  212  is off, if the external power supply is not available, the voltage at terminal  201  and ACDET pin  228  will collapse, thus enabling terminal  201  power removal detection by controller.  
         [0020]     Another improvement in the topology is that transistor  213  is connected in series with transistor  205 . This arrangement, together with modifications in the controller logic to allow comparison between the voltages at pins VCC  224  and VPACK  241 , enables the implementation of airline mode without additional components in the power management section. The following states related to charge and airline mode are implemented in the controller internal logic:  
                                                       AC adapter       SWITCH 212   SWITCH 204   SWITCH 213   SWITCH 205           detected   VCC &gt; VPACK   (diode bypass)   (ac to system)   (batt to system)   (pwm ctrl)   MODE                   NO   Don&#39;t care   OFF   OFF   ON   ON   PACK CONNECTED                               TO SYSTEM       YES   YES   PULSED   ON   ON   PWM   ADAPTER TO                           CONTROL   SYSTEM,                               CHARGING PACK       YES   NO   PULSED   ON   OFF   OFF   ADAPTER TO                               SYSTEM, PACK                               ISOLATED FROM                               SYSTEM (AIRLINE                               MODE)                  
 
         [0021]     Diodes  214  and  215  provide a continuous power path for the controller supply to ensure that a lock-up condition does not exist during power up conditions. This guarantees that controller  202  always has power, independently of the state of switches  205 ,  213 ,  204  and  212  whenever an external supply is connected to terminal  201  or a pack is connected to terminal  211 . The inrush current during adapter insertion is minimized by connecting the buck converter switch driver to the system terminal  210 . This allows a reduction in the value of capacitor  209  connected to node  250 . Capacitor  209  in the present invention is dimensioned only to filter transients at node  250 . Note that the same configuration used in  FIG. 1  can still be implemented by connecting switch  213  to node  250  without affecting the implementation of this embodiment of the present invention.  
         [0022]      FIG. 3  illustrates an alternative embodiment of the present invention with lower series resistance on current charge path, when compared to the embodiment presented in  FIG. 2 .  
         [0023]     As seen in  FIG. 3 , power for the system derives either from an external power source, e.g., an AC wall source, introduced at adapter terminal  301 , or from an internal source, such as a battery  303 , introduced at terminal  311 . Power is output to the system at system terminal  310 . Controller  302  drives transistors  304  and  306  to switch between adapter terminal  301  and battery terminal  311 , and further, as seen therein, regulates power from the adapter terminal  301  to the battery  303  for recharge by controlling buck converter  307 . A Schottky diode  308  is added to isolate the adapter voltage  301  from system terminal  310 . The buck converter circuit  307  facilitates use of power from the external source at the adapter terminal  301  when the voltage from that source is higher than the battery  303  voltage. The buck converter  307  duty cycle is set by the controller  302  to achieve the desired charge current and charge voltage. The charge current information is fed back to the controller  302  through pins  326  SRP and  327  SRN. The battery  303  voltage is fed back to the controller via a resistive divider connected to pin BATP  340 . In addition to that the duty cycle signal at /PWM pin  325  is level shifted to provide the necessary gate voltage levels for the external PMOS transistor  305 .  
         [0024]     This arrangement, together with modifications in the controller logic to allow comparison between the voltages at pins VCC  329  and VPACK  341 , enables the implementation of airline mode without additional switches in series with the PWM converter switch. The battery pack is charged by the buck converter  307 . The following states related to charge and airline mode are implemented in the controller internal logic:  
                                                                   SWITCH   SWITCH   SWITCH                   AC       312   304   306   SWITCH   SWITCH       adapter       (diode   (ac to   (batt to   305   331   OPERATION       detected   VCC &gt; VPACK   bypass)   system)   system)   (pwm ctrl)   (airline)   MODE                   NO   Don&#39;t care   OFF   OFF   ON   OFF   ON   PACK                                   CONNECTED TO                                   SYSTEM       YES   YES   PULSED   ON   OFF   PWM   ON   ADAPTER TO                           CONTROL       SYSTEM,                                   CHARGING                                   PACK       YES   NO   PULSED   ON   OFF   OFF   OFF   ADAPTER TO                                   SYSTEM, PACK                                   ISOLATED                                   FROM SYSTEM                                   (AIRLINE MODE)                  
 
 Diodes  314  and  315  provide a continuous power path for the controller supply to ensure that a lock-up condition does not exist during power up conditions. This guarantees that the controller always has power, independently of the state of switches  305 ,  306 ,  304  and  312  whenever an external supply is connected to terminal  301  or a battery pack is connected to terminal  311 . The inrush current during adapter insertion is minimized by connecting the buck converter switch driver to the system terminal  310 . This allows a reduction in the value of capacitor  309  connected to node  350 . Capacitor  309  is dimensioned only to filter transients at node  350 . Note that the same configuration used in  FIG. 1  can still be implemented by connecting switch  306  to node  350  without affecting the implementation of this invention. 
 
         [0026]     Although a preferred embodiment of the method and system of the present invention has been illustrated in the accompanied drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.