Abstract:
Traditionally, system loads are placed in parallel with the battery. This simple topology wastes the available power if the USB power and/or wall adapter is present. Recent topologies have made some improvements by powering the load by the maximum available voltage. Thus, if a USB power source or wall adapter is present, the load is powered by them rather than the battery, thus improving the system efficiency. However, since the USB power and wall adapter power are current limited, if the load requires higher current than the current limited USB or adapter, then the entire system is powered at voltage of the battery. The present invention further improves the system efficiency by distinguishing the load and powering the constant power loads by the maximum voltage and placing the constant current loads in parallel with the battery.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a battery charging and power management circuit. 
     BACKGROUND OF THE INVENTION 
     Long battery life is an essential feature for any portable devices, particularly laptops, PDAs, and mobile phones. These mobile devices typically have a battery charger capable of being charged with a wall adapter or through a universal serial bus (USB) connection. Currently available battery charger designs are generally deficient in number of ways. 
     In one design, power from a higher voltage source is not properly utilized which causes the battery to discharge rather than being charged in certain cases. 
     In another design, the load of the system is not being properly distinguished and managed, which leads to unnecessary discharge of the battery power. 
     Accordingly, it is desirable to have a battery charging system that addresses the above deficiencies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The present invention is described with reference to the accompanying drawings. 
         FIGS. 1A-B  illustrate block circuit diagrams of a charger fed topology. 
         FIGS. 2A-B  illustrate block circuit diagrams of an intermediate voltage bus. 
         FIGS. 3A-B  illustrate block circuit diagrams of a power system. 
         FIGS. 4A-B  illustrate block circuit diagrams of a power system according to an embodiment of the present invention. 
         FIG. 5A  illustrates exemplary power requirements for the system of  FIG. 3A . 
         FIG. 5B  illustrates exemplary power requirements for the system of  FIG. 4A . 
         FIG. 6  illustrates a method for charging a battery and for providing power to a plurality of loads according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This specification discloses one or more embodiments that incorporate the features of this invention. The embodiment(s) described, and references in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. An embodiment of the present invention is now described. While specific methods and configurations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the art will recognize that other configurations and procedures may be used without departing from the spirit and scope of the invention. 
       FIG. 1A  shows a typical battery charger topology  100  which includes a battery  102 , a system load  104 , a charger  106 , a USB power port  108 , and a wall plug power port  110 . Battery  102  is directly coupled in parallel with system load  104 . The charger  106  is coupled between the battery  102  and the power ports  108  and  110 . 
     The topology  100  is simple in design but is deficient in many ways, one of which is the inefficient use of other available power sources. As shown, the system load  104  is directly connected in parallel with the battery  102 . The charger  106  is located between the battery  102  and the power ports  108  and  110 . 
     In this manner, the voltage of the battery  102  ultimately controls the amount of current drawn by the system load  104 , not the voltage of the USB port  108  or the wall port  110 . This is particularly disadvantageous where a battery of low voltage is used (such as a 3V battery on many portable devices), because the system needs to draw more current from a lower voltage source to meet its power demand as compared to the current drawn from a higher voltage source 
     To illustrate the deficiency above, let&#39;s refer to  FIG. 1B  and assume the following: the battery  102  is a 3V battery, the power requirement of the system load  104  is 1.7 W, and a USB power source is present at 5V. As stated above, the current drawn by the system is controlled by the voltage of the battery. Thus, the current drawn by system load  104  is 566 mA, 1.7 W/3V (I=P/V). Since 566 mA is over the current limit of 500 mA of a USB power source, the rest of the 66 mA has to be drawn from the battery. Thus, in this situation, the battery  102  is not being charged by the USB power source. Instead, it is being depleted by the system load  104  even though the charger is connected to the USB power port  108 . 
     Over the years, an alternative topology has been employed to address some of the deficiencies inherent to the charger topology  100 .  FIG. 2A  illustrates a voltage bus topology  200 , an improvement over the topology  100 . 
     As shown in  FIG. 2A , bus topology  200  includes a battery  202 , a system load  204 , a charger  206 , a USB power port  208 , and a wall power port  210 . The topology  200  is mainly different from the topology  100  in that the battery  202  is no longer connected directly in parallel with the system load  204 . Simply stated, the battery  202  is now coupled to an input port of the charger  206  instead of being coupled in parallel with the system load  204 . This architecture offers several advantages over the topology  100 . 
     First, the system load  204  is no longer powered exclusively by the battery  202 . In this topology, the system load  204  is powered by a maximum voltage source (V max ) from one of the three power sources: the battery  202 , the USB power port  208 , or the wall power port  210 . In this manner, the life of the battery  202  may be extended because the topology  200  takes advantage of all available high voltage sources to meet the power demand of the system load  204 . 
     Second, because of the layout configuration of the battery  202  and the charger  206 , it is now possible to charge the battery  202  in certain situations that would not be possible with the topology  100 . For example, using the same criteria used in the topology  100 , let&#39;s assume that the system load  204  power requirement is a constant load of 1.7 W, the V max  available is 5V from the USB port  208 , and the voltage of battery  202  is 3V. In this scenario, the current drawn by the system load  204  would be 340 mA instead of 566 mA because the system is being powered by V max  (5V) instead of the lower battery voltage. Further, the remaining unused 160 mA could be used to charge the battery  202 . 
       FIG. 2B  further illustrates the charger  206 . As shown, another major difference between the topology  100  and the topology  200  is the inclusion of diode  215  which acts as a voltage sensor and selector. The diode  215  is connected between node  220  and node  230 . As shown, node the  220  is coupled to the battery  202 , and the node  230  is coupled to the power port  208  or  210  and to the system load  204 . In this configuration, the load system  204  will always be powered by the highest available voltage. For example, let&#39;s consider the following scenario: the battery voltage is 3V, which places node  220  at 3V; and the charger  206  is connected to a 5V USB voltage source, which means that the node  230  will be at 5V. In this scenario, the diode  215  is reversed biased, therefore current from the battery  202  will not be allowed to pass. In this way, V max  will be at 5V instead of 3V. 
     However, if the charger  206  is not connected to an external power source, then the node  230  will be at 0V. In this situation, the diode  215  will be forward biased and V max  will be at 3V. In this manner, the battery  202  is powering the system load  204 . 
     In general, there are two major types of power supplies, a linear regulator and a pulse-width modulated (PWM) switching regulator. Both types of regulators have their own advantages and disadvantages, but each has its own niche in certain types of applications. For example, for low noise applications, linear regulators are preferred, and for noise tolerant applications, switching regulators are used, as they are more power efficient than linear regulators. Linear regulators act as a constant current load, i.e., the input (supply) current is same as the load current irrespective of the input voltage. Whereas, switching regulators act as a constant power load, i.e., the input current drawn by the regulator decreases as the input voltage increases for a given load. Most electronic devices, if not all, contain both types of regulators. For example, mobile phones and portable music players typically have several linear regulators in addition to switching regulators. 
     A linear regulator is best suited for a low noise applications because its output exhibits very little to no electrical noise. The response time of a linear regulator is also very short. However, a linear regulator is inefficient and can only have one output voltage. For this reason, many devices contain several linear regulators. 
     As mentioned, a switching regulator is preferably used to power a load that requires constant power. A switching regulator is more energy efficient than a linear regulator and can have more than one output voltage. However, switching regulator is more electrically noisy than a linear regulator. 
       FIG. 3A  illustrates a power supply system  300  that includes both types of regulators. The system  300  includes a battery  302 , a system load  304 , a charger  306 , a USB power port  308 , a wall power port  310 , switching regulators  312 , and linear regulators  314 . The system  300  has an intermediate voltage bus topology having the switching regulators  312  and linear regulators  314  coupled between the system load  304  and V max , at node  330 . As shown, both the switching regulators  312  and the linear regulators  314  draw power from the node  330 , which is the maximum voltage between the battery  302 , the USB power port  308 , and the wall power port  310 . 
       FIG. 3B  illustrates the power supply system  300  being powered by a 5V voltage source, such as the USB power port  308 .  FIG. 3B  further illustrates a diode  315  being coupled between the node  330  and node  320 , which is coupled to the battery  302 . Similar to the diode  215 , the diode  315  is used to monitor whether another power supply is present other than the battery  302 . In the case of  FIG. 3B , a 5V voltage is provided by the USB port  308 . Thus, the diode  315  is reversed biased, making the node  330  have a voltage of 5V. 
     Similar to the topology  200 , the power supply system  300  will be able to charge the battery  302  in certain situations where it would not be possible with the topology  100 . The system  300 , however, can be further improved to allow for power saving where the combined current requirement of both the switching regulators  312  and the linear regulators  314  exceeds 500 mA. If, for example, the current requirement of both regulators is 600 mA total, the USB power port  308  will not be able to deliver this amount because its current is limited to 500 mA. As a result, the node  330  will be forced to 3V or below and the entire current load of 600 mA will be supplied by the battery, assuming a 3V battery is used. 
       FIG. 4A  illustrates a power system  400  according to an embodiment of the present invention. The power system  400  includes a battery  402 , a system load  404 , a charger/power management module  406 , a USB power port  408 , a wall power port  410 , a switching regulator  412 , and a linear regulator  414 . The input of the switching regulator  412  is coupled to V max . In this configuration, the input current to the switching regulator  412  decreases as V max  increases because the switching regulator  412  is a constant power source. Hence, the larger the available voltage, the less current is needed to generate the required power. In the system  400 , only portions of the system load  404  that require a constant power source are coupled to the switching regulators  412 . Other portions of the system load  404  that require a constant current source are coupled to the linear regulators  414 . 
       FIG. 4B  illustrates the system  400  in further details. As shown, an input node  425  of the linear regulator  414  is coupled to node  420  instead of V max  as in the case of the system  300 . The node  420  is connected to the battery  402  so that the linear regulator  414  is directly connected to the battery  402 . In the system  400 , all of the linear regulators  414  are connected in parallel with battery  402 . All of the switching regulators  412  are powered from V max , which is similar to the system  300 . This configuration is advantageous in a number of ways. 
     First, types of the system load  404  are intelligently separated into constant power loads and constant current loads. This allows all loads to be properly powered by switching regulator  412  and linear regulator  414 . 
     Second, the switching regulator  412  may still take advantage of the intermediate voltage bus design by having its input coupled to V max  as opposed to the battery voltage in the topology  100 . In this manner, constant power may be provided using the maximum voltage available (V max ) and thus reducing the amount of current drawn by the switching regulators  412 . In most cases, the current drawn by the switching regulator  412  will be less than the maximum current that the USB port  408  could provide, which is 500 mA. Any excess or unused current may then be used to charge the battery or be redirected to the linear regulator  414 . This latter concept will be further explained below. In any case, this design helps improve power efficiency and extend the life of the battery  402 . 
     Third, since the linear regulator  414  is directly coupled to the output node of the battery  402 , a low constant current load may be directly powered by the battery  402 . This may seem disadvantageous at first glance, however, if the charger  406  is coupled to a USB power source, any excess or unused current by the switching regulator  412  may be used to charge the battery  402 , or to supplement the current needs of the linear regulator  414 . 
     To illustrate, let&#39;s compare the system  300  and the system  400  in  FIG. 5A  and  FIG. 5B , respectively, and assume the following: the batteries  302  and  402  are 3V batteries, the power requirement of each switching regulator shown is 1.7 W, each USB power source is at 5V, and the constant current requirement of each linear regulator is 200 mA. In this scenario, the total current required by both switching regulator and linear regulator would exceed 500 mA, the current limit of the USB power port. Since the current requirement exceeds the amount the power port  308  could provide, V max  of the system  300  is forced to 3V (the same level as battery  302 ). As a result, the current drawn by the switching regulator  312  is equal to 1.7 W/3V, which is 566 mA. As shown, 500 mA of the 566 mA can be provided by the USB power source. The other 66 mA has to come from the battery  302 . This results in a total current drain of 266 mA from the battery  302 . 
     Applying the same scenario to the system  400  would results in a total current drain of 40 mA from the battery  402 . Since the linear regulator  414  is directly coupled to the battery  402  output node, its load does not contribute to the total amount of the current switching regulator  412  may draw from V max . Since the battery  402  directly provides the 200 mA, V max  is allowed to stay at the voltage of the external power source. As a result, the total current drawn by the switching regulator  412  is equal to 1.7 W/5V, which is 340 mA as opposed to 566 mA in the system  300 . The excess 160 mA may then be used to charge the battery  402  or used to supplement the 200 mA needed by the linear regulator  414 . 
     In the exemplary illustrations of  FIGS. 4B and 5B , a diode has been used as the power management module to select the maximum voltage source to power the switching regulator load. However, for those well versed in the relevant art, it is apparent that a diode can be replaced with other circuitry including a transistor switch. One node of the transistor switch can be coupled to the input port of the switching regulator and the second node of the switch is coupled to the battery. The switch is normally off if a power source is present and turns on only if no other power source with voltage higher than battery voltage is present. 
       FIG. 6  illustrates a method  600  for charging the battery  402  and for providing power to the switching regulator  412  and the linear regulator  414 . In step  610 , the system load  404  is partitioned into two separate portions, a constant power portion and a constant current portion. The switching regulator  412  provides the constant power supply for the constant power portion of the system load  404 . Whereas, the linear regulator  414  provides the constant current supply for the constant current portion of the system load  404 . 
     In step  620 , the constant power portion of the system load  404 , including the switching regulator  412 , is coupled to the node  415 , which is the V max  between the battery  402  and the power ports  408  or  410 . 
     In step  630 , the constant current portion of the system load  404 , including the linear regulator  414 , is coupled in parallel to the battery  402 . In this way, a low constant current load may be directly powered by the battery  402 . 
     In step  640 , any excess or unused current by the switching regulator  412  may be used to charge the battery  402  or to supplement the current needs of the linear regulator  414 . 
     In step  650 , if the current requirement of both the switching regulator  412  and the linear regulator  414  exceeds 500 mA, then the amount of current over 500 mA will be drawn from the battery  402 . In this way, the system  400  takes advantage of available external power sources to supplement its overall current requirement. Additionally, when the current requirement of the system  400  is lower than 500 mA, then the amount of unused current (left over from the 500 mA) can be used to charge the battery  402 . 
     CONCLUSION 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.