Patent Application
20080238203
The present invention relates to a battery charging and power management circuit.
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 high 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 probably 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.
The present invention is described with reference to the accompanying drawings.
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.
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, system load 104 is directly connected in parallel with the battery 102. Charger 106 is located between battery 102 and power ports 108 and 110. In this manner, the voltage of battery 102 ultimately controls the amount of current drawn by system load 104, not the voltage of USB port 108 or 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's refer to
Over the years, an alternative topology has been employed to address some of the deficiencies inherent to charger topology 100.
As shown in
First, system load 204 is no longer powered exclusively by battery 202. In this topology, system load 204 is powered by a maximum voltage source (Vmax) from one of the three power sources: battery 202, USB power port 208, or wall power port 210. In this manner, the life of battery 202 may be extended because topology 200 takes advantage of all available high voltage sources to meet the power demand of system load 204.
Second, because of the layout configuration of battery 202 and charger 206, it is now possible to charge battery 202 in certain situations that would not be possible with topology 100. For example, using the same criteria used in topology 100, let's assume that system load 204 power requirement is a constant load of 1.7 W, the Vmax available is 5V from USB port 208, and the voltage of battery 202 is 3V. In this scenario, the current drawn by system load 204 would be 340 mA instead of 566 mA because the system is being powered by Vmax (5V) instead of the lower battery voltage. Further, the remaining unused 160 mA could be used to charge battery 202.
However, if charger 206 is not connected to an external power source, then node 230 will be at 0V. In this situation, diode 215 will be forward biased and Vmax will be at 3V. In this manner, battery 102 is powering system load 204.
In general, there are two major types of power supply, linear regulator and pulse-width modulated (PWM) switching regulator. Both types of regulator 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 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 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 regulator. For example, mobile phones and portable music players typically have several linear regulators in addition to switching regulators.
Linear regulator is best suited for low noise application because its output exhibit very little to no electrical noise. The response time of linear regulator is also very short. However, linear regulator is inefficient and can only have one output voltage. For this reason, many devices contain several linear regulators.
As mentioned, switching regulator is preferably used to power a load that requires constant power. Switching regulator is more energy efficient than linear regulator and can have more than one output voltages. However, switching regulator is more electrically noisy than linear regulator.
Similar to topology 200, power supply system 300 will be able to charge battery 302 in certain situations where it would not be possible with topology 100. System 300, however, can be further improved to allow for power saving where the combined current requirement of both switching regulators 312 and linear regulators 314 exceeds 500 mA. If, for example, the current requirement of both regulators is 600 mA total, USB power port 308 will not be able to deliver this amount because it is current limited to 500 mA. As a result, 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.
First, types of system load 404 are intelligently separated into constant power load and constant current load. This allows all loads to be properly powered by switching regulator 412 and linear regulator 414.
Second, switching regulator 412 may still take advantage of the intermediate voltage bus design by having its input coupled to Vmax as opposed to the battery voltage in topology 100. In this manner, constant power may be provided using the maximum voltage available (Vmax) and thus reducing the amount of current drawn by switching regulators 412. In most cases, the current drawn by switching regulator 412 will be less than the maximum current that 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 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 battery 402.
Third, since linear regulator 414 is directly coupled to the output node of battery 402, a low constant current load may be directly powered by battery 402. This may seems disadvantageous at first glance, however, if charger 406 is coupled to a USB power source, any excess or unused current by switching regulator 412 may be used to charge battery 402 or to supplement the current needs of linear regulator 414.
To illustrate, let's compare system 300 and 400 in
Applying the same scenario to system 400 would results in a total current drain of 40 mA from battery 402. Since linear regulator 414 is directly coupled to battery 402 output node, its load does not contribute to the total amount of current switching regulator may draw from Vmax. Since battery 402 directly provide the 200 mA, Vmax is allowed to stay at the voltage of the external power source. As a result, the total current drawn by switching regulator 412 is equal to 1.7 W/5V, which is 340 mA as opposed to 566 mA in system 300. The excess 160 mA may then be used to charge battery 402 or used to supplement the 200 mA needed by linear regulator 414.
In the exemplary illustrations of
In step 620, the constant power portion of system load 404, including switching regulator 412, is coupled to node 415, which is the Vmax between battery 402 and power port 408 or 410.
In step 630, the constant current portion of system load 404, including linear regulator 414, is coupled in parallel to battery 402. In this way, a low constant current load may be directly powered by battery 402.
In step 640, any excess or unused current by switching regulator 412 may be used to charge battery 402 or to supplement the current needs of linear regulator 414.
In step 650, if the current requirement of both switching regulator 412 and linear regulator 414 exceeds 500 mA, then the amount of current over 500 mA will be drawn from battery 402. In this way, system 400 takes advantage of available external power sources to supplement its overall current requirement. Additionally, when the current requirement of system 400 is lower than 500 mA, then the amount of unused current (left over from the 500 mA) can be used to charge battery 402.
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.
