Battery supported power supplies are used for a variety of applications. Often a battery output voltage must be regulated prior to being utilized in a system. For example, as shown in FIG. 1 an information handling system 100 may include a battery power source 110 which supplies a battery output voltage Vbat 120. The battery output voltage Vbat 120 may be coupled to a voltage regulator 130 which generates at the output terminal a regulated voltage Vreg 140 from the battery output voltage Vbat. The regulated voltage Vreg may be provided to a variety of other system components 150.
A wide range of types of systems may include circuitry such as shown in FIG. 1, one such system is an information handling system. As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
In a typical application of the circuitry of FIG. 1, the battery output voltage Vbat may have a varying voltage range that is typically higher and less controlled than the desired power supply voltage range required by the other system components 150 of the information handling system. Thus the voltage regulator regulates the Vbat voltage 120 to the desired level necessary for the proper operation of the other system components 150. For example, the Vbat voltage may range for 4.2V to 3.0V over the life of a battery and it may be desired that the Vreg voltage range be 3.3V to 3.0V at the output voltage terminal. As used herein “battery life” refers to the useful charge life of a single charge of the battery. However, most voltage regulation circuitry requires some differential between the input voltage and the output voltage. Thus, if the Vbat voltage drops to 3.0V, the voltage regulator 130 may only be able to supply a regulated voltage Vreg that is less than 3.0 V. In this fashion, the full voltage range of the Vbat voltage 120 may not be useable as at the low end of the voltage range the voltage may not be sufficiently high to support the required Vreg voltage levels.
One application of voltage regulators in information handling system such as shown in FIG. 1 is provide an uninterruptible power supply (UPS) that includes a battery power supply source and other system power supply sources (such as sources derived from AC power provided from the public power grid). Typically the battery power source may be provided to maintain power in the event the system power supply sources are not available. Such a system that may be formed in an information handling system is shown in FIG. 2. FIG. 2 illustrates the power supply inputs and outputs for a voltage regulation circuit that may be used to form an UPS. As shown in FIG. 2, in addition to the battery output voltage Vbat 120 provided at one terminal as shown, two additional output voltages V1 220 and V2 222 are provided at the output terminals of a first and second power supply respectively. (for example 5V power sources). Diodes 226 are provided between the output voltages and a voltage regulator 230 as shown. The voltage regulator 230 may be a low-dropout (LDO) linear voltage regulator which may operate when the input voltage barely exceeds the desired output voltage. The voltage regulator 230 provides the regulated voltage Vreg 140. As shown, the voltage regulator 230 may include a voltage input IN, a voltage output OUT, and a shutdown/enable input SHDN to shutdown the regulator and to disable the output Vreg power supply. A wide range of LDO voltage regulators are known in the art, such as for example, the Maxim MAX1935 or the Micrel MIC5235.
Using the exemplary voltage levels described above with reference to FIG. 1, the battery output voltage Vbat may vary from 4.2V to 3.0V. In typical applications the voltage drop across the diodes may be 0.35V and the voltage regulator 230 may require an input voltage that is 0.25V greater than the desired output voltage. To achieve the minimum desired Vreg voltage level of 3.0V, the input voltage at the IN input must be at least 3.25V and the corresponding minimum Vbat voltage level must be 3.6V. Thus, when the battery discharges such that Vbat is less than 3.6V the battery will no longer support the required Vreg voltage range. In such circumstances, the discharge capacity of the battery from 3.6V to 3.0V is not utilized and hence the battery life will be reduced. This is exacerbated considering that the average battery life loss is between 15 to 30% of the total battery life depending upon discharge characteristics of the battery cell type being utilized.