Selective dual input low dropout linear regulator

Details Selective dual input low dropout linear regulator Selective dual input low dropout linear regulator

1998-11-20

2001-03-06

Berhane, Adolf (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

Reexamination Certificate

active

06198262

ABSTRACT:

BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to power supplies for personal computers and more particularly to low dropout linear regulators.
Background: PC Power Supplies
Many PC power supplies are of the same basic design. A typical topology is Constant Voltage Half-Bridge Forward Converting Switching power supplies, usually known simply as switching supplies. Constant voltage means that the output voltage is always the same as the current changes with changing power requirements. Half-Bridge Forward Converting is the type of switching design. The main advantages of these power supplies over other designs are their high efficiency, low heat dissipation, small size, and affordable prices.
While all PC power supplies operate in a similar manner, there can be wide variations in quality and performance. Standards certification, the manufacturer's reputation, and the following basic technical parameters are useful when testing, evaluating, and specifying a computer power supply.
AC Ripple, also known as PARD (periodic and random deviation) measures the root-mean-square RMS (average) voltage of all AC components on the DC output. This average number can be deceptive because it does not provide information on the presence of periodic switching spikes. RMS AC Ripple measurements should be accomplished by peak voltage measurements to assure switching spikes are not excessive (i.e., <200 mV).
Load regulation, more accurately called voltage load regulation, measures the output voltage change from minimum load (minimum current sourced) to maximum load (maximum current sourced). In general, the voltage tends to drop off as the current rises and Load Regulation is a negative number. In practice, power supply manufacturers rarely indicate whether regulation is positive or negative.
Line regulation, more accurately called voltage line regulation, measures the output voltage change from minimum AC input to maximum AC input. The typical 115VAC power supply is designed to accept an AC input ranging from 90VAC to 135VAC with little change in its DC outputs.
The Mean Time To Failure (MTTF) is a useful parameter to specify the quality of a system. The MTTF is the expected time that a system will operate before the first failure occurs. The MTTF is calculated by applying a mathematical formula to the individual component failure rates. A MTTF of 30,000 hours is fairly common for PC power supplies, equating to around 3.5 years of continuous use.
Efficiency is simply the ratio of output power to input power. For a computer power supply this ratio is usually between 65-85%; the other 15-35% being dissipated as heat during AC to DC conversion. Efficiency is important for a couple of reasons. First, the less heat dissipated, the better. Excessive heat can cause shortened lifecycles and induce poor system performance. Second, greater efficiency means money saved on electric bills. Often efficiency is a design choice; increased efficiency may sacrifice load regulation and other parameters.
A current and future consideration is the direction of the EPA's Energy Star Program. Presently, there are no specifications for power supplies, only for systems. For ‘Green’ certification, the computer, not including monitor, must not exceed 30 W of power consumption in the low-power (inactive) state. Efficient power supplies help computer makers meet ‘Green’ certification.
Background: Power Conservation and Battery Powered Endurance
There are three basic approaches to extending the battery powered endurance of a portable computer. The simplest way is to specify components at the lowest economical power consumption. Thus, for instance, CMOS integrated circuits and liquid crystal displays (LCDs) will normally be used. An equally simple way is to increase battery capacity. However, both of these routes rapidly encounter limits which are set simply by the tradeoff of the cost of lower-power components or of the elimination of functionality, with user expectations.
The third way is to use power-management algorithms so that, at almost every instant, all components are being operated in the lowest-power mode for their current demands. Thus, for example, a processor which is not currently executing a program may be placed into “sleep” mode, to reduce its overall power consumption. For another example, substantial power savings can be achieved simply by stopping the system clock (or by slowing down the system clock to a very low rate). For another example, it is common practice, in portable computers with an LCD display, to provide backlighting for use of the display under low-light conditions since this backlighting consumes relatively large amounts of power, it will normally be turned off after a short period of inactivity (or even, alternatively, after a short duration regardless of activity), until the user again demands backlighting.
All of these lines of approach have some inherent limits. For example, it is hard to foresee any integrated circuit technology which would be more economical and more power-efficient than low-power low-voltage CMOS being produced by the century's end. While some further improvement in this area is foreseeable, no revolutionary improvements appear likely. Moreover, in practice, such improvements are largely outside the control of system designers: when lower-power chips are sampled, system design houses will buy them; but system design houses cannot greatly accelerate the pace of introduction of such chips.
It is also true that the smartest power-management programs cannot reduce the time fraction during which the user wishes to look at the display, or enter data through the keyboard. However, in this area there does appear to be room for improvement, and system design improvements can help achieve power efficiency.
Many power management schemes have been proposed in which parts of the system are shut down during periods of inactivity. These approaches tend to extend the usable working time of the system between recharges. (One example of a portable computer system with power-monitoring functions is described in U.S. Pat. No. 4,980,836 to Carter et al., which is hereby incorporated by reference. Another source of proposed teachings regarding power-management functions is provided by the DS1227 product preview, contained in the 1988 data book of Dallas Semiconductor Corporation, which is also hereby incorporated by reference.)
In addition, it has been recognized that management of the charging and discharging cycles of Ni-Cd batteries can help to extend their life.
Either of these power-management functions requires some intelligent control. The conventional way to implement control mechanisms has been using the main microprocessor (CPU). The necessary control program steps are inserted into the BIOS software (basic input/output system software), which is stored in ROM.
Background: Sleep Mode
Laptop computer systems will typically have an automatic power-down function. Since some of the components use significant power, even when no computation or input is occurring, the system will send itself into a standby or sleep mode if the user has not provided any input for a given period of time (e.g., 30 seconds or five minutes). (Sleep mode may not normally be entered, however, if new information is still being written to the display.)
There are various enhancements which have been proposed to the scheme. For example, it may be desirable to blank the display after a certain length of inactivity and shut down the system clock only after an additional length of inactivity.
Thus, there may be more than one reduced-power mode. For example, a “standby” mode may be used to transiently power-down subsystems (such as the display or the hard disk) without stopping the CPU. For deeper inactivity, a “sleep” mode can also be entered, in which nearly all functions of the system arc turned off. From the standpoint of power consumption, entering sleep mode is almost the same as turning a conventional nonportable machine off (except that data will not be lost).
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