Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-10-23
2002-10-08
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S034000
Reexamination Certificate
active
06462964
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention specifically relates to powering computer systems where switch-mode DC is created to power the internal components of the system. It has particular applicability in new designs where microprocessors have high demands and power changes. Such can relate to the area of powering low voltage, high current electronics. As mentioned, though, the invention is applicable in the field of computing, and much of the following description is presented in that context. It should be understood, however, that other embodiments are in no way limited to the field of computing, and are applicable to a wide variety of circumstances wherein a variety of power absorbing loads which absorb electrical power may abruptly change their power absorbing characteristics (that is to say, their impedance may undergo a rapid change). They are also applicable if such loads are separated physically such that the voltage which may be dropped across the dynamic impedance of the power carrying conductors is a significant fraction of the voltage delivered to such loads. They are also increasingly applicable to applications wherein design tradeoffs are forcing a steady decrease in operating voltages. Such situations may arise in telecommunications, radar systems, vehicle power systems and the like, as well as in computing systems. Further, the DC/AC converter itself may have applications in broader and other contexts as well.
The architecture of computing systems has undergone tremendous changes in the recent past, due principally to the advance of microcomputers from the original four-bit chips running at hundreds of kilohertz to the most modern 32 and 64 bit microprocessors running at hundreds of megahertz. As the chip designers push to higher and higher speeds, problems arise which relate to thermal issues. That is, as the speed of a circuit is increased, the internal logic switches must each discharge its surrounding capacitance that much faster. Since the energy stored in that capacitance is fixed (at a given voltage), as the speed is increased, that energy, which must be dissipated in the switches, is dumped into the switch that many more times per second. Since energy per second is defined as power, the power lost in the switches therefore increases directly with frequency.
On the other hand, the energy stored in a capacitance increases as the square of the voltage, so a capacitor charged to two volts will store only 44% of the energy stored in that same capacitor charged to three volts. For this reason, a microcomputer designed to operate at two volts will, when run at the same speed, dissipate much less power than the same microprocessor operating a three volts. So there is a tendency to lower the operating voltage of microprocessors.
Other considerations cause the microprocessor to exhibit a lower maximum speed if operated at a lower voltage as compared to a higher operating voltage. That is, if a circuit is operating at full speed, and the voltage on that circuit is simply reduced, the circuit will not operate properly, and the speed of the circuit (the “clock speed”) may have to be reduced. To maintain full speed capability and still operate at lower voltage, the circuit often must be redesigned to a smaller physical size. Also, as the size of the circuitry is reduced, and layer thickness is also reduced, the operating voltage may need to be lowered to maintain adequate margin to avoid breakdown of insulating oxide layers in the devices. For the past few years, these steps have defined the course of microprocessor design. Key microprocessor designers, seeking the maximum speed for their products, have therefore expended considerable effort trading off the following considerations:
higher speed chips are worth more money;
higher speed chips must dissipate more heat;
there are limitations to removal of that heat;
lower voltages reduce the heat generated at a given speed; and
smaller devices run faster at a given voltage.
Of course, there are many, many important trade-off considerations beyond these, but the above list gives the basic elements which relate to same aspects of the current invention. The result of these considerations has been for the microprocessor designers to produce designs that operate at lower and lower voltages. Early designs operated at five volts; this was reduced to 3.3. to 3.0, to 2.7, to 2.3, and at the time of writing the leading designs are operating at 2.0 volts. Further reductions are in store, and it is expected that future designs will be operated at 1.8, 1.5, 1.3, 1.0, and even below one volt, eventually perhaps as low as 0.4 volts.
Meanwhile, advances in heat removal are expected to permit processors to run at higher and higher heat dissipation levels. Early chips dissipated perhaps a watt; current designs operate at the 30 watt level, and future heat removal designs may be able to dissipate as much as 100 watts of power generated by the processor. Since the power dissipated is proportional to the square of the operating voltage, even as the ability to remove heat is improved, there remains a tendency to run at lower operating voltages.
All of this is driven by the fundamental consideration: higher speed chips are worth more money. So the designers are driven to increase the speed by any and all means at their disposal, and this drives the size of the chips smaller, the voltages lower, and the power up. As the voltage drops the current increases for a given power, because power is voltage times current. If at the same time improvements in heat removal permit higher powers, the current increases still further. This means that the current is rising very rapidly. Early chips drew small fractions of an ampere of supply current to operate, current designs use up to 15-50 amperes, and future designs may use as much as 100 amperes or more.
As the speed of the processors increase, the dynamics of their power supply requirements also increase. A processor may be drawing very little current because it is idling, and then an event may occur (such as the arrival of a piece of key data from a memory element or a signal from an outside event) which causes the processor to suddenly start rapid computation. This can produce an abrupt change in the current drawn by the processor, which has serious electrical consequences.
Inductance is the measure of energy storage in magnetic fields. All current-carrying conductors have associated with the current a magnetic field, which represents energy storage. It is well known by workers in the art that the energy stored in a magnetic field is half the volume integral of the square of the magnetic field. Since the field is linearly related to the current in the conductor, it may be shown that the energy stored by a current carrying conductor is proportional to half the square of the current, and the constant of proportionality is called the “inductance” of the conductor. The energy stored in the system is supplied by the source of electrical current, and for a given power source there is a limit to the rate at which energy can be supplied, which means that the stored energy must be built up over time. Thus the presence of an energy storage mechanism naturally slows down a circuit, as the energy must be produced and metered into the magnetic field at some rate before the current can build up.
The available voltage, the inductance, and the rate of change of current in a conductor are related by the following equation, well known by those skilled in the art:
V=L*∂I/∂t,
where L is the inductance of the conductor, and ∂I/∂t is the rate of change of current in the conductor.
This equation states that the voltage required to produce a given current change in a load on a power system increases as the time scale of that change is reduced, and also increases as the inductance of any connection to that load is increased. As the speed of microprocessors is increased, the time scale is reduced, and as the available voltage is reduced, this equation requires the inductance to be dropped proporti
Gurov Gennady G.
Ledenev Anatoli V.
Porter Robert M.
Advanced Energy Industries Inc.
Berhane Adolf Deneke
Santangelo Law Offices P.C.
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