Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-06-28
2001-04-03
Le, Dinh T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S056000, C327S077000, C327S050000
Reexamination Certificate
active
06211726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to electronic load circuits, and more particularly to a low-voltage, high-current load circuits for use in testing power supplies or the like for computers and systems of this type.
2. Description of the Related Art
In the design and production of power supply modules for computer systems and the like, it is necessary to have load circuits which simulate the operation of the computer itself in the way the voltage and current levels presented by the load vary with time and other conditions. For example, the load presented to the power supply by the computer system may switch between high-current and low-current when the computer goes into a power-down or sleep mode as power management mechanisms go into effect. Or, current spikes may occur when starting up equipment such as a hard drive, or at boot-up when large capacitive loads are being charged. Likewise, power-up self test creates a widely variable load as all of the peripheral equipment is exercised.
Previous load circuits used for test purposes in the manufacture of computer systems or the like have not been able to operate at low voltages such as the supply voltage levels being specified for contemporary microprocessor chips and memory chips. For example, supply voltage levels of 3.3V have ben used for some time, and levels of 1.7v or 1.5V are coming into common usage. At these low voltage levels, and at high currents of sometimes hundreds of amps, the available equipment is not able to accurately simulate varying load currents, nor represent the loading exhibited by a computer system.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide an improved electronic load of the type used for testing regulated power supplies.
It is another object of the present invention to provide an improved low-voltage, high-current electronic load circuit.
It is yet another object of the present invention to provide an improved low-voltage, high-current electronic load circuit which simulates the operations of a computer system under varying load conditions.
The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.
According to one embodiment of the invention, an electronic load circuit provides a variable load current at a high amp level, at low-voltage so that contemporary voltage supplies of perhaps 1.5V may be tested. This load is used for testing voltage supply circuits for computer systems or the like. A number of parallel, high-current MOS transistors of low internal resistance are used as a constant-current load. Current in the load path is sensed by a resistor connected in series with all of the transistors, and this resistor is of the order of the effective internal resistance of the source-to-drain paths of the parallel transistors and connecting links to these transistors via a circuit board, connector terminals, etc. The sensed voltage across this resistor provides a feedback signal to a high-gain op-amp, the output of which is compared to a variable input signal to produce a gate drive voltage for the transistors. The input signal may be varied to simulate the variable loading exhibited by a computer system. It is important that the current sensing arrangement including the sensing resistor is of low resistance.
REFERENCES:
patent: 5881014 (1999-03-01), Ooishi
Daun-Lindberg Timothy Charles
Miller Michael Lee
Felsman, Bradley, Vaden, Gunter & Dillon
International Business Machines - Corporation
Le Dinh T.
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