Genrad, Inc.

Karl Karash

Anthony J Suto

Charles P Smith

Moses Khazam

Fadi H Daou

Steen Bentzen

An output circuit (62) for generating a signal in the form of a voltage between an output signal node and an output reference node (60) receives power from a pair of voltage regulators (Q1 and 68, Q2 and 70). The regulators are connected in power-circuit series so as to be powered by the difference between the output potentials of two opposite-polarity supplies without a direct low-impedance connection between the power-supply ground (73) and the output reference node (60). To avoid large current flow in any external path between an output reference node (60) of an electronic circuit and the ground node (73) of its power supply, a current sensor (R1, R2, 86) senses the net current that the power supplies provide to the circuitry that includes the regulators, and it controls variable loads (Q3, Q4) that selectively drive current into and draw current from the reference node (60) so as to drive the net current to zero.

Ground-loop interruption circuit

To avoid component damage due to the presence of an incorrect voltage on the power bus of an electrical system when the system's power supply is turned on, the system carries out a self-testing procedure before power up to detect fault-indicating low impedance paths in the power bus. For this, the system includes a test power supply which delivers to the bus during the self-testing routine test voltages which are much lower than those supplied to the bus by the main supply. In accordance with the self-testing routine, the main power supply is turned on upon completion of the routine only if no low impedance paths are detected in the bus. As the supply voltages are applied to the bus, they are compared with preselected limits. If any voltage is not within its limits, the system provides an indication to that effect and/or shuts down the system.

Self-protecting power bus testing system

A foldback power supply (12) is used in an automatic testing device for application of power to a device under test (17). Connection to the device under test is made by means of relay contacts (32, 34, 36, and 38). Arcing and unacceptable transients are avoided by means of a current sink (40) in parallel with the power supply (20). The current sink is operated to draw more than the rated current of the power supply so that the power-supply voltage drops to an acceptable level and the stored energy is simultaneously dissipated. The relay contacts (32, 34, 36, and 38) can then be opened or closed without unacceptably large transients and without the time delays that might otherwise be encountered in waiting for energy dissipation of the energy in the energy-storage elements of the power supply (12) and the device under test (17).

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Lowell, MA, United States of America

Karl Karash