Interface circuits between powered down devices and a bus

Details Interface circuits between powered down devices and a bus Interface circuits between powered down devices and a bus

1993-08-20

1995-03-14

Westin, Edward P.

Electrical transmission or interconnection systems

Nonlinear reactor systems

Parametrons

307443, 361 91, H03K 190175

Patent

active

053979419

ABSTRACT:
In accordance with the teachings of this invention, a novel interface circuit is incorporated in a lower voltage circuit, allowing that circuit to properly interface with a higher voltage bus even when the lower voltage circuit is powered down. In accordance with the teachings of this invention, a pass transistor is used which connects the lower voltage circuit to the bus during normal operation, and which disconnects the lower voltage circuit from a bus when desired, such as when the lower voltage circuit is powered down. Additional circuit means are provided to ensure that the voltage across the pass transistor does not exceed a safe level, such as by utilizing voltage divider circuitry for dividing the bus voltage so that only a portion of the bus voltage appears across the pass transistor. In one embodiment of this invention, the voltage divider is formed of resistors, diodes, load devices, or combinations thereof.

REFERENCES:
patent: 4574273 (1986-03-01), Atsumi
patent: 4616143 (1986-10-01), Miyamoto
patent: 4926070 (1990-05-01), Tanaka
patent: 5130883 (1992-07-01), Edwards
patent: 5319259 (1994-06-01), Merrill
A Tidal Wave of 3-V ICs Opens Up Many Options, Electronic Design, Aug. 20, 1992 Issue, pp. 39-47, by Dave Bursky.
IBM Technical Disclosure Bulletin. "Overvoltage Protection Circuit," vol. 30, No. 12, May 1988, New York US. pp. 96-97.

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