Claims
- 1. In a field bus network comprising a two-wire bus extending between a source of DC and a controller at a first end and a plurality of remote sensing or actuating devices at a second end, the two-wire bus comprising a first wire and a second wire, said wires carrying both a data signal and DC power, and having a spur circuit comprising first and second conductors coupled respectively to said first and second wires of said bus, an apparatus to limit current in said spur circuit comprising a selectively controllable current limiting circuit coupled between said first and second conductors, said circuit being responsive to current flowing in said spur circuit and including a variable impendence transistor device coupled to one of said first and second conductors for raising the impedance of said spur circuit in response to an over current condition.
- 2. The apparatus of claim 1 further including a sensing circuit coupled to said spur circuit for detecting said over current condition and for controlling the impedance of said first transistor device.
- 3. The apparatus of claim 2 wherein an output of said sensing circuit is coupled to a gate of said first transistor device.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of Application No. 09/771,152, filed Jan. 26, 2001 now U.S. Pat. No. 6,369,997 which is a continuation of Application No. 09/344,408, filed Jun. 24, 1999 now U.S. Pat. No. 6,366,437.
US Referenced Citations (10)
Continuations (2)
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Number |
Date |
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09/771152 |
Jan 2001 |
US |
Child |
09/866187 |
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US |
Parent |
09/344408 |
Jun 1999 |
US |
Child |
09/771152 |
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US |