Back to results
US 5,396,394 AGranted
ISDN device line protection circuit
AssigneeInternational Business Machines Corporation
InventorTimothy W. Gee
Life of this patent
Estimating the term…
Loading patent…
Loading patent…
AssigneeInternational Business Machines Corporation
InventorTimothy W. Gee
Estimating the term…
A line protection circuit for an ISDN device includes a pair of identical, NMOS field effect transistors connected between the device and opposite terminals of one winding of an isolation transformer. Each device has one N region connected to an output line from the ISDN device, a second N region connected to one winding terminal, a grounded channel or P region and a gate connected to a source of positive logic voltage. During normal operation, the FETs pass current provided by a constant current source within the ISDN device without attenuation. If a power surge occurs elsewhere in the ISDN network, the voltage at one of the FETs is be clamped to ground while the voltage at the other FET rises only until FET cut-off occurs. If power is removed from the FETs, at least one PN junction will always be reverse biased to isolate the protected ISDN device from the remainder of the network.
A line protection circuit for connecting a device having first and second input/output leads to opposite terminals of a coupling element, said circuit including:
For use in connecting an ISDN device having two input/output leads to the remainder of an ISDN network through a coupling element having first and second terminals, a line protection circuit interposed between the input/output leads and the coupling element, said circuit comprising:
Dependencies are inferred from the claim text.