High-voltage protection circuitry in a data access arrangement
View Patent ↗A data access arrangement (DAA) having improved surge protection. The DAA incorporates a high voltage clamping device functioning to protect line side circuitry from signal paths created by EMI capacitors. In one embodiment of the invention, EMI capacitors are added between the “plus” and “minus” terminals of the diode bridge of the DAA to balance and reduce noise injection onto the TIP and RING lines. These EMI capacitors also reduce EMI interference. However, by adding EMI capacitors on this side (the “rectified side” or “line side”) of the diode bridge, a high voltage signal path to earth ground is created that may have deleterious effects on the line side circuitry. To effectively negate undesirable signal paths through the EMI capacitors, the DAA includes a high voltage clamping device (e.g., a MOV, SIDACTor™, gas discharge tube or similar device) disposed between the plus and minus terminals of the diode bridge for suppressing high voltage spikes. The high voltage clamping device limits the voltage seen by the line side circuitry as a result of high voltage longitudinal surges by providing a current path from the plus terminal to the minus terminal of the diode bridge, thereby effectively bypassing the line side circuitry. The present invention recognizes and takes advantage of the fact that the diodes of a typical diode bridge are capable of withstanding the peak currents associated with most voltage surges.
1. A data access arrangement for use in a communications device having a chassis ground, the data access arrangement circuit comprising:
programmable line side circuitry, including network interface circuitry;
a diode bridge having a first pair of terminals for coupling data signals to a network connection and a second pair of terminals coupled to the network interface circuitry;
a high voltage clamping device disposed between the second pair of terminals;
a first capacitor coupled between the chassis ground and one of the terminals of the second pair of terminals; and
a second capacitor coupled between the chassis ground and the other terminal of the second pair of terminals;
thereby limiting a maximum voltage to which the programmable line side circuitry can be exposed to substantially a voltage rating of the high voltage clamping device for longitudinal and metallic high voltage surges.
2. The data access arrangement of claim 1 , further comprising:
at least one additional high voltage clamping device disposed between the terminals of the first pair of terminals.
3. The data access arrangement of claim 1 , the communications device having a chassis ground, further comprising:
a third capacitor coupled between the chassis ground and one of the terminals of the first pair of terminals; and
a fourth capacitor coupled between the chassis ground and the other terminal of the first pair of terminals.
4. The data access arrangement of claim 1 , wherein the network connection is an RJ-11 jack for coupling to a telephone line.
5. The data access arrangement of claim 1 , wherein the high voltage clamping device is a metal oxide varistor.
6. The data access arrangement of claim 1 , wherein the high voltage clamping device is a SIDACTor™.
7. The data access arrangement of claim 1 , the high voltage clamping device having a maximum specified voltage rating between 410 volts and 455 volts at a maximum specified current rating between 5 amps and 50 amps.
8. The data access arrangement of claim 1 , further comprising:
system side circuitry configurable to communicate with a host system; and
a high voltage isolation barrier having a first side and a second side, the first side coupled to the network interface circuitry and the second side coupled to the system side circuitry.
9. The data access arrangement of claim 8 , the high voltage isolation barrier comprising a capacitor.
10. The data access arrangement of claim 1 operating in substantial compliance with an xDSL modem standard.
11. The data access arrangement of claim 1 operating in substantial compliance with a home networking protocol.
12. A data access arrangement for use in a communications device having a chassis or earth ground, the data access arrangement circuit comprising:
programmable line side circuitry, including network interface circuitry;
a diode bridge having a first pair of terminals for coupling data signals to a network connection and a second pair of terminals coupled to the network interface circuitry;
a first high voltage clamping device disposed between the chassis ground and one of the terminals of the second pair of terminals;
a second high voltage clamping device coupled between the chassis ground and the other terminal of the second pair of terminals;
a first capacitor coupled between the chassis ground and one of the terminals of the second pair of terminals; and
a second capacitor coupled between the chassis ground and the other terminal of the second pair of terminals;
thereby limiting a maximum voltage to which the programmable line side circuitry can be exposed to substantially a voltage rating of the high voltage clamping device for longitudinal and metallic high voltage surges.
13. The data access arrangement of claim 12 , wherein the high voltage clamping device is a metal oxide varistor.
14. A communications device comprising:
a chassis ground;
host processing circuitry;
system side circuitry coupled to the host processing circuitry;
programmable line side circuitry, including network interface circuitry;
a voltage isolation barrier having a first side and a second side, the first side coupled to the network interface circuitry and the second side coupled to the system side circuitry;
a diode bridge having a first pair of terminals for coupling data signals to a network connection and a second pair of terminals coupled to the network interface circuitry;
a high voltage clamping device disposed between the terminals of the second pair of terminals;
a first capacitor coupled between the chassis ground and one of the terminals of the second pair of terminals of the diode bridge; and
a second capacitor coupled between the chassis ground and the other terminal of the second pair of terminals of the diode bridge;
thereby limiting a maximum voltage to which the programmable line side circuitry can be exposed to substantially a voltage rating of the high voltage clamping device for longitudinal and metallic high voltage surges.
15. The communications device of claim 14 , wherein the high voltage clamping device is a metal oxide varistor.
16. The communications device of claim 14 , wherein the network connection is an RJ-11 jack for coupling to a telephone line.
17. The communications device of claim 14 , the high voltage isolation barrier comprising a capacitor.