Overcurrent and overvoltage protection method and architecture for a tip and ring subscriber line interface circuit
View Patent ↗A circuit for protecting a plurality of tip/ring SLIC cards during over current or over voltage conditions. A diode pair corresponding to each tip/ring pair provides positive voltage over voltage protection in a negative powering scheme. Two thyristors provide negative over voltage protection. Tip conductors of half of the SLICs connect to the cathode of one of the thyristors. The ring conductors corresponding to each of these tips connects to the cathode of the other, or second, thyristor. The remaining tips are connected to the cathode of the second thyristor. The rings corresponding to these remaining tips connect to the cathode of the first thyristor. This alternating connection of tips and rings provides twice the current capacity of a single thyristor, while cutting in half the potential holding current through either of the thyristors, thus increasing the likelihood of automatic return to normal operation following cessation of negative over voltage.
1. A protection circuit for protecting a plurality of tip/ring-pair subscriber line interface circuits (“SLIC”) comprising:
a first switching means for shunting energy to ground having a cathode connected to a first node, an anode connected to ground and a gate connected to the cathode of a first gate diode that is reverse biased by a negative supply voltage; and
a second switching means for shunting energy to ground having a cathode connected to a second node, an anode connected to ground and a gate connected to the cathode of a second gate diode that is reverse biased by the negative supply voltage, the first and second nodes being alternatingly connected to the tip and ring wires of each successive pair of the plurality of tip/ring pairs.
2. The protection circuit of claim 1 further comprising for each tip/ring pair, a positive-voltage diode-pair having a third diode and a fourth diode, the anode of the third diode being connected to the tip wire and the anode of the fourth diode being connected to the ring wire, the cathodes of each being connected to ground; and
for each tip/ring pair, a second diode pair having a fifth diode and a sixth diode, the cathode of the fifth diode being connected to the tip wire and the cathode of the sixth diode being connected to the ring wire with the anodes of the fifth and sixth diodes being alternatingly connected to the first and second nodes.
3. The protection circuit of claim 1 wherein the switching means are thyristors.
4. The protection circuit of claim 1 wherein the switching means are transistors.
5. The protection circuit of claim 1 further comprising a first over current protection means serially connected between the tip conductor and the SLIC and a second current protection means serially connected between the ring conductor and the SLIC.
6. The protection circuit of claim 5 wherein the first and second over current protection means is a fuse.
7. The protection circuit of claim 6 wherein the fuse is selected to comply with Telcordia GR-1089 standards.
8. The protection circuit of claim 5 wherein the over current protection means is a positive temperature coefficient device.
9. The protection circuit of claim 1 further comprising a first ferrite bead device serially connected between the tip conductor and the SLIC and a second ferrite bead device serially connected between the ring conductor and the SLIC.
10. The protection circuit of claim 1 further comprising a first battery feed resistor serially connected along the tip conductor between the SLIC and the point by which the tip conductor connects to its corresponding node and a second battery feed resistor serially connected along the ring conductor between the SLIC and the point by which the ring conductor connects to its corresponding node.
11. A protection circuit for protecting a plurality of tip/ring-pair subscriber line interface circuits (“SLIC”) having a positive powering scheme comprising:
a first switching means for shunting negative potential energy to ground having a cathode connected to a first node, an anode connected to ground and a gate connected to the cathode of a first gate diode that is reverse biased by a negative supply voltage;
a second switching means for shunting negative potential energy to ground having a cathode connected to a second node, an anode connected to ground and a gate connected to the cathode of a second gate diode that is reverse biased by the negative supply voltage, the first and second nodes being alternatingly connected to the tip and ring wires of each successive pair of the plurality of tip/ring pairs;
a third switching means for shunting positive potential energy to ground having an anode connected to a third node, a cathode connected to ground and a gate connected to the anode of a third diode that is reverse biased by a positive supply voltage; and
a fourth switching means for shunting positive potential energy to ground having an anode connected to a fourth node, a cathode connected to ground and a gate connected to the anode of a fourth diode that is reverse biased by the positive power supply, the third and fourth nodes being altematingly connected to the tip and ring wires of each successive pair of the plurality of tip/ring pairs.
12. The protection circuit of claim 11 further comprising for each tip/ring pair, a positive-voltage diode-pair having a fifth diode and a sixth diode, the fifth diode having its anode connected to the tip wire and the sixth diode having its anode connected to the ring wire, the cathodes of each being altematingly connected to third and fourth nodes; and
for each tip/ring pair, a second diode pair having a seventh diode and a eighth diode, the cathode of the seventh diode connected to the tip wire and the cathode of the eighth diode connected to the ring wire with the anodes of the seventh and eighth diodes being altematingly connected to the first node and the second node.
13. The protection circuit of claim 11 wherein the switching means are thyristors.
14. The protection circuit of claim 11 wherein the switching means are transistors.
15. The protection circuit of claim 11 further comprising a first over current protection means serially connected between the tip conductor and the SLIC and a second current protection means serially connected between the ring conductor and the SLIC.
16. The protection circuit of claim 15 wherein the first and second over current protection means is a fuse.
17. The protection circuit of claim 16 wherein the fuse is selected to comply with Telcordia GR-1089 standards.
18. The protection circuit of claim 15 wherein the over current protection means is a positive temperature coefficient device.
19. The protection circuit of claim 11 further comprising a first ferrite bead device serially connected between the tip conductor and the SLIC and a second ferrite bead device serially connected between the ring conductor and the SLIC.
20. The protection circuit of claim 11 further comprising a first battery feed resistor serially connected along the tip conductor between the SLIC and the point by which the tip conductor connects to its corresponding third or fourth node and a second battery feed resistor serially connected along the ring conductor between the SLIC and the point by which the ring conductor connects to its corresponding third or fourth node.