Solid state overvoltage protection circuit

• Main Author: WEBB, MONTY F
• Format: Patent
• Language: English; French; German
• Published: 03.01.1990
• Subjects: CALCULATING; COMPUTING; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER; COUNTING; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRIC DIGITAL DATA PROCESSING; ELECTRICITY; EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS; GENERATION; PHYSICS; TELEPHONIC COMMUNICATION

An overvoltage protection circuit (16) for electronic equipment, such as telecommunications equipment (10), computers and instrumentation equipment, having tip and ring lines (TR) includes a first voltage sensitive switch (30) having first and second terminals. The first terminal of the first switch is connected to the tip line (T). A second voltage sensitive switch (32) includes first and second terminals. The first terminal thereof is connected to the second terminal of the first voltage sensitive switch (30), and the second terminal thereof is connected to the ring line (R). A third voltage sensitive switch (34) includes first and second terminals. The first terminal is connected to the second terminal of the first voltage sensitive switch and to the first terminal of the second voltage sensitive switch. The second terminal of the third voltage sensitive switch is connected to ground potential. The switches are conductive when a respective voltage threshold is exceeded. In one embodiment, the sum of the voltage thresholds of the first and third voltage sensitive switches is approximately equal to the sum of the voltage thresholds of the second and third voltage sensitive switches, such that the circuit is conductive when either of the thresholds of the first and third voltage sensitive switches or the second and third voltage sensitive switches are exceeded. In another embodiment, the holding current of the third voltage sensitive switch is lower than that of either the first or second switch. In this combination, the third switch turns on first, then both the first and second switches turn on in unison and hold the lines in balance during switching.