Data circuit surge protection

Sources of overvoltage surges posing threats to digital equipment are discussed. The ideal protection for data circuits must have high discharge capacity, fast response time, precise clamping voltage, and be almost transparent on the line. Those characteristics are obtained with hybrid circuitry which is made of a gas tube on the input stage and a diode on the output stage. Once the surge passes the primary protector without being stopped, it is clamped down by the solid state diode first, and then the bulk of the energy (99%) is handled by the gas tube. The diode provides a response time in the range of 1 nanosecond. It handles only 1% of the total energy dissipated. The diode must have a tight clamping ratio in order to reduce as much as possible the risk window. Location of the data circuit surge protector and installation precautions are discussed.<>