General Information

Surge voltages represent an increasing threat to electronic equipment such as data processing systems. Figures published by electronics insurance companies show that the occurrence of damage to equipment of this kind due to surge voltages is doubling every three to four years. Operators of electronic equipment usually receive compensation from insurance companies for the damage done to their hardware. Unfortunately, damage to software and the large expenses incurred when the equipment fails are often not covered.

In many cases, surge voltages cause damage to the circuit and the coupling due to switching actions or lightning discharges, or may be the components in the circuit. The extent of damage is to a large degree dependent on the dielectric strength of the components and on the energy, which is available for conversion in the circuit, in question.

In a circuit which operates a 230 V AC relay, a coupled voltage of 500 V resulting from switching inductive consumers, for example, is considered to be a surge voltage. However, this is hardly likely to cause any damage because it does not even reach 2.5 times the nominal voltage and is only present very briefly, lasting only milliseconds.

The situation in a 5 V DC circuit connected to an IC is rather different. The same surge voltage reaches a value, which is 100 times the nominal value and is definitely destructive. The dielectric strength of an IC is several powers of ten lower than that of a relay. Surge voltages can be caused by galvanic coupling due to switching actions or lightning discharges, or may be the result of inductive or capacitive couplings from other sources. Such surge voltages in electronic equipment are known as transient voltages, or just "transients". Their ascent times are extremely rapid (only a few milliseconds) and after peaking, they fall off relatively slowly over a period of several tens to several hundreds of milliseconds.

In order to prevent surge voltages from destroying sensitive electronic equipment, the conductors in whom the surge voltage occurs must be short-circuited to the equipotential bonding very rapidly.

Depending on different application and power requirements for surge voltage protection, the right protection module can be selected from the wide range of surge arresters.

Surge voltage protection is a part of the overall technical field of electromagnetic compatibility (EMC).