Use of a metal-oxide varistor with a series spark gap across themains

摘要

Protection of electronic equipment from damage and upset bytransient overvoltages on the AC supply mains is an important problem inelectromagnetic compatibility; metal oxide varistors are commonly usedfor this purpose. To obtain the lowest clamping voltage during a surge,varistors with a nominal conduction current of 1 mA DC at 200 V arebeing used on mains with a nominal voltage of 120 V RMS. The authordiscusses the use of a series spark gap with a metal oxide varistor toachieve both a small clamping voltage and a long life time for thesurge-protective circuit. A metal oxide varistor with a nominalconduction current of 1 mA DC at 100 V, in series with a 250 V DC sparkgap, may be suitable for connection to the mains with a nominal voltageof 120 V RMS. Extinguishing follow current in the gap and attenuatingthe remnant that propagates downstream prior to the conduction of thespark gap are discussed in detail