A fast acting protection circuit for transistorised voltage regulators using series control elements

Protection of the control element against overload conditions is one of the major requirements of transistorised voltage regulators. Overload of any kind can cause catastrophic damage in a matter of microseconds to transistors and possibly to other semi-conducting devices used in such units and, to be of any value, protective gear must act almost instantaneously. The use of a silicon controlled rectifier (S.C.R.) offers an interesting possibility for the solution of this problem. The design of a novel protection circuit using an S.C.R. and a sensing transistor is discussed and results obtained with a typical voltage regulator circuit using a fast acting S.C.R. protection unit are presented.