Application of transistors to d.c./d.c. convertors

The availability of germanium junction transistors capable ofpassing collector currents up to 12 amp and of withstanding collectorvoltages up to 100 volts has led to considerable interest in the developmentof d.c./d.c. convertors for driving mobile equipments. Theseconverters offer considerable advantages over vibrators and rotarygenerators for producing h.t. supplies from secondary batteries. Theadvantages generally claimed are higher overall efficiency, no movingparts so that maintenance is reduced giving greater reliability, and aconsiderable saving in weight. A description of push-pull circuits normally used is given, togetherwith design procedure and analysis of convertor losses. A number offailures occurred in these convertors, even though it was consideredthat the transistors were being operated within the manufacturers´ ratings. This problem is discussed, and reasons for the failures areput forward. To achieve good reliability under exacting service conditions, it is recommended that the use of push-pull circuits be restrictedto nominal 12-volt inputs. Attention is drawn to a convertor circuitof novel design that has proved very reliable and can be used withinputs up to 30 volts.