TRANSISTORS AND JUNCTION DIODES 857 



is shown over the range of ambient temperatures normally (Micouiitered 

 in central offices. 



5. CONCLUSIONS 



It is seen from the above discussion that semiconductor junction 

 diodes and transistors have a wide field of application in power con- 

 \'ersion and control. Certain difficulties remain to be overcome, among 

 which the \'ariation of the device characteristics with ambient tempera- 

 ture appears to be the most troublesome at the present time. It has l)een 

 shown that these variations with temperature can be minimized by two 

 methods. First through the use of thermistors (negative temperature 

 coefficient) or nickel-wire resistors (positive temperature coefficient) 

 and second, through the employment of circuits in which the tempera- 

 ture variations of one element are balanced out by similar temperature 

 variations in a complementary element. Thus, errors due to temperature 

 changes can be minimized by further reduction of the sensiti\nty of the 

 device characteristics to ambient temperature changes and by improved 

 uniformit}' of the devices. 



Another important aspect of the circuits covered in this paper is their 

 freedom from dependence on auxiliary sources of dc potential. In most 

 cases it is possible to power the regulating circuit directly from the regu- 

 lated output, thereby eliminating the necessity for the transformers, 

 rectifiers and filters usually needed to furnish plate potential for the 

 regulating tubes and voltage standards. 



The regulating circuits discussed in this paper are of the checkback 

 type. In all of them, there must first be an error in the load voltage to 

 start and maintain the regulating action. The load voltage Avill only 

 return to precisely the original value if the regulating amplifier has 

 infinite gain. These effects, however, are common to all closed-loop feed- 

 back regulating systems. Transistors and junction diodes, at their 

 present stage of development seem well suited for use in checkback 

 circuits having a high quality reference potential, for the feedback 

 principle helps to minimize residual errors due to changes in the device 

 characteristics with, changes in ambient temperature. 



Of course, the small size, long life and high efficiency of these semi- 

 conductor junction devices will also be very gratifying to the design 

 engineers. 



6. ACKNOWLEDGMENTS 



The authors wish to acknowledge the assistance of C. W. Van 

 Duyne of Bell Telephone Laboratories and the personnel in his group. 



