844 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



3.13. Multistage Transistor Shunt Regulator 



In Fig. 13 two additional transistors have been added to the simple 

 shunt regulator of Fig. 12 in order to increase the accuracy of regulation. 

 The first stage (subscript 1 is used for the transistor currents in this stage) 

 compares the output potential to the reference voltage, drives the second 

 stage (subscript 2) which in turn drives the third stage (subscript 3). 

 The first stage transistor operates in a similar fashion to the transistor 

 in Fig. 12, except that its collector current now is the base current of the 

 second transistor. The collector current of the second transistor is the 

 base current of the third' transistor. The second and third stage tran- 

 sistors amplify the collector current of the first transistor. The shunt 

 regulating current is the sum of the currents in all three transistors. An 

 examination of Fig. 13 mil reveal that the first transistor is an n-p-n, 

 the second transistor is a p-n-p, and the third transistor is an n-p-n 

 and that no coupling networks are used. This illustrates the advantages 

 of complementary symmetry. 



In Fig. 13 different sizes are specified for the three transistors. The 

 transistor shown for the first current amplifier might be a 50-milliwatt 

 transistor operating at a collector potential of about 10 volts. Then the 

 maximum base current of the second stage p-n-p transistor should not 

 exceed 5 milliamperes and, with an assumed current amplification of 20 

 times, the maximum collector current of the second stage could be 100 

 milliamperes Such a transistor has been developed. With 100 milli- 

 amperes flomng into the base of the large n-p-n transistor and an 

 assumed current amplification of 20 times the maximum shunt regulator 

 current would be about 2 amperes which would compensate for consider- 

 able load current variations. Large size transistors such as would be 

 necessary in the third stage are now under exploratory development 

 within the industry.^ 



The circuit in Fig. 12 can be modified to use a p-n-p transistor and 

 several other modifications can be made. Similar modifications can be 

 made in the circuit sho^vn in Fig. 13. It is not mthin the scope of this 

 article, however, to show all the permutations and combinations of 

 transistor regulator circuits that are usable. Section 3.2 below covers 

 some typical transistor series regulator circuits. 



3.2. Series Regulators 



Precise voltage control can be obtained with shunt regulators but 

 series regulator circuits are usually more efficient. This comes about 

 because the shunt regulator wastes the shunt current plus the voltage 



