850 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



A voltage proportional to the regulated output is connected to the base 

 of transistor {Tl). Fixed resistors are sho\Mi in the base circuit of {Tl) 

 in Fig. 18, but a variable potentiometer could be used. The reference 

 voltage diode "s" applies a constant reference voltage to the base of 

 transistor {T2). If the output \'oltage tends to increase, more collector 

 and emitter current flows in transistor {Tl) due to the increase in its 

 base-to-emitter voltage. This increase in emitter current of transistor 

 (Tl) flows through resistor (Rl) and tends to raise the emitter voltage of 

 transistor {T2). Since the base potential of transistor {T2) is fixed, the 

 effect is to decrease the base-to-emitter voltage of {T2) and its collector 

 and emitter currents decrease. The result is an increase in Id and an 

 almost equal decrease in Ic2 • If the two saturation A\indings on the mag- 

 netic amplifier are oppositely poled, the changes in Id and /^o represent 

 a net decrease in the control ampere turn input to the magnetic amplifier. 

 As before, the magnetic amplifier responds by absorbing more voltage. 

 If, however. Id and 7^2 both increase equally due to an increase in am- 

 bient temperature, no net change is made in the control ampere turn 

 input to the magnetic amplifier. Thus if the two transistors are perfectly 

 matched, and the reference voltage diode has a low temperature co- 

 efficient, temperature changes will have little effect on the output regu- 

 lated voltages. 



A further advantage is the reduced variations in the current through 

 the reference voltage diode. As in the case of the other circuits additional 

 stages of transistor or magnetic amplification can be added to increase 

 the loop gain and the precision of regulation. 



4. APPLICATIONS 



4.1. General 



The last sections of this discussion cover some specific applications of 

 the principles discussed above. Section 4.21 covers a one-stage transistor 

 shunt regulated rectifier as a grid battery eliminator for phase controlled 

 thyratron tube rectifiers. Section 4.22 covers a transistor voltage am- 

 plifier circuit as a grid battery eliminator for magnitude controlled 

 thyratron tube rectifiers. A two-volt, three-ampere regulated rectifier 

 covered in Section 4.31 illustrates how a low voltage, high current, 

 regulated rectifier with a transistor and magnetic amplifier control 

 circuit can be obtained. Section 4.32 covers a 65-volt, 200-ampere regu- 

 lated rectifier for telephone central office battery charging. It uses the 

 p-n junction rectifier devices covered in Section 2.1 and a modification 



