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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



to base (6) of the transistor. This latter voltage is made a little smaller 

 than the emitter voltage so that the base (6) is positive with respect to 

 the emitter. Now assume that the load voltage increases for some reason 

 such as an increase in the line voltage or a decrease in the load current. 

 A portion of the increased load voltage appears across points 2 and 3 of 

 potentiometer (P), and tends to make the base voltage more negative. 

 Since the base is slightly positive with respect to the emitter, the net 

 effect of making the base more negative is to decrease the base-to-emitter 

 voltage. Through transistor action, the collector current, which is also 

 the saturation current of magnetic amplifier, decreases and the ac im- 

 pedance of the line windings rises. The line windings absorb more input 

 voltage and the output voltage is brought back very nearly to the 

 original value before the change. 



The circuit of Fig. 16 is of interest because it can control larger 

 amounts of power than can be handled by transistors alone and, in ad- 

 dition, it is capable of faster regulating action than an all-magnetic 

 regulating circuit with the same loop gain. The use of the transistor in 

 this circuit eliminates the need for one or more stages of milliwatt-size 

 magnetic preamplifiers. 



3.33. Increased Gain in Voltage Regulators 



Additional amplification to improve the regulation can be added to 

 Fig. 16 in two ways. Several stages of transistor current amplification 

 can be added or more magnetic amplifier stages can be used. Of course 



AC 

 LINE 



SATURATION 

 CURRENT 



LINE 

 WINDING 



SATURATION 

 WINDING 



LINE 

 WINDING 



POWER 

 RECTIFIER 



MAGNETIC AMPLIFIER 



^ 



REGULATING 

 RESISTANCE 



— vw — 



REFERENCE 



VOLTAGE 



DIODE 



I LOAD 



TRANSISTOR 



CURRENT 

 AMPLIFIER 



REGULATED 

 OUTPUT 

 CURRENT 



Fig. 17 — Transistor control circuit for a magnetic amplifier regulated rectifier 

 with constant current regulation. 



