TI{A\SIST()i;S AXD JUXCTIOX DIODKS 



847 



'lliis ciicuit is phased so thai tlie load cunciit will he increased when it 

 is too sinall and decreased when it is too large. Tlie values of the regulat- 

 ing resistor and the r(^fer(Mic(> \'oltage deteiinine the value of the regulated 

 load curi'ent. Additional curKMit amplifier stages can be included or the 

 circuit can l)e modified to chaiig(> the series transistor to the miiuis lead 

 as covered above. 



3.3. Transislors Combined With Magnet ic Amplifiers 



3.31. General 



Transistors can be used to control directly the flow of power to a load 

 as pointed out in the sections on series and shunt regulators. However, 

 their direct use is limited to moderate voltages (below 100 volts) or 

 moderate currents (up to 1 ampere) with transistors now contemplated. 



3.32. T7-ansisfors as DC Preamplifiers 



In cases where regulation of higher power is retjuired, it is expedient 

 to comliine transistor circuits with other devices having higher power- 

 handling capacity. One type of combination is shown in Fig. 16, where 

 a transistor is used to amplify weak dc error signals to a magnitude suf- 

 ficient for driving a magnetic power amplifier. 



In Fig. 1(3, emitter (e) of the n-p-n transistor is held at a fixed negative 

 \oltage with respect to the positive output of the power supply by the 

 reference voltage diode ("*S"')- Another negative voltage derived from the 

 output voltage of the power supply through potentiometer (P) is applied 



AC 



LINE 



SATURATION 

 CURRENT 



LINE 

 WINDING 



SATURATION 

 WINDING 



'V-T' 



LINE 

 WINDING 



— ^m- — 



POWER 

 RECTIFIER 



MAGNETIC AMPLIFIER 



REFERENCE 



VOLTAGE 



DIODE 



ADJUSTABLE 

 POTENTIOMETER 



lb " 



n-p-n TRANSISTOR 



CURRENT AMPLIFIER 



WITH PHASE 



REVERSAL 



T 



REGULATED 

 OUTPUT 

 VOLTS 



Fig. 16 — Transistor coiitiol circuit tor a magnetic amplifier regulated rectifier 

 with constant voltage regulation. 



