TRANSISTORS AND ,11 "\<TI()X DIODES 



851 



of the transistor control (.'ircuits for magnetic ampliiier regulation covered 

 in Section 3.36. 



4.2. Grid Battery Eliminators 



4.21. Phase Controlled Thyratron Tube Rectifiers 



In thyratron tube regulated rectifiers the standard potential for the 

 checkback regulator is often obtained from dry cells. The annual replace- 

 ment of dry cell batteries is an appreciable maintenance expense, par- 

 ticularly in those cases where the rectifiers are installed in isolated or 

 unattended locations. This section covers a transistor shunt regulated 

 rectifier as a substitute for the dry batteries. Its circuit is illustrated in 

 Fig. 19. 



The circuit in Fig. 19 is the same as Fig. 12 with the addition of the 

 compounding resistor and the thermistor. The compounding resistor is 

 added to compensate for the slope of the reference voltage diode in its 

 saturation voltage region (see Fig. 6). The thermistor is added to com- 

 pensate for ambient temperature varitions of this diode and the tran- 

 sistor. 



The compovniding resistor adds ac line voltage compounding. The 

 transistor base current regulating signal in Fig. 19 is increased by the 

 compounding resistance whenever the ac voltage is increased. By select- 

 ing the proper ohmic value of the compounding resistor, the circuit in 

 Fig. 19 can be arranged so it will deliver constant output voltage into a 

 constant resistance load when the ac voltage is varied from 85 per cent 



TRANSFORMER 



RECTIFIER 

 BRIDGE 



REGULATING 

 RESISTOR 



COMPOUNDING 

 RESISTOR 



^A^v 



THERMISTOR 



n-p-n 



TRANSISTOR " 



SHUNT 

 REGULATOR 



REFERENCE 



VOLTAGE 



DIODE 



PLUS 



T — 



REGULATED 



OUTPUT 



VOLTS 



±-_ 



Fig. 19 — Grid -bat ten' eliminator for i)lias(>-coiit rolled thyratron rectifier. 



