THE TYPE PI CARRIER SYSTEM 



377 



the semiconductor rectifier bridge CRl, the voltage control circuit rep- 

 resented by that part of Fig. 21 enclosed in dashed lines, and the energy- 

 storage circuit represented by the battery. 



Rectification is obtained with germanium rectifiers that are very effi- 

 cient, have long life with negligible aging, and are very compact phys- 

 ically. The output of this rectifier is not constant, because the output 

 voltage will vary with the ac input voltage and the dc load current drawn 

 by the carrier terminal. Thus a i-egulating circuit must be provided. 



The regulating network senses the voltage across the battery and 

 compares this voltage to a reference obtained from a silicon junction 

 diode biased in the reverse dirction.^ Any error in the output voltage 

 is converted to a current signal in the first amplifier stage and amplified 

 by the second stage transistor Q2. The amplified error current is then 

 used to control the impedance of transistor Ql which acts as a current 

 shunt around the battery. 



The fundamentals of the operation of this regulating system are shown 

 in Fig. 22. If the load voltage is too high, the network adjusts the re- 

 sistance of transistor Ql so that some of the rectifier output current is 

 shunted around the load. The load voltage will then return very quickly 

 to the regulated value. Because the rectifier circuit must not be over- 

 loaded by a discharged battery, some form of current limiting must be 

 provided; this is automatically taken care of by resistor Rl. The rectifier 

 is capable of supplying indefinitely the current that would be drawn to 

 charge a battery after a very long power failure. 



The storage battery is shown in Fig. 23 near the bottom of the power 

 plant housing. It is a new design with a hfgh specific gravity sulphuric 



^ D. H. Smith, Silicon Allo}^ Junction Diode as a Reference Standard, A.I.E.E., 

 Communication and Electronics, No. 16, pp. 645-651, Jan. 1955. 



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Fig. 22 — Simplified schematic and regulation characteristic of ac power supply 



