TRANSISTORS AND JUNCTION DIODES SoS 



4.22. Magnitude Controlled Thyratron Tube Rectifiers 



The grid battery eliminator covered in Section 4.21 is also usable in 

 magnitude controlletl thyratron tuV)e regulated rectifiers but a simj)le, 

 less expensive circuit can be used for this aijplication. It is illustrated 

 in Fig. 20. A simplified schematic of the thyratron rectifier is also shown 

 in Fig. 20 and the grid battery eliminator is the portion of the circuit 

 enclosed by the dotted line. It is actually a transistor voltage amplifier 

 circuit. This type of circuit has not been covered previously in this dis- 

 cussion so its operation is described in some detail below. 



Referring to Fig. 20 a portion of the output potential is compared to 

 the reference potential by the base and emitter connections to the tran- 

 sistor. The chfference between these two potentials causes the base cur- 

 rent h to flow. This base current is amplified by the current gain of the 

 transistor and it results in flow of collector current Ic , through the Re 

 collector resistance. The voltage drop across Re is the negative grid 

 potential applied to the thyratron tube. Now when the output potential 

 is increased the base current is increased, the collector current is in- 

 creased, the voltage drop across the Re resistor is increased and the 

 negative grid potential at the thyratron tube is increased. This ^^dll 

 dela}'^ the firing of the thyratron and thus reduce the output potential. 



If the ohmic value of the Re resistor in Fig. 20 is zero the voltage 

 amplification of this transistor circuit will be about 10, or a small change 

 in the output potential will result in about 10 times this change in the 

 thyratron grid potential. This is ^'oltage amplification added to the 

 circuit by the grid battery eliminator and a voltage gain of 10 is more 

 than present circuits can use. The emitter resistance Re reduces the 

 voltage amplification of the grid battery eliminator to reasonable pro- 

 portions. 



The Rt resistance in the potentiometer circuit of Fig. 20 is wound wdth 

 nickel resistance Anre. Its positive temperature coefficient of resistance 

 compensates the grid battery eliminator circuit for the temperature 

 effects in the reference voltage diode and the transistor. This nickel wire 

 resistance accomplishes the same result as the thermistor in Fig. 19. This 

 is another method of compensating transistor regulator circuits for 

 ambient temperature variations. 



The "Adjust Output Volts" potentiometer and the auxiliary rectifier 

 shown in Fig. 20 are part of the present magnitude controlled thyratron 

 tube rectifiers. The auxiliary rectifier adds some ac line voltage com- 

 pounding to the rectifier regulation. It is also used with a time delay 

 relay circuit, not shown, to bias the grid potential of the thyratron tubes 



