TRANSISTOR PULSE REGENERATIVE AMPLIFIERS 



109 



O 



voltage across the coupling transformer, which is approximately constant 

 during the pulse duration, causes an increasing magnetizing current to 

 be subtracted from the initial feedback. When the feedback current can 

 no longer support the required output current, the circuit turns off. In 

 a synchronized amplifier the value of the feedback transformer mutual 

 inductance may be specified to give the desired degree of stability at the 

 end of the predetermined pulse length. Thus, the least stable condition 

 occurs at the end of the pulse duration and is under the circuit designer's 

 control. At other times during the pulse duration the circuit is more 

 stable, which reduces the possibility of premature turn-off. 



Other considerations, such as stability variations with output current, 

 power dissipation, and output voltage regulation, depend upon whether 

 the output load is in series or in shunt with the feedback loop. Therefore, 

 these considerations are discussed in connection with output coupling in 



n+i: 1 



(a) COMMON BASE 



(b) COMMON EMMITER 



n+1 



(C) COMMON COLLECTOR 



P + CVc 



te 



(d) ASSUMED TRANSISTOR 

 EQUIVALENT CIRCUIT 



Lg = LEAKAGE INDUCTANCE OF TRANSFORMER 

 n = TURNS RATIO FOR COMMON EMMITER CONNECTION 



CCq = LOW FREQUENCY VALUE OF COMMON BASE 

 SHORT CIRCUIT CURRENT GAIN 



CVq = CUTOFF RADIAN FREQUENCY OF Ot 



Fig. 6 — Transformer coupled blocking oscillator circuits. 



