TRIGGERED PULSE GENERATORS 



Miller run-down continues, the anode current rising steadily, until the 

 potential difference developed across the cathode resistor by the rising anode 

 current once more makes the cathode sufficiently positive to cut off anode 

 current at the suppressor. Flyback then occurs. Phantastron waveforms 



_A. 



Suppressor 



Level at 

 which 

 anode 

 current 

 cut off 



Anode 



— i= — I Cathode 



- Screen 

 -Grid 



Figure 16.24 



have the form of Figure 16.24. The Phantastron may also be triggered by 

 negative pulses applied to anode or control grid. 



Triggered Miller transitron 



This extremely simple circuit {Figure 16.25) is a combination of the Blumlein 

 integrator and transitron, but it should be noted that the sense of the transi- 

 tron bias is the reverse of that used in the transitron square wave generator. 



HT+ 



Trig, in 



In the latter the suppressor bias is, if anything, rather positive, so that in the 

 quiescent state the anode current is large and the screen current small. In 

 this circuit the suppressor is biased so that anode current is just cut off. 



A positive trigger pulse appHed to the suppressor allows anode current to 

 flow, reducing the screen current. There is thus a rise in screen potential 

 which is passed on to the suppressor via C, so that the suppressor bias 

 continues to be held off after the trigger pulse ends. Miller run-down ensues, 



246 



