Current Build-Up in Avalanche Transistors with Resistance Loads

A transient analysis for the avalanche transistor is carried out through the use of a diffusion model described in terms of charge variables. Basically, the current as a function of time is calculated by taking the gradient of the minority carrier charge stored in the base region. Two methods of approximating the distribution of stored charge are described. Good agreement has been obtained between calculated and experimental results; it is found that the rise time for the resistance-load case is about four times that for a capacitance-load case which produces the same peak current. A practical pulse generator circuit is described in which the resistance load takes the form of a delay-line. The performance of this circuit is compared with that of a capacitance-load relaxation oscillator; while the rise time of the former is longer, the pulse shape is more easily controlled.