Stability of transistors in avalanche region

The stability in an avalanche transistor is shown to depend in a very simple way on emitter-base voltage and on collector current. This dependence is quite general, since it is common to transistors of various types and structures (n-p-n, p-n-p, Ge, Si, planar, micro alloy diffused, mesa and drift); moreover the stability conditions show that the punch-through hypothesis is not essential to explain recently observed spontaneous oscillations in avalanche transistors with open emitters. Furthermore, a very simple equivalent circuit is given, which proves to be useful in describing the principal characteristic of avalanche oscillation.