Three terminal measurements of current amplification factors of controlled rectifiers

Abstract

By treating the Silicon Controlled Rectifier as a hook transistor and measuring its current amplification factor as a function of frequency, the small-signal low-frequency alphas\alpha_{n0}and\alpha_{p0}of the n-p-n and p-n-p transistor sections constituting the Controlled Rectifier can be separately determined, together with fnand fp, their respective cutoff frequencies. Repeating these measurements at a number of bias currents, coupled with a numerical integration, enables one to separate the component dc currents of the two transistor sections as well as their dc alphas αnand αP. Measurements indicate that switching from high to low impedance is controlled by\alpha_{n0} + \alpha_{p0} = 1and not\alpha_{n} + \alpha_{p} = 1as has hitherto been implied. There are good theoretical reasons for this which have led to a redefinition of the breakover conditions. These are shown to be given by infinite output admittance and not infinite current as has so far been thought to be the case.\alpha_{n0}and\alpha_{p0}were also measured and plotted as a function of voltage bias.