Saturation Current

Author: Leonard Krugman

Another important transistor characteristic is the saturation current I_co. This is the collector current that flows when the emitter current is zero. In properly functioning transistors, I_co is in the vicinity of 10 microamperes; the value is considerably higher in defective transistors. The saturation current is composed of two components. The first is formed by thermally generated carriers which diffuse into the junction region. The second component is an ohmic characteristic which is caused by surface leakage across the space charge region, from local defects in the germanium, or from a combination of these two factors. The ohmic component may be separated from the true or thermally caused value by measuring the collector current at different values of collector voltage.