Accurate measurement of lifetime of excess base stored charge at high collector currents

The lifetime τ
S
of the excess base stored charge of the saturated bipolar transistor is an important parameter of the charge-control model. A commonly used method for measuring τ
S
is based on measuring the storage time t
s
in an inverter circuit. At high collector currents, it is difficult to measure the base current I
BS
which is necessary to drive the transistor to the edge of saturation, because of uncertainty in
V_{B'C'}
caused by the voltage drops across the collector and base spreading resistance inside the transistor. This paper presents new methods for measuring I
BS
, τ
S
, and the current gain at the edge of saturation, and gives experimental results. The methods are very simple and are especially useful at high collector currents. In addition, we give principles for choosing the input "on" pulse width for measuring τ
S
.