Comparison of N-P-N transistors and N-P-N-P devices as twenty-ampere switches

A series of 20-ampere silicon n-p-n transistors and three-terminal n-p-n-p switches have been developed, and their characteristics are compared with respect to high-current switching applications. At the present time, collector-emitter voltages of the transistors are generally lower than those of the switches, which may exceed 400 volts. The n-p-n transistors are somewhat simpler to produce than the n-p-n-p structures. However, the ultimate current-handling capacity of the latter type of device is greater, because of the uniform current density. The saturation voltage drops at 20 amperes are comparable, being in the order of one to two volts. The switch has a distinct advantage in the turn-on speed, while the transistor has the equally important advantage that the base retains control for turn-off.