Magnetic-amplifier control of switching transistors

THE POWER-HANDLING ABILITY of a transistor can be increased by about a factor of 10, relative to class A operation, by operating in the switching mode.¹ Much greater stability also is achieved, inasmuch as a switching transistor operates only at cutoff or saturation and minor variations in the linear transistor parameters do not affect operation. These features have been exploited in a number of recently developed devices which use the transistor as a switch. The advantages of the switched mode of operation are similarly attractive in constructing a linear amplifier. The average output of a switching transistor can be linearly controlled if ratio of “on” time to “off” time is varied by a pulse-width modulation technique. A series of circuits have been developed which use the variable-width output pulse of an audio-frequency magnetic amplifier as a means of linearly controlling the output of switching transistors.