Pulse-Width Control of Transistors

Duty cycle, or pulse width, modulation can be used to advantage in transistor circuits where the desired output is a direct current or slowly varying voltage such as required in proportional control systems. For a prescribed transistor dissipation, several times greater load power can be controlled by this technique than with class A operation. Conversely, for a given load power, the transistor can be operated at lower dissipation and thus at higher temperatures than is permissible with conventional modes of operation. Circuits have been devised for several different types of load circuits and also for signal generation. Combination of the duty-cycle modulation generation and output circuits yields a unique direct current amplifier.