Transistors as power-conversion devices

Summary form only given. Under contract to the Power Sources Branch of the Squier Laboratories, we have been studying the application of power transistors as dc-to-ac power-conversion devices. Basically a transistor oscillator is used to replace the more conventional vibrator in battery-operated equipment. There are many advantages to be gained from such a substitution and indeed in many respects the transistor is able to meet specifications that would be impossible with mechanical vibrators. A simple push-pull circuit, which was originally developed at Squier Laboratories, has proved to have almost ideal characteristics. The circuit oscillates with square waveforms in such a manner that the transistors operate very close to their maximum possible efficiency. In addition to the two transistors the only other necessary components are a transformer and rectifiers if a dc output is desired. There are no critical components, and efficient operation can be obtained even with a reasonable mismatch between the transistors. The basic circuit is not always self-starting; however, methods have been developed which will ensure that the oscillations will start under full load. If a load slightly in excess of full load is placed on the circuit, the oscillations cease and both transistors shut off, which prevents further transistor failures as a result of temporary shorts in the load.