The push-pull converter is probably one of the oldest switching regulator type circuits. It was first used in the 1930’s with mechanical vibrators functioning as the switch. When transistors became available push-pull converters were used as free-running oscillators in the primary of many automobile communication converters.
Some recreational vehicles still use this free-running type of oscillator converter in de-to-de converters as well as in dc-to-ac inverters.
A typical push-pull converter circuit is shown in Figure 6-6.