Multiple cores used to simulate a variable volt-second saturable transformer for application in self-oscillating inverters

THE NONLINEAR characteristics of rectangular-hysteresis-loop magnetic cores have often been usefully combined with the nonlinear large-signal characteristics of transistors. A particularly fruitful combination is the magnetic-coupled multivibrator in which two switching transistors are combined with suitable windings on a single square-loop core.^1–3 A significant contribution to this class of square-wave inverters is found in the work of R. L. Van Allen,⁴ who employed two square-loop cores to control output frequency. These cores were made to operate on asymmetrical minor loops by means of a bias from a constant current source. More recently, W. A. Geyger⁵ obtained variable frequency characteristics in a magnetic-coupled multivibrator by employing a saturable reactor controlled by an autotransformer in parallel with the load. Since these various magnetically coupled multivibrators have been thoroughly analyzed and discussed in the literature, their operation will not be reviewed in this paper.