Disclosed is a power inverter which converts voltage from a DC source into high frequency rectangular alternating voltage pulses which are transferred to a load via a transformer with a ferromagnetic core having no air gap. An additional indicator winding on the transformer, which is connected to a differential circuit which in turn is connected to a control circuit, makes it possible to control the process of the reversal of the magnetization of the core. Switching on the primary winding takes place when the permeability of the transformer's core achieves its maximum. This special feature makes it possible to minimize the size of the transformer, while allowing transferring maximum energy to the load with minimum of the magnetization frequency and losses.