Operation of inverter with transformer and DC load in voltage step-down (BUCK) and step-up (BOOST) control cases from reactor-capacitor filter in DC supply circuit with commutated in duration of converter input shortening capacitor of the filter is examined. Such operation modes can be applied for stabilization of inverter output load voltage in a wide range of DC supply voltage variations. When supply voltage is low, the converter operates in BOOST case, but when it is sufficiently high – in BUCK case. In BUCK control case capacitor of the filter is directly connected to input of converter providing function of voltage source for converter. In BOOST operation case when input of the converter is periodically shortened, the DC source can provide properties of current source and the capacitor has to be disconnected from the filter. Application of both control cases allows obtaining constant load voltage at variations in a relatively large range of supply voltage of the scheme. On the basis of operation analysis diagrams of voltages and currents of main elements of the scheme are developed. Main mathematical relations are obtained in both BUCK and BOOST cases both with continuous and discontinuous input current of converter transformer. Comparison of calculation results using the obtained expressions with computer simulation results confirms good coincidence. As investigation results demonstrate, capacitance of the filter capacitor by volume have to be chosen for BUCK case, but operation voltage capacitor have to conform to converter input voltage in BOOST case i.e., which is higher as supply voltage. Inductance of filter reactor has to conform to the conditions in BOOST control case, when reactor periodically is connected through switches of converter in parallel to DC supply source. Computer simulation of the scheme in both operation cases confirms accuracy of the developed diagrams for shape of voltages and currents of elements.