The paper deals with mathematical model of single-phase bridge inverters which outputs voltage is controlled by a pulse-width notching. The transistors in the inverter circuit are turned on and off so as to produce zero periods of equal length, for unipolar modulation, or negative voltage for bipolar modulation. The D.C. source is being a fixed level of voltage. Suppose the notching frequency to be constant for all frequency of the fundamental squarewaves and to be fixed on 500 Hz. The output inverter’s voltage is expressed by an analytical formula based on Fourier complex series. On the base of output voltage, the waveforms of the output currents are analytically calculated for different inverter’s loads.