Abstract: A pulse-inverter, especially a transistor inverter, is required to generate a system of polyphase output voltages as symmetrical as possible, having, for instance, trapezoidal waveforms. For this purpose, several reference voltages having different waveforms are generated wherein each section of an output voltage coincides with a section of a reference voltage. These reference voltages are pulse-width-modulated with a high-frequency sampling frequency and an inverted sampling frequency to form pulse width modulated reference voltages and pulse width modulated inverted reference voltages, respectively. The pulse-width-modulated reference voltages and pulse width modulated inverted reference voltages are coupled to the control lines of the inverter switches so as to generate, section by section, the output voltages having the reference waveform.

Abstract: A power line control circuit receives audio-frequency signals from a pulsed inverter that is transformer-coupled to the power line. A filter circuit is connected between the inverter and the coupling transformer primary circuit to transmit the audio signals and prevent power line frequencies from reaching the inverter. A magnitude-measuring circuit determines when output current from the inverter exceeds a certain value and controls an intervening circuit to reverse, briefly, the state of conductivity of the inverter.