A new generation of PWM ringing generators for telecommunications

Pulse width modulated (PWM) ringing generators, based on a new topology that permits very compact and efficient ringing, are proposed. The DC/AC principle of conversion utilizes a single-stage double-flyback converter that operates with a HF square-wave carrier which is modulated by a low-frequency sinusuoidal modulating signal. The galvanic isolation between DC-source and AC-load is obtained directly in this stage so that no additional stage or isolation transformer is required. The application of the new topology makes it possible to develop a new generation of ringing generators with high overall efficiency, reduced size and weight, excellent dynamic response, inherent galvanic isolation and very low audible noise. The simplicity of the scheme allows the production cost of ringing generators for telecommunications to be lowered. The design of a plug-in type ringing generator for the ITALTEL digital switching exchange is described. A comparison between the new design and the old one is given