DC-DC CONVERTER FOR SYNCHRONIZING SUBSCRIBER CIRCUIT

摘要

PURPOSE:To eliminate the generation of noise at voice band, by synchronizing a switching frequency of a DC-DC converter with an operating clock of a subscriber interface circuit. CONSTITUTION:A DC voltage applied to an input side is converted into AC with a transistor (TR)5 switched at a driving circuit 4 and applied to the primary winding of a transformer. An AC voltage of the secondary winding of the transformer is rectified and applied as an operating voltage of a subscriber line interface circuit (not shown). The output voltage is monitored at an output monitor circuit 2, which controls an output voltage to a prescribed value through the control of on-off ratio of the TR5 via a pulse width control circuit 3 and the drive circuit 4 with the output. As a clock CLK' applied to the circuit 3, an operating clock CLK of coder/decoder of the subscriber line interface is frequency-divided at a synchronizing clock forming circuit 6.