Call tone control for telephone handset

摘要

The calling tone control has a control device (MP), a bridge circuit containing electronic switching elements coupled to the control device and a loudspeaker (LSP), directly connected across the bridge diagonal. The bridge circuit is supplied from a DC/DC converter (WDL), connected on the input side to the 2-wire telephone line (a/b). The switching elements are controlled in opposing pairs for controlling the loudspeaker, with the pulse-width ratio determined by the ratio of the signal width to the signal period of the control signal (TRF) provided by the control device.