Abstract: A tone supplying device generates various tone signals which an exchange can provide for public subscribers. Address signals generated by a counting operation of a first counter are inputted to a plurality of tone tables, which in turn successively output a tone signal corresponding to each of the address signals and provide same to a corresponding buffer through a corresponding latch. The first counter allows the tone selecting signals and the address signals to be generated in the tone tables so as to successively output corresponding tone signals therefrom and, at the same time, supply the tone selecting signals to the cadence selecting circuit so as to allow the cadence selecting circuit to select any one of cadence data inputted thereto from the cadence table and to output it.

Abstract: An uninterruptible power supply circuit has a first power supply unit for supplying a first power supply voltage; a second power supply unit for supplying a second power supply voltage which is lower than the first power supply voltage; a back-up power supply unit for supplying a back-up power supply voltage; a charge current control unit for receiving the first power supply voltage and for controlling a charge current which is supplied to the back-up power supply unit according to a capacity of the back-up power supply unit; a reverse current protection unit connected between the second power supply unit and an output node connected to an output terminal; an overcharge protection unit connected between the back-up power supply unit and the output node, for protecting the back-up power supply unit from being overcharged; and a relay unit which is driven by the first power supply voltage and forms a path for outputting the back-up power supply voltage to the output node when the first power supply voltage is c