Abstract: A telephony system includes a plurality of local network terminations connected to a street cabinet in turn connected to an exchange. The street cabinet has a power supply for supplying voltage, a clock for generating a master ringer signal, and a modulator for modulating the voltage with the ringer signal. The filters extract the DC voltage and the ringer signal. The extracted DC voltage and the extracted ringer signal obviate the prior art requirements to provide a separate DC power supply and a separate clock within each local network termination, thereby avoiding duplication of components within each local network termination.

Abstract: A cordless telephone set including a master set and at least one personal set connected to a telephone line via the master set, in which the personal set has a detecting section for detecting whether the personal set is placed in a state wherein a battery within the personal set is charged by a charger, control keys including an outside line key, and a controller for connecting the personal set to the telephone line via the master set when it detects that the personal set is placed in the state not charged based on an output signal from the detecting section.

Abstract: Apparatus powered from a communications line minimizes current drawn from the line by use of a variable power supply having a DC to DC conversion circuit controlled by an oscillator. The output of the DC to DC conversion circuit in a first lower power drawing mode is used to power a tone detection circuit which monitors the line for a wake-up tone. On receipt of an appropriate wake-up tone, the tone detection circuit provides an interrupt signal to a microprocessor which, in response, causes an increase in the oscillator frequency. The increased oscillator frequency then increases power drawn from the line via the DC to DC conversion circuit for operation in a second higher power drawing mode.

Abstract: In a private branch exchange system which includes a private branch exchange accommodating a plurality of line wires and extensions for switching lines between the two, and telephones, which are usable in the event of a power failure, connected to the extensions, the line wires and the power-failure telephones are connected when power feed to the private branch exchange is no longer performed owing to a power failure or the like. When power feed is restored, the call status of the power-failure telephone is monitored and, if it is found that a call is in progress.

Abstract: In a digital data communications device for use in an ISDN environment, a power supply apparatus and method are provided for energizing telephone danger circuitry or other alerting mechanisms. Embodiments of the present invention employ signal generators which control switching circuitry that converts a low voltage DC power source into a low voltage alternating current. A step-up transformer is used to convert or transform this low voltage into a high voltage alternating current, which is rectified and filtered to generate a high voltage direct current. The signal generators also control the switching circuitry which applies this high voltage direct current to an alerting mechanism and alternately provides a path to discharge energy which may be stored in the alerting mechanism, causing the alerting mechanism or other ringer circuitry to resound.

Abstract: A battery charging system (10) includes a charger (12), power supply (14), electrical device (16), external battery (18), and peripheral device (20). The charger (12) provides connections between the various components such that the electrical device (16), which is a portable electronic device, may communicate with the peripheral device (20). The components are kept small by providing the power supply (14) with a feedback input (26). The power supply generates a voltage output (24) which is at a preselected differential above the feedback level, thus minimizing overhead voltage levels and allowing efficient linear regulation in the electrical device (16) for battery recharging.

Abstract: A communication terminal device including a first switch provided between a button and an intermediate member, and a second switch provided below the intermediate member such that when the button is depressed, both the first and second switches are surely switched on. Both the switches are electrically insulated from each other. Wiring is made such that one of those switches may operate a telephone circuit connected directly to a telephone line while the other switch may operate a main communication unit operating with a commercial power source. Even when the commercial power source is interrupted due to a power stoppage, at least the telephone circuit is operable, so that the terminal device is capable of fulfilling at least the function of a telephone set and ensuring insulation between the telephone unit and the main communication unit.

Abstract: A power source control circuit for a telephone set, includes a power source switch, a detecting circuit, a power hold circuit, and a control circuit. The power source switch supplies an external power to the telephone set. The detecting circuit detects an off-hook operation of the telephone set or an incoming signal arriving at a line. The power hold circuit holds the power source switch in an ON state for a predetermined time period on the basis of an output from the detecting circuit. The control circuit is activated by supply of the external power and transmits an extension signal for extending the ON state of the power source switch within the predetermine time period.

Abstract: An enhanced subscriber line interface circuit for a digital switching system which includes a line configuration and protection circuit connection tot he subscriber line and to a thick-film hybrid module. The thick-film hybrid module comprises a high voltage interface circuit and a PCM conversion circuit. The high voltage interface circuit provides power to the subscriber line, converts received analog voice signals transmitted from the subscriber instrument into differential voltage voice signals and detects the subscriber lines status. The PCM conversion circuit is connected to the high voltage interface circuit and is disposed to convert received differential voice signals into PCM digital signals.

Abstract: An arrangement for feeding the subscriber's lines (10) of a public exchange with reduced line current upon the occurrence of a power failure, when the temperature within the public exchange or the temperature of individual components, mounted on circuit boards on which line interface circuits are present, exceeds a predetermined reference value, when the length of a subscriber's line is less than a line length reference value, or when the conversation time on a subscriber's line exceeds a conversation time reference value. All subscriber's lines or individual subscriber's lines only are fed with the reduced line current for a restricted time (FIG. 5B).

Abstract: An enhanced high voltage line interface circuit for a digital switching system over which a connection is established between a digital switching system and a subscriber instrument via a subscriber loop. The high voltage line interface circuit includes in combination circuits that provide power to the subscriber loop and convert received analog voice signals transmitted from the subscriber instrument into differential voltage voice signals for subsequent conversion to digital data for use by the digital switching system. Additionally, differential voltage voice signals from the digital switching system are converted to analog voice signals for transmission along the subscriber loop to the subscriber instrument. The high voltage line interface circuit further includes circuits that detect and monitor the subscriber loop status and develop digital logic output signals that are used to report the status of the loop to a digital switching system controller.

Abstract: A circuit (4) for generating metering pulses (P) includes a multiplier circuit (MULT), a bandpass filter (BF), a comparison circuit (COMP) and a ramp signal generator (RAMP). A current (IC) from the ramp signal generator is multiplied (MULT) by an alternating voltage (VTXX) such as to form the metering pulse (P), which is transmitted, together with a speech signal (SP), to a subscriber (1) for registration. The output voltage (UF) of the bandpass filter (BF) is compared with a reference voltage (UR) in the comparison circuit (COMP). The output (9a) of the comparison circuit is electrically conductive only when the filter voltage (UF) exceeds the reference voltage (UR). When control signals (D) open a switch (SW), a capacitor (C1) is charged by a first current generator (10). The capacitor voltage (VC) incresases linearly and controls proportionally the current (IC) of the ramp signal generator (RAMP).

Abstract: A power supply (ringer power supply) for a telephone exchange comprising a first switching circuit for receiving and subjecting direct current to high frequency switching by means of a switching element, a converter transformer connected to the switching circuit, a smoothing circuit connected to the secondary side of the converter transformer, a second switching circuit connected to the output stage of the smoothing circuit and used for switching the input current by means of a transistor bridge of a plurality of transistors for being alternately turned on, a direct-current bypassing diode connected between the input and output terminals of each transistor, a driving circuit for driving each of the transistors in accordance with a predetermined driving signal, and a driving signal generator circuit for generating the driving signal for setting timing to prevent the period during which a transistor is turned on from overlapping the one during which another transistor is subsequently turned on, permitting a red

Abstract: Battery feed circuits function to supply a predetermined current to the communication pair and include circuitry to counteract the effects of balanced longitudinal signals which appear on the communication pair. Prior art battery feed circuits use either expensive matched power resistors or matched and tracking current sources to provide both the dc current and the necessary balance. The subject battery feed circuit separates the two functions: a pair of poorly matched inexpensive power resistors provide the basic dc current; and associated pair of low power electronic circuits supply compensation signals to provide the necessary balance. The compensation signals are applied to the power resistors in a manner to obtain precision resistor (.+-.0.1%) characteristics from the inexpensive (.+-.5%) power resistors.

Abstract: When a floating battery feed circuit is used to power telephone lines, it is desirable to provide an anti-corrosion biasing circuit to keep the voltage on the tip and ring conductors from becoming positive. This can be done using an anit-corrosion circuit that sinks a dynamic amount of current from the tip conductor. A line circuit including such biasing is, however, incompatible with special lines such as PBX lines that rely on a grounded tip conductor in the talk state. In accordance with the present invention, a constant current is supplied from a ground reference circuit to the ring conductor of such special lines only when loop current is flowing. The magnitude of this supplied current is such that the anti-corrosion circuit holds the tip conductor sufficiently close to ground potential to allow the proper operation of circuits connected to the special lines.

Abstract: A substantial reduction in the common-mode noise generated by a switching-mode power converter is achieved by incorporating a multifilar-wound transformer into the converter in such manner that the inter-winding capacitances cause a cancellation of common-mode, noise components at the converter output.