Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M1/00—Substation equipment, e.g. for use by subscribers
  • H04M1/26—Devices for calling a subscriber
  • H04M1/30—Devices which can set up and transmit only one digit at a time
  • H04M1/31—Devices which can set up and transmit only one digit at a time by interrupting current to generate trains of pulses; by periodically opening and closing contacts to generate trains of pulses
  • H04M1/312—Devices which can set up and transmit only one digit at a time by interrupting current to generate trains of pulses; by periodically opening and closing contacts to generate trains of pulses pulses produced by electronic circuits
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M19/00—Current supply arrangements for telephone systems
  • H04M19/08—Current supply arrangements for telephone systems with current supply sources at the substations

Definitions

• This invention relates to telephone subsets and in particular to tele ⁇ phone subsets incorporating an electronic line switch, sometimes known as a line interface circuit.
• the electrical line switch fulfils a number of functions including the hook-switch function, that is, the line switch acts as a hook-switch when a hook-switch control signal is selectively applied to the line switch, a hook-switch control signal being generated when the user brings the subset into the off-hook mode.
• ⁇ his control signal may, for example, be provided by a ten number repetory tone/pulse dialler chip or a microprocessor. —
• the dialler chip In a subset provided with a conventional mechanical hook-switch and dialler chip, the dialler chip is provided with its operating power from current derived from the exchange battery and drawn over the exchange line through the hook-switch. As soon as the subset is brought into the off- hook mode the hook-switch contacts operate and adequate operating voltage is extended to the dialler chip which can then function.
• an object of the present invention to provide a cir ⁇ cuit arrangement which will provide the dialler chip with sufficient oper ⁇ ating current upon initial connection, and re-connection after subsequent un-plugging of the subset, without the need to draw excessive on-hook bleed current.
• a circuit will be referred to as A Dialler Chip Ener izing Circuit.
• a telephone sub ⁇ set circuit arrangement comprising a first and second line terminal means for respectively connecting to conductors of an exchange line, a trans ⁇ mission circuit means connected between said line terminal means, a line switch means whose switching element is formed by a conductive path of a controllable semiconductor switch means having a control element coupled to oa output of a control means associated with said transmission circuit means, said switching element being serially connected in the subset cir ⁇ cuits' loop current circuit, said control means having a first input means coupled to hook-switch means for applying hook-switch mode signals to said output of the control means for switching said switching element accord ⁇ ingly, said control means deriving a power supply from current drawn from exchange battery via the first line terminal means and the conductive path of said line switch means to power terminal means associated with said con ⁇ trol means, wherein said circuit arrangement further comprises a bleed cir ⁇ cuit for bleeding a current of a predetermined magnitude from said exchange 0line, a first controllable semiconductor switch
• the circuit arrangement further includes a voltage regu ⁇ lation means which regulates the voltage across the power terminals of the control means during off-hook operation.
• Fig. 1 is a schematic circuit of part of a subset circuit arrangement showing the invention in its simplest form.
• Fig. 2 is a circuit diagram of a telephone subset incorporating an em ⁇ bodiment of the present invention.
• Fig. 3 is a circuit diagram of the embodiment of Fig. 2 with the addi ⁇ tion of a regulation circuit. Best Mode Of Carrying Out The Invention
• the circuit shown comprises a ten number repetory tone/pulse dialler chip 1, having a dial pulse output A, a power terminal C a common voltage rail terminal D and hook-switch (HS) input X and Y; a line switch 2 having its switching circuit (not shown) coupled across out- puts J and K and its control circuit (not shown) coupled to input L. Also coupled to input L Is the e ⁇ mitter electrode of an NPN transistor TRl whose base element is connected to the junction of resistor R2 and the collector of the NPN transistor TR2. A bleed resistor Rl couples 1.1 terminal (not shown) to the junction of resistor R2 and the collector of transistor TRl as well as to power terminal C via diode Dl.
• Diode Dl may preferably com ⁇ prise three serially connected diodes.
• a storage capacitor Cl is connected across power terminal C and the common voltage rail D.
• Power terminal C is also coupled to the base element of transistor TR2 via zener diode D2. Coupled to the base element of transistor TR2 is a delay network comprising resistor R3 and capacitor C2.
• the common voltage rail terminal D is cou ⁇ pled to line terminal L2 (not shown).
• the voltage across capacitor Cl begins to rise, when the volt ⁇ age across capacitor Cl reaches the minimum operating voltage of the dialler chip required to control the line switch, typically 1.8v, because of the characteristics of zener diode D2, a relatively significant current begins to flow into the network comprising resistor R3 and capacitor C2.
• the values of resistor R3 and capacitor C2 are such that only after the voltage across Cl reaches approximately 3v, well above the minimum line switch operating voltage, will the voltage across capacitor C2 have risen to a magnitude sufficient to cause transistor TR2 to saturate.
• Charged storage capacitor Cl now providing adequate operating voltage at terminal C of the dialler chip so that when the subset is brought into the of -hook mode and hook-switch HS operates, the dialler chip produces the required signal at terminal A which is applied to input L of the line switch 2 to render the line switch conducting and allow the subset to operate normally.
• the subset circuit arrangement comprises line terminals LI and L2 connected across the AC points of a polarity guard de ⁇ vice in the form of a diode bridge PG.
• a tone ringer (not shown) is also connected across the line terminals.
• Across the DC points of bridge PG is a telephone transmission circuit TX.
• Dialler chip 1 is also connected across the DC points of bridge PG and in parallel with transmission circuit TX.
• the dialler chip may be, for example, an OKI MSM6052 chip, and in- eludes a dial pulse output A, a mute signal output B, a power terminal C, common voltage rail terminal D, dual-tone multifrequency (ETMF) output E, an earth recall output F, a DC characteristic adjustment signal output G, a plurality of Inputs 1-28 from a key pad (not shown) associated with the subset, and Inputs X and Y from an associated hook-switch HS.
• Serially connected between the DC positive point of polarity guard PG and the trans ⁇ mission circuit TX is the main switching path of the line switch circuit comprising a main switch in the form of a complementary configuration of transistors TR*.
• a control transistor TR3 whose base element is coupled to output A of dialler chip 1 and to the emitter of transistor TRl ⁇ the Dialler Chip Energizing Circuit comprising transistors TRl and TR2, bleed resistor Rl, diodes Dl and D2, resistor R2, storage capacitor Cl, and delay elements consisting of resistor R3 and capacitor C2.
• the operation of the Dialler Chip Energizing Circuit part of the cir ⁇ cuit shown in Fig. 2 is Identical to that of Fig. 1.
• the operation of the line switch shown In Fig. 2, assuming normal operating voltage at terminal C, is as follows: When brought into the off-hook mode, the operation of the hook-switch contacts HS is sensed by dialler chip 1 whereupon a mute signal Is applied to output B which mutes the transmission circuit TX; a signal is applied to output G which turns on a shunt circuit (not shown). A signal is applied to output A which turns on the control transistor TR3 of the line switch which in turn switches on transistor TR4 and TR5.
• transistor TR5 Upon operation of transistor TR5 a current loop is provided via line terminal LI, positive point of polarity guard PG, resistor R4, collector/emitter junction of transistor TR5, shunt circuit in parallel with transmission circuit TX, negative point of polarity guard PG to L2. After about 400 m/s the shunt circuit and the mute signal are removed leaving the transmission circuit TX in the current loop.
• the subset arrangement shown is substantially identical to that shown in Fig. 2 except for the addition of the regulation circuit elements which comprise transistors TR6 and TR7, resistor R6 and diode D6 and a decoupling element C3.
• the emitter/collector path of TR7 is serially connected between the line switch switching path and terminal C of dialler chip 1 and its base element is connected to the collector element of transistor TR6 whose base element is coupled to the base element of transistor TR2.
• Diode D6 is included in the base/emitter circuit of transistor TR6 in order to ensure that the Dialler Chip Energizing Circuit is not mis- operated by the regulation circuit.
• the forward characteristics of diode D6 are such that during the operation of the Dialler Chip Energizing Cir ⁇ cuit, no significant current flows through transistor TR6.

Landscapes

• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Interface Circuits In Exchanges (AREA)
• Telephone Set Structure (AREA)
• Mobile Radio Communication Systems (AREA)
• Structure Of Telephone Exchanges (AREA)
• Devices For Supply Of Signal Current (AREA)
• Telephonic Communication Services (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=3772105

Family Applications (1)

Country Status (5)

Cited By (4)

Families Citing this family (1)

Citations (5)

Family Cites Families (1)

• 1988
  • 1988-02-22 AU AU13449/88A patent/AU606397B2/en not_active Expired - Fee Related
  • 1988-02-22 JP JP50178788A patent/JPH02503254A/ja active Pending
  • 1988-02-22 WO PCT/AU1988/000046 patent/WO1988008234A1/en not_active Application Discontinuation
  • 1988-02-22 EP EP19880901774 patent/EP0363362A4/en not_active Withdrawn
  • 1988-12-08 DK DK683888A patent/DK683888A/da not_active Application Discontinuation

Patent Citations (5)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events