Telephone set illumination circuit

Claim 2

Apparatus for illuminating a telephone set comprising, in combination: a source of illumination; a local battery for providing power to said source of illumination; means responsive to a transition from an on-hook to an off-hook mode in said set for applying said battery to said source; means for applying a trickle charge to said battery from a telephone line connected to a source of d.c. power; and means including a timing circuit for limiting the duration of operation of said battery applying means.

Claim 3

Apparatus in accordance with claim 1 wherein said source of illumination comprises at least one light-emitting diode.

Claim 4

Apparatus in accordance with claim 2 wherein said trickle charge applying means comprises tip and ring terminals connectable to a telephone line, means connecting said terminals by way of a series combination of a resistor, and a dual function circuit element for preventing a reverse voltage from damaging said locaL battery and for preventing a low line voltage during speech transmission from discharging said local battery.

Claim 5

Apparatus in accordance with claim 3 wherein said dual function circuit element comprises a diode.

Claim 6

Apparatus in accordance with claim 4 including means connecting one terminal of said light-emitting diode to a terminal common to said dual function diode and said battery and means including the drain-source path of a transistor connecting the other terminal of said light-emitting diode to said ring terminal, said timing circuit comprising the series combination of a resistive and a capacitive element connected between said tip lead and the gate electrode of said transistor.

Claim 7

Apparatus in accordance with claim 5 including means for rapidly discharging said capacitive element thereby ensuring readiness for an immediately following illumination cycle.

Claim 8

Apparatus in accordance with claim 6 wherein said discharging means comprises a thyristor connected between a junction common to said resistive and capacitive elements of said timing circuit and said ring terminal, and means connecting the gate electrode of said thyristor to said tip terminal thereby to prevent said thyristor from being triggered in an off-hook set and for limiting the current flow through said thyristor.

Claim 9

Apparatus in accordance with claim 7 wherein said gate electrode connecting means comprises the series combination of a resistive element and a diode.

Claim 10

Apparatus for illuminating a telephone set comprising, in combination: an electrical circuit having tip and ring terminals connectable to the corresponding terminals of a telephone line having d.c. voltage applied thereto from a central office; said circuit including a local battery; a source of illumination; means responsive to a transition from an on-hook to an off-hook mode by said set for applying energizing current from said battery to said source; means for limiting the operation of said battery applying means to a period of time sufficient to enable the illumination of said set during dialing; and means for applying a trickle charging current from said line to said battery.

Claim 11

Apparatus for illuminating a telephone set comprising, in combination: an electrical circuit having tip and ring terminals connectable to the corresponding terminals of a telephone line having d.c. voltage applied thereto from a central office; said circuit including a local battery; a source of illumination; means responsive to a transition from an on-hook to an off-hook mode by said set for applying energizing current from said battery to said source; means for limiting the operation of said battery applying means to a period of time sufficient to enable the illumination of said set during dialing; and means for applying a trickle charging current from said line to said battery.

Claim 12

Apparatus in accordance with claim 9 wherein said limiting means includes a capacitor which determines the period of time during which the illuminating source is energized, and means for rapidly discharging said capacitor thereby to permit the initiation of illuminating cycles in rapid succession.