Luminous indicator with zero standby power

• US 4,017,847 A
• Filed: 11/14/1975
• Issued: 04/12/1977
• Est. Priority Date: 11/14/1975
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Burford, Thomas Maynard, Westerman, George Raymond
• Primary Examiner(s): Curtis, Marshall M.
• Application Number:
  US05/631,921
• Time in Patent Office: 515 Days
• Field of Search: 340/336, 340/324 R, 315/161, 315/164, 315/171, 315/131, 315/170
• US Class Current: 345/46
• CPC Class Codes: G06F 11/325 by lamps or LED's
• CPC Class Codes: G08B 5/36 using visible light sources
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

In a luminous indicator circuit, a plurality of luminous elements are connected in series relation to form a series circuit which is supplied through a constant current device. A solid state switching device is placed in parallel with each luminous element (e.g., LED). A control circuit including switches connected to a D.C. source determines the conduction of each solid state switch, so that the associated luminous element is controlled independently of the other luminous elements in the series circuit. The control circuit includes switching means which supplies voltage to the indicator circuit only when at least one luminous element is activated. Circuit protection against unwanted transient voltages is provided.

Claims

1. An indicator circuit comprising a plurality of LED elements each having an anode and a cathode, said LEDs being connected in like polarity series relation to form a series circuit having an anode end and a cathode end;

a voltage source having first and second terminals;

a switching device for each LED comprising a path connected in parallel with said LED and a control electrode;

first means connected to said control electrode for applying a first signal to said control electrode for rendering said path conductive and for applying a second signal to said control electrode for rendering said path nonconductive;

each first means comprising a switch having first and second terminals, a first diode having an anode and a cathode, a first transistor having a collector, an emitter and a base, and a first impedance;

said voltage source first terminal being connected to said switch first terminal;

said switch second terminal being connected to said first diode anode;

said first diode cathode being connected to said first transistor collector and to said control electrode;

said first transistor emitter being connected to said voltage source second terminal through said first impedance;

means for applying a predetermined current to said series circuit only when at least one of said switches is closed comprising a plurality of second diodes each having an anode and a cathode, a second transistor and a third transistor each having a collector, an emitter and a base, and second, third and fourth impedances;

one second diode anode being connected to the second terminal of one of said switches;

the cathode of each second diode being connected to the anode end of said series LED circuit and to said second transistor collector through said second impedance;

said second transistor collector being connected to said second transistor base, the base of each first transistor, and the base of said third transistor;

said second transistor emitter being connected through said third impedance to the voltage source second terminal;

said third transistor collector being connected to the cathode end of said series LED circuit; and

said third transistor emitter being connected to said voltage source second terminal through said fourth impedance.

2. An indicator circuit according to claim 1 wherein each switching device comprises fourth and fifth transistors each having a collector, an emitter and a base;

said fourth transistor emitter being connected to said fifth transistor collector and to said LED anode;

said fourth transistor collector being connected to said fifth transistor base;

said fourth transistor base being connected to said first diode cathode; and

said fifth transistor emitter being connected to said LED cathode.

3. A luminous indicator circuit according to claim 2 further including a plurality of third diodes each having an anode and a cathode, each third diode being associated with one of said switches, each third diode anode being connected to said voltage source second terminal;

each third diode cathode being connected to the second terminal of the associated one of said switches.

4. An indicator circuit comprising a plurality of LEDs each having an anode and a cathode, said LEDs being connected in like polarity series relation to form a series circuit having an anode end terminal and a cathode end terminal, a voltage source having first and second terminals, a switching device associated with each LED comprising a selectively conductive path connected in parallel with said associated LED and a control electrode for controlling the conductive state of said path, first means connected to said control electrode for applying a first signal to said control electrode to render said path conductive and for applying a second signal to said control electrode to render said path nonconductive, means connected between said voltage source second terminal and said series circuit cathode end terminal for applying a controlled current to said series LED circuit, and means connected between said voltage source first terminal and said series LED circuit anode end terminal responsive to a second signal being applied to at least one of said switching devices for applying voltage from said voltage source to said series LED circuit whereby voltage is removed from said indicator circuit when all of said LEDs are nonluminous.