INTENSITY CONTROL FOR LIGHT-EMITTING DIODE DISPLAY

• US 3,787,752 A
• Filed: 07/28/1972
• Issued: 01/22/1974
• Est. Priority Date: 07/28/1972
• Status: Expired due to Term

• Current Assignee: Dennis G. Delay
• Original Assignee: Dennis G. Delay
• Inventors: Delay, Dennis G.
• Primary Examiner(s): Saalbach, Herman Karl
• Assistant Examiner(s): Mullins, James B.
• Application Number:
  US05/276,017
• Time in Patent Office: 543 Days
• Field of Search: 315/84.5,84.6,169R,169TV 313/18D 340/336 307/228,311
• US Class Current: 327/544
• CPC Class Codes: G01R 13/405 using a plurality of active, i.e. light emitting, e.g. electro-luminescent elements, i.e. bar graphs
• CPC Class Codes: G04G 9/0088 by controlling light sources, e.g. electroluminescent diodes

Abstract

A plurality of light-emitting diode elements which are unmatched in light output at the lower portions of their forward current ranges and which form an integrated illuminated visual display are activated by a power supply arrangement which applies to each diode element a series of independent power pulses of sufficient power to activate each diode element to saturation and into light-emitting condition in a frequency range which appears to the human eye to be steady illumination, the power supply arrangement being provided with a control feature for selectively varying the duration of the power pulses in order to vary the apparent intensity of the illuminated display, and also provided with current limiting means to limit the current passed by each diode element, during each power pulse and its activation thereby, to a given upper range of forward current in which the light-emitting diode element light outputs are substantially matched and in which optimum light emission efficiency is achieved.

Claims

1. An improved solid state electrical instrument system for achieving uniform intensity of an illuminated visual display arrangement, comprising in combination:

a plurality of light-emitting diode elements arranged in the visual display arrangement, said elements being unmatched in light output over the lower portions of their forward current ranges and matched at a given upper portion of the forward current ranges;

a power supply means for generating a continuous series of independent electrical power pulses at a frequency above which said diode elements when activated appear to the human eye to be continuously illuminated, each of said pulses being of more than sufficient power to activate said diode elements in their given upper portions of their forward current ranges, and including control means for selectively varying the duration of the power pulses to vary the apparent intensity of the visual display arrangement formed by said diode elements; and

forward current limiting means connected to receive said pulses for limiting the forward current through the diode elements on each power pulse to a predetermined given upper portion of their forward current range in which the light outputs of the light-emitting diode elements are substantially evenly matched.

2. The improved system of claim 1 wherein said forward current limiting means further comprises:

divider means receiving and biasing said pulses; and

regulating means receiving said biased pulses and for regulating the current output of said pulse within the predetermined portion of the forward current range of said diode elements.

3. The improved system of claim 2 wherein said divider means comprises:

a regulated voltage source;

a first resistor connected at one terminal to the output of said power supply means; and

a second resistor connected between said regulated voltage source and the other terminal of said first resistor.

4. The improved system of claim 3 wherein said regulating means comprises:

a transistor having an emitter connected to said regulated voltage source, a base connected to said other terminal of said first resistor, and a collector connected to said diode elements; and

capacitor means connected between said regulated voltage source and ground.

5. The improved system of claim 4 wherein said power supply means further comprises:

a sawtooth oscillator circuit means for producing a sawtooth wave;

a differential comparator unit receiving the sawtooth wave and a selected DC reference voltage from said circuit means for producing an output pulse of regulated duration.

6. The improved system of claim 5 wherein said control means includes a selectively adjustable means for varying the level of the selected DC reference voltage to said comparator unit.