Control of light intensity using pulses of a fixed duration and frequency

• US 8,421,368 B2
• Filed: 05/15/2009
• Issued: 04/16/2013
• Est. Priority Date: 07/31/2007
• Status: Active Grant

• Current Assignee: Saco Technologies Inc. (Madison Square Garden Sports Corp.)
• Original Assignee: LSI Industries Incorporated
• Inventors: Jalbout, Bassam D., Wong, Brian
• Primary Examiner(s): PHILOGENE, HAISSA
• Application Number:
  US12/466,688
• Publication Number:
  US 20090261746A1
• Time in Patent Office: 1,432 Days
• Field of Search: 315/291, 315/292, 315/307, 315/312, 315/360, 315/362, 315/209.R, 363/97
• US Class Current: 315/291
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

A method and circuit to control the intensity of lights, illumination fixtures, and displays using pulses of a fixed duration and a fixed frequency (FD/FF) is provided. In particular, the method may be used to control one more light sources. By varying the number of pulses in a control burst, the total current flowing through the light source may be precisely controlled providing greater accuracy than other methods, such as, for example, PWM or variable pulse frequency. The FD/FF technique may be used in conjunction with any number of light sources, and finds particular application in LED displays and for any type of LED illumination fixture.

Claims

1. A processing device comprising:

a processor configured to generate a current switch control signal supplied to a current switch and to time a start and end of each pulse within a timing cycle, wherein the current switch is configured for connection to a first power potential, a second power potential, and a light source, and including an input to receive a current switch control signal to place the switch in one of an ON state and an OFF state including a timing cycle with a series of pulses of fixed duration and fixed frequency within the timing cycle to cause current to flow from the first potential to the second potential through the light source during the ON state to cause the light source to emit light of a desired intensity over the timing cycle.

2. The device of claim 1 wherein the light source is a light emitting diode.

3. The device of claim 1 wherein the light source is an array of light emitting diodes.

4. The device of claim 1 wherein the length of the timing cycle is constant and the intensity of the light source is varied by changing the number of pulses from one timing cycle to another timing cycle.

5. The device of claim 1 wherein the duration of each pulse of the current switch control signal is equal to the period of time between pulses in the timing cycle.

6. The device of claim 1 wherein the duration of each pulse of the current switch control signal is less than or equal to the period of time between pulses in the timing cycle.

7. The device of claim 1 wherein the device has an initial condition before flow of current through the current switch and the period time between pulses of the timing cycle is longer than the period of time for the circuit to return to the initial condition after a pulse of the timing cycle.

8. The device of claim 1 wherein the number of pulses in a timing cycle varies from zero to a maximum number corresponding to an intensity level of the light source from zero to a maximum intensity.

9. The device of claim 1 wherein persistence of human vision views the intensity of the light source as increasing with the increasing total current flow through the light source between timing cycles of the control signal without perceiving any visible defects from the light source.