LINEAR CONTROL DEVICE, SYSTEM AND METHOD FOR COLOR RENDERING OF RGB LEDS

Abstract

Linear control of RGB LED for generating ambient lighting with variable color is accomplished by using multiple linear regulators to vary LED intensity via analog dimming. Each regulator controls current through a given color LED which in turn varies the LED intensity. Given the wavelength shift of LEDs at various drive currents and perceived intensity difference to the human eye, for different colors, the current regulator response may be non-linear and unique depending upon the desired color. Further, the linear drive current regulation can be accomplished using voltage mode or current mode control. The device, system and methodology, each using RGB LEDs, can reproduce any color on the Cartesian Color Coordinate system.

Claims

1. A linear control device for color rendering of an RGB LED comprising: an RGB LED that emits light; and multiple linear regulators to vary intensity of the light emitted by the RGB LED via analog dimming; wherein each linear regulator controls current through the RGB LED to enable varying the light intensity of the RGB LED such that the color of light emitted is controlled.

2. The linear control device of claim 1 wherein the linear drive current regulation is accomplished using a voltage mode control.

3. The linear control device of claim 1 wherein the linear drive current regulation is accomplished using a current mode control.

4. The linear control device of claim 1 further comprising a microprocessor that generates a control signal wherein the signal is pre-programmed to fit a unique non-linear curve required for the color intensity needed to reproduce a desired CIELUV coordinate location for the RGB LED.

5. A linear control system for color rendering of a plurality of RGB LEDs comprising: a plurality of RGB LEDs, each RGB LED being functionally adapted to emit light; and multiple linear regulators to vary intensity of the light emitted by the plurality of RGB LEDs via analog dimming; wherein each linear regulator controls current through the plurality of RGB LEDs to enable varying the light intensity of the RGB LEDs such that the color of light emitted is controlled.

6. The linear control system of claim 5 wherein the linear drive current regulation is accomplished using a voltage mode control.

7. The linear control system of claim 5 wherein the linear drive current regulation is accomplished using a current mode control.

8. The linear control system of claim 5 further comprising a microprocessor that generates a control signal wherein the signal is pre-programmed to fit a unique non-linear curve required for the color intensity needed to reproduce a desired CIELUV coordinate location for the plurality of RGB LEDs.

9. A method for color rendering of a plurality of RGB LEDs via linear control comprising the steps of: providing a plurality of RGB LEDs, each RGB LED being functionally adapted to emit light; and providing multiple linear regulators to vary intensity of the light emitted by the plurality of RGB LEDs via analog dimming; wherein each linear regulator controls current through the plurality of RGB LEDs to enable varying the light intensity of the RGB LEDs such that the color of light emitted is controlled.

10. The linear control method of claim 9 wherein the linear drive current regulation step is accomplished using a voltage mode control.

11. The linear control method of claim 9 wherein the linear drive current regulation step is accomplished using a current mode control.

12. The linear control method of claim 9 further comprising the step of providing a microprocessor that generates a control signal wherein the signal is pre-programmed to fit a unique non-linear curve required for the color intensity needed to reproduce a desired CIELUV coordinate location for the plurality of RGB LEDs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic drawing of a circuit configured to function in accordance with the device, system and method of the present invention.

[0010] FIG. 2 is a graph illustrating the linear to non-linear color algorithm input as compared to the output values.

DETAILED DESCRIPTION

[0011] As discussed above, linear control of RGB LED for generating ambient lighting with variable color is accomplished by using multiple linear regulators to vary LED intensity via analog dimming. Each regulator controls current through a given color LED which in turn varies the LED intensity. Given the wavelength shift of LEDs at various drive currents and perceived intensity difference to the human eye, for different colors, the current regulator response may be non-linear and unique depending upon the LED color being controlled. Further, the control can be accomplished using voltage mode or current mode control. Voltage mode control offers the advantage of being “load independent” but less accurate. Current mode control has the advantage of accuracy at the expense of more complex feedback. The system, using RGB LEDs, can reproduce any color on the Cartesian Color Coordinate system.

[0012] FIG. 1 shows one embodiment of an analog regulator circuit for a colored LED array that is configured in accordance with the present invention. This circuit operates with a 14V DC bus and a series parallel LED array (not shown, but which would be in parallel with the LEDs D1, D2 and D3). This embodiment does not show signal control processed via a microprocessor or a description of the response shape (TBD). V1 is a simulating PWM control source which gets filtered by R3, R4, C1, and C2. This is for simulation purposes only and was a quick way to size and validate the power structure.

[0013] On the actual embodiment, the control signal, applied to U3's non-inverting terminal, will be generated by a microprocessor. The signal will be programmed to fit the unique non-linear curve required for the exact color intensity needed to reproduce the desired “CIELUV” coordinate location (CIE 1976 (L*, u*, v*) color space, or CIELUV, is a two dimensional color space adopted by the International Commission on Illumination and is used extensively used for applications that deal with colored lights).

[0014] Referring now to FIG. 2, it shows the requested intensity value 10 in the x-axis as compared to the scaled value 11 in the y-axis that is required to compensate for the color shift given a linear drive current for R, G and B output. The lines on the chart show true linear 12, scaled R output 13, scaled G output 14 and scaled B output 15. The algorithm used will change based on temperature, LED manufacturer, LED package, etc.

[0015] In summary, linear current control of an LED, or any load for that matter, is not a new idea. In fact linear, or analog, control of loads was the original control method prior to digital. The present invention differs from present technology because the feedback used to generate the control signal will have to be non-linear and compensate for anomalies and characteristics associated with driving LED at current levels not specified by the LED manufacturer. The unusual feature is using analog drive current to create various colors, with RGB LED, necessitated by the need for exceptionally low EMI emissions. The advantage to this is the ability to operate multicolored lights in an MRI environment with no emissions.

[0016] Possible applications include analog dimming of white lights in the MRI scan room; the addition of wavelength shifted phosphor coated white LEDs to increase the color rendering index and correlated color temperature of white light generated with RGB for task lighting.