Illumination device and method for avoiding an over-power or over-current condition in a power converter

Abstract

An illumination device and methods are provided herein for avoiding over-current and over-power conditions in one or more power converters included within the illumination device. The illumination device may include at least a plurality of light emitting diode (LED) chains, a driver circuit, at least one power converter, and a control circuit. In some embodiments, the control circuit may be generally configured for determining a maximum safe current level and / or a maximum safe power level attributed to the power converter(s) at a present operating temperature, and for adjusting respective drive currents supplied to the plurality of LED chains by the driver circuit, so as not to exceed the maximum safe current level or the maximum safe power level at the present operating temperature. In some embodiments, a temperature sensor may be included within the illumination device for measuring the operating temperature presently associated with the power converter(s).

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001]The present application is a reissue of U.S. Pat. No. 9,485,813, issued on Nov. 1, 2016 from U.S. application Ser. No. 14 / 604,870, filed Jan. 26, 2015, which is hereby incorporated by reference herein in its entirety. RELATED APPLICATIONS[0002]This application is related to commonly assigned U.S. patent application Ser. Nos. 14 / 314,451, which published on Dec. 31, 2015 as U.S. Patent Application Publication No. 2015 / 0377699; 14 / 314,530, which published on Dec. 31, 2015 as U.S. Patent Application Publication No. 2015 / 0382422; 14 / 314,580, which issued on Jul. 12, 2016 as U.S. Pat. No. 9,392,663; 14 / 471,057, which issued on Jul. 12, 2016 as U.S. Pat. No. 9,392,660; and 14 / 471,081, which published on Mar. 3, 2016 U.S. Patent Application Publication No. 2016 / 0066384. The entirety of these applications is incorporated herein by reference.BACKGROUND OF THE INVENTION[0003]1. Field of the Invention[0004]This invention relates to illumination devi...

AI Technical Summary

Benefits of technology

[0022]In some embodiments, the control circuit and method may determine a maximum lumens value that can be safely produced by all LED chains at a predetermined safe temperature (e.g., 25° C.) to achieve a particular chromaticity setting. The chromaticity setting may be received by the interface or may be stored within the illumination device, and may be detected by the control circuit. In some embodiments, the control circuit and method may be configured for determining the maximum lumens value upon receiving the chromaticity setting, or only upon detecting a change in the chromaticity setting.

[0026]In some embodiments, the control circuit and method may determine a target lumens value that can be safely produced by all LED chains at the present operating temperature to achieve a particular chromaticity setting and a particular brightness setting without exceeding the maximum safe current level or the maximum safe power level associated with the at least one power converter. The chromaticity and brightness settings may be received by the interface or may be stored within the illumination device, and may be detected by the control circuit. In some embodiments, the control circuit and method may be configured for determining the target lumens value upon detecting the brightness setting, or only upon detecting a change in the brightness setting.

[0031]When operating temperatures are less than or equal to the predetermined safe temperature (e.g., 25° C.), the method described thus far provides a precise lumen output for the particular lamp settings (e.g., chromaticity, brightness and / or white mix settings) selected for the illumination device. Above the predetermined safe temperature, the scale factor applied to the target lumens value scales the lumen output with temperature, so as not to exceed the maximum safe power level or the maximum safe current level associated with the power converters at the present operating temperature. This avoids an “over-power” or “over-current” condition in the power converters, which improves lamp efficiency and prevents saturation of the inductive core.

[0033]In other embodiments, one or more of the method steps described above may be repeated a predetermined number of times to minimize errors before the drive currents are adjusted. For example, as the scale factor reduces with increasing temperatures above 25° C., the target lumens value decreases, which improves LED efficiency and changes the relative drive currents between the LED chains. When this occurs, it may be beneficial to recalculate the chromaticity values that are expected for each LED chain at the new drive currents to provide a more accurate representation of the maximum lumens value.

[0038]Depending on the brightness settings and operating temperature, the step of adding the subtraction (or multiplication result) to the scale factor to update the scale factor may cause the scale factor to gradually increase or decrease. As expected, increasing scale factor values increase the target lumens value, and thus, increase the drive currents supplied to the LED chains, the total power drawn by all LED chains, and eventually the operating temperature. Decreasing scale factor values have the opposite effect. By updating the scale factor value to account for changes in operating temperature over time, the control circuit and method ensures that the respective drive currents supplied to the LED chains will not cause an over-power or over-current condition in the power converters.

Problems solved by technology

As described in more detail herein, the first power converter may have a maximum safe power level and the second power converters may each have a maximum safe current level, above which the inductive core of the power converters saturates, potentially causing the power converter to overheat and fail.

The maximum safe power / current levels attributed to the power converters are not always consistent and tend to vary with operating temperature, once the operating temperature exceeds a predetermined safe temperature.

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