BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout.
With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings:
FIG. 1 illustrates a high level block diagram of a backlighting system exhibiting a separate controllable voltage source for each of a plurality of LED strings of a single color according to the principle of the invention;
FIG. 2 illustrates a high level functional block diagram of an LED string controller, a plurality of current limiters, a controllable voltage source, a plurality of LED strings of a single color of the backlighting system of FIG. 1 and a color sensor according to a principle of the invention;
FIG. 3 illustrates a high level flow chart of the operation of the LED string controller of FIGS. 1, 2 to test the LED strings prior to full operation according to a principle of the invention;
FIG. 4 illustrates a high level flow chart of the operation of the LED string controller of FIGS. 1, 2 to control the voltage of the controllable voltage source so as to minimize excess power dissipation while ensuring a balanced current flow through each of the LED strings of the same color, and to further monitor the PWM dynamic range and increase the current flow through the LEDs when the PWM duty cycle has reached a predetermined maximum according to a principle of the invention;
FIG. 5 illustrates a high level flow chart of an initialization operation for the LED string controller of FIGS. 1, 2 and 8 to measure the chrominance impact of a failure of each of the LED strings, calculate the required change in current to compensate for the failure and store the changes according to a principle of the invention;
FIG. 6A illustrates a high level flow chart of the operation of the LED string controller of FIGS. 1, 2 and 8 to periodically check the voltage drop across each of the current limiters and the actual current flow through the LED strings so as to detect one of a short circuited LED and an open circuited LED string, set an error flag in the event that a short circuited LED has been detected, adjust the current of the remaining strings to compensate for the open LED string in accordance with the stored values of FIG. 5 and renter the high level flow chart of FIG. 4 so as to update the control of the controllable voltage source according to a principle of the invention;
FIG. 6B illustrates a high level flow chart of the operation of the LED string controller of FIGS. 1, 2 and 8 to periodically check the voltage drop across each of the current limiters and the actual current flow through the LED strings so as to detect one of a short circuited LED and an open circuited LED string, disable the LED string associated with the detected short circuited LED, adjust the current of the remaining strings to compensate for the open or disabled LED string in accordance with the stored values of FIG. 5 and renter the high level flow chart of FIG. 4 so as to update the control of the controllable voltage source according to a principle of the invention;
FIG. 7 illustrates an arrangement of LED strings in a matrix which allows for improved compensation of a failed LED string by other LED strings according to a principle of the invention;
FIG. 8 illustrates a high level functional block diagram of an LED string controller, a plurality of current limiters, a controllable voltage source, a plurality of white LED strings and a photo-sensor according to a principle of the invention;
FIG. 9 illustrates a high level flow chart of the operation of the LED string controller of FIG. 8 to select a particular LED string, or a function of the LED strings, to feedback for control of the controllable voltage source, and to further monitor the PWM dynamic range and increase the current flow through the LEDs when the PWM duty cycle has reached a predetermined maximum according to a principle of the invention; and
FIG. 10 illustrates a high level flow chart of the operation of the LED string controller of FIG. 2 comprising internal current limiters in accordance with the principle of the current invention to prevent thermal overload resulting from power dissipation of the internal current limiters.
Patent Application
20070195025
