Apparatus for driving multi-color LED strings

摘要

An apparatus comprises red, green and blue LED strings each having a corresponding switching circuit. Each LED string is divided into a plurality of LED segments. The three LED strings are connected in parallel or in series. Each LED string may be connected in series with a respective current source or share a common current source. A controller controls each switching circuit so that the number of LED segments connected in series in the red, green or blue LED string can be respectively controlled according to a color setting signal and the voltage level of an input voltage. A first control method is provided for controlling the apparatus having a constant input voltage and a second control method is provided for controlling the apparatus having a periodically time-varying input voltage.

主权项

1. An apparatus for driving multi-color LED strings, comprising:
an input voltage; a multiplexing switch having first, second and third inputs and an output; a red LED string having a plurality of red LEDs controlled by a corresponding switching circuit, said red LED string having a positive end connected to said input voltage and a negative end connected to said first input of said multiplexing switch; a green LED string having a plurality of green LEDs controlled by a corresponding switching circuit, said green LED string having a positive end connected to said input voltage and a negative end connected to said second input of said multiplexing switch; a blue LED string having a plurality of blue LEDs controlled by a corresponding switching circuit, said blue LED string having a positive end connected to said input voltage and a negative end connected to said third input of said multiplexing switch; a current source having a first end connected to said output of said multiplexing switch and a second end connected to ground; a controller receiving a color setting signal and sending a plurality of controlling signals to each of the switching circuits, and multiplexing signals to control said multiplexing switch; wherein said controller controls respective numbers of LEDs connected in series in the red, green and blue LED strings through the corresponding switching circuits, and the duration that said current source is turned on for each of the red, green and blue LED strings according to said color setting signal.