Single Inductor Serial-Parallel LED Driver

Abstract

An LED driver circuit is disclosed that can drive a plurality of LED strings that are arranged in parallel, each LED string having a plurality of component LEDs that are series-connected. The LED strings can be the same type of LEDs in each string, or have different types of LEDs from one string to another. The LED driver includes a voltage control loop that dynamically regulates the output voltage across the parallel arrangement of LED strings. The output voltage is dynamically adjusted to accommodate the LED string with the largest operational voltage drop. This enables LED displays to constructed using different types of LEDs strings, but still supply the LED strings in a power efficient manner. Further, each LED string also includes its own individual current regulation loop so that the current, and therefore brightness, of each LED string can be individually adjusted.

1 . A light emitting diode (LED) circuit, comprising:
 a plurality of LED strings connected in parallel with each other, each LED string including a plurality of component LEDs connected in series;   a minimum voltage selector circuit to select the LED string with the largest voltage drop across its terminals, and output a minimum voltage associated with said selected LED string with said largest voltage drop;   a voltage control loop receiving said minimum voltage from said minimum voltage selector, said voltage control loop generating an output voltage sufficient to drive said plurality of LED strings based on said minimum voltage; and   a plurality of current regulation loops, each current regulation loop determining a regulated current for a corresponding one of said plurality of LED strings.