Patent ID: 7800316

Claim:
A light emitting diode (LED) driver comprising: a first controller comprising: a first voltage input terminal; a first output terminal; a first current source coupled to the first voltage input terminal, the first current source having at least one terminal for connection to a first LED to drive the first LED; a first detector coupled to the first voltage input terminal for detecting whether a voltage across the first voltage input terminal and the first output terminal is above a first threshold, the first threshold being a voltage greater than that needed to turn on the first LED; a normally-on first bypass switch having a first current handling terminal coupled to the first voltage input terminal, the first bypass switch having a second current handling terminal, the first detector being coupled to a control terminal of the first bypass switch to turn the first bypass switch off when the voltage across the first voltage input terminal and first output terminal is above the first threshold; a second controller comprising: a second voltage input terminal coupled to the second current handling terminal of the first bypass switch; a second output terminal coupled to the first voltage input terminal of the first controller; a second current source coupled to the second voltage input terminal, the second current source having at least one terminal for connection to a second LED to drive the second LED; a second detector coupled to the second voltage input terminal for detecting whether a voltage across the second voltage input terminal and the second output terminal is above a second threshold, the second threshold being a voltage greater than that needed to turn on the second LED; a normally-on second bypass switch having a first current handling terminal coupled to the second voltage input terminal, the second bypass switch having a second current handling terminal, the second detector being coupled to a control terminal of the second bypass switch to turn the second bypass switch off when the voltage across the second voltage input terminal and the second output terminal is above the second threshold; whereby the first detector does not turn off the first bypass switch when the voltage detected by the first detector is below the first threshold, so that the first bypass switch substantially connects the second voltage input terminal to the first voltage input terminal to bypass the second controller, and whereby the first detector turns off the first bypass switch when the voltage detected by the first detector is above the first threshold, allowing the second controller to receive a current through its second voltage input terminal.