LED current bias control using a step down regulator

摘要

A step down switching regulator circuit that is particularly well-suited to drive high power LEDs includes a crossover conduction mode (XCM) control circuit that maintains operation at the crossover point between continuous conduction mode (CCM) and discontinuous conduction mode (DCM). This XCM operation provides an inductor current waveform that ramps up and down between zero and a desired maximum current. One or more comparators in the XCM control circuit can be used to control switching between the inductor current ramp up and ramp down phases. In this manner, complex feedback loop logic and PID controlled PWM signal generation logic can be avoided, and the need for external sense resistors and associated interface pins can be eliminated.