Analysis and Design of a Digital-Controlled Single-Stage Series-Type LED Driver With Independent N-Channel Output Currents

In the applications such as mixed-color light emitting diode (LED) lighting system, LED drivers are always required to provide constant current for each LED string and each current should be controlled independently. For this purpose, a single-stage series-type LED driver with independent control of N-channel output currents is proposed in this paper. The function of power factor correction can be realized inherently to obtain high power factor. N active output units, each one made up of a power switch, a diode, and an output filter capacitor, are series-connected to form the series-type N-channel outputs structure. According to different current reference values, N-channel output currents can be independently regulated just by sampling each output current to adjust the duty cycle of each secondary output-switch automatically. The operating principle and independent closed-loop control strategy of the proposed LED driver with N = 3 are analyzed as an example in detail. Finally, the quantitative parameter design method for a 120 W prototype is elaborated. And, the experimental results are presented to verify the effectiveness of the LED driver and the correctness of parameter design method.