Multi-channel constant current (MC3) LLC resonant LED driver

Multi-channel LED drivers are required in many applications, such as display backlighting, indoor lighting and street lighting. The LED driver should have the capability of providing multiple constant current source regardless to the LED forward voltage variations. Moreover, how to achieve current sharing between multiple LED channels is also challengeable in these applications. In this paper, a multi-channel constant current (MC³) LLC resonant LED driver is proposed. The LLC converter is controlled to operate as a constant current mode LED driver. By employing the multiple transformer structure, one single-stage driver can drive multiple LED channels, simplifying the driving scheme and circuit complexity. A DC block capacitor is utilized to balance the currents between two LED channels driven by the same transformer. After considering LED´s i-v characteristic, the LLC current gain characteristic is proposed and derived to describe a LLC converter with current-controlled output. Instead of constant resistive load considered in LLC voltage gain characteristic derivation, a non-linear LED load is modeled and used in AC equivalent circuit to derive LLC current gain characteristic. A design methodology for MC³ LLC LED driver has been developed based on the proposed LLC current gain characteristic. A 100kHz, 200W, 4-channel MC³ LLC LED driver is designed and simulated to verify the proposed circuit and design method.