Lightning Surge Robustness Analysis and Optimization for an LED Driver Based on a Flyback Converter

The lightning surge robustness of a light-emitting diode (LED) driver based on a flyback converter has been experimentally investigated. It is demonstrated that the surge failure in the driver results from the burnout of the super-junction vertical double-diffused MOS (SJ-VDMOS). The high residual surge voltage causes the SJ-VDMOS to go into breakdown, resulting in a large number of impact ionizations. It is also shown that the impact ionization centers in the device are enlarged and shifted toward the bottom of trench gate with the increased surge stress. As a result, the generated holes preferentially flow along the p-body region near trench gate, finally triggering the parasitic BJTs and destroying the device. Next, a low-cost protection scheme that includes both a first-stage discharge network and a novel SJ-VDMOS with higher surge robustness is proposed to improve the lightning surge capability of the LED driver, increasing the robustness by more than a factor of 10.