Modeling of the cascode switching structure used in Flyback converter for achieving
fast startup in the deeply dimmed phase-cut LED driver is presented in this draft.
The cascode structure’s inherent instability and oscillation issue is modeled and
analyzed quantitatively. Three solutions are proposed to stabilize the structure
and suppress the unstable voltage oscillation. Solutions are studied using the
proposed model for design robustness. And this model can be further applied to the
popular new high voltage (for example 650V) cascode GaN FET technology.
Experimental results of a 20W phase-cut dimmable LED driver are demonstrated to
verify the proposed modeling method and solutions.