Influence of isolation transformer leakage inductance on constant current output of Class D series–parallel LCC‐type resonant converter for light‐emitting diode lighting application

This research studied the influence of isolation transformer leakage inductance on the output current of Class D series–parallel LCC‐type resonant converters for light‐emitting diode lighting applications. Through theoretical analysis and simulation of the resonant tank impedance over a wide operation frequency range, an impedance peak was discovered at light load condition, with the peak value increasing with decreases in output load. This impedance peak will cause double‐peak voltage and current gain of the resonant tank; moreover, the peak of the gain curve, which is introduced by leakage inductance of the isolation transformer, is located at the designed inductive operation region. These characteristics bring challenges to realising a wide operational range and designing short‐circuit protection. To minimise these influences, the leakage inductance value should be controlled by a winding method, and the operational frequency range should be well designed.