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.