Duty Control Extended Describing Function History of engineering & technology LED driver LLC Converter LLC converter LLC resonant converter LLC resonant converters PV micro-inverter Small Signal Modeling ZVS auxiliary circuit adjustable leakage inductance aircraft power conversion asymmetric pulse width modulation asymmetric pulse width modulation (APWM) battery charging bidirectional power conversion center-tapped transformer control current mode control dual output converter flux walking flux-balance control loop high efficiency high switching frequency integrated transformer isolation dc-dc converter magnetizing current estimation power converter pulse frequency modulation (PFM)