Current source is used in auxiliary power supplies, battery chargers, and LED drivers. The battery chargers are required to provide constant current within a wide output voltage range, similar to LED drivers. The load-independent (LI) Class-E inverter is a promising topology for such applications since it can realize zero-voltage switching (ZVS) within a wide load range. Class-E current source can be achieved by converting constant voltage (CV) Class-E inverter to current source with a trans-susceptance network or using parallel resonant topology. The design and analysis of LI Class-E inverters usually assume a high-Q resonant load tank so that the load current/voltage is sinusoidal. While this is the case in RF applications, it's not required in DC-DC power conversion. Besides, high-Q design leads to high inductance and increased voltage/current stress on the resonant components, increasing converter volume, loss, and cost. This work aims to provide a design guideline for the CC Class-E inverter when significant harmonics are present by reflecting the trade-off between load range and voltage stress, with the help of a modified frequency domain analysis method to eliminate the iteration existing in the time domain analysis. Output current variation and voltage stress can be automatically quantified when circuit parameters vary. Generalized load range contours are obtained to guide the circuit design. With the help of the analysis, a 10-W dual-output Class-E gate power supply is designed with optimized magnetics and reduced isolation capacitance. Compared with CC Class-E based on trans-susceptance network, the parallel resonant CC Class-E inverter has smaller part counts due to its low-order resonant network. However, the current topology suffers from limited maximum output power. In this work, a coupled-inductor based parallel resonant CC Class-E inverter is proposed with more than 2 times maximum power without increasing part counts. / Doctor of Philosophy / Current source is used in auxiliary power supplies, battery chargers, and LED drivers. The battery chargers are required to provide constant current within a wide output voltage range, similar to LED drivers. The load-independent (LI) Class-E inverter is a promising topology for such applications since it can realize zero-voltage switching (ZVS) within a wide load range. This work aims to provide a new design guideline for the CC Class-E inverter when significant harmonics are present by reflecting the trade-off between load range and voltage stress, with the help of a modified frequency domain analysis method to eliminate the iteration existing in the time domain analysis. Output current variation and voltage stress can be automatically quantified when circuit parameters vary. Generalized load range contours are obtained to guide the circuit design. With the help of the analysis, a 10-W dual-output Class-E gate power supply is designed with optimized magnetics and reduced isolation capacitance. Compared with CC Class-E based on trans-susceptance network, the parallel resonant CC Class-E inverter has smaller part counts due to its low-order resonant network. However, the current topology suffers from limited maximum output power. In this work, a coupled-inductor based parallel resonant CC Class-E inverter is proposed with more than 2 times maximum power without increasing part counts.