An Improved Class-E Current Inverter With Two Coupled Inductors for Isolation and Power Scaling Without Affecting Switch Voltage Stress

Loads such as light-emitting diodes and wireless chargers need to be driven by a current source with a wide range of output power. The Class-E parallel resonant inverter was suggested recently as a topology capable of supplying a constant current. It is suitable when the load and the source are not required to share the same ground, and when the load power/voltage is sufficiently low to prevent MOSFET's (body) diode conduction. Two coupled inductors that integrate the two original inductors and a transformer are added to the aforementioned inverter to provide common ground for the source and load or galvanic isolation. Interestingly, even though a transformer is incapable of stepping up the power, the maximum power of the improved inverter is boosted by the effective turns ratio of the coupled inductors. The duty ratio remains at the same 0.5 without diode conduction, and the switch's voltage stress is essentially constant. An equivalent circuit model is derived to simplify the inverter design. A design procedure is suggested for the integrated magnetics and is demonstrated by a 6.78 MHz prototype driving 1-A peak into a load varying between 1 and 40 Ω (23.6 W) without diode conduction.