An induction furnace employing a 100 kHz MOSFET full-bridge current-source load-resonant inverter

An induction furnace using a current-source, full-bridge load-resonant MOSFET inverter suitable for melting small amounts of precious metal (gold and platinum) is presented. Melting times of 25 seconds were achieved at a power level of approximately 900 watts. A parallel resonant topology was employed to resonate at 100 kHz. The full-bridge or H-bridge output stage was used to provide power input to the load in two quadrants. Two important reasons for utilising the current-fed, full-bridge topology in this application are: (1) it has an inherent short-circuit protection capability; and (2) it has a simple design structure, using few components, which has been proved to be advantageous over the other inverter topologies. The induction-heating load is driven at its resonant frequency, by the inverter. This ensures maximum efficiency and power transfer, with zero voltage switching. A simple but effective gate drive and control timing circuit was applied. The compact layout of the inverter suppressed ringing between parasitic lead-inductance connections and the drain-source capacitance of the MOSFETs. The induction furnace operates effectively in open loop throughout the heating cycle. The performance was tested on a 100 kHz prototype, rated at approximately 1 kW. An analysis and experimental results are presented.