Solid-state high-frequency electric process heating power supplies

A detailed critical review has been made of both solid state power devices and circuit topologies with emphasis on their application to high frequency electric process heating power supplies operating between 3and 30 MHz. A number of prototype units have been designed and constructed and their suitability for high frequency induction heating and dielectric heating applications investigated. Desirable qualities being robustness, tolerance to load mismatch, ease of design, simplicity and cost of constituent components as compared with present day valve equipment The experience gained in these investigations has resulted in the choice of the power MOSFET as the most appropriate device and Class E amplifier as being the most applicable circuit topology for the generation of RF power for high frequency electric process heating applications. A practical and theoretical study has been made of the limitations of the power MOSFET as a high frequency switching device. The effect of source feedback on the switching speed of T03 packaged devices has been investigated by the addition of a second source terminal in a specially modified T03 package. Novel drive circuits have been developed enabling high frequency switching of both power and RF MOSFETs. These have been employed in inverters operating at 3.3 MHz at power levels up to 600 W and at frequencies between 7 and 27 MHz at power levels over 100 W, with conversion efficiencies of up to 95%.