Power source device for high-frequency induction heating

Claim 1

A high-frequency induction heating apparatus for induction heating a steel production for surface quenching, said apparatus comprising a heating coil for applying high-frequency power to the surface of said steel product and a self-excited high-frequency power source for supplying high-frequency power to said heating coil, said self-excited high-frequency power source comprising a D.C. source of power, an oscillating element adapted to be energized by said D.C. source of power, a matching transformer having a primary winding and a secondary winding, a plurality of capacitors and high-speed switching means, said heating coil being connected to said secondary winding, said primary winding having a plurality of taps each provided at a position of said primary winding including a different number of turns so as to permit the tapped portions of said primary winding to impedance-match with said secondary winding of said matching transformer and said heating coil connected to said secondary winding at a plurality of frequencies suitable for performing induction heating of said steel product in time-division fashion according to a size, shape and state of said steel product, each of said capacitors being adapted to be combined with a predetermined one of said taps to form a tank circuit for said oscillating element, the natural frequency of which tank circuit is the frequency corresponding to said predetermined tap of said plurality of frequencies, said high-speed switching means being adapted to switch connections of said tank circuits to said oscillating element to perform induction-heating in time-division fashion using high-frequency power at said plurality of frequencies.