static converter and inverter for induction heating device and heating device comprising such a converter induction

摘要

An induction heating apparatus comprising a static converter including a bidirectional controlled switch having a main thyristor and a diode connected in parallel to conduct in opposite directions. The converter comprises a first circuit for protection against the spurious turning on of the thyristor caused by overshoot voltages due to the sudden interruption of the current flowing through the charging inductor when the switch is turned off. This protection circuit comprises, connected in series across the charging inductor, a diode and a capacitor which is charged through the diode when the voltage across the inductor terminals becomes positive, and discharged through a current-limiting resistor and an auxiliary thyristor into the gate of the main thyristor for triggering it periodically. A novel second circuit for protection against excessive rates of rise of the voltage across the thyristor is also provided, including a resistor and a capacitor in series, connected in parallel with the inductance of the resonant commutating circuit.