Apparatus for heating an electrically conductive cooking utensil by magnetic induction

Claim 1

An induction heating apparatus comprising: a heating unit including a plurality of heater coils connected with each other in parallel; a static power converter connected between said heating unit and a low-frequency a.c. power source for converting the low-frequency power into a high-frequency power and supplying said high-frequency power to said heating unit thereby causing said heater coils to produce time-varying magnetic fields, said converter including a switching circuit connected in parallel with said heating unit and said power source for producing said high-frequency power with a frequency substantially equal to a frequency with which the switching circuit is triggered; and control means including a reference voltage generator, a current detector for producing a voltage representative of current flowing through said heater coils, said current detector comprising magnetic cores respectively linked with lines connected to said heater coils, a plurality of windings each comprising turns wound on a corresponding one of said magnetic cores, a rectifier connected to said windings, and a timing capacitor connected to said rectifier for storing said voltage across said timing capacitor, a single comparator connected to said reference voltage generator and current detector for producing an ON signal when the voltage from said current detector is lower than the reference voltage of said reference voltage generator and for producing an OFF signal when the voltage from said current detector exceeds the reference voltage, a pulse generator connected to said comparator for producing pulses when receiving said ON signal and ceasing to produce pulses when receiving said OFF signal, and a gate pulse supply circuit connected to said pulse generator and said switching circuit for triggering said switching circuit in response to said pulses from said pulse generator.