Pan detector for induction heating apparatus

An induction heating apparatus comprising, a resonant circuit including an induction heating coil inductively coupled in operation to an inductance load;

• a gate-controlled switching device and a unidirectional conductive device connected in inverse parallel relation therewith, a power supply circuit connected in operation to a source of alternating current to supply an excitation potential across the main terminals of the gate-controlled switching device, means for supplying a train of gating-on pulses to the control gate of said gate-controlled switching device for permitting said switching device to be switched on and off at a frequency tuned to the resonant circuit to generate in said resonant circuit an energization current which drives the induction heating coil to cause heating of the inductance load;
• detecting means for generating a first signal representative of the magnitude of the inductive coupling between said inductance load and the heating coil;
• comparing means for generating a second signal when the first signal reaches a variable reference level;
• manual adjusting means for permitting the adjustment of the inductive coupling at a desired value;
• means for varying the variable reference level in accordance with the adjustment of the inductive coupling;
• and means responsive to the second signal for enabling said gating-on supplying means at intervals which are sufficiently long so that no significant heating occurs in said inductance load.