Output power control of induction cooking inverter

Claim 2

A solid state cooking appliance for inductively heating a cooking utensil comprising an induction heating coil mounted adjacent a utensil support, a solid state inverter controlled by power device means and operated at a variable ultrasonic frequency to generate a train of oscillatory pulses with a variable delay interval therebetween corresponding to nonconducting intervals of said power device means, to thereby achieve high output power control of the power supplied to said induction heating coil, said inverter circuit including commutating capacitor means and inductive energy storage means comprised by a reset transformer having a primary winding connected to store energy during conducting intervals of said power device means and to discharge energy during the delay intervals between consecutive current pulses that serves to recharge said commutating capacitor means to sustain circuit oscillation, and low output power control means for selectively controlling the amount of energy discharged by said reset transformer primary winding to variably recharge said commutating capacitor means and thereby provide a plurality of low output power levels, said low output power control means comprising a circuit including a secondary winding of said reset transformer and an auxiliary solid state device.

Claim 3

An appliance according to claim 1 wherein said auxiliary solid state device is a thyristor that is rendered conductive at a variable time during each delay interval between consecutive current pulses.

Claim 4

An appliance according to claim 2 wherein said reset transformer primary winding and power device means are connected in series between a pair of unidirectional voltage input terminals, and said secondary winding and thyristor are also connected in series between said input terminals.

Claim 5

A solid state cooking appliance for inductively heating a cooking utensil comprising an induction heating coil mounted adjacent a utensil support, a solid state inverter circuit operated at a variable ultrasonic frequency to generate a train of oscillatory current pulses with a variable delay interval therebetween to achieve high output power control of the power supplied to said induction heating coil, said inverter circuit including inductive energy storage means connected to discharge energy during the delay intervals between consecutive current pulses to sustain circuit oscillation, and low output power control means for selectively controlling the amount of energy discharged by said inductive energy storage means, said inductive energy storage means being a reset transformer with a primary winding for energy storage, said low output power control means comprising a circuit including a secondary winding of said reset transformer and an auxiliary solid state device, said auxiliary solid state device being an uncontrolled device that is conditioned for conduction at a predetermined time during each delay interval between consecutive current pulses, wherein said reset transformer secondary winding is a tapped secondary winding, and said low output power control means further includes switch means for connecting said uncontrolled device to a selected tap on said tapped secondary winding to obtain stepped control of the low output power.

Claim 6

A solid state cooking appliance for inductively heating a cooking utensil comprising an induction heating coil mounted adjacent a utensil support, a solid state inverter circuit operated at a variable ultrasonic frequency to generate a train of oscillatory current pulses with a variable delay interval therebetween to achieve high output power control of the power supplied to said induction heating coil, said inverter circuit including inductive energy storage means connected to discharge energy during the delay intervals between consecutive current pulses to sustain circuit oscillation, and low output power control means for selectively controlling the amount of energy discharged by said inductive energy storage means, said inductive energy storage means being a reset transformer with a primary winding for energy storage, said low output power control means comprising a circuit including a secondary winding of said reset transformer and an auxiliary solid state device, said auxiliary solid state device being an uncontrolled device that is conditioned for conduction at a predetermined time during each delay interval between consecutive current pulses, wherein said reset transformer secondary winding is a tapped secondary winding, and said low output power control means further includes switch means for connecting said uncontrolled device to a selected tap on said tapped secondary winding to obtain stepped control of the low output power.

Claim 7

A solid state cooking appliance for inductively heating a cooking utensil comprising an induction heating coil mounted adjacent a substantially non-metallic utensil support for producing an alternating magnetic field, a series resonant inverter including a commutating capacitor and main solid state power device means for converting an input supply voltage to an ultrasonic frequency wave that drives said induction heating coil, said inverter further including a reset transformer having inductively coupled primary and secondary windings with said primary winding being connected to recharge said commutating capacitor, and output power control circuit means comprising said secondary winding and a series connected auxiliary solid state device for variably controlling the recharge of said commutating capacitor to obtain a plurality of different output power levels as set by the user.

Claim 8

A solid state cooking appliance for inductively heating a cooking utensil comprising an induction heating coil mounted adjacent a substantially non-metallic utensil support for producing an alternating magnetic field, a series resonant inverter including a commutating capacitor and main solid state power device means for converting an input supply voltage to an ultrasonic frequency wave that drives said induction heating coil, said inverter further including a reset transformer having inductively coupled primary and secondary windings with said primary winding being connected to recharge said commutating capacitor, and output power control circuit means comprising said secondary winding and a series connected auxiliary solid state device for variably controlling the recharge of said commutating capacitor to obtain a plurality of different output power levels as set by the user.

Claim 9

An appliance according to claim 5 wherein said inverter and output power control circuit means are both connected between a pair of input terminals, and said auxiliary solid state device is a gate controlled thyristor that is rendered conductive at a variable time after the voltage across said reset transformer secondary winding exceeds a value related to the supply voltage, to obtain continuous control of the output power over a predetermined range.

Claim 10

An appliance according to claim 5 wherein said inverter and output power control circuit means are both connected between a pair of input terminals, said auxiliary solid state device is a diode, and said reset transformer secondary winding is a tapped secondary winding, and said output power control circuit means further includes a user controlled switch for connecting said auxiliary diode to a selected tap on said tapped secondary winding to obtain stepped control of the output power over a predetermined range.