Induction heating appliance circuit that produces relatively high frequency signals directly from a relatively low frequency AC power input

Claim 2

A cooking appliance, comprising an inductive heating element for inductively heating a magnetically responsive utensil positioned over an electrically nonconductive gap away from said inductive heating element; and high frequency current fed inverter means for generating directly from a relatively low frequency AC power input signal high frequency electric signals to energize said inductive heating element whereby the latter produces a magnetic flux output signal for effecting inductive heating of such magnetically responsive utensil; said high frequency current fed inverter means comprising a low frequency circuit portion and a high frequency circuit portion, the latter comprising a bridge circuit having four side arms and a diagonal arm; said low frequency circuit portion comprising input means for receiving such AC power input signal, and a relatively large input inductor having a magnitude of inductance such that said input inductor appears as a relatively low impedance to such AC power input signal and as a relatively high impedance to high frequency signals in said high frequency circuit portion thereby to reduce feedback of such high frequency signals to said input means and the sources of such AC power input signal; said high frequency circuit portion being coupled to said low frequency circuit portion and comprising at least one inductor, at least one capacitor, and high frequency switch means for periodically connecting said at least one inductor and said at least one capacitor in a high frequency LC resonant circuit in response to high frequency gating signals supplied to said high frequency switch means to close the same, said input inductor in said low frequency circuit portion being coupled to said high frequency circuit portion and further having a magnitude of inductance to provide relatively constant current during respective cycles of such high frequency signals to charge said at least one capacitor when said high frequency switch means is open, said at least one capacitor being coupled relative to said high frequency switch means and said at least one inductor for supplying a high frequency discharge current through said at least one inductor when said high frequency switch means is closed, and said high frequency switch means being coupled to said at least one capacitor and said at least one inductor to receive the reverse resonant current and voltage in said high frequency LC resonant circuit to effect cut off and opening of said high frequency switch means.

Claim 3

A cooking appliance as set forth in claim 1, said input means comprising input terminals, and said bridge circuit comprising two opposed nodes at which power is supplied to said bridge circuit, at least one of said nodes being coupled through said input inductor to one of said input terminals, two of said bridge circuit side arms being connected in series between said two nodes on one side of said bridge circuit and the other two of said side arms being connected in series between said two nodes on the other side of said bridge circuit.

Claim 4

A cooking appliance as set forth in claim 2, said diagonal arm of said bridge circuit being connected to the junction of two of said side arms on one side of said bridge circuit and to the junction of two of said side arms on the other side of said bridge circuit.

Claim 5

A cooking appliance as set forth in claim 3, said high frequency switch means comprising two SCR's, each being connected in diagonally opposed side arms of said bridge circuit.

Claim 6

A cooking appliance as set forth in claim 4, said SCR's being connected facing in opposite directions to conduct current in opposite directions between said nodes.

Claim 7

A cooking appliance as set forth in claim 5, wherein said at least one capacitor is connected in said bridge circuit diagonal arm, and there are two of said inductors, each being connected in a respective one of the remaining diagonally opposed side arms of said bridge circuit.

Claim 8

A cooking appliance as set forth in claim 6, wherein there are two of said inductive heating elements, each being positioned in the cooking appliance for inductively heating respective magnetically responsive cooking utensils, said inductive heating elements forming at least part of said two inductors, respectively.

Claim 9

A cooking appliance as set forth in claim 2, said diagonal arm of said bridge circuit being connected to the junction of two side arms on one side of said bridge circuit and to the junction of two side arms on the other side of said bridge circuit, and said high frequency switch means comprising at least one SCR connected in said bridge circuit diagonal arm.

Claim 10

A cooking appliance as set forth in claim 8, said at least one capacitor comprising a pair of capacitors, each being connected in a respective diagonally opposed side arm of said bridge circuit, and said at least one inductor comprising a pair of inductors, each connected in a respective one of the remaining diagonally opposed side arms of said bridge circuit.

Claim 11

A cooking appliance as set forth in claim 1, wherein said input means comprises a pair of input terminals, said high frequency circuit portion comprising first and second bridge circuits; each of said bridge circuits having a first node connected to receive power from a respective input terminal and a common connected second node, first and second series connected pairs of side arms, each of said pairs of side arms being connected between said nodes and in parallel with respect to each other, and a diagonal arm connected between the junction of the two side arms of said first pair and the junction of the two side arms of said second pair; said at least one inductor comprising a plurality of inductors, each comprising a first split inductor including two mutually inductively coupled halves respectively connected in diagonally opposed side arms of said first bridge circuit, and a second split inductor including two mutually inductively coupled halves respectively connected in diagonally opposed side arms of said second bridge circuit; said at least one capacitor comprising a first pair of capacitors, each being connected in a respective remaining diagonally opposed side arm of said first bridge circuit, and a second pair of capacitors, each being connected in a respective remaining diagonally opposed side arm of said second bridge circuit; and said high frequency switch means comprising a pair of SCR's, each being connected in the diagonal arm of a respective one of said bridge circuits; and further comprising a pair of voltage equalizing resistors, each being connected in parallel with a respective one of said bridge circuits across the two nodes thereof.

Claim 12

A cooking appliance as set forth in claim 10, further comprising a pair of RC snubber circuits, each being connected in parallel with a respective one of said bridge circuits between the two nodes thereof.

Claim 13

A cooking appliance as set forth in claim 10, further comprising a third bridge circuit connected in parallel with said first bridge circuit across the two nodes thereof, and a fourth bridge circuit connected in parallel with said second bridge circuit across the two nodes thereof; each of said third and fourth bridge circuits comprising first and second parallel connected pairs of side arms connected between two respective nodes on opposite sides of said bridge circuit and a diagonal arm connected between the junction of the side arms on one side of said bridge circuit and the junction of said side arms on the other side of said bridge circuit, a pair of capacitors, one connected in each of the diagonally opposed side arms of said bridge circuit, an SCR connected in the diagonal arm of said bridge circuit, and a work coil, including two mutually inductively coupled halves, each of which is connected in one of the remaining diagonally opposed side arms of said bridge circuit.

Claim 14

A cooking appliance as set forth in claim 12, wherein said SCR's connected in said first and third bridge circuits face in the same direction to conduct current through the respective inductors in said respective bridge circuits in a direction from a first one of said input terminals toward a second one of said input terminals, and said SCR's in said second and fourth bridge circuits face in the same direction to conduct current through the respective work coils in said respective bridge circuits in a direction from said second one of said input terminals toward said first one of said input terminals, and said inductive heating element including a plurality of the same, each being comprised of a respective one of said work coils.

Claim 15

A cooking appliance as set forth in claim 4, each of said SCR's being connected facing in the same direction to conduct current in a direction from one of said nodes toward the other of said nodes.

Claim 16

A cooking appliance as set forth in claim 14, said inductive heating element comprising an inductive work coil, said at least one capacitor being connected in said bridge circuit diagonal arm, and said at least one inductor comprising two halves of said inductive work coil, each of said halves exhibiting an inductance and generating a magnetic flux output in response to a current therethrough, each of said work coil halves being connected in a respective one of the remaining diagonally opposed side arms of said bridge circuit, and said work coil halves being mutually inductively coupled.

Claim 17

A cooking appliance as set forth in claim 15, said SCRs being adapted for alternate energization.

Claim 18

A cooking appliance, comprising an inductive heating element for inductively heating a magnetically responsive utensil positioned over an electrically nonconductive gap away from said inductive heating element; and high frequency current fed inverter means for generating directly from a relatively low frequency AC power input signal high frequency electric signals to energize said inductive heating element whereby the latter produces a magnetic flux output signal for effecting inductive heating of such magnetically responsive utensil; said high frequency current fed inverter means comprising a low frequency circuit portion and a high frequency circuit portion; said low frequency circuit portion comprising input means for receiving such AC power input signal, and a relatively large input inductor having a magnitude of inductance such that said input inductor appears as a relatively low impedance to such AC power input signal and as a relatively high impedance to high frequency signals in said high frequency circuit portion thereby to reduce feedback of such high frequency signals to said input means and the sources of such AC power input signal; said high frequency circuit portion being coupled to said low frequency circuit portion and comprising at least one inductor, at least one capacitor, and high frequency switch means for periodically connecting said at least one inductor and said at least one capacitor in a high frequency LC resonant circuit in response to high frequency gating signals supplied to said high frequency switch means to close the same, said input inductor in said low frequency circuit portion being coupled to said high frequency circuit portion and further having a magnitude of inductance to provide relatively constant current during respective cycles of such high frequency signals to charge said at least one capacitor when said high frequency switch means is open, said at least one capacitor being coupled relative to said high frequency switch means and said at least one inductor for supplying a high frequency discharge current through said at least one inductor when said high frequency switch means is closed, and said high frequency switch means being coupled to said at least one capacitor and said at least one inductor to receive the reverse resonant current and voltage in said high frequency LC resonant circuit to effect cut off and opening of said high frequency switch means; wherein there are a plurality of said inductive heating elements, each being positioned in the cooking appliance for inductively heating respective magnetically responsive cooking utensils, and said high frequency current fed inverter means includes means for supplying such high frequency electric signals selectively to each of said plurality of inductive heating elements; wherein said input means comprises a first power input terminal and a relatively neutral input terminal across which a first AC power input signal is supplied, and a second power input terminal, said second power input terminal and said neutral input terminal receiving a second AC power input signal such first and second AC power input signals being 180° out of phase with respect to each other; said high frequency circuit portion comprising first and second bridge circuits each having a pair of opposed nodes to which power is supplied from said neutral input terminal and a respective one of said power input terminals, and four side arms and a diagonal arm; and wherein there are a plurality of said inductors, one of said inductors being connected in one arm of one of said bridge circuits and another of said inductors being connected in one arm of the other of said bridge circuits, and there are at least two of said capacitors, one of said capacitors being connected in a second arm of each of said bridge circuits, respectively, and there are a plurality of said high frequency switch means, one of said high frequency switch means being connected in each of said bridge circuits, respectively, for periodically connecting a respective inductor and capacitor in a respective high frequency LC resonant circuit.

Claim 19

A cooking appliance, comprising an inductive heating element for inductively heating a magnetically responsive utensil positioned over an electrically nonconductive gap away from said inductive heating element; and high frequency current fed inverter means for generating directly from a relatively low frequency AC power input signal high frequency electric signals to energize said inductive heating element whereby the latter produces a magnetic flux output signal for effecting inductive heating of such magnetically responsive utensil; said high frequency current fed inverter means comprising a low frequency circuit portion and a high frequency circuit portion; said low frequency circuit portion comprising input means for receiving such AC power input signal, and a relatively large input inductor having a magnitude of inductance such that said input inductor appears as a relatively low impedance to such AC power input signal and as a relatively high impedance to high frequency signals in said high frequency circuit portion thereby to reduce feedback of such high frequency signals to said input means and the sources of such AC power input signal; said high frequency circuit portion being coupled to said low frequency circuit portion and comprising at least one inductor, at least one capacitor, and high frequency switch means for periodically connecting said at least one inductor and said at least one capacitor in a high frequency LC resonant circuit in response to high frequency gating signals supplied to said high frequency switch means to close the same, said input inductor in said low frequency circuit portion being coupled to said high frequency circuit portion and further having a magnitude of inductance to provide relatively constant current during respective cycles of such high frequency signals to charge said at least one capacitor when said high frequency switch means is open, said at least one capacitor being coupled relative to said high frequency switch means and said at least one inductor for supplying a high frequency discharge current through said at least one inductor when said high frequency switch means is closed, and said high frequency switch means being coupled to said at least one capacitor and said at least one inductor to receive the reverse resonant current and voltage in said high frequency LC resonant circuit to effect cut off and opening of said high frequency switch means; wherein there are a plurality of said inductive heating elements, each being positioned in the cooking appliance for inductively heating respective magnetically responsive cooking utensils, and said high frequency current fed inverter means includes means for supplying such high frequency electric signals selectively to each of said plurality of inductive heating elements; wherein said input means comprises a first power input terminal and a relatively neutral input terminal across which a first AC power input signal is supplied, and a second power input terminal, said second power input terminal and said neutral input terminal receiving a second AC power input signal such first and second AC power input signals being 180° out of phase with respect to each other; said high frequency circuit portion comprising first and second bridge circuits each having a pair of opposed nodes to which power is supplied from said neutral input terminal and a respective one of said power input terminals, and four side arms and a diagonal arm; and wherein there are a plurality of said inductors, one of said inductors being connected in one arm of one of said bridge circuits and another of said inductors being connected in one arm of the other of said bridge circuits, and there are at least two of said capacitors, one of said capacitors being connected in a second arm of each of said bridge circuits, respectively, and there are a plurality of said high frequency switch means, one of said high frequency switch means being connected in each of said bridge circuits, respectively, for periodically connecting a respective inductor and capacitor in a respective high frequency LC resonant circuit.

Claim 20

A cooking appliance as set forth in claim 17, at least one of said nodes of each of said bridge circuits being coupled through said input inductor to an input terminal; and in each of said bridge circuits two of said side arms being series connected between said two nodes on one side of said bridge circuit and two of said side arms being series connected between said two nodes on the other side of said bridge circuit, and said diagonal arm being connected to the junction of said two side arms on one side of said bridge circuit and to the junction of said two side arms on the other side of said bridge circuit.

Claim 21

A cooking appliance as set forth in claim 18, in each of said bridge circuits said high frequency switch means comprising two SCR's, each being connected in diagonally opposed side arms of said bridge circuit, said one capacitor being connected in said diagonal arm of said bridge circuit, and there are two of said inductors, each of said inductors being connected in a respective one of the remaining diagonally opposed side arms of said bridge circuit; said inductive heating elements each forming at least part of said inductors, respectively.

Claim 22

A cooking appliance as set forth in claim 19, in each of said bridge circuits said SCR's are connected facing in opposite directions to conduct current in opposite directions between said nodes.

Claim 23

A cooking appliance as set forth in claim 20, wherein there are two relatively large ones of said input inductors, one of said input inductors being connected between said first power input terminal and one of said nodes of said first bridge circuit and the other of said input inductors being connected between said second power input terminal and one of said nodes of said second bridge circuit.