1.  Field of Invention
This invention relates to a new and improved induction heating and cooking unit having little or no stand-by power loss, so as to afford as substantial reduction in the energy consumed in the performance of a cooking task. 
Further, the invention relates to an induction cooking unit for use in home and commercial induction cooking ranges, which is capable of safely being used with existing or known metal base pans or other cooking vessels of any type without risk of damage to the induction cooking unit.  The invention also relates to the matter of providing maximum protection to the user of the induction cooking unit against accidental burns which can be caused by small metallic articles which would become heated when left on the cooking surface unless the induction power is turned off while the unit is not being used for cooking. 
2.  Background of Invention
U.S. Pat.  No.  3,710,062 issued Jan. 29, 1972 to Philip H. Peters, Jr. for Metal Base Cookware Induction Heating Apparatus Having Improved Power Supply and Gating Control Circuit Using Infra-Red Temperature Sensor and Improved Induction Heating Coil Arrangement -- Assigned to the Environment/One Corporation of Schenectady, N.Y., describes and claims a range top induction cooking unit for use in home and commercial ranges.  The induction cooking unit descried in U.S. Pat.  No.  3,710,062 was designed to inductively heat pans and other metal base cookware which are fabricated from stainless steel, iron, titanium, and other similar lossy metallic materials.  In U.S. Pat.  No.  3,886,342 - issued May 27, 1975, Philip H. Peters, Jr., Inventor -- Improved Induction Cooking Unit Having All Pan Safe Operation, Wide Range Power Control and Low Start-Up and Shut-Down Transients -- Assigned to the Environment/One Corporation of Schenectady, N.Y., an improved all-pan induction cooking unit is disclosed which can be safely used with pans or other metal base cookware of any description without risk of serious damage to the induction cooking unit.  The induction cooking unit described in U.S. Pat.  No.  3,886,342 is designed to operate from a conventional residential or commercial source of alternating current, and converts the alternating current to a full wave rectified direct current that then supplies a solid-state inverter which generates a current at a frequency of the order of 20 kilohertz in an induction cooking coil.  An induction cooking unit that also is capable of operation with pans or other metal base cookware of all types and materials, and which is somewhat similar in construction and operation, is described in U.S. Pat.  No.  3,898,410 -issued Aug. 5, 1975 -- Philip H. Peters, Jr., Inventor -- Improved AC to RF Inverter Circuit for Induction Cooking Unit -- Assigned to the Environment/One Corporation. 
The present invention comprises a further improved all-pan induction cooking unit similar to those described in U.S. Pat.  No.  3,886,342 and U.S. Pat.  No.  3,898,410, but which is designed to have an essentially zero stand-by power loss and to discriminate between a proper, lossy pan load and one which is fabricated from or externally clad with aluminum, copper, or other highly conductive material, and which further discriminates against small articles such as knives, forks, spoons, spatulas, etc.,  and does not turn on in the presence of such articles.  As a consequence of these characteristics, the improved unit possesses greatly improved overall operating efficiency, safety, while beIng used in a kitchen or other area for the preparation and cooking of foodstuffs.