Cooktop appliance with improved power control

A heating apparatus comprising:

• at least one electric resistive heating unit adapted for energization by an external standard domestic AC power supply having a predetermined RMS output voltage;
• user actuable input means for enabling the user to select from a plurality of predetermined power settings for said heating unit;
• control means responsive to said user actuable input means, for controlling the output power of said heating unit;
• switch means responsive to said control means for selectively coupling said heating unit to the external power supply;
• said control means being operative to selectively switch said switch means at one of a plurality of switching rates to apply power pulses from said power supply to said heating unit, each pulse comprising one cycle of the AC power signal from the external power supply, each switching rate defining a power pulse repetition rate effective to apply a corresponding RMS voltage level to said heating unit;
• each of said user selectable power settings having associated with it a corresponding one of said switching rates, the maximum user selectable power setting having a corresponding switching rate which defines an RMS voltage level less than the RMS output voltage whereby the heating unit can be designed to operate at an RMS voltage less than the RMS output voltage of the external power supply;
• said control means further comprising means for detecting the transition from an OFF power setting to a non-OFF power setting and wherein said control means is operative to effectuate a power pulse repetition rate corresponding to an overdrive RMS voltage level higher than that corresponding to the maximum user selectable power setting for a transient heat up period to rapidly heat the unit to its radiant temperature thereby providing visual indicator to the user that said heating unit has been turned On;
• means for measuring the elapsed time since the entry of the last occurring OFF setting by the user;
• and means for controlling the duration of the transient heat up period as a function of said elapsed time, to prevent over-heating a heating unit pre-heated from a previous use.

An electric cooking appliance adapted for energization by a standard AC domestic household power supply having an output power signal characterized by a predetermined RMS voltage level, said cooking appliance comprising:

• a plurality of electric resistive heating units designed by steady state energization at a maximum RMS voltage level less than the RMS voltage level of the power signal from a standard domestic household power supply;
• user actuable input selection means for enabling the user to select one of a plurality of available power settings including an Off setting for each of said heating units;
• power control means responsive to said user actuable input means for independently controlling the output power of each of said heating units;
• switch means associated with each of said heating units and responsive to said control means;
• each of said switch means being operative to selectively couple its associated heating unit to the external power supply;
• said control means being operative to selectively switch each of said switch means at one of a plurality of switching rates, each rate defining a corresponding predetermined RMS voltage level to be applied to the associated one of said heating units;
• each of said user selectable power settings having associated with it a corresponding one of said switching rates, the maximum user selectable power setting having a corresponding switching rate which establishes an effective RMS voltage level less than the RMS level of the power signal from the power supply, whereby each of said heating units can be designed to operate at an effective steady state RMS voltage less than the RMS level of the power signal from the power supply;
• said control means further comprising means for detecting the transition from an OFF power setting to a non-OFF power setting and said control means being operative to effectuate a switching rate which establishes an overdrive RMS voltage level higher than that corresponding to the maximum user selectable power setting for a transient heat up period to rapidly heat the unit to its radiant temperature thereby providing visual indicator to the user that said heating unit has been turned On;
• said power control means further comprising means for determining when the total current drawn by said heating units is greater than a predetermined limit and means for reducing the effective voltage level applied to each of said heating units to reduce the total current to within acceptable limits.

An electric cooking appliance adapted for energization by a standard AC domestic household power supply having an output power signal characterized by a predetermined RMS voltage level, said cooking appliance comprising:

• a plurality of electric resistive heating units designed for steady state energization at a maximum RMS voltage level less than the RMS voltage level of the output power signal from the external power supply;
• user actuable input selection means enabling the user to select one of a plurality of power settings including an OFF setting for each of said heating units;
• power control means responsive to said user actuable input means for independently controlling the output power of each of said heating units;
• switch means associated with each of said heating units and responsive to said control means;
• each of said switch means being operative to selectively couple its associated heating unit to the external power supply;
• said control means being operative to selectively switch each of said switch means at one of a plurality of switching rates, each rate defining a corresponding RMS voltage level to be applied to the associated one of said heating units;
• each of said user selectable power settings having associated with it a corresponding one of said switching rates, the maximum user selectable power setting having a corresponding switching rate which defines an RMS voltage level less than the RMS level of the power signal from the power supply;
• said power control means further comprising means for determining when the total current drawn by said heating units is greater than a predetermined limit and means for reducing the effective voltage level applied to each of said heating units to reduce the total current to within acceptable limits.