Induction heat cooking apparatus

• US 3,889,090 A
• Filed: 11/15/1973
• Issued: 06/10/1975
• Est. Priority Date: 06/15/1973
• Status: Expired due to Term

• Current Assignee: Raymond W. Mackenzie
• Original Assignee: Raymond W. Mackenzie
• Inventors: Mackenzie, Raymond W.
• Primary Examiner(s): Reynolds, Bruce A.
• Application Number:
  US05/416,327
• Time in Patent Office: 572 Days
• Field of Search: 219/10.49,10.77,10.79,10.75 321/4,18,43,44,45,45S 331/117,109,183 318/332 307/240,272
• US Class Current: 219/626
• CPC Class Codes: H05B 6/062 for cooking plates or the like

Abstract

There is disclosed cooking apparatus for heating a cooking utensil by magnetic induction from the work coil in a series resonant circuit driven by an oscillator operating at and tracking with the resonant frequency of the series resonant circuit, the apparatus being provided with structural, operating, and safety features, including (a) protection against high Q loads, (b) closed loop coil current regulation, (c) a mininum dummy load which dissipates less power with low Q load on the oscillator than with high Q load, (d) unique oscillator start circuit independent supply source, (e) Q-responsive feedback in control loop, and (f) line switch coupled to control reference selector.

Claims

1. In apparatus for heating a cooking utensil by magnetic induction and operative with DC power supply lines, said apparatus comprising the combination of:

induction coil means adapted to be coupled to cooking utensil;

series resonant circuit means including coil means;

DC power supply means including said DC power supply lines for supplying power to said induction coil means;

switching means connected to said DC power supply lines for converting DC power to AC power, and for energizing said series resonant circuit means;

means connected to said induction coil means and to said DC power supply lines for providing a signal representative of voltage excursions of said induction coil means under resonance condition of operation beyond the voltage level of said DC power supply lines;

means for controlling the voltage level of said DC power supply lines in response to said signal, wherein said signal comprises a component that is a non-linear function of the Q of said induction coil means;

said means for controlling being adapted to lower said DC voltage level in response to said signal when the Q of said induction coil means increases; and

means responsive to the Q of said induction coil means and operative beyond a predetermined high value of said Q to modify said signal for providing continued operation of the apparatus. 5. in an induction heat cooking apparatus comprising a resonant circuit having a frequency in the ultrasonic range including a heating coil and capacitor means connected in series resonance with the inductance of said heating coil, a source of DC power for supplying energy to said heating coil, switching means consisting of first and second power transistor means connected to said DC source and transformer means responsive to said resonant circuit for feeding back current to drive said first and second power transistor means reciprocally in the switching mode at the frequency of resonance of said heating coil, said apparatus further comprising phase shifting means connected between the input of said transformer means and the output thereof for synchronizing the response of said first and second power transistor means to said frequency of resonance by introducing a phase advance between operation of said resonant circuit and driving of said first and second power transistor means to compensate for inherent slowness in response of said first and second power transistor means.

2. The apparatus of claim 1 with the means responsive to the Q of said induction coil means including a dummy load, said dummy load dissipating less power for low Q values of said induction coil means.

3. The apparatus of claim 2 with said dummy load being connected to said means for providing a signal.

4. The apparatus of claim 3 with said means for providing a signal including a transformer having primary and secondary windings and first and second diodes each connected between a corresponding one of said DC power supply lines and one end of said primary winding, the polarity of each of said diodes being arranged to block conduction from the associated DC power supply line to said primary winding, and to be conductive in relation to said voltage excursions, said secondary winding being connected to said means for controlling;

said dummy load consisting in a resistor inserted in series with said primary winding to dissipate power as a function of said Q.

6. The apparatus of claim 5, with said transformer means including a primary winding connected in circuit with said capacitor means and said heating coil, secondary winding means operative with said primary winding and adapted to drive said first and second power transistor means alternately for each alternation of said heating coil in response to said resonant circuit, and wherein said phase shifting means includes an inductance shunted across said primary winding.

7. The apparatus of claim 5 with said transformer means including a primary winding connected in circuit with said capacitor means and said heating coil, secondary winding means operative with said primary winding and adapted to drive said first and second power transistor means alternately for each alternation of said heating coil in response to said resonant circuit, and wherein said phase shifting means includes an inductance provided by the inductive characteristics of said primary winding and said secondary winding means.