Static power switching system for induction heating

An induction heating apparatus, which comprises:

• a source of unidirectional electrical power;
• a parallel LC network including an induction heating coil;
• a switch circuit including a power switching transistor coupled between the power source and the LC network for applying electrical energy from the power source to the network upon closure to produce current flow in the induction heating coil that generates a magnetic field and creates an oscillatory voltage across the transistor;
• and
• a control circuit for applying base drive to the power transistor beginning at the point of minimum voltage across the switch circuit to put energy into the induction heating coil.

An induction heating apparatus, which comprises:

• a source of unidirectional electrical power;
• a parallel LC network including an induction heating coil;
• a switch circuit coupled between the power source and the LC network for applying electrical energy from the power source to the network upon closure to produce current flow in the induction heating coil that generates a magnetic field and creates an oscillatory voltage across the switch circuit;
• first means for detecting the falling portion of each cycle of the oscillatory voltage across the switch circuit;
• second means for detecting the point of minimum voltage across the switch circuit;
• third means connected to the first detection means and the second detection means for producing a switch circuit control signal pulse;
• and
• fourth means for monitoring the amplitude level of the oscillatory voltage across the switch circuit to establish the duration of the switch circuit control signal pulse produced by said third means.

A static power switching system which comprises:

• a source of unidirectional electrical power;
• a power switching element coupled to the power source and adapted to be gated by a control signal pulse for supplying unidirectional electrical power from the power source;
• a parallel LC network including an induction coil coupled to the power switching element for receiving unidirectional electrical power supplied from the switch and developing an oscillatory voltage thereacross, the network being adapted for power take-off through the magnetic field of the induction coil;
• and
• a switch control circuit for generating control signal pulses to repetitiously gate the power switching element and provide current drive therethrough to the parallel LC network putting energy into the induction coil, the switch control circuit generating a control signal pulse beginning at the minimum point of the oscillatory voltage developed across the switching element.

An induction heating apparatus, which comprises:

• a source of unidirectional electrical power;
• a parallel LC network including an induction heating coil;
• a switch circuit including a power switching transistor coupled between the power source and the LC network for applying electrical energy from the power source to the network upon closure to produce current flow in the induction heating coil that generates a magnetic field and creates an oscillatory voltage across the transistor;
• first means for detecting the negative-going portion of each cycle of the oscillatory voltage across the switch circuit;
• second means for detecting the point of minimum voltage across the switch circuit;
• a flip-flop device having a data input connected to the first detection means and a clock input connected to the second detection means for producing a transistor base drive signal pulse;
• and
• means for monitoring the amplitude level of the oscillatory voltage across the switch circuit to establish the duration of the transistor base drive signal pulse produced by the flip-flop device.