EXTENDED OUTPUT POWER CONTROL OF INVERTER

• US 3,842,338 A
• Filed: 04/20/1973
• Issued: 10/15/1974
• Est. Priority Date: 12/27/1971
• Status: Expired due to Term

• Current Assignee: John P. Walden
• Original Assignee: John P. Walden
• Inventors: Walden, John P.
• Primary Examiner(s): Shoop, Jr., William H.
• Application Number:
  US05/352,880
• Time in Patent Office: 543 Days
• Field of Search: 307/240,252J,252M 219/10.49,10.77 321/43,44,45R,45C,45ER
• US Class Current: 363/124
• CPC Class Codes: H02M 7/523 with LC-resonance circuit in the main circuit
• CPC Class Codes: H05B 6/062 for cooking plates or the like
• CPC Class Codes: H05B 6/1281 with flat coils

Abstract

A single-thyristor series resonant inverter used to drive an induction heating coil is operated at a variable frequency over a limited ultrasonic range in known manner to obtain high output power control. The low output power range is extended by using the secondary winding of a reset transformer and a series connected auxiliary solid state device to limit the amount of recharge energy supplied to the commutating capacitor by the primary winding during non-oscillating intervals of the inverter.

Claims

1. A wide range output power inverter connected between a pair of unidirectional voltage input terminals comprising a series resonant circuit comprising a commutating capacitor and a pair of alternately conducting main power devices which are operated at a variable frequency within a selected frequency range to generate a train of oscillatory pulses with a variable delay interval therebetween, to thereby achieve high output power control, a reset transformer having inductively coupled primary and secondary windings, said primary winding being operatively connected to said series resonant circuit and input terminals to store energy during conducting intervals of said main power devices and discharge energy during the delay intervals between consecutive oscillatory pulses that serves to recharge said commutating capacitor and sustain circuit oscillation, and low output power control means for obtaining a plurality of low output power levels while operating within said selected frequency range by controlling the amount of energy discharged by said primary winding and thereby variably recharging said commutating capacitor, said low output power control means comprising a circuit including said reset transformer secondary winding and a series connected auxiliary thyristor device that is selectively rendered conductive at a variable time during said delay intervals.

2. A circuit according to claim 1 wherein said low output power control means is connected between said unidirectional voltage input terminals to return energy to the supply.

3. A wide range output power inverter connected between a pair of unidirectional voltage input terminals comprising a series resonant circuit comprising a commutating capacitor and a pair of alternately conducting main power devices which are operated at a variable frequency within a selected frequency range to generate a train of oscillatory pulses with a variable delay interval therebetween, to thereby achieve high output power control, a reset transformer having inductively coupled primary and secondary windings, said primary winding being operatively connected to said series resonant circuit and input terminals to store energy during conducting intervals of said main power devices and discharge enerGy during the delay intervals between consecutive oscillatory pulses that serves to recharge said commutating capacitor and sustain circuit oscillation, and low output power control means for obtaining a plurality of low output power levels while operating within said selected frequency range by controlling the amount of energy discharged by said primary winding and thereby variably recharging said commutating capacitor, said low output power control means comprising a circuit including said reset transformer secondary winding, a series connectable auxiliary diode, and a switch for connecting said auxiliary diode to a selected tap on said secondary winding, said secondary winding having a plurality of taps.

4. A circuit according to claim 3 wherein said low output power control means is connected between said unidirectional voltage input terminals to return energy to the supply.