High-efficiency tuned inverter circuit

Abstract

A simple single-ended inverter circuit efficiently converts a DC input voltage to an AC output voltage. The circuit, which functions as a self-contained Class C oscillator, comprises an energy-storing inductor and an energy-storing tank capacitor in circuit with a saturable core feedback transformer operable to provide intermittent feedback current to effect periodic conduction of a single power transistor. When this transistor is non-conductive, resonant interchange of energy occurs between the inductor and tank capacitor; periodic energy transfer from the inductor both charges the capacitor and also supplies a load, and energy transfer from the capacitor to the inductor provides reset current to the saturable transformer.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In a single-ended Class C oscillator having a tuned L-C tank circuit, the improvement comprising: power transistor means having a control element; and   saturable core feedback transformer means for supplying intermittent feedback signals to the control element of the transistor means in order to effect periodic transistor means conduction.   
     
     
       2. The oscillator of claim 1 wherein the feedback transformer means comprises a current transformer. 
     
     
       3. An inverter circuit connected to a unidirectional voltage at an input and being operable to provide an alternating voltage at an output, comprising: energy-storing inductor means connected to the voltage input;   power transistor means having a control element;   saturable core feedback transformer means having a primary winding in circuit with the inductor means and the transistor means and having a secondary winding for providing intermittent feedback current to the control element of the transistor means in order to effect periodic transistor means conduction; and   energy-storing tank capacitor means in circuit with the power transistor means and the output for interchange of energy with the inductor means when the transistor means in non-conductive, discharge of the capacitor means serving to provide periodic reset current to the saturable transformer means.   
     
     
       4. The inverter circuit of claim 3 and rectifier means in series with the transistor means. 
     
     
       5. The inverter circuit of claim 3 and diode means connected to the control element of the transistor means in order to limit the maximum control element voltage to a predetermined level. 
     
     
       6. An inverter circuit connected to a DC voltage at an input and being operable to provide an AC voltage at an output connected to a load comprising: energy-storing inductor means connected to the voltage input;   power transistor means having a base, an emitter and a collector;   saturable core feedback transformer means having a primary winding in series with the inductor means and the transistor means and having a secondary winding connected in circuit with the base-emitter junction thereof in order to provide intermittent feedback current thereto in order to effect periodic transistor means conduction; and   energy-storing tank capacitor means connected in parallel with the power transistor means and the output for interchange of energy with the inductor means when the transistor means is non-conductive;   whereby periodic energy transfer from the inductor means serves to charge the capacitor means and supply energy to the load and periodic energy transfer from the capacitor means to the inductor means serves to provide reset current to the saturable transformer means.   
     
     
       7. The inverter circuit of claim 6 and rectifier means in series with the transistor means. 
     
     
       8. The inverter circuit of claim 6 and diode means connected across the base-emitter junction of the transistor means in order to limit the control element voltage to a predetermined level. 
     
     
       9. The inverter circuit of claim 6 and a capacitor for coupling the load to the inverter output. 
     
     
       10. The inverter circuit of claim 6 and clamping means in circuit with the inverter input for limiting the value of the instantaneous positive output voltage. 
     
     
       11. The inverter circuit of claim 10 wherein the clamping means comprises a transformer winding tightly coupled to the inductor means. 
     
     
       12. The inverter circuit of claim 10 wherein the clamping means comprises a clamping transformer winding tightly coupled to the inductor means and further comprises an additional winding on the feedback transformer means in circuit with the clamping transformer winding and the inverter circuit input. 
     
     
       13. An inverter circuit connected to a DC voltage input and being operable to provide a segmented sine wave voltage output, comprising: at least one power transistor means comprising a base, an emitter and a collector;   tank circuit means in circuit with the transistor means and the output and comprising an inductor and a capacitor operable to interchange energy when the transistor means is non-conductive; and   means for providing drive current to the transistor means to effect periodic conduction thereof, each conduction period being initiated when the emitter-collector voltage of the transistor means is substantially zero in magnitude.   
     
     
       14. The inverter circuit of claim 13 wherein the drive current means is operable to effect transistor means conduction once during each full cycle of the voltage output. .Iadd. 
     
     
       15.  An inverter circuit adapted to provide an AC output voltage and comprising: semiconductor switching means connected with a source of DC voltage as well as with a tank circuit means, said switching means having control terminals and output terminals, said control terminals being provided with a signal operative periodically and alternatingly to render said switching means in an ON-state and in an OFF-state, said ON-state being characterized by an ON-time during which the switching means exhibits a relatively low resistance to the flow of electric current, said OFF-state being characterized by an OFF-time during which said switching means exhibits a relatively high resistance to the flow of electric current, said tank circuit means: (i) having an inductor and a capacitor operable to resonantly interact, (ii) having a natural resonance frequency, (iii) being operative to cause the AC output voltage to be, at least in part, sinusoidal in waveshape, independent of frequency, and (iv) being connected with said output terminals; and   saturable reactor means connected in circuit between said output terminals and said control terminals and operative: (i) to provide said signal, and (ii) by way of its saturation characteristics, to determine the duration of said ON-time. .Iaddend.