Inverter device

An inverter device for providing a high frequency alternating voltage to a load, which comprises:

• a full-wave rectifier to provide a pulsating DC voltage from an input AC voltage;
• a smoothing circuit for receiving the rectifier output to provide a smoothed DC voltage, said smoothing circuit comprising a smoothing capacitor, choke coil means, and a first switching element which operates to flow through said choke coil means current from said full-wave rectifier so as to supply the same with electromagnetic energy when it is turned on and to release said electromagnetic energy into said smoothing capacitor when it is turned off to thereby accumulate said smoothed DC voltage across said smoothing capacitor;
• an inverter including:
• said first switching element common to said smoothing circuit;
• a second switching element connected in series with said first switching element across said smoothing capacitor;
• a load circuit connected across said second switching element, said load circuit including said load, an oscillation capacitor and inductance which define a series oscillation circuit;
• said series oscillation circuit, in response to said first and second switching elements driven to alternately turn on and off at a high frequency for switching said smoothed DC voltage accumulated at said smoothing capacitor, providing an oscillating current composed of first and second current flowing through said load in opposite directions to each other for effecting an inverter operation, said first and second currents alternating to flow for a nominal on-time duration determined by a circuit constant of said series oscillation circuit itself;
• said first switching element operating for switching said smoothed DC voltage to provide said first current through said load circuit while charging said oscillation capacitor thereby;
• said second switching element connected to said series oscillation circuit to be self-excited in response to the termination of said first current to start flowing said second current from said oscillation capacitor through said series oscillation circuit and to continue flowing said second current for a fixed time interval of said nominal on-time duration;
• said inverter device further including:
• a controller having detector means for detecting termination of said second current and exciting said first common switching element at a timing dependent upon said termination of said second current so as to start flowing said first current;
• and
• said controller having timer means for separately controlling an actual on-time duration for flowing said first current within said nominal on-time duration following the said nominal on-time duration of said second current, while leaving said second current to flow for an fixed time interval of said nominal on-time duration.

An inverter device for providing a high frequency alternating voltage to a load, which comprises:

• a full-wave rectifier to provide a pulsating DC voltage from an input AC voltage;
• a smoothing circuit for receiving the rectifier output to provide a DC voltage, said smoothing circuit comprising a smoothing capacitor, choke coil means, a bypass diode inserted in series therebetween which series combination is connected across said full-wave rectifier, and a switching element which operates to flow through said choke coil means current from said rectifier so as to supply the same with electromagnetic energy when it is turned on and to release said electromagnetic energy through said bypass diode into said smoothing capacitor when it is turned off to thereby accumulate a resulting smoothed DC voltage across said smoothing capacitor;
• an inverter including:
• the switching element which is common to said smoothing circuit for switching said DC voltage accumulated at said smoothing capacitor at a high frequency;
• a parallel oscillation circuit connected across said load, said parallel oscillation circuit including an oscillation capacitor and an inductance, said parallel oscillation circuit connected in series with said switching element across said smoothing capacitor such that, upon turn-on of said switching element, said parallel oscillation circuit is supplied with energy by a current flowing from said smoothing capacitor and that, upon turn-off of said switching element, it provides an oscillating voltage to said load which oscillates at a cycle determined by a circuit constant of said oscillation circuit, said oscillating voltage composed of first and second voltages each continuing for a nominal on-time duration substantially equal to a half of said cycle;
• said oscillating voltage being cooperative with said DC voltage accumulated in said smoothing capacitor to apply a resulting oscillation AC voltage to said load for providing thereto an oscillating current;
• said inverter device further comprises:
• a blocking diode inserted in series between said switching element and said choke coil means with an anode of said blocking diode connected between a point between an anode of said bypass diode and said choke coil means;
• a controller for controlling an actual on-time duration of said switching element within said nominal on-time duration in order to regulate said voltage accumulated in said smoothing capacitor at a desired level while keeping said oscillation AC voltage acting upon said load.