High frequency AC/AC converter with PF correction

A high-frequency electronic apparatus comprising:

• first and second input terminals for supplying a low frequency pulsating DC voltage to the high-frequency apparatus,
• first and second semiconductor controlled switching devices,
• an inductor,
• a rectifier element,
• an energy storage capacitor,
• means for coupling said first and second semiconductor controlled switching devices, said inductor, said rectifier element and said energy storage capacitor in circuit to said input terminals so as to form a high-frequency DC/AC inverter circuit, and
• a control circuit having output means coupled to control electrodes of the first and second semiconductor controlled switching devices so as to alternately trigger said first and second semiconductor controlled switching devices on and off at a high-frequency, said control circuit including means for triggering said first and second semiconductor controlled switching devices to produce a duty cycle that repetitively sweeps between a maximum duty cycle value and a minimum duty cycle value at a low frequency.

A power supply for deriving a high frequency AC voltage for a load from a DC supply voltage comprising:

• first and second input terminals for connection to a source of pulsating DC supply voltage,
• means coupling said input terminals to a circuit comprising an inductor, a rectifier element, a first switching transistor, a storage capacitor and a first diode connected together so that when the first switching transistor is turned on current flows from the input terminals through the first switching transistor, the inductor and the rectifier element and when the first switching transistor is turned off the inductor supplies a charge current to the storage capacitor via said first diode,
• a DC/AC inverter circuit coupled to said storage capacitor and comprising a second switching transistor, said first switching transistor, and output means for connection to said load, and
• a control circuit independent of an input voltage at said input terminals and responsive at least to a voltage on the storage capacitor and having an output coupled to the control electrodes of the first and second switching transistors so as to alternately trigger said first and second switching transistors on and off at a high frequency.