Controllable-duty-cycle power supply for microwave oven magnetron and the like

Claim 1

A controllable-duty-cycle power supply for connection between a sinusoidal power source and a load consuming appreciable amounts of power only if a minimum voltage applied thereto is exceeded, comprising: a power transformer having a primary winding connected to said source and a high-voltage secondary winding having first and second ends; a capacitance element connected in electrical series connection with said secondary winding first end and said load; means connected to the junction between said capacitance element and said load for allowing unidirectional flow of current in only one of the directions toward and from said junction; a non-linear resistance element in electrical series connection with said unidirectional means across said load; said non-linear resistance element providing a relatively high resistance for all voltages thereacross less than a predetermined breakdown voltage which is less than said minimum voltage and sufficiently large to prevent application of said minimum voltage to said load, and providing a relatively low resistance when the voltage thereacross exceeds said breakdown voltage; a gateable element in electrical parallel connection with said non-linear resistance element, said gateable element having a breakdown voltage greater than said non-linear resistance element and less than said minimum voltage and being controllable to conductive and nonconductive conditions respectively to cause the voltage across said load to be respectively at least said minimum voltage and less than said minimum voltage and said load to be respectively power-consuming and non-power-consuming responsive respectively to first and second amplitudes of a controlling signal; and means for providing said controlling signal of said first amplitude at a frequency at least two orders of magnitude higher than the frequency, at all phase angle relationships of each cycle, of said sinusoidal power source and with a controllable ratio of the time interval during which said relatively high frequency control signal is present to the entire time interval between successive intervals of control signal.