Resonant-flyback power supply with filament winding for magnetron and the like loads

In a power supply of the resonant-flyback type for energizing a self-rectifying load, through which a current flows only when a voltage of predetermined polarity and magnitude is exceeded thereacross, from a secondary winding of a transformer having a primary winding having a mutual inductance to said secondary winding, said primary winding being connected between an operating potential source and a controlled-current path of a switching device, said switching device also having an input terminal for receiving a signal from circuit means for controlling said controlled-current path between conduction of current in a first portion of each of a plurality of operating cycles and essentially non-conduction of current during a remaining portion of each of said operating cycles;

• and an electrical capacitance effectively connected in parallel across the mutual transformer inductance to resonate said mutual inductance at a frequency greater than the frequency at which said circuit means switches said device;
• and wherein the load requires a separate source of additional energy even when said current does not flow through said load, the improvement comprising:
• an additional secondary winding upon said transformer for supplying said additional energy to said load whenever said power supply is in operation;
• means for sensing the magnitude of current flowing through said controlled-current path of said switching device;
• over-voltage sensing means including a third transformer secondary winding having a voltage thereacross substantially proportional to the instantaneous voltage appearing across said transformer primary winding;
• said circuit means including:
• a flip-flop logic element having a set S input, a reset R input and an output providing a signal having first and second levels respectively responsive to the presence of an enabling signal at said set S and said reset R inputs respectively;
• first means receiving the flip-flop logic element output signal for respectively enabling and disabling current flow through said switching device controlled-current path responsive to the presence respectively of said first and second output levels;
• astable multivibrator means for periodically providing said enabling level signal to said set S input of said flip-flop logic element;
• second means for receiving a load control input signal having first and second levels respectively determining if current can or cannot flow through said controlled-current path;
• third means coupled to said second means for preventing application of said enabling level signal to said set S input whenever said load control input signal is at said second level;
• fourth means for providing an enabling level signal to said reset R input whenever the flow of current in said controlled-current path exceeds a predetermined magnitude, to terminate the flow of current in said controlled-current path whenever said current sensing means senses a current exceeding said predetermined magnitude;
• and
• fifth means for reducing said predetermined magnitude of said fourth means whenever the voltage across said transformer third secondary winding exceeds a predetermined value.