Switching power supply

A switching power supply adapted for use with an input DC power supply comprising:

• an input reactor;
• a transformer having at least a primary winding and a secondary winding;
• said primary winding of said transformer connected to said DC power supply through said input reactor;
• a rectifying and smoothing circuit connected to said secondary winding of said transformer;
• a main semiconductor switch connected in series with said primary winding;
• a first diode connected in opposite parallel with said main semiconductor switch;
• a series circuit including a capacitor and an auxiliary semiconductor switch, said series circuit connected in parallel with said primary winding and said main semiconductor switch;
• a second diode connected in opposite parallel with said auxiliary semiconductor switch;
• and
• a third diode interposed between said primary winding and said auxiliary semiconductor switch.

A switching power supply comprising:

• a rectifier effective to convert an AC voltage to a DC voltage;
• a transformer having at least a primary winding, a secondary winding and a tertiary winding;
• a semiconductor switch connected in series with said primary winding;
• said primary winding connected to said rectifier through said tertiary winding;
• an electrolytic capacitor connected in parallel with said semiconductor switch and said primary winding;
• a smoothing and rectifying circuit connected to said secondary winding;
• said smoothing and rectifying circuit being effective to deliver DC electric power to a load;
• said semiconductor switch being effective to regulate said DC electric power when said semiconductor switch is switched ON and OFF;
• and
• a high-speed reverse-recovery diode interposed between said tertiary winding and a connection point of said electrolytic capacitor and said primary winding.

A switching power supply comprising:

• a rectifier effective to convert an AC voltage to a DC voltage;
• a transformer having at least a primary winding, a secondary winding, a tertiary winding and a quaternary winding;
• a first semiconductor switch connected in series with said primary winding;
• said rectifier being connected in parallel with said first semiconductor switch and said primary winding;
• a smoothing and rectifying circuit connected to said secondary winding;
• said smoothing and rectifying circuit being effective to deliver DC electric power to a load;
• said semiconductor switch being effective to regulate said DC electric power when said semiconductor switch is switched ON and OFF;
• a first series circuit including said quaternary winding, a diode and an electrolytic capacitor;
• said first series circuit connected in parallel with said first semiconductor switch and said primary winding;
• a second semiconductor switch connected in series with said tertiary winding;
• and
• said second semiconductor switch and said tertiary winding connected in parallel with said electrolytic capacitor.

A switching power supply adapted for use with an input DC power supply comprising:

• a transformer having at least a primary winding and a secondary winding;
• a main semiconductor switch connected in series with said primary winding;
• said primary winding connected to said DC power supply;
• a smoothing and rectifying circuit connected to said secondary winding;
• said smoothing and rectifying circuit being effective to deliver DC electric power to a load;
• a series circuit including a resonance capacitor, a resonance reactor and an auxiliary semiconductor switch;
• said series circuit connected in parallel with said main semiconductor switch;
• said main semiconductor switch being switched OFF when said switching power supply drives a light load substantially smaller than a rated load;
• and
• said auxiliary semiconductor switch being effective to regulate said light load when said auxiliary semiconductor switch is switched ON and OFF.

A switching power supply adapted for use with an input DC power supply comprising:

• a main power supply effective to supply electric power to a rated load;
• said main power supply including a first transformer;
• said first transformer having at least a first primary winding;
• said at least first primary winding connected to said DC power supply;
• a first semiconductor switch connected to said at least first primary winding;
• a first integrated circuit connected to said first semiconductor switch effective to drive and control said first semiconductor switch;
• a sub power supply effective to supply electric power to a load substantially smaller than said rated load;
• said sub power supply including a second transformer;
• said second transformer having at least a second primary winding;
• said at least second primary winding connected to said DC power supply;
• a second semiconductor switch connected in series with said at least second primary winding;
• and
• a second integrated circuit connected to said second semiconductor switch effective to drive and control said second semiconductor switch.

A DC-DC power supply comprising:

• a transformer having at least one primary connected across a source of DC;
• a first switch in series with said at least one primary;
• a snubber capacitor in parallel with said first switch;
• said snubber capacitor and a self-inductance of said transformer having a predetermined resonance relationship;
• a second switch;
• a reactive circuit in series with said second switch;
• a series combination of said second switch and said reactive circuit being connected in parallel with said first switch;
• and
• said reactive circuit having a series resonant frequency effective, when said second switch is closed, to discharge charge in said snubber capacitor in a time short enough to reduce at least one of a current and a voltage substantially to zero before said first switch must be closed, whereby said first switch closes at substantially zero current.