Method and apparatus for multiple output regulation in a step-down switching regulator

In a switching regulator having a magnetic storage device including a first output and a second output, a first switching device coupled to a primary winding of said magnetic storage device, a second switch device coupled to said primary winding of said magnetic storage device, a control circuitry coupled to said first output, to said second output, to said first switching device and to said second switching device, a current sensing device measuring a current through said primary winding of said magnetic storage device, said current sensing device coupled to said primary winding and to said control circuitry, a method of regulating output voltages of said switching regulator comprising the steps of:

• detecting a voltage of said first output being in regulation;
• detecting a voltage of said second output being out of regulation by comparing the voltage of said second output to a first reference voltage;
• turning on said first switching device;
• turning off said first switching device;
• turning on said second switching device;
• turning off said second switching device when one of a first event, a second event, a third event and a fourth event occurs;
• wherein said first event is said current becoming substantially zero;
• wherein said second event is said current exceeding a pre-determined limit value;
• wherein said third event is an end of a clock cycle;
• wherein said fourth event is an end of a pre-determined time period.

In a switching regulator having a magnetic storage device including a first output and a second output, a first switching device coupled to a primary winding of said magnetic storage device, a second switching device coupled to said primary winding of said magnetic storage device, a control circuitry coupled to said first output, to said second output, to said first switching device and to said second switching device, a current sensing device for sensing a current through said primary winding of said magnetic storage device, said current sensing device coupled to said primary winding and to said control circuitry, a method of regulating output voltages of said switching regulator comprising the steps of:

• detecting a voltage of said first output being in regulation;
• detecting a voltage of said second output being out of regulation by comparing the voltage of said second output to a first reference voltage;
• turning on said second switching device;
• turning off said second switching device when one of a first event, a second event, a third event and a fourth event occurs;
• wherein said first event is said current becoming substantially zero;
• wherein said second event is said current exceeding a pre-determined limit value;
• wherein said third event is an end of a clock cycle;
• wherein said fourth event is an end of a pre-determined time period.

A method of regulating a switching regulator comprising the steps of:

• changing a current in a first direction through a primary winding of a magnetic storage device until a first output coupled to said primary winding is in regulation;
• changing said current in a second direction through said primary winding of said magnetic storage device to supply power to a second output coupled to said magnetic storage device until one of a first event, a second event, a third event and a fourth event occurs;
• wherein said first event is said current becoming substantially zero;
• wherein said second event is said current exceeding a pre-determined limit value;
• wherein said third event is an end of a clock cycle;
• wherein said fourth event is an end of a pre-determined time period.

A switching regulator having a transformer with a primary and at least one secondary winding and having a first regulator output coupled to one end of the primary winding and a second regulator output coupled to the secondary winding, a second end of the primary winding being coupled to switches for controllably coupling the second end of the primary winding to a first supply voltage and to a second supply voltage, comprising:

• a controller for:
• controlling the switches to provide currents through the primary of the transformer to maintain the first regulator output above a first predetermined voltage;
• and,
• controlling the switches to provide time rates of change of currents through the primary of the transformer to maintain the second regulator output above a second predetermined voltage.