Dual-input low drop out voltage regulating circuit and controlling circuit including the same

A switching power converter, configured to convert an input voltage to an output voltage which is lower than the input voltage, wherein the switching power converter comprises:

• a power input terminal configured to receive the input voltage;
• a bias terminal configured to receive the output voltage;
• and
• a dual-input voltage regulating circuit, comprising:
• a first input terminal, configured to receive the input voltage through the power input terminal;
• a second input terminal, configured to receive the output voltage through the bias terminal;
• and
• an output terminal, configured to provide a regulated output voltage;
• wherein the dual-input voltage regulating circuit is configured to draw power from at least one of the input voltage and the output voltage;
• and
• wherein when the regulated output voltage is maintained at a first voltage value, the dual-input voltage regulating circuit draws power from both the input voltage and the output voltage;
• and when the regulated output voltage is maintained at a second voltage value, the dual-input voltage regulating circuit draws power from the input voltage and does not draw power from the output voltage.

A voltage regulating method, comprising:

• controlling, by a first sub voltage regulating circuit, a first current provided from a first input terminal to an output terminal,
• controlling, by a second sub voltage regulating circuit, a second current provided from a second input terminal to the output terminal;
• receiving, by the first sub voltage regulating circuit, a feedback voltage that is indicative of an output voltage on the output terminal and a first reference voltage;
• receiving, by the second sub voltage regulating circuit, the feedback voltage and a second reference voltage, wherein the first reference voltage is lower than the second reference voltage;
• determining, by the first sub voltage regulating circuit, whether the feedback voltage becomes lower than or equal to the first reference voltage by comparing the feedback voltage to the first reference voltage;
• and
• determining, by the second sub voltage regulating circuit, whether the feedback voltage becomes lower than the second reference voltage by comparing the feedback voltage to the second reference voltage;
• wherein when the feedback voltage becomes lower than the second reference voltage but higher than the first reference voltage, the second sub voltage regulating circuit provides the second current from the second input terminal to the output terminal and the first sub voltage regulating circuit does not provide the first current from the first input terminal to the output terminal, and when the feedback voltage becomes lower than or equal to the first reference voltage, the first sub voltage regulating circuit provides the first current from the first input terminal to the output terminal and the second sub voltage regulating circuit provides the second current from the second input terminal to the output terminal.