Voltage detection method and circuit and associated switching power supply

摘要

In one embodiment, a method of detecting a voltage can include: (i) generating a first current according to a first voltage and a converting resistor; (ii) charging a detection capacitor by the first current during a first time period of a switching cycle of a switching power supply; (iii) charging the detection capacitor by a second current during a second time period of the switching cycle; (iv) detecting a voltage across the detection capacitor to obtain a detection voltage at an end time of the second time period, where the first time period includes a rising portion of a current flowing through the inductor, and the second time period includes a decreasing portion of the inductor current; and (v) determining a state of a present output voltage of the switching power supply according to the detection voltage.

主权项

1. A method of detecting a voltage, the method comprising:
a) generating a first current according to a first voltage and a converting resistor; b) charging a detection capacitor by said first current during a first time period of a switching cycle of a switching power supply, wherein said first voltage comprises an excitation voltage on an inductor of said switching power supply during said first time period; c) charging said detection capacitor by a second current during a second time period of said switching cycle, wherein said first and second currents flow in opposite directions; d) detecting a voltage across said detection capacitor to obtain a detection voltage at an end time of said second time period, wherein said first time period comprises a rising portion of a current flowing through said inductor, and said second time period comprises a decreasing portion of said inductor current; and e) determining a state of a present output voltage of said switching power supply according to said detection voltage, wherein said converting resistor comprises a proportion of a predetermined output voltage of said switching power supply and said second current; wherein: a) said present output voltage of said switching power supply is determined to be greater than said predetermined output voltage when said detection voltage is greater than an initial voltage of said detection capacitor at a beginning of said switching cycle; b) said present output voltage of said switching power supply is determined to be equal to said predetermined output voltage when said detection voltage is equal to said initial voltage of detection capacitor; and c) said present output voltage of said switching power supply is determined to be less than said predetermined output voltage when said detection voltage is less than said initial voltage of detection capacitor.