Patent ID: 7564903

Claim:
A sampling circuit for receiving a reflected voltage signal from an auxiliary winding of a transformer; said sampling circuit comprising: a time-delay unit, coupled to receive a switching signal for generating a delay-time signal as said switching signal is disabled, wherein said switching signal is used to switch said transformer via a switch; a signal-generating unit, coupled to receive said delay-time signal, said switching signal, and said reflected voltage signal for generating a discharge-time signal and sampling signals; wherein said sampling signals are sequentially generated; a sampling unit, coupled to receive said sampling signals for sampling said reflected voltage signal to hold capacitors respectively; wherein said hold capacitors generate hold voltages; a buffer circuit, coupled to said hold capacitors for obtaining a higher voltage of hold voltages to be a buffer signal; and a comparison circuit, coupled to said buffer circuit to compare said buffer signal with a level-shift signal for generating a stop signal; wherein said level-shift signal is resulted from by adding a threshold signal with said reflected voltage signal; said stop signal is enabled once said level-shift signal is lower than said buffer signal; wherein said discharge-time signal is enabled as said switching signal is disabled; said stop signal disabling said discharge-time signal; a pulse width of said discharge-time signal being correlated to a discharge time of said transformer; said sampling signals starting to generate after an end of said time-delay signal; said stop signal terminating said sampling signals; a feedback signal being generated in accordance with said buffer signal after said stop signal being generated; wherein said feedback signal is corrected to an output voltage of said transformer.