 coupled to a sensing circuit, when the power switch turns ON, the sensingcircuit generates a current sense signal according to current through the primary winding, the input voltage detection circuit comprising: a rising time detection circuit, which detects a period of time during which the current sense signal rises from alow reference level to a high reference level to generate a timing signal; and a determination circuit, which generates a determination signal according to the timing signal for determining whether the input signal is a high voltage or a low voltage.  