1. A controller for a switching regulator of a LED lighting system, comprising:a current monitor, used to sense a LED current passing through a current sensing resistor of the switching regulator, and to generate a sensing current; and
a voltage divider, connected to the current monitor, used to receive the sensing current to generate a first through third divided voltages, wherein the first divided voltage is larger than the second divided voltage, and the second divided voltage is larger than the third divided voltage;
an integration circuit, connected to the voltage divider, used to compare the second divided voltage with a reference voltage, and to generate an integration voltage across a RC circuit thereof accordingly; and
a comparator circuit, connected to the integration circuit and the voltage divider, used to compare the integration voltage with the first divided voltage and the third divided voltage, and to generate a driving signal.