A switching power converter circuit includes a power switch for operating an inductor to convert the input voltage to the output voltage to drive a load circuit; and a control circuit, including: a pulse width modulation circuit comparing an output related signal with a ramp signal to generate a pulse width modulation signal for controlling the power switch, wherein the output related signal is related to the output voltage; an error amplifier circuit generating an error amplified signal according to a difference between the output related signal and a reference signal; and a ramp signal generation circuit generating the ramp signal, wherein an amplitude of the ramp signal is determined according to the input voltage and the output voltage; and/or the slope of the ramp signal is determined according to the error amplified signal.