A pulse width modulated (PWM) controller includes a triangle wave generation circuit generating a triangle wave signal to oscillate between an upper limit voltage and a lower limit voltage. The upper limit voltage and the lower limit voltage are adjustable in response to changes in the power supply voltage. A pulse generation circuit is coupled to the triangle wave generation circuit and a minimum duty cycle setting voltage, and is configured to generate a PWM pulse signal with a minimum duty cycle determined by the relative magnitude of the triangle wave signal and the minimum duty cycle reference voltage. In an embodiment, the minimum duty cycle is increased when the power supply voltage is lower than a predetermined reference voltage.