A switching regulator circuit is provided. The switching regulator circuit includes an oscillator circuit which includes a capacitor, a switch, a comparator, a variable resistor, and a modulating signal generation circuit. The capacitor is arranged to receive a first current to provide a ramp voltage. Also, the variable resistor is arranged to receive a second current to provide a reference voltage. The resistance of the variable resistor is modulated based on a modulating signal. The comparator is arranged to compare the ramp voltage with a reference voltage to provide a clock signal. Further, the switch is arranged to discharge the capacitor when the clock signal is asserted. The modulating signal generation circuit is arranged to provide the modulating waveform as a sawtooth signal, or other type of modulating waveform suitable for spread-spectrum modulation. Accordingly, the clock signal is a spread-spectrum clock signal.