Method and circuit for switching source modulation frequency

A circuit for switching a source of a modulation frequency used in a direct current to direct current (DC to DC) converter, wherein said DC to DC converter generates an output voltage to drive a system and said modulation frequency is used for modulating a pulse width modulation (PWM) circuit in said DC to DC converter, comprising:

• an oscillator for providing said modulation frequency;
• a clock generator providing said modulation frequency;
• and
• a first multiplexer electrically connected between said oscillator and said clock generator for allowing said oscillator to provide said modulation frequency before said output voltage is used to drive said system and said source of said modulation frequency is switched from said oscillator to said system clock by said first multiplexer according to a system stabilized signal generated from said system after said system is driven by said output voltage.