Abstract: This invention provides a high speed controller and switching mode power supply. The high speed controller includes PWM control chip, providing high speed PWM function; output circuit: sending out PWM working signal or frequency modulation working signal. FM enhancement network: inducing feedback signals from CFB and VFB circuitry to vary the oscillation frequency of the PWM control chip, and boost up the frequency modulation function. The FM enhancement network is an unique circuitry to alter the operation characteristics of the PWM control chip. In this respect the high speed controller can be regarded as a new PWM/FM controller which can work simultaneously both in PWM mode and in FM mode in accordance to the load conditions of DC/DC converter output. The efficiency of medium to high power supply using the new design as controller IC would increase at least 5% to 8% higher than other power supplies.