A ripple voltage suppression apparatus includes a DC/DC converter and a control circuit. The DC/DC converter has a power electronic switch. The control circuit has a voltage detector detecting a DC output voltage of the DC/DC converter, a ripple voltage suppression circuit receiving the detected DC output voltage to generate an AC control signal for controlling an AC component of a duty ratio of the power electronic switch, an output voltage regulation circuit receiving the detected DC output voltage to generate a DC control signal for controlling an DC component of a duty ratio, an adder adding the AC and DC control signals to form a combined control signal, and a PWM circuit converting the combined control signal into a PWM signal to control the power electronic switch. Only the DC output voltage of the DC/DC converter has to be detected for the control circuit.