A DC-DC converter includes an error amplifier that includes an operational transconductance amplifier (OTA), a compensation circuit, and a fast transient controller. The OTA includes a compensation resistor, a compensation capacitor of C.sub.z, and a Miller circuit. The equalization capacitance generated by the compensation capacitor and the Miller circuit is (1+k) C.sub.z. The Miller circuit includes three transistors operated in the triode region. The ratio of the current through the transistors is 1:mk:(1-m)k. The current through the compensation capacitor in a second mode is (1+mk) times that in a first mode. The fast transient controller switches the Miller circuit between the first and second modes according to a feedback voltage dependent on the output voltage of the DC-DC converter.