A regulator circuit includes an operational amplifier, a buffer, a power transistor, a first feedback circuit, a current sensor, and second feedback circuit. The operational amplifier drives a first node with a first voltage generated by amplifying a difference between an input voltage and a feedback voltage. The buffer drives a second node with a second voltage generated by buffering the first voltage. The power transistor has a drain receiving a supply voltage, a gate connected to the second node, and a source connected to a third node. The current sensor generates a first sensing current based on the second voltage. The second feedback circuit generates a plurality of feedback currents corresponding to a ripple of the output voltage and enhances a speed at which the ripple is reduced by providing at least one of the plurality of feedback currents to the third node.