Abstract: The described invention relates to a regulator circuit.A transistor Q1 receives at an input terminal 1 an input voltage having D.C. and A.C. components and provides a regulated D.C. output voltage at an output terminal 4. The transistor Q1 lies in the negative feedback path of an operational amplifier 6 between an output 9 and an input 5 of that amplifier. The amplifier 6 also has a reference voltage input 8. A second operational amplifier 19 also receives the reference voltage at one input 20 and at its other input 18 receives a D.C. potential representative of the D.C. input component and has an output terminal 21 coupled to the output terminal 4 in such a manner as to regulate the value of the D.C. input component by control of current drawn through the transistor Q1. A third operational amplifier 32 also receives the reference voltage at one input 33 and at a second input 31 receives the A.C. component of the input voltage and passes the A.C.