Patent ID: 6987403

Claim:
A regulator circuit, comprising: an integrated circuit operational amplifier forming a driver circuit for driving a FET being external to said integrated circuit and having gate and source electrodes and having a threshold voltage, the operational amplifier including: a differential amplification stage with a first input terminal and a second input terminal, said differential amplification stage including a first current flow path, a second current flow path, and a common constant current source commonly biasing said first and second current flow paths, and said differential amplification stage receiving an operating voltage defined by a first operating potential and a second operating potential; an output load resistor connected in one of said first and second current flow paths, a current flowing through said one current flow path being controlled by a voltage between said first and second input terminals of said differential amplification stage and being substantially independent of variations of either the first operating potential or the second operating potential; a feedback circuit connecting an output of the operational amplifier to an input of the operational amplifier; said output load resistor being connected between the gate and source electrodes of the external FET to be driven; said differential amplification stage and said output load resistor forming an output stage of the operational amplifier; said output load resistor having a resistance value chosen to provide a voltage across the gate and source electrodes of the external FET near to or substantially equal to the threshold voltage of the external FET when said first and second input terminals of said differential amplification stage are set to equal potential values.