A modified class G amplifier for active magnetic bearings

To improve the overall efficiency of a transconductance amplifier loaded by the high inductance and low resistance typical of the magnetic bearing coils, a modified class G amplifier has been developed. A third transistor has been connected from ground to output, in order to obtain high efficiency coil discharge. A simple theoretical characterization has been used to provide some diagrams to optimize the power efficiency as a function of a nonconstant load such as that due to a rotor unbalance. Experimentalal results are reported showing a good agreement with the developed theory.