A power-efficient transconductance amplifier for wide-band high current calibrations

In the paper a transconductance amplifier capable of accurate amplifying currents from 1 mA up to 60 A rms within the frequency range from 40 Hz to 70 Hz with or without the presence of higher harmonics components is presented. Its sophisticated topology consists of a supreme control loop and an inner hybrid power amplifier with an output transformer. The hybrid power amplifier, which acts as a self-oscillating system, is composed of a superior three-stage class AB linear power amplifier and an inverter. The latter provides a full load current while the former filters the waveform ripple. In this way a power efficient system is obtained whose efficiency at a full output power is some 90%.