Efficiency-improved high-voltage analog power amplifier for driving piezoelectric actuators

A novel high-voltage analog power amplifier derived from a well-known complementary class B amplifier is presented in this paper. The amplifier offers improved efficiency when driving capacitive loads such as piezoelectric multilayer actuators, while maintaining a high level of signal quality, peak power and low electromagnetic radiation. The main drawback of a class B amplifier in comparison to other power amplifiers is low efficiency, resulting in extensive power-loss in the two complementary transistors of the amplifier stage. Power-loss can be reduced by minimizing the voltage drop across the collector-emitter path of the transistors when a high collector current occurs. The proposed circuit uses an additional capacitor to recover up to one half of the charge stored in the actuator whenever the actuator is being discharged. The capacitor offers an additional power supply rail next to the positive and negative supply voltage of the amplifier stage. Switching the power supply net of the power transistors between the different supply rails, in order to reduce the voltage drop across the transistors, minimizes power-loss. The development of the amplifier was triggered by the introduction of a new piezoelectric motor and the requirements concerning signal quality and electromagnetic radiation. Therefore, in this paper, the circuit is analyzed using application-specific sinusoidal control signals which are used to drive the motor. Following the analytical investigation of the circuit, the amplifier is tested in an experiment measuring power consumption with a pure reactive load, and the level of distortion caused by the amplifier. In the experiment, a power-loss reduction of 47% was achieved in comparison with a class B stage. The amplifier processed a peak power of 160 W. The proposed amplifier showed total harmonic distortion of THD = 0.60% maximum. Distortions of a pure class B amplifier in the same setup were measured at THD = 0.25%