In this article, force and self-excitation driving methods for ultrasonic transducers are compared with each other in sense of their transient amplitude behavior in the presence of nonlinearities. An equivalent circuit transducer model is simplified to a series oscillator. The simplified model is averaged by the Van der Pol method in order to reduce the system at hand to its amplitude dynamics. The transient amplitude behavior of both driving methods is presented in an analytical form. At high vibration amplitudes, the system's natural frequency varies due to the nonlinear stiffness of the piezoelectric material and the vibration amplitude is likely to break down due to the jump phenomena. Therefore, the averaged models are extended by the nonlinear effects. From the amplitude behavior analysis of both systems, it follows that self-excitation is the preferable driving method in sense of obtaining a high operation bandwidth and a stable oscillation. © The Author(s) 2012.