As one of high power characteristics of the piezoelectric ceramics in Pb(Mn1/3Nb2/3)O-3-PbTiO3-PbZrO3 system, the limit vibration velocity (v(max)), is defined as the vibration velocity that generate the fixed temperature rise was evaluated. From this system, a new material with a higher v(max) of 0.79 m/s which is 1.7 times larger than conventional Pb(Mn1/3Sb2/3)O-3-PbTiO3PbZrO3 system was found. By using this new material, piezoelectric transformers were made and the output electric power (P) of the transformers were measured at R-L = (omega.C-d2)(-1) [load resistance (R-L), resonant angular frequency (omega), output damping capacitance (C-d2)] and at other fixed resistances. The P of the piezoelectric transformer was measured on this condition, however, measured values of P were smaller than that of the conventional material. In order to clarify this phenomenon, an equivalent circuit including stray capacitance (C-f) of the load circuit was proposed. Simulation results by using this equivalent circuit showed that, 1. The load resistance giving the maximum output power decreases. as C-f increases. 2. The maximum output power decreases, as C-f increases. 3. When C-d2 of the piezoelectric transformer is small, the effect of C-f on the piezoelectric transformer becomes large. Therefore, a high dielectric constant (epsilon) is a required characteristic of the piezoelectric ceramic materials for use in the piezoelectric transformer; except for the usually high v(max) and high electromechanical coupling coefficient (K).
