LOW SIGNAL ANALYSIS OF PIEZOELECTRIC TRANSFORMERS

The transmission matrix, that depends on frequency, has been proved to be useful to characterize piezoelectric transformers behaviour at low signal. It shows at which frequency the device is able to step up the voltage and which parameters describe its behaviour, taking into account not only the voltage but also the output current. In order to compare their performances, these parameters were measured or computed for ceramic disc-shaped transformers, working in their first or higher modes, and also for plate-shaped ones. Parameters Go and 2 allow an analysis of the suitability of a device for each application, depending on input-output impedance and voltage gain required. An analysis of the validity boundaries of this model has been made, taking into account that mechanical quality Q falls down when stress and temperature increase.