It is well known that power density of piezoelectric transformers is limited by mechanical stress. The power density of
piezoelectric transformers calculated by the stress boundary can reach 330 W/cm3. However, no piezoelectric
transformer has ever reached such a high power density in practice. The power density of the piezoelectric transformer is
limited to 33 W/cm3 typically. This fact implies that there is another physical limitation in piezoelectric transformer. In
fact, it is also known that piezoelectric material is constrained by vibration velocity. Once the vibration velocity is too
large, the piezoelectric transformer generates heat until it cracks. To explain the instability of piezoelectric transformer,
we will first model the relationship between vibration velocity and resulting heat by a physical feedback loop. It will be
shown that the vibration velocity as well as the heat generation determines the loop gain. A large vibration velocity and
heat may cause the feedback loop to enter into an unstable state. Therefore, to enhance the power capacity of
piezoelectric transformer, the heat needs to be dissipated. In this paper, we used commercial thermal pads on the surface
of the piezoelectric transformer to dissipate the heat. The mechanical current of piezoelectric transformers can move
from 0.382A/2W to 0.972A/9W at a temperature of 55°C experimentally. It implies that the power capacity possibly
increases 3 times in the piezoelectric material. Moreover, piezoelectric transformers that are well suited in applications of
high voltage/low current becomes also well suited for low voltage/high current power supplies that are widely spread.
This technique not only increases the power capacity of the piezoelectric transformer but also allows it to be used in
enlarged practical applications. In this paper, the theoretical modeling will be detailed and verified by experiments.
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