Mitsuru Yamamoto

Step-Down Piezoelectric Transformer for AC-DC Converters

In this paper, a new piezoelectric transformer for AC-DC converters is presented. This piezoelectric transformer, with a multilayered construction in the thickness direction, operates in a fundamental contour-extensional vibration mode. Output impedance is designed to be low, approximately several tens of ohms. First, we simulated the design of the transformer using equivalent circuit method and finite element method (FEM) analyses. We calculated that the transformer could work with an eficiency higher than 95% and a gain of 0.4 at a resonant frequency of 140 kHz. Second, we fabricated a transformer of 14 mm length, 14 mm width and 5.8 mm thickness and examined it. It was found that the transformer exhibited a 0.4 gain and 96.3% efficiency at 135 kHz, when the temperature increase was 30°C. We applied the transformer to the fabrication of an AC-DC converter using a half-bridge zero voltage switching circuit, and examined the converter. It was found to achieve good line and load regulation, and the highest efficiency of 90% was obtained for Vin=80–120 Vac, Vout=13 Vdc, and Iout= 0.8–1.5 A.

Combined PWM and PFM control for universal line voltage of a piezoelectric transformer off-line converter

A new control method for an AC/DC converter using a piezoelectric transformer is presented. The combination of pulse width modulation and pulse frequency modulation makes it possible to control the output voltage, and its adaptability to a worldwide range of input voltage variation. The AC/DC converter implemented on a printed circuit board is experimentally evaluated, and as a result, good controllability is successfully achieved. The highest efficiency of 86% was obtained at an input voltage of AC 90-270 V, output voltage of 17 V, load current of 0.57-1.4 A, and operating at frequencies around 107 kHz.

New control method of piezoelectric transformer converter by PWM and PFM for wide range of input voltage

A new control method of a piezoelectric transformer (PT) converter by PWM and PFM is presented. The combination of an active-clamp circuit and a resonant circuit makes it possible to control the output voltage of the PT converter by PWM at a fixed switching frequency and PFM at a fixed duty ratio. The PT converter implemented on a printed circuit board was experimentally evaluated and a good controllability was successfully achieved.

Tonpilz Piezoelectric Transducer with a Bending Piezoelectric Disk on The Radiation Surface

In recent years, it has become necessary to use wide-band signals in various kinds of signal processing and communication technology fields. One of these is the field of underwater acoustic technology, and therefore wide-band transducers are needed in this field. To address this need, we developed a Tonpilz piezoelectric transducer with a bending piezoelectric disk on the radiation surface of the front mass. This transducer was designed by providing a bending piezoelectric disk on the radiation surface of the front mass of a conventional Tonpilz piezoelectric transducer to enable it to generate in two resonance modes: the longitudinal vibration resonance mode and the bending vibration resonance mode of the bending disk. Coupling these two resonance modes makes it possible to achieve low-frequency transmission, and wide-band signals can be attained by adjusting the phase in the two modes. We obtained the optimum design dimensions of the transducer through analysis using the finite element method (FEM), and constructed a prototype based on the analysis. Experiments verified that the measured results for the prototype correspond well to the simulation results and that the bandwidth can be widened without changing the external size of the conventional transducer.

Piezoelectric transformer for 30 W output AC-DC converters

A piezoelectric transformer using AC-DC converters is described that has a multilayered construction in the thickness direction and operates in contour-extensional vibration mode. The output impedance is designed to be low - approximately several tens of ohms. Testing of a fabricated transformer 14 mm long, 14 mm, wide, and 5.8 mm showed that it had a 0.4 gain, 26 W output power, and 96.3% efficiency at 135 kHz when the temperature increase was 30/spl deg/C. A fabricated AC-DC converter with this transformer had good line and load regulation and a maximum efficiency of 90.2%.