Considerations on Step-Down Piezoelectric Transformers

Masatosi Imori, Yoshinobu Unno1, and Yasumasa Kanada2

ICEPP, University of Tokyo7-3-1 Hongo, Bunkyo-ku Tokyo 113-0033, Japan

1KEK1-1 Oho, Tsukuba, Ibaraki 305-0801 Japan

2Information Technology Center, University of Tokyo2-11-16 Yayoi, Bunkyo-ku Tokyo 113-8658, Japan

Equivalence Circuit of Step-Down PT

PT Newly Provided by Tokin

R concerns input voltage

• Let input voltage be 120 V and the current through R be 100 mA,

• Then power to the transformer is 12 W and the power dissipated by R is less than 100 mW .

• Power loss at R is less than 1 %.

• R becomes smaller for the lower input voltage.

Dependence of Impedance on Frequency

Resistance of Electrode is Rd

• Impedance becomes minimum around a serial resonance

• Impedance becomes maximum around a parallel resonance

• Influence of Rd on resonance is different between the serial and the parallel resonances

• The resistance of the electrode is identified with Rd by the experiment where the influence is measured by changing number of the layers

Optimal Resistance

• Cd2 is the capacitance in the equivalence circuit. Let f be the carrier frequency, then optimal resistance Rop is defined by

• The load equal to the optimal resistance attains the maximum efficiency

opd2

1R where 2 f

C

Capacitance Cd2 to match load

EQ L2

8R R

Let output capacity be 2 V 4A, then RL= 0.5Ω, and REQ= 0.4Ω.

Let f be 100 kHz then Capacitance Cd2 to match load is about 4 μF

Stacked Ceramic Capacitor

Recently

Number of Layers 1000

Thickness of Layer ~ 1μ

Capacitance up to 100 μF

Stacked Piezoelectric Actuator

Layer Made of Piezoelectric Material

Sheet of Electrode

Polarization

Step-Down Piezoelectric Transformer

PT of Large Output Current

• Tokin Corporation is a branch of NEC Corporation. Tokin people talked to NEC people about the development of such the low voltage step-down PT.

• The decision about the development will be based on prospects of such the transformers, where the demand for the transformers in a high energy physics is not considered so much as we expect.

Dedicated Power Supply

• Low voltage step-down PT’s, which can be manufactured without further development or studies, are characterized by the optimal resistance around or larger than 10 Ω.

• An efficient power supply using the PT can be implemented for the load larger than 10 Ω.

• It is better to prepare a dedicated power supply to each channel.

Ground Isolation at Individual Channels

Due to the ground isolation at the individual channels, the dedicated power supplies will contribute to reducing the noises caused by ground loops.

Isolation Coupler Using PT

The PT with a simple driver and a receiver could work as an isolation coupler

Example of Ceramic Gyro to See Possible Size of Isolation Coupler

Acknowledgement

We would like to thank Tokin Corporation