GB2296836A

GB2296836A - A piezoelectric transformer

Info

Publication number: GB2296836A
Application number: GB9426319A
Authority: GB
Inventors: Irv Kon
Original assignee: PM Co Ltd
Current assignee: PM Co Ltd
Priority date: 1994-12-29
Filing date: 1994-12-29
Publication date: 1996-07-10
Also published as: GB9426319D0

Abstract

A voltage multiplier comprises an elongate piezo electric element 10 which is supplied with an alternating voltage at electrodes 13 across its minor axis. Electrodes 14 pick up a multiplied voltage developed across the major axis of the element 10. <IMAGE>

Description

VOLTAGE MULTIPLIER The invention relates to an electric voltage multiplier.

There is a requirement in many situations for voltage multiplier and traditionally. certainly in most power supply circuits, transformers are used. It is also possible to use electrical oscillators or similar in which capacitor switching is used to convert a low voltage to a higher voltage. Transformers tend to be bulky and can lead to significant losses due to inherent heating of the transformer core and generation of stray electromagnetic fields. With capacitor switching, significant voltage increases are normally not easy to achieve reliably.

It is an object of the invention to reduce these problems by providing a voltage multiplier which can be small in size, have minimum losses and produce a high ratio between input and output voltages.

According to the invention there is provided a low power electrical voltage multiplier comprising an elongate piezo electric element having a transverse axis and a longitudinal axis, means for applying an alternating input voltage supply across the transverse axis to cause the element to oscillate mechanically and means for simultaneously collecting an output voltage developed across the longitudinal axis by the mechanical oscillations.

The input voltage is preferably arranged to be at a frequency substantially equal to the natural mechanical resonance frequency of the piezo electric element.

The longitudinal axis is at least ten times as long as the transverse axis.

Voltage multipliers according to the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a schematic circuit diagram of one multiplier; Figure 2 shows a schematic circuit diagram of another multiplier; Figure 3 shows a schematic circuit diagram of a further multiplier; and Figure 4 shows a piezo electric element of Figure 1 in more detail.

Referring to the drawings, in Figure 1 a piezo electric element 10 has a minor transverse axis 11 and a major longitudinal axis 12.

The longitudinal axis is about ten times longer than the transverse axis. A first pair of opposing contacts 13 are mounted against outer surfaces of the element 10 to apply an alternating voltage transversely across the element 10. A second pair of contacts 14 are mounted on opposite end surfaces of the element 10 to receive an output voltage generated by the element. An oscillator 15 is connected to the contacts 13 and supplied by a d.c. voltage supply 16, conveniently a 3 volt battery.

The output of the oscillator 15 is preferably variable such that both the voltage range and the frequency of its output can be adjusted.

In use, the peak voltage applied across the contacts 13 is nominally 10 volts or somewhat less and the frequency is equal or substantially equal to the mechanical resonance frequency of the element 10, typically say 7000 cps.

In Figure 2, the contacts 13 are supplied by a square wave multivibrator comprising three invertors 20, 21 and 22. A pair of invertors 23 and 24 act together to supply square waves of opposite polarity across the contacts 13.

In Figure 3, a rectifier circuit 25 in the form of a voltage double is connected to the contacts 14. The multiplier in Figure 3 thus serves to multiply or increase a direct current input voltage for the battery 16 to provide a direct current output at across terminals 26.

In Figure 4, the element 10 has thin outside coatings 8 and 9 of silver or nickel as shown. The element 10 has a rectangular cross-section being 1.5 mm wide and 0.6 mm thick and is 19 mm long, that is the element has a width to length ratio in excess of 1 to 10. Typically. the output voltage of the multiplier developed across the contacts 14 is between 60 and 120 giving a multiplying factor of 6 to 12.

The described multipliers are very small in overall size and can provide reliable multiplying ratios of, say, up to a ten or twenty or more. The described multipliers can be typically used in a wrist watch for driving a small illuminating dial or other visual indicating elements. Where maintenance of the actual output voltage level is critical, the described multipliers can be provided with closed loop control circuits and/or phase lock loops, known per se, to stabilise the voltage and/or frequency of the multiplier outputs.

Claims

1. A low power electrical voltage multiplier comprising an elongate piezo electric element having a transverse axis and a longitudinal axis, means for applying an alternating input voltage supply across the transverse axis to cause the element to oscillate mechanically and means for simultaneously collecting an output voltage developed across the longitudinal axis by the mechanical oscillations.

2. A multiplier according to claim 1, in which the input voltage is arranged to be at a frequency substantially equal to the natural mechanical resonance frequency of the piezo electric element.

3. A multiplier according to claim 1 or 2, in which the longitudinal axis is at least ten times as long as the transverse axis.

4. Voltage multipliers substantially as herein described with reference to the accompanying drawings.