Actuating circuit of piezoelectric transformer and actuating method thereof

• US 5,866,969 A
• Filed: 10/23/1997
• Issued: 02/02/1999
• Est. Priority Date: 10/24/1996
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Honbo, Nobuaki, Shimada, Yasuhei
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US08/956,795
• Time in Patent Office: 467 Days
• Field of Search: 363/131, 363/133, 363/134, 310/314, 310/316, 310/318, 310/319
• US Class Current: 310/318
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: H10N 30/804 for piezoelectric transformers conversion of DC or AC power H02M; for operating discharge lamps H05B41/282

Abstract

An actuating circuit of a piezoelectric transformer which is small in thickness and size and has a wide input voltage range is developed. In the actuating circuit of the piezoelectric transformer, when a sine wave outputted from a AGC circuit is input to a delta-sigma modulator, the sine wave switches output driver and switches a second output driver through an invertor with a 1-bit quantized bit signal so as to generate a pulse signal having an amplitude of power supply voltage Vdd from the GND potential. Actuating waves output from the output drivers and are applied to 1 piezoelectric transformer extracting resonance frequency of a piezoelectric transformer through a filtering effect provided with an input capacitance of the piezoelectric transformer and coil converting the 1-bit quantized bit signal into a sine wave. Consequently, since the piezoelectric transformer can be operated with the sine wave, the piezoelectric transformer can be actuated efficiently.

Claims

1. An actuating method of a piezoelectric transformer which outputs a voltage from secondary terminals, actuated by a voltage input to primary terminals, comprising the steps of:

generating an analog high frequency voltage;

converting said high frequency voltage to a digital signal;

converting said digital signal into a first high frequency voltage having a predetermined amplitude whose frequency is proximal to the resonance frequency of the piezoelectric transformer and an inverted high frequency voltage which has opposite phase to the first high frequency voltage having the same predetermined amplitude;

applying the first high frequency voltage to a primary electrode of the piezoelectric transformer;

extracting the output high frequency current from the secondary electrode of the piezoelectric transformer;

applying the first high frequency voltage to a primary electrode of the piezoelectric transformer;

extracting the output high frequency current from the secondary electrode of the piezoelectric transformer;

converting the extracted high frequency current into a high frequency voltage; and

feeding back the high frequency voltage to the A/D converting step.

2. The actuating method of a piezoelectric transformer claimed in claim 1, wherein said digital signal is a 1-bit quantized bit signal obtained by oversampling the high frequency voltage.

3. The actuating method of a piezoelectric transformer as claimed in claim 2, wherein a voltage amplitude of the 1-bit quantized bit signal is used as a voltage of a dc power supply.

4. The actuating method of a piezoelectric transformer as claimed in claim 3, wherein, even if the dc voltage value varies, a voltage component of a first frequency included in the 1-bit quantized bit signal input to the primary terminals is fixed.

5. The actuating method of a piezoelectric transformer as claimed in claim 4, wherein the actuating signal to be inputted to the primary terminals is inputted through a band-pass filter which passes the first frequency.

6. The actuating method of a piezoelectric transformer as claimed in claim 4, wherein the actuating signal to be input to the primary terminals is input through a low-pass filter which passes the first frequency.

7. An actuating circuit of a piezoelectric transformer which outputs a voltage from a secondary terminal, actuated by a voltage input to primary terminals comprising:

a frequency sweeping oscillating circuit for generating a pulse signal of a second frequency higher than twice a first frequency which is the resonance frequency of the piezoelectric transformer;

a frequency divider circuit for dividing the pulse signal into the first frequency of said piezoelectric transformer;

a first band-pass filter for passing a sine wave of the first frequency of an output of said frequency divider circuit;

a delta-sigma modulator for converting the sine wave into a 1-bit quantized bit signal by oversampling the sine wave with the second frequency;

a first output driver for converting the output of the delta-sigma modulator to a first actuating high frequency voltage having amplitude of predetermined dc power to input into a first primary electrode of the piezoelectric transformer; and

a second output driver for converting the output of the delta-sigma modulator to an opposite phase actuating high frequency voltage having the same amplitude but opposite phase to the first actuating high frequency voltage to input a second primary electrode of the piezoelectric transformer.

8. The actuating circuit of a piezoelectric transformer as claimed in claim 7, further including a second band-pass filter for passing the first frequency after having been converted into the high frequency voltage having the amplitude of the dc power supply.

9. The actuating circuit of a piezoelectric transformer as claimed in claim 7, further including a low-pass filter for passing the first frequency after having been converted into the first actuating high frequency voltage.

10. The actuating circuit of a piezoelectric transformer as claimed in claim 7, further including an actuating voltage control circuit for controlling a voltage component of the first frequency of the actuating voltage to a fixed level.

11. The actuating circuit of a piezoelectric transformer as claimed in claim 8, further including an actuating voltage control circuit for controlling to fix a voltage component of the first frequency of the actuating voltage.

12. The actuating circuit of a piezoelectric transformer as claimed in claim 9, further including an actuating voltage control circuit for controlling to fix a voltage component of the first frequency.