Piezoelectric transformer inverter

• US 6,013,969 A
• Filed: 03/30/1999
• Issued: 01/11/2000
• Est. Priority Date: 03/31/1998
• Status: Expired due to Fees

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Noma, Takashi, Morishima, Yasuyuki
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/281,683
• Time in Patent Office: 287 Days
• Field of Search: 310/316, 310/318, 363/16, 363/97, 363/131, 323/355
• US Class Current: 310/318
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: H05B 41/2822 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations

Abstract

A boosting drive circuit includes first and second series combinations of a coil and a transistor. The two series combination of a coil and a transistor are connected in parallel. The middle points between the coils and the transistors are connected to respective primary electrodes of a piezoelectric transformer. The transistors are alternately operated with a two-phase drive circuit. Thus, a boosting drive circuit providing for the class "semi-E" operation is formed. A driving voltage control circuit controls an average voltage applied to the input terminal of the boosting drive circuit to ensure that current on the secondary electrode side of the piezoelectric transformer is controlled at a predetermined value is provided between the input power supply and the boosting drive circuit. A driving frequency control circuit changes the driving frequency of the transistors in the boosting drive circuit in such a manner that the phase difference between an alternating voltage applied to the primary electrodes of the piezoelectric transformer and an alternating current flowing in the load is controlled at a predetermined value.

Claims

1. A piezoelectric transformer inverter comprising:

a piezoelectric transformer for converting an alternating voltage applied across its primary electrodes to an alternating current which is supplied to a load connected to its secondary electrode;

a boosting drive circuit made up of a first series combination of a first coil and a first switching element for applying a voltage to one of said primary electrodes of said piezoelectric transformer, a second series combination of a second coil with a second switching element for applying a voltage to another of said primary electrodes of said piezoelectric transformer, and a two-phase drive circuit for alternately driving said first and second switching elements;

a driving voltage control circuit connected between an input terminal of said series combinations and an input power supply and adapted to control an average voltage applied to said input terminal of said series combinations whereby current on a secondary electrode side of said piezoelectric transformer is maintained at a constant level; and

a driving frequency control circuit which controls a driving frequency at which said first and second switching elements are driven in such a manner that the phase difference between said alternating voltage applied to said primary electrodes of said piezoelectric transformer and said alternating current flowing supplied to said load is maintained at a predetermined value.

2. A piezoelectric transformer according to claim 1, wherein:

said voltage applied to one of said primary electrodes of said piezoelectric transformer is located at a point intermediate of said first coil and said first switching element; and

said voltage applied to said another of said primary electrodes of said piezoelectric transformer is located at a point intermediate of said second coil and said second switching element.

3. A piezoelectric transformer according to claim 1, wherein said coils comprise autotransformers connected between the output of said driving voltage control circuit and said primary electrodes of said piezoelectric transformer, said autotransformers having intermediate terminals which are connected to respective ones of said switching elements.

4. A piezoelectric transformer according to one of claim 1, wherein said coils comprise a boosting transformer whose secondary winding is connected across said primary electrodes of said piezoelectric transformer.

5. A piezoelectric transformer according to claim 1, wherein the phase difference between the alternating voltage applied to said primary electrodes of said piezoelectric transformer and the alternating current flowing in said load is set at 90°

±

45°

.

6. A piezoelectric transformer according to claim 1, wherein the phase difference between the alternating voltage applied to said primary electrodes of said piezoelectric transformer and the alternating current flowing in said load is set at 270°

±

45°

.

7. A piezoelectric transformer according to claim 1, wherein said driving voltage control circuit includes a third switching element for switching the supply of the input power supply voltage to said boosting drive circuit, and a circulation current retaining means, the switching frequency of said third switching element being at least double said driving frequency.

8. A piezoelectric transformer according to claim 1, wherein said driving voltage control circuit includes a third switching element for switching the supply of the input power supply voltage to said boosting drive circuit on and off, and a circuit which causes said third switching element to be turned on and off with a period which is longer than that of said driving frequency.

9. A piezoelectric transformer according to claim 1, wherein said driving voltage control circuit includes a third switching element for switching the supply of the said input power supply voltage to said boosting drive circuit on and off, a coil located between said switching element and said boosting drive circuit, and a circulation current retaining means and a smoothing capacitor connected to respective opposite sides of said coil.

10. A piezoelectric transformer inverter comprising:

a piezoelectric transformer having one of its primary electrodes grounded and adapted to convert an alternating voltage applied to the other of its primary electrodes to an alternating current which is supplied to a load connected to its secondary electrode;

a boosting drive circuit containing a series combination of a coil and a switching element for applying a voltage to said other of said primary electrodes of said piezoelectric transformer;

a driving voltage control circuit connected between an input terminal of said series combination and an input power supply and adapted to control an average voltage applied to said input terminal of said series combination so that a current on said secondary electrode side of said piezoelectric transformer is maintained at a constant level; and

a driving frequency control circuit which controls a driving frequency of said switching element in such a manner that a phase difference between said alternating voltage applied to said primary electrode of said piezoelectric transformer and said alternating current supplied to said load is maintained at a constant value.

11. A piezoelectric transformer according to claim 10, wherein said voltage applied to said other of said primary electrodes of said piezoelectric transformer is located at a point intermediate of said coil and said switching element.

12. A piezoelectric transformer according to claim 10, wherein the phase difference between the alternating voltage applied to said primary electrode of said piezoelectric transformer and said alternating current flowing in said load is set at 90°

±

45°

.

13. A piezoelectric transformer according to claim 10, wherein the phase difference between the alternating voltage applied to said primary electrode of said piezoelectric transformer and said alternating current flowing in said load is set at 270°

±

45°

.

14. A piezoelectric transformer according to claim 10, wherein said driving voltage control circuit includes a switching element for switching the supply of said input power supply voltage to said boosting drive circuit on and off, and a circulation current retaining means, the switching frequency of said switching element being at least double said driving frequency of said boosting drive circuit.

15. A piezoelectric transformer according to claim 10, wherein said driving voltage control circuit includes a switching element for switching the supply of said input power supply voltage to said boosting drive circuit on and off, and a circuit which causing said switching element to be turned on and off intermittently at a period which is longer than that of said driving frequency of said boosting drive circuit.

16. A piezoelectric transformer according to claim 10, wherein said driving frequency control circuit includes a switching element for switching the supply of said input power supply voltage to said boosting drive circuit on and off, a coil located between said switching element and said boosting drive circuit, and a circulation current retaining means and a smoothing capacitor connected to respective opposite sides of said coil.