JP2002359968A - Method of driving piezoelectric transformer, and piezoelectric transformer type inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem when a quasi-sinusoidal wave is generated by utilizing the resonance caused by the capacity component of a piezoelectric transformer and an inductance component of the preceding stage, that the deviation of a resonance frequency becomes larger due to the temperature characteristic and tolerance of an LC. SOLUTION: A variable voltage device 1 outputs a set voltage V1 to an integrator 2, so that the secondary-side current Is of the piezoelectric transformer 6 becomes a set value. The integrator 2 outputs a difference voltage V1 which is obtained by integrating the voltage Vd-V1 obtained, by subtracting the set voltage V1 from the voltage Vd corresponding to the current Is to a V/F converter 3. The converter 3 outputs the converted driving frequency f of the transformer 6 to a class-D amplifier 4. The amplifier 4 outputs a PWM rectangular wave, obtained by A/D-converting the frequency f and the rectangular wave, is impressed on the primary side of the transformer 6 directly via an LPF or via a wound transformer T. In this case, only the fundamental wave of the PWM rectangular wave is impressed on the primary side of the transformer 6, because the higher harmonic component of the rectangular wave is deleted by means of the LPF.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of a piezoelectric transformer used in a lighting device of a cold cathode tube and the like, and a piezoelectric inverter driven by the driving method.

[0002]

2. Description of the Related Art The prior art will be described with reference to FIGS.
FIG. 5 is a block diagram illustrating a conventional piezoelectric transformer driving method. In the figure, a variable voltage device 1 outputs a set voltage V1 to an integrator 2 so that a secondary current Is of a piezoelectric transformer 6 becomes a set value, and the integrator 2 outputs a voltage Vd corresponding to the secondary current Is. The difference voltage Vs obtained by integrating the voltage Vd-V1 obtained by subtracting the set voltage V1 is output to the V / F converter 3, and the V / F converter 3 outputs the converted piezoelectric drive frequency f to the amplifier 24. Outputs the piezoelectric transformer driving frequency f to the piezoelectric transformer 6.

FIG. 6 is an explanatory diagram of an amplifier circuit in a conventional piezoelectric transformer driving method. In the figure, the IC sets switching elements Q1 and Q2 to a piezoelectric transformer driving frequency f.
Is a switching control circuit that switches at
Numerals 1 and 2 are transformers having a primary and secondary winding ratio of 1: n. From the transformer T1, the first half of the switching frequency is 1 /
A half-wave sine wave for two cycles is output, and a half-wave sine wave for a half cycle of the latter half of the switching frequency is output from the transformer T2. These combined shape waves become pseudo sine waves, which are driven by applying them to the primary side of the piezoelectric transformer 6.

FIGS. 7A to 7C are diagrams for explaining voltage waveforms applied to a piezoelectric transformer in a conventional piezoelectric transformer driving method. (A) is a composite output waveform when the capacitance component C of the piezoelectric transformer 6 and the inductance component L at the previous stage match the resonance frequency, and (b) is a composite output waveform (crossover) when LC is insufficient. (C) shows a composite output waveform when the LC is too large (the crossover has a break in the waveform).
It is.

[0005]

However, in the conventional driving method, a pseudo sine wave is generated by utilizing the resonance caused by the capacitance component of the piezoelectric transformer and the inductance component at the preceding stage, and is applied to the primary side of the piezoelectric transformer. However, in this method, since the capacitance component and the inductance component have temperature characteristics and tolerance, the deviation of the resonance frequency with respect to the control frequency of the IC may be large, and the efficiency characteristics are unstable. . Further, in the conventional example, since a plurality of transformers T1 and T2 were used, miniaturization was restricted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is possible to suppress the influence on the efficiency characteristics due to the fluctuation of the capacitance component and the inductance component, and to improve the stability of the efficiency characteristics. It is an object to provide a method and a compact piezoelectric transformer type inverter.

[0007]

According to the present invention, there is provided a piezoelectric transformer driving method according to the present invention, in which a variable voltage generator is arranged so that a secondary current Is flowing through a secondary side of a piezoelectric transformer becomes a set value. The integrator 2 outputs the set voltage V1 from the voltage Vd corresponding to the secondary current Is.
The voltage Vd-V1 obtained by subtracting 1 is integrated, the integrated difference voltage Vs is output to the V / F converter 3, and the V / F converter 3
Is the piezoelectric transformer driving frequency f converted by the difference voltage Vs.
Is output to the class D amplifier 4, the class D amplifier 4 converts the piezoelectric transformer driving frequency f into a PWM rectangular wave, and removes this harmonic component from the PWM rectangular wave by the LPF 5 directly or through the winding transformer T. It is characterized in that it is output to the piezoelectric transformer 6.

In the piezoelectric transformer type inverter according to the present invention, the piezoelectric transformer driving frequency f is added and the PWM
A class D amplifier 4 for outputting a rectangular wave, and a piezoelectric transformer 6 driven by applying an output from the class D amplifier 4 directly or through a winding transformer T to remove an harmonic component in an LPF 5 It has features.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric transformer driving method according to the present invention is a method of converting a piezoelectric transformer driving frequency into a PWM rectangular wave with a class D amplifier and applying a sinusoidal voltage with a harmonic component reduced by an LPF to the piezoelectric transformer. Therefore, the stability of the efficiency characteristics can be improved.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a piezoelectric transformer driving method according to an embodiment of the present invention. FIG.
The same reference numerals denote the same elements, and a description thereof will be omitted.

In FIG. 1, a variable voltage device 1 has a set voltage V1 such that a secondary current Is of a piezoelectric transformer 6 has a set value.
Is output to the integrator 2, and the integrator 2 subtracts the set voltage V1 from the voltage Vd corresponding to the secondary-side current Is, and outputs a voltage Vd−
A difference voltage Vs obtained by integrating V1 is output to the V / F converter 3,
The V / F converter 3 outputs the converted piezoelectric transformer driving frequency f to the class D amplifier 4.

The class D amplifier 4 has a piezoelectric transformer driving frequency f
And outputs a PWM rectangular wave obtained by A / D conversion of. This output P
The WM square wave is applied to the primary side of the piezoelectric transformer 6 via the LPF 5 directly or via the winding transformer T. In this case, the harmonic component of the PWM rectangular wave is eliminated by the LPF 5, so that the piezoelectric transformer driving frequency f, which is the fundamental wave, is directly or via the winding transformer T.
It will be applied to the next side.

In FIG. 1, reference numeral 7 denotes a load of the piezoelectric transformer 6, reference numeral 8 denotes a detection circuit for detecting the secondary current Is of the piezoelectric transformer 6, and reference numeral 9 denotes a conversion of the AC voltage from the detection circuit 8 into a DC voltage. It is a rectifier circuit for conversion.

FIG. 2 is a diagram for explaining generation of a PWM rectangular wave in the piezoelectric transformer driving method of the present invention. The piezoelectric transformer driving frequency f (sine wave) is switched by a triangular wave (a sawtooth wave is also possible), and is converted into a pulse having a width corresponding to the voltage, that is, a PWM rectangular wave.

FIG. 3 is a diagram for explaining a class D amplifier used in the piezoelectric transformer driving method according to the present invention. The voltage of the triangular wave from the triangular wave oscillator 11 and the piezoelectric transformer driving frequency f are compared by the comparator 12, and if the piezoelectric transformer driving frequency f voltage> the triangular wave voltage, a positive voltage pulse is output, and the piezoelectric transformer driving frequency f voltage <the triangular wave voltage In this case, a negative voltage pulse is output.

FIG. 4 is a diagram for explaining LPF characteristics in the piezoelectric transformer driving method of the present invention. The vertical axis indicates the level of the spectrum of the PWM rectangular wave, and the horizontal axis indicates the piezoelectric transformer driving frequency f, the switching frequency fs, and a harmonic group thereof. As indicated by the dashed line, the LPF passes only the piezoelectric transformer drive frequency f, so that it can be demodulated without power loss.

[0017]

As described above, the piezoelectric transformer driving method of the present invention has a structure in which a class D amplifier generates a voltage with reduced harmonic components and applies the voltage to the piezoelectric transformer without lowering the efficiency. As a result, it is possible to apply a pseudo sine wave, which is less affected by LC resonance, to the primary side of the piezoelectric transformer, suppress the influence on the efficiency characteristics due to fluctuations of the capacitance component and the inductance component, and improve the stability of the efficiency characteristics. An improved compact piezoelectric transformer type inverter can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a piezoelectric transformer driving method according to an embodiment of the present invention.

FIG. 2 shows a PWM in the piezoelectric transformer driving method of the present invention.
It is a figure explaining generation of a square wave.

FIG. 3 is a diagram illustrating a class D amplifier used in the piezoelectric transformer driving method of the present invention.

FIG. 4 is an LPF in the piezoelectric transformer driving method of the present invention.
It is a figure explaining a characteristic.

FIG. 5 is a block diagram illustrating a conventional piezoelectric transformer driving method.

FIG. 6 is a diagram illustrating a driving circuit in a conventional piezoelectric transformer driving method.

FIGS. 7A to 7C are diagrams illustrating voltage waveforms applied to a piezoelectric transformer in a conventional piezoelectric transformer driving method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 variable voltage device 2 integrator 3 V / F converter 4 class D amplifier 5 LPF 6 piezoelectric transformer 7 load 8 detection circuit 9 rectifier circuit 11 triangular wave oscillator 12 comparator 24 amplifier V1 set voltage Vs difference voltage Is secondary current Vd 2 Voltages sw1 to 4 corresponding to the secondary currents Switch T transformer T1 transformer T2 transformer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K072 AA19 AC02 BC07 CA16 CB10 GB20 HA10 5H730 AA06 AS11 EE48 EE59 FD33 FF02 FG05

Claims (2)

[Claims] The variable voltage device (1) is a piezoelectric transformer (6).
The set voltage (V1) is output to the integrator (2) so that the secondary current (Is) flowing to the secondary side of the set value becomes the set value, and the integrator (2) corresponds to the secondary current (Is). Voltage (V
d) minus the set voltage (V1) (Vd−V)
1) and outputs the integrated difference voltage (Vs) to the V / F converter (3). The V / F converter (3) converts the piezoelectric transformer drive frequency (f) converted by the difference voltage (Vs). ) Is output to the class D amplifier (4). The class D amplifier (4) sets the piezoelectric transformer drive frequency (f) to P
WM is converted to a WM square wave, and this PWM square wave is directly or wound through a low-pass filter LPF (5).
Output to a piezoelectric transformer (6) via a piezoelectric transformer. 2. A class D amplifier (4) to which a piezoelectric transformer driving frequency (f) is added and which outputs a PWM rectangular wave; and an output from the class D amplifier (4) is a harmonic by an LPF (5). And a piezoelectric transformer (6) driven directly or through a winding transformer T excluding components.