JPH08149851A - Piezoelectric transformer driver - Google Patents

Abstract

PURPOSE: To get large power with small circuit loss and besides with small size and also, to enable this driver to automatically follow the change of drive frequency of a piezoelectric transformer, by constituting a high frequency circuit mainly of a dielectric element, an active element, and a phase shifter. CONSTITUTION: A piezoelectric transformer 1 is an electric-mechanical amount converting element using piezoelectric ceramics. A high frequency circuit 2 being a piezoelectric transformer driver is connected between the terminals of the primary input terminals 3 and 3' of the piezoelectric transformer 1. The high frequency circuit 2 is composed of a dielectric element 6, an active element 7, and a phase shifter 8. A discharge lamp 5 is connected between the secondary terminals 4 and 4' of the piezoelectric transformer 1. In this example, since the phase shifter 8 and the active element 7 are connected directly with each other, the high frequency circuit 2 is effective in case that the load is light, etc. In case that the input power is several waits or under, in case that the load is light, or in other such cases, the change of the drive frequency becomes slow, so it can be used, following the change enough.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer drive device, and more particularly to a high frequency circuit for driving a piezoelectric transformer used in a discharge lamp lighting device or the like.

[0002]

2. Description of the Related Art Conventional piezoelectric transformers are mainly developed as flyback transformers for televisions. By enlarging the size of the piezoelectric transformer, the heat radiation area is increased to suppress the temperature rise to a low level. By making it dense and reducing the internal loss,
The input / output ratio is designed to be in the linear region. Since these piezoelectric transformer drive devices were mainly driven in the linear region or in the vicinity of the boundary between the linear region and the non-linear region, whether to use a separately-excited oscillation type drive circuit using a crystal oscillator, a piezoelectric resonator, or the like. , Hartley and Colpitts analog oscillator circuits are used.

[0003]

When an output of a large current with a relatively high voltage is taken out to a capacitive load by a separately excited drive circuit using a crystal oscillator or a piezoelectric ceramic resonator, the piezoelectric transformer generates heat. There is a problem that the brightness of the discharge lamp is reduced. Moreover, in the drive circuit by the analog oscillation circuit of Hartley and Colpitts, one to one for each device
Since the adjustment of the piezoelectric transformer and the high frequency drive circuit is required, the number of steps is increased and it is not suitable for mass production as the drive circuit of the piezoelectric transformer. Further, the conventional analog type self-excited oscillation circuit driven by a sine wave has a circuit efficiency of about 30 to 50% of that of a class A or class B amplifier, and is not suitable for battery driving.

In addition, when used for a long time, a phase difference between a sine wave voltage and a current occurs due to heat generation of the piezoelectric transformer and the circuit system, the power factor gradually decreases, and the brightness of the discharge lamp decreases. It had the drawback of falling.

[0005]

In recent years, piezoelectric transformers have been used not only for inductive or resistive loads that consume a small output current, such as in conventional flyback transformers of televisions. Driving of a capacitive load such as a discharge lamp that requires a relatively large current at a high voltage has been studied. To drive such a load,
There has been a demand for a self-excited oscillation type drive circuit that has a small circuit loss, has no adjustment, has a small number of parts, can produce a small power output, and can automatically track changes in the drive frequency of the piezoelectric transformer due to heat generation. There is. Therefore, the present invention was developed in response to the above-mentioned demand, and is a piezoelectric transformer which is a high-frequency circuit having a relatively small number of parts, which is composed of an inductive element, an active element, a phaser, and a resonance circuit. Provided is a drive device for driving the.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a piezoelectric transformer drive device according to a first embodiment of the present invention. In the figure, 1 is a piezoelectric transformer to be driven, which is an electro-mechanical quantity conversion element using piezoelectric ceramics. 3, 3 '
The (ground side terminal) is the primary side input terminal of the piezoelectric transformer 1, and the high frequency circuit 2 which is the piezoelectric transformer driving device according to the present invention is connected between the both terminals. The high frequency circuit 2 is composed of an inductive element 6, an active element 7 and a phase shifter 8. 5 is a secondary output terminal 4 of the piezoelectric transformer 1,
It is a discharge lamp connected between 4 '(ground side terminal).

FIG. 2 is a block diagram showing a piezoelectric transformer drive device according to a second embodiment of the present invention. Similarly in the figure, 1 is a piezoelectric transformer to be driven,
It is an electric-mechanical quantity conversion element using piezoelectric ceramics. 3, 3 '(ground side terminals) are primary side input terminals of the piezoelectric transformer 1, and a high frequency circuit 9 which is a piezoelectric transformer driving device according to the present invention is connected between these terminals. The high frequency circuit 9 is composed of an inductive element 6, an active element 7, a phase shifter 8 and a resonance circuit 10. Reference numeral 5 is a discharge lamp connected between the secondary side output terminals 4 and 4 '(ground side terminal) of the piezoelectric transformer 1.

Next, the high frequency circuit 9 of the piezoelectric transformer driving device according to the second embodiment of the present invention will be described with reference to FIGS.
Will be described in more detail. The inductive element 6 is an active element 7 that serves as an amplification section or a switching section such as a transistor.
Is connected between the collector part of the above and a DC power source (not shown) of about 12V to 24V. The inductive element 6 is composed of a coil having a self-inductance of about 2 to 4 millihenries.

Active element 7 including the transistor
When an AC signal of about several volts which is fed back from the phase shifter 8 is applied to the base part of the active part 7, the active element 7 composed of the transistor or the like conducts during the time period when the signal has a positive potential and is not amplified. Switching operation.

The current flowing through the inductive element 6 connected to the collector of the active element 7 composed of a transistor or the like is turned on or off according to the base signal of the active element 7.
Since the state of is repeated, an electric vibration phenomenon occurs. Since an oscillating current having a different direction flows in the inductive element 6 and a counter electromotive force is generated to generate a so-called kickback voltage, in a direct-current power supply of about + 12V to 24V, the active element 7 composed of the transistor or the like is used. At the output section (collector section), an AC signal that is two to three times the power supply voltage and boosted to about plus 30V to 70V is obtained.

An active element 7 including the above-mentioned transistor or the like
The phase of the signal returned to the base of the active element 7 and the phase of the signal passing through the active element 7 and appearing at the collector thereof are 18
Since the phase relationship is 0 degree different, it is necessary to invert the phase of the output signal and apply positive feedback in order to sustain the oscillation phenomenon. It is also necessary to keep the gain above 1.

The phase shifter 8 is composed of a four-terminal output transformer using an inductive element, one terminal of the input section 2 is connected to the collector section of the active element 7, and the other terminal is connected to the collector section of the active element 7. The terminals are the upper electrode terminals 3 of the input part of the piezoelectric transformer 1.
It is connected to the. The input side coil and the output side coil of the 4-terminal output transformer (phase shifter 8) are configured such that the winding directions are opposite to each other, so that the output side with respect to the signal phase applied to the input section is The terminals are configured to rotate the phase by 180 degrees. One of the terminals of the output section 2 is connected to the ground terminal, and the other terminal is connected to the base of the active element 7 composed of a transistor or the like. The gain in the loop can be adjusted with a coil.

A parallel type resonance circuit 10 is constructed by connecting a capacitive element to the output side two terminals of the phase shifter 8 in parallel with the output side coil. The resonance frequency of the resonance circuit 10 is set to be substantially equal to or a little lower (capacitive) than the resonance frequency determined by the shape of the piezoelectric transformer 1 which also serves as a piezoelectric oscillator.

With the above structure, the piezoelectric transformer 1 and the resonance circuit 10 function as a tuning circuit and complement each other. Therefore, the piezoelectric transformer 1 and the resonance circuit 10 immediately respond to the primary side coil of the phase shifter 8 (the primary side coil of the resonance circuit). Since the frequency is automatically tracked so that the current always has the maximum value, the mechanical amplitude of the piezoelectric transformer is
Feedback that tries to keep constant so as to follow temperature changes, frequency changes, load changes, etc. works.

In the first embodiment, the phase shifter 8 and the active element 7 are used.
Is directly connected, the high frequency circuit 2 shown in the first embodiment is effective when the load is light. If the input power is less than a few watts or the load is light,
Since the drive frequency changes slowly with the passage of time, it can be used sufficiently after the change. The circuit operation is
Since it is almost the same as the high frequency circuit 9, detailed description thereof will be omitted.

FIG. 3 shows an example of a substantial wiring diagram of the high frequency circuit 9 which is a piezoelectric transformer driving circuit according to the present invention. Practically, the AC power supply K1 of 100 V is connected to the diodes D1 and D
A DC power source obtained by stabilizing the capacitor C1 with a rectifier using 2, D3 and D4 as a bridge circuit is used.

The inductive element 6 is an inductance (coil) L1. The inductance L1 is an active element 7
Is connected to the collector of the transistor T1.

On the emitter side of the transistor T1,
A biasing resistor R1 is connected to the ground.

The phase shifter 8 is an integrated structure including the resonance circuit 10 and a ferrite core. The coil L2 on the primary side includes the collector of the transistor T1 and
It is connected to the primary side input section of the piezoelectric transformer.

The resonance circuit 10 is constructed by connecting a capacitor C2 in parallel with the secondary coil L3.

[0021]

The high frequency circuit, which is the piezoelectric transformer driving device of the present invention, has a total number of parts of several parts. Since it is a self-excited driving system, the resonance frequency of the piezoelectric transformer is about ± 10%. Even if it changes, it can be connected to the piezoelectric transformer without requiring circuit adjustment. Further, by combining the inductive element and the active element, the power supply voltage can be boosted to about 2 to 3 times, and the impedance matching with the high impedance piezoelectric transformer can be realized at the same time. Therefore, there is also an effect that the efficiency of the entire device can be dramatically improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a piezoelectric transformer driving device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a piezoelectric transformer drive device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing an example of a substantial wiring diagram of a high-frequency circuit that is a piezoelectric transformer driving device of the present invention.

[Explanation of symbols]

 1 Piezoelectric transformer 2, 9 High frequency circuit 6 Inductive element 7 Active element 8 Phaser 10 Resonance circuit

Claims (7)

[Claims] 1. A high-frequency circuit for driving a piezoelectric transformer, wherein the high-frequency circuit is mainly composed of an inductive element, an active element, and a phaser. 2. A piezoelectric transformer drive device for driving a piezoelectric transformer, wherein the high frequency circuit mainly comprises an inductive element, an active element, a phaser and a resonance circuit. 3. A high frequency circuit for driving a piezoelectric transformer, wherein the high frequency circuit is mainly composed of an inductive element, an active element, a phaser and a resonance circuit, and the primary side of the piezoelectric transformer is a part of the high frequency circuit. A piezoelectric transformer drive device characterized in that it operates as a self-excited oscillation system. 4. A high-frequency circuit for driving a piezoelectric transformer, wherein the high-frequency circuit mainly includes an inductive element for boosting power supply and impedance conversion and a phase converter in an output part of a transistor, and outputs from the phase converter. A piezoelectric transformer driving device characterized in that a signal is fed back to the transistor through a capacitive element or the like. 5. The piezoelectric transformer drive device according to claim 1, wherein the phase shifter comprises an output transformer having an inductive element. 6. The resonance circuit uses a parallel resonance circuit in which a capacitive element is provided in parallel with an output part of a phase shifter using a 4-terminal output transformer with an inductive element, and a mechanical amplitude of a piezoelectric transformer is The piezoelectric transformer drive device according to claim 2 or 3, wherein the piezoelectric transformer drive device is controlled so as to be always constant by following a temperature change, a frequency change, a load change, and the like. 7. A high frequency circuit for driving a piezoelectric transformer including an inductive element, an active element, a phaser and a resonance circuit is connected to the direct current power source by using a direct current power source obtained by rectifying an alternating current power source by a rectifier circuit using a diode. A piezoelectric transformer driving device characterized by comprising: