JP2000152660A - Power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter which allows improving power supply efficiency without being effected by a kind of piezoelectric transformer and its load circuit. SOLUTION: In an inverter 1, comprising a piezoelectric transformer 3 for outputting a boosted voltage which is boosted in the predetermined boosting rate from an input AC voltage and switching circuits 13, 14 for generating with a switching operation the AC signal supplied to the piezoelectric transformer 3, trimming elements 18, 19 are further provided to operate the switching circuits 13, 14 in a quasi-class E or class E operating region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for generating an AC voltage using a piezoelectric transformer, and more particularly, to a power supply for generating an AC signal for supplying a load circuit such as a cold cathode fluorescent tube using the piezoelectric transformer. It concerns the device.

[0002]

2. Description of the Related Art As a power supply device of this kind, the applicant has already proposed an inverter device 31 shown in FIG. 3 (Japanese Patent Application No. 10-158522). This inverter device 31
The piezoelectric transformer 3 generates a pseudo sine wave AC voltage to be supplied to the cold cathode fluorescent tube 2 used for a backlight for a liquid crystal or the like. As a specific configuration, the inverter device 3
1 is a piezoelectric transformer 3 and a driving circuit 3 for the piezoelectric transformer 3
2 is provided. The drive circuit 32 generates an AC signal SAC by a push-pull operation by being alternately controlled to be in an ON state in synchronism with the switching signal SS, and the DC power supply unit 10 equivalently constituting a constant current source. Channel type FETs 13 and 14, and an inverter circuit 15 for inverting the switching signal SS and supplying the inverted signal to the gate of the FET 13.
And a switching coil 16 with an intermediate terminal (center tap). In this case, the DC power supply unit 1
Numeral 0 is provided with a DC power supply 11 and a choke coil 12 for constituting a constant current source. The coil 16 is configured by connecting windings 17a and 17b that are magnetically coupled to each other by a magnetic core provided therein in series.

In the inverter device 31, the FET 13 and the FET 14 are alternately controlled to be turned on in synchronization with the switching signal SS to perform switching by a so-called zero volt switch in a quasi-E or E-class operation region. In this case, FET13 and FET14
The power loss due to switching the charge stored in the parasitic capacitance inside is avoided by the zero volt switch, whereby the AC signal SAC is generated with high efficiency. Next, the piezoelectric transformer 3 is connected to the input terminals 3a and 3b.
The AC signal SAC applied therebetween is boosted with a predetermined gain, and the boosted AC output signal SO is output to the cold cathode fluorescent tube 2 via the output terminal 3c. As a result, the cold-cathode fluorescent tube 2 is turned on with a luminance corresponding to the voltage of the AC output signal So.

[0004]

However, the inverter device 31 proposed by the present applicant has the following improvements. That is, in the inverter device 31, the power supply efficiency of the device is originally improved by causing the FETs 13 and 14 to perform switching by the zero volt switch in the quasi-E or E-class operation region. On the other hand, as shown in FIG. 2, the drive circuit 32 in the inverter device 31 is equivalently represented as an output inductance having a value Lo, and the piezoelectric transformer 3 and the cold cathode fluorescent lamp 2 are equivalent as a load circuit RL of the drive circuit 32. Is represented by In this case, if the parallel susceptance component and the series reactance component in the load circuit RL are set to a value B and a value X, respectively, and the resistance component is set to a value R, in order for the FETs 13 and 14 to operate in the class E operation region, And the equation must be satisfied. When the following equations and the conditions of the equations are almost satisfied, the FETs 13 and 14 operate in the quasi-E class operation region. BR · 0.186 ··· Formula X / R = 1.152 ··· Formula

On the other hand, the above-mentioned susceptance component B and reactance component X fluctuate in accordance with the type of the piezoelectric transformer 3, variations in element characteristics in manufacturing, the frequency of the AC signal SAC, and the like. In particular, for the susceptance component B, when the laminated piezoelectric transformer 3 is operated by the central drive, the single-plate Rosen-type piezoelectric transformer 3 is operated in the primary mode, the secondary mode, or the tertiary mode. , Several times larger. A laminated piezoelectric transformer 3 having the same thickness as the single-plate Rosen-type piezoelectric transformer 3 is used.
Is manufactured, the susceptance component B of the multilayer piezoelectric transformer 3 is several times larger than that of the single-plate Rosen piezoelectric transformer 3. Further, the resistance component R also varies according to the type of the cold cathode fluorescent tube 2 as a load. Therefore, the piezoelectric transformer 3 and the cold cathode fluorescent tube 2
FETs 13 and 14 may not always have quasi-E
It does not always operate in the class or E class operation region, and it is difficult to ensure the zero volt switch. In this case, when the zero volt switch is not performed, the power loss at that time increases quadratically as the voltage of the charge stored in the parasitic capacitance of the FETs 13 and 14 increases. For this reason, there is a demand for the development of an inverter device that operates with high efficiency without being affected by the types of the piezoelectric transformer 3 and the cold cathode fluorescent tubes 2.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide a power supply device capable of improving the power supply efficiency of a device without being affected by the type of a piezoelectric transformer or its load circuit. Main purpose.

[0007]

According to a first aspect of the present invention, there is provided a power supply device comprising: a piezoelectric transformer for boosting an input AC voltage at a predetermined boosting ratio and outputting the boosted AC voltage; and an AC signal supplied to the piezoelectric transformer. And a switching circuit that generates a switching operation by
A trimming element for operating the switching circuit in the quasi-E or E-class operation region is provided.

According to a second aspect of the present invention, in the power supply device of the first aspect, the switching circuit is constituted by a push-pull circuit including a pair of switching elements.

According to a third aspect of the present invention, in the power supply device according to the first or second aspect, the trimming element is constituted by at least one of an inductive element and a capacitive element.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a power supply device according to the present invention is applied to an inverter device 1 will be described below with reference to the accompanying drawings. Note that the same components as those of the inverter device 31 are denoted by the same reference numerals, and redundant description will be omitted.

As shown in FIG. 1, the inverter device 1 comprises:
It includes a piezoelectric transformer 3 and a drive circuit 4 for driving the piezoelectric transformer 3. The drive circuit 4 includes a DC power supply unit 10 including a DC power supply 11 and a choke coil 12, FETs 13 and 14 corresponding to switching elements in the present invention, and an inverter circuit, similarly to the drive circuit 32 in the conventional inverter device 31. 15 and a switching coil 16. in this case,
The coil 16 is configured by connecting windings 17a and 17b in series, one end 16a of which is connected to the drain of the FET 13 and an inductor 18 described later, and the other end 16b of which
The intermediate terminal 16 c, which is connected to the drain 14 and the other input terminal 3 b of the piezoelectric transformer 3, and is a connection point between the two windings 17 a, 17 b, is connected to one end of the choke coil 12.

Further, the inverter device 1 is different from the inverter device 31 in that an inductor 18 and capacitors 19 and 20 as trimming elements are provided as necessary. By adjusting the respective values of these trimming elements 18 to 20, the FETs 13 and 14 are controlled by the quasi-E, regardless of the types of the piezoelectric transformer 3 and the cold cathode fluorescent tube 2.
Operates in Class-E or Class-E operating range.

The piezoelectric transformer 3 is composed of, for example, a Rosen type using a ceramic material modified with a third component or an additive based on a lead zirconate titanate-based ceramic (PZT). . This piezoelectric transformer 3 has an AC signal S at input terminals 3a and 3b.
When AC is applied, the AC signal SAC is boosted with a predetermined gain,
The boosted output AC signal SO is applied to the output terminal 3 by the piezoelectric effect.
Output from c. In the embodiment of the present invention, the piezoelectric transformer 3 is not particularly limited, but has a resonance frequency of 116 KH.
In z, the power value of the output AC signal So is configured to be 2 W.

On the other hand, the cold-cathode fluorescent tube 2 as a load circuit of the inverter device 1 is used for a backlight of a liquid crystal display of a notebook type personal computer. The applied voltage is about 1200 Vrms, the applied voltage required for normal lighting is about 500 Vrms, and the current consumption is about 2.5 mA or more.
It is 5 mA.

Next, the overall operation of the inverter device 1 will be described.

First, adjustment of the trimming element will be described with reference to FIG. FIG. 2 shows an equivalent circuit of the driving circuit 4 and the piezoelectric transformer 3 and the cold cathode fluorescent tube 2.
Is shown as an equivalent load circuit RL. For example, when the input capacitance of the piezoelectric transformer 3 is more than the susceptance component B required to satisfy the above equation (see FIG. 4), an inductor for canceling the extra susceptance component B is replaced with a capacitor 19. Is connected between the input terminals 3a and 3b of the piezoelectric transformer 3. Conversely, when the input capacitance of the piezoelectric transformer 3 is less than the required susceptance component B, an inductor 18 is provided to equivalently compensate for the insufficient susceptance component. In this case, a capacitor 19 having the same capacity as the shortage may be connected in parallel between the input terminals 3a and 3b of the piezoelectric transformer 3 without disposing the inductor 18. As a result, it is possible to adjust the susceptance component B, whose value varies in particular according to the type of the piezoelectric transformer 3, to the most appropriate value for the FETs 13 and 14 to operate in the quasi-E or E-class operation region. As a result, the susceptance component B and the resistance component R shown in the figure satisfy the above equation. Note that the resistance component R means the total resistance value of the internal resistance of the piezoelectric transformer 3 and the input resistance of the cold cathode fluorescent tube 2.

When the reactance component inside the piezoelectric transformer 3 is more than the reactance component X (see FIG. 2) required to satisfy the above equation, a capacitor 20 for canceling the extra reactance component is used. Is arranged. Conversely, when the reactance component of the piezoelectric transformer 3 is less than the required reactance component X, a choke coil having an inductance equal to the shortage is provided instead of the capacitor 20. As a result, the above equation is satisfied by the reactance component X and the resistance component R shown in FIG.

On the other hand, in a steady state after the operation, when the switching signal SS is at a high level, the FET 14 and the FET 13 are controlled to be on and off, respectively. At this time, the choke coil 12 performs pseudo-constant current control by limiting the output current of the DC power supply 11. At the same time, energy is accumulated in the winding 17b of the coil 16 by the flow of current. on the other hand,
From one end 16a of the coil 16, the FET 13
Is controlled to the ON state, the current ILa based on the energy stored in the winding 17a is released. At this time, a voltage VDa which is approximately 3.5 times the output voltage Vo of the DC power supply 11 is generated at the drain of the FET 13. The current ILa is supplied to the inductor 18, one input terminal 3a of the piezoelectric transformer 3, the inside of the piezoelectric transformer 3,
The other input terminal 3b of the piezoelectric transformer 3 and the FET1
4 can be conducted. Thereby, the piezoelectric transformer 3 is connected to the input terminal 3
a and 3b are boosted with a predetermined gain, and the boosted AC output signal SO is output to an output terminal 3
The light is output to the cold cathode fluorescent tube 2 via the line c.

Next, when the switching signal SS is at a low level, the FET 13 and the FET 14 are controlled to be on and off, respectively. At this time, energy is accumulated in the winding 17a of the coil 16 by the current flowing. On the other hand, the other end 16b of the coil 16
Thereafter, a current ILb based on the energy stored in the winding 17b when the FET 14 is controlled to the ON state immediately before that is released. At this time, a voltage VDb, which is approximately 3.5 times the output voltage Vo of the DC power supply 11, is generated at the drain of the FET. Also, the current ILb
Is conducted through the other input terminal 3 b of the piezoelectric transformer 3, the inside of the piezoelectric transformer 3, the one input terminal 3 a of the piezoelectric transformer 3, the inductor 18, and the current path including the drain and source of the FET 13. As a result, the AC signal SAC is applied between the input terminals 3a and 3b of the piezoelectric transformer 3. In these processes, both FETs 13, 1
4 performs the zero volt switch in the quasi-E class or E-class operation region, so that the power supply efficiency of the inverter device 1 is improved. Next, the piezoelectric transformer 3 is connected to the input terminals 3a and 3b.
The AC signal SAC applied therebetween is boosted with a predetermined gain, and the boosted AC output signal SO is output to the cold cathode fluorescent tube 2 via the output terminal 3c.

As described above, according to the inverter device 1, the inductor 18, the capacitor 19,
By arranging a trimming element such as 20, it is possible to make both FETs 13 and 14 perform the zero volt switch operation reliably in the quasi-E or E-class operation region. As a result, the power supply efficiency of the inverter device 1 can be improved. In addition, by using an inductive element or a capacitive element without using a resistor that may cause power loss as a trimming element, power loss due to the trimming element is prevented.

Note that the present invention is not limited to the configuration shown in the above-described embodiment of the invention, and can be appropriately changed.
For example, a capacitor may be provided in place of the inductor 18 in order to satisfy the above equations and the equations according to the type of the piezoelectric transformer 3 and the like. In addition, the arrangement position of each trimming element is not limited to the above-described position,
It can be arranged at any position as long as the expression and the position satisfying the expression. Further, each trimming element may be an element of a type whose value can be varied. Also,
Matching means for impedance matching between at least one of the impedance between the FETs 13 and 14 and the piezoelectric transformer 3 and the impedance between the piezoelectric transformer 3 and the cold cathode fluorescent tube 2 may be appropriately provided.

The load circuit is not limited to the cold cathode fluorescent tube 2 and may be another load.
Not limited to ET1, a transistor or the like may be used. Further, the switching circuit is not limited to the push-pull circuit, and may be configured as a single output type. Also, FE
As for the load side circuits of T13 and T14, a transformer can be used instead of the coil 16. In addition, a DC / DC converter can be configured by disposing a rectifying and smoothing circuit on the load side of the piezoelectric transformer 3 in the inverter device 1.

[0023]

As described above, according to the power supply device of the first aspect, the switching circuit can be operated in the quasi-E class or E-class operation region by the trimming element. As a result, the power efficiency of the power supply device as a whole can be improved.

According to the power supply device of the second aspect,
Since the switching circuit of the push-pull circuit can be operated in the quasi-E or E-class operation region by the trimming element, even when a high-voltage and high-power AC voltage is supplied to the piezoelectric transformer, the switching circuit can be used. Of the power supply device, thereby improving the power supply efficiency of the power supply device as a whole.

Further, according to the power supply device of the third aspect, since the trimming element is formed in at least one of the inductive element and the capacitive element, power loss due to the trimming element can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an inverter device 1 according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the inverter device 1 according to the embodiment of the present invention and a conventional inverter device 31.

FIG. 3 is a circuit diagram of a conventional inverter device 31.

[Description of Signs] 1 Inverter device 3 Piezoelectric transformer 4 Drive circuit 13 FET 14 FET 18 Inductor 19 Capacitor 20 Capacitor

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[Procedure amendment]

[Submission date] January 19, 2000 (2000.1.1)
9)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

According to a first aspect of the present invention, there is provided a power supply apparatus comprising: a piezoelectric transformer for boosting an input AC voltage at a predetermined boosting ratio and outputting the boosted AC voltage; And a switching circuit configured to generate an AC signal to be supplied to the piezoelectric transformer by a switching operation by a switching operation. BR × 0.186..., And X / R = 1.152 ... formula (however, "B",
“X” and “R” are equivalent parallel susceptance components, series reactance components, and parallel resistance components in a load circuit including a piezoelectric transformer, respectively.)
And a trimming element for operating the switching circuit in an operation region that substantially satisfies the condition represented by:

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

According to a second aspect of the present invention, in the power supply unit of the first aspect, the trimming element is configured by at least one of an inductive element and a capacitive element.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

According to a third aspect of the present invention, there is provided the power supply unit according to the second aspect, wherein the trimming element is constituted by an element whose value can be varied.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

The load circuit is not limited to the cold cathode fluorescent tube 2 and may be another load.
Not limited to ET1, a transistor or the like may be used. Further, a transformer can be used instead of the coil 16 for the load-side circuits of the FETs 13 and 14. Also,
By providing a rectifying and smoothing circuit on the load side of the piezoelectric transformer 3 in the inverter device 1, a DC / DC converter can be configured.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

[0023]

As described above, according to the power supply device of the present invention, the switching circuit of the push-pull circuit can be operated in the quasi-E or E-class operation region by the trimming element. Even when a high-voltage and high-power AC voltage is supplied to the piezoelectric transformer, the efficiency of the switching circuit can be increased, and as a result, the power supply efficiency of the entire power supply device can be improved. In addition, since the trimming element is configured as at least one of the inductive element and the capacitive element, power loss due to the trimming element can be prevented.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K072 AA01 AA19 BA03 BC01 BC07 GA02 GB14 GC04 HA10 HB03 5H007 BB03 CA02 CB04 CB06 CC07 5H730 AA14 AS11 DD02 DD04 EE48 FG01 ZZ19

Claims (3)

[Claims] 1. A power supply device comprising: a piezoelectric transformer that boosts an input AC voltage at a predetermined boost ratio and outputs the boosted AC voltage; and a switching circuit that generates an AC signal to be supplied to the piezoelectric transformer by a switching operation. A power supply device comprising a trimming element for operating a switching circuit in a quasi-E or E-class operation region. 2. The power supply device according to claim 1, wherein said switching circuit comprises a push-pull circuit including a pair of switching elements. 3. The power supply device according to claim 1, wherein the trimming element includes at least one of an inductive element and a capacitive element.