JPH10164848A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converter in which the power conversion efficiency of a piezoelectric transformer can be maximized regardless of fluctuation of circuit components and the output can be regulated. SOLUTION: A piezoelectric transformer drive circuit 3 is controlled by a frequency control circuit 7 to supply a piezoelectric transformer 4 with a driving voltage V3 . The piezoelectric transformer 4 is driven with the driving voltage V3 to supply a load 2 with an output (voltage V4 , current I4 ). An output voltage detection circuit 5 detects the output voltage V4 which is then fed to a differentiation circuit 6 thus obtaining a differentiated value. The frequency control circuit 7 decreases (sweeps) the frequency continuously sarting from a frequency f0 higher than a resonance frequency fA. When a frequency f1 close to the resonance frequency fA is reached, the differentiated value of detection voltage obtained from the differentiation circuit 6 substantially goes zero. The frequency control circuit 7 stops frequency sweeping and sustains the frequency (t) of the driving voltage V3 at the resonance frequency f1 . According to the arrangement, power conversion efficiency η of the piezoelectric transformer 4 can be kept at a level very close to a maximum level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter using a piezoelectric transformer.

[0002]

2. Description of the Related Art In recent years, in a power conversion device having a discharge lamp or the like as a load, a piezoelectric transformer, which can be made smaller and more efficient than an electromagnetic transformer, has attracted attention as an alternative to the electromagnetic transformer. Japanese Patent Application Laid-Open No. 7-220888 discloses an example of a power conversion device for enabling continuous discharge of a discharge lamp using such a piezoelectric transformer. Hereinafter, the conventional apparatus described in this publication will be described.

FIG. 33 is a block diagram showing the above-mentioned conventional device, FIG. 34 is a circuit diagram of the self-excited driving circuit 26 in FIG. 33, and FIG. 35 is a current detecting circuit 32 in FIG.
FIG. 36 shows the discharge lamp La and the piezoelectric transformer 28.
3 is a characteristic curve showing the characteristic of FIG. As shown in the figure, the power conversion device 20 has a chopper circuit 24 for raising or lowering a DC voltage Va from a DC power supply 22 to an arbitrary voltage, and an output voltage Vb of the chopper circuit 24 is Is input to

The driving circuit 26 applies a periodically inverted voltage Vc to a piezoelectric transformer 28. The piezoelectric transformer 28 is made of a piezoelectric ceramic element as described later, and generates high power on the output side by applying the above-described voltage. This piezoelectric transformer 28
Is applied to a discharge lamp La such as a cold-cathode tube to ignite it and continue the discharge.

The discharge lamp La is connected to a current detection circuit 32 for detecting a current (lamp current) flowing through the discharge lamp La. The detected value controls the output of the piezoelectric transformer 28 to control the discharge of the discharge lamp La. Light emission amount controller 3 for adjusting the light emission amount
3 is connected. Specifically, the light emission amount control unit 3
Reference numeral 3 denotes an error amplifying circuit 36 for amplifying a difference voltage between a voltage indicating a detection value from the current detection circuit 32 and a reference voltage 34, and an output pulse width is varied based on the error voltage from the circuit 36. A pulse width control circuit (PWM) 38 using pulse width modulation is used. The control signal output from the control circuit 38 controls the pulse width of the chopper circuit 24 to adjust the output voltage Vb. I have.

Here, the driving circuit 26 and the piezoelectric transformer 28
Will be described with reference to FIG. As shown, the drive circuit 26 is a self-excited drive circuit,
Two transistors, for example, a first switch transistor 40 composed of a PNP transistor and a second switch transistor 42 composed of an NPN transistor are connected to each other to form a complementary output. The emitter of the first switch transistor 40 is connected to one terminal A1 to which the voltage Vb is applied, and the emitter of the second switch transistor 42 is connected to the other terminal A2.
Connected to. In order to control the base currents of the two transistors 40 and 42, a transistor 44 composed of, for example, a PNP transistor is provided.

[0007] to the terminal A1, the base of the second switch transistor 42 is connected via a first resistor R ₀₁ and a first diode D _01, the first diode D ₀₁
Is provided so as to be on the base side. The base of the first switch transistor 40 is connected to a second resistor R
₀₂ , and connected to the collector of the transistor 34. A second diode _D02 having the collector side in the forward direction is connected to the collector of the first resistor _R01 and the connection point of the first diode _D01. Connected between The emitter of the transistor 34 is connected to the terminal A2, and the base is connected to the third resistor _R03 .

On the other hand, the piezoelectric transformer 28 has a thin plate-shaped piezoelectric ceramic element 46 formed by firing, for example, lead zirconate titanate. The length, width, and thickness of the ceramic element 46 are, for example, 28 mm, 7.5 mm, respectively.
It is set to about 2.0 mm. A pair of input electrodes 48 and 50 obtained by, for example, silver baking are formed on the upper and lower surfaces of the driving section on the left side of the ceramic element 46 in the drawing. Further, an output electrode 54 is formed on the end face of the power generation unit, which is the right half of the ceramic element 46, and the feedback electrode 52 is juxtaposed at a distance. The area of each electrode 48, 50, 54 is
It is stipulated that the capacitance formed between these electrodes is set to an optimum value. One input electrode 48 is connected to the terminal A1, and the other input electrode 50 is connected to a connection point between the collectors of the first and second switch transistors 40 and 42. The feedback electrode 52 has a third resistance R
Connected to ₀₃ . The terminal A1 is connected to the current detection circuit 32.
And the output electrode 54 is connected to the other electrode 58 of the discharge lamp La.

On the other hand, the current detection circuit 32 is composed of a pair of diodes D ₀₃ and D ₀₄ connected in parallel so that their directions are opposite to each other, as shown in FIG. A variable resistor _R05 is connected in series to a diode _D03 provided so that the electrode 54 is directed forward, and a detection voltage indicating a current value is output from the movable terminal 60.

Next, the operation will be described. First, the DC voltage Va from the DC power supply 22 is boosted or stepped down by the control signal from the pulse width control circuit 38 by the chopper circuit 24 to output a DC voltage Vb, and this voltage is input to the drive circuit 26. This drive circuit 26 is a piezoelectric transformer 2
A voltage Vc that is periodically inverted is applied to the piezoelectric transformer 8 to cause the piezoelectric transformer 28 to expand and contract. Then, the piezoelectric transformer 28
A voltage is generated by the piezoelectric effect, a part of the voltage is returned to the drive circuit 26 as a self-excitation feedback signal, and most of the voltage is supplied to the discharge lamp La to ignite it and continue discharging. Become.

The lamp current of the discharge lamp La at this time is detected by a current detection circuit 32, and the detected voltage is compared with a reference voltage 34 by an error amplifier circuit 36 to output an error voltage. Based on the error voltage, the pulse width control circuit 38
By generating a control signal by performing pulse width modulation and supplying the control signal to the chopper circuit 24 as described above, the output voltage Vb is controlled, and the light emission amount of the discharge lamp La is adjusted.

Here, the operation of the driving circuit 26 will be specifically described. In FIG. 34, when a DC voltage Vb is first applied to the terminals A1 and A2, a current flows through the first resistor _R01 and the first diode _D01 to the base of the second switch transistor 42. Is turned on, and the voltage Vc is applied to the input electrodes 48 and 50 of the piezoelectric transformer 28.
(Vb) is applied, and the input capacitance of this portion is charged.

The charging causes a negative voltage to be generated at the feedback electrode 52, and this voltage causes the base of the transistor 44 to be forward-biased via the third resistor _R03, and the transistor 44 is turned on. Then, this transistor 4
By turning on 4, the first switch transistor 40 is turned on, the second switch transistor 42 is turned off, and the input capacitance of the piezoelectric transformer 28 is discharged. Due to this discharge, a positive voltage is generated at the feedback electrode 52, so that the base of the transistor 44 is reverse-biased via the third resistor _R03, and the transistor 44 is turned off, so that the first switch transistor 40 is turned off. ,
The second switch transistor 42 is turned on again. Thereafter, the same operation is repeated, and a high-frequency voltage is applied to the input electrodes 48 and 50 of the piezoelectric transformer 28. As a result, a boosted high-frequency voltage is generated between the input electrode 48 and the output electrode 54, and this high-frequency voltage is applied to the electrodes 46 and 48.
To discharge a discharge lamp La such as a cold-cathode tube.

[0014]

Generally, the resonance characteristics of the output of the piezoelectric transformer 28 with respect to the load are as shown in FIG. 37, and the power conversion efficiency η of the piezoelectric transformer 28 at this time is shown in FIG.
Varies depending on the frequency f of the voltage Vc for driving the piezoelectric transformer 28, and the power conversion efficiency η of the piezoelectric transformer 28 becomes highest when it matches the frequency f _A of the output resonance point (resonance peak). Meanwhile, the resonance characteristics of the piezoelectric transformer 28 is Q-factor high, the width of the frequency f ₁ to be the substantially the same characteristics as the characteristics when the resonance frequency f _A is very narrow (Fig. 3
7).

By the way, in the above-mentioned conventional device, the piezoelectric transformer 28 is operated by self-oscillation, so that the operating frequency of the piezoelectric transformer 28 is determined by the natural frequency of the piezoelectric transformer 28 itself. However, when the load fluctuates, the frequency of the output resonance peak (the frequency at which the power conversion efficiency η of the piezoelectric transformer 28 peaks) f _A or the frequency f _{1 at} which characteristics similar to the above are obtained are obtained.
It is difficult to fix the operating frequency of the device. Further, since the operating frequency by components variation such as a resistor R ₀₃ to give self励信issue of the piezoelectric transformer 28 to the switching element (transistor 44) is changed, the operating frequency as described above in the resonance frequency f _A (or f ₁₎ It is very difficult to fix.

As described above, the conventional device has a problem that the power conversion efficiency η of the piezoelectric transformer 28 cannot be maximized and cannot be maintained. An object of the present invention is to provide a power conversion device that can always maximize the power conversion efficiency of a piezoelectric transformer and can adjust the output even if there are variations in circuit components and the like. is there.

[0017]

According to a first aspect of the present invention, there is provided a piezoelectric transformer including a piezoelectric transformer, the piezoelectric transformer having a frequency equal to or near the resonance frequency at which the power conversion efficiency of the piezoelectric transformer is maximized. Conversion means for driving the piezoelectric transformer to supply power to the load; and adjustment means provided on at least one of the input side and the output side of the conversion means for adjusting the output from the conversion means to the load. The power conversion efficiency of the piezoelectric transformer can always be maximized to achieve high efficiency even when there is variation in circuit components, and the output to the load can be adjusted by the adjusting means.

According to a second aspect of the present invention, in the first aspect of the present invention, when the resonance frequency fluctuates, the driving frequency of the piezoelectric transformer is corrected to a frequency equal to or close to the resonance frequency after the fluctuation. The power conversion efficiency of the piezoelectric transformer can always be maximized by the auxiliary means to achieve high efficiency even when the resonance frequency fluctuates due to a change in the impedance of the load.

According to a third aspect of the present invention, in the first aspect of the present invention, the conversion means constitutes an inverter. The invention according to claim 4 is the invention according to claim 1,
It is characterized in that the load is a discharge lamp, the discharge lamp as a load can be started and steadily lit reliably, and even if there is a temperature change, the power conversion efficiency of the piezoelectric transformer can always be maximized and high efficiency can be obtained, and The output of the discharge lamp can be adjusted by the adjusting means.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the adjustment means comprises a chopper circuit provided on the input side of the conversion means, and the output can be easily adjusted with a simple configuration. According to a sixth aspect of the present invention, in the first aspect of the present invention, the adjusting means comprises a step-down chopper circuit, and outputs the output of the step-down chopper circuit without smoothing.

According to a seventh aspect of the present invention, in the first aspect of the present invention, the adjusting means adjusts an output by controlling a duty ratio or a switching frequency of the chopper circuit having a switch element for interrupting an input. And a control circuit that performs the control. According to an eighth aspect of the present invention, in the third aspect of the present invention, the adjustment means is integrated with the inverter, so that the number of circuit components can be reduced and the size can be reduced.

According to a ninth aspect of the present invention, in accordance with the eighth aspect of the present invention, there is provided a simple configuration comprising means for separately controlling the inverter and means for varying a resonance frequency of a resonance system of the inverter. The output can be easily adjusted by the configuration.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a block diagram showing a first embodiment of the present invention. In this embodiment, the DC power supply 1
, The piezoelectric transformer 4 is provided, and power is supplied to the load 2 by driving the piezoelectric transformer 4 at a frequency f _{1 that} is the same as or near the resonance frequency f _{A at} which the power conversion efficiency η of the piezoelectric transformer 4 is maximized. And an adjusting means B provided on the input side of the converting means A for adjusting the output from the converting means A to the load 2. The piezoelectric transformer 4 may be the same as the piezoelectric transformer 28 in the conventional example.

The converting means A includes a piezoelectric transformer 4 and a piezoelectric transformer driving circuit 3 which receives the voltage V ₂ adjusted by the adjusting means B and outputs a periodically changing voltage V ₃ to drive the piezoelectric transformer 4. , an output voltage detection circuit 5 for detecting the output voltage V ₄ of the piezoelectric transformer 4, a differentiating circuit 6 to obtain the differential value of the detection voltage of the output voltage detection circuit 5, depending on the differential value of the detected voltage obtained from the differentiating circuit 6 It has and a frequency control circuit 7 for variably controlling the frequency f of the driving voltage V ₃ of the piezoelectric transformer 4 Te. Instead of the output voltage detection circuit 5 may be used an output current detection circuit for detecting an output current I ₄ of the piezoelectric transformer 4.

On the other hand adjusting means B includes an output adjustment circuit 8 for outputting a desired voltage V ₂ by adjusting the DC voltages V ₁ from the DC power source 1, the output adjusting circuit based on detected voltage of the output voltage detection circuit 5 8 switching element (to be described later)
Width control circuit 9 for controlling ON time (pulse width)
And FIG. 2 shows a specific example of the piezoelectric transformer drive circuit 3, in which a choke coil La and a switching element Sa are connected in series between output terminals of an output adjustment circuit 8, and a piezoelectric transformer 4 is connected to both ends of the switching element Sa. It is configured. FIG. 3 shows a frequency control circuit 7.
And a drive signal V ₃ (see FIG. 2B) applied to the piezoelectric transformer 4. That is, the driving voltage V ₃ applied to the piezoelectric transformer 4 is half-wave sinusoidal waveform in this case.

FIG. 4 shows another specific example of the piezoelectric transformer driving circuit 3 in which a pair of switching elements Sb ₁ and Sb ₂ are connected in series between the output terminals of the output adjusting circuit 8 and the switching on the low potential side is performed. which are connected to the piezoelectric transformer 4 via a choke coil Lb in parallel with the element Sb _2. FIG. 5 shows a drive signal for the switching elements Sb ₁ and Sb ₂ output from the frequency control circuit 7 (see FIGS. 5A and 5B) and a drive voltage V ₃ applied to the piezoelectric transformer 4 (see FIG. 5). (See (c)). That is, the driving voltage V ₃ applied to the piezoelectric transformer 4 is a sinusoidal waveform in this case. FIG. 6 shows another specific example of the piezoelectric transformer drive circuit 3. A series circuit of choke coils Lc ₁ and Lc ₂ and switching elements Sc ₁ and Sc ₂ is connected in parallel between output terminals of an output adjustment circuit 8. With the choke coil Lc ₁ and the switching element S
which are connected to the piezoelectric transformer 4 during the connection points and the choke connection points coil Lc ₂ and the switching element Sc ₂ c _1. FIG. 7 shows the driving signals (see FIGS. 7A and 7B) of the switching elements Sc ₁ and Sc ₂ output from the frequency control circuit 7 and the driving voltage V ₃ applied to the piezoelectric transformer 4 (FIG. (See (c)). That is, the driving voltage V ₃ applied to the piezoelectric transformer 4 is a sinusoidal waveform in this case.

FIG. 8 shows the piezoelectric transformer driving circuit 3 further.
Another specific example is shown, in which a pair of
Switching element Sd₁, Sd_TwoSeries circuit and a pair
Switching element Sd_Three, Sd_FourIn parallel with the series circuit of
Connection and switching elements in each series circuit.
Child Sd₁, Sd_Two, Sd_Three, Sd_FourBetween the connecting points
The lance 4 is connected. FIG. 9 shows the frequency.
Switching element Sd output from number control circuit 7₁~
Sd_FourDrive signals (see FIGS. 7A to 7D) and piezoelectric signals
Drive voltage V applied to transformer 4_Three(See figure (e)
). In this case, the voltage is applied to the piezoelectric transformer 4.
Drive voltage V_ThreeIs a square waveform that is periodically inverted
Becomes As described above, the piezoelectric transformer driving circuit 3
Drive voltage V _ThreeThe piezoelectric transformer 4 is excited by the
Output voltage V_FourIs obtained, and in this embodiment,
The conversion means A converts the DC input voltage V_TwoThe AC output voltage
V_FourIt is configured as an inverter that converts to

On the other hand, FIG. 10 shows a specific example of the output adjusting circuit 8, together with the connecting switching elements Q ₁ consisting of a bipolar transistor through a choke coil L ₁ between the output terminals of the DC power supply 1, the switching element Q ₁ , A diode C ₁ and a capacitor C ₁ are connected in series at both ends of the capacitor C ₁ , and an output voltage V ₂ is taken out from both ends of the capacitor C ₁ . By switching element Q ₁ is turned on and off by a drive signal from the pulse width control circuit 9, the voltage V ₂ obtained by boosting the input voltages V ₁ is output. Note that the pulse width control circuit 9 performs control (PWM control) for varying the pulse width of the drive signal so that the detection voltage of the output voltage detection circuit 5 becomes a predetermined level. It is possible to adjust the power to be applied. FIG. 11 shows the output adjustment circuit 8.
Other showing a specific example, a switching element Q ₂ and the diode D ₂ consisting of bipolar transistors with series connected between the output ends of the DC power source 1, the output voltage from both ends of the diode D ₂ via a choke coil L ₂ and it has a step-down chopper circuit which is to extract the V _2. In this case, the switching element Q ₂ is connected to the pulse width control circuit 9.
Is turned on and off by the drive signal from
Voltage V ₂ obtained by stepping down an input voltage V ₁ is output.

FIG. 12 shows the driving power for driving the piezoelectric transformer 4.
Pressure V_ThreeOutput from the piezoelectric transformer 4 with respect to the frequency f
Voltage V_Four(Or the output current I_Four)
FIG. As is apparent from FIGS.
Dynamic voltage V_ThreeIs the output voltage V of the piezoelectric transformer 4
_Four(Or the output current I_Four) Is the peak resonance frequency
f_A, The power conversion efficiency η of the piezoelectric transformer 4 is maximized.
It approaches the maximum value. Therefore, in this embodiment, the piezoelectric
Drive voltage V output from transformer drive circuit 3 _ThreeFrequency
The number f is the resonance frequency f_AFrequency f which is the same as or near₁
So that the piezoelectric transformer
The drive circuit 3 is controlled.

As shown in FIG. 12, the frequency control circuit 7 first generates the drive voltage V ₃ having a frequency f ₀ higher than the resonance frequency f _A, and continuously generates the frequency f of the drive voltage V ₃ therefrom. The switching element Sa included in the piezoelectric transformer drive circuit 3 so as to lower (sweep)
.. Are controlled. Thus, the output voltage V ₄ of the piezoelectric transformer 4 gradually increases as the frequency f decreases, and when the output voltage V ₄ becomes a frequency f ₁ near the resonance frequency f _A at which the output voltage V ₄ reaches a peak, the output voltage V ₄ is given from the differentiating circuit 6. The differential value dV ₄ / dt of the detected voltage obtained becomes substantially zero. Therefore, when the differential value dV ₄ / dt ≒ 0, the frequency control circuit 7 stops sweeping the operating frequency of the switching elements Sa... And maintains the operating frequency at that time. also the frequency f of the driving voltage V ₃ outputted from the 3 is maintained at f = f _1, so that output voltage V ₄ of the piezoelectric transformer 4 is in a state close to the peak value,
The power conversion efficiency η of the piezoelectric transformer 4 becomes a value very close to the maximum value.

Alternatively, the frequency control circuit 7 is constituted by a microcomputer, and when the frequency f of the drive voltage V ₃ is continuously reduced (swept) from the initial frequency f ₀ , the differentiation circuit is provided at intervals of a short time Δt. Differential value d from 6
V ₄ / dt is taken, and the n-th differential value (dV ₄ / dt)
_n and the previous (n-1) th differential value (dV ₄ / dt) _{n- 1}
And (dV ₄ / dt) _n <(dV ₄ / dt)
_Since the frequency f becomes the frequency f ₁ near the resonance frequency f _A when the relationship of _n−1 is established, the frequency f is detected and the sweep of the frequency f is stopped, and the frequency f of the drive voltage V _{3 is} reduced.
May be maintained at f = f ₁ . When an output current detection circuit is used instead of the output voltage detection circuit 5, the output voltage detection circuit 5 is almost the same except that the differential value is dI ₄ / dt instead of dV ₄ / dt.

On the other hand, after the driving frequency f of the piezoelectric transformer 4 in the converting means A becomes f = f ₁ as described above, in the adjusting means B, the pulse width control circuit 9 outputs the signal from the output voltage detecting circuit 5. The detection voltage is compared with a reference value held by the pulse width control circuit 9 itself, and the pulse width of a drive signal for turning on / off the switching elements Q ₁ of the output adjustment circuit 8 is varied according to the difference voltage. Thus, the output from the conversion means A to the load 2 is adjusted to be substantially constant.

As described above, according to the present embodiment, the piezoelectric transformer 4 is driven at a frequency f _{1 which} is the same as or near the resonance frequency f _{A at} which the power conversion efficiency η of the piezoelectric transformer 4 is maximized.
Is driven, the power conversion efficiency η of the piezoelectric transformer 4 can always be maximized even if there are variations in the components constituting the circuit. In addition, the provision of the adjusting means B makes it possible to adjust the output to the load 2.

When a discharge lamp is used as the load 2, the frequency control of the conversion means A may be performed after the discharge lamp is turned on. (Embodiment 2) FIG. 13 is a block diagram showing a second embodiment of the present invention. As shown in FIG. 13, the present embodiment has the same basic configuration as that of the first embodiment. Therefore, the common components are denoted by the same reference numerals, and description thereof will be omitted. Will be described only. The feature of the present embodiment is that, when the resonance frequency f _A of the piezoelectric transformer 4 fluctuates, the correction means for correcting the drive frequency f of the piezoelectric transformer 4 to a frequency f ₁ ′ that is the same as or close to the resonance frequency f _A ′ after the fluctuation. C.

The correction means C comprises a phase control circuit 10 and a frequency control circuit 7. The phase control circuit 10 detects the phase between the output voltage V ₄ of the piezoelectric transformer 4 and the input voltage V _3, and changes the output voltage V ₄ according to the impedance change of the load 2.
When the phase is advanced or delayed from a certain state, a detection signal corresponding to a change in the phase is output to the frequency control circuit 7.

On the other hand, the frequency control circuit 7 receiving the detection signal from the phase control circuit 10 raises or lowers the operating frequency of the switching elements Sa... Provided in the piezoelectric transformer drive circuit 3 again. Thus, varied by the impedance change of the load 2, the power conversion efficiency of the piezoelectric transformer 4 eta is the 'frequency f ₁ of the same or near the' resonance frequency f _A which is a maximum, to correct the frequency f of the driving voltage V ₃ be able to.

The operation of the correcting means C will be described with reference to FIGS.
This will be described in more detail with reference to FIG. FIG. 14 shows a piezoelectric transformer 4
Drive voltage V for driving_ThreeFor the frequency f
Voltage V output from the sense 4_Four(Or output current
I_Four) Is a diagram showing the resonance characteristics of FIG.
Before the impedance changes, the curve b shows the impedance of load 2.
Each resonance characteristic after the dance changes (decreases).
You. FIG. 15 shows an equivalent circuit of the piezoelectric transformer 4.
And a capacitor between the output terminals of the piezoelectric transformer drive circuit 3.
C_TwoAnd the inductance L_Three, Capacitor C_Three, Resistance R
₁And the series circuit of the primary winding of the transformer T is connected in parallel
And the secondary winding of the transformer T and the capacitor C _FourAnd load
2 are connected in parallel.

First, as described in the first embodiment, the conversion method
In stage A, the power conversion efficiency η of the piezoelectric transformer 4 is maximized.
Resonance frequency f_AFrequency f which is the same as or near₁Drive power
Pressure V _ThreeDrives the piezoelectric transformer 4. At this time
The resonance characteristic is represented by a curve a in FIG. Here, load 2
Let's consider the case where the impedance has decreased. At this time
Is the output voltage V of the piezoelectric transformer 4_ThreeThe resonance characteristics of
From the curve a to the curve b (shift to the left)
Wave number f_AAlso f_A’. Also, the piezoelectric transformer
4 output voltage V_FourDecreases from point a on curve a to curve b.
Move to point b above. Thus, the impedance of load 2
In the case where the power is reduced, it is apparent from the equivalent circuit of FIG.
Output voltage V of the piezoelectric transformer 4_FourPhase is delayed.
Therefore, the output voltage V_FourRank
Detects phase delays and frequency-controls the detection signals.
Output to the control circuit 7. As a result, the frequency control circuit 7
Switching element Sa included in electric transformer drive circuit 3
... is the operating frequency f₁Drops continuously from (sweep)
And output voltage detection as described in the first embodiment.
The differential value obtained by differentiating the detection voltage of the circuit 5 by the differentiating circuit 6 is substantially zero.
Stops sweeping the operating frequency when
Shear resonance frequency f_A′₁’
Drive voltage V at (point c on curve B)_ThreeWith the piezoelectric transformer 4
Drive.

On the other hand, when the impedance of the load 2 increases, the resonance frequency f _A ′ increases to f _A (point d on the curve B). it is necessary to the switching elements Sa ... operating frequency f of which includes increased from f ₁ 'to f _1. Here, since the phase of the output voltage V ₄ of the piezoelectric transformer 4 when the impedance of the load 2 increases progresses, the phase control circuit 10
And outputs a detection signal to the frequency control circuit 7. Then, in the frequency control circuit 7,
Switching element S included in piezoelectric transformer drive circuit 3
The operating frequency f of a is continuously increased (swept) from f ₁ ′, and as described in the first embodiment, the differential value obtained by differentiating the detection voltage of the output voltage detection circuit 5 by the differentiation circuit 6 is substantially zero. The sweep of the operating frequency is stopped when the frequency becomes f _{1, and} the frequency f _{1 that} is the same as or near the new resonance frequency f _A is
Driving the piezoelectric transformer 4 in the driving voltage V ₃ of (a point on the curve b).

According to the present embodiment as described above, the piezoelectric
Resonance frequency f of lance 4_AThe piezoelectric transformer
Frequency f after the drive frequency f of the_A’
Frequency f which is the same as or near₁’Correction means C
Equipped, not only the variation of the circuit components but also the load 2
Even if the impedance changes suddenly, the piezoelectric transformer
Frequency f at which the power conversion efficiency η of_ASame as
One or near frequency f ₁To drive the piezoelectric transformer 4
be able to. In this embodiment, the embodiment
Output to load 2 can be adjusted by adjusting means B as in 1
Needless to say, it is noh.

(Embodiment 3) FIG. 16 is a block diagram showing a third embodiment of the present invention, in which the load 2 in Embodiment 2 is a discharge lamp La. Therefore, the other configuration is the same as that of the second embodiment, and the common components are denoted by the same reference numerals and the description thereof is omitted.

FIG. 17 shows the voltage V ₄ output from the piezoelectric transformer 4 with respect to the frequency f of the driving voltage V ₃ for driving the piezoelectric transformer 4 when the load 2 is a discharge lamp La.
Curve C shows the resonance characteristics when the impedance before the discharge lamp La is turned on is almost infinite, and curve D shows the resonance characteristics when the impedance after the discharge lamp La is turned on has a finite value. I have.

Next, the circuit operation of this embodiment will be described. First, before the discharge lamp La is turned on, the frequency control circuit 7 of the conversion means A turns on and off the switching elements Sa... Of the piezoelectric transformer drive circuit 3 at a frequency f ₀ higher than the resonance frequency of the piezoelectric transformer 4. Piezoelectric transformer drive circuit 3
, The piezoelectric transformer 4 is driven by the driving voltage V ₃ (frequency f ₀ ), and the frequency f is gradually reduced from f ₀ . At this time, the output voltage V ₄ of the piezoelectric transformer ₄ is
In rises along the a point on the curve C in the curve C, release it reaches the output voltage V ₄ is the frequency f at the f = f _K in the starting voltage V _A of the discharge lamp La (b point on the curve c) The lamp La starts and the load impedance changes from infinity to a finite value (= R).
To decrease. As a result, the resonance characteristic changes from the curve C to the curve D, and the output voltage V ₄ of the piezoelectric transformer ₄ becomes b
Move from point (starting voltage V _A ) to point c on curve d (decrease)
I do.

As described in the second embodiment, the load impedance
When the dance is infinite, the input voltage of the piezoelectric transformer 4
V_ThreeAnd output voltage V_FourPhase with the load impedance
When the inductance decreases to a finite value R, the output voltage V_Fourof
The phase will be delayed. Then, the discharge lamp La is turned on.
As a result, the resonance characteristic changes from curve C to curve D, and the output voltage V _Four
Moves from point b on curve c to point c on curve d,
The output voltage V is output from the phase control circuit 10 of the correcting means C._FourPhase of
Is detected, the frequency control circuit 7 operates the piezoelectric transformer.
Control of the driving circuit 3 as described in the second embodiment.
Drive voltage V_ThreeFrequency f_KGradually lowering
When the power conversion efficiency η of the piezoelectric transformer 4 is maximized.
Frequency f_AFrequency f which is the same as or near₁Drive voltage V_Three
Is maintained at the frequency f. Also, when the discharge lamp La is turned on,
The output supplied to the discharge lamp La by the adjusting means B
Can be adjusted.

As described above, according to the present embodiment, the load 2
Is a discharge lamp La, the start-up and stable lighting of the discharge lamp La can be reliably performed, and the power conversion efficiency η of the piezoelectric transformer 4 is maximized during the steady lighting of the discharge lamp La, so that the efficiency becomes higher. The output of the electric lamp La can be kept constant. In addition, the discharge lamp La changes due to a temperature change.
Of the second embodiment even when the load impedance of
As described above, the power conversion efficiency η of the piezoelectric transformer 4 can always be maximized by the operation of the correction means C, and the discharge lamp La can be constantly lit with high efficiency and the output can be kept constant. It is needless to say that the same effect can be obtained even if there is variation in circuit components.

The output current of the piezoelectric transformer 4 is detected.
An output current detection circuit is provided in series with the discharge lamp La to detect the output current.
Output current to the pulse width control circuit 9 of the adjusting means B
In this case, the output adjustment circuit 8 is controlled by the pulse width control circuit 9.
Is pulse width controlled to keep the output current of the discharge lamp La constant.
It is also possible. (Embodiment 4) This embodiment is different from Embodiments 1 to 3 above.
FIG. 18 discloses a specific example of the output adjustment circuit 8 in FIG.
The circuit diagram is shown. That is, the DC power supply 1 and the piezoelectric
Bipolar transistor between transformer drive circuit 3
Switching element Q_ThreeConnected in series for output adjustment
A circuit 8 is configured. This switching element Q_ThreeIs
Square wave drive signal given from pulse width control circuit 9
(See FIG. 19A). Sand
That is, as shown in FIG. _Threeof
Output voltage V of piezoelectric transformer 4 when on_Four(Output current
I_Four) Is supplied to the load 2 and detected by the output voltage detection circuit 5.
The output voltage V is determined based on the integrated value of the output detection voltage. _FourOne
In order to make the pulse width constant, the pulse width control circuit 9
The width W (see FIG. 19A) is adjusted and PWM control is performed.
Output voltage V_FourIs adjusted.

According to the present embodiment, only one switching element is required for the configuration of the output adjustment circuit 8, and the circuit can be downsized. (Embodiment 5) FIG. 20 is a block diagram showing a fifth embodiment of the present invention. As shown in FIG. 20, the present embodiment has the same basic configuration as that of the first embodiment. Therefore, the common components are denoted by the same reference numerals, and description thereof will be omitted. Will be described only. The feature of the present embodiment is that the adjusting means B is provided on the output side of the converting means A, specifically, the output adjusting circuit 8 is provided between the piezoelectric transformer 4 and the output voltage detecting circuit 5.

FIG. 21 shows a specific circuit example of the output adjusting circuit 8 according to the present embodiment, in which a switching element Q ₄ composed of a bipolar transistor connected in series between the piezoelectric transformer 4 and the output voltage detecting circuit 5, the output side of the conversion means a during off element Q ₄ is constituted by a resistor R ₂ to avoid becoming a no load condition. This switching element Q ₄ is turned on by the pulse width control circuit 9.
WM is controlled, thereby it is the adjustment of the output voltage V ₄ of the conversion means A (piezoelectric transformer 4) are performed. In addition,
Operation of the conversion means A is common to Embodiment 1, the power conversion efficiency η of the piezoelectric transformer 4 in the present embodiment are controlled frequency f of the driving voltage V ₃ to maximize always maintained high circuit efficiency it can.

(Embodiment 6) This embodiment discloses a specific example of the output adjustment circuit 8 in Embodiment 5 described above.
FIGS. 22A and 22B are circuit diagrams thereof. FIG.
(A) In the circuit example shown in, the piezoelectric transformer 4 and the output voltage output adjustment circuit a series circuit of a switching element Q ₅ consisting of impedance elements Z and bipolar transistor having a suitable impedance connected in parallel between the detection circuit 5 8 are configured. That is, the pulse width control circuit 9
When the switching element Q ₅ is turned on and off by,
The output voltage V ₄ is changed by inserting the impedance element Z in parallel to the output side of the piezoelectric transformer 4 only when turned on, and the on-time of the switching element Q ₅ is changed by the output voltage detection circuit 5 and the pulse width control circuit 9. Thus, the output (= V ₅ ) supplied to the load 2 can be adjusted.

[0050] Further, FIG. 22 in the circuit example shown in (b), the impedance element Z and an output adjusting circuit 8 are connected in series between the parallel circuit of the switching elements Q ₅ and the piezoelectric transformer 4 and the output voltage detection circuit 5 Is configured. That is,
When the switching element Q ₅ by the pulse width control circuit 9 in the case of this circuit example is turned off, the impedance element Z only when off is inserted in series between the piezoelectric transformer 4 and the output voltage detection circuit 5 output voltage V ₄ changes in the load by changing the oN time of the switching element Q ₅ by the output voltage detection circuit 5 and a pulse width control circuit 9 2
Can be adjusted (= V ₅ ).
It should be noted that the impedance element Z may be constituted by a resistor, an inductance or a capacitor alone or in combination.

(Embodiment 7) FIG. 23 is a block diagram showing a seventh embodiment of the present invention. As shown in FIG.
Since the basic configuration of the present embodiment is the same as that of the first embodiment, common portions are denoted by the same reference numerals, and description thereof will be omitted. Only the features that are characteristic of the present embodiment will be described. The feature of this embodiment lies in that the piezoelectric transformer drive circuit 3 of the conversion means A and the output adjustment circuit 8 of the adjustment means B are integrally formed as a piezoelectric transformer drive circuit 11 having an output adjustment function. Figure 24 is a piezoelectric transformer drive circuit having an output adjusting function of the present embodiment (hereinafter, simply piezoelectric abbreviated as transformer drive circuit) shows a specific circuit example of 11, a so-called four switching element S ₂₁ to S ₂₄ are bridge-connected It is configured as a full-bridge type inverter circuit. These switching element S ₂₁ to S _24, the drive signals two sets of switch elements located diagonally S ₂₁ and S _24, S ₂₂ and S ₂₃ is supplied from the pulse width control circuit 9 'as shown in FIG. 25 Are alternately turned on and off. As a result, a rectangular wave whose polarity is periodically inverted as shown in FIG. 25 is applied to the piezoelectric transformer 4 connected between the connection points of the sets of the switch elements S ₂₁ and S ₂₄ and S ₂₂ and S ₂₃ . The driving voltage V ₃ ′ is output,
The piezoelectric transformer 4 is driven.

[0052] Here, by thinning the pulse width control circuit 9 'a drive signal for the set S ₂₂ and S ₂₃ of one of the switch elements during a time width W ₁ as shown in FIG. 25, the time width W ₁ In the period, the driving voltage V ₃ ′ of the piezoelectric transformer 4
Negative voltage disappears and decreases. That is, the output voltage V ₄ ′ of the piezoelectric transformer 4 can be changed by changing the drive voltage V ₃ ′ of the piezoelectric transformer 4. Therefore, the output voltage V ₄ ′ of the piezoelectric transformer 4 can be adjusted by varying the time width W ₁ by the pulse width control circuit 9 ′. As in the first embodiment, the operating frequency of the piezoelectric transformer drive circuit 11 (the frequency f of the drive voltage V ₃ ′) is changed by the frequency control circuit 7 to the resonance frequency f at which the power conversion efficiency η of the piezoelectric transformer 4 is maximized.
It is the frequency f ₁ of the same or near the _A.

According to the present embodiment, a part of the adjusting means B (output adjusting circuit) is integrally formed with the inverter circuit constituting the converting means A, so that the number of parts can be reduced and the size can be reduced. There is an advantage that it can be achieved. Note that FIG.
As shown in (2), if the correction means C provided with the phase control circuit 10 is provided in the conversion means A, not only the variation of the circuit components but also the impedance of the load 2 suddenly changes, as in the second embodiment. _A frequency f _{1 that} is equal to or close to the resonance frequency f _{A at} which the power conversion efficiency η of the piezoelectric transformer 4 is maximized.
Thus, the piezoelectric transformer 4 can be driven.

(Eighth Embodiment) This embodiment discloses another specific example of the piezoelectric transformer drive circuit 11 in the seventh embodiment, and FIG. 27 shows a circuit diagram thereof. Piezoelectric transformer drive circuit 11 in this embodiment, a series circuit of the inductance L ₁₁ and the switch element S _11, with bridges connected in parallel to the DC power source 1 and a series circuit of inductance L ₁₂ and the switch element S _12, S ₁₃ The drive voltage V ₃ ′ to the piezoelectric transformer 4 is extracted from between the connection point between the inductance L ₁₁ and the switch element S _{11 and} the connection point between the switch elements S ₁₂ and S ₁₃ .

Next, the operation of the piezoelectric transformer drive circuit 11 will be described with reference to FIG. Each switching element S ₁₁ to S ₁₃ are turned on and off by the drive signal provided from the pulse width control circuit 9 '. Switching element S ₁₂ connected in series to the inductance L ₁₂ is held in the normal ON state, the remaining switching element S _11, S ₁₃ are turned on and off alternately. When switch element S ₁₁ is on and S ₁₃ is off,
Energy is stored by the output of the DC power source 1 through the switching elements S ₁₁ to the inductance L _11. Inductance L ₁₂ which has already been accumulated energy simultaneously resonate with the capacitive component of the piezoelectric transformer 4, the piezoelectric transformer 4 is negative resonant voltage V ₃ 'is output.

Meanwhile, when the switch element S ₁₁ is turned off, S ₁₃ is on, with the energy is accumulated in the inductance L ₁₂ through the switching element S _12, S ₁₃ by the output of the DC power source 1, already energy storage inductance L ₁₁ being resonates with the capacitance component of the piezoelectric transformer 4, a positive resonant voltage V ₃ 'is output to the piezoelectric transformer 4. Therefore, if the switch elements S ₁₁ and S ₁₃ are turned on and off alternately, a substantially sinusoidal AC voltage (drive voltage) V ₃ ′ as shown in FIG. 28 is output to the piezoelectric transformer 4.

[0057] Here, if the pulse width control circuit 9 'the switching element S ₁₂ is synchronized with the switching element S ₁₁ by by on and off during the time width W ₂ as shown in FIG. 28, the output to the piezoelectric transformer 4 The driving voltage V ₃ ′ can be changed. That is, the time t ₁ ~t ₂ in FIG. 28
When the switch element S ₁₂ in the period are turned off and the switch element S ₁₁ at this time is off, since S ₁₃ is on, resonates with the capacitance component of the inductance L ₁₁ and the piezoelectric transformer 4 energy is accumulated The positive drive voltage V ₃ ′ (= V ₃₁ ) is output to the piezoelectric transformer 4. Further, since the switching element S ₁₂ at this time is off, the energy is not accumulated in the inductance L _12. Next, at time t ₂ ~t ₃
Switching element S ₁₂ is turned on in the period, S ₁₁ is turned on, the S ₁₃ is turned off, the switch element is an inductance L ₁₁ S
Although energy through the ₁₁ is accumulated, the piezoelectric transformer 4 driving voltage V ₃ is output to the 'negative voltage V ₃₂ becomes the resonance of the capacitive component of the inductance L ₁₂ and the piezoelectric transformer 4 which energy is not stored, Its absolute value is from time t ₁
lower than the drive voltage V ₃₁ of the period of t _2. Thereafter, the operation until time t ₇ are alternately repeated, the driving voltage V ₃ '
The negative part of 低下 decreases and decreases. Therefore, the output voltage V ₄ ′ of the piezoelectric transformer 4 can be adjusted by varying the time width W ₂ by the pulse width control circuit 9 ′.

As in the first embodiment, the operating frequency of the piezoelectric transformer drive circuit 11 (the frequency f of the drive voltage V ₃ ′) is controlled by the frequency control circuit 7 so that the power conversion efficiency η of the piezoelectric transformer 4 is maximized. is the frequency f ₁ of the same or near the f _a. (Embodiment 9) In the present embodiment, another specific example of the piezoelectric transformer drive circuit 11 in Embodiment 7 is disclosed, and FIG. 29 shows a circuit diagram thereof.

The piezoelectric transformer drive circuit 11 in this embodiment is configured as a so-called full bridge type inverter circuit in which four switch elements S _{31 to} S ₃₄ are connected in a bridge. These switch elements S _{31 to} S ₃₄ are composed of series-connected switch elements S ₃₁ and S ₃₂ and S ₃₃ and S ₃₄ shown in FIG.
0 alternately turned on and off for each set by a drive signal supplied from the pulse phase control circuit 12 as shown in, the switching element S ₃₁ by changing the phase of the on and off by the pulse phase control circuit 12 S ₃₂ , the time during which _S33 and _S34 are simultaneously turned on can be changed. That is, the power supplied to the load 2 is adjusted by changing the time during which the piezoelectric transformer 4 is connected to the power supply.

Next, the operation of the piezoelectric transformer drive circuit 11 will be described with reference to FIG. Each of the switch elements S _{31 to} S ₃₄ is turned on / off by a drive signal provided from the pulse phase control circuit 12. When the switch element S ₃₁ is turned on and S ₃₂ is turned off at time t ₁ , the positive drive voltage V ₃ ′ is output to the piezoelectric transformer 4 because the switch element S ₃₄ is already on at that time. When the switch element S ₃₄ at time t ₂ is turned off, S ₃₃ are turned on, drive voltage V ₃ 'is zero. Then switching element S ₃₂ at time t ₃ and is turned on, the S ₃₁ is turned off, because the switch element S ₃₃ has already been turned on, the piezoelectric transformer 4 negative driving voltage V ₃ 'is output. Further switching element S ₃₄ is turned on at time t _4, the S ₃₃ is turned off, the driving voltage V ₃ 'is zero. Thereafter, the above operation is repeated, and a rectangular wave drive voltage V ₃ ′ that is periodically inverted and has a pause period is output to the piezoelectric transformer 4.

[0061] Here, changing the phase of the on-time of the switching element S ₃₃ and S ₃₄ to the switch elements S ₃₁ and S _32,
If the phase difference θ between the two is increased, the idle period of the drive voltage V ₃ ′ is increased, and the time width W ₃ of the output period is reduced. Therefore, the drive voltage V ₃ ′ decreases, the power supplied to the load 2 decreases, and the power amount can be adjusted. Therefore, if the switch elements S _{31 to} S ₃₄ are driven by the pulse phase control circuit 12 so as to vary the phase difference θ, the output voltage V ₄ ′ of the piezoelectric transformer 4 can be adjusted. As in the first embodiment, the operating frequency (frequency f of the driving voltage V ₃ ′) of the piezoelectric transformer driving circuit 11 is set to the resonance frequency f _{A at} which the power conversion efficiency η of the piezoelectric transformer 4 is maximized by the frequency control circuit 7. It is the frequency f ₁ of the same or near.

(Embodiment 10) This embodiment discloses another specific example of the piezoelectric transformer drive circuit 11 in Embodiment 7 and FIG. 31 shows a circuit diagram thereof. The piezoelectric transformer drive circuit 11 according to the present embodiment includes a pair of switch elements S ₄₁ and S ₄₂ connected in series to the DC power supply 1, and a drive voltage of the piezoelectric transformer 4 from one switch element S ₄₂ via a variable inductance Lp _1. V ₃ ′ is taken out. Each of the switch elements S ₄₁ and S ₄₂ is alternately turned on / off by a drive signal supplied from the frequency control circuit 7.
Turned off. As a result, the variable inductance Lp ₁ and the capacitive component of the piezoelectric transformer 4 resonate, and an AC drive voltage V ₃ ′ is output to the piezoelectric transformer 4.

[0063] Here, the inductance control circuit 1 variably controls the inductance of the variable inductance Lp ₁
The driving voltage V ₃ ′ can be increased or decreased by changing the inductance value of the variable inductance Lp ₁ , and as a result, the output voltage V
By changing ₄ ′, the power supplied to the load 2 can be adjusted. As in the first embodiment, the operating frequency (frequency f of the driving voltage V ₃ ′) of the piezoelectric transformer driving circuit 11 is set to the resonance frequency f _{A at} which the power conversion efficiency η of the piezoelectric transformer 4 is maximized by the frequency control circuit 7. It is the frequency f ₁ of the same or near.

(Embodiment 11) In the present embodiment, another specific example of the piezoelectric transformer drive circuit 11 in Embodiment 7 is disclosed, and FIG. 32 shows a circuit diagram thereof. The piezoelectric transformer drive circuit 11 in the present embodiment includes a pair of switch elements S ₅₁ and S ₅₂ connected in series to the DC power supply 1 and a variable capacitor Cp ₁ connected in parallel to one of the switch elements S ₅₂ via an inductance L _5. And the variable capacitor C
The driving voltage V ₃ ′ of the piezoelectric transformer 4 is extracted from both ends of p ₁ . Each switch element S ₅₁ , S ₅₂
Are alternately turned on and off by a drive signal supplied from the frequency control circuit 7. As a result, the inductance L ₅
, The variable capacitor Cp ₁ and the capacitance component of the piezoelectric transformer 4 resonate, and the AC drive voltage V ₃ ′ is
Output to

Here, a capacitance control circuit 14 for variably controlling the capacitance value of the variable capacitor Cp ₁ is provided, and the drive voltage V ₃ ′ can be increased or decreased by changing the capacitance value of the variable capacitor Cp ₁ . As a result, the piezoelectric transformer 4
Of varying the output voltage V ₄ 'can adjust the power supplied to the load 2. In addition, similarly to the first embodiment,
The operating frequency of the piezoelectric transformer drive circuit 11 (the frequency f of the drive voltage V ₃ ′) is controlled by the frequency control circuit 7 to the resonance frequency f _{A at} which the power conversion efficiency η of the piezoelectric transformer 4 is maximized.
The frequency f ₁ is the same as or close to the frequency f ₁ .

[0066]

According to a first aspect of the present invention, a piezoelectric transformer is provided, and power is supplied to a load by driving the piezoelectric transformer at a frequency equal to or near the resonance frequency at which the power conversion efficiency of the piezoelectric transformer is maximized. And the adjusting means provided on at least one of the input side and the output side of the converting means for adjusting the output from the converting means to the load. There is an effect that the power conversion efficiency can always be maximized to achieve high efficiency, and the output to the load can be adjusted by the adjusting means.

According to the second aspect of the present invention, when the resonance frequency fluctuates, the driving frequency of the piezoelectric transformer is corrected to a frequency equal to or close to the resonance frequency after the fluctuation, so that the impedance of the load is reduced. Even when the resonance frequency fluctuates due to the change, there is an effect that the power conversion efficiency of the piezoelectric transformer can always be maximized and the efficiency can be increased by the auxiliary means.

According to the fourth aspect of the present invention, since the load is a discharge lamp, the discharge lamp as the load can be started and steadily lit reliably, and the power conversion efficiency of the piezoelectric transformer can always be maximized even if there is a temperature change. This has the effect that the efficiency can be increased and the output of the discharge lamp can be adjusted by the adjusting means. According to the fifth aspect of the present invention, since the adjusting means comprises a chopper circuit provided on the input side of the converting means, there is an effect that the output can be easily adjusted with a simple configuration.

According to the eighth aspect of the present invention, since the adjusting means is integrated with the inverter, there is an effect that the number of circuit components can be reduced and the size can be reduced. The invention of claim 9 is
Since there are means for separately controlling the inverter and means for varying the resonance frequency of the resonance system of the inverter,
The output can be easily adjusted with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment.

FIG. 2 is a circuit diagram showing a specific example of a piezoelectric transformer driving circuit in the above.

FIG. 3 is a waveform chart for explaining the above operation.

FIG. 4 is a circuit diagram showing a specific example of a piezoelectric transformer drive circuit in the above.

FIG. 5 is a waveform chart for explaining the above operation.

FIG. 6 is a circuit diagram showing a specific example of the piezoelectric transformer drive circuit in the above power supply system.

FIG. 7 is a waveform chart for explaining the above operation.

FIG. 8 is a circuit diagram showing a specific example of a piezoelectric transformer drive circuit in the above power supply circuit.

FIG. 9 is a waveform chart for explaining the above operation.

FIG. 10 is a circuit diagram showing a specific example of the output adjustment circuit of the above.

FIG. 11 is a circuit diagram showing a specific example of the output adjustment circuit in Embodiment 1;

FIG. 12 is a diagram for explaining the operation of the above.

FIG. 13 is a block diagram showing a second embodiment.

FIG. 14 is a diagram for explaining the operation of the above.

FIG. 15 is a circuit diagram showing an equivalent circuit of the piezoelectric transformer in Embodiment 1;

FIG. 16 is a block diagram showing a third embodiment.

FIG. 17 is a diagram for explaining the operation of the above.

FIG. 18 is a circuit diagram illustrating a specific example of an output adjustment circuit according to a fourth embodiment.

FIG. 19 is a waveform chart for explaining the above operation.

FIG. 20 is a block diagram showing a fifth embodiment.

FIG. 21 is a circuit diagram showing a specific example of the output adjustment circuit in Embodiment 1;

FIGS. 22A and 22B are circuit diagrams illustrating specific examples of an output adjustment circuit according to the sixth embodiment.

FIG. 23 is a block diagram showing a seventh embodiment.

FIG. 24 is a circuit diagram showing a specific example of the piezoelectric transformer drive circuit in the above power supply system.

FIG. 25 is a waveform chart for explaining the above operation.

FIG. 26 is a block diagram showing another configuration of the above.

FIG. 27 is a circuit diagram showing a specific example of a piezoelectric transformer drive circuit according to the eighth embodiment.

FIG. 28 is a waveform chart for explaining the above operation.

FIG. 29 is a circuit diagram showing a specific example of a piezoelectric transformer drive circuit according to a ninth embodiment.

FIG. 30 is a waveform chart for explaining the above operation.

FIG. 31 is a circuit diagram showing a specific example of a piezoelectric transformer drive circuit according to a tenth embodiment.

FIG. 32 is a circuit diagram showing a specific example of a piezoelectric transformer drive circuit according to the eleventh embodiment.

FIG. 33 is a block diagram showing a conventional example.

FIG. 34 is a circuit diagram showing a specific example of a main part of the above.

FIG. 35 is a circuit diagram showing a specific example of the current detection circuit in Embodiment 1;

FIG. 36 is a view for explaining the operation of the above.

FIG. 37 is a view for explaining the above operation.

[Explanation of symbols]

 A conversion means B adjustment means 1 DC power supply 2 load 3 piezoelectric transformer drive circuit 4 piezoelectric transformer 5 output voltage detection circuit 6 differentiating circuit 7 frequency control circuit 8 output adjustment circuit 9 pulse width control circuit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H05B 41/02 H05B 41/24 Z 41/24 41/29 C 41/29 H01L 41/08 A

Claims (9)

[Claims] 1. A converter comprising a piezoelectric transformer, driving the piezoelectric transformer at a frequency equal to or near the resonance frequency at which the power conversion efficiency of the piezoelectric transformer is maximized to supply power to a load, and a converter. And an adjustment means provided on at least one of the input side and the output side of the power supply for adjusting the output from the conversion means to the load. 2. The electric power according to claim 1, further comprising a correction unit that corrects the driving frequency of the piezoelectric transformer to a frequency equal to or close to the resonance frequency after the fluctuation when the resonance frequency fluctuates. Conversion device. 3. The power converter according to claim 1, wherein said converter comprises an inverter. 4. The power converter according to claim 1, wherein said load is a discharge lamp. 5. The power converter according to claim 1, wherein said adjusting means comprises a chopper circuit provided on an input side of said converting means. 6. The power converter according to claim 1, wherein said adjusting means comprises a step-down chopper circuit, and outputs the output of the step-down chopper circuit without smoothing. 7. The adjusting means includes a chopper circuit having a switch element for interrupting an input, and a control circuit for controlling an output by controlling a duty ratio or a switching frequency of the switch element. The power converter according to claim 1. 8. The power converter according to claim 3, wherein said adjusting means is integrated with said inverter. 9. A means for separately controlling the inverter.
9. The power converter according to claim 8, further comprising means for varying a resonance frequency of a resonance system of the inverter.