JP2001238469A - Piezoelectric transformer inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer inverter, where a control circuit part is reduced to be suitable for forming an IC chip, and at the same time an input voltage range can be widened. SOLUTION: A coil and a transistor (Q1) are connected to one of the primary- side electrodes of a piezoelectric transformer (5), and a coil (2) and a transistor (Q2) are connected to the other. A discharge tube (6) is connected to the secondary side of the piezoelectric transformer (5), a current flowing in the discharge tube (6) is detected by a resistor (R8), and the current is controlled by a drive frequency control circuit (3) so that the current becomes constant. A third transistor (Q3) is connected between the other ends of the first and second coils (1 and 2) and an input voltage, the voltage between the primary-side electrodes of the piezoelectric transformer is detected by resistors (R1 and R2), and the transistor (Q3) is made to turn on and off, thus reliving increase in an average output voltage, even if input voltage is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric transformer inverter, and more particularly to a piezoelectric transformer inverter for lighting a discharge tube such as a cathode tube used for a backlight of a liquid crystal display.

[0002]

2. Description of the Related Art FIG. 11 is a block diagram showing an example of a conventional piezoelectric transformer inverter.
No. 4 publication. In FIG. 11, a booster circuit 20 turns on and off two transistors Q1 and Q2 alternately. Electromagnetic energy is accumulated in the coils 1 and 2 during the on-periods of the transistors Q1 and Q2, and during the off-periods of the transistors Q1 and Q2, a half-wave sinusoidal voltage is generated by LC resonance of the coils 1, 2 and the input capacitance of the piezoelectric transformer 5. Is input to the piezoelectric transformer 5. Two transistors Q1,
By alternately driving Q2, push-pull driving is performed, and the voltage difference between the primary electrodes of the piezoelectric transformer 5 becomes substantially a sine wave.

The frequency control circuit 23 varies the drive frequency of the booster circuit 20 so as to control the current flowing to the load at a constant level. Further, when the input voltage VDD increases,
A drive voltage control circuit 22 is provided to avoid the phenomenon that the current flowing through the coils 1 and 2 increases and the drive frequency of the piezoelectric transformer 5 increases and the loss of the inverter increases. The on / off duty of the transistor of the drive voltage control circuit 22 is controlled such that the peak voltage of the side voltage is controlled to a constant value. The operation of the drive voltage control circuit 22 realizes a circuit with less reduction in efficiency even when the input voltage range is wide. This conventional piezoelectric transformer inverter is characterized in that the output of the oscillator driving the drive voltage control circuit 22 is divided by two by the frequency divider circuit 21 to provide a drive signal for the booster circuit 20, and is suitable for a one-chip IC. Circuit configuration.

[0004]

However, FIG.
The conventional piezoelectric transformer inverter described in (1) has a problem that the control circuit portion is large, the circuit scale is large, and the mounting area is large. The conventional example shown in FIG. 11 has a circuit configuration suitable for a one-chip IC, and it is useful to form a one-chip IC in order to reduce the mounting area. However, in an actual application, the input voltage range may be wide or narrow, and conversely, if a single-chip IC is used, the degree of freedom in design may be reduced, resulting in a high-cost circuit. That is, even in an application in which the input voltage range is narrow and the performance can be sufficiently obtained without the drive voltage control circuit 22, an expensive IC based on the premise of the drive voltage control circuit 22 must be used. There was a problem of getting it.

Therefore, a main object of the present invention is to suppress an increase in the output voltage of a transistor for chopping an input voltage even if the input voltage increases, to reduce a decrease in conversion efficiency of an inverter, and to achieve a simple circuit configuration. It is an object of the present invention to provide a piezoelectric transformer inverter that can be realized by the above.

[0006]

The invention according to claim 1 is
A piezoelectric transformer for converting an AC voltage input to the primary side into a voltage and outputting the converted voltage to the secondary side; a first coil and a first transistor connected to one of the primary electrodes of the piezoelectric transformer; Detecting a second coil and a second transistor connected to the other of the primary electrodes, a discharge tube connected to the secondary side of the piezoelectric transformer, and a current flowing through the discharge tube;
A drive frequency control circuit for variably controlling the frequency of a drive signal for alternately controlling the conduction of the first transistor and the second transistor so that the current value is substantially constant; and the other terminals of the first and second coils A third transistor inserted between a connection point of the piezoelectric transformer and an input power supply; a current holding circuit connected between a connection point of the first and second coils and a ground potential; A primary inter-electrode voltage divider for detecting a voltage between the electrodes, and a third transistor that is controlled to conduct using the output of the primary inter-electrode voltage divider, so that the third transistor is activated even when the input voltage increases. And a control circuit for controlling an increase in the average output voltage of the transistors.

According to a second aspect of the present invention, there is provided a piezoelectric transformer for converting an AC voltage inputted to the primary side to output to a secondary side, and a first transformer connected to one of the primary side electrodes of the piezoelectric transformer. The second coil and the second transistor connected to the other coil and the first transistor and the other of the primary side electrodes of the piezoelectric transformer, the discharge tube connected to the secondary side of the piezoelectric transformer, and the discharge tube A drive frequency control circuit for detecting a current and variably controlling a frequency of a drive signal for alternately controlling conduction of the first transistor and the second transistor so that the current value becomes substantially constant; A third transistor inserted between the connection point of the other terminal of the coil and the input power supply, a current holding circuit connected between the connection point of the first and second coils and the ground potential, 1st and 2nd tran Control for controlling conduction of the third transistor using a signal obtained by subjecting the driving signal of the transistor to waveform processing, so that even if the input voltage increases, the average output voltage of the third transistor is controlled to be reduced. And a circuit.

According to the third aspect of the present invention, a piezoelectric transformer for converting an AC voltage inputted to the primary side into a voltage and outputting the converted voltage to the secondary side, and a secondary terminal connected to one of the primary side electrodes of the piezoelectric transformer. And a first transistor having an intermediate terminal connected to the first transistor.
An autotransformer, a second autotransformer having a secondary terminal connected to the other of the primary electrodes of the piezoelectric transformer, and an intermediate terminal connected to the second transistor, and a discharge connected to the secondary side of the piezoelectric transformer. A drive frequency control circuit for detecting a current flowing through a tube and a discharge tube and variably controlling a frequency of a drive signal for alternately controlling conduction of a first transistor and a second transistor so that the current value becomes substantially constant. And a third transistor inserted between the primary terminals of the first and second autotransformers and the input power source, and a third transistor between the primary terminals of the first and second autotransformers and the ground potential. , A voltage dividing circuit between the primary electrodes for detecting the voltage between the primary electrodes of the piezoelectric transformer, and a third transistor using the output of the voltage dividing circuit between the primary electrodes. To control continuity Ri and a control circuit for controlling such an increase in the average output voltage of the third transistor is relaxed even when the input voltage increases.

According to a fourth aspect of the present invention, the voltage to be detected by the primary electrode voltage dividing circuit is changed to a voltage between the intermediate terminals of the first and second autotransformers. .

[0010] In the invention according to claim 5, a piezoelectric transformer for converting an AC voltage input to the primary side and outputting the converted voltage to the secondary side, and a secondary terminal connected to one of the primary side electrodes of the piezoelectric transformer. And a first transistor having an intermediate terminal connected to the first transistor.
An autotransformer, a second autotransformer having a secondary terminal connected to the other of the primary electrodes of the piezoelectric transformer, and an intermediate terminal connected to the second transistor, and a discharge connected to the secondary side of the piezoelectric transformer. A driving frequency control circuit for detecting a current flowing through the discharge tube and variably controlling a frequency of a driving signal for alternately controlling conduction of the first transistor and the second transistor so that the current value becomes substantially constant; , First
A third transistor inserted between the primary terminal of the second autotransformer and the input voltage; and a third transistor connected between the primary terminal of the first and second autotransformers and the ground potential. By controlling conduction of the third transistor using a current holding circuit and a signal obtained by performing waveform processing on the drive signals of the first and second transistors, the average output voltage of the third transistor can be increased even when the input voltage increases. And a control circuit that controls so that the increase in

[0011] In the invention according to claim 6, claims 1 to 5 are provided.
The brightness of the discharge tube is adjusted by intermittently controlling conduction of the third transistor according to any one of the above with a PWM signal.

[0012]

FIG. 1 is a block diagram showing a configuration of a piezoelectric transformer inverter according to a first embodiment of the present invention. In FIG. 1, one of the primary input electrodes of the piezoelectric transformer 5 is connected to the coil 1 and the drain of the transistor Q1, and the other input electrode is connected to the coil 2 and the drain of the transistor Q2. The sources of transistors Q1 and Q2 are connected to the ground potential. A secondary output electrode of the piezoelectric transformer 5 is connected to a discharge tube 6 as a load, and a tube current flowing through the discharge tube 6 is converted into a voltage (VFB) by a tube current detection resistor R8.

The drive frequency control circuit 3 controls the frequency of the drive signal for the transistors Q1 and Q2 so that VFB becomes substantially constant, that is, the tube current becomes substantially constant.
The other ends of the coils 1 and 2 are connected to the drain of the transistor Q3 and the cathode of a diode D1 which is a current holding circuit. The source of transistor Q3 is connected to the input power supply, and the anode of diode D1 is connected to ground potential. A resistor R1 is connected to the primary electrode of the piezoelectric transformer 5.
And R2 are connected to each other, and a connection point between the resistors R1 and R2 is connected to the ground potential via a resistor R3. Here, a voltage dividing circuit between the primary electrodes is constituted by the resistors R1 to R3.

[0014] Voltage at connection point of resistors R1 to R3 (Vmd)
Is connected to the transistor Q via the Zener diode ZD1.
4 base. The emitter of transistor Q4 is connected to ground potential, and the collector is connected to the base of transistor Q5. The base of the transistor Q5 is further connected to a remote ON / OFF signal input terminal via a resistor R4, and to the ground potential via a resistor R5.

The collector of the transistor Q5 is connected to a totem-pole current amplifying circuit 4 composed of a resistor R6, a transistor Q6 and a transistor Q7, and its output is a gate signal of the transistor Q3. Also, the remote ON / OFF signal is an ON / OF signal of the drive frequency control circuit 3.
Also used for F. The burst dimming signal is input to the base of the transistor Q8 via the resistor R7,
8 is connected to the base of transistor Q5. The emitter of transistor Q8 is grounded.

FIG. 2 and FIG. 3 are voltage waveform diagrams of respective parts in FIG. Next, a specific operation of the piezoelectric transformer inverter according to the first embodiment of the present invention shown in FIG. 1 will be described with reference to FIGS. Remote ON / O
When the FF signal is turned on (H level), the transistor Q
5 is turned on, the output voltage Vg3 of the totem pole current amplifier circuit 4 becomes “L” level as shown in FIG.
The transistor Q3 is turned on, and the input voltage is supplied to the piezoelectric transformer 5. At the same time, the drive frequency control circuit 3 starts operating according to the remote ON / OFF signal.

FIG. 2 shows the gates of the transistors Q1 and Q2.
Voltages Vg1 and Vg2 with a phase difference of 180 ° shown in (b) and (d) and a duty of 50% are input. The transistors Q1 and Q2 are alternately turned on by this voltage, electromagnetic energy is stored in the corresponding coils 1 and 2, and a sinusoidal resonance voltage is input to the piezoelectric transformer 5 during the off period of the transistors Q1 and Q2. Transistor Q1,
Since Q2 turns on and off alternately, FIGS. 2 (a) and 2 (c)
Is applied to the primary electrode of the piezoelectric transformer 5, and as a result, a voltage having a substantially sinusoidal waveform is input between the primary electrodes of the piezoelectric transformer 5.

The piezoelectric transformer 5 boosts the input voltage and supplies it to the discharge tube 6, and the tube current starts to flow. Now, Japanese Patent Laid-Open No. 9-1
In the same manner as in the piezoelectric transformer driving circuit described in Japanese Patent Application Laid-Open No. 07684, control is performed based on a frequency-boosting ratio curve of the piezoelectric transformer. If the tube current flows more than the desired set value, VFB detected by resistor R8
Becomes larger than a predetermined value, and the drive frequency control circuit 3 detects this, and changes the frequency of the drive signals Vg1 and Vg2 applied to the transistors Q1 and Q2 in a direction to increase. As a result, control is performed so that the step-up ratio of the piezoelectric transformer 5 decreases, the tube current decreases, and returns to a desired set value.
Conversely, if the tube current is less than the desired set value, VF
Control is applied in a direction in which B decreases and the frequency of the drive signal decreases, and control is again performed so that the tube current returns to a desired value.

Next, a case where the input voltage becomes large will be considered with reference to FIG. As the input voltage increases, the transistors Q1 and Q2 shown in FIGS.
Of the drain voltage Vd1 and Vd2 is going to increase. When the voltage dividing point voltage Vmd of the resistors R1 to R3 shown in FIG.
4 turns on. Then, the transistor Q5 turns off,
The signal Vg3 shown in FIG. 2G becomes "H" level, the transistor Q3 is turned off, and the input voltage is not supplied. As a result, the energy stored in the coils 1 and 2 while the transistors Q1 and Q2 are on decreases, and the drain voltages Vd1 and Vd2 decrease. That is, when the input voltage increases, the increase in the input voltage of the piezoelectric transformer 5 is suppressed.

By connecting the resistors R1, R2 and R3 as shown in FIG. 1 and setting the resistor R1 = R2, the peak voltage of the voltage dividing point voltage Vmd becomes (R2 ///) of the peak voltage of the drain voltages Vd1 and Vd2. R3) / ｛(R2 // R3) + R
1｝ = (R1 // R3) / {(R1 // R) + R2} times. Here, R2 // R3 indicates a parallel combined resistance value of R2 and R3.

The frequency of Vmd is equal to the drain voltage Vd
1, twice the frequency of Vd2. Vmd> (Vz + Vb
e) is near the voltage peak of the drain voltage Vd1 or Vd2, and it can be seen that the transistor Q3 is off in the vicinity of the peak. Here, the transistor Q4
When the Zener diode ZD1 is connected in series to the base of the first and the Zener voltage of the Zener diode ZD1 is appropriately selected, the temperature dependency of the base-emitter voltage Vbe and the temperature dependency of the Zener voltage Vz can be canceled. That is, the temperature dependency of the threshold voltage at which the transistor Q3 is turned off can be reduced.

The output of the transistor Q3 has a rectangular waveform as shown in FIG.
An example of the average value of p) is shown in FIG. As is clear from FIG. 4, even when the input voltage increases, the increase in the output voltage of the transistor Q3 is moderated, the increase in the coil current and the increase in the driving frequency of the piezoelectric transformer are suppressed, and the width of the efficiency decrease can be reduced. . As is apparent from FIG.
To increase the period during which p is off (increase the off-duty), the peak of Vmd must be increased. That is, the drain voltages Vd1 and Vd2 must be higher, and thus Vchop must be higher. For this reason, in the first embodiment, it is impossible in principle to make the input voltage of the piezoelectric transformer 5 constant. However, the first embodiment can be realized with a very simple circuit configuration as compared with the prior art, and is highly effective for cost reduction. Furthermore, when the input voltage range is narrow, circuit components such as the transistor Q3 may be omitted, and thus there is an advantage that design flexibility increases.

Next, the burst dimming function will be described. The burst dimming is sometimes called PWM dimming or duty dimming. The brightness of the discharge tube is adjusted by turning on / off the discharge tube at a frequency of 100 to several hundreds Hz and changing its on-duty. Means the function to do. Although the discharge tube is actually turned on and off intermittently, by setting the frequency to 100 Hz or more, the lighting / extinguishing of the light is invisible to the human eye, and the brightness of the discharge tube is uniformly increased. Seems to be changing.

As a burst dimming signal, a rectangular wave signal having a frequency of about 100 to several hundred Hz shown in FIG. When the burst signal is at the H level, the transistor Q8 is turned on, the transistors Q5 and Q3 are turned off, the supply of voltage to the piezoelectric transformer 5 is stopped, and the discharge tube 6 is turned off. FIG. 3 shows a waveform diagram of each part waveform at this time.

As shown in FIG. 3 (i), if the duty of the L level of the burst dimming signal is widened, the discharge lamp lighting duty is widened and the brightness of the tube is increased. Conversely, if the L level duty of the burst dimming signal is reduced, the brightness of the tube is reduced. That is, the luminance can be varied by adjusting the duty of the burst dimming signal.

A burst signal is also input to the drive frequency control circuit 3 in the same manner as described in JP-A-9-107684, and a hold function is provided so that the drive frequency does not fluctuate when the burst signal is at the H level. By doing so, good dimming can be realized. In the embodiment shown in FIG. 1, burst dimming can be easily realized by adding only one transistor Q8, so that the circuit cost can be reduced.

FIG. 5 is a circuit diagram showing a piezoelectric transformer inverter according to a second embodiment of the present invention. In FIG.
The configuration different from that of FIG. 1 will be described below. One of the primary input electrodes of the piezoelectric transformer 5 is an autotransformer 1
1, and an intermediate terminal of the autotransformer 11 is connected to the drain of the transistor Q1. The other input electrode of the piezoelectric transformer 5 is an auto transformer 12
And an intermediate terminal of the auto transformer 12 is connected to the drain of the transistor Q2. The drive frequency control circuit 3 controls the frequency of the drive signal of the transistors Q1 and Q2 so that the voltage of the tube current detection resistor R8 becomes substantially constant, that is, the tube current becomes substantially constant, as in FIG. Although the burst dimming signal is input to the drive frequency control circuit 3 in FIG. 1, the burst dimming function is omitted in FIG.

The primary terminals of the autotransformers 11 and 12 are connected to the drain of the transistor Q3 and the cathode of a diode D1 as current holding means. The primary terminals of the auto transformers 11 and 12 are further grounded via resistors R9 and R10, and a capacitor C1 is connected to the resistor R10 in parallel.

The voltage at the connection point of the resistors R9 and R10 (Vrc
t) is grounded via resistors R12 and R11,
The connection point of R2 and R11 is connected to the base of transistor Q4. The emitter of transistor Q4 is grounded, and the collector is connected to the base of transistor Q5. The remote O is connected to the base of the transistor Q5 via the resistor R4.
An N / OFF signal is supplied and grounded via a resistor R5. The collector of the transistor Q5 is connected to the totem-pole current amplifier circuit 4 composed of the resistor R6 and the transistors Q6 and Q7 in the same manner as in FIG. 1, and its output becomes the gate signal of the transistor Q3.

The remote ON / OFF signal is given to the drive frequency control circuit 3 as a signal for turning it on / off. Further, a connection point of the resistors R1 and R2 connected to the drains of the transistors Q1 and Q2 is supplied with Vrct via a capacitor C2. here,
The resistors R1 and R2 and the capacitor C1 constitute a voltage dividing means between the primary electrodes.

FIG. 6 is a waveform diagram of each part shown in FIG.
Next, a specific operation of the piezoelectric transformer inverter shown in FIG. 5 will be described with reference to FIG. By using the auto-transformers 11 and 12 in place of the coils 1 and 2 shown in FIG. 1, the voltages (Vd1 ', Vd2') input to the piezoelectric transformer 5 as shown in FIGS. )
Is the drain voltage (Vd1,
Vd2). Now, Auto Truss 11,
Assuming that the primary / secondary turns ratio of 1:12 is 1: n, Vd1 '
/ Vd1 = 1 + n. Thereby, the piezoelectric transformer 5
It is effective when used for high output applications where the step-up ratio is insufficient.

In the second embodiment, on / off control of the transistor Q3 is different from that of the first embodiment shown in FIG. That is, in the second embodiment,
The output voltage of the transistor Q3 is divided by the resistors R9 and R10 and rectified by using the capacitor C1. When the rectified voltage (Vrct) becomes larger than Vbe × (1 + R12 / R11), the transistor Q4 turns on, the transistor Q5 turns off, and the voltage supply from the transistor Q3 stops.

However, this alone requires the transistor Q3
Is in a half-on state, that is, a state similar to that of a series regulator, so that the loss in the transistor Q3 becomes extremely large, which is not practical. Then, the resistors R1 and R
2 through the capacitor C2 to Vr
ct. Thereby, the average value of Vrct is maintained at approximately Vbe × (1 + R12 / R11),
As shown in FIG. 6F, Vrct pulsates at twice the driving frequency of the piezoelectric transformer 5.

The pulsation of Vrct causes the transistor Q4
Is turned on and off, so that the transistor Q3 is not in the half-on state, and is switched and does not cause an increase in loss. FIG. 7 shows the result of measuring the average value of the output voltage (Vchop) of the transistor Q3 when the input voltage was varied. It can be seen that by employing the circuit configuration of this embodiment, the input voltage dependence of Vchop can be reduced as compared with the embodiment shown in FIG. However, to turn on and off the transistors Q4 and Q3 exactly, Vr
The magnitude of the pulsation of ct needs to be a certain degree (about several hundred mV or more), and Vc is the same as in the first embodiment of FIG.
It is impossible in principle to keep hop constant. In other words, the accuracy is worse than that of the related art in that the change of Vchop is only suppressed to some extent. But,
The feature is that the circuit configuration can be simplified.

Further, in this embodiment, the voltage of Vrct is divided by the resistors R11 and R12 and applied to the base of the transistor Q4.
Will change. However, on the other hand, FIG.
Since the Zener diode ZD1 shown in (1) can be made unnecessary, there is an effect that the circuit cost can be reduced if it is used in an application where the temperature dependence of Vchop does not pose a practical problem.

In the second embodiment, Vmd is the intermediate voltage between the transistors Q3 and Q4.
Similar effects can be expected by detecting the intermediate voltage between the primary electrodes of the piezoelectric transformer 5 in the same manner as in the embodiment.

FIG. 8 is a view showing a piezoelectric transformer inverter according to a third embodiment of the present invention. In FIG.
One of the primary input electrodes of the piezoelectric transformer 5 is connected to the coil 1 and the drain of the transistor Q1, and the other input electrode is connected to the coil 2 and the drain of the transistor Q2. The drive frequency control circuit 3 controls the frequency of the drive signal of the transistors Q2 and Q3 so that the tube current detected by the tube current detection resistor R8 becomes substantially constant, as in the embodiment of FIGS. .

A transistor Q3 is connected to the other ends of the coils 1 and 2.
Is connected to the cathode of a diode D1 as a current holding means. The input voltage is applied to the source of the transistor Q3, and the anode of the diode D1 is grounded. One ends of capacitors C3 and C4 are connected to the gates of the transistors Q1 and Q2, respectively.
Resistors R13 and R14 are connected between the other ends of the terminals 3 and C4 and the ground, and these capacitors C3 and R13 and the capacitors C4 and R14 form a differentiating circuit.
Gate voltage Vg output from drive frequency control circuit 3
1, Vg2 are differentiated by these differentiating circuits, and Vdf1,
Synthesized by diodes D2 and D3 as Vdf2,
It becomes the voltage Vdf3 across the resistor R15. Where the resistance R
13, R14, R15 and capacitors C2, C3, C
4 and the diodes D2 and D3 constitute a drive signal waveform processing circuit.

The drain of the transistor Q3 is connected to a resistor R9,
R10 is grounded, and a resistor C is connected to the resistor R10.
1 are connected in parallel. The midpoint voltage (Vrct) of the resistors R9 and R10 is connected to the diode D via the capacitor C2.
, D3 and a resistor R15, and a transistor Q via a Zener diode ZD1.
4 base. The emitter of transistor Q4 is grounded, and the collector is connected to the base of transistor Q5. A remote ON / OFF signal is applied to the base of the transistor Q5 via the resistor R4. The base of the transistor Q5 is grounded via the resistor R5. Further, a totem pole current amplifier circuit 4 is connected to the collector of the transistor Q5.

FIG. 9 is a waveform diagram of each part of the piezoelectric transformer inverter shown in FIG. Next, the operation of the piezoelectric transformer inverter shown in FIG. 8 will be described with reference to FIG. The third embodiment is different from the second embodiment shown in FIG. 5 in that a drive signal for the transistors Q1 and Q2 is used to generate the pulsation of Vrct instead of using the input voltage of the piezoelectric transformer 5. Is different. By passing the driving signals of the transistors Q1 and Q2 through a differentiating circuit composed of CR, Vdf1 and Vdf in FIGS.
The pulsation waveform shown by df2 is obtained. This is diode D
By inputting the signal to a circuit including D2, D3 and a resistor R15, the waveform is processed into a Vdf3 waveform as shown in FIG. The average voltage of Vrct is kept at approximately Vbe + Vz according to the same principle as the embodiment of FIG. At this time, the average voltage of the output (Vchop) of the transistor Q3 is (Vbe + Vz) × (1 + R21 / R22).

Since the signal of the voltage Vdf3 is injected into the Vrct voltage via the capacitor C2, the Vrct voltage has a pulsating waveform as shown in FIG. With the pulsation signal, the transistors Q4, Q5, and Q3 are turned on and off, and the average output of the transistor Q3 can be suppressed from increasing when the input voltage increases, as in the embodiments of FIGS. .

The portions other than the portion that generates the pulsation of Vrct are the same as those in the embodiment shown in FIGS. 1 and 5, and the description is omitted here.

FIG. 10 is a view showing a piezoelectric transformer inverter according to a fourth embodiment of the present invention. In the fourth embodiment, the auto-transformers 11 and 12 shown in FIG. 5 are connected in place of the coils 1 and 2 shown in FIG. 8, and a resistor R9 and the drain of the transistor Q3 shown in FIG. The coil 13 is connected, and a capacitor C1 is connected between the connection point between the coil 13 and the resistor R9 and the ground. The other configuration is the same as that of FIG.

The operation of the fourth embodiment is almost the same as that of the third embodiment shown in FIG. 8, except that the autotransformers 11 and 12 are used instead of the coils 1 and 2 so that the piezoelectric transformer 5 To the transistors Q3 and Q4
There is an advantage that the drain voltage can be higher than the drain voltage. Also,
The primary to secondary turns ratio of the autotransformers 11 and 12 is 1:
Assuming that n, voltage boosting of 1 + n times can be expected by the autotransformers 11 and 12, so that it is effective to use the piezoelectric transistor 5 in a high output application in which the boosting ratio of the piezoelectric transistor 5 is insufficient as in the second embodiment.

The fourth embodiment differs from the third embodiment in FIG. 8 in that the output voltage (Vchop) of the transistor Q3 is smoothed by the coil 13 and the capacitor C1 and then divided by resistance. However, in this embodiment,
The extra coil 13 is disadvantageous in terms of cost, but has the following advantages.

First, the capacity of the capacitor C2 can be selected relatively freely. In the third embodiment, the voltage of Vdf3 is set to Vrct via the capacitor C2.
At this time, Vdf3 is connected to the capacitors C1,
The capacity is divided by C2. That is, if the capacitor C1 is increased in order to increase the stability of the control, the capacitance of the capacitor C2 must be increased accordingly. However, if the capacitance of the capacitor C2 is increased, the impedance of the differentiating circuit is also reduced accordingly. It has to be designed, and there is a problem that the power consumption of the differentiating circuit increases.

On the other hand, in the fourth embodiment shown in FIG. 10, since the voltage dividing resistor R10 has no parallel capacitance, the capacitance of the capacitor C2 can be freely selected, and the power consumption of the differentiating circuit can be reduced. Can be suppressed.

Further, as a second advantage, since the output voltage of the smoothing circuit of the coil 13 and the capacitor C1 is maintained at a relatively low voltage and almost constant voltage, this smoothed voltage is used as the power supply voltage of the drive frequency control circuit. It is possible. By using such a configuration, for example, a C-MOS circuit having a low withstand voltage can be used as the drive frequency control circuit 3, which is effective in reducing the power consumption of the control circuit.

[0049]

As described above, in the invention according to the first aspect, even when the input voltage increases, the increase in the output voltage of the transistor for chopping the input voltage can be suppressed, and the decrease in the conversion efficiency of the inverter can be reduced. Since the same effect as described above can be realized with a much simpler circuit configuration, there is a great effect on circuit cost reduction. further,
When the input voltage range is narrow, circuit components such as the third transistor may be omitted, which has an effect of increasing design flexibility.

Also, when performing burst dimming, the circuit driving the transistor for chopping the input voltage can be stopped / driven by one transistor, so that burst dimming can be realized with a very simple circuit configuration. This has the effect.

According to the second aspect of the present invention, there is provided a circuit for smoothing the output of the transistor for chopping the input voltage while dividing the resistance by resistance, and pulsating the smoothed voltage with the primary voltage of the piezoelectric transformer. As compared with the first aspect, an increase in the average output voltage of the chopping transistor can be further suppressed. For this reason, the reduction in the conversion efficiency of the inverter can be further reduced, and the number of components does not increase so much, so that the effect of realizing the circuit at low cost is not adversely affected.

Further, by using an auto-transformer instead of the coil, the input voltage of the piezoelectric transformer can be preliminarily boosted, so that there is an effect that the boosting is not insufficient even in an application requiring a large output.

According to the third and fifth aspects, the duty control of the input voltage chopping transistor can be realized with a very simple circuit configuration in the same manner as in the first and second aspects. This has the effect that a circuit can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a piezoelectric transistor inverter according to a first embodiment of the present invention.

FIG. 2 is a waveform chart showing waveforms of respective units according to the first embodiment.

FIG. 3 is a waveform chart showing waveforms of respective units according to the first embodiment.

FIG. 4 is a graph showing a relationship between an input voltage and an average output voltage of a chopping transistor when the first embodiment is used.

FIG. 5 is a diagram illustrating a piezoelectric transformer inverter according to a second embodiment of the present invention.

FIG. 6 is a waveform chart showing waveforms of respective units according to the second embodiment of the present invention.

FIG. 7 is a graph showing a relationship between an input voltage and an average output voltage of a chopping transistor when the second embodiment is used.

FIG. 8 is a diagram showing a piezoelectric transformer inverter according to a third embodiment of the present invention.

FIG. 9 is a waveform chart showing waveforms of respective units according to the third embodiment.

FIG. 10 is a diagram illustrating a piezoelectric transformer inverter according to a fourth embodiment of the present invention.

FIG. 11 is a diagram illustrating an example of a conventional piezoelectric transformer inverter.

[Explanation of symbols]

1,2,13 coil, 3 drive frequency control circuit, 4
Totem pole current amplifier, 5 piezoelectric transformer, 6
Discharge tubes, 11, 12 Autotransformers, Q1-Q7 transistors, R1-R15 resistors, C1-C4 capacitors, D1-D3 diodes, ZD1 Zener diodes.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K072 AA01 CA16 DE02 GA10 HA04 5H007 BB03 CA02 CB06 CC12 CC32 CC35 DA03 DB03 DC02 EA02 5H730 AA14 AA15 AS11 BB13 BB86 DD04 DD28 EE48 FD31 FG05 FG07

Claims (6)

[Claims] 1. A piezoelectric transformer for converting an AC voltage input to a primary side into a voltage and outputting the converted voltage to a secondary side, and a first transformer connected to one of primary electrodes of the piezoelectric transformer.
A second coil and a second transistor connected to the other of the coil, the first transistor, and the primary electrode of the piezoelectric transformer; a discharge tube connected to a secondary side of the piezoelectric transformer; A drive frequency control circuit that detects a current flowing through the tube, and variably controls a frequency of a drive signal that alternately controls conduction of the first transistor and the second transistor so that the current value becomes substantially constant; A third transistor inserted between a connection point of the other terminal of the first and second coils and an input power supply, and a third transistor connected between a connection point of the first and second coils and a ground potential; A current holding circuit, a voltage dividing circuit between the primary electrodes for detecting a voltage between the primary electrodes of the piezoelectric transformer, and a voltage dividing circuit for the third transistor using an output of the voltage dividing circuit between the primary electrodes. Control continuity It allows characterized by comprising a control circuit in which the input voltage is controlled to increase the average output voltage of the third transistor is relaxed even when the increase of the piezoelectric transformer inverter. 2. A piezoelectric transformer for converting an AC voltage input to a primary side into a voltage and outputting the converted voltage to a secondary side, and a first transformer connected to one of primary electrodes of the piezoelectric transformer.
A second coil and a second transistor connected to the other of the coil, the first transistor, and the primary electrode of the piezoelectric transformer; a discharge tube connected to a secondary side of the piezoelectric transformer; A drive frequency control circuit that detects a current flowing through the tube, and variably controls a frequency of a drive signal that alternately controls conduction of the first transistor and the second transistor so that the current value becomes substantially constant; A third transistor inserted between a connection point of the other terminal of the first and second coils and an input power supply, and a third transistor connected between a connection point of the first and second coils and a ground potential; The input voltage is increased by controlling the conduction of the third transistor by using a current holding circuit and a signal obtained by subjecting the drive signals of the first and second transistors to waveform processing. Characterized in that also provided with a control circuit for controlling such an increase in the average output voltage of the third transistor is relaxed,
Piezoelectric transformer inverter. 3. A piezoelectric transformer for converting an AC voltage inputted to a primary side into a voltage and outputting the converted voltage to a secondary side, a secondary terminal being connected to one of primary electrodes of the piezoelectric transformer,
A first autotransformer having an intermediate terminal connected to a first transistor, and a second autotransformer having a secondary terminal connected to the other of the primary electrodes of the piezoelectric transformer and an intermediate terminal connected to a second transistor. A discharge tube connected to the secondary side of the piezoelectric transformer, and a current flowing in the discharge tube, and the first transistor and the second transistor are connected so that the current value becomes substantially constant. A drive frequency control circuit for variably controlling the frequency of a drive signal for alternately controlling conduction; a third transistor inserted between a primary terminal of the first and second autotransformers and an input power supply; A current holding circuit connected between the primary terminals of the first and second autotransformers and a ground potential; and a voltage dividing circuit between primary electrodes for detecting a voltage between the primary electrodes of the piezoelectric transformer. , Using the output of the primary electrode voltage divider circuit, the third
A control circuit for controlling conduction of the transistors so that the average output voltage of the third transistor is reduced even when the input voltage increases. Piezoelectric transformer inverter. 4. The apparatus according to claim 3, wherein a voltage to be detected by said voltage dividing circuit between primary electrodes is changed to a voltage between intermediate terminals of said first and second autotransformers. Piezoelectric transformer inverter. 5. A piezoelectric transformer for converting an AC voltage input to a primary side into a voltage and outputting the converted voltage to a secondary side; a secondary terminal connected to one of primary electrodes of the piezoelectric transformer; A first autotransformer connected to a first transistor, a second autotransformer having a secondary terminal connected to the other of the primary electrodes of the piezoelectric transformer, and an intermediate terminal connected to a second transistor; A discharge tube connected to the secondary side of a piezoelectric transformer, and a current flowing through the discharge tube is detected, and the first transistor and the second transistor are alternately turned on so that the current value becomes substantially constant. A drive frequency control circuit for variably controlling the frequency of the drive signal to be applied; a third transistor inserted between a primary terminal of the first and second autotransformers and an input power supply; 2 o A current holding circuit connected between a primary terminal of the heat transformer and a ground potential, and conducting control of the third transistor using a signal obtained by subjecting the drive signal of the first and second transistors to waveform processing. A control circuit that controls the average output voltage of the third transistor to be reduced even when the input voltage increases.
Piezoelectric transformer inverter. 6. The piezoelectric device according to claim 1, wherein the brightness of the discharge tube is adjusted by intermittently controlling the conduction of the third transistor by a PWM signal. Transformer inverter.